Echocardiography in the Dog, Cat and Horse, Porciello, 2009

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Echocardiography in the Dog, Cat and Horse 
Francesco Porciello 
Welcome to the online version of Echocardiography in the Dog, Cat and Horse. 
Echocardiography can give wonderful insights into the cardiovascular function of domestic 
animals, but it can be difficult to understand. ECHOCARDIOGRAPHY IN THE DOG, CAT 
AND HORSE will help the general practitioner learn the benifits and limitations of an 
echocardiographic examination, illustrate image acquisition techniques for the beginning 
ultrasonographer, and provide reference values for experienced practitioners. 
Firstly, I would like to express my gratitude for the digital English language edition of the 
Manual of Echocardiography in the Dog, the Cat and the Horse. The digital edition exceeded 
my expectations in terms of ease of use and image quality. I hope that the manual will be of 
help to VINners in their professional development, specifically in improving their 
echocardiographic interpretative skills. 
I examined the entire text and could not identify any section that did not faithfully interpret 
my original thoughts and published text. The faithful reproduction of the Italian text was 
achieved with the cooperation of Dr. Mark Rishniw, who assisted me in both the preparation 
of the original Italian version (where he contributed a chapter on congenital diseases) and 
also in translating the Italian text into English. Other collaborators who contributed chapters 
to the original Italian manual, and to whom I am equally grateful, include my colleague and 
friend, Dr. Francesco Birettoni, who was instrumental in preparing the figures and images to 
the quality observable in both the published and digital editions. Consequently, I would like 
to include both of these cardiologists as collaborators on the title page of the digital edition. 
Additionally, I would like to credit Dr. Rishniw with the co-authorship of the chapter on 
Congenital Cardiac Diseases, and Dr. Birettoni with the co-authorship of the section on feline 
cardiomyopathies in the Chapter on Acquired Cardiac Diseases. 
Finally, I would like to thank Dr. Paul Pion for believing in me and providing me with the 
opportunity to publish this manual in an international forum, thereby bestowing on me the 
honor of having my work read and used throughout the world. I would also like to thank Dr. 
Eliana Poletto, the publisher of the original Italian text, for extending me the opportunity to 
reach a broader audience via the digital edition. 
Perugia, 19 April 2009 
Francesco Porciello 
Chapter 1 - Introduction 
Echocardiograph 
224 
In 1950, Keidel used ultrasound to examine the heart, and by the mid-50's, together with 
Elder and Hertz, he established the basis for ultrasound techniques to describe certain aspects 
of cardiac anatomy and systolic and diastolic cardiac function. In subsequent years, Holmes 
popularized the use of echocardiography in human medicine in the United States. The 
technique was initially used for the appraisal of mitral stenosis, but its application in the 
diagnosis of pericardial effusion and in the evaluation of the cardiac chambers evoked an 
enthusiastic response from much of the scientific community. Coincidentally, experiments 
with ultrasound provided the first two-dimensional images of the canine and feline abdominal 
organs. 
Echocardiography was introduced into veterinary medicine over two decades ago. It offered a 
non-invasive method of examining the structure and function of the heart and large vessels in 
animals, allowing investigators to obtain images that could be utilized in both clinical 
practice and research. 
This technique, despite its limitations (due mainly to the difficulties of transferring 
methodology standardized in humans to domestic animals), provides an extremely useful 
addition in evaluating cardiac pathophysiology. The ability to observe dynamic images of the 
heart allows the echocardiogram to complement the physical examination and the recording 
of a detailed history. In fact, echocardiography relies on the sequential collection and 
interpretation of the basic diagnostic procedures (such as a thorough physical examination 
and history) to prevent imprecise or misleading diagnoses, and is used in conjunction with 
these other diagnostic steps, rather than as a "short cut " to the diagnosis. 
Of fundamental importance is the ability to recognize a "physiological" finding and 
consequently to distinguish physiological variations from pathology. One must always 
remember that a single echocardiographic projection (view) cannot demonstrate all the 
clinically important findings - it is important to confirm anatomical and functional anomalies 
using alternate views as well as performing multiple measurements of cardiac function. It is 
well recognized in the practice of echocardiography that the initial impression obtained from 
a particular view often suggests pathology that is subsequently refuted by additional 
echocardiographic imaging using different views or modalities (e.g. Doppler or color Doppler 
examination). This "rule" of substantiating findings with a complete echocardiographic 
examination must be adhered to by all diagnostic echocardiographers in order to maintain 
scientific rigor and accurate clinical interpretations. 
The term echocardiogram refers to a collection of images that use ultrasound to examine the 
heart and to record information in the form of "echoes", which are reflected ultrasonic waves. 
The maximum frequency detectable by the human ear approaches 20,000 cycles/sec (20 
kHz). The frequencies used in echocardiography range from 2 to more than 7 million 
cycles/sec (2 to >7 MHz). Techniques originally employed in veterinary echocardiography 
consist of monodimensional (M-mode) and bi-dimensional (B-mode or 2D-mode) imaging, 
which, in recent years, have been augmented by Doppler techniques used for the study of 
blood flow and myocardial kinetics. 
Doppler echocardiography requires equipment that has only recently gained popularity in 
veterinary medicine, due to the fact that equipment cost has dropped substantially, together 
with technological developments in image processing and acquisition and portability 
allowing marketing of portable units that offer great performance with few problems. Until 
recently, few people understood how to properly apply the more complex echocardiographic 
techniques (namely pulsed wave or continuous wave Doppler), but the scene today is 
decidedly different. Reference intervals have been characterized in many situations and for 
many animal species of interest allowing accurate diagnostic and prognostic interpretation. 
The primary clinical development of echocardiographic techniques (both regular and 
Doppler) for dogs and cats occurred in the 1980s. The first cardiovascular applications of 
ultrasound in the horse however, originated in the latter half of the 1970s, but progress in 
equine imaging has been slower than in small animals because of probe design that is 
primarily directed towards advances in imaging human patients, thereby limiting imaging 
depth and penetrating power. 
Use of both M-mode and B-mode imaging allows acquisition of information about the 
morphology and the dimensions of the cardiac chambers and walls, as well as changes to the 
valves, the parietal and valvular endocardium, the pericardium and pericardial space, the 
structures immediately connected to the heart and the roots of the great vessels. B-mode 
imaging, which provides a realistic image of the heart in motion, lends itself to qualitative 
assessments, while precise linear measurements can be acquired with the M-mode imaging, a 
graphical representation of the movements of the various structures imaged over time. 
However, with newer processing technology, many of the limitations with B-mode imaging 
(specifically low frame-rates)have been overcome and many traditional M-mode calculations 
can be adequately obtained from 2D images. 
The development of Doppler techniques through the late 1980s provided additional 
diagnostic capabilities that allow appraisal of blood flow blood within vessels and cardiac 
chambers. Specifically, this methodology evaluates five fundamental characteristics of blood 
flow: direction, quality (laminar or turbulent), speed, timing and location. Several types of 
Doppler echocardiography exist: spectral Doppler (comprised of continuous wave and pulsed 
wave technologies), and color Doppler, both of which (like standard M-mode and B-mode 
imaging) involve the emission and reception of sound waves and various graphical 
representations of these sound waves. However, with Doppler imaging, it is the velocity and 
direction of the sound waves that is of interest, rather than just the location of the reflective 
surface. As with traditional echocardiographic images, Doppler echocardiography allows one 
to obtain "anatomic" (color Doppler) or "graphical" (spectral Doppler) representations of 
blood flow in which the variables of location, timing, quality, speed and direction can be 
determined. With spectral Doppler, these variables are represented within a cartesian system 
of reference. On the other hand, color Doppler echocardiography, introduced to clinical 
veterinary practice in the early 1990s, allows for an immediate survey of blood flow in the 
various regions of the heart and vessels and, compared to spectral Doppler, often provides 
"exciting" images by integrating direction, quality and timing of blood flow with real-time 
two-dimensional images. 
To date, there is no evidence of either acute or chronic adverse biological effects from the use 
of diagnostic ultrasonography on either patients or ultrasonographers, with the exception of 
fetal imaging. Therefore, the benefits of these methodologies in veterinary patients far exceed 
any risks that may be associated with their use. However, it is good practice to minimize the 
time of exposure to ultrasound waves and to use the lowest possible power settings that allow 
diagnostic quality imaging. The more intuitive ultrasound techniques, such as B-mode and 
color Doppler echocardiography, should not be relied upon exclusively, at the omission of 
spectral Doppler or M-mode methods. Rather, the clinician must know the diagnostic 
potential of each imaging technique and be able to choose the most appropriate technique for 
each specific patient, understanding that the information obtained from each 
echocardiographic technique is complementary to the others, and that the most accurate 
diagnosis incorporates the assimilation of information from all these techniques. 
The advantages of echocardiography, compared to other diagnostic imaging techniques, are 
essentially due to its safe and practical nature, and can be inferred from the following salient 
characteristics: 
 The examination is painless for humans and domestic animals alike. Therefore, it can 
usually be performed without sedation and can be repeated frequently because of the absence 
of known acute or cumulative side effects; 
 Imaging is safe, even if practiced on pregnant or young animals; 
 The equipment is often portable, lending itself to examinations "in the field" or outside of a 
specific examination room; 
 A complete M-mode and B-mode examination does not generally require more than 30 
minutes; if a Doppler examination is also performed, the complete study usually takes just 15 
minutes longer; 
 The technique is valid for screening and early diagnosis of subclinical or occult pathologies 
or in monitoring inherited cardiac diseases, allowing clinicians to document changes in the 
clinical status over time; 
 In some specific forms of cardiac disease, the echocardiogram represents the only 
diagnostic test capable of providing diagnostic and prognostic information; 
 Echocardiography is relatively cheap to perform with few overhead costs beyond those 
associated with purchasing or leasing the equipment; it consumes little material with the 
exception of imaging gel and printing paper (and, of course, electricity!) 
Chapter 2 ‐ Acquisition Of The Echocardiographic Image 
SEARCH RESULT #: 1 
TITLE: Principles of Ultrasound Physics 
AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20489&O=VIN 
 
Sound waves have been employed for centuries in medicine, for example, in percussion during a physical 
examination, where hands and ears work like a rudimentary echocardiogram -- sounds are sent deep into 
tissues and the returning echoes are analyzed with a stethoscope or naked ear. With echocardiography, or 
ultrasonography, the "resolution" of the percussive examination has been improved by moving the transmitted 
sounds to very high frequency spectra and employing electronic reception and analysis of the reflected sounds 
- basically, "better hands and ears". Specifically, ultrasonography is the graphical representation of the analysis 
of the reflected sound waves, or echoes, generated by transmission and reflection of VHF sound waves through 
tissues. Ultrasonography is based on the elastic property of acoustic waves, which can be stretched and 
compressed, penetrate tissues and reflect from tissue interfaces. These elastic acoustic waves are related to 
the speed of sound by frequency and wavelength according to the formula: 
speed of sound = wavelength x frequency (c = λ x ν) 
A sound wave can only travel through a medium (e.g. air, water, tissue). A single compression and 
expansion of the medium constitutes a single acoustic cycle and multiple cycles constitute an ultrasound wave. 
The term "ultrasound" indicates that the sound waves used for imaging have a frequency that exceeds 20 kHz 
making them imperceptible to the human ear. 
The speed with which these waves propagate through an object is directly proportional to the density of the 
object. In echocardiography, the speed of sound turns out to be almost constant since, in most tissues, the 
speed of sound ranges from 1500 to 1600 m/sec. In clinical ultrasonography, the accepted speed of sound is 
assumed to be 1542 m/sec. The density of objects propagating the sound waves also determines the degree of 
resistance that the sound waves encounter. The amount of cohesion between molecules that constitute the 
different tissues results in differing degrees of resistance to the passage of the ultrasound. For this reason, 
most of the ultrasound waves that encounter fibrous tissues are reflected and not transmitted to deeper 
regions, while those that propagate through liquid structures, like a cyst or blood vessel, are barely reflected. 
It should be emphasized, however, that substances with too low a density, such as air, also fail to propagate 
ultrasound waves because there are too few molecules to propagate the sound wave. The difference in the 
acoustic impedance of various objects forms the essence of clinical ultrasound, as it allows the definition of 
acoustic interfaces that variably reflect ultrasound waves. These interfaces represent the various tissues 
through which the sound wave passes. 
While passing from tissues of low to high acoustic impedance, the ultrasound waves are modified by the 
angle of contact with the tissue interface and the incident surface. As long as the angle of incidence is equal to 
90°, acoustic interfaces having a smooth surface allow almost complete (specular) reflection of the ultrasound 
waves. Ultrasound waves that hit objects having a high acoustic impedance at an angle of 90° result in echoes 
that return to the transmission source, allowing the operator to establish the exact depth of the reflecting 
structure. That depth is equal to the product of the speed of sound waves through tissue (1542m/sec) and 
half of the time that elapses between their transmission and their reception (d=v*t/2). In situations where the 
angle of incidence is not exactly 90°, the ultrasound beam is partially reflected at an angle that equals the 
angle of incidence (i.e., a non-specular reflection) and partially refracted through the tissue. In these 
circumstances, the magnitude of the refractive deviation, caused by the marginally varied speed of propagation 
of the ultrasound waves through various tissues, is proportional to the differences of the acoustic impedance of 
the two tissues or objects (Figure 2.1). Incidentally, this forms the basis of many common acoustic artifacts 
discussed below. For a structure to either reflect or refract a sound wave, however, it must be at least as thick 
as a quarter of the length of the incident sound wave. Therefore a wave of 7.5 MHz can be reflected from 
structures > 0.038 mm thick, while a wave with a frequency of 2.5 MHz requires structures to be at least 
0.15mm thick to reflect or refract the wave. This explains why the spatial resolution of an ultrasound probe is 
directly proportional to its frequency, as will be detailed later. 
Click on the image to see a larger view 
Figure 2.1. Schematic representation of reflection and refraction of the ultrasound beam. In A the angle of incidence 
of the wave A with the surface of the tissue is less than 90°, resulting in a partial non-specular reflection (Al) and a 
partial transmission through the tissues with a specific angle of refraction (All). In B, the angle of incidence between 
the sound wave B and the tissue surface is equal to 90°. Therefore, the sound is partially reflected in a specular 
fashion (Bl) and partially transmitted through the tissue without refraction (Bll). 
Structures that are smaller than the ultrasound wavelength and have rough surfaces produce non-specular 
reflections or acoustic dispersion. An ultrasound wave crossing cellular or connective-tissue interfaces results in 
the formation of infinite echoes that are reflected in various directions which, together, determine the 
characteristic echogenic properties of parenchyma and viscera. 
Reflection, refraction, dispersion and thermal absorption determine the fate of sound waves through tissues, 
and together, they define acoustic attenuation (i.e., the loss of energy from the sound wave). This attenuation 
is directly proportional to the frequency of the ultrasound waves and is largely a function of the interaction 
between sound waves and the ultrastructural components of the tissues (Figure 2.2). For this reason, high 
frequency ultrasound probes have smaller penetration depth compared to low frequency probes. This 
relationship between the frequency of ultrasound waves and their attenuation in various tissues is illustrated in 
Table 2.1. Probes are described by a unit of measurement called "half-power distance", which is the distance at 
which the power of a sound wave is 50% of the emitted power. As can be seen in Table 2.1, the half-power 
distance for sound waves propagating through air is very short. This is why it is often necessary shave hair and 
to apply acoustic gel close to the tissue of interest, both of which reduce the interposition of air between probe 
and patient which would otherwise inhibit the examination. 
Click on the image to see a larger view 
Figure 2.2. Schematic representation of the phenomenon 
of attenuation. The ultrasound beam A, passing through 
the object, collides with (and is reflected by) fewer 
particles than ultrasound beam B. This difference is 
determined by the wavelength. Over a similar distance, 
ultrasound beam B will be attenuated more than 
ultrasound beam A since the energy of the beam is 
reduced by every contact with the particles in the tissue - 
the more contacts with particles, the lower the depth of 
penetration. 
The ultrasound probes, or transducers, act as both transmitters and receivers of the ultrasound waves. Their 
"hearts" are made of piezoelectric crystals that, when subjected to an electrical current, become deformed, 
producing sound waves of a specific frequency. Upon reflection from tissue interfaces, the sound waves impact 
these same crystals, causing them to vibrate at a specific frequency, which in turn is converted into an 
electrical current with a potential difference (voltage) that is correlated with the number of the returning 
echoes. 
The transmission and reception of sound waves by the transducers do not occur simultaneously. Instead, 
after a brief transmission burst or "pulse" of sound waves (usually 2-3 cycle lengths), the transducers activate 
their reception mode and listen for reflected echoes. Thus, the transducer spends well over 99% of the time 
receiving and <1% of the time transmitting. The frequency of repetition of the pulses (PRF - Pulse Repetition 
Frequency) expresses the number of ultrasound pulses per second (and is therefore expressed in Hertz). The 
duration of each ultrasound pulse is inversely proportional to the operating frequency of the probe - the lower 
the probe frequency, the longer the pulse duration. The PRF is directly proportional to the probe frequency. 
This is important, since in order to obtain an accurate image, it is necessary that the transducer receives all the 
echoes generated by the first pulse prior to transmitting a second pulse. Otherwise, echoes from deep 
structures with a longer travel time, if received after transmitting the second pulse, would be misinterpreted as 
having been reflected faster than they really were and would be assigned a more superficial reflecting 
interface. This phenomenon, associated with some of the more common acoustic artifacts, can be reduced by 
decreasing the PRF when high-frequency probes are used to interrogate deep tissues. Reduction of PRF, 
however, necessarily reduces the temporal resolution of the image, since fewer pulses are transmitted. 
Table 2.1. Half-power distance of the ultrasound waves in objects of ultrasonographic 
interest. 
Tissue 
Half power distance (cm) 
2 MHz probe 5 MHz probe 
Water 380 54 
Blood 15 3 
Soft Tissues 1.5 0.5 
Muscle 0.75 0.3 
Bone 0.1 0.04 
Air 0.05 0.01 
Resolution is the ability to identify two points lying above and below each other or beside each other. It is 
therefore obvious that the higher the resolution of an image, the greater the detail of the structures being 
imaged. The important types of resolution in ultrasonography are axial (up-down), lateral (side-to-side) and 
temporal (sweep speed) resolution. 
Axial, or longitudinal resolution is the ability to distinguish two points positioned on the same line as the 
propagated incident ultrasound wave (i.e. points that lie above and below each other, relative to the 
transducer). Axial resolution is greatly influenced by the transducer frequency, such that, for two points to be 
distinguished from each other, they need to be separated by a distance that is at least half the wave-length of 
the transmitted pulse. Therefore, the axial resolution is directly proportional to the operating frequency of the 
probe (Figure 2.3). 
Click on the image to see a larger view 
Figure 2.3. Schematic representation of axial resolution. 
The ultrasound beam emitted from the 3MHz probe A has 
a wavelength that does not allow visualization of particle 
2. The axial resolution for probe B probe, with a 
frequency of 6 MHz allows visualization of particle 2, 
because the wavelength is halved, and therefore collides 
with and is reflected from particle 2. 
Lateral resolution is the ability to distinguish two points at the same distance from the ultrasound source, but 
on different longitudinal or radial axes. In practical terms, it is the relative resolution of points along the same 
circumference, perpendicular to the longitudinal axis (Figure2.4). In order to best understand this type of 
resolution in the context of an ultrasound image, which is the product of multiple adjacent ultrasound beams, it 
is important to realize that these beams, while passing through tissues, diverge radially as their distance from 
the transducer increases. This results in the formation of the so-called "near" and "far" fields within the 
ultrasound image. The near field is the area interposed between the transducer and the point at which the 
ultrasound beams begin to diverge; beyond this point is the far field. Obviously, the lateral resolution within 
the near field is better than that within the far field (Figure 2.5). The magnitude of the divergence of the 
ultrasound beams in the far field is inversely proportional to both the transmission frequency and the width of 
the transmitting surface of the probe. Thus, a high-frequency probe has a better lateral resolution than a low-
frequency probe, and a linear probe has a much better lateral resolution and a bigger near field than a sector 
probe or a curvilinear probe. The point at which the ultrasound beams begin to diverge is known as the focal 
point and is considered the point at which the optimal lateral resolution is obtained. On many machines, this is 
adjustable or multiple focal points can exist, allowing maximal lateral resolution at several near field locations 
or depths (Figure 2.6). 
Click on the image to see a larger view 
 
 
Figure 2.4. Schematic representation of lateral resolution. (A) Particles 1, 3, 5 and 7, which lie in the image field are 
not visualized, and therefore do not contribute to the formation of the echocardiographic image. (B) Increasing the 
number of ultrasound beams of appropriate wavelength results in all 7 particles in the image field being visualized, 
and therefore contributing to the image. 
 
 
Figure 2.5. Schematic representation of the decrease in 
lateral resolution with increasing depth of imaging. In the 
near-field sectors, the ultrasound waves are effectively 
parallel and in close proximity to each other, allowing 
them to intercept all the particles in the field (A); 
however, in the far-field sectors, the waves diverge, so 
that some of the particles that are similarly spaced as 
those in the near-field sector cannot be visualized (B). 
Figure 2.6. Schematic representation of the variation of 
lateral resolution by means of focusing the ultrasound 
beam. Ultrasound waves above and at the focal point 
(indicated by the arrow) are nearly parallel, thereby 
improving the lateral resolution in these sectors. Distant 
to the focal point the waves diverge, reducing lateral 
resolution. 
Temporal resolution is the capacity to refresh the images visualized on the screen such that the structures on 
the screen change with changes in shape and position of the structures being imaged. Temporal resolution is 
generally defined by the frame rate. A way of understanding the concept of temporal resolution is to imagine 
early cinematography, where images were recorded with mechanical cameras that acquired only a few 
photographs per second. When these films were subsequently played, the movements of objects and people 
appeared jerky and discontinuous. The slow sampling rate of the early cameras resulted in phases of 
movement that were either captured as photos or were lost, penalizing the fluidity of movement in playback. 
In the sub-section about technical characteristics of transducers, the importance of temporal resolution in 
echocardiography will be detailed with methods of changing the frame rate to optimize the image. 
Box 2.1 summarizes the main concepts of the physics of ultrasound, as utilized in clinical echocardiography. 
Box 2.1 
Ultrasound. Sound waves with frequencies greater than 20 kHz. For diagnostic purposes, 
ultrasound frequencies range from 2 to >10 MHz. The speed of ultrasound waves in tissues is 
assumed to be constant at 1542 m/sec. The relationship between speed, frequency and wavelength 
is represented by the following equation: 
speed (m/sec) = frequency (Hz) x wavelength (m) 
If speed is constant, the frequency is necessarily inversely proportional to the wavelength. The 
term ultrasound beam identifies a series of ultrasound waves that propagate through an object in a 
single direction and are transmitted at the same time from the same source. The image field (image 
sector) is defined by a series of ultrasound beams of negligible thickness arranged side-by-side, and 
is typified by two-dimensional echocardiography. 
Acoustic impedance is the product of the density of tissue and the speed of sound in the tissue: 
acoustic impedance (z) = speed (v) x tissue density (ρ) 
However, since the speed of sound in tissue is constant, the acoustic impedance depends 
exclusively on the density of the tissue. From the difference between acoustic impedance of two 
adjacent tissues, the percentage of reflected and transmitted sound at the tissue interface can be 
determined as the sound wave passes from one tissue to the other. The amount of the reflected 
echo is directly proportional to the difference in acoustic impedance between the two tissues. 
Generally, the differences between the acoustic impedance of animal tissues are minimal allowing 
most sound waves to penetrate through the tissue interface. This characteristic is beneficial in 
clinical ultrasonography, because the beam is not entirely reflected from an interface, but is largely 
transmitted beyond the interface, and therefore able to reflect off deeper interfaces, allowing the 
operator to visualize structures at multiple depths. Bone and gas have very high and very low 
acoustic impedance, respectively. Consequently, the ultrasound beam, when it meets a tissue-bone 
or tissue-gas interface, is virtually completely reflected and is therefore unable to reflect off deeper 
structures. Therefore, when imaging, it is necessary to choose an acoustic window that avoids 
placing bone or gas between probe and organ being visualized. The same reasoning lies behind the 
use of an acoustic coupling gel applied to the skin of the patient so that the sound waves avoid the 
interposition of air between probe and skin. 
Reflection. When an ultrasound beam meets an interface of a tissue that is smooth and 
perpendicular to the direction of propagation of the ultrasound, with dimensions comparable to the 
wavelength of the ultrasound wave, the phenomenon of the specular reflection occurs. 
Dispersion. The dispersion of the ultrasound beam occurs when the sound wave meets a series of 
small and irregular interfaces in the parenchyma of an organ. The term of non-specular or diffuse 
reflection is also used. Dispersion is independent of the angle of incidence of the beam. Many small 
echoes are formed that, cumulatively, become visible. These echoes are responsible for the 
"characteristic architecture" of the parenchyma of many organs. The dispersion increases with 
transducer frequency. 
Absorption. Refers to the conversion of the mechanical energy of the sound wave into thermal 
energy. Heat is produced by friction between tissue molecules which vibrate longitudinally at the 
same frequency as the ultrasound wave. 
Attenuation.Is the loss of power of an ultrasound beam either before reaching a tissue interface, 
where it would be reflected, as well as after reflection during the return of the reflected wave to the 
transducer, such that some of the sound waves constituting the beam fail to reach the transducer. 
The attenuation is directly proportional to the frequency of the ultrasound wave and is affected by 
absorption, reflection and dispersion of the ultrasound beam. Distal to structures that cause a high 
degree of attenuation, areas lacking echoes are produced (shadows), while distal to structures that 
cause a low degree of attenuation, stronglyechogenic areas are produced (enhancement). 
PRF or pulse repetition frequency. The ultrasound waves used in clinical ultrasonography occur 
in pulses, emitted as salvoes or pulses of 2 or 3 wavelengths. After transmitting the pulse, the 
transducer then listens for returning echoes. In order to accurately interpret the distance between 
the probe and imaged structures, all of the echoes generated by a pulse must be received before 
transmitting the next pulse. The time between successive pulses is known as the PRF. Lower 
frequency probes with greater penetrating depth of the ultrasound beam have a lower PRF to allow 
sufficient time between pulses for all reflected sound waves to be detected. 
Resolution of the image. Refers to the ability to distinguish two points, or the position of a single 
point over time. The greater the resolution the smaller the distance between the two points that 
can be distinguished. 
 Axial resolution refers to the ability to distinguish two points along the longitudinal axis of 
the ultrasound beam (one above the other). This is determined by the operating frequency 
of the transducer - high frequencies, which have short wavelengths, can distinguish 
reflections of structures that are extremely close together. 
 Lateral resolution refers to the ability to distinguish two adjacent points perpendicular to 
the longitudinal axis of the ultrasound beam. This depends on the degree of divergence of 
the ultrasound waves that constitute the beam which, in turn, is influenced by the 
dimensions and shape of the transducer surface, and the distance from the transducer. 
The shape and dimensions of the transducer surface determine the number of parallel 
beams that can be emitted, which in turn affects the lateral resolution. The final factor that 
affects lateral resolution is the focusing of the ultrasound waves to a focal point where the 
resolution is maximal. 
Since axial resolution is generally higher than lateral resolution, due to greater flexibility of 
frequency than of probe design, it is advisable that all the measurements possible should be 
obtained along the longitudinal axis of the ultrasound beam. In an echocardiographic image, it is 
possible to recognize areas with different resolutions. 
 Fresnel Zone: Very close to the probe, this zone has complex interference phenomena that 
makes it difficult, if not impossible, to distinguish structures. 
 Fraunhofer Zone: This zone lies beyond the focal zone, where ultrasound waves diverge 
quickly at the expense of resolution. This is effectively the "far-field". 
 Focal Zone: This zone is the part of the image field where the resolution of the images is 
optimal. It surrounds the focal point by several centimeters and represents the area where 
the ultrasound beam is narrowest. 
 
SEARCH RESULT #: 2 TITLE: Formation of the Image; Artifacts AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20490&O=VIN 
 
FORMATION OF THE IMAGE 
Two-dimensional and M-mode echocardiography use identical fundamental principles of ultrasound. The 
electrical circuits of the ultrasound system supply pulses to one or more piezoelectric crystals within the 
transducer head which function both as transmitters and receivers of ultrasound waves. During the 
transmission phase, the electronic circuit generates a short discharge (from 500 to 1500 pulses/sec) of 
alternating current, which vibrates the piezoelectric crystals at a specific frequency, creating the ultrasound 
pulse. This pulse, penetrating through tissues, meets acoustic interfaces which create ultrasonic reflections 
along small planes with the number of reflected waves being proportional to the difference of acoustic 
impedance between the objects. The returning echoes hit the piezoelectric crystals within the transducer, 
causing them to vibrate at a specific frequency. The strength of the vibration and the number of vibrating 
crystals create an electrical current with a potential difference proportional to the intensity of the echoes. A 
gray scale is then assigned for every potential difference (with white being most intense, and black 
representing a complete absence of echoes) with an image displayed on the screen similar to that displayed in 
Figure 2.7. In order to place a particular point at a specific location on the screen, the ultrasound system first 
calculates the distance of the source of the echoes from the transducer by means of the formula D = V x T/2, 
where T= the time from transmission to reception of the sound wave at the transducer and V = the velocity of 
sound through tissues (1542m/s). 
Click on the image to see a larger view 
Figure 2.7. Schematic representation of the formation of 
the image by the echocardiographic machine. Structures 
with different acoustic impedance are represented on the 
monitor by various shades of gray. In this simplistic 
cartoon, the outline of the bony tissues is represented on 
the screen as a white image (indicating highly echogenic 
tissues), even though in reality all the ultrasound waves 
would be reflected from the proximal periosteal surface. 
ARTIFACTS 
The ultrasound machine can also produce images that are not accurate, or do not truly represent anatomical 
structures, but rather are the consequences of exaggerations or limitations of physical characteristics of 
ultrasound waves that result from interactions with specific normal or pathological structures. 
The echocardiographic image, therefore, must be examined and interpreted in its entirety, both in terms of 
morphology and function as well as "echo-structurally" (i.e., with consideration to the acoustic patterns 
characteristic of the tissues being imaged), always considering whether reflections are real or artifactual. 
Reverberation 
Reverberation artifact results in multiple perfect (specular) reflections, caused by two highly reflecting 
interfaces, an example of which is the skin-probe interface. In echocardiographic images, reverberation 
appears as numerous equidistant, parallel hyperechogenic curved lines, beginning at the probe-skin interface 
(top of the image) and extending some distance into the image. Reverberation artifact occurs when the 
reflected echo is intense and, upon reaching the transducer, it interacts with the crystal. Part of the energy of 
the echo is transformed into an electrical current and is recorded as a luminous point on the screen, while the 
other part is reflected back into the tissue and travels to the same interface that had created the original 
reflection, is reflected from this interface a second time and returns to the transducer. Since the time to the 
second detection is double that of the first, the second reflection is denoted on the screen as a second point at 
twice the depth of the first. This repeated reflection can occur several times, resulting in a series of ever-
deepening points on the screen (Figure 2.8). 
Click on the image to see a larger view 
Figure 2.8. Reverberation artifact: This appears as 
multiple highly echogenic evenly spaced arcs of increasing 
circumference. 
Mirror Effect 
Mirror effect is a particular type of reverberation artifact produced by an interface of moderately high 
reflectivity (e.g. the pericardium) that is less intense than those producing typical reverberation artifacts. In 
practical terms, the artifact usually appears deep to the white line that is causing the relatively intense 
reflection (e.g. a pericardial reflection) as a repetition of some particular structure or organ below the actual 
location of the true structure (Figure 2.9). 
Click on the image to see a larger view 
Figure 2.9. Mirror Artifact. The left ventricle (A) and left 
atrium (B) are "mirrored" in the lower part of the image 
(AI and BI), giving rise to a false image separated from 
the real oneby a white hyperechoic line (the 
pericardium). 
Spontaneous Echocardiographic Contrast 
Spontaneous echocardiographic contrast (smoke) is visualized as the appearance of small areas of medium 
echogenicity that move within the cardiac chambers or vessels, consistent with the flow of blood. The origin of 
this artifact is generally attributed to microaggregates of red blood cells that tend to occur with 
hypercoagulable states or low flow conditions (stasis). Spontaneous echo contrast is also a normal 
phenomenon in the horse, and less frequently in the dog. It is considered abnormal in cats (Figure 2.10). The 
ability to see spontaneous echo contrast is somewhat dependent on the transducer frequency, and has been 
reported in mice using ultra-high-frequency transducers (50MHz). 
Click on the image to see a larger view 
Figure 2.10. Spontaneous echocardiographic contrast: 
appears as hyperechoic points within the cardiac 
chambers that, in real time, move and swirl with blood 
flow. 
Side Lobe Artifacts 
These are diffuse reflections that originate lateral to the structures that actually reflect the beam. The physics 
behind side-lobe artifacts are relatively complex. Echocardiographically, they appear as weak gray curvilinear 
objects just lateral to the central echocardiographic field (Figure 2.11). Because these artifacts are extremely 
weak, they are generally only visible when the central beam penetrates liquid (hypoechoic) structures such as 
cardiac chambers. This type of artifact is often visible within the left atrium, where reflections of the ventricular 
endocardium beside the left atrium are visualized within the left atrium (Figure 2.11). The artifact can be 
eliminated by optimizing the image or centering the hypoechoic (fluid-filled) structure on the image, which 
reduces the number of ultrasound rays that hit the lateral parenchyma. 
Click on the image to see a larger view 
Figure 2.11. Side lobe artifact. This is caused by the 
erroneous positioning of echoes originating lateral to the 
site of the artifact. These artifacts usually become visible 
within cardiac chambers (which are hypoechoic and are 
positioned beside hyperechoic structures, such as the 
pericardium). 
Acoustic Enhancement 
This phenomenon occurs distal to poorly-reflective tissues, mostly collections of fluid (e.g., cysts), where areas 
directly distal to the fluid-filled cavity are hit by ultrasound waves of greater intensity than adjacent areas that 
do not have fluid cavities proximal to them. The waves that have passed through the proximal fluid region are 
attenuated minimally by the fluid. Therefore, the areas distal to the fluid cavities appear brighter than the 
adjacent areas (Figure 2.12). 
Click on the image to see a larger view 
Figure 2.12. Distal enhancement. The structures 
indicated by the arrows appear highly echogenic, when 
the ultrasound waves meet an acoustic interface between 
tissues of very different acoustic impedance. Generally, 
distal enhancement occurs deep to hypoechoic structures, 
which attenuate few sound waves - this allows the tissue 
interface immediately distal to the hypoechoic structure to 
reflect more sound waves than neighboring tissue. 
Acoustic Shadows 
These are zones on the echocardiographic image where the reflections are very weak or totally absent. The 
shadow zone appears, therefore, as an "asonic" or dark area of variable shape which can be distinct or can 
fade. The artifact occurs as a result of failure of reflection of any sound waves because of attenuation of the 
waves in tissues proximal to the area. As such, these artifacts occur immediately distal to tissues with very 
high acoustic impedance, which inhibit the passage of any ultrasound waves. Typically, acoustic shadows are 
caused by bones, calculi or gas (Figure 2.13). Gaseous shadows differ from bone/calcium shadows. 
Click on the image to see a larger view 
Figure 2.13. Acoustic shadow artifact: in this example, 
the shadow artifacts appear as two vague and indistinct 
triangular areas devoid of echoes, because the ultrasound 
waves have been totally reflected by two highly reflecting 
structures (ribs). 
 
 
ECHOCARDIOGRAPHIC EQUIPMENT 
Echocardiographic equipment essentially comprises the monitor, the body of the machine (including the 
keyboard, loudspeakers, computer, and a frame with wheels) and probes or transducers (Figure 2.14). (Please 
refer to the section on echocardiographic probes for more detail about these.) 
Click on the image to see a larger view 
Figure 2.14. Ultrasound machine of the type used in 
veterinary teaching hospitals. The unit has been adapted 
to allow portability in a hospital environment where the 
machine is used for imaging both small and large animals. 
The echocardiographic unit is usually connected to a printer, video recorder or digital image storage (most 
common on new machines) for recording of images and movies, allowing permanent documentation of the 
examination and subsequent post-hoc analysis. Many machines also allow the operator to perform 
measurements and calculations on pre-recorded images at some time after the actual examination (off-line 
analysis). Newer systems also provide stand-alone imaging software for image analysis at a computer separate 
from the ultrasound machine. Some portable echocardiographic units, like the one in Figure 2.15, are equipped 
with LCD screens, substantially reducing the dimensions of the system and increasing portability. Occasionally, 
these units can be connected to a traditional screen for better visualization. All machines come with the ability 
to attach an electrocardiograph (Figure 2.16) which permits recording of a synchronized ECG tracing with the 
echocardiographic image. Synchronous ECG recording allows the user to accurately identify systolic or diastolic 
frames. This is important for evaluating timing of certain events and specific indices such as the pre-ejection 
period. It is considered good echocardiographic practice to connect the ECG whenever performing an 
examination. In some situations, experienced echographers may omit the ECG. However, this can limit the 
value of the diagnostic information obtained during the examination. 
Click on the image to see a larger view 
 
 
Figure 2.15. Portable ultrasound machine, equipped 
with an LCD display in order to reduce the size and 
weight. 
Figure 2.16. Portable ultrasound machine mounted on a 
cart and connected to cables for the simultaneous recording 
of the electrocardiogram. 
Echocardiographic Controls 
The controls present on most machines include: 
 Those that regulate the dimensions and the position of the image; 
 Those that influence the quality and the intensity of the image. 
The depth control regulates the distal limit of the ultrasonic field and therefore the relative sizes of the 
imaged organs. It does not regulate the depth to which the ultrasound beam travels, but only the depth to 
which reflected waves are processed (recall the relationship between velocity, time and depth). The lesser the 
depth, the larger the structures in the near-field will appear. It is important to understand that reducing the 
depth of field, even if it offers better recognition of fine details (e.g., fine irregularities of a surface that would 
have otherwise appeared smooth, or a high-frequency small amplitude vibration of a valve), will reduce the 
overall image quality by increasing graininess and pixilation. The reference depth scale always appears to the 
left or right of the image and is automatically adjusted with changes in depth and allows experienced operators 
to estimate the size of structures or organs without specific measurement (Figure 2.17). Usually the scale is in 
0.5cm or 1cm increments, often with highlighted 5cm increments. 
Click on the image to see alarger view 
Figure 2.17. Portions of the ultrasound screen. On the 
left of the ultrasound image is the grey scale, and the 
depth scale, in centimeters. The small triangle next to the 
scale is the focal point, which can be positioned by the 
operator. Next to the apex of the image field, (in this case 
to the right of the apex) is another triangle indicating the 
position of the probe in relation to the image. 
The other scale of reference on an ultrasound image appears at the bottom of the screen when imaging in 
either Doppler mode or M-mode, and identifies the timing or speed of the image scrolling (Figure 2.18). It 
generally denotes 1 second intervals (or fractions of a second). Speed controls allow the operator to alter the 
"sweep speed", so as to provide greater or lesser detail to temporal events. With standard imaging, a 
moderate sweep speed is used and is increased when examining fine details of the oscillations of various 
structures, when imaging subjects with high heart rates (Figure 2.19), or when obtaining extremely precise 
temporal measurements. 
Click on the image to see a larger view 
 
Figure 2.18. Schematic representation of the monodimensional (M-mode) diagram of an oscillating point (producing a 
sine wave). In A, the sweep speed of the image is fast so that approximately 3.5 sec are displayed on the screen. In 
B, the sweep speed is much slower resulting in 7 sec being displayed on the screen. On the left of the diagrams is the 
depth scale. 
Figure 2.19. M-mode image of the relatively fast cardiac 
activity recorded in a cat. The sweep speed of the image 
(3 sec per screen) is set up to obtain a suitable temporal 
resolution for the differentiation of several cardiac cycles 
(arrows). 
Many systems allow regional amplification of the image, via the so-called "zoom" function, which can also be 
done off-line in the more sophisticated machines. Expert operators often zoom in on specific regions or 
structures when performing 2-dimensional imaging, preferring smaller but more detailed views of specific 
structures and their movements. Using the zoom function takes practice, because the general references that 
the operator uses to optimize the image or to identify what is being examined, are often lacking. 
All systems have a sector size control which allows the operator to control the angular dimension of the 
image field (effectively, the size of the image slice), allowing the operator to reduce or increase the field 
visualized on the screen (Figure 2.20). Generally, the more the visualized area is reduced (the smaller the 
slice), the better the performance of the ultrasound machine because of reduced image processing. 
Specifically, the frame rate improves when the visualized area is reduced, which in turn allows improved 
visualization of rapidly moving structures. Therefore, in echocardiography, it is advised to use the smallest 
effective sector. This is especially important for color Doppler imaging. 
Click on the image to see a larger view 
 
 
Figure 2.20. Image fields of different width. In echocardiography, as narrow a field as possible is preferred (B or C), 
in order to optimize the frame rate and the reproduction of the movements of cardiac structures. In fact, the larger 
the field of view, the lower the number of images that can be acquired every second (in this panel, the frame rates 
vary from 62 frames/sec in A to 83 frames/sec in B and 127 frames/sec in C). 
Note: Imm/S = frame rate (frames/sec) 
Additional controls allow flipping of an image in either a horizontal or vertical plane to allow standard 
positioning of the image. 
Most of the controls found on an echocardiographic unit regulate the quality and the intensity of the image. 
Total input power (or gain) can be controlled on all units to increase or reduce the intensity of the reflected 
sound waves. However, because the intensity of the ultrasound waves decreases as they pass through the 
body, the echoes returning from the far field are weaker than those returning from the near field. Without 
correcting for this discrepancy, deeper structures of similar physical characteristics, or an organ that occupies 
both near and far fields, would appear to be heterogeneous in echogenicity with the more distant regions 
appearing less echoic than proximal regions. In order to overcome this problem, all echocardiographic units 
have a series of controls that allow reduction of the gain of near-field echoes and intensification of far field 
echoes called Time Gain Compensation (TGC) controls, that affect gain within very specific depths. Using TGCs 
(Figure 2.21), it is possible to adjust the image observed on the screen, increasing or reducing the 
amplification (gain) of selected regions. Expert ultrasonographers adjust the TGCs for every patient and 
frequently readjust throughout the examination to provide an optimal image. 
Click on the image to see a larger view 
Figure 2.21. Ultrasound machine console: 1) Time-Gain 
Control potentiometers for regulating gain at different 
depths (2) Track ball, analogous to a computer mouse, 
for moving cursors on the screen (3) Controls for 
selecting different ultrasound applications (2D, M-mode, 
Doppler etc); (4) Image freeze button (5) Control for 
adjusting overall image gain; (6) Controls for adjusting 
Doppler and Color Doppler gain; (7) Control for angle 
correction of pulsed-wave Doppler beams; (8) 
Alphanumeric keyboard; (9) Control panel for adjusting 
depth, focus, frequency, and image size (zoom); (10) 
Control panel for adjusting Doppler settings; (11) 2D-hold 
button for providing reference images during spectral 
Doppler interrogation; (12) Control for setting the 2D 
update rate during spectral Doppler imaging; (13) 
Spectral Doppler baseline adjustment; (14) Image 
capture/store/record button; (15) Control panel for 
selecting imaging pre-sets, probes, and patient 
information, retrieving archived images, and setting up 
default pre- and post-processing settings; (16) Control 
panel for performing measurements and calculations of 
ultrasound images. 
Some low-end units only have controls for adjusting the total power (or total gain), the mid-field gain and far-
field gain. A good rule-of-thumb for setting the gain is to begin every examination with the total gain set at 
approximately 50%, the near-field gain around 25% and the far-field gain at 75%. This usually results in 
reasonable image and allows the operator flexibility in additional adjustments. 
Echocardiographic units have additional power controls, which alter the output power of the ultrasound 
waves, as compared to gain controls which alter the amplification of the echoes received by the transducer 
(input power). Some machines allow the amplification of weak signals and the attenuation of more intense 
signals. Output power is usually set at 100% unless performing fetal examinations. 
Additional controls are available for sensitivity, attenuation, edge enhancement and rejection. Sensitivity 
controls are filters that suppress low intensity reflected signals. These low-intensity reflections are usually 
responsible for creating slight graying of areas that should appear black. Therefore, eliminating these signals 
improves the "blackness" of anechoic structures. Conversely, attenuation controls filter high-intensity signals 
thereby reducing the impact of hyperechoic structures on image quality. Edge enhancement filters allow 
greater contrast between interfaces. 
Increasing the output power increases the density of the transmitted ultrasound waves, increasing the image 
brightness, and allowing visualization of structures with weaker reflections. However, if the gain is too high, the 
brightness of the more echoic structures may drown out echoes of the less echoic structures. A fundamental 
concept for the correctinterpretation of images is that every image is the result of the application of a specific 
"code" which assigns a specific level of gray to each specific intensity of the reflected ultrasound signal. 
Intensity of reflections is displayed along a gray scale (from white to black). Additionally, it is possible to use 
various scaling to alter the image, providing high-contrast or low-contrast images, by adjusting the "gray scale 
gamma curve" (Figure 2.22). Most of these are pre-programmed, and allow the operator to select an overall 
gray scale range, rather than doing manual adjustments. For optimal echocardiographic visualization, it is 
always preferable to select range curves that provide strong differences between tissues, such as valves, 
chordae tendineae, serosa, endocardium, and anechoic regions, such as cardiac chambers or vessels (Figure 
2.23). In other words, use range curves providing a high-contrast image with a broad but limited gray scale 
range. However, selecting gray scales that provide excessive contrast diminish the more subtle differences 
within tissues such as myocardium and may reduce the diagnostic quality of the image. The pre-programmed 
gray scale options vary in number between units. Additionally, colorized scales are also available, and these 
can offer advantages in certain situations, especially when imaging pericardial effusions, because the human 
eye can discriminate between colors better than grays. 
Click on the image to see a larger view 
 
Figure 2.22. Two dimensional echocardiographic image with different range curves: In panel A, a broad linear grey-
scale range has been utilized; in panel B the gray-scale curve accentuates the grays. 
 
 
Figure 2.23. Two dimensional echocardiographic image (A) with a high-contrast sigmoidal grey-scale curve (B) that 
accentuates the differences between the hypoechoic and hyperechoic structures. 
Other controls alter image quality by including or excluding reflected ultrasound pulses of specific intensities. 
One of these is the DNF (Dynamic Noise Filter), which eliminates some frequencies that cause image flutter on 
the monitor. This filter, installed on machines with mechanical sector probes, should be inactivated during an 
echocardiographic examination as it affects the imaging of valve motion. Similarly, persistence filters, which 
"smooth" the image by slightly overlapping successive images, should be turned off during echocardiographic 
examinations so that fine and rapid motion can be detected. 
The speed of acquisition of the images from the transducer (FR - Frame Rate) can be modified by the 
operator to some extent. In general with echocardiography, image quality is enhanced by high frame rates. 
The FR can usually be identified on the screen as a frequency (frames/sec) (Figure 2.20: Note: Imm/S = frame 
rate (frames/sec)). 
In abdominal ultrasonography, where relatively immobile organs are studied, a low FR does not create a 
problem; indeed, it can help to reduce the effect of small vibrations caused by oscillation of the transducer 
head. On the other hand, in echocardiography, a higher FR improves visualization of structures that move at a 
relatively high speed, such as valves. Therefore, with echocardiography the FR is most important factor 
affecting the generation of an accurate image and the operator must always attempt to use settings that favor 
a high FR. Another fundamental difference between systems designed for cardiology vs general imaging is the 
number of focal points. Since the FR is inversely proportional to the number of focal points, the FR in 
echocardiographic units utilizes a single focus, which is then manually positioned during the examination to 
optimize the region being interrogated. Generally, the focal point is positioned towards the distal end of the 
cardiac image, since image resolution proximal to the focal point does not suffer as much as that distal to the 
focal point. 
Box 2.2 summarizes some features of echocardiographic equipment that affect the rate of image acquisition. 
Box 2.3 summarizes the features of controls that influence the quality of images. 
Box 2.2 
Frame rate - this is the number of images formed per second. This is dependent on the maximum 
depth of the returning echoes being processed. The greater the depth, the longer the time 
necessary for the return of the echoes to the transducer and, consequently, the lower the FR. The 
wider the image sector, the lower the FR. The more focal points, the lower the FR. Thus, in order to 
maximize FR, the image field should be narrow, shallow and unifocal. 
Frame averaging - This averages the frames, resulting in a reduction of the differences between 
the various images, reducing the graininess of the image, but reducing edge resolution. The FR and 
frame averaging are inversely related. 
Box 2.3 
Rejection levels - These set the limits for eliminating weaker echoes (which do not contribute in a 
meaningful way to the formation of the image) from all the depths. 
Gain control - This amplifies all the returning echoes in uniform way, regardless of the depth at 
which they were reflected. 
Time gain compensation - These controls amplify specific regions of the ultrasound image (i.e., 
only reflected echoes with specific time signatures). These controls allow the operator to 
compensate for the natural attenuation of echoes from distal fields. 
Gray scale - Two-dimensional images are portrayed on the screen along a gray scale. In situations 
where it is important to distinguish differences between low-intensity echoes or between high-
intensity echoes, more levels of gray are assigned (low contrast). In situations where it is more 
important to distinguish differences between high-intensity and low-intensity echoes, the gray scale 
is reduced (high contrast). In echocardiography, where both of these situations are important, the 
gray scale has a sigmoidal shape (Figure 2.23), which provides a relatively well-contrasted image 
with a broad gray scale range. 
Power control - This modifies the voltage applied to the piezoelectric crystals to generate the 
pulse. Increasing the voltage increases of intensity of the ultrasound beam and, consequently, of 
the returning echoes, producing a brighter image. 
All ultrasound machines have dedicated computer hardware and software designed for image processing, 
display and storage. In addition to improving and displaying the images, the digital processor also allows the 
operator to perform various measurements and to store images in a buffer from which a specific image can be 
selected to be studied in detail. The stored and saved digital data (which today can occupy gigabytes of 
memory per study) can be re-examined remotely at a later time. Therefore, modern echocardiographic units 
are increasingly more and more powerful computers with immense real-time processing capabilities for 
generating high-quality images, measurement packages dedicated to the various imaging applications (2-
dimensional, M-mode and Doppler) and large drives for archiving of studies. 
 
SEARCH RESULT #: 2TITLE: Transducers AUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20492&O=VIN
 
Ultrasound waves are created by the piezoelectric effect, which is an example of the transformation of an 
electric field applied to a particular material (e.g. quartz or disc of ceramic material) into an elastic sound 
wave. This piezoelectric effect is reversible: the transducer not only produces ultrasound waves, but also 
detects and decodes the reflections (echoes) of these waves and converts them into an electrical current. With 
ultrasound transducers, many crystals are arranged along a surface, effectively constituting many point 
sources of ultrasound waves, which, when summed, produce a wave front or beam.Today, transducers are mostly electronic rather than mechanical. Electronic (phased-array) transducers are 
composed from tightly packed synthetic crystals arranged on a flat or curved surface such that the ultrasound 
waves emitted by each crystal remain near-parallel as they progress from the probe surface to the tissues 
being imaged. If the piezoelectric crystals are arranged on a flat surface (as with linear probes, such as the one 
depicted in Figure 2.24), the shape of the ultrasound field is rectangular (Figure 2.25). This shape limits the 
possibility of interrogating organs "hidden" behind other structures of the body, as in thoracic imaging where 
the ribs and lungs are positioned between the probe surface and the heart. However, because of the parallel 
nature of the ultrasound waves with linear probes, lateral resolution is maximal. To overcome the issue of 
imaging "around" interfering structures, such as bones or air, some probes have a small surface with a 
diverging beam (sector scanner) that can "squeeze" between interfering structures, at a cost of resolution. A 
curvilinear probe, or microconvex probe is a compromise between linear and sector probes. 
Click on the image to see a larger view 
 
Figure 2.24. A linear ultrasound probe. Figure 2.25. The rectangular ultrasound field that is obtained with 
a probe whose crystals are arranged linearly (linear probe from 
Figure 2.24). 
The probe characteristic that determines the imaging depth is the transmission frequency: the lower the 
frequency, the greater the imaging depth. The higher the probe frequency, the lower the maximum power that 
can be used to produce ultrasound waves, which leads to increased attenuation of the beam. Therefore, for 
feline echocardiography where image depth is usually <6 cm, probes with frequencies >7.5 MHz are generally 
used, although some feline patients may require lower-frequency probes to obtain an image. Additionally, 
Doppler imaging is often improved with lower-frequency probes than would be used for the same animal with 
2D imaging. Optimal probe selection is determined case-by-case and species-by-species (5 vs 3.5 vs 2.25 
MHz). Interestingly, depth limitations for low-frequency probes (2-3 MHz) are largely assigned by 
manufacturers, usually to a maximal depth of 30 cm, since greater depths are not required for imaging human 
patients. This can affect equine examinations, where cardiac structures may lie more than 30 cm from the 
probe. 
These days, many probes are multifrequency probes, able to generate several different frequencies. This is 
controlled digitally and provides a benefit to veterinary ultrasonographers because it reduces the number of 
probes that need to be purchased in order to cover the range of animal sizes to be examined. However, with 
multifrequency probes, the frequency that offers the best performance is the central frequency so the other 
frequencies are often underutilized. 
The anatomical and topographical objects that impede the 2-dimensional ultrasound beam through narrow 
acoustic windows used in echocardiography obviously do not represent a problem for a single linear ultrasound 
beam (effectively, an ultrasound wave). This feature is used in M-mode or Doppler imaging. Of course, a linear 
ultrasound beam cannot penetrate through bones or lungs; however, given that the thickness of the beam is 
negligible, these beams can find room through the narrowest of acoustic windows. 
Transducers used in echocardiography can be classified into 4 types based on the type of ultrasound beam 
transmission. 
Convex Transducers 
These represent a variation of linear transducers, and have crystals mounted in an arc to reduce the effective 
contact surface with the subject's body. The image field is consequently created by divergent ultrasound 
waves, slightly distorting the image. Convex transducers can be further classified as: 
 Convex, with a curvature surface > 20 millimeters; 
 Microconvex, with a curvature surface < 20 millimeters (Figure 2.26). 
These probes can be used for B-mode, M-mode and Doppler imaging (spectral and color). However, they are 
limited by relatively low frame rates. 
Click on the image to see a larger view 
Figure 2.26. An electronic microconvex probe with a 
frequency of 6.5 MHz. Note that the transmitted beam is 
relatively narrow because of the curving of the surface, 
and is comparable to the size of a wedding band. 
Mechanical Sector Transducers 
These transducers have crystals that generate ultrasound waves of a single frequency, which are rapidly 
oscillated or rotated by a mechanical motor. (In some probes, known as annular array probes, 2 arrays of 
crystals with different emission frequencies were used to double the frequency range.) Generally, in 
mechanical sector transducers, the movement is produced by a mechanical arm in the head of the probe 
connected to a motor. The angle of the image field is normally 90°, but it can also be wider or narrower. The 
reduced contact surface and the shape of the ultrasound beam make sector scanners the optimal type of probe 
for echocardiography (Figure 2.27). A disadvantage of mechanical transducers is their overall size (relatively 
large) and their delicate nature making them susceptible to damage if dropped or hit. These probes can be 
used for all echocardiographic applications. 
Click on the image to see a larger view 
Figure 2.27. Mechanical sector probes. The upper probe 
has a frequency of 3.5 MHz allowing imaging to 
approximately 30 cm. The lower probe, on the other hand 
has two piezoelectric crystals that produce ultrasound 
waves of different frequencies. This allows the operator to 
select multiple frequencies with the same probe - in this 
case 5 and 7.5 MHz. Note the markers on the probe that 
allow the sonographer to identify the orientation of the 
transducer by touch. 
Pencil Probes 
These are very specific transducers (Figure 2.28) and are the simplest form of transducer, emitting a single 
linear continuous ultrasound beam. They were the original probes used for M-mode imaging. Subsequently, M-
mode functionality was supplanted by continuous-wave Doppler. Thus, today, they are used solely for 
continuous-wave Doppler imaging as ancillary transducers on systems that do not have continuous-wave 
Doppler capability in the sector transducers (see chapter 3, Continuous-wave Doppler). Pencil probes provide 
very high-fidelity wave-wave Doppler images having only a single function and being low-frequency probes, 
and they are relatively cheap (~$2,000) but require substantial training to use. 
Click on the image to see a larger view 
Figure 2.28. A low-frequency "pencil" probe with a 
transmission frequency of 2 MHz. 
Phased Array Sector Transducers 
These transducers were developed with the evolution of digital electronics (Figure 2.29). The contact surface of 
the probe is relatively flat and small - generally smaller than mechanical sector transducers. The synthetic 
piezoelectric crystals are parallel to each other and activated in a very rapid regular sequence by software in 
the unit. The high cost of these transducers is sometimes an impediment to general veterinary use but they 
are becoming increasingly popular. Phased array probes can accommodate high frame rates and are used in 
all cardiac applications. The processing capability with many systems that offer phased-array probes allows for 
dual imaging (e.g. simultaneous real-time 2-dimensional and M-mode, or 2-dimensional and spectral Doppler) 
although at some expense to image quality. Very new probes can even provide two orthogonal 2-dimensional 
views simultaneously. In most systems currently used in veterinary medicine, pulsed-wave Doppler imaging is 
optimized by "inactivating" the simultaneous 2D imaging via "stand-by" mode to allow dedicated image 
processing tothe pulsed-wave signal. When using these probes for continuous wave Doppler, dual imaging is 
not possible. 
Click on the image to see a larger view 
Figure 2.29. A phased-array electronic sector probe, 
used in cardiology, with a frequency of 3.5 MHz. The low 
transmission frequency of this probe makes it most suited 
for use in larger animals. 
 
 
SEARCH RESULT #: 1 
TITLE: Techniques of Acquiring the Echocardiographic Image 
AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20493&O=VIN 
 
ECHOCARDIOGRAPHIC IMAGING TECHNIQUES 
This section describes the techniques of performing B-mode and M-mode echocardiographic examinations. In 
the dog and cat, these techniques use the same acoustic windows and imaging planes as the Doppler 
techniques that are detailed later. In the horse, the imaging techniques are similar, but some points require 
additional explanation and are dealt with in the chapters on equine echocardiography. 
The graphical representations of M-mode and B-mode images are completely different from each other (Box 
2.4). Essentially, B-mode imaging displays cardiac anatomy and shape in realistic format. The M-mode image 
does not reproduce an anatomical reality, but produces a representation of the movements of a very specific 
cross-section of the heart over time. 
The M-mode image in Figure 2.30 represents, along the vertical axis, the depth of the region being imaged 
with the region closest to the transducer at the top and the region furthest away at the bottom of the image. 
Time is represented on the horizontal axis. Each tissue interface that generates an echo is represented by a 
single point. A serial acquisition of linear vertical images allows them to be stacked side-by-side, creating an 
image that displays the positions of these points relative to the transducer over time. Because these linear 
vertical images are acquired very rapidly, the change in position of these points is represented on the M-mode 
diagram as a line or small sine-wave. If the object approaches the transducer, the line moves up; if the object 
moves away from the transducer, the line moves down (Figure 2.30). If the movement is repeated in cyclical 
fashion, this will be obvious on the diagram. The degree of movement is represented by the amplitude of the 
deflection of the points. Movement perpendicular to the ultrasound beam cannot be detected by M-mode 
imaging. 
Click on the image to see a larger view 
Figure 2.30. Monodimensional diagram demonstrating 
movement of the heart, as it appears on the screen in 
real-time. The reference 2D scan is seen in the upper 
portion of the image, on which an arrow denotes the 
movement of the specific portions of the heart (two-
headed arrow, and single-headed arrow); the lower 
portion represents the M-mode image, with the arrows 
corresponding to the same movements of the same 
structures as seen in the 2D image. The sweep speed 
allows about 3 seconds to be displayed. T0 and T1 indicate 
two moments, in which the examined structures are in 
different positions at different points in the cardiac cycle 
(diastole and systole). 
Box 2.4 
A-mode (amplitude mode) ultrasonography is no longer used in diagnostic imaging (with the 
exception of ophthalmology) and is only of historical interest in echocardiography. An A-mode 
image somewhat resembles a spectrogram, with the echoes appearing on the monitor as spikes of 
different amplitude along a horizontal baseline. The height of the spike represents the intensity of 
the signal, and the distance along the X-axis represents the distance from the transducer. A-mode 
ultrasound allows very precise measurements of distance between reflective interfaces, thereby 
finding utility in ophthalmology. Depth resolution is optimal but lateral resolution is null and 
temporal resolution is absent. 
B-mode (brightness mode) ultrasonography is similarly archaic, but the principle of B-mode 
imaging is used in M-mode and 2D imaging. With B-mode imaging, the reflected sound waves are 
ascribed a pixel of a specific intensity along a vertical straight line. The brightness of a pixel, 
represented along a gray scale, is proportional to the amplitude of the echo, while its position on 
the screen corresponds to the depth from which the echo originated. Depth resolution is optimal but 
lateral resolution is null and temporal resolution is absent. 
M-mode (motion mode) ultrasonography (also known as TM-mode or Time-Motion mode) produces 
a tracing that represents the depth along the vertical axis, and time along the horizontal axis. It 
utilizes B-mode imaging technology along a single ultrasound beam, but acquires multiple linear B-
mode images at a very high frequency and displays them along the horizontal time axis. 
Consequently, pixels that represent specific tissue interfaces of moving structures appear to move 
closer or further away from the transducer, producing a wavy line. M-mode echocardiography has 
been extensively utilized in the past and is still used in veterinary practice, because the high axial 
resolution allows precise measurements of thickness, diameters and movement of cardiac 
structures. Because temporal resolution is also very high, exact measurements of the duration of 
cardiac events and their precise timing can be obtained. (New generation high-end ultrasound 
machines have processing capabilities that allow 2D imaging at frame rates that approach those 
obtainable in M-mode imaging - 150-200Hz - allowing similar axio-temporal resolution to M-mode 
imaging.) Depth resolution is optimal, lateral resolution is null and the temporal resolution is 
optimal. 
Real time (real-time) or 2D-mode (two-dimensional) ultrasonography refers to the ability to 
visualize the echocardiographic image in motion. The image that appears on the screen is 
composed of a series of B-mode lines, adjacent to each other, resulting in a gray scale rectangular 
or fan-shaped field of view. The simultaneous display of adjacent B-mode lines results in an 
anatomical cross-section of the organ being examined. Every B-mode line is obtained and 
processed virtually instantaneously, producing the image that appears on the screen. Every line of 
the image effectively represents one monodimensional ultrasound beam. Every line remains on the 
screen until it is replaced by its successor. The frequency with which the images are projected 
depends on the depth of origin of the echoes (which determines the pulse repetition frequency). 
Therefore, the deeper the image field, the longer the time necessary for the return of echoes to the 
transducer and therefore the lower the frame rate. Depth resolution is optimal, lateral resolution is 
optimal and temporal resolution is variable and dependent on the frame rate. 
During a complete echocardiographic examination, both the M-mode and two-dimensional techniques are 
routinely used as they provide different and complementary information. It should be emphasized that the 
ultrasonographer must not rely or depend on only one echocardiographic technique. Each imaging technique 
can inform the clinician, allowing him or her to analyze the case from different points of view. However, with 
advances in image acquisition and processing, frame rates (which previously limited temporal and spatial 
resolution in two-dimensional imaging and prevented accurate measurements) have increased phenomenally, 
allowing clinicians to obtain many measurements with two-dimensional images that could previously only be 
obtained with M-mode imaging. 
M-mode imaging is often done with two-dimensional guidance because the two-dimensional images offer an 
immediate and more intuitive interpretation of morphology and spatial orientation of the various cardiac 
structures. More recently, "anatomic M-mode" has been developed allowingthe ultrasonographer to identify a 
line (not parallel to the ultrasound beam) along which the M-mode image is to be acquired. Imaging frame 
rates and image processing then allow real-time calculation and reconstruction of a virtual M-mode in the 
chosen plane. This allows a more accurate alignment of cardiac structures along which measurements are 
made. 
Two-dimensional echocardiography has gained wide popularity because it provides information that is not 
easily obtained with M-mode imaging. By taking advantage of the rapid movement of the ultrasound beam, 
two-dimensional echocardiography can examine the shape of the heart and the movements of various 
structures. 
The motion of various cardiac structures with two-dimensional echocardiography is independent of their 
direction in regards to the axis of the ultrasound waves (unlike M-mode, where movement is only detected in 
the plane of the ultrasound beam). Contiguous ultrasound beams form a fan-shaped image field and all the 
information from the beams is processed by the computer which assigns a bright point on the screen for every 
detected echo, providing each point with specific spatial coordinates for the duration of a single screen sweep. 
The corresponding image, therefore, is also fan-shaped, reconstructed from all the acquired echo locations 
along each beam, and displayed almost simultaneously. The image is conventionally displayed on the monitor 
with the transducer position at the top of the screen, such that superficial structures are at the top of the 
screen, and deeper structures are lower down the screen. The exact location of explored organs will always 
vary, depending on the orientation and position of the transducer. Changing the position of the probe on the 
surface of the body and altering the axis of the imaging plane allows the experienced sonographer to produce a 
mental three-dimensional reconstruction of the organ being imaged. Recently, 3-dimensional reconstructions 
have become possible; initially, as post-processed stacks of 2-dimensional images acquired during a sweeping 
scan, and more recently, as real-time reconstructions, demonstrating the advances in computer processing 
power over the last decade. However, real-time 3D echocardiographic imaging is still in its infancy. 
The image produced by standard two-dimensional echocardiography is easily interpreted because of the 
multiple shades of gray associated with the various structures that are based on the intensity of the echoes. 
This phenomenon is termed "echogenicity" of tissue - areas that reflect high intensity echoes are termed 
echogenic or hyperechoic and are depicted as white on the screen (adipose tissues, connective tissues, bony 
or calcified structures); whereas areas that reflect low intensity echoes are termed hypoechoic, and are 
depicted as dark gray on the screen (for example, muscle tissue). Areas from which echoes are not reflected 
appear black and are termed anechoic (blood and non-cellular fluid; increasing concentrations of cells in the 
fluid will increase the echogenicity of the fluid). 
Contrast echocardiography is a particular two-dimensional echocardiographic technique that utilizes 
intravenous injections of ultrasonographic contrast material to modify the acoustic impedance of the blood or 
tissue. By injecting a contrast agent into a peripheral vein or a cardiac chamber, the density of the blood is 
increased and the induced microcavitation acts as a powerful reflector of ultrasound waves. 
 
SEARCH RESULT #: 2TITLE: Acoustic Windows and Positioning and Restraint of 
the Patient AUTHOR(S):ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20494&O=VIN 
 
To ensure that the images of the heart are clear and unobstructed by other structures of the body, it is 
necessary to use so-called "acoustic windows". Since the bones and lungs prevent the passage of ultrasound 
waves, there is a limited choice of positions of the probe on the thoracic wall that allow the cone of ultrasound 
waves to reach the heart without encountering ribs, sternebrae or thick portions of lung. 
Consequently, 3 standard acoustic windows have been characterized in small animals: 
 Right parasternal window 
 Left apical window 
 Left cranial window 
The right parasternal window (Figure 2.31) normally requires the transducer to be positioned between the 
3rd and 6th intercostal spaces (generally the 4th or 5th), and between the sternum and the costochondral 
junction. 
Click on the image to see a larger view 
Figure 2.31. The area corresponding to the right 
parasternal acoustic window in the dog. 
The left apical window (Figure 2.32) is obtained by positioning the probe at the level of the 5th, 6th or 7th 
intercostal space close to the sternum. 
Click on the image to see a larger view 
Figure 2.32. The area corresponding to the left apical 
acoustic window in the dog. 
The left cranial window (Figure 2.33) is obtained by placing the transducer in the 3rd or 4th intercostal space 
between the sternum and costochondral junction. 
Click on the image to see a larger view 
Figure 2.33. The area corresponding to the left cranial 
acoustic window in the dog. 
A fourth, less common window can also be included in this discussion - the subxiphoid window (Figure 2.34). 
This view is rarely used, but is useful in specific cases, as it provides optimal alignment along the apico-basilar 
axis of the heart and into the aorta. Thus, Doppler imaging of the flow of blood in the ascending aorta is 
optimized because blood flow is parallel to the ultrasound beam. Occasionally this view can be used to obtain 
satisfactory 2D cardiac images in very small animals. A suprasternal window, utilized in human 
echocardiography to interrogate the ascending aorta and aortic arch, is not used in veterinary 
echocardiography. 
Click on the image to see a larger view 
Figure 2.34. The area corresponding to the subxiphoid 
acoustic window in the dog. 
These windows allow the sonographer to obtain virtually all the images of the heart for M-mode, two-
dimensional and Doppler interrogation. 
It is important to recognize that the dimensions of the acoustic windows vary from subject to subject and 
thus, it is often necessary to perform numerous small adjustments in probe positioning to obtain a 
representative image. Additionally, variations in pathology or anatomy can necessitate non-conventional probe 
positioning to optimally image the region in question. 
The examination can be performed with the animal placed in lateral recumbency or standing. If lateral 
recumbency is preferred, it is necessary to use a split-level table. The lower level provides a support for the 
sonographer's elbow, while the upper one, equipped with several openings or cut-outs, accommodates the 
patient (Figure 2.35). The author prefers a table with a height-adjustable lower level and with the upper level 
having concentric inlaid circular rings that can be added or removed to suit the size of the animal (Figure 
2.36). Removing the cover provides an opening suitable for examining cats and small dogs. If the opening in 
the table is too large, the patient may sag into it, which can become uncomfortable or stressful to the patient, 
making it difficult to restrain or image. A larger patient, once placed in lateral recumbency, may react to 
corrective positioning because caudal or cranial movements can cause edges of the ribcage to hit the edge of 
the window or cause the head to fall off the edge of the table. 
Click on the image to see a larger view 
 
Figure 2.35. An example of a two-tiered echocardiography table for use with dogs and cats. (A) The position of the 
sonographer's arm can be seen, with the elbow resting on the lower level, while the window in the upper level allows a 
wide range of probemovements. (B) Right lateral recumbency and gentle restraint of a canine patient. 
Click on the image to see a larger view 
Figure 2.36. Details of the windows and inserts of the 
upper level of the echocardiography table. Concentric 
interlocking rings allow optimization of patient positioning 
and comfort, which results in better imaging. 
Regardless, the fenestrated echocardiography table provides the best option for imaging cardiac patients. With 
properly sized openings and correctly positioned and restrained patients, imaging is usually uneventful, quick 
and non-stressful. 
Patients can be imaged on the table in one of two orientations - head to the left, feet towards the 
sonographer, or head to the right, and feet away from the sonographer. These orientations are determined 
purely by personal preference. The former orientation allows a single assistant to restrain the patient by 
straddling the patient and holding both fore and hind limbs. However, the sonographer is more likely to get 
kicked or pawed by a poorly restrained patient or have the machine scratched or damaged. The latter position 
requires either 2 assistants (one cranial, one caudal), or a sandbag system for the hindlimbs and an assistant 
at the head of the patient. 
A relatively small number of subjects (approximately 15%) do not tolerate lateral recumbency, while other 
patients (maybe 10%) have clinical conditions (especially respiratory compromise) preventing this type of 
positioning. Finally, some giant breeds are simply too big to position on an echocardiographic table or too 
heavy to lift without risking injury to technicians. In these cases, it is necessary to opt for a standing position. 
The author sometimes prefers this position for a cursory examination or to acclimatize the patient before 
placing them in lateral recumbency. Recent studies suggest that imaging canine patients in a standing position 
is equally reliable as in lateral recumbency. 
One should also consider that sometimes, in order to restrain a patient in lateral recumbency, multiple 
assistants are required (as explained above). However, with the patient standing, only a single assistant is 
usually required (Figure 2.37). 
Click on the image to see a larger view 
Figure 2.37. Patient restraint when an echocardiographic 
exam is performed with the animal in a standing position. 
For these reasons it is recommended that the clinician becomes proficient at imaging patients in all these 
positions and even becomes capable of imaging patients who cannot assume either position. For example, the 
author finds it best to image very young kittens or puppies with the patient in his lap, as these patients are not 
able to be restrained manually very easily. However, if patients are placed in non-standard imaging positions, 
the images should be interpreted cautiously. 
The author has never required patients to be sedated or chemically restrained during imaging. However, on 
occasion, chemical restraint may be necessary, although clinicians need to evaluate the risks of such 
procedures to the patient and the potential effects on cardiac function and hemodynamics. Various 
combinations of narcotic cocktails are available that minimally affect function, and may permit examination of 
fractious or uncooperative individuals (such as puppies or cats). Additionally, in situations with limited technical 
support, mild sedation may allow a more thorough evaluation than would otherwise be possible. 
OPTIMIZATION OF THE IMAGE 
The image should be optimized prior to commencing an echocardiographic examination and recording images. 
First, where possible, the appropriate imaging "mode" should be selected that loads pre-set filter and gain 
settings which have been optimized for cardiac imaging. Next, overall and regional gain should be adjusted; 
the image depth should be adjusted so that the heart occupies the entire screen with the left ventricular wall 
near the bottom of the image field; and the focal point should be set in the lower third of the image field. 
Finally, the sector width should be adjusted to optimize the frame rate without compromising the view of the 
structures being imaged. As imaging progresses, the sonographer should make additional small adjustments as 
necessary to provide the optimum images of various cardiac structures or regions of interest. 
 
SEARCH RESULT #: 3TITLE: Two-dimensional EchocardiographyAUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20495&O=VIN 
 
The two-dimensional echocardiograph provides an intuitive, anatomical two-dimensional view of cardiac 
structures in real-time, thereby allowing examination of cardiac function and morphology. 
The ultrasound beam produced by sector probes commonly used for 2D echocardiography is fan-shaped. It 
can be oriented so as to obtain a large number of views of the heart, allowing simultaneous visualization of 
both atrial and ventricular chambers, cardiac valves, myocardial walls, endocardium and pericardium, roots of 
the aortic and pulmonary arteries and atrio-venous junctions of the vena cavae and pulmonary veins. 
Additionally, 2D images provide a guide for orienting the M-mode and Doppler cursors correctly. The dynamic 
nature of the 2D image permits the operator to estimate both global and regional myocardial function and 
valve movement. 
While using the same acoustic window but varying the angle of the probe and rotating it clockwise or 
counter-clockwise, it is possible to visualize various cross-sections and, consequently, various structures or 
different parts of the same structures. By orienting the beam parallel or perpendicular to the main structure 
being examined, the sonographer can obtain either a long-axis or short-axis view of a particular structure 
(usually heart or vessels). 
Before discussing the views that can be obtained from the various acoustic windows, it is necessary to briefly 
examine the terms "long axis" and "short axis". For every anatomical structure of echocardiographic interest, a 
"short axis" view is defined not by its sphericity, but as the view that provides the smallest dimension of the 
structure (Figure 2.38). This applies to both the whole heart and the right and left ventricles separately. By 
convention, the long-axis and short-axis views of the atria and the atrioventricular valves are defined along the 
same planes as the long and short-axis views of the ventricles. However, the short-axis views of the aortic 
valve are somewhat obliqued from the short-axis views of the ventricles. Additionally, the plane of the aorta is 
essentially at a right angle to the plane of the pulmonic valve (Figure 2.39). The aortic and pulmonic long-axis 
views are obtained by simultaneously visualizing the outflow tract, roots and a maximal post-valvular portion 
of each vessel (Figure 2.40); the short-axis view of the aortic valve is orthogonal to its long-axis view. A short-
axis view of the pulmonic valve is not obtainable using standard acoustic windows. 
Click on the image to see a larger view 
 
Figure 2.38. Schematic representation of the (A) long 
and (B and BI) short axes of the two sides of the heart: 
the right side is closer to the transducer, while the left 
heart is toward the bottom of the image. 
Figure 2.39. Schematic representation of the aortic 
annulus (1) and the pulmonic annulus (2). The aortic 
valve is seen in short axis (cross-section), while the 
pulmonary valve lies in long axis. 
Figure 2.40. Schematic representation of the 
visualization of the aorta in long axis. The ellipse indicates 
the valvular annulus; the long axis of the root of the 
vessel is labeled "a", while the vessel wall is labeled "w". 
In addition to rotating the probe clock-wise or counter-clockwise to obtain different axes and views of various 
cardiacstructures, it is also possible to vary the angular orientation of the probe on the chest. Slight 
modifications in the angle of incidence between the probe and the chest wall permit the sonographer to modify 
the images obtained along a particular axis. Indeed, most of the serial images in a particular axial orientation 
are produced by gently tilting the probe in one direction or the other with minimal (if any) rotation. 
Simply put, rotating the transducer allows the transition from the long-axis view to the short-axis view of a 
structure, while tilting the transducer provides multiple cross-sections of the structure along a particular axis. 
Orientating the probe to obtain long- and short-axis views is possible because every probe with a rectangular 
surface area produces a fan of ultrasound waves that extend along the long-axis of the probe face with 
effectively no lateral dimension to the fan (Figure 2.41). 
Click on the image to see a larger view 
Figure 2.41. Schematic representation of the scanning 
plane of a phased-array sector probe. 
With probes that have a circular cross section, it becomes impossible to characterize the orientation of the 
probe without the aid of markers on the transducer body that indicate the orientation of the ultrasound beam. 
These markers are usually easily felt with the thumb or fingers, and may be illuminated. Generally, an 
experienced operator will be able to determine the probe orientation by the image obtained on the screen. 
However, in some instances, when structures do not appear as they would be expected, understanding the 
correct orientation of the probe is essential for understanding the correct orientation of the structures being 
imaged. From a practical standpoint, it is generally better to learn to perform a standard series of views using 
the actual images as reference points rather than by remembering specific theoretical guidelines and views a 
priori. This is analogous to trying to learn to ride a bicycle without actually pedaling - the theory provides a 
reasonable starting point, but the execution is always very different from the theory. Having said all this, 
modern ultrasound equipment permits any view to be flipped either horizontally or vertically on the screen, so 
that even if the transducer is held incorrectly, the corrected view can be projected on the screen (Figure 2.21). 
In the following descriptions, the rotational angles of the transducer are referenced to the cranio-caudal axis 
of the animal, forming a specific angle with the axis of the transducer plane. If these two axes (animal and 
transducer plane) are orthogonal, the rotational angle of the probe is equal to 90°, while, if they are parallel, 
the rotational angle equals 0° (Figure 2.42). The reference angle is defined as the angle in the dorsocranial 
quadrant of these 2 axes. Thus, when the probe is positioned to obtain a right parasternal long-axis 4-chamber 
view (Figure 2.43), the axis of the probe is rotated approximately 60° (Figure 2.44). In practice, the probe is 
positioned as if pointing at the contralateral scapula, in a line parallel with the ribs between which it is 
positioned. In this view, both ventricles and atria are seen, as well as the mitral and tricuspid valves, the 
chordae tendineae and their corresponding papillary muscles. By convention, the ventricular apex is placed to 
the left of the image, and the atria to the right; the right heart is at the top of the screen, and the left heart 
occupies the center and lower portions of the image field (Figure 2.45). 
Click on the image to see a larger view 
 
Figure 2.42. System of reference for the rotational movements of the probe around the longitudinal axis during an 
examination. The black dorsocranial quadrant is used as a reference quadrant to define the rotational angles. For 
example, when the imaging plane is horizontal, the angular rotation is equal to 0°; if, however, the probe is slowly 
rotated perpendicular to the former plane, the rotational angle is now equal to 90°. (A) right flank; (B) left flank. 
 
Figure 2.43. Schematic representation of the right 
parasternal 4-chamber long axis view. 
Figure 2.44. Positioning of the ultrasound probe (rotation 
angle of 60°) to obtain the right parasternal 4-chamber long 
axis view. 
Figure 2.45. Right parasternal long-axis 4-chamber 
view. The right heart is at the top of the image, the left 
heart is at the bottom of the image. Atria are on the right 
of the image, ventricles are on the left of the image. 
By slightly rotating the probe cranially (reducing the rotational angle by 15o), and slightly tilting the probe 
cranially (reducing the angle of incidence with the thorax), while remaining in the same intercostal space 
(Figure 2.47), one obtains the right parasternal long-axis left ventricular outflow view, in which it is possible to 
visualize the left ventricle, left ventricular outflow tract (LVOT), aortic valve cusps, aortic bulb and ascending 
aorta (Figure 2.48). With careful manipulation, it is possible to observe the left coronary osteum in this view. 
By moving the probe one rib-space cranially, and slightly rotating the probe cranially from the right 
parasternal long-axis 4-chamber view (rotational angle approximately 50°), it is often possible to obtain the 
right parasternal oblique LV view which allows visualization of the long-axis of the right ventricular outflow and 
pulmonic valves (Figure 2.46). This view is seldom used in small animals, but is often used in horses and 
cattle. 
Click on the image to see a larger view 
 
 
Figure 2.46. An oblique right parasternal long-axis view for the optimization of right ventricular outflow tract and the 
pulmonary valve. A) schematic representation. B) echocardiographic image. 
Figure 2.47. Positioning of the ultrasound probe 
(rotation angle of 45°) to obtain the right parasternal left 
ventricular outflow view. 
 
 
Figure 2.48. Right parasternal left ventricular outflow view. A) schematic representation. B) echocardiographic 
image. 
The right parasternal short axis views are obtained by using the 4-chamber long-axis view as a point of 
reference. From this long-axis position, the probe is rotated cranially by 90° (rotational angle of -30°) (Figure 
2.49). It should be possible now to recognize the typical shape of the left ventricle in cross-section at the level 
of the papillary muscle in the central and lower portion of the screen, while in the upper portion of the screen, 
the right ventricle appears as a crescent shaped structure partially encircling the left ventricle (Figure 2.50). 
The other short-axis cross-sections from the apex to the base of the heart are obtained largely by tilting the 
probe (changing the angle of incidence with the chest) towards and away from the operator, with the apex 
being ventrocaudal and the base being craniodorsal. Tilting the probe in this fashion, with minimal rotational 
adjustments, produces the following views from the apex (Figure 2.51), through papillary muscles (Figure 
2.50), the chordae tendineae (Figure 2.52) and mitral valves (Figure 2.53). These projections, except for the 
very apical-most views, also include cross-sections of the right ventricle which appears as a crescent shaped 
hypoechoic region adjacent and proximal to the interventricular septum. 
Click on the image to see a larger view 
Figure 2.49. Positioning of the ultrasound probe 
(rotation angle of -30°) to obtain the right parasternal 4-
chamber short axis view. 
 
 
Figure 2.50. Right parasternal 4-chamber short-axis view at the level of the papillary muscles. A) schematic 
representation. B) echocardiographic image. 
 
 
Figure 2.51. Right parasternal 4-chamber short-axis view just above the level of the cardiac apex. A) schematic 
representation. B) echocardiographic image.Figure 2.52. Right parasternal 4-chamber short-axis view at the level of the chordae tendineae. A) schematic 
representation. B) echocardiographic image. 
 
 
Figure 2.53. Right parasternal 4-chamber short-axis view at the level of the mitral valve. A) schematic 
representation. B) echocardiographic image. 
Finally, by tilting further cranio-dorsally, the base of the heart comes into view, with aortic valves in the center 
encircled by the left atrium in the lower left region of the image, the tricuspid valves in the upper region of the 
image and the pulmonic valves in the right side of the image (Figure 2.54). The pulmonic valves and main 
pulmonary artery are often best imaged by moving the transducer cranially one intercostal space, and sliding it 
down the chest towards the sternum slightly, and then tilting it dorsally (decreasing the thoracic incident 
angle). The right pulmonary artery can often be seen traversing across the roof of the left atrium near the 
bottom of the screen, while the ascending aorta is seen in cross-section in the middle of the screen, and the 
tricuspid valve and right atrium occupy the near-field regions (Figure 2.55). 
Click on the image to see a larger view 
 
 
Figure 2.54. Right parasternal 4-chamber short-axis view at the level of the cardiac base. A) schematic 
representation. B) echocardiographic image. 
 
 
Figure 2.55. Right parasternal 4-chamber short-axis view at the level of the bifurcation of the pulmonary arteries. A) 
schematic representation. B) echocardiographic image. 
There are several important technical considerations that allow optimization of the short-axis views. It is often 
easy to obtain an oblique short-axis view rather than a true orthogonal view. This can be circumvented by 
moving the probe until the short-axis mitral valve view is obtained (Figure 2.53) with both valve commissures 
visible as the "fish mouth" within the ventricular cavity. From this position, the probe can be tilted 
craniodorsally towards the base, or ventrocaudally towards the apex to obtain the relevant cross-sectional 
views. 
Transducer placement for the left apical view is relatively easy to find by using the point of the maximal 
cardiac impulse as a reference; however, the correct alignment of the probe is not nearly as intuitive, 
demanding rigorous alignment of the ultrasound beam with the long-axis of the heart. Therefore, it is 
important to remember that the main axis of the heart is directed from a left ventrocaudal position (which 
corresponds with the maximal cardiac impulse) to a right craniodorsal position. The right ventricle extends 
craniodorsally from the right sternal region, while the left ventricle extends dorsally (and slightly cranially) 
from the left sternal region. Therefore, if the transverse plane of the heart in the thoracic cage is considered, 
cutting longitudinally through both ventricles, the angular rotation of the probe with respect to the craniocaudal 
axis of the patient is approximately 100° with the transducer tilted cranially (Figure 2.56). 
Click on the image to see a larger view 
Figure 2.56. Positioning of the ultrasound probe 
(rotation angle of 100°) to obtain the left apical 4-
chamber view. 
The cross-sections obtainable from the left apical view are, therefore, all in long axis originating at the cardiac 
apex. Of these, the apical 4-chamber view is the standard view, with the two ventricles and the two atria 
visualized simultaneously along with the atrioventricular valves and the septae. The standard orientation of the 
image on the screen is to position the apex at the top of the screen, and the atria in the far-field, with the left 
ventricle on the right of the screen and the right ventricle on the left. This results in the atrioventricular valves 
opening towards the transducer during diastole (Figure 2.57). In this view, it is possible to examine the relative 
sizes of the ventricular chambers, to verify integrity of the septae, and to examine the movement of the 
valves. Additionally, this view allows examination of ventricular compliance through the appraisal of pre-
systolic and pre-diastolic volumes and dimensions. This view is also utilized to examine myocardial function by 
tissue Doppler examination. 
Click on the image to see a larger view 
 
 
Figure 2.57. Left apical 4-chamber view. A) schematic representation. B) echocardiographic image. 
Rotating the probe to a rotation angle of approximately 110° and tilting even more cranially (Figure 2.58), one 
obtains the apical 5-chamber view which consists of the 4 cardiac chambers and the left ventricular outflow 
tract and aortic valve and root (Figure 2.59). 
Click on the image to see a larger view 
Figure 2.58. Positioning of the ultrasound probe 
(rotation angle of 110°) to obtain the left apical 5-
chamber view. 
 
 
Figure 2.59. Left apical 5-chamber view. A) schematic representation. B) echocardiographic image. 
By rotating the probe 90°, the left apical 2-chamber view can be obtained (Figures 2.60-2.61). Slight 
adjustment to this angle and the thoracic incident angle allows visualization of less standard views of the LVOT 
(Figures 2.62-2.63). 
Click on the image to see a larger view 
Figure 2.60. Positioning of the ultrasound probe 
(rotation angle of 45°) to obtain the left apical 2-chamber 
view. 
 
 
Figure 2.61. Left apical 2-chamber view. A) schematic representation. B) echocardiographic image. 
Figure 2.62. Positioning of the ultrasound probe 
(rotation angle of 30°) to obtain the left apical LVOT (3-
chamber) view. 
 
 
Figure 2.63. Left apical 3-chamber LVOT view. A) schematic representation. B) echocardiographic image. 
The left cranial view is obtained by moving the probe cranially 1-2 intercostal spaces. The probe is oriented 
dorsocaudally and rotated approximately 45° (Figure 2.64) to obtain the long axis view, where the long axis of 
the left ventricle, LVOT and ascending aorta can be visualized (Figure 2.65). With correct orientation, the aorta 
appears virtually horizontal on the screen. By convention, the ventricular apex is on the left of the screen and 
the ascending aorta is on the right. Subsequently, with slight tilting of the longitudinal axis of the probe 
directing the ultrasound beam ventrally, it is possible to view the right atrium and tricuspid valve (Figure 2.66) 
while the opposite tilt reveals the pulmonic valve and pulmonary artery (Figure 2.67). A modification of this 
view allows visualization of a patent ductus arteriosus (Figure 2.68). 
Click on the image to see a larger view 
Figure 2.64. Positioning of the ultrasound probe 
(rotation angle of 45°) to obtain the left cranial long-axis 
view of the left ventricle and left ventricular outflow tract. 
 
 
Figure 2.65. Left cranial long-axis view of the left ventricular outflow tract. A) schematic representation. B) 
echocardiographic image. The arrow is pointing at the pulmonary valve. 
 
 
Figure 2.66. Left cranial long-axis view of the right heart. A) schematic representation. B) echocardiographic image. 
 
 
Figure 2.67. Left cranial long-axis view of the right ventricular outflow tract and pulmonary artery. A) schematic 
representation. B) echocardiographic image. 
 
Figure 2.68. Left cranial oblique view angled to allow visualization of the ductus arteriosus. A) schematic 
representation. B) echocardiographic image. * = ampulla of the ductus. The image in panel B is rotated approximately 
60° clockwise compared to the diagram in panel A. 
A 90° rotation of the probe (angular rotation of 135°) (Figure 2.69) produces the short-axis view of the aortic 
bulb encircled by the right heart. In this view, the circular aorta appears in the center of the screen, while the 
right atrium and tricuspid valves are on the left of the screen,with the valves opening towards the top of the 
screen in diastole. The right ventricular outflow tract and pulmonic valve can be seen in the upper right region. 
Small sections of the left atrium can often be seen in the lower right of the image (Figure 2.70). 
Click on the image to see a larger view 
Figure 2.69. Positioning of the ultrasound probe 
(rotation angle of 45°) to obtain the left cranial short-axis 
view of the base of the heart. 
 
 
Figure 2.70. Left cranial short-axis view of the base of the heart. A) schematic representation. B) echocardiographic 
image. 
Box 2.5 lists all the acoustic windows and the views obtained in each window used in the dog and the cat. 
Box 2.5 
Right parasternal window - With the transducer place between intercostal spaces III and VI, 
between the sternum and costochondral junction, the following views can be obtained: 
 Long axis 4-chamber view 
 Long axis LVOT view 
 Short axis view at the level of the: 
 Apex of the left ventricle, 
 Papillary muscles left ventricle, 
 Chordae tendineae of the mitral valve, 
 Mitral valves, 
 Aortic valves and left atrium 
 Right ventricular outflow 
Left apical window - With the probe positioned between intercostal spaces V through VII as close 
as possible to the sternum, the following views can be obtained: 
 Apical 2-chamber view with the LV and LA; 
 Apical 4-chamber view 
 Apical 5-chamber view 
 Long-axis LVOT view 
Left cranial window - With the probe positioned between intercostal spaces III and IV and 
between the sternum and costochondral junction, the following views can be obtained: 
 Long axis LVOT view 
 Long axis RVOT view 
 Short axis view of the aortic root, encircled by the right heart 
 Long axis view of the right atrium and right ventricular inflow 
The direct visualization of cardiac structures, chambers and their relationships to one another, as well as the 
kinetic relationships of every portion of myocardium and of the valves, permits the sonographer to assess 
many aspects of cardiac anatomy and function. Unfortunately, despite the versatility that characterizes two-
dimensional echocardiography, many of these assessments are based on subjective observations and their 
quality and accuracy is dependent on the experience of the sonographer. However, with improved frame rates 
and resolution of newer equipment, precise measurements can now be made from two-dimensional images 
rivaling the precision of M-mode measurements. Additionally, the correct orientation of the image and 
positioning of the cursors during measurements allows the operator to more accurately identify the true 
regions and structures being measured. Finally, certain measures of cardiac performance, such as estimates of 
cardiac volume are more accurately obtained from 2D measurements than M-mode measurements. 
 
SEARCH RESULT #: 4TITLE: Monodimensional EchocardiographyAUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20488&O=VIN 
 
M-mode echocardiography allows the sonographer to obtain precise measurements of cardiac structures and to 
examine their movement over time (e.g., velocity of mitral valve opening, ejection time, pre-ejection period, 
duration of ventricular diastolic filling, etc). 
Most M-mode imaging uses the right parasternal views. Most machines allow the M-mode cursor to be 
superimposed on the two-dimensional image for correct alignment. Once the correct alignment is obtained, the 
M-mode imaging is activated, often with a dual screen display - a static, periodically updated 2D image 
showing the approximate alignment and the dynamic M-mode image (Figure 2.71). The M-mode cursor can 
then be adjusted using a trackball or thermal pad, usually by alternating between the 2D image and the M-
mode image, without adjusting the probe position. This is possible since the selection of one of the possible M-
mode projections simply involves selecting one of the projected ultrasound waves that are used to compose 
the 2D image. Since the sweep speed of M-mode image is variable, the number of cardiac cycles displayed on 
a single screen can be optimized to provide the best temporal resolution for examining the timing of specific 
events. Generally, a fast sweep speed allows the best measurement of rapid cardiac events. A general concept 
that always applies to M-mode is that, in order to correctly estimate the thickness or diameter of cardiac 
structures, the beam must cross them orthogonally (at right angles) and the field of view must encompass the 
most distant portions of the structures being examined. Additionally, correct measurement requires 
measurement from leading edge to leading edge of the structure being measured. 
Click on the image to see a larger view 
Figure 2.71. Positioning of the cursor for the M-mode 
imaging of a transventricular view, using the right 
parasternal long axis view for reference. 
Figures 2.72.a and b represent the two right parasternal long-axis 2D views and the various M-mode views 
that can be obtained by moving the ultrasound beam from the caudoventral (A) to cranio-dorsal (E) aspects 
(apical to basilar), (Figure 2.72.b). Figure 2.72.c shows the series of images as they appear on the monitor. In 
position A the right ventricular wall (RVW), interventricular septum (IVS) and left ventricular wall can all be 
visualized. In this position, the diameters of both ventricles are small, but these progressively increase as the 
scan slices proceed towards the positions B and C. Between these last two positions, the chordae tendineae 
(CT) and the leading edge of the anterior mitral valve cusp (AML) become apparent, with the posterior mitral 
valve cusp coming into view by position D. As the posterior cusp disappears in position E, the anterior cusp "is 
transformed" into the posterior wall of the aorta (PAoW). In position E, one can identify, beginning at the 
thoracic wall in the near field, the right ventricular outflow, the anterior wall of the aorta, the aortic valve, 
posterior wall of the aorta and finally, the left atrium. 
Click on the image to see a larger view 
 
 
Figure 2.72. Schematic representation of the standard right parasternal long-axis two dimensional views: (A) 4-
chamber view and (B) LVOT view. The M-mode representation in (C) demonstrates a sweep of the probe from apex to 
base, through the planes labeled A, B, C, D and E in the upper panels. 1 = M-mode appearance of the mitral valve in 
diastole; 2 = M-mode appearance of the aortic valve in systole; 3 = M-mode appearance of the tricuspid valve in 
diastole. 
With an image series like the one described above, it is possible to estimate the systolic and diastolic 
movement of the myocardium and valves, to estimate the change in wall thickness during contraction and 
relaxation, to measure the difference between systole and diastole of the ventricles (shortening fraction), and 
to compare the left atrial dimension with the aortic root dimension. 
Once a satisfactory image is obtained and frozen on the screen, at least 3 cardiac cycles should be used to 
obtain measurements which are then averaged to provide an estimate. These can be selected by scrolling 
through the saved images - most machines store 10-30 seconds of M-mode recording for subsequent review. 
Measurement packages are provided with all machines to partially automate the calculation of cardiac 
measurements. These packages use a calibrated scale which is displayed on the Y-axis of the image. The 
actual measurements are displayed on the screen as bright vertical lines (Figure 2.73), and are often precise to 
within 10ths or 100ths of millimeters. 
Click on the image to see a larger view 
 
 
 
Figure 2.73. Transventricular M-mode tracing. 
A) Schematic representation with anelectrocardiographic reference trace. Telediastole corresponds to the Q wave of 
the QRS and telesystole to the T-wave. B) Echocardiographic image. On the lower margin of the image, the 
measurements of various parts of the ventricle in systole and diastole are displayed, along with ejection fraction (EF) 
and the shortening fraction (FS). C) Schematic representation of pathological variations of transventricular M-mode 
tracings. 1 = left ventricular volume overload; 2 = paradoxical motion of the interventricular septum in the presence 
of right ventricular enlargement; 3 = left ventricular dilated cardiomyopathy; 4 = severe pericardial effusion; 5 = mild 
pericardial effusion; 6 = pericardial effusion with cardiac tamponade; 7 = akinesia of the interventricular septum; 8 = 
left ventricular concentric hypertrophy. 
The numerical data obtained are usually stored in a report format and can often be compared to reference 
values which can be pre-programmed into the echo machine. Table 2.2 shows an example of reference 
intervals used in the author's institution for comparing various measurements obtained in various species or 
different sizes of animals. 
Table 2.2. Reference ranges for M-mode measurements. 
Measurement 
 Cat Dog Dog Dog Dog Dog Dog Horse 
4.5 kg 9 kg 13.5 kg 18 kg 27 kg > 34 kg 
Ao/LA 2D 1.5-1.7 1.5-1.7 1.5-1.7 1.5-1.7 1.5-1.7 1.5-1.7 1.5-1.7 
EPSS 3 3 3-5 3-6 3-9 3-9 3-9 
VDD 32-52 
IVSd 2.5-5 4.8-8 5.7-8.1 6.5-8.3 7.2-8.6 7.8-10.2 8-11.6 19-43 
LVIDd 11-16 23.5-33.5 28.5-35.5 33-38.5 36.5-41 43-50.5 46.5-58 80-130 
LVWd 2.5-5 3.8-7.1 4.8-7.2 5.7-7.3 6.2-7.7 6.9-9.2 7-10.8 20-40 
IVSs 5-9 7.7-12.4 8.9-12.5 10-12.6 10.9-13 11.5-15.1 11.6-17.2 35-62 
LVIDs 6-10 12.5-21 16.5-23 20.5-25 24-28 29-36 32-42 43-79 
LVWs 4-9 5.5-10.5 7-10.8 8.3-11 9.3-11.5 10.5-14 11-16.5 32-56 
EF (%) 60-80 60-80 60-80 60-80 60-80 60-80 60-80 60-80 
SF (%) 29-55 33-38 33-38 33-38 33-38 33-38 33-38 32-55 
See also the VIN Canine Echocardiography Calculator. 
The M-mode tracing of the left ventricle is obtained by arranging the probe so that the ultrasound beam 
crosses the interventricular septum perpendicularly and meets the free wall at or slightly above the level of the 
insertion of the chordae tendineae onto the papillary muscles (Figure 2.72.b). The measurement of the 
interventricular septum, the free wall and the ventricular chamber is performed in end diastole (telediastole) 
and end systole (telesystole). If a synchronous electrocardiographic tracing is displayed, end-diastole is 
assumed to occur at the onset of the QRS complex. If no ECG is available, end-diastole is identified as the 
moment before the septum and free wall begin to thicken and move towards each other. However, in some 
instances, there may be asynchrony of the movement of the LV walls. In this case, the identification of systole 
and diastole are left to the operator's discretion. 
The thickness of the LV free wall is variable, being thickest between the papillary muscles and thinnest just 
apical to the mitral annulus. 
In order to visualize the mitral valve, the M-mode cursor must be directed towards the left atrium, until both 
valvular cusps are visualized. The LVOT should not be visible in this view - if it can be seen, the cursor position 
is too basilar and should be adjusted slightly apically (Figure 2.72.c). The image represented in Figure 2.74 
demonstrates this. The point of maximal valvular excursion in early diastole is named the E-point (Early 
diastolic opening) and the nadir of early diastolic closing is termed the F-point. Together, these 2 points create 
a line termed the E-F slope, which represents the balance of pressures between the LA and LV. The distance 
between the interventricular septum and the E-point of the mitral valve is termed the E-point-septal separation 
(EPSS), which is often used as a measure of myocardial systolic function. With atrial systole, additional blood is 
forced through the mitral opening resulting in an additional excursion of the valve edges, termed the A-wave. 
As the atrium begins to relax, the valve begins to close once more. The subsequent onset of ventricular systole 
completes this valve closure, which is identified as the C-point. Therefore, the movement of the septal cusp in 
diastole resembles the letter "M" while the posterior (free-wall) cusp resembles the letter "W". Figure 2.75 
identifies these points on an M-mode image of the mitral valves. 
Click on the image to see a larger view 
 
 
Figure 2.74. Schematic representation of the transmitral 
M-mode tracing. D = onset of mitral diastolic opening; E 
= early peak opening of the mitral valve corresponding to 
passive ventricular filling; F = diastolic flutter of the 
mitral cusps; A = late peak opening of the mitral valve 
corresponding to atrial contraction; C = closing of the 
valve during the ventricular systole; E-IVS (EPSS) = 
distance between the E-point and the interventricular 
septum (E-point to septal separation). 
Figure 2.75. Transmitral M-mode tracing. On the lower 
edge of the image, some of the measurements used in 
evaluation of cardiac function and mitral valve motion are 
displayed. The excursion D-E is expressed in centimeters; 
the E-F slope is expressed in cm/sec; EPSS (or E-IVS) = 
distance between the E point and the interventricular 
septum is express in centimeters; the D-E slope is 
expressed in cm/sec; interval A-C, expressed in msec. 
By orienting the ultrasound beam dorsocranially (towards the base), the aortic valves, aortic root and 
ascending aorta can be visualized (Figure 2.72). In this view, the interventricular septum "is transformed" into 
the anterior aortic wall while the septal cusp of the mitral valve becomes the posterior aortic wall. Between 
these two walls, it is possible to visualize, albeit with difficulty, the aortic valves. During ventricular systole, 
these valves are open, creating a stretched hexagon (so-called aortic box); during diastole, the valves are 
closed, producing a single solid line (Figure 2.76). 
Click on the image to see a larger view 
Figure 2.76. Schematic representation of the transaortic 
M-mode tracing. 1 = open aortic valve in systole; 2 = 
aortic valve closure in diastole. The vertical line in line 
with the Q-wave of the QRS complex signifies the 
beginning of ventricular electrical systole, while the 
second vertical line indicates the beginning of ventricular 
ejection. The space between the two lines, indicated with 
acronym PEP, represents the pre-ejection period. Finally, 
the space comprised between the opening and the closing 
of aortic valve (LVET) represents the ventricular ejection 
time. 
The two aortic walls move parallel to each other, towards the transducer in systole and away from the 
transducer in diastole. The left atrium can be visualized distal to the posterior aortic wall. In both dogs and 
cats, the position of the cursor and the rotation of the heart are such that the M-mode cursor usually transects 
the left auricle, rather than the body of the left atrium. Using this scanning plane it is possible to measure the 
left atrium (actually the left auricle) and aortic systolic and diastolic dimensions, the systolic excursion of the 
aortic valves, the ventricular ejection time (LVET) which is measured as the duration of aortic valve opening, 
and, if synchronized with the ECG, the pre-ejection period (PEP) which represents isovolumic contraction and is 
measured from the onset of the QRS complex to the opening of the aortic valves. Finally, the ratio of LA (left 
auricle) to aorta can be calculated. 
Figure 2.77 demonstrates these various measurements. 
Click on the image to see a larger view 
Figure 2.77. Transaortic M-mode tracing synchronized 
with an ECG tracing. 1 = onset of ventricular systole; 2 = 
onsetof the ejection period; 3 = end of the ejection 
period. 
Box 2.6 
Transventricular projection. The beam is directed so that it crosses the interventricular septum 
perpendicularly and meets the left ventricular free wall at the tip of the papillary muscles near the 
insertion of the chordae tendineae. 
In this position, the following systolic and diastolic measurements can be obtained: 
 Right ventricular dimensions (RVDs/d) 
 Interventricular septal thickness (IVSs/d) 
 Left ventricular dimensions (LVDs/d) 
 Left ventricular free wall thickness (LVWs/d) 
Echocardiographic findings of specific pathologies will be detailed in subsequent chapters. However, 
briefly, in dilated cardiomyopathies, there is an increase of LVDs/d and, occasionally, also of 
RVDs/d. These changes are often associated with normal or reduced measures of IVSs/d and 
LVWs/d. On the other hand, in concentric hypertrophy and hypertrophic cardiomyopathy, the 
ventricular diameters are often decreased, together with an increase of thickness of IVSs/d and 
LVWs/d. (Figure 2.73.c). 
Transmitral projection. The beam is oriented towards the heart base until it intersects the 
edges of the mitral valve cusps. This results in the characteristic M-mode image, in which the 
diastolic movements of the septal cusp create a shape similar to the letter "M", while those of the 
posterior (free wall) cusp create a shape similar to the letter "W". 
Using this image it is possible to measure the E-point septal separation (EPSS), the E-F slope, 
and to observe atrial systole by virtue of detection of the A-wave. 
Figure 2.78 represents the normal M-mode image of mitral valves. 
Click on the image to see a larger view 
Figure 2.78. Schematic representation of 
pathological variations of the transmitral M-mode 
tracing. 1 = normal; 2 = mitral stenosis; 3 = 
mitral insufficiency; 4 = left ventricular dilated 
cardiomyopathy; 5 = flutter of the septal mitral 
cusp; 6 = chronic mitral valve disease; 7 = 
chronic aortic insufficiency; 8 = severe aortic 
insufficiency or altered left ventricular relaxation. 
Transaortic projection. If the beam is directed still more dorsocranially, additional structures 
come into view: 
 Anterior wall of the aortic root 
 Base of the aorta at the level of the aortic valves which form an elongated hexagon (aortic 
box) during systole 
 Posterior wall of the aortic root 
 Left atrium/auricle 
From this view, it is possible to measure the width of the aortic root (Ao) and to compare it with 
the diameter of the left atrium/auricle (LA, LAu), and to measure the LV ejection time. 
Because the cursor usually transects the left auricle rather than the body of the left atrium in 
dogs and cats (unlike humans), the LA/Ao is often calculated more accurately from the two-
dimensional image in a right parasternal short-axis or long-axis view (Figure 2.79). 
Click on the image to see a larger view 
Figure 2.79. Two-dimensional echocardiographic 
image of the base of the heart in short axis from 
right, optimized to calculate the relationship 
between diameter of the body of the left atrium 
(b) and the aortic annulus (a) - the LA/Ao. 
Alterations in the movement, position and shape of the aortic valve cusps can indicate various 
pathologies. Figure 2.80 demonstrates a normal M-mode image and some images obtained in 
specific pathologies. 
Click on the image to see a larger view 
Figure 2.80. Schematic representation of 
pathological variations of the transaortic M-mode 
tracing. 1 = normal; 2 = aortic stenosis; 3 = 
aortic endocarditis; 4 = valve flutter; 5 = bicuspid 
aortic valve; 6 = reduced cardiac flow; 7 = fibrous 
aortic valve; 8 = severe aortic insufficiency; 9 = 
mid-systolic closure of the aortic valve in 
hypertrophic cardiomyopathy. 
 
In veterinary medicine, the three fundamental M-mode projections, summarized in Box 2.6, can be obtained 
either from the two-dimensional right parasternal long-axis or short-axis images (Figure 2.81). There are 
theoretical benefits to using each of these views to obtain the M-mode image, and the measurements obtained 
in each do not necessarily agree with each other. Thus, sonographers should be consistent at least within 
patients, as to which method they use to obtain the M-mode view, so that sequential exams can be compared. 
Additionally, certain M-mode projections are more easily or consistently obtained in one or the other view. For 
example, the transmitral projection is more easily obtained in the long-axis view, although experienced 
sonographers are usually able to reproduce their measurements in either view. 
Click on the image to see a larger view 
 
 
Figure 2.81. Positioning of the cursor (m) for M-mode imaging using the 2D image for reference in right short-axis 
view through the left ventricle (A), the mitral valve (B) and aortic valve (C). 
Reference intervals for the various M-mode measurements have been calculated by numerous authors and 
some of these are represented in Tables 2.3 and 2.4. For the LA/Ao, large and various reference intervals exist 
which are dependent on the method used to calculate them. Thus the sonographer should always state how 
the LA/Ao was measured. 
Table 2.3. Echocardiographic reference values in some canine breeds. 
Breed Weight LVDd LVDs LVWd LVWs IVSd IVSs SF 
Kg mm mm mm mm mm mm % 
Poodle 3 16-28 8-16 4-6 6-10 47 
Beagle 8.9±1.5 19.5-33.1 8.9-22.5 4.4-12 7.6-15.2 4.5-8.9 6.6-12.6 40 
WHWT 10.3±0.9 17.4-40.2 12.6-27.4 4-8.8 7.2-12.4 4.1-9.7 5.2-15.2 35 
Cocker spaniel 12.2±2.25 27.2-40.4 16.6-27.8 5.7-10.1 34.3 
Corgi 8-19 28-40 12-23 6-10 8-13 44 
Pointer 19.2±2.8 34.4-44 20.5-30.1 5.7-8.5 9-14.1 4.7-9.1 8.6-12.6 35.5 
Afghan hound 17-36 33-52 20-37 7-11 9-18 33 
Hound 26.6±3.5 28.1-50.14 25.5-39.5 8.7-15.5 10.9-19.7 7.2-14 8.2-18.6 25.3 
Hound 29.1±3.7 40.7-53.1 28.1-38.5 8.2-15 10-16.8 28.8 
Boxer 28±7.1 30-50 26.8 6-14 11-19 5-13 9-17 33 
Golden retriever 23-41 37-51 1.8-3.5 8-12 10-19 39 
Doberman 34.7-45.5 25.9-36.9 5.6-10.4 8.3-14.1 21.7 
Doberman 36 38.5-55.1 24.2-37.4 8.4-10.8 14.1 8.4-10.8 13-15.6 34.2 
Mastiff Spanish 52.4±3.3 44.9-50.5 26.8-31.2 8.9-10.5 14.4-16 9-10.6 14.6-16.6 39.2 
Terranova 47-69.5 44-60 29-44 8-13 11-16 7-15 11-20 30 
Alan 52-75 44-59 34-45 10-16 11-19 12-16 14-19 25 
Irish wolfhound 50-80 46-59 33-45 9-13 11-17 9-14.5 11-17 28 
Table 2.4. Echocardiographic reference values in the cat. 
LVDd LVDs LVWd LVWs IVSd IVSs LA Ao 
12-18 5-10 < 5 < 9 < 5 < 9 8-13 8-11 
 
SEARCH RESULT #: 5TITLE: Echocardiographic Measurements and Indices of 
Cardiac FunctionAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20496&O=VIN 
 
Using measurements from the two-dimensional and M-mode images, it is possible to calculate numerous 
indices of cardiac function, primarily left ventricular function. These can be divided into indices of systolic 
function, which is the ability to contract and eject blood from the ventricle, and diastolic function, which defines 
the ability to receive blood into the ventricle in diastole. Numerous pathologies reduce one or the other or both 
of these functions resulting in substantial modifications of the volume of blood filling the ventricles in diastole 
(preload), or of the ejected volume, which, together with other complex variables, constitutes afterload. 
This section describes the indices of ventricular systolic (and to a much lesser extent, diastolic) function 
(with corresponding reference intervals) that can be calculated from two-dimensional and M-mode 
echocardiographic images. With these two techniques, it is possible to estimate the systolic and diastolic 
function of the left ventricle, the systolic thickening of ventricularwalls and their absolute thicknesses. 
Additionally, the mass of the left ventricle and the size of the left atrium can be calculated. 
Doppler echocardiography is generally required to estimate ventricular diastolic function and will be 
discussed in subsequent chapters. 
The first measures of clinical interest are the linear measurements obtained from the transventricular, 
transmitral and transaortic M-mode projections. As described briefly earlier, with concentric hypertrophy of the 
left ventricle, the thickness of the interventricular septum and left ventricular free wall is increased, while the 
systolic and diastolic diameters of the ventricular chamber may be decreased. In dilated cardiomyopathy, the 
systolic and diastolic left ventricular dimensions are usually increased and E-point-septal-separation (EPSS) is 
also increased. The ventricular walls may or may not be thinner in diastole, but will display systolic 
abnormalities such as decreased thickening or rate of thickening. The LA/Ao is often enlarged with both of 
these conditions. 
Study of Left Ventricular Function 
Two-dimensional echocardiography is often used to study left ventricular function in dogs, cats and horses 
because endocardial and epicardial borders can be easily identified throughout the cardiac cycle in several 
anatomical planes. 
These images can be used to extrapolate several parameters or indices of cardiac function, including systolic 
and diastolic volumes, ejection fraction, cardiac output and myocardial mass. Several geometric models have 
been proposed and evaluated for the estimation of cardiac volume and mass from 2D echocardiography. Most 
of these geometric models have been validated in humans, but few have been examined in domestic animals. 
Additionally, while these models may reasonably approximate volumes in normal hearts, they may have 
limitations with disease states which often have altered ventricular geometry. 
Regardless of the model chosen to estimate volumes from 2D imaging, precise quantitation of the volume 
may not be possible. However, in many situations, a precise measure of volume may be clinically irrelevant. 
Often, clinicians simply wish to determine if the calculated volume markedly differs from previously estimated 
volumes in the same patient, or from reference intervals established in other patients. This may simply be a 
measure that is normalized to a baseline measurement or expressed as a percentage change making any 
errors in absolute measurement clinically insignificant. 
All currently available echocardiographic machines provide software for calculating left ventricular 
functionality using two-dimensional measurements or images. Various geometric algorithms are incorporated, 
all of which assume the ventricle has an elliptical shape. The formulae generally require measurements of the 
cross-sectional area of the LV as well as the long-axis dimension which are then fitted to a model describing a 
variation on an ellipsoid. (The ellipsoid is a geometric figure in which the cross section is circular, and the 
longitudinal shape is elliptic; with the maximal diameter of the cross section equal to half the maximum 
dimension of the longitudinal axis (Figure 2.82).) The volume of the ellipsoid is calculated by measuring the 
cross-sectional perimeter and the long axis dimension, or simply measuring the short axis dimension from 
which the cross-sectional area and the long-axis dimension are estimated (effectively the same as is calculated 
in M-mode estimates of volume). Two-D estimates are somewhat more accurate than M-mode estimates of 
volume if all dimensions are measured (i.e. cross-sectional area and long-axis dimension) rather than 
assumed. 
Click on the image to see a larger view 
Figure 2.82. Schematic representation of the geometric 
figure, the ellipsoid. 
However, due to the substantial time necessary to obtain accurate images both in short-axis and long-axis, the 
ambiguity about the utility of volumetric measurements from a clinical diagnostic standpoint, and the 
considerable controversy about which models most accurately estimate volume, these measurements are 
relatively underutilized in veterinary imaging. 
Figure 2.83 shows images obtained in a left apical 4-chamber view in systole and diastole. The short-axis 
dimension and long-axis dimension can be obtained simultaneously from this view allowing estimation of 
systolic and diastolic volumes, and thereby, ejection fraction. 
Click on the image to see a larger view 
Figure 2.83. Study of left ventricular function via 
calculation of the chamber volumes in diastole and 
systole, using a truncated ellipse method. 
The measurements obtained in this fashion can be used to estimate the following indices (provided heart rate 
is known): 
 Diastolic volume (milliliter) 
 Systolic volume (milliliter) 
 Stroke volume (milliliter) 
 Ejection fraction (%) 
 Cardiac output (l/min) 
The Dodge single plane method uses the following geometric algorithm to estimate the volume of an 
ellipsoid: 
 Diastolic volume (milliliter) = (8 x LVAd2)/(3 x π x LVLd) 
 Systolic volume (milliliter) = (8 x LVAs2)/(3 x π x LVLs) 
These volumes can then be used to estimate the following: 
 Ejection fraction (%) = (diastolic volume - systolic volume)/diastolic volume x 100 
 Stroke volume (milliliter) = diastolic volume - systolic volume 
 Cardiac output (l/min) = (stroke volume x heart rate) /1.000 
Other formulae provide different estimates of volumes. For example, the method of disks (modified Simpson's 
method) uses a trace of the ventricular cavity in systole and diastole from the long-axis or apical view, and 
assumes a spherical cross-sectional geometry at every point along the long axis of the ventricle. These disks, 
which have a measurable thickness, are then summated to produce a volume. Figure 2.84 shows an example 
of calculation of volume using a method of disks. 
Click on the image to see a larger view 
 
Figure 2.84. Study of left ventricular function via calculation of the chamber volumes in diastole (A) and systole (B), 
using the modified Simpson's rule (sum of discs). 
The methods used to estimate volume can be used to estimate myocardial mass, but these calculations are 
rarely (if ever) used clinically, and are outside the scope of a practical echocardiography handbook. 
In addition to estimating volumes and mass of the left ventricle, 2D imaging allows the subjective appraisal 
of regional wall movement, thickening and appearance. It is possible, therefore, to identify global as well as 
regional alterations in contractility which can be labeled as hyperkinetic, hypokinetic or akinetic. 
Although the preceding paragraphs have focused on two-dimensional echocardiography in estimating cardiac 
function, M-mode echocardiography can also provide valuable information about global cardiac function. The 
various measurements previously described, which can be obtained from the three standard monodimensional 
views, can be used to evaluate specific measures of cardiac function, such as shortening fraction, E-point-
septal separation, and systolic time intervals. 
The fractional shortening of the left ventricle is used in order to estimate the global systolic function. The 
fractional shortening is estimated applying the following formula: 
FS% = (LVIDd - LVIDs) /LVIDd x 100 
The value is provided as a percentage and normally lies between 30% and 40% with minor variations due to 
age, breed and size. However, it must always be remembered that fractional shortening is not a direct measure 
of the ventricular systolic myocardial function because it is dependent on preload, afterload and contractility. 
The fractional shortening is effectively a normalized difference, and therefore, ignores the absolute 
measurements. This can lead to misinterpretationsof contractility by inexperienced observers. 
An example that may help elucidate the concept of fractional shortening is the variation of fractional 
shortening in compensated mitral insufficiency. Small animal species and breeds have an increase in FS 
because of a reduction of afterload, due to the fact that the ejection of the left ventricle is facilitated by the 
presence of two "paths" (out the aorta and back into the left atrium), with the left atrium presenting a low 
"impedance" for ejection - thus there is no increase in contractility, but merely a reduction in afterload. On the 
other hand, in larger breeds, the chronic volume overload (increase of the preload) induced by valvular 
pathology results in myocardial failure, that, coupled with a reduced afterload, can preserve the fractional 
shortening within the normal range. For these reasons, FS should always be evaluated together with either an 
absolute systolic or diastolic measurement. 
Other radiometric M-mode indices of clinical interest are outlined in Box 2.7 below. These indices are 
generally considered to be body-weight independent. Many of these radiometric indices (with the exception of 
LA/Ao and EF) are underutilized in practical echocardiography for various reasons: either their correlation with 
specific pathologies is poorly defined, they are poorly reproducible or very operator dependent, or because a 
similar index is more reliably and easily obtained from 2D images. 
Box 2.7 
LA/Ao (normal M-mode values: 0.8-1.2) 
An increase of LA/Ao is a sign of left atrial enlargement. However, this index, when measured 
from M-mode images in small animals effectively compares the left auricle to the aorta, rather than 
the body of the left atrium, and therefore assumes parallel increases in auricular size and left atrial 
size. 
RVDd/LVDd (normally the RVDd is approximately 1/3rd of the LVDd) 
This ratio is subject to changes in either ventricle. Similarly, bilateral change may preserve the 
radiometric relationship. It is rarely used. 
Percentage of systolic thickening of the interventricular septum 
% IVS = (IVSs - IVSd) /IVSd 
(Normal values are approximately 40%) 
Wall thickening diminishes with reduction of contractility of the segment transected by the M-
mode beam. 
Percentage of systolic thickening of the free wall of the left ventricle 
% LVW = (LVWs - LVWd) /LVWd 
(Normal values are approximately 40%) 
As for %IVS, free wall thickening is affected by contractility of the segment transected by the M-
mode beam. 
Ejection Fraction 
EF = (LVVol.d - LVVol.s)/LVVol.d 
(Normal values are approximately 60%) 
Ventricular volumes (Vol) in M-mode analysis are generally determined using the highly inaccurate 
TEICHOLZ formula: 
Vol = 7 LVD3/(2.4 + D) 
where 2.4 represents the factor of correction and D is expressed in centimeters. 
This formula assumes that the left ventricle is oval with the long axis twice the size of the short 
axis. This simplistic assumption, inherent in modeling complex structures from a single 
measurement, provides inaccurate estimates of volume in small animals and humans. 
The systolic time intervals (STI) are clinically important in the assessment of systolic function. These are 
comprised of the ventricular ejection time (LVET), the preejection period (PEP), the velocity of circumferential 
fiber shortening (Vcf) and the ratio of LVET/PEP. 
These indices do not directly assess ventricular contractility, but instead provide estimates of systolic 
function. Their calculation is more laborious than fractional shortening, especially because PEP (and therefore 
LVET/PEP) requires an ECG to be synchronized with the M-mode tracing. Because of this, many practitioners 
omit measuring STI even though they may provide better estimates of systolic function than fractional 
shortening. However, STI are also affected by preload, afterload and heart rate (i.e., they are "load-
dependent") and therefore, of limited value in many cases. 
The PEP corresponds to the so-called isovolumetric contraction and represents the period between mitral 
valve closure and aortic valve opening. During this time, the ventricle is developing pressure to eject blood. In 
cases of systolic failure, this rate of pressure development is reduced, thereby prolonging the PEP. However, in 
the presence of substantial mitral insufficiency, the PEP is affected by the "offloading" of ventricular volume 
into the LA and therefore does not accurately represent isovolumic contraction (since there is no isovolumic 
contraction). 
The speed of circumferential shortening is estimated similarly to fractional shortening, with the exception 
that the LVDd is multiplied by the LVET, with the linear measure expressed in centimeters and time in seconds: 
Vcf = (LVDd - LVDs)/(LVDd x LVET) 
STI are very dependent on heart rate. It may be sufficient for most practitioners to remember that in DCM, 
which has both decreased contractility and increased preload, the Vcf and LVET both decrease, while the PEP 
and PEP/LVET both increase. In mitral insufficiency, Vcf remains normal while LVET decreases and the PEP and 
PEP/LVET both increase. In aortic stenosis, which constitutes a classic model of increased afterload, LVET 
increases and PEP/LVET decreases. 
Semiquantitative Visual Appraisal of the Alterations of Regional Left Ventricular Wall 
Motion 
This type of appraisal is of particular importance in human medicine where the ischemic myopathy constitutes 
the dominant form of pathology. However, in veterinary species, ischemic heart disease is rare, so this type of 
evaluation has not been routinely performed until recently when tissue Doppler imaging introduced regional 
evaluation of wall motion. The principles of both TDI and the method described below are similar. Additionally, 
ischemic injury is suspected in some cats and might benefit from such regional wall function analysis. While the 
exact utility of regional wall motion remains undetermined in most veterinary species, this section briefly 
describes a relatively simple 2D echocardiographic analysis method that has been utilized in human cardiology. 
For the visual semiquantitative appraisal of left ventricular regional myocardial kinetics, one starts with the 
left apical 4-chamber and 2-chamber views, then progresses to the right parasternal outflow view. In each 
view, the left ventricular myocardium is divided into 6 segments (Figure 2.85). In the right parasternal short-
axis view at the level of the mitral valves and the papillary muscles, the myocardium is divided into 5 
segments (Figure 2.86). Thus, 28 different segments are created and recorded in the course of the 
echocardiographic examination. They are then individually examined and scored as follows: normal contraction 
= 1 point; hypokinesis = 2 points; akinesis = 3 points; dyskinesis = 4 points; not assessed = 0 points. 
Click on the image to see a larger view 
 
 
Figure 2.85. Subdivision of the left ventricle into 
segments in long axis, for the visual semiquantitative 
appraisal of alterations of wall motion. 
Figure 2.86. Subdivision of the left ventricle into 
segments in short axis, for the visual semiquantitative 
appraisal of alterations of wall motion. 
It is also possible to calculate an index of contractility from the left apical 4-chamber and 2-chamber views by 
summing the scores of all the segments evaluated in the 2 views and dividing this total by the number of 
segments that were evaluated. Therefore, in the best scenario, where one has evaluated all 12 segments of the 
two views and assigned 1 point to every segment, the index of contractility is equal to 1. In the human field, 
the contractility index is used to estimate the risk of sudden death secondary to myocardial infarction. Subjects 
with an IC >2 have a 10-fold increase in riskof death within the first year after an advanced infarct compared 
to patients with an IC between 1.1 and 1.49 and 3-fold increase compared to patients with IC between 1.5 and 
1.99. 
Currently, no veterinary studies exist that have examined this method in small animals. Whether there is any 
indication for this type of evaluation remains to be determined. Additionally, it might prove useful for 
evaluating cardiac function in athletic horses. 
 
SEARCH RESULT #: 6TITLE: Contrast Echocardiography AUTHOR(S): ADDRESS 
(URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=20497&O=VIN 
 
In some circumstances, it is diagnostically useful to increase the echogenicity of the blood by means of 
intravenous injection of substances capable of reflecting ultrasound waves. Normally, blood appears anechoic 
in two-dimensional echocardiography, although in horses (and occasionally in other animals), it is possible to 
visualize spontaneous echocardiographic contrast due to rouleaux formation of equine red cells (Figure 2.10). 
In other domestic species, this phenomenon has been associated with various cardiac and non-cardiac 
pathologies, such as neoplasia, septicemia, DIC, exercise-induced pulmonary hemorrhage and conditions that 
reduce the velocity of blood flow or induce blood stasis. 
Injectable contrast media allow visualization of relatively slow and laminar currents (for example, the 
transatrial flow in atrial septal defects or patent foramen ovale). Shunt defects that are normally difficult to 
diagnose can be better visualized by using contrast media (Figure 2.87) and observing passage of contrast 
media through the defects, or swirling of non-contrasted blood into the contrasted blood. Two examples of 
congenital shunting defects in which contrast echocardiography is useful are presented in Box 2.8. Several 
additional human applications of contrast echocardiography are currently not utilized in veterinary 
echocardiography. These include myocardial perfusion imaging, enhanced endocardial detection in difficult-to-
image patients, and Doppler imaging when Doppler signal quality is poor. 
Click on the image to see a larger view 
Figure 2.87. Contrast echocardiography. The arrows 
mark hyperechoic points that represent an interface 
between blood and the contrast agent, in this case, air. 
There are various commercial echo-contrast media that are used routinely in human studies. Some, like 
Echovist®, are made of a suspension of galactose microparticles, while others use microsonicated albumin. 
Most of these are too large to pass through the pulmonary capillary bed. Levovist®, developed in 1995, and 
some newer contrast agents developed more recently have the ability to pass through the lungs allowing 
visualization of the left heart, the aorta and several other peripheral arteries. Additionally, some contrast 
agents preferentially enhance myocardium, allowing identification of regional myocardial perfusion defects. 
A practical, safe and cheap alternative is the use of aerated normal saline or 5% glucose solution. To 
perform a contrast echocardiogram, the radial vein is catheterized with a short extension tube and 3-way 
stopcock. In dogs, a 10ml syringe is loaded with saline or glucose solution and 0.5-2 ml of blood is aspirated 
into the syringe. This provides some protein which alters surface tension of the solution and allows air bubbles 
to remain in suspension longer. The syringe is disconnected from the stopcock, and a small amount of air (1-
2ml) is aspirated into the syringe. The entire solution is vigorously shaken, until a small amount of foam forms. 
The excess foam is ejected from the syringe and the syringe is reattached to the stopcock. Once the required 
echocardiographic image is obtained, all or some of the contents of the syringe are rapidly injected into the 
catheter while recording the echocardiogram. The bolus usually reaches the heart within 2-3 seconds and 
illuminates the right heart with a hyper-reflective fluid. The left heart is then examined for presence of bubbles, 
which indicates a right-to-left shunt. Alternatively, the right heart is examined for evidence of a contrast filling 
defect (an area without contrast), which indicates a left-to-right shunt. In cats, this procedure is down-scaled 
appropriately but performed in an identical fashion. 
While, this type of contrast echocardiogram has been reported to cause transient air emboli in humans if 
significant right-left shunting occurs, no side effects have been reported in small animals. 
Additionally, a contrast pericardiogram can be performed to verify the positioning of a pericardial catheter 
when draining pericardial effusion. A small injection of agitated saline into the catheter will rapidly illustrate the 
position of the catheter tip either within the pleural space or pericardial space. 
Box 2.8 
Contrast Echocardiography in atrial septal defects- In left-right shunts, a filling defect may be 
visualized near the atrial septum within the right atrium, because non-contrasted blood flowing 
through the defect displaces the contrasted blood entering the right atrium from the cranial vena 
cava. However, this should not be confused with inflow of blood from the caudal vena cava (which 
is also non-contrasted). Additionally, with careful examination, some bubbles will usually be 
observed within the left atrium and left ventricle because these defects usually have bidirectional 
flow. 
In the case of a right-left shunt, microbubbles appear almost immediately within the left atrium 
as well as the right atrium and right ventricle. 
Contrast echocardiography in ventricular septal defects- In most cases of left-right shunts, a 
filling defect in the right ventricle can be visualized, originating as a stream of non-contrasted blood 
from the site of the defect. If the septal defect is modest, the contrast study may be negative. 
With right-left ventricular septal defects, bubbles will appear within the left ventricle or, more 
commonly, in the aorta since blood is shunted from the right ventricle directly into the LVOT and 
aorta. 
 
 
Chapter 3 ‐ Doppler 
SEARCH RESULT #: 1 
TITLE: Introduction 
AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24101&O=VIN 
 
Doppler echocardiography enhances the echocardiographic examination because it allows the clinician to 
quantitatively and qualitatively characterize intracardiac and extracardiac blood flow. Additionally, the 
incorporation of audible sound with Doppler technology allows the clinician to further characterize blood flow 
patterns and, on occasion, to localize or identify flow disturbances using auditory rather than visual cues. 
Unfortunately, Doppler echocardiography has suffered a similar fate to M-mode and 2D echocardiography, in 
that, as it has increased in popularity, it has tended to be overutilized at the expense of older or more 
complicated techniques. This especially applies to color Doppler imaging, which, by virtue of providing an 
anatomico-physiologically intuitive depiction of blood flow abnormalities, has encouraged the clinician to 
forsake other equally important modalities of cardiac evaluation, such as 2D or spectral Doppler imaging, or 
even a good physical evaluation. It should be stressed that the three commonly used Doppler technologies 
(color, pulsed-wave and continuous-wave) provide complementary, rather than redundant, information about 
most cardiac patients. 
Continuous-wave Doppler is based on the continuous emission and simultaneous continuous reception of 
sound waves, which permits the clinician to measure high-velocity blood flow but compromises the ability to 
localize the source of the flow. On the other hand, in pulsed-wave Doppler, the emission of each ultrasound 
pulse is separated from andprecedes the reception of the reflected echoes which limits the ability to measure 
velocity but allows localization of the blood flow. Both of these techniques depict flows in a continuously 
updated (real-time) spectral graphical format that is not intuitive to the untrained observer (in the same way 
as M-mode imaging is not intuitive) because this graphical output does not provide an anatomical 
representation of the cardiac structures. Instead, analogous to M-mode imaging, a Cartesian system is used to 
display instantaneous blood flow velocities as a function of time. Such a graphical display allows the clinician to 
measure blood flow velocities and timing of blood flow with high precision. 
Color Doppler is an evolution and fusion of pulsed-wave Doppler and 2D imaging in which blood flow 
velocities and flow direction are represented by different colors. Traditionally, blood flow approaching the 
transducer is represented by red colors; flow receding from the transducer is represented by blue colors; and 
fluid stasis appears black. Color Doppler information is usually integrated with 2D imaging, providing an 
intuitive representation of the location and quality of blood flow. However, it can also be used with M-mode 
imaging to obtain more precise timing of flows as well as more complex analysis of cardiac function. Color 
Doppler contains the same limitations as pulsed-wave Doppler, namely, limited ability to measure velocity of 
blood flow. 
 
SEARCH RESULT #: 2 TITLE: The Doppler EffectAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24102&O=VIN 
 
The Doppler Effect, first identified by Christian Johann Doppler in 1842, described the variation in frequency of 
light emitted by dual star systems because of their movement relative to the observer. This phenomenon 
applies to all waves and specifies that waves emitted from an approaching source reach the observer with a 
higher frequency than waves emitted from a static source, and those emitted from a receding source have a 
lower frequency than waves emitted from a static source. Additionally, this phenomenon applies equally to 
waves reflected from moving targets. In the case of Doppler echocardiography, the transducer acts as both the 
transmitter and receiver of the ultrasound waves, while blood cells act as the moving targets from which the 
sound waves are reflected. Those moving towards the transducer reflect the sound waves at a higher 
frequency than the frequency emitted by the transducer, while those moving away from the transducer reflect 
the sound waves at a lower frequency than that emitted by the transducer (Figure 3.1). 
Click on the image to see a larger view 
Figure 3.1. Principles of Doppler echography. Panel A 
shows a beam of ultrasound waves of a single frequency 
parallel to the blood flow. Under these conditions the 
frequency of the reflected sound wave decreases (B) or 
increases (C) relative to the transmitted frequency, 
depending on whether the flow is away from or towards 
the probe. The black wave: transmitted wave; the red 
wave: reflected wave. 
The difference between the emitted and reflected frequencies is known as the Doppler shift. The greater the 
velocity of the target (towards or away from the emitting source), the greater the Doppler shift. The 
relationship between Doppler shift and target velocity with respect to ultrasound waves in tissues is described 
by the Doppler equation: 
Fd = [(2vcosα)/C]Ftrans 
 Where Fd (Hz) = Doppler shift (Ftrans-Frefl) 
 Ftrans (Hz) = transmitted frequency 
 v (m/s) = velocity of the target (towards or away from the transducer) 
 α = angle of incidence between the transmitted beam and the direction of the target 
 C (m/sec) = speed of sound in tissue (1542 m/sec) 
Rearranging this equation we get: 
v=(Fd*c)/(2*ftrans*cosα) 
which allows the target velocity to be determined by measuring the Doppler shift. The Doppler shift is maximal 
when the transmitted sound wave is parallel to the direction of movement of the target (i.e., α=0°, cosα=1). 
As the angle of incidence between the transmitted sound wave and the direction of the target increases (i.e., 
as α increases), the Doppler shift decreases. This results in an underestimation of the velocity of the moving 
target (Figure 3.2) but can be corrected mathematically by accounting for the angle of incidence (cosα). In 
Doppler echocardiography, the direction of the target equates with the direction of blood flow, while the 
transmitting source is the transducer. Thus, the more parallel the ultrasound beam is to the direction of blood 
flow, the more accurately the velocity can be measured. The ultrasound machine assumes that the direction of 
flow is parallel to the transmitted beam (cosα=1), and therefore allows the angle to be defined by the 
sonographer if the angle is significantly different from 0° so that the appropriate correction can be incorporated 
into the Doppler shift calculation. Figure 3.3 displays the electronic goniometer that is superimposed on the 2D 
image and aligned with the presumed direction of blood flow. An angle of incidence between the ultrasound 
beam and the direction of blood flow <20° results in negligible error and does not require correction, however, 
angles >20° require manual angle correction, and angles >60° create unacceptable errors in velocity 
estimation and should not be used when measuring blood flow. 
Click on the image to see a larger view 
 
 
Figure 3.2. Principles of Doppler echography. This figure 
shows three angles of incidence of the Doppler axis with 
respect to the direction of blood flow. With an angle equal 
to 0° (parallel to flow), the maximum velocity can be 
obtained. As the incident angle increases, the flow 
velocity is underestimated, until, at an angle of 90° to the 
direction of flow, no velocity can be measured. 
Figure 3.3. Two-dimensional echocardiographic image 
demonstrating the Doppler axis, represented by the 
dashed line, and the sample volume with an angle 
correction (represented by the two horizontal parallel 
lines and the oblique line respectively). 
Used in this manner, Doppler echocardiography should be able to measure the maximum velocity of blood flow 
at specific locations. In cases where optimal alignment is impossible, angle correction should theoretically allow 
the clinician to still measure the velocity of blood flow accurately. However, angle correction can only be 
utilized with pulsed-wave Doppler, which is unable to estimate high-velocity flows (due to technical limitations 
discussed later in this chapter). Angle correction is not available with continuous-wave Doppler, which is used 
specifically to estimate high-velocity blood flow, and should be taken into consideration by clinicians when 
performing continuous-wave interrogations of flow. Incorrect alignment always results in an underestimation of 
the maximum velocity because the cosine of the incident angle is <1 (see equation above). This can be seen in 
the following example: if the angle of incidence is 20°, the velocity is underestimated by approximately 6% (a 
relatively small error). However, if the angle of incidence is 60°, the error increases to 50%. In real terms, a 
velocity of 3m/s would be estimated to be 2.82m/s with a 20° angle error, but 1.5m/s with a 60° error in 
alignment. Obviously, the latter would result in a substantial diagnostic error. 
While the transmitted and reflected ultrasound waves used in Doppler echocardiography are outside the 
range of human hearing (Mhz), the Doppler shift is very small (in the order of a few kHz). Thus, this difference 
can be electronically assigned a sound of the same frequency and played through speaker systems built into all 
ultrasound machines. This allows the clinician to audibly characterize the qualityof the blood flow in the 
interrogated region, where higher notes indicate higher velocities and lower notes indicate lower velocities 
(when flow is laminar). 
Audio amplification of Doppler sounds can disturb some animals during the examination although many 
tolerate the sounds without concern. In most cases, audio amplification is not essential for spectral Doppler 
interrogation but is often useful when using dedicated continuous-wave probes (see Chapter 2 - Pencil Probe 
section) that do not allow simultaneous 2D visualization. In such cases, audio amplification allows the 
experienced clinician to guide the Doppler beam into the best alignment with flow by sound alone. 
The Doppler shift is represented as a spectral graphical image where the vertical axis represents the Doppler 
shift (kHz) (which is translated into a measure of velocity in m/s) and the horizontal axis represents time (sec). 
The individual velocities of the red blood cells within a column of moving blood are not exactly equal, and, 
depending on the section interrogated, various flow profiles can be obtained (Figure 3.4). Thus, the sum of the 
red blood cell velocities in the specific region being interrogated does not result in a single Doppler frequency 
(or a single velocity), but rather, they provide a range of frequencies which correspond to a distribution of 
individual velocities around a mean velocity. Graphically, the individual red blood cell velocities are subjected 
to a Fast Fourier Transformation and displayed as a basal frequency range or velocity range at each point in 
time (Figure 3.5). The more similar the individual velocities, the brighter and smaller the instantaneous point; 
the wider the spectrum of individual velocities, the broader the instantaneous point. Cumulatively during the 
cardiac cycle, these points are summated to form a flow profile. The more similar the velocities at each point in 
time throughout the cardiac cycle, the cleaner the flow profile; the more variable the velocities at each point, 
the broader and more "smeared" the flow profile (Figure 3.6). Laminar flow is characterized by blood cells 
moving with similar, relatively low velocities, and results in a narrow and sharp flow profile on a spectral 
pulsed-wave Doppler display with a "hollow" center (Figure 3.6 C). Turbulent flow, which contains blood cells 
moving with markedly varying and high velocities, results in a broad, solid flow profile (Figure 3.10). 
Click on the image to see a larger view 
 
Figure 3.4. Examples of types of blood flow observed in 
physiological conditions (A), cases of anemia or 
decreased viscosity (B), and in the presence of a 
narrowing (stenosis) creating turbulence (C). 
Figure 3.5. Fast Fourier Transform. Schematic 
representation of the velocity/time curves, obtained by 
pulsed-wave Doppler in the appraisal of a laminar flow 
that accelerates and decelerates uniformly. The measured 
maximum speeds of flow, symbolically represented by the 
horizontal arrows, correspond to the apex of each 
respective parabola. 
 
Figure 3.6. Spectrum of the speeds of flow through the pulmonary artery. Decreasing the angle of incidence between 
the Doppler beam and the direction of the flow (gradually from A to C) results in a narrowing of the velocity profile. 
The quality of the flow profile is not only affected by the quality of the blood flow (laminar vs turbulent), but 
also by alignment. With incident angles >20°, the signal quality suffers because of increased low-frequency 
variability resulting in spectral broadening of the signal and a "dirty" flow profile (Figure 3.6). 
 
SEARCH RESULT #: 3TITLE: Interpretation of Spectral Doppler 
ImagesAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24103&O=VIN 
 
The instantaneous velocity of blood flow calculated by continuous-wave and pulsed-wave Doppler methods is 
displayed on a continuously updated Cartesian graph. Instantaneous velocities are represented on the vertical 
axis and time is represented on the horizontal axis. The summation of these instantaneous velocities over time 
results in a flow profile, also termed the Doppler spectrum. 
By convention, the baseline represents a zero Doppler shift (and therefore zero velocity) (Figure 3.7). Flow 
towards the transducer is represented as a flow profile above the baseline, while flow away from the 
transducer is represented as a flow profile below the baseline. The baseline can be manually adjusted to vary 
the maximum measurable velocity in a particular direction. Figures 3.7 and 3.8 demonstrate the effect of 
baseline adjustment on the maximum measurable velocities in the same patient. In Figure 3.7, with a 
relatively central baseline position, the maximum positive velocity that can be measured is 1.19m/s, while in 
Figure 3.8, where the baseline is positioned at the bottom of the screen, the maximum positive velocity that 
can be measured is now 1.67m/s. Additionally, baseline adjustment allows the sonographer to optimize the 
display of the flow profile in question. 
Click on the image to see a larger view 
 
Figure 3.7. Spectrum of flow obtained with pulsed-wave 
Doppler. The baseline, indicating a velocity of 0 m/s 
divides the tracing into flow away from the probe with 
negative profiles (below the baseline), and flow towards 
the probe with positive profiles (above the baseline). In 
this example, the velocity of the flow directed towards the 
transducer exceeds the maximum measurable value of 
1.19 m/sec, resulting in the phenomenon of aliasing. This 
is represented by peaks originating at the lower edge of 
the tracing (arrows) and directed towards the baseline. In 
reality, if the display was not velocity-limited, the correct 
position of these peaks would be on top of the positive 
peaks that are apparent above the baseline (at the 
locations marked by the "x"s) and directed upward. 
Figure 3.8. The same profile as in Figure 3.7 after 
moving the baseline down to increase the measurable 
velocity. The profile of the waves can be seen in its 
entirety above the baseline (no aliasing). 
The further the Doppler sampling is performed from the transducer, the lower the maximal measurable 
velocity. 
The Doppler spectral display is usually projected on the lower half of the screen, while a 2D image is 
projected on the upper half of the screen on which a cursor, representing the Doppler beam alignment, is 
superimposed. Additionally, a synchronous ECG can be simultaneously displayed (Figure 3.9). With pulsed-
wave Doppler, the simultaneously displayed 2D image has, in addition to the Doppler beam alignment, two 
parallel lines that transect this beam perpendicularly, and represent the sample volume ("sample gate") at 
which the Doppler signals are being interrogated. The sample volume can be positioned at any point along the 
Doppler beam, which can also be adjusted across the 2D image. Additionally, the approximate incident angle 
can be displayed at the sample volume with a line that transects both the sample volume and beam at a 
variable angle. 
With continuous-wave Doppler, there is no specific sample volume, but sound waves are continuously 
transmitted and simultaneously collected and analyzed from all points along the ultrasound beam. The 
velocities from every point along the ultrasound beam are simultaneously displayed on the screen creating a 
solid flow profile with a peak velocity measurable along the edge of the profile (Figure 3.9). 
Click on the image to see a larger view 
Figure 3.9. Continuous-wave Doppler tracing of mitral 
inflow in mitral stenosis. The synchronized 
electrocardiographic tracing can be seen bisecting the 2D 
reference image and the spectral Doppler tracing. 
The velocity spectrum is displayed in a grey scale, the intensity of which represents the numberof blood cells 
traveling at a specific velocity. 
Spectral Doppler provides a non-invasive method of evaluating cardiac function. It provides both qualitative 
information (laminar vs turbulent flow) and quantitative information (e.g. pressure gradients, stroke volume, 
and various indices of systolic and diastolic function). The most commonly assessed variables include the 
timing of flow; the maximum velocity of specific flows; the acceleration, deceleration and duration of flows; 
and the intervals between flow. Additionally, the morphology of specific flow profiles can often be subjectively 
interpreted to provide a diagnosis. This is discussed more comprehensively in subsequent sections. 
Turbulent Flow 
Normally, intracardiac and intravascular flow is laminar. Additionally, flow is pulsatile, characterized by 
simultaneous acceleration and deceleration of red blood cells within the central flow zone. Thus, during a 
pulsed-wave Doppler examination, a sample volume positioned within this central flow zone results in a sharp 
clean flow profile. In many cardiac conditions, flow becomes turbulent due to passage through a narrow orifice 
from a region of high pressure to one of low pressure, which results in rapid acceleration beyond the orifice. As 
the velocity of the cells increases in the low-pressure area, laminar flow is disrupted (Figure 3.4). Turbulent 
flow is characterized by a large range of individual cellular velocities and directions resulting in a broad Doppler 
spectrum (Figure 3.10). Characterization of flow quality is a feature exclusive to pulsed-wave Doppler imaging. 
Continuous wave Doppler is unable to determine flow quality (laminar vs turbulent) because it is non-selective 
in the sampling position (i.e., it has no sample volume), but samples flows at all points along the ultrasound 
beam (Figure 3.11). 
Click on the image to see a larger view 
 
 
Figure 3.10. Pulsed-wave spectral Doppler tracing of 
turbulent blood flow in mitral insufficiency in a dog. 
Because blood cells within the sample volume are moving 
at different speeds, different directions and very high 
speeds away from the probe, the spectral diagram shows 
a diffusely grayish area (arrow), rather than a clean 
envelope associated with laminar flow (as seen in Figure 
3.8). 
Figure 3.11. Continuous wave spectral Doppler tracing of 
mitral inflow. The velocity profile is diffusely grayish 
(arrow.) However, in this case, it is impossible to 
determine if the flow in this region is laminar or turbulent 
since, with continuous-wave Doppler, the velocity profile 
always appears white-grayish and without a clean 
envelope. 
Evaluation of the Pressure Gradient 
With perforative or obstructive lesions (e.g., mitral insufficiency, ventricular septal defects, valvular stenoses), 
there is often a difference in pressures upstream and downstream of the lesion. Pressure upstream of the 
lesion is necessarily higher than the downstream pressure; otherwise, blood would not flow across the lesion. 
This difference in pressures results in an increase in velocity downstream of the lesion proportional to the 
difference in pressures between the two sides of the lesion, as defined by the equation: 
P1V1=P2V2 
where P1 and P2 are pressures above and below the lesion, and V1 and V2 are velocities above and below the 
lesion. 
If the downstream velocity increases substantially, turbulent flow develops. 
The fixed relationship between velocity and pressure is exploited by the Bernoulli equation to calculate the 
differences in pressure across perforative or stenotic lesions. While the Bernoulli equation is complex, a 
simplification can be used clinically to estimate the pressure differences in many situations. The simplified or 
modified equation is derived from the following: 
P1- P2=1/2ρ(V22-V12) 
where V1 is the maximal upstream velocity; 
V2 is the maximal downstream velocity 
ρ is an inertial and viscosity constant 
P1 is the maximal upstream pressure 
P2 is the maximal downstream pressure 
If V2 >>>V1 (i.e. downstream velocity is much greater than upstream velocity), V1 can be ignored, 
simplifying the Bernoulli equation (originally described by Hatle) into the clinically applicable form: 
ΔP=4V22 
This equation only works if there is a large difference between velocities. Otherwise, the unmodified equation 
described above must be used to calculate the pressure gradient. 
Normal flow across cardiac valves is of low velocity, ranging from 0.25m/s to 1.7m/s (depending on the 
specific valve). With obstructive or perforative lesions, velocities across the lesion depend on the severity of 
the obstruction and the pressure differences between the compartments "straddling" the lesion and can exceed 
8 m/s. Flow velocities of this magnitude require the use of continuous-wave Doppler imaging for accurate 
measurement. 
Measurement of Stroke Volume 
Stroke volume is theoretically measurable using spectral Doppler and 2D imaging. Stroke volume is the volume 
of blood ejected during one cardiac cycle. Volume is effectively a product of linear measurements in 3 
dimensions: breadth, height and width. Thus, if one measures these three linear dimensions, one can calculate 
a volume. 
Spectral Doppler provides a measure of velocity (m/s) over time. Thus, the integral of the velocity*time 
curve (the velocity time integral, or VTI) results in a unidimensional length measurement (m). 2D imaging 
allows one to measure the cross-sectional area (m2) of the region at which the spectral Doppler signal was 
obtained (Figure 3.12). Multiplying the cross-sectional area by the VTI results in a volume measurement for 
one cardiac cycle - the stroke volume: 
SV=CSA*VTI 
Click on the image to see a larger view 
Figure 3.12. Determination of stroke volume. The 
cardiac output (the volume of blood expelled from the left 
ventricle in a minute) can be calculated using the 
formula: CO= heart rate x VTI x πr2. This figure shows 
the measurement of the diameter of the aortic valve 
orifice which, divided by 2, provides the variable "r" used 
in the formula of calculation of stroke volume and cardiac 
output. 
If the SV is multiplied by the heart rate, cardiac output is calculated: 
CO=SV*HR 
While this is theoretically valid, estimates of SV and CO by Doppler/2D echo are wildly inaccurate. A surrogate 
measure of SV is simply measuring the VTI. This is often used in human anesthesiology, where changes in VTI 
in the same patient during a procedure may reflect changes in CO, alerting the anesthesiologist to an alteration 
of the hemodynamic state of the patient. 
 
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Aliasing 
Pulsed-wave Doppler has a maximum measurable Doppler shift frequency (velocity) that can be 
unambiguously measured. This upper limit is termed the Nyquist limit. The Nyquist limit is determined by the 
pulse repetition frequency of the Doppler signal: 
Ny=0.5PRF 
When the Doppler shift exceeds the Nyquist limit, aliasing occurs. With aliasing, velocities exceeding the 
Nyquist limit are displayed on the opposite side of the baseline creating an illusion of bidirectional blood flow 
(Figure 3.13). With very high velocity flows, the signal is superimposed multiple times over the spectral display 
creating a single solid column rather than a typical flow profile (Figure 3.14). 
Click on the image to see a larger view 
 
Figure 3.13. Phenomenon of the aliasing recording of the 
velocity of mitral inflow by pulsed-wave Doppler. The two 
peaks marked 1 and 2 are, in fact, projections towards 
the top of the graph that should be positioned on top of 
the truncated wave-forms visible above the baseline and 
labeled1' and 2'. 
Figure 3.14. Spectral diagram of pulsed-wave Doppler of 
left ventricular outflow in a dog with aortic insufficiency. 
The turbulent regurgitation is represented by the uniform 
grayish areas (T), interspersed between the laminar 
systolic flow that can be seen directed away from the 
probe. Since the maximum velocity of the systolic flow 
exceeds the Nyquist limit, aliasing occurs. In the figure, 
the laminar flow begins in the point "a" (near the bottom 
of the tracing) and is directed towards the bottom. It then 
aliases around to the top of the tracing (at a') and heads 
away from the transducer in a tapering profile towards 
the baseline (b). It crosses the baseline once more and 
aliases a second time, with the tip of the profile appearing 
at the top of the tracing (b'). 
Aliasing can be corrected in four ways. Some machines have an optional setting that activates a high pulse-
repetition frequency (HPRF), which involves the transmission of multiple pulses during the same period of time 
normally dedicated to a single pulse. This substantially increases the Nyquist limit, but is limited to flows 
relatively close to the transducer because it is necessary that all the transmitted pulses are received during the 
reception period (which is dependent on the depth from which they are reflected; see Chapter 2 - paragraph 
above Table 2.1 for a description of the PRF and HPRF issues ). 
An alternative method of limiting aliasing is to use a low-frequency probe. From the Doppler equation, it is 
clear that the Doppler shift is proportional to the transmitted frequency, so that when a low-frequency probe is 
used; the frequency shift for a particular velocity is lower, resulting in a larger range of velocities that fall 
below the Nyquist limit. 
The third method of reducing aliasing, as described previously, involves the adjustment of the baseline 
opposite the direction of measured flow. This often allows a substantial increase in measurable velocities. 
The fourth method to reduce aliasing is to inactivate real-time simultaneous 2D imaging during Doppler 
imaging. This allows better processing of Doppler information and increases the PRF. 
Continuous-wave Doppler is not subject to a Nyquist limit and is able to measure an infinite range of 
velocities. 
Range Ambiguity 
The further transmitted sound waves have to travel to their target, the longer the return time for the reflected 
sound waves. Thus, for distant targets, the PRF is automatically reduced so that sufficient sampling time exists 
between pulses to detect reflected sound waves. This results in a reduced Nyquist limit and consequently, 
reduced maximum measurable velocity. If the PRF is unacceptably high, some reflected waves from one pulse 
are detected during the sampling period of the subsequent pulse, thus creating the phenomenon of range 
ambiguity. These late-detected waves may have a substantially different Doppler shift from the appropriately 
detected waves that are reaching the transducer at the same time, thus creating a ghosting effect. 
Valvular Movement Artifacts 
When valves transect the Doppler beam during systolic or diastolic movement, brief, sharp and bright artifacts 
are created. These artifacts often span both sides of the baseline, are relatively small, and usually border the 
onset and cessation of flow of blood through that particular valvular orifice, which can facilitate the 
measurement of systolic or diastolic flow phases. These artifacts can be reduced or eliminated with specific 
filters and should not be confused with blood flow (Figure 3.15). 
Click on the image to see a larger view 
Figure 3.15. Spectral diagram of Continuous wave 
Doppler of high velocity systolic flow in a case of aortic 
stenosis. The sharp spikes denoted by the letter "s" are 
caused by the collision of the Doppler beam with moving 
valve cusps. 
 
SEARCH RESULT #: 5 TITLE: The Doppler Apparatus AUTHOR(S): ADDRESS (URL): 
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Doppler echocardiography capability is generally available in most ultrasound machines. Obviously, older 
machines may lack color Doppler capabilities and may have transducers incapable of performing all types of 
Doppler imaging. Probe characteristics have been described in Chapter 2. However, some methods exist to 
optimize the utility of spectral and color Doppler imaging. As with 2D and M-mode imaging, optimization of the 
display by adjusting filtering and scaling is advisable, as is the ability to record and store images and cine-
loops of representative imaging segments. Of greatest importance in image optimization are: 
 The type of transducer 
 The frame rate of the system 
Transducers 
The best Doppler imaging generally requires transducer frequencies that are lower than those used for optimal 
2D imaging for a particular patient. For example, in cats and small dogs, Doppler imaging is often best with 
probes in the 5MHz range; while for large dogs, probes with a frequency of 2-3MHz are best. Newer probes 
incorporate dual-frequency capabilities which allow optimal simultaneous 2D and Doppler resolutions. 
As with 2D imaging, image resolution and sampling depth capability are inversely related in pulsed-wave and 
color Doppler imaging. This may not be as immediately apparent to the reader; however, use of a probe with 
an inappropriately low frequency will reduce the number of reflected sound waves in a small pet, resulting in a 
weak signal. These limitations do not affect continuous-wave Doppler imaging - a 2MHz probe is equally 
capable of detecting maximum flows in a cat as in a horse. 
Frame Rate 
Spectral Doppler analysis involves relatively simple processing (even compared to 2D imaging), because it is 
based on analysis of a single ultrasound beam. On the other hand, color Doppler imaging requires substantial 
processing capabilities that are only now becoming commonplace in clinical ultrasonography (with the constant 
evolution of microprocessing capacity). This is due to the fact that, in color Doppler, there is a field of pulsed-
wave signals that are being processed simultaneously, colorized and superimposed on a dynamic 2D image. 
This complex processing necessarily reduces the frame rate, although with new generation machines, frame 
rates have substantially improved with newer microprocessors. Regardless of the quality of color imaging 
capability, frame rates are optimized by limiting the size of the sample volume to the smallest area as 
diagnostically possible. 
Newer digital machines have frame rates in color Doppler mode above 60Hz, but frame rates >15Hz are 
acceptable. The practical concern with low frame rates in color Doppler is the need to synchronize the 
hemodynamic (color Doppler) and mechanical (2D) events. Careful interpolation of the information from color 
Doppler and 2D images is required to accurately represent flow and myokinetic events, so as to preserve the 
temporal resolution of the 2D image without losing the corresponding color flow data. The ability to adequately 
perform these tasks is additionally impacted by imaging species with high heart rates, where exceedingly slow 
frame rates provide suboptimal images and loss of valuable information. Most newer echocardiography 
machines have sufficient processing capability to process information without substantial loss of quality. 
An example of the consequences of asynchronous display of color Doppler and 2D images is seen in Figure 
3.16. In this example, the dyssynchrony of mitral flow and mitral movement leads one to conclude that there is 
diastolic flow across a closed mitral valve. In other cases, very brief flows (<20msec) may appear to be 
considerably longer if the updating of the color Doppler image is slow. 
Click on the image to see a larger view 
Figure3.16. Example of asynchrony between the 2D 
image and the color Doppler caused by a slow frame rate 
(10 frames/sec). The slight delay in updating of the 2D 
image erroneously results in the appearance of diastolic 
flow towards the transducer (red) even though the AV 
valves are closed. 
 
SEARCH RESULT #: 6TITLE: Pulsed-wave DopplerAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24106&O=VIN 
 
PW Doppler imaging is generally used to interrogate diastolic atrioventricular flows and systolic outflows. These 
flows generally have relatively low velocities in normal animals (approx 1m/s). Additionally, PW Doppler is used 
to precisely identify the location of the transition from laminar to turbulent flow, or to confirm that turbulent 
flow exists. It is unable to determine the absolute velocity of the turbulent flow; this requires continuous-wave 
Doppler imaging. 
Imaging of atrioventricular flow requires imaging from the cardiac apex to provide optimal alignment of 
transvalvular flow with the Doppler beam. This is obtained using the left apical views and occasionally the 
subxiphoid view. The Doppler beam is directed across the middle of the AV annulus, then the sampling volume 
is positioned along this axis at the level of the tips of the valve leaflets during early diastole (i.e., slightly within 
the ventricular chamber) (Figure 3.17). This usually provides virtually parallel alignment with inflow. 
Click on the image to see a larger view 
Figure 3.17. Schematic representation of the positioning of the Doppler axis and the sample volume for the 
evaluation of mitral inflow (A) and potential mitral regurgitation (B), using the left apex parasternal view. Analogous 
positions used in evaluation of the tricuspid flow are depicted in C and D. 
The mitral inflow profile has two peaks, which correspond to the two diastolic events - early diastolic inflow and 
atrial systole. The distance between successive mitral inflow signals is variable and depends on the patient's 
heart rate. Flow is minimal between the two diastolic flow events (i.e., mid-diastole) and should not be 
detectable in systole if the Doppler probe is correctly positioned (Figure 3.18). Valve artifacts, described 
earlier, are often observed with the transducer in this position and should not be ascribed any clinical 
significance (Figure 3.19). 
Click on the image to see a larger view 
 
Figure 3.18. Spectral diagram of pulsed-wave Doppler 
mitral inflow in a normal dog. Early diastolic inflow (E) 
and atrial systolic inflow (A) can be clearly seen. Between 
the two peaks a very low velocity flow (diastasis) can be 
appreciated in the first and third sets of inflow signals. On 
the other hand, no flow can be appreciated between the 
A-wave and the subsequent E-wave (during ventricular 
systole). 
Figure 3.19. Spectral diagram of pulsed-wave Doppler 
mitral inflow in a normal dog. In this case, obvious signals 
of ventricular systolic flow (S) can be seen due to 
malpositioning of the sample volume within the 
ventricular cavity. D = diastasis. 
The early and atrial mitral diastolic flow peaks are defined by the letters E (Early) and A (Atrial). The E-wave is 
associated with passive early diastolic inflow, while the A-wave represents flow associated with atrial systole. It 
is occasionally necessary to slightly adjust the sample volume to obtain the optimal diastolic mitral profile. 
However, it is important to recognize that positioning of the sample volume closer to the atrial annulus will 
alter the magnitude of the E and A waves, resulting in an increased A wave which can simulate patterns 
observed in certain pathologies. 
Tricuspid inflow is similar to mitral inflow, but generally has lower velocity and less well defined peaks 
(Figure 3.20). If the sample volume is positioned within the right atrium, physiological tricuspid insufficiency 
can be frequently observed, which creates additional flow signals below the baseline. 
Click on the image to see a larger view 
Figure 3.20. Spectral diagram of pulsed-wave Doppler 
tricuspid inflow in a normal dog. The main parameters 
used in qualitative and quantitative evaluation of 
transvalvular flow can be seen in the lower part of the 
image. E = peak early diastolic inflow velocity; A = peak 
late diastolic inflow velocity; TAcc = early diastolic 
acceleration time (in msec); Vavg = average velocity in 
cm/sec; TD = deceleration time (duration of the EF slope) 
expressed in msec; VTI = velocity-time integral 
expressed in centimeters. [Publisher's note: Vmedia 
translates to Vavg] 
The analysis of transmitral diastolic flows provides variables that are used in the evaluation of diastolic 
ventricular function, and occasionally, mitral valve function. These include: 
 Diastolic inflow period (from onset of the E-wave to end of the A-wave) 
 Maximum E-wave velocity 
 Maximum A-wave velocity 
 Ratio of E and A waves (Figure 3.21) 
 E-wave acceleration time 
 E-wave deceleration time (Figure 3.22) 
Click on the image to see a larger view 
Figure 3.21. Schematic representations of the various 
relationships of the proportions, the E and A waves in 
normal conditions (A), reduced ventricular myocardial 
compliance (B) and altered relaxation (C). 
Figure 3.22. Spectral diagram of pulsed-wave Doppler 
mitral inflow in a normal dog. The main parameters used 
in qualitative and quantitative evaluation of transvalvular 
flow can be seen in the lower part of the image. E = peak 
early diastolic inflow velocity; A = peak late diastolic 
inflow velocity; TAcc = early diastolic acceleration time (in 
msec); Vavg = average velocity in cm/sec; TD = 
deceleration time (duration of the EF slope) expressed in 
msec; VTI = velocity-time integral expressed in 
centimeters. [Publisher's note: Vmedia translates to 
Vavg] 
Additionally, with slight adjustment of the sample volume towards the aorta, it is possible to detect left 
ventricular systolic flow, which then allows the measurement of several additional indices: 
 The isovolumic relaxation time (from the end of aortic flow to the onset of mitral flow, (Figure 3.23) 
 The isovolumic contraction time (from the end of mitral inflow to the onset of aortic flow) 
 The myocardial performance index (which is a global measure of myocardial function that sums both 
isovolumic periods and divides this by the aortic ejection time) 
Click on the image to see a larger view 
Figure 3.23. Isovolumic relaxation time (IVRT) 
determined on a pulsed-wave Doppler tracing, obtained 
by positioning the Doppler sample volume in between 
mitral inflow and left ventricular outflow. The narrow 
space between the end of the flow away from the 
transducer (end of systole) and the beginning of flow 
towards the transducer (onset of inflow) represents the 
IVRT. 
Table 3.1 summarizes some clinically relevant PW Doppler reference intervals provided by various 
investigators: 
Table 3.1. 
 Dog (cm/sec) Cat (cm/sec) 
Aortic velocity 106-157 102 
Pulmonic velocity 84-125 102 
Mitral E-wave velocity 75-94 69 
Mitral A-wave velocity 53-64 54 
Tricuspid E-wave velocity 56-86 60 
Tricuspid A-wave velocity 58-62 
Mitral E/A 1.3-1.5 
Tricuspid E/A 1.6 
Once atrioventricular diastolic flow has been evaluated, the sample volume is repositioned into the atrium at 
the level of the annulus to identify any mitral insufficiency, which, if present, will present as high-velocity flow 
away from the transducer. The deeper the sample volume is positioned within the atrium, the less evident is 
the diastolic flow profile. As the sample volume is moved towards the roof of the left atrium, pulmonary venous 
inflow patterns become discernable. Moving into the pulmonary veins, one can begin to analyze pulmonaryflow, which can also be used to evaluate diastolic ventricular function (Figure 3.24). 
Click on the image to see a larger view 
Figure 3.24. Pulsed-wave Doppler spectral diagram of 
pulmonary venous flow. The "S" indicates the flow into 
the left atrium during the ventricular systole, while "D" 
indicates flow through the atrium during early ventricular 
diastolic filling. The "R" indicates retrograde flow (into the 
pulmonary veins) during atrial contraction. 
The regurgitant flows obtained by placing the sample volume as described above are formed by high-velocity 
particles that move in turbulent fashion. Therefore, in case of mitral insufficiency, pulsed-wave Doppler usually 
indicates only turbulent high-velocity transmitral systolic flow at the location of the sample gate, but cannot 
determine the direction of flow nor maximum flow velocity. In order to determine direction and velocity, it is 
necessary to use continuous wave Doppler, positioned along the same imaging plane. With pulsed-wave 
Doppler it is not possible to clearly characterize the two mitral flows that occur on the same axis (systolic and 
diastolic) in patients with mitral insuffiency, since each occurs in the opposite direction and on opposite sides of 
the mitral valve, while the sample volume can only be positioned at one of these locations at any one time. 
Continuous-wave Doppler is not subject to this limitation, as it detects all flows along the line of interrogation, 
without assigning a location to these flows. This can be confusing if various flows occur simultaneoulsy in 
different directions along the scan axis, but continuous wave Doppler maximizes the ability to visualize normal 
and pathological flows that occur at different times along the same axis. 
In the apical 5 chamber view, it is possible to align the Doppler beam with the left ventricular outflow tract 
(LVOT) into the ascending aorta. The sampling volume can be positioned in LVOT at the level of the valve or at 
the level of the open aortic valve tips (Figure 3.26). In some patients, this alignment is best achieved with a 
subxiphoid approach. This view is particularly useful in Boxers and barrel-chested dogs, such as bulldogs and 
pugs, but is less useful in deep-chested dogs because of the distance from the probe to the aortic valve. 
Click on the image to see a larger view 
Figure 3.25. Continuous-wave Doppler diagram of mitral 
regurgitant flow. E and A waves are visible above the 
baseline, consistent with diastolic atrioventricular flow. 
MR indicates a high speed turbulent systolic flow signal 
below the baseline. 
 
Figure 3.26. Schematic representation of the positioning of the Doppler axis and the sample volume for the 
evaluation of aortic flow using the left apical 5-chamber view. In A, the sample volume is positioned in the left 
ventricular outflow tract just below the valve. In B, the Doppler sampling occurs between the aortic bulb and aortic 
root. 
The aortic flow profile observed with PW Doppler has a triangular shape with a narrow base and tall sides (an 
isosceles triangle) with a slightly steeper acceleration slope than deceleration slope (Figure 3.27). The flow is 
away from the transducer and, therefore, displayed below the baseline. Peak velocities range from 0.9 to 
1.7m/s although normal flows can exceed 2m/s in some animals. Additionally, there is substantial beat-to-beat 
variation of the peak velocity in some patients that is dependent on the diastolic duration and respiratory cycle. 
A similar phenomenon is observed with pulmonic valve outflow signals (Figure 3.28). Peak velocity also 
increases slightly as the sample volume is moved from the LVOT into the aorta. 
Click on the image to see a larger view 
 
Figure 3.27. Spectral pulsed-wave Doppler diagram left 
ventricular outflow in a normal dog. The main parameters 
used in qualitative and quantitative evaluation of 
transvalvular flow can be seen in the lower part of the 
image. E = peak early diastolic inflow velocity; Vmin = 
peak systolic velocity (cm/sec); GPmin = peak pressure 
gradient across the aortic valve, expressed in mmHg; 
Vavg = average velocity in cm/sec; GPavg = average 
pressure gradient; VTI = velocity-time integral expressed 
in centimeters; TAcc = acceleration time expressed in 
msec. [Publisher's note: Vpicco translates to Vmin; 
GPpicco translates to GPmin; Vmedia translates to Vavg; 
and GPmedio translates to GPavg.] 
Figure 3.28. Respiratory variation of the speed of 
transpulmonary valve flow measured with pulsed-wave 
Doppler, resulting from hemodynamic and pressure 
changes secondary to respiration. The arrow indicates a 
particularly slow flow profile, probably due to a premature 
ventricular contraction. 
Pulmonary blood flow is interrogated from the right parasternal short axis view (Figure 3.29). Optimum 
alignment with blood flow is sometimes achieved with the oblique view from the right parasternal position or 
with a left cranial short-axis view (Figure 3.30). The pulmonary flow profile is similar to the aortic flow profile, 
but is generally smaller and may be slightly more rounded during both acceleration and deceleration (Figure 
3.31). Normal peak velocities approach 1m/s. 
Click on the image to see a larger view 
 
Figure 3.29. Schematic representation of the positioning of the Doppler axis and the sample volume for the 
evaluation of pulmonic valve flow using the right parasternal short axis view. In A, the sample volume is positioned at 
the distal end of the right ventricular outflow tract, just proximal to the pulmonic valve. In B, the Doppler sampling 
occurs in the pulmonary artery. 
 
Figure 3.30. Schematic representation of the positioning of the Doppler axis and the sample volume for the 
evaluation of pulmonic valve flow. In A, the oblique right parasternal oblique view is used in order to optimize 
visualization of the RV outflow tract. In B, the sample volume is positioned using the left cranial view, which also 
optimizes the visualization of the RV outflow tract. 
Figure 3.31. Schematic representation of the spectral 
pulsed-wave Doppler profile of normal transpulmonary 
flow. 
With both pulmonary and aortic valves, careful PWD interrogation may identify valvular insufficiencies whose 
flow profiles vary with the severity of the insufficiency and the diastolic pressure gradients across the valve. 
Pulmonic insufficiency with a velocity <3m/s is sometimes observed with PWD in normal dogs, but may require 
careful interrogation to be detected (Figure 3.32). 
Click on the image to see a larger view 
Figure 3.32. Spectral pulsed-wave Doppler tracing of 
transpulmonary flow in a normal dog. The sample volume 
is positioned on the ventricular side of the pulmonary 
valve, allowing the recording of systolic flow (1) and 
diastolic regurgitation (2) with maximum speed less than 
2 m/sec. 
PWD can also be used to identify left-to-right shunting septal defects, both within the atria and ventricles. 
Interrogation of the suspect region is performed in right parasternal short and long-axis views on both sides of 
the septum. 
 
SEARCH RESULT #: 7TITLE: Continuous-wave DopplerAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24107&O=VIN 
 
CWD requires specific transducers that are equipped with two piezoelectric crystals that work simultaneously 
and independently - one functions as a transmitter that emits a continuous beam, the other as a receiver that 
continuously receives reflected signals. In this way, the PRF is effectively infinite so that no limit to velocity 
detection exists. There is no sampling gate, but rather reflected waves along the entire ultrasound beam are 
analyzed simultaneously, resulting in a solid flow profile. For this reason, CWD is unable to localize thesource 
of the reflected sound-waves. During CWD imaging, all other imaging is suspended and is only updated 
periodically. 
As with PWD, proper beam alignment principles described earlier should be followed. Additionally, care 
should be taken to avoid interrogating regions where distinct concomitant flows may transect the beam as this 
may lead to misinterpretations of flow velocity. This is especially problematic when inappropriate beam 
alignment is used, such as attempting to examine the aortic valve in the right parasternal long-axis view, 
where concurrent mitral insufficiency flow may be simultaneously detected and misinterpreted as aortic 
stenosis. However, in most cases, CWD is used to measure the peak velocity of lesions previously identified 
with PWD. Additionally, experienced sonographers are often able to identify the source of the high velocity flow 
by subtle differences in the shape of the flow profile across different valves or the corresponding diastolic flow 
profiles. Therefore, it is recommended to adhere to the recommended views when interrogating specific valves 
and to be cognizant of potential confounding flows. This also underscores the need to perform a detailed and 
complete examination, rather than just one aspect, so that multiple levels of evidence can be assimilated into a 
final diagnosis. 
In horses, it is almost impossible to align the Doppler beam with the inflow and outflow tracts of the left 
heart from the apical view because the equine sternum prevents this view from being obtained. Instead, 
suboptimal oblique views are required. 
 
SEARCH RESULT #: 8TITLE: Analysis of Spectral Doppler SignalsAUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24108&O=VIN 
 
The morphology of the spectral Doppler profiles can provide important clinical information beyond a simple 
measure of velocity. 
Flow profiles in aortic and pulmonic insufficiency are characterized by a gently sloping plateau shape when 
they are not associated with elevations in ventricular diastolic pressure (Figure 3.33). However, if ventricular 
diastolic pressure increases substantially through diastole, the diastolic pressure gradient across the valve 
decreases substantially, resulting in a marked reduction in regurgitant velocity and a more steeply sloped 
wave-form (Figure 3.34). One measure of severity of the insufficiency is the measurement of the diastolic 
pressure half-time, which is the time taken for the diastolic pressure to decrease to 50% of the peak diastolic 
pressure. The more rapid the increase in intraventricular pressure (or decrease in aortic pressure), the shorter 
the pressure half-time (Figure 3.34). However, with small insufficiencies or poor alignment, it is possible to 
produce a diastolic wave-form that has an apparent short pressure half-time. Additionally, no measures of 
pressure half-time exist in veterinary species that can identify the severity of the insufficiency. It is probably 
sufficient to observe the overall shape of the insufficiency profile. 
Click on the image to see a larger view 
 
 
Figure 3.33. Spectral continuous-wave Doppler tracing 
of aortic insufficiency. The systolic flow is seen below the 
baseline; while the diastolic regurgitant flow is above the 
baseline and directed toward the transducer, and has a 
typical sloping profile. 
Figure 3.34. The measurement of the diastolic pressure 
half-time of aortic regurgitation. Notice that, after it 
begins with a tall positive peak, the regurgitant velocity 
diminishes rapidly with the concomitant rise in 
intraventricular pressure. The half-time (TD), seen at the 
bottom of the figure with other measures of flow, is equal 
to 226.67 msec. A half-time < 300 msec is considered 
indicative of severe aortic insufficiency. 
Table 3.2 presents the systolic and diastolic pressures in various cardiac chambers and great vessels as well as 
alterations that may be observed in the more common cardiac diseases, which allow the sonographer to 
interpret the results of spectral Doppler investigations. 
Table 3.2 
 Systolic pressure 
mmHg 
Diastolic pressure 
mmHg 
Mean pressure 
mmHg 
Right atrium 4-6 0-4 2-5 
Right ventricle 15-30 < 5 
Pulmonary artery 15-30 5-15 8-20 
Left atrium 5-12 < 8 < 10 
Left ventricle 95-150 < 10 
Aorta 95-150 70-100 80-110 
Mitral insufficiency 
Left atrium 
Dilative cardiomyopathy 
Left ventricle 
Left atrium 
Aorta 
Aortic stenosis 
Left ventricle 
Pulmonary stenosis 
Right ventricle 
PDA with left to right shunt 
Pulmonary artery 
Left atrium 
Aorta - 
Left ventricle - 
Fixed aortic and pulmonic obstructions create a slightly biconvex flow profile with a higher velocity than 
normal. The severity of the obstruction is proportional to the peak velocity. Spectral broadening or turbulent 
flow is seen with PWD, and the peak velocity is usually obtained with CWD. In some cases, the acceleration 
slope adopts a concave shape during the latter portion, a so-called "dagger" or "horsetail" shape, indicating a 
dynamic component to the obstruction (Figure 3.35). This is often exacerbated by high sympathetic tone 
because of increased contractility. In cats, dynamic obstruction is often observed as a singular finding without 
fixed obstruction, frequently found in hypertrophic obstructive cardiomyopathy. 
Click on the image to see a larger view 
Figure 3.35. Spectral continuous-wave Doppler tracing 
of aortic stenosis. The concave conformation of the 
acceleration phase (arrow) suggests a dynamic 
obstruction to LV outflow. 
Occasionally, the pulmonic systolic flow profile is altered by loss of the convexity of the deceleration slope, 
instead adopting a concave form. This is seen with severe pulmonary hypertension and may accompany 
reduced peak systolic velocities and results from sudden systolic elevation of pulmonary artery pressures in a 
non-compliant pulmonary arterial system (Figure 3.36). Similarly, in some instances of mitral insufficiency, 
where there is severe elevation in left atrial pressure, a late systolic reduction in regurgitant flow may be 
observed (Figure 6.12). 
Click on the image to see a larger view 
Figure 3.36. Spectral pulsed-wave Doppler 
transpulmonary flow. The scythe-like conformation 
(arrows) of the deceleration phase suggests elevated 
pulmonary arterial pressure. 
Evaluation of Diastolic Ventricular Function 
All machines equipped with Doppler capabilities should have software capable of estimating diastolic function; 
however, this method of function analysis has many limitations, is technically challenging, and dependent on 
the skill of the operator. Additionally, these indices should not be evaluated in isolation but only with additional 
measures of cardiac performance. 
It is possible to measure isovolumic relaxation time, early ventricular filling time, peak early filling velocity 
(E-wave), early diastolic deceleration time, and peak atrial filling velocity (A-wave) using spectral Doppler. 
These variables are often altered with diastolic ventricular dysfunction and are described in Box 3.1. 
Box 3.1. Spectral Doppler variables used in evaluating diastolic ventricular function. 
Isovolumic relaxation time. This is the time between the end of ventricular ejection and the start 
of transmitral inflow. It is necessary to visualize both aortic and mitral flow profiles simultaneously 
by positioning the sampling volume midway between the mitral valve and outflow tract (Figure 
3.23). 
Early ventricular filling (passive diastolic phase). This represents the time from the mitral 
valve opening to the peak velocity of the E-wave (Figure 3.37). 
Click on the image to see a larger view 
Figure 3.37. Measurement of transmitral earlydiastolic acceleration time with pulsed-wave 
Doppler. 
Peak E-wave velocity. This is peak early diastolic mitral inflow velocity. Together with peak atrial 
flow, it allows the calculation of the E/A ratio, which is usually >1 in normal individuals. 
Early filling deceleration time. This is the time from the peak E-wave velocity to the baseline at 
the end of early diastolic filling. 
Late ventricular filling (atrial contraction). This is the peak of the flow associated with atrial 
contraction and is used to estimate the E/A ratio. 
In general, changes associated with decreased diastolic function due to impaired relaxation include a decrease 
in peak E-wave velocity, an increase in peak A-wave velocity, an E/A ratio <1, a decreased IVRT, decreased 
early acceleration and prolonged early deceleration. 
Changes associated with reduced compliance, such as dilated cardiomyopathy, may demonstrate a short 
early deceleration time, a short IVRT, an exaggerated E wave peak velocity and increased E/A ratio. 
However, in small animals, these variables are relatively unreliable in the species which most commonly 
suffer from diastolic abnormalities (cats with hypertrophic cardiomyopathy, dogs with DCM) and are rarely 
evaluated clinically. 
 
SEARCH RESULT #: 9TITLE: Color Doppler ImagingAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24109&O=VIN 
 
Color Doppler can be considered an extension of PWD technology, where a large number of sample volumes 
are analyzed simultaneously. The Doppler information is colorized rather than displayed spectrally and is 
superimposed over a concurrently acquired 2D image in a field that is adjustable in size and position. As such, 
it is a semiquantitative imaging method because specific numerical data are generally unavailable. In PWD, a 
single beam intersects the flow, while with color Doppler, tens or hundreds of beams are projected radially 
from the transducer with multiple sample volumes along each beam (Figure 3.38). This creates multiple angles 
of incidence with the flow, which allows estimations of multiple flow velocities and directions that are compiled 
to display an overall flow pattern. These multiple velocities are assigned specific colors or tones that create the 
overall color display. 
Click on the image to see a larger view 
Figure 3.38. Schematic representation of the sampling 
used in color Doppler. Multiple pulsed-wave sample 
volumes are simultaneously acquired and processed, and 
assigned a specific color based on the flow direction and 
velocity. 
Physical principles of PWD are equally applicable to CD. Thus, the Doppler equation, Nyquist limit, aliasing, and 
the angle of incidence with the direction of flow are all valid considerations in CD. Because of the great 
processing requirements, the Nyquist limit is necessarily lower with CD than with PWD. 
Standard 2D imaging views are used with CD. The sampling region is defined by a border on the screen, 
which can be moved and sized freely to position it over the region of interest (Figure 3.39). However, to 
optimize the CD resolution, this sampling region should be kept as small as possible. High quality systems offer 
higher frame rates during CD imaging, which avoids some of the synchronization problems discussed 
previously. 
Click on the image to see a larger view 
Figure 3.39. The color Doppler sample window is 
overlaid on the 2D image to produce the typical color 
Doppler display. The color-coded visualization of flow 
occurs only within the sample window. 
By convention, absence of flow is assigned no color; a positive Doppler shift (flow towards the transducer) is 
assigned various shades of red; a negative Doppler shift (flow away from the transducer) is assigned various 
shades of blue. These can be remembered by the acronym "BART" (Blue Away, Red Towards). It is, however, 
possible to assign various color profiles. 
Increasing velocities of flow are assigned progressively lighter shades of the respective colors, approaching 
white at the Nyquist limits. Additionally, some color profiles are able to display spectral broadening by 
incorporating tonal variations of the primary color. 
When the CD mode is activated, a color scale appears on the screen which defines the Nyquist limits 
associated with the particular setup. The black region in the middle of the scale represents the baseline (zero 
flow) (Figure 3.40). The upper and lower extremes of the scale approach white and define the maximum 
velocities (Nyquist limit). If these velocities are exceeded, a CD form of aliasing occurs, analogous to that with 
PWD, where velocities in excess of the Nyquist limit are assigned colors from the opposite end of the scale. 
Thus, when flow towards the transducer (red) exceeds the Nyquist limit, it is suddenly assigned a light blue 
color, and vice versa. 
Click on the image to see a larger view 
Figure 3.40. Scale bars for coding velocity in color. In A, 
the baseline (0) is positioned so as to divide the scale bar 
into equal parts. In B and C, the baseline is moved 
towards the top and the bottom respectively. Adjusting 
the scale as in (B) allows evaluation of flows away from 
the transducer while adjusting them as in (C) facilitates 
evaluation of flows towards the transducer. In both cases, 
the maximum measurable speed is increased, reducing 
the phenomenon of aliasing. 
To somewhat overcome this problem, the baseline can be adjusted to increase the maximal measurable 
velocity of the flow being examined (Figure 3.40). However, because of the relatively low Nyquist limits with 
CD, normal flow can sometimes suffer from aliasing artifact. Nonetheless, experienced sonographers can easily 
identify aliasing artifact and rarely confuse it with turbulent flow (Figure 3.41). 
Click on the image to see a larger view 
Figure 3.41. Phenomenon of aliasing with color Doppler. 
The sampling in this instance is in the LVOT and 
ascending aorta. The flow leaving the left ventricle, 
colored blue, accelerates to the level of the aortica valve 
so much that it exceeds the maximum measurable speed, 
with a consequent inversion of the color coding into the 
red portion of the scale despite the fact that the direction 
of flow has not changed. 
CD echocardiography is generally used to identify location, direction and timing of flow abnormalities (as for 
PWD). Turbulent flow that greatly exceeds the Nyquist limit adopts a mosaic pattern because various velocities 
and directions are assigned to each of the many sample volumes that make up the sampling region. 
Occasionally, it is possible to estimate the direction of turbulent blood flow by identifying the dominant color in 
the mosaic pattern; however, this is often not possible. In most cases, this is not necessary because the 
sonographer can view the development of turbulent flow in real time or examine a synchronous ECG tracing 
and determine, based on the cardiac cycle and the location of the abnormal flow, in what direction the blood 
should be flowing (Figure 3.42). The most accurate means of identifying the timing of flow with CD is to 
integrate it with M-mode imaging. For example, in order to determine the duration of turbulent flow through an 
insufficient aortic valve, an M-mode scan of the aortic valve can be projected with the CD image to provide an 
accurate measure of the temporal extent of the turbulent flow (Figure 3.43). Additionally, newer methods exist 
which utilize color M-mode imaging to examine cardiac performance, but these are outside the scope of this 
manual and have not been evaluated in domestic species. 
Click on the image to see a larger view 
 
 
Figure 3.42. Color coding of turbulent flow (a "mosaic" 
pattern) caused by systolic regurgitation across an 
insufficient mitral valve. 
Figure3.43. Timing of aortic regurgitation by color M-
mode imaging. In normal conditions, only the systolic flow 
(S) would be present. However, In this case of valvular 
insufficiency, turbulent flow can be observed during the 
mid- and late diastolic phase (D). 
CD has an incredibly high sensitivity and has allowed the identification of many flow patterns and physiological 
anomalies that were previously undetectable by spectral Doppler methods. However, this high sensitivity can 
result in false positive interpretations, especially when CD is relied upon exclusively for the diagnosis. In 
practice, CD can accelerate the identification of a lesion for the clinician who can then dedicate more time to a 
thorough analysis of the abnormality with other echocardiographic methods. 
Box 3.2 lists the main technical manipulations that allow image optimization. 
Box 3.2. Controls for optimizing CD imaging. 
Several adjustments are advisable when moving from 2D imaging to CD imaging. 
1. Reduce total gain or increase the grey-scale rejection filter. This increases the availability of 
pixels without a grey-scale assignment, which can then be used for color pixilation within 
the cardiac chambers. 
2. Increase color gain before placing the probe on the patient until instantaneous pixilation 
appears; then slowly reduce the gain so that this pixilation disappears. This provides the 
optimum gain for the probe. 
3. Reduce low-frequency gain of the CD signals (rejection filters). This reduces "flash" artifacts 
that are created by movements of cardiac structures rather than blood flow. 
4. Reduce the size of the overall ultrasound image sector (overall image size) to include just 
the relevant structures; also reduce the size of the sampling area of the CD to the region 
of interest. These will optimize the frame rate during CD scanning. 
If these adjustments and proper beam alignment fail to produce a satisfactory image, it may be 
necessary to use a probe with a lower frequency or use a different view to image the area of 
interest. 
Variance 
Variance is the difference in flow within individual pixels compared with the mean flow in the sampling region. 
This can be electronically assigned by the ultrasound machine to those pixels which have velocities that differ 
substantially from the mean velocity. Generally, as flow velocity increases, variance increases, even with 
laminar flow. Variance options with certain CD scaling packages may enhance the image appearance. 
Click on the image to see a larger view 
Figure 3.44. Turbulent flow in severe aortic insufficiency. 
The color scale bar is shown on the left of the image. 
Advantages of Color Doppler Echocardiography 
There are numerous advantages or benefits of CD. First, because of the large area available for imaging, it is 
much easier to evaluate large regions of the heart and identify flow anomalies quickly. It has become 
substantially easier to detect very small shunting lesions or trace insufficiencies that would remain undetected 
by spectral Doppler imaging and often are not auscultable. Additionally, CD enables easier alignment of 
spectral Doppler beams into the region of interest for additional evaluation. 
 
SEARCH RESULT #: 10TITLE: Acquisition of CD ImagesAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24110&O=VIN 
 
IMAGING FROM THE RIGHT HEMITHORAX 
Right Parasternal Long Axis View 
Because the heart in the RPLA view is largely perpendicular to the CD ultrasound beams, most flow through the 
cardiac chambers and into the aorta has a low velocity due to a large incident angle between the Doppler beam 
and the direction of flow. However, this reduces complications of aliasing increasing the ability to distinguish 
normal and high-velocity flows of mitral, tricuspid or aortic insufficiency, as well as flows through atrial and 
ventricular septal defects (which are often directed to the right and left of the sampling area along the septal 
walls). Slight adjustment of the probe ventro-caudally on the chest wall, and corresponding angulation to 
reposition the cardiac image, provides a more "apical" orientation to the 4-chamber view improving alignment 
with transmitral flows, which appear red, and left ventricular systolic flows, which appear blue. With diastolic 
inflow, blood initially enters the left ventricle towards the transducer (red) until it reaches the cardiac apex; at 
this point it reverses and proceeds along the septal margin into the LVOT, appearing as a blue signal (Figure 
3.45). In the right parasternal LVOT view, blood moving into the LVOT and aorta during systole often exceeds 
the CD Nyquist limit and aliasing is usually observed (Figure 3.45). 
Click on the image to see a larger view 
 
Figure 3.45. Normal diastolic flow in a normal dog from 
the right parasternal long axis view. (A) Early diastole; 
(B), mid-diastole; (C) late diastole. 
Right Parasternal Short Axis View 
Laminar and turbulent flow can be easily observed in all short axis views. During mid-diastole, at the level of 
the papillary muscles, CD imaging often produces a dual-color image with blue and red colors dividing the 
ventricular chamber into two halves - a blue septal half and a red free-wall half (Figure 3.46.a). Moving into 
the short axis atrio-aortic view allows visualization of any insufficiencies of the aortic and mitral valves. Careful 
examination of the coaptation of the mitral or aortic valve cusps may provide better anatomical localization of 
eccentric insufficiencies and abnormal systolic flows (Figure 3.46.b and 3.46.c). Anatomical localization can 
sometimes be improved by inactivating the color Doppler on still images or cine-loops using specific functions 
incorporated into the equipment (Figure 3.46.d). 
Click on the image to see a larger view 
 
 
Figure 3.46. Color Doppler images of left ventricular (A) and aortic valve (B and C) flows in a normal dog from the 
right parasternal short-axis view. (A), mid-diastolic LV flow (red flow from the LA into the LV; blue flow from the LV 
into the LVOT); (B) early systolic aortic flow; (C) late systolic aortic flow; (D) absence of flow through the aortic valve 
during ventricular diastole. 
Optimizing for the right ventricular inflow and outflow, one can see diastolic flow into the right ventricle across 
the tricuspid valve in red on the left side of the image, and in blue on the right side of the image as blood 
moves into the RVOT (Figure 3.47.a). Occasionally, the junction of these color (directional) changes has a 
black line where flow is exactly perpendicular to the transducer. In some views, vena caval inflow can be seen 
in the right atrium and is usually towards the transducer (red). As systole commences, blood is ejected into the 
pulmonary artery away from the transducer (blue). As it progresses, flow velocity increases and aliasing can 
sometimes be observed (Figure 3.47). This view is used to demonstrate dynamic and fixed RV obstructions and 
pulmonic or tricuspid stenosis, as well as VSD flow and tricuspid insufficiency. Optimizing the view for the 
pulmonic valve, one can often observe trace or mild pulmonic insufficiency during diastole (red); pulmonary 
artery turbulence in systole with pulmonic stenosis; and continuous turbulence with patent ductus arteriosus. 
Click on the image to see a larger view 
 
 
Figure 3.47. Color Doppler images of right ventricular 
inflow and outflow from right parasternal short-axis view 
in a normal dog. Flow occurs from left to right, 
accelerating through the pulmonary valve. (A) Early 
diastolic flow from RA to RV; (B) systolic flow in the 
RVOT; (C) systolic acceleration of flow across the 
pulmonary valve. 
Imaging From the Left Hemithorax 
The left apical views allow optimal evaluation of flows across theatrioventricular valves and flow into the aorta. 
Pulmonary vein inflows can be observed from the roof of the left atrium (red). Similarly, flows across the 
atrioventricular valves in diastole are red. During mid-to-late diastole, blood entering the ventricle is reflected 
from the apex into the LVOT and thus assumes a blue color (Figure 3.48). As systole commences, left 
ventricular blood is ejected into the aorta, often at velocities that produce aliasing artifacts. These views are 
often used to identify transmitral and transaortic flow disturbances (insufficiencies and stenoses) because they 
provide the most parallel alignment with the beam. These views can also provide good images of tricuspid 
valve inflow and regurgitation. However, the distance to these valves from the transducer can sometimes 
reduce the frame rate and image quality, especially in larger breeds or when using probes with too high a 
frequency. 
Click on the image to see a larger view 
 
 
Figure 3.48. Color Doppler images of diastolic flow in the 
left heart of a normal dog from the left apical view. (A) 
early diastole; (B) mid-diastole; (C) late diastole. 
Optimal views of the tricuspid valve and right heart inflow are usually in the left cranial short-axis view where 
inflow is directed towards the transducer (red) (Figure 3.49). Right ventricular outflow and pulmonary artery 
flow is better visualized in the left cranial views and is directed away from the transducer (blue). This view 
often provides good visualization of a patent ductus arteriosus where turbulent continuous flow can be 
observed in the pulmonary artery. 
Click on the image to see a larger view 
Figure 3.49. Color Doppler images of diastolic right 
atrioventricular flow in a normal dog from the left cranial 
short-axis view. The aorta can be seen in the center of 
the image, encircled by the right heart, and optimized for 
visualization of the tricuspid valve. 
Non-Standard Views of Diagnostic Utility 
To image the caudal vena cava with CD, the transducer can be positioned between the 9th and 12th intercostal 
spaces on right side. Manipulation of the probe allows long-axis visualization of the caudal vena cava and 
hepatic veins. Flow in these vessels is often very slow so rejection filters should be inactivated to permit 
detection of low frequency signals. Examination of the large hepatic veins can be used to verify congestion 
associated with right heart failure. With severe right heart failure, flow reversal in these vessels can 
occasionally be observed (Figure 3.50). 
Some cranial thoracic vessels can be observed via a supracostal view, however most animals do not tolerate 
probe placement at the thoracic inlet. Similarly, transesophageal imaging is uncommon in veterinary patients 
due to the need for anesthesia. 
Click on the image to see a larger view 
 
Figure 3.50. Color Doppler images of enlarged hepatic veins in a case of right heart failure. The normal flow is blue 
(A), directed away from the transducer. In B, flow reversal (red) can be appreciated, secondary to the hepatic venous 
congestion. 
 
SEARCH RESULT #: 11TITLE: Quantitative and Qualitative Analysis of 
FlowAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24111&O=VIN 
 
There are several goals in CD image analysis: 
 Comprehensive evaluation of flows in specific anatomic regions; 
 Evaluation of flows during different points of the cardiac cycle; 
 Recognition of normal flow; 
 Recognition of abnormal flow. 
As previously mentioned, CD is particularly useful in identifying flow disturbances, most commonly those 
associated with valvuloplasties and shunting lesions. 
CD allows an easy semi-quantitative evaluation of regurgitation. With trace insufficiency, especially those 
that are physically undetectable, one must always consider that these may be physiological variants or minor 
pathologies that may never progress beyond the level being observed and are simply a function of the very 
high sensitivity inherent in modern CD imaging technology. 
Interpretation of CD images in real-time is sometimes difficult and dependent on the experience of the 
sonographer. High heart rates and complex flow patterns provide an "information overload" to the untrained 
observer, who is unable to mentally filter the extraneous information and concentrate only on the relevant 
portions of the images. Therefore, it is often useful to use cine-loop recordings, or recordings that allow images 
to advance a frame at a time, to identify specific flow patterns or anomalies. 
CD in Valve Disease 
Valvular insufficiencies and stenoses are easily identified with CD because they always exhibit flow patterns 
that are either in abnormal directions or have altered velocities from normal flows resulting in turbulence and 
aliasing. Several views are utilized to identify the origin, duration, direction, size and timing of the abnormal 
flow. CD findings should always be correlated with 2D, M-mode and spectral Doppler findings to ascribe clinical 
significance to the flow anomalies observed with CD. CD analysis alone is rarely sufficient to determine the 
severity of the lesion associated with the flow disturbance. Some small or hemodynamically insignificant lesions 
can produce substantially altered flow detectable by CD, while some very large lesions may fail to produce 
turbulent flow. Thus, CD should not be used as a sole means of quantifying severity of the lesion. 
CD in Shunting Lesions 
Both intra- and extracardiac shunts are easily identifiable with CD imaging. Left-to-right shunts are usually 
turbulent (with the exception of interatrial shunting) due to the difference in pressures across the lesion and 
the resistive nature of most of these lesions (i.e. a relatively small orifice). With large non-resistive shunting 
lesions, turbulence is not observed; shunt direction is determined with CD simply by observing the direction of 
flow across the lesion. Similarly, right-to-left shunts rarely exhibit turbulent flow and are detected by observing 
the direction of flow at different points in the cardiac cycle. Because of the potential for false positive findings 
in non-turbulent shunting lesions, multiple views should be obtained to confirm the diagnosis. 
Regurgitant Jet Size in the Evaluation of Mitral Insufficiency 
CD can provide useful information about the severity of mitral insufficiency but should not be used as a sole 
means of ascribing a degree of severity. A small jet is only associated with mild insufficiency, and therefore 
cannot be the cause of left atrial enlargement. A large jet is usually associated with more severe regurgitation 
and usually causes some increase in left atrial volume. However, an apparently large jet may be associated 
with only moderate disease. Several factors influence the ability to detect a regurgitant jet including the 
direction of the jet (along the wall or into the middle of the chamber), the image resolution, the gain of the CD, 
the probe selection, and filter settings. Studies have demonstrated that predicting the regurgitant volume 
using CD in humans is unreliable; regurgitant volume is more accurately determined with 3-dimensional color 
Doppler echocardiography (currently unavailable in veterinary medicine). 
Some authors have attempted to provide a measure of severity by providing an estimate of the area of the 
regurgitant jet, or a ratio of the regurgitant jet and left atrium. This method is flawed because of the technical 
factors affecting the variability of imaging of jets (listed above). Additionally, ratiometric quantitation assumes 
that the larger the ratio, the larger the regurgitant jet volume. However, if two jets of similar volume are 
observed in two differently-sized atria, the ratios will necessarily be different. Similarly,jets that occupy a 
similar portion of the left atrium in dogs with different left atrial size will have different volumes. This can be 
seen in the example below: 
 20kg dog 
with a normal LA 
20kg dog 
with severe LA enlargement 
Left atrial volume 100ml 500ml 
Jet/LA area 20% 20% 
Regurgitant volume 20ml 100ml 
In this example, it is obvious that two jets that have a similar jet/LA area ratio can have substantially different 
regurgitant volumes. The findings in the right column may be seen in situations where the patient has 
myocardial failure as the primary cause of the increased left atrium with secondary or coincident mitral 
insufficiency. In such a case, the percentage of the left atrium occupied by the jet does not reflect the 
magnitude of the regurgitation. Similarly, a jet that occupies a large percentage of a normal left atrium will 
have a high jet/LA area ratio but cannot be classified as severe. Assessment of severity should consider the 
size of the left atrium as the primary determinant of severity, with the absolute or relative jet size being a 
subsidiary measure of severity (Figure 3.51). Additionally, a large regurgitant jet or one that occupies a large 
percentage of the left atrium, regardless of the left atrial size, may be of prognostic value as it may indicate 
more severe valvular pathology, and therefore, may mandate more careful monitoring of the patient. 
Click on the image to see a larger view 
 
Figure 3.51. Color Doppler images of mitral 
regurgitation. (A) mild regurgitation; (B) moderate 
regurgitation; (C) severe regurgitation, with the 
regurgitant wave extending to the pulmonary veins and 
occupying a large percentage of the area of the left 
atrium. 
Proximal Isovelocity Surface Area Method (PISA) 
This method can theoretically provide an objective and independent measure of the severity of insufficiency. 
The method examines the blood in the left ventricle as it accelerates towards an incompetent valve during 
systole. Laminar flow in the ventricle accelerates from all directions towards the incompetent valve equally 
creating a semicircular pattern of increasing velocities. If the radius of the semicircle is measured at a singular 
isovelocity line, an instantaneous volume can be estimated. By multiplying this volume by the duration of the 
regurgitant jet, the regurgitant volume can be determined: 
Volume= velocity x time x 2πr2 
where velocity is the velocity at the isovelocity line, t is the duration of the regurgitant jet, and r is the radius 
of the semicircle delineated by the isovelocity line. 
This method has been evaluated in dogs, but did not accurately estimate volume. Additionally, it is technically 
challenging to perform and requires specific adjustments of the flow profile to optimize the image prior to 
analysis. 
 
Chapter 4 ‐ Echocardiographic Diagnosis of Cardiac Disease 
 
Introduction 
Echocardiograph 
 
18291409 
Modern biotechnology, such as ultrasonography, has provided the clinician with an 
unparalleled non-invasive means of investigating cardiac disease. However, despite the 
relative ease, safety and potentially low cost of such diagnostic technology, clinicians should 
always be cognizant of the importance of the critical application of diagnostic tests, and 
utilize them appropriately in the course of disease investigation rather than as a substitute for 
a proper and ordered clinical approach to the patient. The clinician should be aware before 
ascribing a pathological diagnosis to echocardiographic findings that, as with any physical or 
instrumental diagnostic test, echocardiography is not immune to misinterpretations of 
findings. Such diagnostic misinterpretations are often the result of artifacts or procedural or 
technical errors that, with appropriate training, should be recognizable as such, especially on 
review of the examination. Additionally, even a clinician relatively untrained in 
echocardiography should be able to identify such misinterpretations by confirming the 
apparent echocardiographic findings with repeat or alternate testing. 
While many potential reasons for performing an echocardiogram exist, in most patients the 
major justification is the prior auscultation of a cardiac murmur. However, in such cases, the 
clinician cannot focus their echocardiographic examination on the suspected lesion and 
ignore the rest of the cardiovascular system which may harbor concurrent, clinically relevant 
pathology, but should perform a complete examination in the majority of cases. Such a 
complete cardiac examination generally consists of 2D, M-mode and Doppler imaging (often 
both spectral and color Doppler) which provides a comprehensive anatomic, functional and 
hemodynamic assessment. This often necessitates a longer examination but increases the 
sensitivity and specificity of the diagnostic testing, and results in fewer misinterpretations. 
Exceptions may exist where patients are screened for occult cardiac disease. Similarly, not all 
patients with murmurs warrant an echocardiographic examination. 
The paragraphs above serve as a warning that it is insufficient to proceed directly to the 
suspected diagnosis with the most direct test (for example, the use of color Doppler to 
confirm the presence of mitral insufficiency) without also determining the effect of such a 
finding on the anatomy and hemodynamics of the affected cardiac components (e.g., the 
magnitude of the volume overload, potential etiologies of the valvular insufficiency, 
alterations of systolic performance, presence of secondary pulmonary hypertension) that 
together characterize more completely the patient's clinicopathologic status. Using the 
example of mitral insufficiency, the solitary detection of an insufficiency with color Doppler 
without the supplementary echocardiographic evaluations, provides little if any information 
about potential interventions and prognosis. On the other hand, a complete echocardiographic 
examination, together with a proper physical and radiographic evaluation, often provides the 
most complete assessment of the patient, and allows the most appropriate strategies for 
patient care to be adopted. 
Conversely, it is important to realize that echocardiography often provides the only non-
invasive method to accurately and rapidly diagnose several congenital cardiac diseases that 
would otherwise require complex and invasive antemortem diagnostic procedures. While the 
author does not want to overemphasize the importance of echocardiography in cardiac 
disease diagnosis, the advent of this technology in the recent past has enabled clinicians to 
clarify the pathogenetic mechanism of some clinical findings while refuting the importance of 
others, and to assist in the diagnosis of certain complex cardiac disorders that previously were 
the exclusive domain of the pathologist. 
 
Chapter 5 ‐ Congenital Cardiac Defects 
SEARCH RESULT #: 1 
TITLE: Classification of Congenital Cardiac Defects 
AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24113&O=VIN 
 
Cardiac defects can be classified by several means. They can be classified by their hemodynamic 
consequences: shunting (volume overloading) or obstructive (pressure overloading) or a combination of both 
of these categories. They can be also classified embryologically: defects of septation, persistence of embryonic 
structures, and malformation of chambers or valves. Again, some defects span these categories. No one 
system of classification is completely categorizing - there are exceptions that do not conform to any single 
system. 
Shunting Defects 
Shunting defects include defects that shunt from the left-sided circulation to the right-sided circulation, and 
vice versa. They also include defects that shunt from one chamber toanother. The former include patent 
ductus arteriosus, ventricular septal defects and atrial septal defects. The latter include valvular malformations 
(dysplasia) resulting in insufficiency. Left-to-right shunting defects are much more common than right-to-left 
shunting defects. Blood is shunted from the left side to the right side most commonly because RESISTANCE to 
blood flow is much less in the pulmonary circulation than the systemic circulation, and fluid dynamics dictate 
that fluids will always flow along paths of least resistance. Left-to-right shunting defects "steal" some of the 
stroke volume from the systemic circulation, resulting in a transient decrease in systemic blood pressure, 
which is rapidly normalized by fluid retention to a volume equal to that "stolen" by the shunt. Thus, left-to-
right shunting defects result in a total increase in blood volume and a volume overload of the parts of the 
circulation involved in the shunt. To determine which parts of the circulation are affected by the shunted blood 
volume, one simply needs to follow a hypothetical red-blood cell from the start of the shunt, around the 
circulatory tree, back to the shunt. All the chambers and vessels through which the hypothetical red blood cell 
flows are subject to the volume overload. The degree to which the volume overload occurs depends on the size 
of the shunt (i.e. the volume of the shunt). There are a few exceptions that need to be considered (discussed 
below in the relevant sections). 
Right-to-left shunting defects are relatively rare. They generally occur either because the resistance to flow 
into the pulmonary circulation exceeds resistance to flow into the systemic circulation for some reason 
(discrete obstructions or generalized increase in vascular resistance) or right ventricular diastolic compliance is 
decreased (i.e. a stiff right ventricle). This creates a path of least resistance for the fluid from the right side to 
the left side. In such cases, the systemic circulation perceives no "loss" of fluid since a normal stroke volume 
enters the aorta (i.e., it is simply bypassing the lungs +/- left heart). Therefore, there is no fluid retention and 
the total blood volume is normal. 
Obstructive Defects 
Obstructive defects generally increase the resistance to blood flow across the region spanned by the defect. 
This results in an increased afterload of the chamber immediately upstream of the defect, with consequent 
compensatory hypertrophy. 
Combinational (Complex) Defects 
These defects include both obstruction to flow and shunting of blood. 
 
SEARCH RESULT #: 2TITLE: PDA (Leftto-Right Shunting)AUTHOR(S):ADDRESS 
(URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24114&O=VIN
 
Epidemiology 
Patent ductus arteriosus (PDA) is the most common congenital defect in dogs. Several breeds are predisposed 
to PDA: Poodles, German Shepherds, Collies, keeshonds, American Cocker Spaniels, Maltese Terriers. Females 
develop PDA twice as often as males (2:1). The disorder is inherited, but does not follow simple Mendelian 
patterns. 
Pathophysiology 
Left-to-right shunting PDA is the most common form of PDA. Blood is ejected from the ventricle into the aorta. 
A portion of this stroke volume is shunted through the PDA because of low resistance of the pulmonary 
vasculature compared to the systemic vasculature. The amount of shunting is determined by the impedance of 
the two circulations and the size of the PDA orifice. The shunted volume of blood re-circulates through the 
pulmonary system, back to the left atrium and into the left ventricle. 
Simultaneously, less blood is pumped into the systemic circulation. This causes neurohormonal activation, 
with subsequent fluid retention and increase in plasma volume to restore the systemic stroke volume to 
normal. Thus, the left ventricular stroke volume ultimately consists of the effective systemic stroke volume and 
the shunt volume. This creates a volume overload of the pulmonary circulation, left atrium and left ventricle. 
Clinical Signs 
A continuous murmur, loudest in systole, can be ausculted, with a point of maximal intensity under the left 
axilla (in the 2nd intercostal space dorsal to the costochondral junction). A systolic mitral murmur is often 
ausculted. In some instances, the PDA murmur may be ausculted on the right side. If the shunting is severe 
enough, left-sided congestive heart failure (pulmonary edema) develops. 
Echocardiographic Findings 
2D echocardiography. The LV chamber is enlarged in diastole because of the increased volume. Generally, 
the degree of chamber enlargement is proportional to the size of the PDA (the bigger the LV, the bigger the 
PDA) (Figure 5.1). The LV chamber is enlarged in systole because of increased afterload. The fractional 
shortening is normal, or decreased if myocardial failure is present. The LV wall thickness is normal because of 
eccentric hypertrophy. The left atrium is enlarged because of increased volume. In the author's experience, for 
a similar degree of left ventricular enlargement, the LA is not as large in PDA as it is with mitral valve 
insufficiency (congenital or acquired). The pulmonary arteries and veins are enlarged because of increased 
volume. 
Click on the image to see a larger view 
Figure 5.1. Eccentric hypertrophy of the left atrium and 
ventricle in a 7 year old German shepherd with a patent 
ductus arteriosus. 
The PDA can occasionally be visualized from the right parasternal short-axis view (Figure 5.2.c). However, it is 
best visualized from a modified left-cranial long-axis or modified left-cranial short-axis view. This view is 
difficult to obtain even for experienced echocardiographers. (Figure 5.2) 
Click on the image to see a larger view 
 
Figure 5.2. Echocardiographic image (A) and schematic 
representation (B) of the PDA opening into the main 
pulmonary artery from the left cranial window. Ductal 
flow is directed from the lower portion of the image 
towards the transducer. (C) A right parasternal short-axis 
view at the heart base, optimized for the pulmonary 
artery, demonstrating pulmonary arterial enlargement. 
The diameter of the pulmonary artery (2.54cm) is 
substantially larger than the diameter of the aorta 
(1.07cm). 
In older dogs with left-to-right shunting PDA, the heart often looks like that of a dog with dilated 
cardiomyopathy, often with a low shortening fraction. 
M-mode. The left heart chambers are enlarged in systole and diastole, with a normal or slightly decreased 
shortening fraction (Figure 5.3). 
Click on the image to see a larger view 
 
Figure 5.3. Transventricular M-mode tracings in a dog with a PDA. (A) An image from an old dog in which the defect 
has been diagnosed late. Myocardial failure is apparent as demonstrated by the low fractional shortening and 
increased end-systolic diameter. (B) An image from an 8 week Chihuahua puppy where systolic function is largely 
preserved but eccentric hypertrophy is evident. 
Spectral Doppler. Continuous-wave Doppler of the pulmonary artery from the right-parasternal short-axis 
view demonstrates a continuous high-velocity flow signal towards the pulmonic valves (i.e., towards the 
transducer). If the PDA is relatively small, flow may be limited to systole. In these cases, only a systolic 
murmur will be ausculted. Peak flow velocities are usually >4.5m/s (Figure 5.4). 
Click on the image to see a larger view 
Figure 5.4. Continuous wave Doppler of flow through the 
PDA. The flow is continuous during the entire cardiac 
cycle, but the velocity increases in systole and diminishes 
in diastole. 
Color Flow Doppler. Color-flow Doppler of the pulmonary artery from the right parasternal short-axis view 
demonstrates a continuous turbulent flow within the main pulmonary artery (Figure 5.5). Examinationof the 
pulmonic or mitral valves often shows insufficiency. 
Click on the image to see a larger view 
Figure 5.5. Color Doppler image showing turbulent 
diastolic flow within the pulmonary artery in a dog with a 
PDA. Pulmonic insufficiency is also present, represented 
as a small red "flame" originating at the valvular cusps. 
 
SEARCH RESULT #: 3TITLE: PDA (Right-to-Left Shunting; "Reverse" 
PDA)AUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24115&O=VIN 
 
Epidemiology 
Right-to-left shunting PDA appears to be more prevalent in American Cocker Spaniels. 
Pathophysiology 
In fetal circulation, most blood bypasses the pulmonary vasculature by passing through the ductus arteriosus 
and the atrial septal ostia. This is due to high pulmonary vascular resistance. Immediately after birth, the 
pulmonary vascular resistance drops substantially, and the ductus arteriosus closes. If the ductus fails to close, 
left-to-right shunting results. If the pulmonary vascular resistance remains high or increases dramatically 
shortly after birth due to profound left-to-right shunting, and the ductus fails to close, right-to-left shunting 
results because blood takes the path of least resistance. Because pressure in the pulmonary artery is the same 
as systemic pressure, there is no turbulence and no murmur with right-to-left PDA. The PDA opens into the 
descending aorta, so de-oxygenated blood enters the descending aorta selectively, resulting in a differential 
cyanosis. 
Clinical Signs 
There is no auscultable murmur. Clinical signs usually develop after 1 year and consist of hindlimb ataxia with 
exercise. Differential cyanosis - cyanosis caudally and normally oxygenated mucosae cranially - can be 
detected by examining mucosa caudally and cranially. 
Echocardiographic Findings 
2D echocardiography. The right ventricle is thickened because the increased afterload provided by the high 
pulmonary vascular resistance causes concentric right ventricular hypertrophy. The left ventricular chamber is 
normal or small because of decreased blood flow through the pulmonary vasculature (decreased preload) to 
the left heart. The ductus can sometimes be visualized in the same left-sided views as left-to-right shunting 
PDA. 
Doppler echocardiography. Continuous wave Doppler examination of the pulmonary valve in diastole may 
demonstrate high-velocity pulmonary insufficiency, consistent with high pulmonary artery pressures. The 
pulmonary pressure gradient in diastole should measure approximately 4-4.5m/s. 
Contrast echocardiography. A bubble study should be performed to diagnose right-to-left shunting PDA. 
An initial injection should be performed while imaging the heart and ascending aorta to rule out intracardiac 
shunting. A second injection should then be performed while imaging the abdominal aorta, to demonstrate 
presence of microbubbles in the systemic circulation (Figure 5.6). 
Click on the image to see a larger view 
Figure 5.6. Contrast ultrasonography of the abdominal 
aorta after injecting microbubbles into the peripheral 
venous circulation. After excluding an intracardiac shunt, 
the finding of bubbles within the abdominal aorta 
indicates the presence of a right-left extracardiac shunt, 
most often a "reverse" PDA. 
 
SEARCH RESULT #: 4ITLE: Persistent Left Cranial Vena Cava (PLCVC)AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24116&O=VIN 
 
Epidemiology 
No population characteristics are known about this defect. 
Pathology and Pathophysiology 
Technically, persistence of the left cranial vena cava is a persistent embryonic structural shunting defect since 
blood from the left cranial part of the body (left side of the head, left arm) is diverted through a persistent 
embryonic structure (left cranial vena cava) from its normal path through the (right) cranial vena cava. 
Normally, the left cranial vena cava regresses during embryological development and forms the great coronary 
vein and coronary sinus. However, in some animals this regression fails to occur, resulting in blood from the 
left cranial venous circulation coursing through the coronary vein and coronary sinus into the right atrium. 
Since the blood ends up in the right atrium and is not subject to any alterations in pressure, the defect is 
incidental and not associated with any clinical signs. 
Echocardiographic Findings 
2-D echocardiography. PLCVC is best visualized in the right parasternal long-axis or short-axis views as a 
dilated hypoechoic chamber at the atrioventricular groove just lateral to the mitral annulus on the long-axis 
view. In the short-axis view, a tube-like structure can often be seen coursing around the caudal border of the 
left atrium and opening into the right atrium near the junction of the caudal vena cava and right atrium (Figure 
5.7). 
Click on the image to see a larger view 
Figure 5.7. Persistent left cranial vena cava in a dog. In 
this image, the dilated coronary vein appears at the 
bottom of the image in the junction between the left atrial 
and left ventricular free walls. 
Contrast echocardiography. Injection of microbubbles into the left cephalic vein shows appearance of 
bubbles first in the persistent vena cava (around the left atrium) and then the right atrium (Figure 5.8). 
Click on the image to see a larger view 
Figure 5.8. Contrast echocardiography showing the 
appearance of microbubbles in the coronary vein (solid 
arrow) after injection of agitated saline into the left 
cephalic vein. Some microbubbles can be seen with the 
right atrium (dashed arrow). 
 
SEARCH RESULT #: 5ITLE: Atrial Septal Defect (ASD)AUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24117&O=VIN 
 
Epidemiology 
Atrial septal defects are rare in dogs and cats. There is no apparent breed predisposition. 
Pathology and Pathophysiology 
Three types of defects exist: ostium primum (most common in cats), ostium secundum (most common in 
dogs) and sinus venosus defects. Additionally, failure to fuse the septum primum and septum secundum 
results in a patent foramen ovale. Ostium primum defects are found just above the atrioventricular junction; 
ostium secundum defects are found in the mid-septum, and sinus venosus defects are found near the roof of 
the atria. Ostium primum defects are often associated with other defects and are usually large. The foramen 
ovale is an embryonic unidirectional valve that allows flow from the right atrium to the left atrium in the fetus. 
It normally closes immediately after birth. Failure to close creates a clinically insignificant defect unless 
complicated by other right-heart defects that can occasionally create right-to-left shunting across the foramen. 
Flow through the ASD is generally left-to-right unless complicated by other defects. Flow is largely diastolic 
during ventricular filling. High compliance of the right ventricle, compared to the left ventricle, results in easier 
distensibility of the right ventricle and accommodation of more volume. Thus, ASDs normally produce right 
ventricular and pulmonary circulatory volume overload. The atria are relatively spared from overload because 
they act as passive conduits during diastolic filling. 
Clinical Findings 
Most ASDs cause no clinical signs because they are too small. Hemodynamically significant ASDs have few 
clinical signs. Occasionally, a murmur of relative pulmonic stenosis or a split second heart sound may be 
ausculted due to the increased right ventricular forward stroke volume. Right-sided congestive heart failure can 
develop. On occasion, where right-to-left shunting develops, systemic (non-differential) cyanosis can occur. 
Echocardiographic Findings 
2-Dimensional echocardiography.The right ventricle is enlarged (eccentrically hypertrophied) if the ASD is 
large enough to cause a volume-overload. Otherwise, the heart may appear normal. Pulmonary artery and 
pulmonary veins may appear enlarged if the circulatory volume is increased. Atria are generally not enlarged 
with isolated secundum defects (Figure 5.9), but may be enlarged with big primum defects, because often the 
atrioventricular valves are affected with primum defects (as part of an atrioventricular cushion defect) (Figure 
5.10). 
Click on the image to see a larger view 
Figure 5.9. Ostium secundum atrial septal defect in a 
dog. If large enough, the defect can result in right 
ventricular and right enlargement. 
 
 
Figure 5.10. Ostium primum atrial septal defect in a dog. Echocardiographic image (A) and schematic representation 
(B). 
The defect can be appreciated in the atrial septum from the right parasternal long or short axis view (Figure 
5.9, 5.10), or from the left apical or left cranial short-axis view, appearing as a distinct loss of echogenicity 
within the atrial septum. In some cases, the defect may be visible only in some views. Patent foramen ovale 
appears as two distinct septal structures encompassing an intraseptal elliptical hypoechoic (fluid-filled) 
structure (Figure 5.11). 
Click on the image to see a larger view 
 
Figure 5.11. Detailed view of a patent foramen ovale in a dog. It is possible to visualize both membranes of the 
foramen within the atrial septum. 2D echocardiographic image (A) and schematic representation (B). 
M-mode. Occasionally, paradoxical ventricular septal wall motion - movement of the ventricular septum 
towards the ventricular posterior wall in diastole due to increased right ventricular diastolic pressures, and low 
left ventricular diastolic pressures - can be detected. 
Spectral Doppler. It is usually difficult to discern trans-septal flow through the ASD. Pulsed-wave Doppler 
of the main pulmonary artery may show increased peak flow velocities and velocity time integrals. Similarly, 
pulsed-wave Doppler examination of tricuspid inflow will show increased E-wave and A-wave velocities, 
especially compared to mitral inflow signals, provided no atrioventricular valvular insufficiencies are present. 
Color Doppler. Color Doppler may show laminar diastolic flow across the atrial septum, usually from left to 
right, bidirectionally or from right to left. With small defects, this is difficult to identify because atrial venous 
inflow signals can mask or distort the trans-septal flow signals. However, sometimes a turbulent jet can be 
observed, especially with small defects (Figure 5.12). Color Doppler examination of the pulmonary valve may 
show high laminar flows, often with aliasing if the ASD is large. If right ventricular or right atrial pressures 
increase, flow may be right-to-left. Color Doppler will also assist in detecting concurrent atrioventricular 
valvular insufficiencies. 
Click on the image to see a larger view 
Figure 5.12. Color Doppler echocardiographic image 
demonstrating a small atrial septal defect in a Spanish 
Great Dane with moderate mitral insufficiency. The small 
jet, labeled ASD, is easily seen because of the increased 
left atrial pressure secondary to the mitral valve disease. 
Contrast Echocardiography. The most sensitive method of detecting ASD or patent foramen ovale is to 
perform a contrast echocardiogram (see method in chapter 2) while imaging the atrial septum and both atria. 
Even with left-to-right shunting defects, there is some right-to-left flow. Thus, microbubbles injected into the 
systemic venous circulation will first appear in the right atrium and cross the septum (through the defect) into 
the left atrium. Appearance of microbubbles in the left atrium is conclusive for a communication at the level of 
the atria (Figure 5.13). 
Click on the image to see a larger view 
 
Figure 5.13. Contrast echocardiography showing the passage of bubbles (arrow) through foramen ovale (see Figure 
5.11) into the left atrium after injection into the cephalic vein. 
 
SEARCH RESULT #: 1 
TITLE: Ventricular Septal Defect (VSD) 
AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24118&O=VIN 
 
Epidemiology 
VSDs are relatively common in the dog. English Springer Spaniels are predisposed. It is also a relatively 
common defect in cats and horses. 
Pathology and Pathophysiology 
The ventricular septum develops by ingrowth of projections from the embryonic cardiac walls and down from 
the valves. In small animals, the vast majority of VSDs are singular perimembranous defects located in the 
region of the membranous (largely non-muscular) septum, just below the right coronary and non-coronary 
cusps of the aortic valve on the left side, and under the septal cusp of the tricuspid valve on the right side. 
Defects in the muscular septum (more apical) are much less common in dogs and cats but are sometimes 
observed in horses. 
Flow across VSDs is largely systolic, especially when the defect is small or moderate, and therefore, 
resistive. During ventricular systole, blood is ejected from both ventricles towards their respective outflow 
tracts. Because of lower pressure in the right ventricular outflow tract than the aorta during systole, some 
blood is shunted from left-to-right. However, because the right ventricle is contracting during this time, the 
blood does not enter the right ventricular cavity but is simply directed out through the right ventricular outflow 
tract into the pulmonary artery. Thus, right ventricular volume overload is NOT a feature of most VSDs. The 
shunted blood adds to the circulating stroke volume from the right ventricle causing a volume overload of the 
pulmonary circulation, and subsequently, the left atrium and left ventricle. Left ventricular stroke volume 
equals the forward (systemic) stroke volume plus the shunted stroke volume. 
With large VSDs, there is no resistance to movement of blood across the defect. Because of increased right 
ventricular diastolic compliance, blood enters the right ventricle during diastole (as with ASDs) as well as 
systole. Intracardiac pressures equalize (the ventricles are now functionally a single chamber with 2 outlets), 
with right ventricular concentric and eccentric hypertrophy. During systole, the lower pulmonary vascular 
impedance allows more blood to flow through the pulmonary circulation resulting in marked overcirculation of 
the pulmonary vascular bed. Pulmonary artery pressures increase because of massively increased flow and due 
to chronic vascular changes, occasionally resulting in reversal of the shunt and right-to-left flow (Eisenmenger 
complex). 
The proximity of the VSD to the aortic cusps often undermines the aortic valves, resulting in aortic 
insufficiency and prolapse of the cusps towards the defect. 
Clinical Findings 
A right-sided systolic murmur is almost always present with left-to-right shunting defects. No murmur is 
ausculted with right-to-left shunting VSDs. The size of the defect determines the development of congestive 
heart failure. With very large (non-resistive) defects, secondary pulmonary hypertension can progress to the 
point of shunt reversal and cyanosis. 
Echocardiographic Findings 
2-dimensional echocardiography. The echocardiographic findings ultimately depend on the size and 
position of the defect. Left ventricular and atrial enlargement (eccentric hypertrophy due to volume overload) 
can occur with larger resistive defects but these chambers remain normal with small defects. Pulmonary 
vascular enlargement may also be noted with large defects. 
The VSD is often best visualized in the right parasternal long-axis outflow view or short-axis view (Figure 
5.14). Small defects often cannot be visualized (Figure5.19.a). Some defects have a thin membrane visible 
that appears to protrude into the right ventricle during systole like a bubble (Figure 5.18). This is a 
membranous aneurism and the defect often perforates the aneurism. In some animals, the aneurism is 
imperforate and no VSD exists. 
The aortic valves often prolapse in diastole and open abnormally in systole. This can be appreciated best in 
the right parasternal long-axis outflow view (Figure 5.15). 
With very large VSDs, the right ventricle is also enlarged and the ventricular walls are thickened (eccentric 
and concentric hypertrophy) consistent with both volume and pressure overload (Figure 5.16). 
Click on the image to see a larger view 
 
 
Figure 5.14. Small membranous ventricular septal defect in a dog. From the right parasternal long axis view (A), the 
defect can be seen at the level of the left ventricular outflow tract just below the aortic valve (arrow) just ventral to 
the tricuspid valve edge. In (B), the same defect (arrow) is visualized from a right parasternal short axis view. 
 
Figure 5.15. Moderate membranous ventricular septal defect in a horse. The aortic right coronary cusp can be seen 
prolapsing through the defect during systole (arrow). The non- coronary cusp, however, opens normally. 2D 
echocardiographic image (A) and schematic representation (B). 
Figure 5.16. Muscular ventricular septal defect in a 
horse. The communication between the two ventricles is 
very large, resulting in the two ventricles functioning as a 
single chamber. The aortic and pulmonary flow, therefore, 
is determined exclusively by the respective vascular 
impedances. 
M-mode. There is no specific value in m-mode echo for diagnosis of VSDs. 
Spectral Doppler. Spectral Doppler is often more sensitive than 2D imaging for identifying small VSDs and 
can be useful in confirming clinical suspicions of a defect thought to be detected by 2D imaging. 
Careful interrogation of the septum with a pulsed wave Doppler probe in the right parasternal short-axis 
view, with the sample volume positioned just inside the right ventricle, will identify a turbulent systolic flow 
pattern towards the transducer. Similar interrogation with a continuous wave Doppler probe will identify a 
similar flow, usually with a peak velocity >4.5m/s, unless substantial pulmonary hypertension (and therefore 
right ventricular systolic hypertension) exists (Figure 5.17). Of course, this is also dependent on the direction 
of the jet in relation to the Doppler beam. Low peak velocity usually indicates massive shunting or improper 
alignment of the Doppler beam. In most cases, continuous-wave Doppler examination of the right ventricular 
outflow tract in the short-axis view will also demonstrate high-velocity turbulent flow as the jet from the VSD 
wraps around the septum and heads away from the transducer towards the pulmonary valve. Pulsed-wave 
Doppler examination of the pulmonary artery will demonstrate increased peak flow velocities and velocity time 
integrals due to the increased stroke volume. 
Click on the image to see a larger view 
 
Figure 5.17. Continuous wave Doppler tracing of flow directed towards the transducer through a small VSD (A) and a 
large VSD (B). In (A), the peak velocity of 4.5 m/sec is indicative of low pressure within the right ventricle. On the 
other hand, the peak velocity of 2.96 m/sec in (B) indicates elevated right ventricular pressure due to pulmonary 
arterial hypertension. 
Color Doppler. This is the most sensitive means of detecting a VSD. Interrogation of the ventricular septum 
just below the tricuspid valve in the right parasternal long-axis view or the short-axis view that shows the 3 
commissures of the aortic valve, will often demonstrate turbulent systolic flow from the left to right if the 
defect is perimembranous or membranous. If the defect is muscular, careful interrogation of the entire 
muscular septum may be necessary to locate the VSD by sweeping the transducer from base to apex in the 
short-axis view. With very small VSDs, this may be the only means of identifying the VSD (Figure 5.19). Even 
with very eccentrically directed jets that can occur when the tricuspid valve adheres to the septum, color 
Doppler will usually be able to identify the lesion. 
Color Doppler evaluation of the aortic valve will demonstrate aortic insufficiency in many cases (Figure 5.20). 
Click on the image to see a larger view 
Figure 5.18. Color Doppler image of the turbulent flow 
from a small VSD in a dog. The jet is directed towards the 
right ventricular free wall demonstrating the reason for 
right-sided systolic murmurs with most VSDs. 
 
Figure 5.19. 2D echocardiographic right parasternal short-axis image of a dissecting VSD in a dog (A). The defect is 
very small and, therefore, not visible without the aid of color Doppler (B) which readily identifies the turbulent flow. 
Figure 5.20. Color Doppler image showing aortic 
insufficiency in a horse with a small VSD and a septal 
aneurism (arrow). The diastolic turbulent flow is directed 
from the center of the aortica valve towards the left 
ventricle. 
Contrast Echocardiography. While this may demonstrate some right-to-left shunting in diastole, with 
microbubbles appearing in the left ventricle, this is generally unnecessary for the diagnosis of VSD. If Doppler 
evaluation is not possible, a contrast study may demonstrate a filling defect at the location of the shunt (see 
Chapter 2). 
With right-to-left shunting perimembranous defects, a contrast study will demonstrate the appearance of 
microbubbles in the aortic root and ascending aorta during systole, and occasionally, within the LVOT or left 
ventricle in diastole. With muscular defects, microbubbles will often appear within the LV before appearing in 
the aorta. 
 
SEARCH RESULT #: 2TITLE: Atrioventricular Valvular DysplasiaAUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24119&O=VIN 
 
Epidemiology 
Dysplasia of the mitral valve is most commonly seen in large breed dogs, such as Mastiffs. It has also been 
reported in Bull Terriers with or without mitral stenosis. Mitral valve dysplasia is often seen together with aortic 
subvalvular stenosis. Tricuspid valve dysplasia is most commonly reported in Labrador Retrievers where it is an 
inherited trait. There are also some anecdotal reports of tricuspid dysplasia in Borzois. Mitral and tricuspid 
malformations occur in cats mostly as part of a complex of defects referred to as endocardial cushion defects. 
We have recognized tricuspid valvular malformations in some older cats, which appear similar to tricuspid 
dysplasia in dogs. However, these cats, despite severe tricuspid regurgitation and congestive heart failure at 
the time of diagnosis, have apparently lived for over a decade without any complications which is not 
consistent with severe tricuspid dysplasia. Recent studies have suggested that these cats, in fact, have a right 
ventricular cardiomyopathy with secondary remodeling of the tricuspid apparatus rather than a congenital 
disease. 
Pathology and Pathophysiology 
Failure of valve closure during systole results in shunting of blood from the ejecting ventricle back into its 
corresponding atrium, identical to acquired valvular insufficiency (see Chapter 6 Mitral Valve Insufficiency and 
Tricuspid Insufficiency). Consequently, both the affected ventricle and atrium enlarge to accommodate the 
regurgitant volume (i.e., eccentric hypertrophy due to volume overload). If severe enough, congestive heart 
failure develops in the dependent circulation. 
Clinical Findings 
A systolic murmur over the mitral valve or tricuspid valve can be ausculted. If severe, congestive heart failure 
develops. 
Mitral Dysplasia 
Echocardiographic Findings 
2-D echocardiography.Clinically important mitral dysplasia results in left ventricular and left atrial 
enlargement with normal wall thicknesses (i.e., eccentric hypertrophy due to volume overload) (Figure 5.21). 
Because this disease is seen mostly in large breed dogs with severe and prolonged disease, myocardial failure 
occurs, characterized by increased end-systolic ventricular dimension and decreased shortening fraction. 
Click on the image to see a larger view 
Figure 5.21. Left atrial and ventricular enlargement 
measured from a right parasternal long axis view in a 2 
year old bull mastiff with mitral dysplasia. The valve 
edges appear relatively normal compared with valves in 
patients with acquired myxomatous mitral valve disease. 
Mitral valve cusps appear largely normal but may fail to appose during systole with a visible gap between the 
valve tips. This is best appreciated in the right parasternal long-axis 4-chamber view (Figure 5.22) but can 
often be visualized in the left apical view. Occasionally, abnormally hyperechoic chordae tendineae can be 
visualized but this is an unreliable and inconsistent finding. Rarely, the valves appear grossly misshapen as is 
commonly seen with acquired valvular disease. 
Click on the image to see a larger view 
Figure 5.22. Apical 4 chamber view of the mitral valve in 
the same patient as the previous figure showing a lack of 
coaptation of the mitral valves in systole. 
M-mode echocardiography. M-mode imaging reveals increased left ventricular diastolic dimensions and 
increased left atrial dimensions and LA/Ao with clinically significant dysplasia. Systolic dimensions are often 
also enlarged due to myocardial failure resulting in a decrease in shortening fraction (Figure 5.23). E-point 
septal separation (EPSS) may be increased as myocardial failure develops. 
Click on the image to see a larger view 
Figure 5.23. Transventricular M-mode image in a dog 
with mitral dysplasia and myocardial insufficiency. Left 
ventricular contractility is reduced as evidenced by 
increased end-systolic dimensions. 
Spectral Doppler. Pulsed-wave Doppler examination of the mitral valve from the left apical 4-chamber view 
shows increased passive inflow (tall E-wave) with the sample volume positioned in the left ventricle, and a 
high-velocity turbulent flow in the left atrium during ventricular systole when the sample volume is positioned 
in the left atrium. Continuous-wave Doppler in the same view shows a high-velocity systolic jet away from the 
transducer (i.e., from the left ventricle to the left atrium). The velocity of the jet is generally >5m/s. Spectral 
Doppler interrogation of the mitral valve should not be performed from the right side as inaccurate measures 
of velocity will be obtained. 
Color Doppler. Color Doppler interrogation of the mitral valve in the right parasternal long-axis or short-
axis view or left apical views demonstrates a regurgitant jet similar to that seen with acquired mitral valve 
disease. 
Tricuspid Dysplasia 
Echocardiographic Findings 
2-D echocardiography. The right ventricular and right atrial are enlarged (i.e., eccentric hypertrophy due to 
volume overload) with normal wall thicknesses. In cases of severe tricuspid dysplasia, the right atrium often 
occupies the majority of the image in most views and rotates the axis of the heart so that standard views are 
difficult to obtain. Often, the left ventricle appears small in severe cases because of decreased preload to the 
left heart and the relative enormity of the right heart (Figure 5.24). 
Click on the image to see a larger view 
Figure 5.24. Severe tricuspid dysplasia in a Labrador 
retriever. The left ventricular diameter appears much 
smaller than the right ventricular diameter. Additionally, 
the tricuspid edges appear abnormally shaped and 
positioned (arrow). 
Tricuspid valve cusps appear abnormal in most cases. Most commonly, the septal cusp of the tricuspid valve 
appears tethered to the septum by very short dysplastic chordae tendineae. The non-septal cusp usually 
appears as a "sail" leaflet, which is enlarged, but unable to close the tricuspid orifice during systole. It is also 
attached to short chordae. In many cases of tricuspid dysplasia, there is virtually no difference between the 
systolic and diastolic orifice (Figure 5.25 and 5.26). 
Click on the image to see a larger view 
 
Figure 5.25. Tricuspid dysplasia in a Golden retriever. The septal cusp appears tethered and restricted from closing 
(arrow). The papillary muscle attached to the elongated free-wall cusp appears prominent. Echocardiographic image 
(A) and schematic representation (B). 
 
Figure 5.26. Severe tricuspid dysplasia in a Labrador retriever. The right atrium occupies most of the image distorting 
the standard projection. The septal border of the tricuspid valve is prevented from closing, and the left heart is small 
because of reduced right ventricular cardiac output. Echocardiographic image (A) and schematic representation (B). 
M-mode echocardiography. M-mode imaging reveals variably increased right ventricular diastolic dimensions 
and increased right atrial dimensions. 
Spectral Doppler. Pulsed-wave Doppler examination of the tricuspid valve from the left apical 4-chamber 
view or right parasternal long-axis view shows increased passive inflow (tall E-wave) during diastole and 
turbulent flow in the right atrium during ventricular systole. Continuous-wave Doppler in the same view shows 
a moderate-velocity systolic jet away from the transducer (i.e., from the right ventricle to the right atrium). 
Velocity of the jet is generally 2.5-3m/s (reflective of a transvalvular pressure gradient of 25-36mmHg). 
Color Doppler. Color Doppler interrogation of the tricuspid valve in the right parasternal long-axis view 
demonstrates a regurgitant jet, similar to that seen with acquired tricuspid valve disease, but often much 
larger (Figure 5.27). 
Click on the image to see a larger view 
Figure 5.27. Color Doppler image from the same subject 
as in Figure 5. 26. Turbulent systolic flow can be seen 
across the tricuspid valve. 
 
 
SEARCH RESULT #: 3TITLE: Aortic Valve DysplasiaAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24120&O=VIN 
 
Epidemiology 
This is rare defect. The author has identified a high incidence of aortic valve malformations in a family of 
Sussex Spaniels. It is commonly identified in horses. 
Pathology and Pathophysiology 
In most cases seen by the author, aortic valve dysplasia results from abnormal division of the aortic cusp, 
producing a bicuspid or quadricuspid valve. These valves often have a failure of coaptation at the commissural 
fornices with resultant aortic regurgitation. The severity of the regurgitation determines the hemodynamic 
consequences. If severe, congestive heart failure and myocardial failure develop. Rarely, valvular stenosis may 
be observed. 
Clinical Findings 
A diastolic murmur over the aortic valve can sometimes be ausculted. If severe, a bounding arterial pulse may 
be present. Pulmonary edema may develop if severe. If stenosis exists, a systolic murmur may be ausculted. 
Echocardiographic Findings 
2-D echocardiography. Left ventricular enlargement occurs proportional to the aortic insufficiency. If severe, 
left atrial enlargement follows because of increased left ventricular diastolic pressures. Also, if severe, 
myocardial failure develops characterized by decreased contractility and increased end systolic dimensions. 
Abnormal valve morphology is best identified in the right parasternal short-axis view or left cranial short-axis 
view. Occasionally, the commissural failure of coaptation can be seen in this view. 
M-mode echocardiography. Left ventricular dimensions in diastole and eventually systole increase dueto 
increased preload and ultimately myocardial failure. Consequently, shortening fraction may initially be 
increased and progressively decrease over time as the condition progresses. The left atrium and LA/Ao may be 
enlarged. Occasionally, unusual morphology of the aortic valve in the right-parasternal short-axis view can be 
detected along with diastolic aortic valve flutter. 
Examination of the mitral valves (usually in the right parasternal short-axis view) often demonstrates 
diastolic mitral valve flutter. This occurs because the regurgitant jet hits the open septal mitral cusp during 
diastole causing it to vibrate (Figure 5.28, also Box 2.6, Chapter 2). E-point-to-Septal Separation (EPSS) may 
be increased for the same reason. 
Click on the image to see a larger view 
Figure 5.28. M-mode tracing from a dog with aortic 
valve dysplasia and valvular insufficiency in which it is 
possible to observe diastolic flutter of the septal border of 
the mitral valve (arrow). 
Spectral Doppler. Continuous-wave Doppler of the left ventricular outflow tract from the left apical 5-
chamber view shows a high-velocity regurgitant diastolic jet towards the transducer (i.e., from the aorta to the 
left ventricle). Early diastolic peak velocity approaches 5m/s. With mild-moderate insufficiency, the jet 
assumes a relatively square shape with little change in peak velocity from early to late diastole (Figure 5.29). 
With severe insufficiency, the jet velocity decreases through diastole due to a decrease in transvalvular 
pressure gradient, both from a decrease in aortic diastolic pressure and increase in left ventricular diastolic 
pressure. Thus, the slope of the velocity profile can be used to estimate the severity of the insufficiency. 
Click on the image to see a larger view 
Figure 5.29. Continuous wave Doppler tracing through 
the aortic valve of a dog with aortic dysplasia and 
insufficiency. The figure shows a high velocity diastolic 
flow, with a flat plateau shape throughout diastole, 
indicative of mild disease. 
Pulsed-wave Doppler of the left ventricular outflow tract during systole may demonstrate laminar flows with 
increased peak velocity because of the increased stroke volume from the left ventricle. If stenosis co-exists, 
turbulent flow may be observed. 
Color Doppler. Color Doppler examination of the aortic valve shows a regurgitant jet of variable size 
depending on the degree of insufficiency. The jet may originate at the center point of the valve closure or from 
the fornices of the affected commissures along the wall of the aorta (Figure 5.30). 
Click on the image to see a larger view 
 
 
Figure 5.30. Color Doppler image of a dysplastic aortic valve can allow visualization of either a centrally directed 
regurgitant jet (A) or an eccentric jet (B). In B, two regurgitant jets secondary to a quadricuspid aortic valve can be 
seen directed along the septal border of the mitral valve. 
 
SEARCH RESULT #: 4TITLE: Cor TriatriatumAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24121&O=VIN 
 
Epidemiology 
There are no obvious predispositions to this condition. Cor triatriatum Dexter (CTD) has been recorded only in 
dogs, while Cor Triatriatum Sinister (CTS) has been documented only in cats. 
Pathology and Pathophysiology 
CTD and CTS arise from abnormalities of development of the sinus venosus valve which is largely an 
embryonic and fetal structure that regresses with septation of the atria. Thus, they are defects of septation; 
however, they do not result in typical shunting lesions but rather act as obstructive lesions. In some cases, 
where the valve fails to regress, it forms an obstruction to atrial inflow from either the caudal vena cava (CTD) 
or from the pulmonary veins (CTS). CTS is very difficult to distinguish from supravalvular mitral stenosis so 
both conditions will be addressed here as CTS. 
Obstruction of inflow increases hydrostatic pressure in the dependent circulation (systemic abdominal venous 
circulation with CTD; pulmonary venous circulation with CTS) and, if severe, ultimately results in congestive 
heart failure. Cats with CTS often have no evidence of CHF for several years despite having the increased 
pulmonary venous pressures from birth. This is thought to be due to development of compensatory 
(secondary) pulmonary artery hypertension as a protective mechanism which reduces pulmonary blood flow. 
On the other hand, most dogs with CTD develop ascites within a few months. 
CTD necessitates shunting of venous blood around the obstruction, so collateral venous drainage develops, 
often through the vertebral or azygous veins. The persistent sinus venosus valve in CTD can incorporate the 
coronary sinus (venous return from the coronary circulation) resulting in dilation of the main coronary vein. 
The persistent sinus venosus valve can be perforate or imperforate. 
CTS often has a concurrent atrial septal defect or patent foramen ovale resulting in left-to-right shunting. 
Echocardiography 
2-D echocardiography. CTD is often not visualized in the standard right-parasternal long axis views because 
the partition is too caudal. It can be seen in the right-parasternal short axis view as a three-chambered atrial 
cluster. Occasionally, the opening between the caudal and cranial atrial chambers can be seen. The caudal 
vena cava is distended. The right ventricle is often small, as is the left heart, due to decreased preload (Figure 
5.31). 
CTD can also be visualized from the left cranial right-ventricular/right-atrial view (Figure 5.32). 
Click on the image to see a larger view 
 
Figure 5.31. 2D image from the right parasternal short 
axis view in a dog with cor triatriatum dexter. The right 
atrium is divided into 2 chambers: a cranial chamber 
(RA1) and a caudal chamber (RA2). A perforation in the 
dividing septum is indicated by the arrow. 
Figure 5.32. Visualization of cor triatriatum dexter in a 
dog, from the left cranial view optimized for the tricuspid 
valve. At the bottom of the image, two right atrial 
chambers (RA1 and RA2) separated by a membrane can 
be seen (arrow). 
Additionally, if the coronary sinus is obstructed, a dilated coronary vein can be seen circling around the back of 
the left atrium along the atrioventricular groove. This often looks like a persistent cranial vena cava (see 
above). 
CTS is usually visualized from the right parasternal long axis or short axis view. It can also be seen in the left 
cranial short-axis view. Supravalvular mitral stenosis is lower in the atrium than a true CTS and both of these 
types of lesions are seen as a shelf across the atrium just above the mitral annulus. 
M-mode. There is no benefit from M-mode evaluation of these conditions. 
Spectral Doppler. Careful interrogation of the right atrium with a perforate CTD can reveal turbulent 
continuous flow from the caudal chamber to the cranial chamber. (Note, the flow is low-velocity enough not to 
produce any audible murmurs.) However, this is a relatively insensitive test. 
Similarly, interrogation of the left atrium near the mitral annulus (from the left apical 4-chamber view) can 
reveal high velocity diastolic flow toward the transducer. 
Color Doppler. Color Doppler is the most sensitive means of identifying perforate CTD. Examination of the 
septum between the caudal and cranial right atrial chambers will identify flow across this region (Figure 5.33). 
With CTS and supravalvular mitral stenosis, flow may be visualized across the atrial septal defects (if 
present). Flow is usually turbulent or near-turbulent with spectral broadening (Figure 5.34). 
Click on the image to see a larger view 
 
Figure 5.33. Color Doppler image from the same subject as in Figure 5.31, showing flow between the 2 right atrial 
chambers. InA, there is a communication through a small perforation in the dividing membrane. In B, two turbulent 
flows can be seen through the intra-atrial membrane. 
Figure 5.34. Cor triatriatum sinister in a cat. Color 
Doppler imaging demonstrates turbulent flow in the lower 
left atrial chamber (LA2) directed at the inter-atrial 
septum, as blood passes through a small perforation of 
the intra-atrial membrane from the upper atrial chamber 
(LA2). 
Contrast Echocardiography. This can be used to help identify CTD. Injection has to be into the saphenous 
vein and results in appearance of microbubbles in the caudal right atrial chamber followed by appearance in 
the cranial chamber either by passing through the perforations in the septation or via collateral circulation. 
 
SEARCH RESULT #: 5TITLE: Atrioventricular Valvular StenosisAUTHOR(S): ADDRESS 
(URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24122&O=VIN 
 
Epidemiology 
Mitral stenosis is reported in English Bull Terriers. It can occur in cats as supravalvular mitral stenosis (see Cor 
Triatriatum Sinistrum). Tricuspid stenosis has no obvious predispositions. Both of these conditions can occur as 
part of regurgitant valvular dysplasia or other complex congenital defects or as a separate condition. 
Pathology and Pathophysiology 
Mitral and tricuspid stenoses cause obstruction to emptying of the atria into the ventricles during ventricular 
diastole. This increases pressure within the atria and dependent venous circulations. If severe enough, 
congestive heart failure results which represents the final stage of the disease. With mitral stenosis, secondary 
pulmonary artery hypertension often develops, preventing pulmonary edema, but instead results in acquired 
pressure overload of the right heart and can result in right heart myocardial failure and right-sided congestive 
failure. 
Echocardiography 
2-D echocardiography. Mitral stenosis results in left atrial enlargement (due to increased afterload) and 
decreased left ventricular dimensions due to decreased preload. Consequently, left ventricular walls may 
measure thicker than normal - an effect known as pseudohypertrophy. The right ventricle may or may not be 
enlarged with thicker walls (concentric hypertrophy). The right atrium will be enlarged if there is right heart 
failure. 
The mitral valves fail to open normally but maintain a domed shape during diastole. They have the 
appearance of the roof of the Pantheon with an opening at the apex. (Figure 5.35) They usually close normally 
but may fail to close because of abnormal chordae tendineae. 
Click on the image to see a larger view 
Figure 5.35. 2D echocardiographic left apical view from a 
dog with mitral stenosis. The valve borders have a domed 
shape in diastole with the tips pointed at each other 
(arrow). 
Tricuspid stenosis results in right atrial enlargement (due to increased afterload) and decreased right 
ventricular dimensions as was described above for the stenotic mitral valve. The left heart is also small 
because of reduced preload. 
The stenotic tricuspid valves also have a domed appearance during diastole. 
M-mode echocardiography. With mitral stenosis, M-mode examination at the level of the mitral valve 
shows a progressive loss of distinct E-wave and A-wave with progressively more severe stenosis. The 2 
diastolic waves are often replaced by a more square-shaped diastolic mitral valve pattern with a reduced E-F 
slope. This is due to a loss of the mid-diastolic phase where flow across the valve approaches zero because the 
continuous pressures in the atrium maintain flow throughout diastole. E-point-to-Septal separation is increased 
because the septal mitral cusp fails to open to its full extent. Left ventricular dimensions are often small and 
left atrial dimensions are enlarged as is the LA/Ao. 
With tricuspid stenosis, M-mode examination through the tricuspid valve shows a pattern identical to that of 
a stenotic mitral valve. The right atrium is enlarged and the right ventricle may appear small. 
Spectral Doppler. Pulsed-wave Doppler examination of inflow of the affected valve with the sample volume 
placed just downstream of the valve orifice shows a marked attenuation of the E-wave and A-waves with a loss 
of the E-wave deceleration. A-wave can be increased in many cases. This often produces a profile reminiscent 
of a church with a tower. Flow may be laminar or turbulent, depending on the degree of stenosis. Ventricular 
inflow has higher peak velocities than normal, and, if stenosis is severe, a lack of a mid-diastolic period of 
diastasis. Continuous wave Doppler also shows a similar inflow pattern and will demonstrate a regurgitant jet if 
the valves are incompetent as well as stenotic (Figures 5.36 and 5.37). 
Outflow velocities from the affected ventricle are often reduced reflecting the decreased preload. 
Click on the image to see a larger view 
 
Figure 5.36. Continuous wave Doppler tracing of the 
mitral inflow in a dog with mitral stenosis. Both E-wave 
and A-wave velocities are increased and the E-wave lacks 
a complete deceleration slope because a pressure 
gradient is maintained throughout diastasis. This gives 
the flow signal a shape similar to a church with a steeple. 
Figure 5.37. Pulsed-wave Doppler recording of mitral 
inflow in a cat with mitral stenosis showing high velocities 
of both E-waves and A-waves. 
Color Doppler. Color Doppler examination shows turbulent or accelerated diastolic flow through the stenotic 
valve into the recipient ventricle. This is often best appreciated in the left apical 4-chamber view, but can 
usually be identified in the right parasternal long-axis 4-chamber view (Figures 5.38 and 5.39). 
Click on the image to see a larger view 
Figure 5.38. Mitral and tricuspid stenosis in a cat imaged 
with color Doppler from a left apical view. High-speed 
diastolic, but still laminar, flow is visible across both 
valves. Both atria appear enlarged. 
 
 
Figure 5.39. Right parasternal long-axis view showing color Doppler imaging of a dog with mitral stenosis. In (A), the 
severe inflow obstruction can be seen by the small turbulent diastolic jet at the valve aperture, and marked left atrial 
enlargement without concurrent left ventricular enlargement; indeed, the LV appears small. This contrasts with the 
mild stenosis in (B), where the turbulent flow is much larger and the chamber dimensions are near-normal. 
 
SEARCH RESULT #: 6TITLE: Aortic Valve StenosisAUTHOR(S) ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24123&O=VIN 
 
Epidemiology 
Congenital aortic stenosis is 2nd most common defect in the dog after the PDA. In >95%, the stenosis is 
subvalvular, while valvular stenosis makes up the remaining 5%; supravalvular stenosis is extremely rare. 
Breeds predisposed to this disease include Boxer, German Shepherd, Newfoundland, German Shorthaired 
Pointer, Bull Mastiff, Rottweiler and Golden Retriever. Aortic stenosis is very rare in horses and cats. 
Pathology and Pathophysiology 
Aortic stenosis causes an obstruction to outflow from the left ventricle resulting in an increased pressure in the 
left ventricle and consequent physiological hypertrophy of the left ventricular myocardium. The stenosis is 
classified by its association with the aortic valve and is subvalvular, valvular or postvalvular (rare). In the most 
common subvalvular form, the less severe cases have fibromuscular nodules along the basilar septum just 
below the coronary ostium. With increasingly severe stenosis, these nodules tend to fuse and encircle the 
outflow tract to varying degrees, creating fibromuscular rings, bands or tunnels, which can incorporate the 
septal cusp of the mitral valve. The valvular form affects only the aortic valve cusps whichoften appear 
nodular or fused. The valvular annulus may appear hypoplastic, making it difficult to distinguish it from the 
prevalvular form. The post-valvular form is due to hypoplasia of the ascending aorta. 
Concurrent mitral stenosis is often detected, especially with severe SAS. Left ventricular remodeling may 
alter mitral valve movement, causing dynamic systolic LV obstruction. 
A pathological classification of subaortic stenosis has been compared to the echocardiographic findings to 
provide an analogous antemortem classification scheme (Table 5.1). 
Table 5.1 
Breed Weight 
(kg) 
LVDd 
(mm) 
LVDs 
(mm) 
LVWd 
(mm) 
LVWs 
(mm) 
IVSd 
(mm) 
IVSs 
(mm) 
SF 
(%) 
Poodle 3 16-28 8-16 4-6 6-10 - - 47 
Beagle 8.9±1.5 19.5-33.1 8.9-22.5 4.4-12 7.6-15.2 4.5-8.9 6.6-12.6 40 
West Highland White 
Terrier 
10.3±0.9 17.4-40.2 12.6-27.4 4-8.8 7.2-12.4 4.1-9.7 5.2-15.2 35 
English Cocker 
spaniel 
12.2±2.25 27.2-40.4 16.6-27.8 5.7-10.1 - - - 34.3 
Corgi 8-19 28-40 12-23 6-10 8-13 - - 44 
Pointer 19.2±2.8 34.4-44 20.5-30.1 5.7-8.5 8.9-14.1 4.7-9.1 8.6-12.6 35.5 
Afgan hound 17-36 33-52 20-37 7-11 9-18 - - 33 
Greyhound 26.6±3.5 28.1-
50.14 
25.5-39.5 8.7-15.5 10.9-19.7 7.2-14 8.2-18.6 25.3 
Greyhound 29.1±3.7 40.7-53.1 28.1-38.5 8.2-15 - 10-16.8 - 28.8 
Boxer 28±7.1 30-50 26.8 6-14 11-19 5-13 9-17 33 
Golden Retriever 23-41 37-51 1.8-3.5 8-12 10-19 - - 39 
Doberman - 34.7-45.5 25.9-36.9 5.6-10.4 8.3-14.1 - - 21.7 
Doberman 36 38.5-55.1 24.2-37.4 8.4-10.8 14.1 8.4-10.8 13-15.6 34.2 
Spanish Mastiff 52.4±3.3 44.9-50.5 26.8-31.2 8.9-10.5 14.4-16 9-10.6 14.6-16.6 39.2 
Terranova 47-69.5 44-60 29-44 8-13 11-16 7-15 11-20 30 
Great Dane 52-75 44-59 34-45 10-16 11-19 12-16 14-19 25 
Irish Wolfhound 50-80 46-59 33-45 9-13 11-17 9-14.5 11-17 28 
Clinical Findings 
A basilar systolic murmur of variable intensity is auscultable. Rarely, a diastolic murmur may be ausculted if 
concurrent aortic insufficiency is severe. A mitral murmur may be ausculted with pronounced concurrent mitral 
dysplasia. Peripheral pulses are usually normal but can be weak. 
Echocardiographic Findings 
2-D echocardiography. A stenotic obstruction can often be visualized in the right parasternal long-axis 
outflow view. This can take the form of a discrete hyperechoic nodule on the septum, a ring-like structure, or a 
narrow tunnel through the LVOT immediately below the valve (Figure 5.40). The aortic valvular leaflets often 
appear hyperechoic and thickened with abnormal motion in subvalvular stenosis due to constant high-velocity 
impact from the subvalvular jet (Figure 5.41). Abnormal morphology and movement are most evident in the 
valvular form of aortic stenosis. The post-stenotic portion of the aorta is dilated. 
Click on the image to see a larger view 
 
Figure 5.40. Right parasternal LVOT view of a subvalvular aortic stenosis in a dog. In (A), the arrow indicates a 
fibrous knob on the interventricular septum. In systole (B) the aortic valve is only partially open, due to the high-
velocity turbulent jet passing through the valve. This jet creates a region of low pressure, resulting in partial systolic 
valve closure. 
Figure 5.41. Right parasternal short axis view of a dog 
with subaortic stenosis. The aortic cusps appear 
thickened. 
With post-valvular forms, the root of the aorta has a smaller diameter than the valvular annulus. 
A right parasternal short-axis view also allows good visualization of the lesion and allows evaluation of each 
valve cusp (Figure 5.42). The LVOT narrowing can be appreciated and compared to valvular annulus as a broad 
measure of severity (Figure 5.43). 
Click on the image to see a larger view 
 
Figure 5.42. Right parasternal short axis view of a dog 
with subaortic stenosis. Thickened cusps can be 
appreciated both along the valve edges and in the mid-
cusp. 
Figure 5.43. Left apical view showing thickened aortic 
valves and a hyperechoic nodule at the base of the aortic 
valve on the septum (arrow). 
The subvalvular abnormality can often be identified in the left apical view. 
In all views, the left ventricular walls appear variably thickened proportional to the severity of the stenosis. 
With more severe lesions, subendocardial hyperechoic regions - especially within the papillary muscles - are 
often visible, suggestive of myocardial fibrosis or ischemia (Figure 5.44). 
Click on the image to see a larger view 
 
 
Figure 5.44. Right parasternal short axis view of the left ventricle in diastole (A) and systole (B) in a dog with 
subaortic stenosis. The ventricle appears thickened in diastole and subendocardial hyperechogenicity is evident 
(arrows). In systole (B), the lumen is obliterated. 
M-mode. Left ventricular myocardial hypertrophy can be variably appreciated. Chamber dimensions are 
usually normal but can be reduced. The aortic valve cusps can be visualized. These often have abnormal 
motion, reduced opening or early partial or complete closure (Figure 2.80). Systolic and diastolic flutter of the 
aortic valve can be detected in some cases (Figure 5.45). If dynamic stenosis exists, this can be detected by 
M-mode imaging of the mitral valve (Figure 6.53). 
Click on the image to see a larger view 
Figure 5.45. M-mode tracing through the aortic valve, in 
which diastolic flutter (during the period marked "D") of 
aortic valves can be seen. This image also allows 
estimation of the proportions of the aorta (Ao) and the 
left atrium (LA). There is suspected left atrial enlargement 
in this patient. 
Spectral Doppler. The left apical view provides the best alignment with left ventricular outflow. With PWD, as 
the sample volume is gradually moved from the outflow tract below the lesion into the aorta, a step-up in 
systolic flow velocity can be detected. With severe stenosis, aliasing will become apparent above the lesion. 
Sampling below the valve may reveal aortic insufficiency as a high-velocity diastolic jet. 
CWD from the same position provides an accurate measure of the systolic velocity and pressure gradient as 
well as aortic insufficiency, if present (Figure 5.46). In most cases, the shape of the systolic jet does not 
discriminate between subvalvular and valvular stenosis. With concomitant dynamic stenosis, the CWD may 
display both the fixed and dynamic wave forms superimposed over each other. 
Click on the image to see a larger view 
Figure 5.46. Continuous wave Doppler tracing of aortica 
flow from the left apical view showing a high velocity 
systolic flow profile (4.65m/s) which corresponds to a 
pressure gradient across the valve of 86.72 mmHg (P1). 
The classification or identification of subaortic stenosis is complicated and varies according to different breeds 
and among investigators especially when differentiating mild stenosis from normal flow. Some breeds, such as 
the Boxer, may have higher normal velocity than other breeds so that, while most breeds have an upper limit 
of 1.7m/s, Boxers may have normal flows >2m/s. Debate exists about how to identify very mildly affected 
Boxer dogs and is often dependent on more than just an evaluation of an outflow velocity. 
Moderate stenosis has a pressure gradient greater than 50mmHg (3.5m/s velocity) while severe stenosis has 
a pressure gradient greater than 80mmHg (4.5m/s). 
Color Doppler. The right parasternal long-axis outflow view can be used to visualize both the systolic 
turbulent flow and any associated insufficiency. The origin of the systolic turbulence can sometimes be 
identified by the location of the vena contracta (zone of accelerated flow) in relation to the aortic valve (Figure 
5.47). The turbulent jet usually extends into the aorta. A diastolic jet originating at the aortic valve can be 
variably identified as a plume-shaped jet, and can be used to identifythe site of the stenosis by comparing the 
locations of the 2 flows (systolic vs diastolic). 
Click on the image to see a larger view 
Figure 5.47. Color Doppler image of transaortic systolic 
flow in subaortic stenosis in a dog showing turbulent 
systolic flow. 
Turbulence can also be detected in the right parasternal short-axis view. This view also permits the 
identification of the specific origin of the diastolic jet. A left apical 5-chamber view often provides the best 
alignment with flow, but is usually not required for color Doppler imaging, and can suffer from problems of 
resolution. 
 
 
SEARCH RESULT #: 1 
TITLE: Ventricular Septal Defect (VSD) 
AUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24118&O=VIN 
Epidemiology 
VSDs are relatively common in the dog. English Springer Spaniels are predisposed. It is also a relatively 
common defect in cats and horses. 
Pathology and Pathophysiology 
The ventricular septum develops by ingrowth of projections from the embryonic cardiac walls and down from 
the valves. In small animals, the vast majority of VSDs are singular perimembranous defects located in the 
region of the membranous (largely non-muscular) septum, just below the right coronary and non-coronary 
cusps of the aortic valve on the left side, and under the septal cusp of the tricuspid valve on the right side. 
Defects in the muscular septum (more apical) are much less common in dogs and cats but are sometimes 
observed in horses. 
Flow across VSDs is largely systolic, especially when the defect is small or moderate, and therefore, 
resistive. During ventricular systole, blood is ejected from both ventricles towards their respective outflow 
tracts. Because of lower pressure in the right ventricular outflow tract than the aorta during systole, some 
blood is shunted from left-to-right. However, because the right ventricle is contracting during this time, the 
blood does not enter the right ventricular cavity but is simply directed out through the right ventricular outflow 
tract into the pulmonary artery. Thus, right ventricular volume overload is NOT a feature of most VSDs. The 
shunted blood adds to the circulating stroke volume from the right ventricle causing a volume overload of the 
pulmonary circulation, and subsequently, the left atrium and left ventricle. Left ventricular stroke volume 
equals the forward (systemic) stroke volume plus the shunted stroke volume. 
With large VSDs, there is no resistance to movement of blood across the defect. Because of increased right 
ventricular diastolic compliance, blood enters the right ventricle during diastole (as with ASDs) as well as 
systole. Intracardiac pressures equalize (the ventricles are now functionally a single chamber with 2 outlets), 
with right ventricular concentric and eccentric hypertrophy. During systole, the lower pulmonary vascular 
impedance allows more blood to flow through the pulmonary circulation resulting in marked overcirculation of 
the pulmonary vascular bed. Pulmonary artery pressures increase because of massively increased flow and due 
to chronic vascular changes, occasionally resulting in reversal of the shunt and right-to-left flow (Eisenmenger 
complex). 
The proximity of the VSD to the aortic cusps often undermines the aortic valves, resulting in aortic 
insufficiency and prolapse of the cusps towards the defect. 
Clinical Findings 
A right-sided systolic murmur is almost always present with left-to-right shunting defects. No murmur is 
ausculted with right-to-left shunting VSDs. The size of the defect determines the development of congestive 
heart failure. With very large (non-resistive) defects, secondary pulmonary hypertension can progress to the 
point of shunt reversal and cyanosis. 
Echocardiographic Findings 
2-dimensional echocardiography. The echocardiographic findings ultimately depend on the size and 
position of the defect. Left ventricular and atrial enlargement (eccentric hypertrophy due to volume overload) 
can occur with larger resistive defects but these chambers remain normal with small defects. Pulmonary 
vascular enlargement may also be noted with large defects. 
The VSD is often best visualized in the right parasternal long-axis outflow view or short-axis view (Figure 
5.14). Small defects often cannot be visualized (Figure 5.19.a). Some defects have a thin membrane visible 
that appears to protrude into the right ventricle during systole like a bubble (Figure 5.18). This is a 
membranous aneurism and the defect often perforates the aneurism. In some animals, the aneurism is 
imperforate and no VSD exists. 
The aortic valves often prolapse in diastole and open abnormally in systole. This can be appreciated best in 
the right parasternal long-axis outflow view (Figure 5.15). 
With very large VSDs, the right ventricle is also enlarged and the ventricular walls are thickened (eccentric 
and concentric hypertrophy) consistent with both volume and pressure overload (Figure 5.16). 
Click on the image to see a larger view 
 
 
Figure 5.14. Small membranous ventricular septal defect in a dog. From the right parasternal long axis view (A), 
the defect can be seen at the level of the left ventricular outflow tract just below the aortic valve (arrow) just 
ventral to the tricuspid valve edge. In (B), the same defect (arrow) is visualized from a right parasternal short axis 
view. 
 
Figure 5.15. Moderate membranous ventricular septal defect in a horse. The aortic right coronary cusp can be seen 
prolapsing through the defect during systole (arrow). The non- coronary cusp, however, opens normally. 2D 
echocardiographic image (A) and schematic representation (B). 
Figure 5.16. Muscular ventricular septal defect in a 
horse. The communication between the two ventricles is 
very large, resulting in the two ventricles functioning as 
a single chamber. The aortic and pulmonary flow, 
therefore, is determined exclusively by the respective 
vascular impedances. 
M-mode. There is no specific value in m-mode echo for diagnosis of VSDs. 
Spectral Doppler. Spectral Doppler is often more sensitive than 2D imaging for identifying small VSDs and 
can be useful in confirming clinical suspicions of a defect thought to be detected by 2D imaging. 
Careful interrogation of the septum with a pulsed wave Doppler probe in the right parasternal short-axis 
view, with the sample volume positioned just inside the right ventricle, will identify a turbulent systolic flow 
pattern towards the transducer. Similar interrogation with a continuous wave Doppler probe will identify a 
similar flow, usually with a peak velocity >4.5m/s, unless substantial pulmonary hypertension (and therefore 
right ventricular systolic hypertension) exists (Figure 5.17). Of course, this is also dependent on the direction 
of the jet in relation to the Doppler beam. Low peak velocity usually indicates massive shunting or improper 
alignment of the Doppler beam. In most cases, continuous-wave Doppler examination of the right ventricular 
outflow tract in the short-axis view will also demonstrate high-velocity turbulent flow as the jet from the VSD 
wraps around the septum and heads away from the transducer towards the pulmonary valve. Pulsed-wave 
Doppler examination of the pulmonary artery will demonstrate increased peak flow velocities and velocity time 
integrals due to the increased stroke volume. 
Click on the image to see a larger view 
 
Figure 5.17. Continuous wave Doppler tracing of flow directed towards the transducer through a small VSD (A) and 
a large VSD (B). In (A), the peak velocity of 4.5 m/sec is indicative of low pressure within the right ventricle. On 
the other hand, the peak velocity of 2.96 m/sec in (B) indicates elevated right ventricular pressure due to 
pulmonary arterial hypertension. 
ColorDoppler. This is the most sensitive means of detecting a VSD. Interrogation of the ventricular septum 
just below the tricuspid valve in the right parasternal long-axis view or the short-axis view that shows the 3 
commissures of the aortic valve, will often demonstrate turbulent systolic flow from the left to right if the 
defect is perimembranous or membranous. If the defect is muscular, careful interrogation of the entire 
muscular septum may be necessary to locate the VSD by sweeping the transducer from base to apex in the 
short-axis view. With very small VSDs, this may be the only means of identifying the VSD (Figure 5.19). Even 
with very eccentrically directed jets that can occur when the tricuspid valve adheres to the septum, color 
Doppler will usually be able to identify the lesion. 
Color Doppler evaluation of the aortic valve will demonstrate aortic insufficiency in many cases (Figure 5.20). 
Click on the image to see a larger view 
Figure 5.18. Color Doppler image of the turbulent flow 
from a small VSD in a dog. The jet is directed towards 
the right ventricular free wall demonstrating the reason 
for right-sided systolic murmurs with most VSDs. 
 
Figure 5.19. 2D echocardiographic right parasternal short-axis image of a dissecting VSD in a dog (A). The defect 
is very small and, therefore, not visible without the aid of color Doppler (B) which readily identifies the turbulent 
flow. 
Figure 5.20. Color Doppler image showing aortic 
insufficiency in a horse with a small VSD and a septal 
aneurism (arrow). The diastolic turbulent flow is directed 
from the center of the aortica valve towards the left 
ventricle. 
Contrast Echocardiography. While this may demonstrate some right-to-left shunting in diastole, with 
microbubbles appearing in the left ventricle, this is generally unnecessary for the diagnosis of VSD. If Doppler 
evaluation is not possible, a contrast study may demonstrate a filling defect at the location of the shunt (see 
Chapter 2). 
With right-to-left shunting perimembranous defects, a contrast study will demonstrate the appearance of 
microbubbles in the aortic root and ascending aorta during systole, and occasionally, within the LVOT or left 
ventricle in diastole. With muscular defects, microbubbles will often appear within the LV before appearing in 
the aorta. 
SEARCH RESULT #: 2TITLE: Atrioventricular Valvular DysplasiaAUTHOR(S): 
ADDRESS (URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24119&O=VIN 
Epidemiology 
Dysplasia of the mitral valve is most commonly seen in large breed dogs, such as Mastiffs. It has also been 
reported in Bull Terriers with or without mitral stenosis. Mitral valve dysplasia is often seen together with aortic 
subvalvular stenosis. Tricuspid valve dysplasia is most commonly reported in Labrador Retrievers where it is an 
inherited trait. There are also some anecdotal reports of tricuspid dysplasia in Borzois. Mitral and tricuspid 
malformations occur in cats mostly as part of a complex of defects referred to as endocardial cushion defects. 
We have recognized tricuspid valvular malformations in some older cats, which appear similar to tricuspid 
dysplasia in dogs. However, these cats, despite severe tricuspid regurgitation and congestive heart failure at 
the time of diagnosis, have apparently lived for over a decade without any complications which is not 
consistent with severe tricuspid dysplasia. Recent studies have suggested that these cats, in fact, have a right 
ventricular cardiomyopathy with secondary remodeling of the tricuspid apparatus rather than a congenital 
disease. 
Pathology and Pathophysiology 
Failure of valve closure during systole results in shunting of blood from the ejecting ventricle back into its 
corresponding atrium, identical to acquired valvular insufficiency (see Chapter 6 Mitral Valve Insufficiency and 
Tricuspid Insufficiency). Consequently, both the affected ventricle and atrium enlarge to accommodate the 
regurgitant volume (i.e., eccentric hypertrophy due to volume overload). If severe enough, congestive heart 
failure develops in the dependent circulation. 
Clinical Findings 
A systolic murmur over the mitral valve or tricuspid valve can be ausculted. If severe, congestive heart failure 
develops. 
Mitral Dysplasia 
Echocardiographic Findings 
2-D echocardiography. Clinically important mitral dysplasia results in left ventricular and left atrial 
enlargement with normal wall thicknesses (i.e., eccentric hypertrophy due to volume overload) (Figure 5.21). 
Because this disease is seen mostly in large breed dogs with severe and prolonged disease, myocardial failure 
occurs, characterized by increased end-systolic ventricular dimension and decreased shortening fraction. 
Click on the image to see a larger view 
Figure 5.21. Left atrial and ventricular enlargement 
measured from a right parasternal long axis view in a 2 
year old bull mastiff with mitral dysplasia. The valve 
edges appear relatively normal compared with valves in 
patients with acquired myxomatous mitral valve disease. 
Mitral valve cusps appear largely normal but may fail to appose during systole with a visible gap between the 
valve tips. This is best appreciated in the right parasternal long-axis 4-chamber view (Figure 5.22) but can 
often be visualized in the left apical view. Occasionally, abnormally hyperechoic chordae tendineae can be 
visualized but this is an unreliable and inconsistent finding. Rarely, the valves appear grossly misshapen as is 
commonly seen with acquired valvular disease. 
Click on the image to see a larger view 
Figure 5.22. Apical 4 chamber view of the mitral valve 
in the same patient as the previous figure showing a 
lack of coaptation of the mitral valves in systole. 
M-mode echocardiography. M-mode imaging reveals increased left ventricular diastolic dimensions and 
increased left atrial dimensions and LA/Ao with clinically significant dysplasia. Systolic dimensions are often 
also enlarged due to myocardial failure resulting in a decrease in shortening fraction (Figure 5.23). E-point 
septal separation (EPSS) may be increased as myocardial failure develops. 
Click on the image to see a larger view 
Figure 5.23. Transventricular M-mode image in a dog 
with mitral dysplasia and myocardial insufficiency. Left 
ventricular contractility is reduced as evidenced by 
increased end-systolic dimensions. 
Spectral Doppler. Pulsed-wave Doppler examination of the mitral valve from the left apical 4-chamber view 
shows increased passive inflow (tall E-wave) with the sample volume positioned in the left ventricle, and a 
high-velocity turbulent flow in the left atrium during ventricular systole when the sample volume is positioned 
in the left atrium. Continuous-wave Doppler in the same view shows a high-velocity systolic jet away from the 
transducer (i.e., from the left ventricle to the left atrium). The velocity of the jet is generally >5m/s. Spectral 
Doppler interrogation of the mitral valve should not be performed from the right side as inaccurate measures 
of velocity will be obtained. 
Color Doppler. Color Doppler interrogation of the mitral valve in the right parasternal long-axis or short-
axis view or left apical views demonstrates a regurgitant jet similar to that seen with acquired mitral valve 
disease. 
Tricuspid Dysplasia 
Echocardiographic Findings 
2-D echocardiography. The right ventricular and right atrial are enlarged (i.e., eccentric hypertrophy due to 
volume overload) with normal wall thicknesses. In cases of severe tricuspid dysplasia, the right atrium often 
occupies the majority of the image in most views and rotates the axis of the heart so that standard views are 
difficult to obtain. Often, the left ventricle appears small in severe cases because of decreased preload to the 
left heart andthe relative enormity of the right heart (Figure 5.24). 
Click on the image to see a larger view 
Figure 5.24. Severe tricuspid dysplasia in a Labrador 
retriever. The left ventricular diameter appears much 
smaller than the right ventricular diameter. Additionally, 
the tricuspid edges appear abnormally shaped and 
positioned (arrow). 
Tricuspid valve cusps appear abnormal in most cases. Most commonly, the septal cusp of the tricuspid valve 
appears tethered to the septum by very short dysplastic chordae tendineae. The non-septal cusp usually 
appears as a "sail" leaflet, which is enlarged, but unable to close the tricuspid orifice during systole. It is also 
attached to short chordae. In many cases of tricuspid dysplasia, there is virtually no difference between the 
systolic and diastolic orifice (Figure 5.25 and 5.26). 
Click on the image to see a larger view 
 
Figure 5.25. Tricuspid dysplasia in a Golden retriever. The septal cusp appears tethered and restricted from closing 
(arrow). The papillary muscle attached to the elongated free-wall cusp appears prominent. Echocardiographic image 
(A) and schematic representation (B). 
 
Figure 5.26. Severe tricuspid dysplasia in a Labrador retriever. The right atrium occupies most of the image 
distorting the standard projection. The septal border of the tricuspid valve is prevented from closing, and the left 
heart is small because of reduced right ventricular cardiac output. Echocardiographic image (A) and schematic 
representation (B). 
M-mode echocardiography. M-mode imaging reveals variably increased right ventricular diastolic dimensions 
and increased right atrial dimensions. 
Spectral Doppler. Pulsed-wave Doppler examination of the tricuspid valve from the left apical 4-chamber 
view or right parasternal long-axis view shows increased passive inflow (tall E-wave) during diastole and 
turbulent flow in the right atrium during ventricular systole. Continuous-wave Doppler in the same view shows 
a moderate-velocity systolic jet away from the transducer (i.e., from the right ventricle to the right atrium). 
Velocity of the jet is generally 2.5-3m/s (reflective of a transvalvular pressure gradient of 25-36mmHg). 
Color Doppler. Color Doppler interrogation of the tricuspid valve in the right parasternal long-axis view 
demonstrates a regurgitant jet, similar to that seen with acquired tricuspid valve disease, but often much 
larger (Figure 5.27). 
Click on the image to see a larger view 
Figure 5.27. Color Doppler image from the same 
subject as in Figure 5. 26. Turbulent systolic flow can be 
seen across the tricuspid valve. 
SEARCH RESULT #: 3TITLE: Aortic Valve DysplasiaAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24120&O=VIN 
Epidemiology 
This is rare defect. The author has identified a high incidence of aortic valve malformations in a family of 
Sussex Spaniels. It is commonly identified in horses. 
Pathology and Pathophysiology 
In most cases seen by the author, aortic valve dysplasia results from abnormal division of the aortic cusp, 
producing a bicuspid or quadricuspid valve. These valves often have a failure of coaptation at the commissural 
fornices with resultant aortic regurgitation. The severity of the regurgitation determines the hemodynamic 
consequences. If severe, congestive heart failure and myocardial failure develop. Rarely, valvular stenosis may 
be observed. 
Clinical Findings 
A diastolic murmur over the aortic valve can sometimes be ausculted. If severe, a bounding arterial pulse may 
be present. Pulmonary edema may develop if severe. If stenosis exists, a systolic murmur may be ausculted. 
Echocardiographic Findings 
2-D echocardiography. Left ventricular enlargement occurs proportional to the aortic insufficiency. If severe, 
left atrial enlargement follows because of increased left ventricular diastolic pressures. Also, if severe, 
myocardial failure develops characterized by decreased contractility and increased end systolic dimensions. 
Abnormal valve morphology is best identified in the right parasternal short-axis view or left cranial short-axis 
view. Occasionally, the commissural failure of coaptation can be seen in this view. 
M-mode echocardiography. Left ventricular dimensions in diastole and eventually systole increase due to 
increased preload and ultimately myocardial failure. Consequently, shortening fraction may initially be 
increased and progressively decrease over time as the condition progresses. The left atrium and LA/Ao may be 
enlarged. Occasionally, unusual morphology of the aortic valve in the right-parasternal short-axis view can be 
detected along with diastolic aortic valve flutter. 
Examination of the mitral valves (usually in the right parasternal short-axis view) often demonstrates 
diastolic mitral valve flutter. This occurs because the regurgitant jet hits the open septal mitral cusp during 
diastole causing it to vibrate (Figure 5.28, also Box 2.6, Chapter 2). E-point-to-Septal Separation (EPSS) may 
be increased for the same reason. 
Click on the image to see a larger view 
Figure 5.28. M-mode tracing from a dog with aortic 
valve dysplasia and valvular insufficiency in which it is 
possible to observe diastolic flutter of the septal border 
of the mitral valve (arrow). 
Spectral Doppler. Continuous-wave Doppler of the left ventricular outflow tract from the left apical 5-
chamber view shows a high-velocity regurgitant diastolic jet towards the transducer (i.e., from the aorta to the 
left ventricle). Early diastolic peak velocity approaches 5m/s. With mild-moderate insufficiency, the jet 
assumes a relatively square shape with little change in peak velocity from early to late diastole (Figure 5.29). 
With severe insufficiency, the jet velocity decreases through diastole due to a decrease in transvalvular 
pressure gradient, both from a decrease in aortic diastolic pressure and increase in left ventricular diastolic 
pressure. Thus, the slope of the velocity profile can be used to estimate the severity of the insufficiency. 
Click on the image to see a larger view 
Figure 5.29. Continuous wave Doppler tracing through 
the aortic valve of a dog with aortic dysplasia and 
insufficiency. The figure shows a high velocity diastolic 
flow, with a flat plateau shape throughout diastole, 
indicative of mild disease. 
Pulsed-wave Doppler of the left ventricular outflow tract during systole may demonstrate laminar flows with 
increased peak velocity because of the increased stroke volume from the left ventricle. If stenosis co-exists, 
turbulent flow may be observed. 
Color Doppler. Color Doppler examination of the aortic valve shows a regurgitant jet of variable size 
depending on the degree of insufficiency. The jet may originate at the center point of the valve closure or from 
the fornices of the affected commissures along the wall of the aorta (Figure 5.30). 
Click on the image to see a larger view 
 
 
Figure 5.30. Color Doppler image of a dysplastic aortic valve can allow visualization of either a centrally directed 
regurgitant jet (A) or an eccentric jet (B). In B, two regurgitant jets secondary to a quadricuspid aortic valve can be 
seen directed along the septal border of the mitral valve. 
SEARCH RESULT #: 4TITLE: Cor TriatriatumAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24121&O=VIN 
Epidemiology 
There are no obvious predispositions to this condition. Cor triatriatum Dexter (CTD) has been recorded only in 
dogs, while Cor Triatriatum Sinister (CTS) has been documented only in cats. 
Pathology and Pathophysiology 
CTD and CTS arise from abnormalities of development of the sinus venosus valve which is largely an 
embryonic and fetal structure that regresses with septation of the atria.Thus, they are defects of septation; 
however, they do not result in typical shunting lesions but rather act as obstructive lesions. In some cases, 
where the valve fails to regress, it forms an obstruction to atrial inflow from either the caudal vena cava (CTD) 
or from the pulmonary veins (CTS). CTS is very difficult to distinguish from supravalvular mitral stenosis so 
both conditions will be addressed here as CTS. 
Obstruction of inflow increases hydrostatic pressure in the dependent circulation (systemic abdominal venous 
circulation with CTD; pulmonary venous circulation with CTS) and, if severe, ultimately results in congestive 
heart failure. Cats with CTS often have no evidence of CHF for several years despite having the increased 
pulmonary venous pressures from birth. This is thought to be due to development of compensatory 
(secondary) pulmonary artery hypertension as a protective mechanism which reduces pulmonary blood flow. 
On the other hand, most dogs with CTD develop ascites within a few months. 
CTD necessitates shunting of venous blood around the obstruction, so collateral venous drainage develops, 
often through the vertebral or azygous veins. The persistent sinus venosus valve in CTD can incorporate the 
coronary sinus (venous return from the coronary circulation) resulting in dilation of the main coronary vein. 
The persistent sinus venosus valve can be perforate or imperforate. 
CTS often has a concurrent atrial septal defect or patent foramen ovale resulting in left-to-right shunting. 
Echocardiography 
2-D echocardiography. CTD is often not visualized in the standard right-parasternal long axis views because 
the partition is too caudal. It can be seen in the right-parasternal short axis view as a three-chambered atrial 
cluster. Occasionally, the opening between the caudal and cranial atrial chambers can be seen. The caudal 
vena cava is distended. The right ventricle is often small, as is the left heart, due to decreased preload (Figure 
5.31). 
CTD can also be visualized from the left cranial right-ventricular/right-atrial view (Figure 5.32). 
Click on the image to see a larger view 
 
Figure 5.31. 2D image from the right parasternal short 
axis view in a dog with cor triatriatum dexter. The right 
atrium is divided into 2 chambers: a cranial chamber 
(RA1) and a caudal chamber (RA2). A perforation in the 
dividing septum is indicated by the arrow. 
Figure 5.32. Visualization of cor triatriatum dexter in a 
dog, from the left cranial view optimized for the tricuspid 
valve. At the bottom of the image, two right atrial 
chambers (RA1 and RA2) separated by a membrane can 
be seen (arrow). 
Additionally, if the coronary sinus is obstructed, a dilated coronary vein can be seen circling around the back of 
the left atrium along the atrioventricular groove. This often looks like a persistent cranial vena cava (see 
above). 
CTS is usually visualized from the right parasternal long axis or short axis view. It can also be seen in the left 
cranial short-axis view. Supravalvular mitral stenosis is lower in the atrium than a true CTS and both of these 
types of lesions are seen as a shelf across the atrium just above the mitral annulus. 
M-mode. There is no benefit from M-mode evaluation of these conditions. 
Spectral Doppler. Careful interrogation of the right atrium with a perforate CTD can reveal turbulent 
continuous flow from the caudal chamber to the cranial chamber. (Note, the flow is low-velocity enough not to 
produce any audible murmurs.) However, this is a relatively insensitive test. 
Similarly, interrogation of the left atrium near the mitral annulus (from the left apical 4-chamber view) can 
reveal high velocity diastolic flow toward the transducer. 
Color Doppler. Color Doppler is the most sensitive means of identifying perforate CTD. Examination of the 
septum between the caudal and cranial right atrial chambers will identify flow across this region (Figure 5.33). 
With CTS and supravalvular mitral stenosis, flow may be visualized across the atrial septal defects (if 
present). Flow is usually turbulent or near-turbulent with spectral broadening (Figure 5.34). 
Click on the image to see a larger view 
 
Figure 5.33. Color Doppler image from the same subject as in Figure 5.31, showing flow between the 2 right atrial 
chambers. In A, there is a communication through a small perforation in the dividing membrane. In B, two 
turbulent flows can be seen through the intra-atrial membrane. 
Figure 5.34. Cor triatriatum sinister in a cat. Color 
Doppler imaging demonstrates turbulent flow in the 
lower left atrial chamber (LA2) directed at the inter-
atrial septum, as blood passes through a small 
perforation of the intra-atrial membrane from the upper 
atrial chamber (LA2). 
Contrast Echocardiography. This can be used to help identify CTD. Injection has to be into the saphenous 
vein and results in appearance of microbubbles in the caudal right atrial chamber followed by appearance in 
the cranial chamber either by passing through the perforations in the septation or via collateral circulation. 
SEARCH RESULT #: 5TITLE: Atrioventricular Valvular StenosisAUTHOR(S): ADDRESS 
(URL): http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24122&O=VIN 
Epidemiology 
Mitral stenosis is reported in English Bull Terriers. It can occur in cats as supravalvular mitral stenosis (see Cor 
Triatriatum Sinistrum). Tricuspid stenosis has no obvious predispositions. Both of these conditions can occur as 
part of regurgitant valvular dysplasia or other complex congenital defects or as a separate condition. 
Pathology and Pathophysiology 
Mitral and tricuspid stenoses cause obstruction to emptying of the atria into the ventricles during ventricular 
diastole. This increases pressure within the atria and dependent venous circulations. If severe enough, 
congestive heart failure results which represents the final stage of the disease. With mitral stenosis, secondary 
pulmonary artery hypertension often develops, preventing pulmonary edema, but instead results in acquired 
pressure overload of the right heart and can result in right heart myocardial failure and right-sided congestive 
failure. 
Echocardiography 
2-D echocardiography. Mitral stenosis results in left atrial enlargement (due to increased afterload) and 
decreased left ventricular dimensions due to decreased preload. Consequently, left ventricular walls may 
measure thicker than normal - an effect known as pseudohypertrophy. The right ventricle may or may not be 
enlarged with thicker walls (concentric hypertrophy). The right atrium will be enlarged if there is right heart 
failure. 
The mitral valves fail to open normally but maintain a domed shape during diastole. They have the 
appearance of the roof of the Pantheon with an opening at the apex. (Figure 5.35) They usually close normally 
but may fail to close because of abnormal chordae tendineae. 
Click on the image to see a larger view 
Figure 5.35. 2D echocardiographic left apical view from 
a dog with mitral stenosis. The valve borders have a 
domed shape in diastole with the tips pointed at each 
other (arrow). 
Tricuspid stenosis results in right atrial enlargement (due to increased afterload) and decreased right 
ventricular dimensions as was described above for the stenotic mitral valve. The left heart is also small 
because of reduced preload. 
The stenotic tricuspid valves also have a domed appearance during diastole. 
M-mode echocardiography. With mitral stenosis, M-mode examination at the level of the mitral valve 
shows a progressive loss of distinct E-wave and A-wave with progressively more severe stenosis. The 2 
diastolic waves are often replaced by a more square-shaped diastolic mitral valve pattern with a reduced E-F 
slope. This is due to a loss of the mid-diastolic phasewhere flow across the valve approaches zero because the 
continuous pressures in the atrium maintain flow throughout diastole. E-point-to-Septal separation is increased 
because the septal mitral cusp fails to open to its full extent. Left ventricular dimensions are often small and 
left atrial dimensions are enlarged as is the LA/Ao. 
With tricuspid stenosis, M-mode examination through the tricuspid valve shows a pattern identical to that of 
a stenotic mitral valve. The right atrium is enlarged and the right ventricle may appear small. 
Spectral Doppler. Pulsed-wave Doppler examination of inflow of the affected valve with the sample volume 
placed just downstream of the valve orifice shows a marked attenuation of the E-wave and A-waves with a loss 
of the E-wave deceleration. A-wave can be increased in many cases. This often produces a profile reminiscent 
of a church with a tower. Flow may be laminar or turbulent, depending on the degree of stenosis. Ventricular 
inflow has higher peak velocities than normal, and, if stenosis is severe, a lack of a mid-diastolic period of 
diastasis. Continuous wave Doppler also shows a similar inflow pattern and will demonstrate a regurgitant jet if 
the valves are incompetent as well as stenotic (Figures 5.36 and 5.37). 
Outflow velocities from the affected ventricle are often reduced reflecting the decreased preload. 
Click on the image to see a larger view 
 
Figure 5.36. Continuous wave Doppler tracing of the 
mitral inflow in a dog with mitral stenosis. Both E-wave 
and A-wave velocities are increased and the E-wave 
lacks a complete deceleration slope because a pressure 
gradient is maintained throughout diastasis. This gives 
Figure 5.37. Pulsed-wave Doppler recording of mitral 
inflow in a cat with mitral stenosis showing high 
velocities of both E-waves and A-waves. 
the flow signal a shape similar to a church with a 
steeple. 
Color Doppler. Color Doppler examination shows turbulent or accelerated diastolic flow through the stenotic 
valve into the recipient ventricle. This is often best appreciated in the left apical 4-chamber view, but can 
usually be identified in the right parasternal long-axis 4-chamber view (Figures 5.38 and 5.39). 
Click on the image to see a larger view 
Figure 5.38. Mitral and tricuspid stenosis in a cat 
imaged with color Doppler from a left apical view. High-
speed diastolic, but still laminar, flow is visible across 
both valves. Both atria appear enlarged. 
 
 
Figure 5.39. Right parasternal long-axis view showing color Doppler imaging of a dog with mitral stenosis. In (A), 
the severe inflow obstruction can be seen by the small turbulent diastolic jet at the valve aperture, and marked left 
atrial enlargement without concurrent left ventricular enlargement; indeed, the LV appears small. This contrasts 
with the mild stenosis in (B), where the turbulent flow is much larger and the chamber dimensions are near-normal. 
SEARCH RESULT #: 6TITLE: Aortic Valve StenosisAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24123&O=VIN 
Epidemiology 
Congenital aortic stenosis is 2nd most common defect in the dog after the PDA. In >95%, the stenosis is 
subvalvular, while valvular stenosis makes up the remaining 5%; supravalvular stenosis is extremely rare. 
Breeds predisposed to this disease include Boxer, German Shepherd, Newfoundland, German Shorthaired 
Pointer, Bull Mastiff, Rottweiler and Golden Retriever. Aortic stenosis is very rare in horses and cats. 
Pathology and Pathophysiology 
Aortic stenosis causes an obstruction to outflow from the left ventricle resulting in an increased pressure in the 
left ventricle and consequent physiological hypertrophy of the left ventricular myocardium. The stenosis is 
classified by its association with the aortic valve and is subvalvular, valvular or postvalvular (rare). In the most 
common subvalvular form, the less severe cases have fibromuscular nodules along the basilar septum just 
below the coronary ostium. With increasingly severe stenosis, these nodules tend to fuse and encircle the 
outflow tract to varying degrees, creating fibromuscular rings, bands or tunnels, which can incorporate the 
septal cusp of the mitral valve. The valvular form affects only the aortic valve cusps which often appear 
nodular or fused. The valvular annulus may appear hypoplastic, making it difficult to distinguish it from the 
prevalvular form. The post-valvular form is due to hypoplasia of the ascending aorta. 
Concurrent mitral stenosis is often detected, especially with severe SAS. Left ventricular remodeling may 
alter mitral valve movement, causing dynamic systolic LV obstruction. 
A pathological classification of subaortic stenosis has been compared to the echocardiographic findings to 
provide an analogous antemortem classification scheme (Table 5.1). 
Table 5.1 
Breed Weight 
(kg) 
LVDd 
(mm) 
LVDs 
(mm) 
LVWd 
(mm) 
LVWs 
(mm) 
IVSd 
(mm) 
IVSs 
(mm) 
SF 
(%) 
Poodle 3 16-28 8-16 4-6 6-10 - - 47 
Beagle 8.9±1.5 19.5-33.1 8.9-22.5 4.4-12 7.6-15.2 4.5-8.9 6.6-12.6 40 
West Highland White 
Terrier 
10.3±0.9 17.4-40.2 12.6-27.4 4-8.8 7.2-12.4 4.1-9.7 5.2-15.2 35 
English Cocker 
spaniel 
12.2±2.25 27.2-40.4 16.6-27.8 5.7-10.1 - - - 34.3 
Corgi 8-19 28-40 12-23 6-10 8-13 - - 44 
Pointer 19.2±2.8 34.4-44 20.5-30.1 5.7-8.5 8.9-14.1 4.7-9.1 8.6-12.6 35.5 
Afgan hound 17-36 33-52 20-37 7-11 9-18 - - 33 
Greyhound 26.6±3.5 28.1-
50.14 
25.5-39.5 8.7-15.5 10.9-19.7 7.2-14 8.2-18.6 25.3 
Greyhound 29.1±3.7 40.7-53.1 28.1-38.5 8.2-15 - 10-16.8 - 28.8 
Boxer 28±7.1 30-50 26.8 6-14 11-19 5-13 9-17 33 
Golden Retriever 23-41 37-51 1.8-3.5 8-12 10-19 - - 39 
Doberman - 34.7-45.5 25.9-36.9 5.6-10.4 8.3-14.1 - - 21.7 
Doberman 36 38.5-55.1 24.2-37.4 8.4-10.8 14.1 8.4-10.8 13-15.6 34.2 
Spanish Mastiff 52.4±3.3 44.9-50.5 26.8-31.2 8.9-10.5 14.4-16 9-10.6 14.6-
16.6 
39.2 
Terranova 47-69.5 44-60 29-44 8-13 11-16 7-15 11-20 30 
Great Dane 52-75 44-59 34-45 10-16 11-19 12-16 14-19 25 
Irish Wolfhound 50-80 46-59 33-45 9-13 11-17 9-14.5 11-17 28 
Clinical Findings 
A basilar systolic murmur of variable intensity is auscultable. Rarely, a diastolic murmur may be ausculted if 
concurrent aortic insufficiency is severe. A mitral murmur may be ausculted with pronounced concurrent mitral 
dysplasia. Peripheral pulses are usually normal but can be weak. 
Echocardiographic Findings 
2-D echocardiography. A stenotic obstruction can often be visualized in the right parasternal long-axis 
outflow view. This can take the form of a discrete hyperechoic nodule on the septum, a ring-like structure, or a 
narrow tunnel through the LVOT immediately below the valve (Figure 5.40). The aortic valvular leaflets often 
appear hyperechoic and thickened with abnormal motion in subvalvular stenosis due to constant high-velocity 
impact from the subvalvular jet (Figure 5.41). Abnormal morphology and movement are most evident in the 
valvular form of aortic stenosis. The post-stenotic portion of the aorta is dilated. 
Click on the image to see a larger view 
 
Figure 5.40. Right parasternal LVOT view of a subvalvular aortic stenosis in a dog. In (A), the arrow indicates a 
fibrous knob on the interventricular septum. In systole (B) the aortic valve is only partially open, due to the high-
velocity turbulent jet passing through the valve. This jet creates a region of low pressure, resulting in partial systolic 
valve closure. 
Figure 5.41. Right parasternal short axis view of a dog 
with subaortic stenosis. The aortic cusps appear 
thickened. 
With post-valvular forms, the root of the aorta has a smaller diameter than the valvular annulus. 
A right parasternal short-axis view also allows good visualization of the lesion and allows evaluationof each 
valve cusp (Figure 5.42). The LVOT narrowing can be appreciated and compared to valvular annulus as a broad 
measure of severity (Figure 5.43). 
Click on the image to see a larger view 
 
Figure 5.42. Right parasternal short axis view of a dog 
with subaortic stenosis. Thickened cusps can be 
appreciated both along the valve edges and in the mid-
cusp. 
Figure 5.43. Left apical view showing thickened aortic 
valves and a hyperechoic nodule at the base of the 
aortic valve on the septum (arrow). 
The subvalvular abnormality can often be identified in the left apical view. 
In all views, the left ventricular walls appear variably thickened proportional to the severity of the stenosis. 
With more severe lesions, subendocardial hyperechoic regions - especially within the papillary muscles - are 
often visible, suggestive of myocardial fibrosis or ischemia (Figure 5.44). 
Click on the image to see a larger view 
 
 
Figure 5.44. Right parasternal short axis view of the left ventricle in diastole (A) and systole (B) in a dog with 
subaortic stenosis. The ventricle appears thickened in diastole and subendocardial hyperechogenicity is evident 
(arrows). In systole (B), the lumen is obliterated. 
M-mode. Left ventricular myocardial hypertrophy can be variably appreciated. Chamber dimensions are 
usually normal but can be reduced. The aortic valve cusps can be visualized. These often have abnormal 
motion, reduced opening or early partial or complete closure (Figure 2.80). Systolic and diastolic flutter of the 
aortic valve can be detected in some cases (Figure 5.45). If dynamic stenosis exists, this can be detected by 
M-mode imaging of the mitral valve (Figure 6.53). 
Click on the image to see a larger view 
Figure 5.45. M-mode tracing through the aortic valve, 
in which diastolic flutter (during the period marked "D") 
of aortic valves can be seen. This image also allows 
estimation of the proportions of the aorta (Ao) and the 
left atrium (LA). There is suspected left atrial 
enlargement in this patient. 
Spectral Doppler. The left apical view provides the best alignment with left ventricular outflow. With PWD, as 
the sample volume is gradually moved from the outflow tract below the lesion into the aorta, a step-up in 
systolic flow velocity can be detected. With severe stenosis, aliasing will become apparent above the lesion. 
Sampling below the valve may reveal aortic insufficiency as a high-velocity diastolic jet. 
CWD from the same position provides an accurate measure of the systolic velocity and pressure gradient as 
well as aortic insufficiency, if present (Figure 5.46). In most cases, the shape of the systolic jet does not 
discriminate between subvalvular and valvular stenosis. With concomitant dynamic stenosis, the CWD may 
display both the fixed and dynamic wave forms superimposed over each other. 
Click on the image to see a larger view 
Figure 5.46. Continuous wave Doppler tracing of 
aortica flow from the left apical view showing a high 
velocity systolic flow profile (4.65m/s) which 
corresponds to a pressure gradient across the valve of 
86.72 mmHg (P1). 
The classification or identification of subaortic stenosis is complicated and varies according to different breeds 
and among investigators especially when differentiating mild stenosis from normal flow. Some breeds, such as 
the Boxer, may have higher normal velocity than other breeds so that, while most breeds have an upper limit 
of 1.7m/s, Boxers may have normal flows >2m/s. Debate exists about how to identify very mildly affected 
Boxer dogs and is often dependent on more than just an evaluation of an outflow velocity. 
Moderate stenosis has a pressure gradient greater than 50mmHg (3.5m/s velocity) while severe stenosis has 
a pressure gradient greater than 80mmHg (4.5m/s). 
Color Doppler. The right parasternal long-axis outflow view can be used to visualize both the systolic 
turbulent flow and any associated insufficiency. The origin of the systolic turbulence can sometimes be 
identified by the location of the vena contracta (zone of accelerated flow) in relation to the aortic valve (Figure 
5.47). The turbulent jet usually extends into the aorta. A diastolic jet originating at the aortic valve can be 
variably identified as a plume-shaped jet, and can be used to identify the site of the stenosis by comparing the 
locations of the 2 flows (systolic vs diastolic). 
Click on the image to see a larger view 
Figure 5.47. Color Doppler image of transaortic systolic 
flow in subaortic stenosis in a dog showing turbulent 
systolic flow. 
Turbulence can also be detected in the right parasternal short-axis view. This view also permits the 
identification of the specific origin of the diastolic jet. A left apical 5-chamber view often provides the best 
alignment with flow, but is usually not required for color Doppler imaging, and can suffer from problems of 
resolution. 
SEARCH RESULT #: 7TITLE: Pulmonary Valve StenosisAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24124&O=VIN 
Epidemiology 
Beagles, bulldogs (both French and English), boxers, Bull Mastiffs, Miniature Schnauzers, Chihuahuas and 
various terrier breeds are predisposed to pulmonic stenosis. The trait appears to be polygenetic in Beagles. 
Pulmonic stenosis is rare in cats and horses. 
Pathology and Pathophysiology 
Pulmonic stenosis causes an obstruction to outflow from the right ventricle into the main pulmonary artery 
resulting in an increased pressure in the right ventricle and consequent physiological hypertrophy of the right 
ventricular myocardium and a post-stenotic dilation. The stenosis is classified by its association with the 
pulmonic valve as either infundibular or fixed subvalvular, valvular or postvalvular (rare). The subvalvular form 
has a similar range of pathological findings as the analogous aortic stenosis. The infundibular form is often 
seen as a muscular hypertrophy and is usually associated with more complex conditions (Tetralogy of Fallot). 
These forms may cause pathological changes of the valves due to constant damage by the high-velocity jet. 
The most common valvular form has several distinct morphologies consisting of annular hypoplasia (with 
concomitant pulmonary artery hypoplasia) or commissural malformation and fusion. The latter is more 
common in most breeds, while the former has been identified in the boxer as a fairly common form. The valves 
in the more common former stenosis are usually tripartite but variably fused along the commissures and often 
have fibrous nodules along the cusp edges or at the fornices of the commissures. 
The post-valvular form usually has a band-like narrowing of the pulmonary artery, usually within the 
pulmonary trunk. The most extreme form of pulmonic stenosis is seen as a pulmonary atresia or pseudoatresia 
involving all 3 segments of the right ventricular outflow. 
A specific form of subvalvular stenosis exists in boxers and bulldogs. An anomalous coronary artery 
supplying the left ventricle originates from the right coronary artery and passes over the top of the RVOT 
compressing it and creating a fibrous subvalvular stenosis (R2A anomaly). 
Pulmonic stenosis can be graded in its severity using the same criteria as aortic stenosis: mild stenosis 
(<50mmHg), moderate stenosis (50-80mmHg), and severe stenosis (>80mmHg). 
Clinical Findings 
A left basilar systolic murmur of variable intensity is ausculted proportionally to the severity of the lesion. With 
severe, long-standing disease, right-sided failure may occasionally occur but, in most cases, right-sided failure 
is indicative of a concomitant tricuspid valve insufficiency. In these cases, a tricuspid murmur should be 
auscultable on the right side. 
Echocardiography 
2D echocardiography. The right parasternalviews usually provide the best images of pulmonic stenosis; in 
most cases demonstrating right ventricular and septal hypertrophy, any potential right ventricular chamber 
enlargement (uncommon), right atrial enlargement (if present), the morphology of the valvular annulus and 
cusps, and the main pulmonary trunk. With severe stenosis, systolic septal flattening may be seen in the short-
axis view due to equalization of intraventricular systolic pressures (Figure 5.48). The left heart may appear 
smaller than normal, especially if right heart failure is present. 
Click on the image to see a larger view 
Figure 5.48. 2D right parasternal long-axis view of a 
dog with pulmonic stenosis. There is marked 
hypertrophy of the right ventricular free wall and the 
interventricular septum, which "crushes" the left 
ventricle. 
 
Figure 5.48.a 2D right parasternal short-axis view of a 
dog with pulmonic stenosis. There is marked 
hypertrophy of the right ventricular free wall and 
hypertrophy and flattening of the the interventricular 
septum. 
Figure 5.48.b 2D right parasternal long-axis view of a 
dog with pulmonic stenosis. There is marked 
hypertrophy of the right ventricular free wall and the 
interventricular septum, which bows into the left 
ventricle, altering the sphericity of the LV cavity. A 
hypertrophied right ventricular papillary muscle can be 
seen within the right ventricle. 
The valves, supravalvular and subvalvular regions can be best examined from the short-axis view. With 
prevalvular stenosis, a hyperechoic endocardial region may be identified protruding into the lumen (Figure 
5.49). With valvular stenosis, the thickened valves can be appreciated and usually assume a "D" shape. 
Nodules or thickening can usually be seen at the origin of the cusps. In systole, the cusps are often domed 
because they are fused (Figure 5.50). Occasionally, the annulus appears narrower than the surrounding 
regions. In these cases, the valves may appear relatively normal or may be dystrophic. 
Click on the image to see a larger view 
 
Figure 5.49. 2D right parasternal short-axis view of a 
dog with pulmonic stenosis optimized for the RVOT and 
pulmonic valve. The two arrows indicate subvalvular 
nodules. The pulmonary valve can be seen below these 
structures and appears to be of normal thickness. 
Figure 5.50. Left cranial view of the RVOT and 
pulmonary valve and artery in a dog with pulmonic 
stenosis. The pulmonary valves appear markedly 
thickened (arrow). 
A post-stenotic dilation of the pulmonary artery is usually appreciated in the short-axis view with valvular and 
subvalvular stenosis. With supravalvular stenosis, the artery appears to narrow for a variable length and to a 
variable degree, and no post-stenotic dilation can be appreciated in many cases (Figure 5.51). 
Click on the image to see a larger view 
Figure 5.51. Right parasternal short-axis view of the 
RVOT, pulmonic valve and pulmonary artery in a dog 
with pulmonic stenosis. The arrow indicates the 
pulmonary valve whose cuspids appear relatively normal 
although prolapsed. The pulmonary artery is markedly 
narrowed at the valvular annulus. 
The left cranial short-axis view can also provide reasonable views of the pulmonic valve and pre- and post-
stenotic regions. 
In cases of pulmonic stenosis associated with a coronary malformation, echocardiography may or may not 
identify the coronary lesion. In the short-axis view, the left coronary ostium (usually found in the middle of the 
left coronary cusp) is undetectable. However, this is not a reliable means of identifying the existence of such 
an anomaly and additional invasive diagnostics are necessary to confirm the anomaly. 
M-mode. Paradoxical septal motion due to septal flattening can be appreciated if present (Figure 5.52). 
Click on the image to see a larger view 
Figure 5.52. Transventricular M-mode tracing of a dog 
with pulmonic stenosis. The right ventricle (RV) is large 
and the interventricular septum (IVS) shows paradoxical 
motion. (The septum moves towards the left ventricular 
free wall in diastole, and away from the LV free wall in 
systole.) 
Spectral Doppler. PWD from the right short axis view, with the sample volume positioned in the RVOT and 
moved across the pulmonic valve, allows identification of the specific location of the stenosis in most cases by 
demonstrating a step-up in the velocity or appearance of aliased flow at the site of the stenosis. If pulmonic 
insufficiency coexists, a diastolic turbulent flow can be appreciated just below the valve. From this same view, 
CWD can determine the maximum velocity across the stenosis providing an estimate of severity (Figure 5.53). 
Click on the image to see a larger view 
Figure 5.53. Continuous wave Doppler across the 
pulmonic valve of a dog with pulmonic stenosis. The 
moderate velocity of the systolic flow (under the 
baseline) denotes a stenosis of mild/moderate severity. 
Diastolic flow is also apparent (arrow) secondary to 
valvular insufficiency. 
Color Doppler. Color Doppler in the right parasternal short-axis view will demonstrate turbulence beginning at 
the level of the stenosis and can help identify the location of the stenosis. A diastolic plume (red) of pulmonic 
insufficiency towards the transducer can often be identified originating at the pulmonic valves (Figure 5.54). 
Click on the image to see a larger view 
 
 
Figure 5.54. Color Doppler of pulmonic stenosis and pulmonary insufficiency in a dog viewed from a left cranial 
window optimized for the pulmonic valve. Turbulent systolic flow (A) is visible within the pulmonary artery and 
diastolic flow (B) is visible within the RVOT. 
SEARCH RESULT #: 8TITLE: Tetralogy of Fallot (TOF)AUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24125&O=VIN 
Epidemiology 
Keeshonds and Bulldogs are predisposed to TOF. It is inherited as a simple recessive condition indicating that a 
single gene is involved. 
Pathology and Pathophysiology 
TOF comprises three defects of development (pulmonary stenosis, overriding aorta, ventricular septal defect) 
and one compensatory response (right ventricular concentric hypertrophy due to pressure overload). Typically, 
the stenosis is severe enough, and the ventricular septal defect is large enough, to allow equalization of the 
ventricular pressures. The high resistance to ejection of blood into the pulmonary artery through the stenosis 
results in ejection of blood from the right ventricle through the non-resistive VSD into the systemic circulation - 
a right-to-left intraventricular shunt - creating a systemic cyanosis. 
There are variations on this theme, with some variability in the size of the VSD and the pulmonary stenosis, 
producing a small left-to-right shunt ("pink TOF"; non-cyanotic) and balanced TOF where flows from each 
ventricle are directed largely into their corresponding great vessels (no net shunting). Occasionally, animals 
may develop conditions similar to TOF that are due to different defects (combined VSD and pulmonary stenosis 
without overriding aorta; pulmonary atresia or hypoplasia with VSD etc). These conditions resemble the 
hemodynamic consequences of TOF. 
Clinical Findings 
Typical TOF develop whole-body cyanosis because the pulmonary stenosis is usually severe. A systolic murmur 
over the pulmonary valve can be ausculted. Secondary polycythemia results. There is no murmur associated 
with the VSD in TOF. 
Echocardiographic Findings 
2-D echocardiography. Right ventricular hypertrophy with very thick ventricular walls can be appreciated in 
the right parasternal long-axis 4-chamber view. Right atrial enlargement, if present, is mild unless there is 
concomitant tricuspid insufficiency (Figure 5.55). In some instances, an additional subvalvularinfundibular 
muscular thickening can be appreciated. 
Click on the image to see a larger view 
Figure 5.55. Tetralogy of Fallot in a Rottweiler from a 
right parasternal long-axis view. The right ventricle is 
markedly thickened and the right atrium is mildly 
enlarged. 
A ventricular septal defect is seen although its location is not typical of most isolated VSDs. In many cases, the 
aorta appears to straddle the VSD appearing to serve both ventricles (Figure 5.56). The pulmonary artery is 
often difficult to find and is usually hypoplastic. The pulmonic valve often appears abnormal with thickened 
cusps. This is best appreciated in either the right parasternal short-axis view or left cranial long-axis view. 
Click on the image to see a larger view 
 
 
Figure 5.56. Tetralogy of Fallot in a Rottweiler and a horse. (A). Right parasternal LVOT view shows the 
malpositioning of the aorta over the interventricular septum in the Rottweiler resulting in the appearance of a 
common outflow from both ventricles. The arrow indicates part of the septal cusp of the tricuspid valve within the 
septal defect. In B, a similar image in a foal shows a marked septal defect (arrow.) 
M-mode echocardiography. There are no specific M-mode characteristics of TOF. 
Spectral Doppler. Pulsed-wave Doppler of the right ventricular outflow tract from the right parasternal 
short-axis view may identify a supravalvular (infundibular) stenosis with acceleration of flow due to muscular 
obstruction of the outflow tract as the cursor is advanced across the stenotic region. Pulsed wave Doppler 
across the VSD will demonstrate laminar flow away from the transducer into the aorta. 
Continuous-wave Doppler of the pulmonic valve shows high velocity flow, often >6m/s across the valve. 
However, this flow is sometimes difficult to identify or correctly align with the probe because of the 
malpositioning of the aorta and pulmonic hypoplasia. 
Color Doppler. Color Doppler interrogation of the pulmonic valve shows turbulent flow through the 
infundibular region and into the pulmonary artery. 
Examination of the VSD shows laminar flow from the right ventricle to the aorta. In cases of severe pulmonic 
hypoplasia, color Doppler can help identify the location of the pulmonary artery. 
Contrast echocardiography. This is generally not required for the diagnosis of TOF. Injection of 
microbubbles into the systemic venous circulation will show flow of bubbles through the right heart across the 
VSD and into the aorta during systole confirming the right-to-left shunting. 
SEARCH RESULT #: 9TITLE: Pericardial DefectsAUTHOR(S): ADDRESS (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24126&O=VIN 
Pericardial defects are generally not identifiable with echocardiography; with the exception of 
pericardioperitoneal diaphragmatic hernias (PPDH). 
Epidemiology 
PPDH is a defect most commonly identified in cats. It is often an incidental finding during thoracic radiography 
but can cause complications. There is some evidence that it may have a genetic component (autosomal 
recessive). It can be seen with other congenital defects, mostly umbilical hernia and pectus excavatum, as well 
as various cardiac defects. 
Pathology and Pathophysiology 
Incomplete separation of the pericardium and diaphragm can result in a communication between the peritoneal 
cavity and pericardial cavity. Abdominal viscera (most often liver and fat) can prolapse through the defect into 
the pericardial cavity. This does not usually cause any cardiac compromise. However, torsion of the abdominal 
viscera can occur. Additionally, respiratory compromise may occur in some instances due to the expansive 
occupation of the thoracic cage by a very large pericardium. 
Clinical Findings 
Heart sounds may be muffled or displaced (usually dorsally). Dyspnea may occur in some cases. Acute 
abdominal complications (intestinal obstruction etc) can occur if viscera within the pericardium become twisted. 
In many cases, deformities of the manubrium or pectus excavatum can be palpated. 
Echocardiographic Findings 
2-D echocardiography. This is the only imaging required for a diagnosis. The cardiac structures appear 
displaced, and initially, may be difficult to locate necessitating unconventional views. Soft-tissue masses, often 
with echogenicity similar to liver, can be identified alongside the cardiac structures. If loops of gas-filled 
intestine occupy the pericardial space, the interference by gas can make cardiac imaging impossible or difficult 
(Figure 5.57). Pericardial effusion (usually mild) can be visualized. 
Abdominal ultrasonography along the diaphragmatic border can reveal the site of the defect if it is large. 
Very small defects may be undetectable by echocardiographic examination. 
Click on the image to see a larger view 
Figure 5.57. Pericardio-peritoneal diaphragmatic hernia 
in a cat. The liver can be seen contacting the right 
ventricular free wall (arrow). The intrapericardial 
location of the liver was confirmed by further 
echocardiographic evaluation. 
 
 
Search Result #: 1 
Title: Ventricular Septal Defect (VSD) 
Author(s): 
Address (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24118&O=VIN 
Epidemiology 
VSDs are relatively common in the dog. English Springer Spaniels are predisposed. It is also a relatively common 
defect in cats and horses. 
Pathology and Pathophysiology 
The ventricular septum develops by ingrowth of projections from the embryonic cardiac walls and down from the 
valves. In small animals, the vast majority of VSDs are singular perimembranous defects located in the region of 
the membranous (largely non-muscular) septum, just below the right coronary and non-coronary cusps of the 
aortic valve on the left side, and under the septal cusp of the tricuspid valve on the right side. Defects in the 
muscular septum (more apical) are much less common in dogs and cats but are sometimes observed in horses. 
Flow across VSDs is largely systolic, especially when the defect is small or moderate, and therefore, resistive. 
During ventricular systole, blood is ejected from both ventricles towards their respective outflow tracts. Because 
of lower pressure in the right ventricular outflow tract than the aorta during systole, some blood is shunted from 
left-to-right. However, because the right ventricle is contracting during this time, the blood does not enter the right 
ventricular cavity but is simply directed out through the right ventricular outflow tract into the pulmonary artery. 
Thus, right ventricular volume overload is NOT a feature of most VSDs. The shunted blood adds to the circulating 
stroke volume from the right ventricle causing a volume overload of the pulmonary circulation, and subsequently, 
the left atrium and left ventricle. Left ventricular stroke volume equals the forward (systemic) stroke volume plus 
the shunted stroke volume. 
With large VSDs, there is no resistance to movement of blood across the defect. Because of increased right 
ventricular diastolic compliance, blood enters the right ventricle during diastole (as with ASDs) as well as systole. 
Intracardiac pressures equalize (the ventricles are now functionally a single chamber with 2 outlets), with right 
ventricular concentric and eccentric hypertrophy. During systole, the lower pulmonary vascular impedance allows 
more blood to flow through the pulmonary circulation resulting in marked overcirculation of the pulmonary 
vascular bed. Pulmonary artery pressures increase because of massively increased flow and due to chronic 
vascular changes, occasionally resulting in reversal of the shunt and right-to-left flow (Eisenmenger complex). 
The proximity of the VSD to the aortic cusps often undermines the aortic valves, resulting in aortic insufficiencyand prolapse of the cusps towards the defect. 
Clinical Findings 
A right-sided systolic murmur is almost always present with left-to-right shunting defects. No murmur is ausculted 
with right-to-left shunting VSDs. The size of the defect determines the development of congestive heart failure. 
With very large (non-resistive) defects, secondary pulmonary hypertension can progress to the point of shunt 
reversal and cyanosis. 
Echocardiographic Findings 
2-dimensional echocardiography. The echocardiographic findings ultimately depend on the size and position of 
the defect. Left ventricular and atrial enlargement (eccentric hypertrophy due to volume overload) can occur with 
larger resistive defects but these chambers remain normal with small defects. Pulmonary vascular enlargement 
may also be noted with large defects. 
The VSD is often best visualized in the right parasternal long-axis outflow view or short-axis view (Figure 5.14). 
Small defects often cannot be visualized (Figure 5.19.a). Some defects have a thin membrane visible that 
appears to protrude into the right ventricle during systole like a bubble (Figure 5.18). This is a membranous 
aneurism and the defect often perforates the aneurism. In some animals, the aneurism is imperforate and no 
VSD exists. 
The aortic valves often prolapse in diastole and open abnormally in systole. This can be appreciated best in the 
right parasternal long-axis outflow view (Figure 5.15). 
With very large VSDs, the right ventricle is also enlarged and the ventricular walls are thickened (eccentric and 
concentric hypertrophy) consistent with both volume and pressure overload (Figure 5.16). 
Click on the image to see a larger view 
 
 
Figure 5.14. Small membranous ventricular septal defect in a dog. From the right parasternal long axis view (A), 
the defect can be seen at the level of the left ventricular outflow tract just below the aortic valve (arrow) just 
ventral to the tricuspid valve edge. In (B), the same defect (arrow) is visualized from a right parasternal short axis 
view. 
 
Figure 5.15. Moderate membranous ventricular septal defect in a horse. The aortic right coronary cusp can be seen 
prolapsing through the defect during systole (arrow). The non- coronary cusp, however, opens normally. 2D 
echocardiographic image (A) and schematic representation (B). 
 
Figure 5.16. Muscular ventricular septal defect in a 
horse. The communication between the two ventricles is 
very large, resulting in the two ventricles functioning as 
a single chamber. The aortic and pulmonary flow, 
therefore, is determined exclusively by the respective 
vascular impedances. 
M-mode. There is no specific value in m-mode echo for diagnosis of VSDs. 
Spectral Doppler. Spectral Doppler is often more sensitive than 2D imaging for identifying small VSDs and can be 
useful in confirming clinical suspicions of a defect thought to be detected by 2D imaging. 
Careful interrogation of the septum with a pulsed wave Doppler probe in the right parasternal short-axis view, 
with the sample volume positioned just inside the right ventricle, will identify a turbulent systolic flow pattern 
towards the transducer. Similar interrogation with a continuous wave Doppler probe will identify a similar flow, 
usually with a peak velocity >4.5m/s, unless substantial pulmonary hypertension (and therefore right ventricular 
systolic hypertension) exists (Figure 5.17). Of course, this is also dependent on the direction of the jet in relation 
to the Doppler beam. Low peak velocity usually indicates massive shunting or improper alignment of the Doppler 
beam. In most cases, continuous-wave Doppler examination of the right ventricular outflow tract in the short-axis 
view will also demonstrate high-velocity turbulent flow as the jet from the VSD wraps around the septum and 
heads away from the transducer towards the pulmonary valve. Pulsed-wave Doppler examination of the 
pulmonary artery will demonstrate increased peak flow velocities and velocity time integrals due to the increased 
stroke volume. 
Click on the image to see a larger view 
 
Figure 5.17. Continuous wave Doppler tracing of flow directed towards the transducer through a small VSD (A) and 
a large VSD (B). In (A), the peak velocity of 4.5 m/sec is indicative of low pressure within the right ventricle. On 
the other hand, the peak velocity of 2.96 m/sec in (B) indicates elevated right ventricular pressure due to 
pulmonary arterial hypertension. 
Color Doppler. This is the most sensitive means of detecting a VSD. Interrogation of the ventricular septum just 
below the tricuspid valve in the right parasternal long-axis view or the short-axis view that shows the 3 
commissures of the aortic valve, will often demonstrate turbulent systolic flow from the left to right if the defect is 
perimembranous or membranous. If the defect is muscular, careful interrogation of the entire muscular septum 
may be necessary to locate the VSD by sweeping the transducer from base to apex in the short-axis view. With 
very small VSDs, this may be the only means of identifying the VSD (Figure 5.19). Even with very eccentrically 
directed jets that can occur when the tricuspid valve adheres to the septum, color Doppler will usually be able to 
identify the lesion. 
Color Doppler evaluation of the aortic valve will demonstrate aortic insufficiency in many cases (Figure 5.20). 
Click on the image to see a larger view 
Figure 5.18. Color Doppler image of the turbulent flow 
from a small VSD in a dog. The jet is directed towards 
the right ventricular free wall demonstrating the reason 
for right-sided systolic murmurs with most VSDs. 
 
 
Figure 5.19. 2D echocardiographic right parasternal short-axis image of a dissecting VSD in a dog (A). The defect 
is very small and, therefore, not visible without the aid of color Doppler (B) which readily identifies the turbulent 
flow. 
 
Figure 5.20. Color Doppler image showing aortic 
insufficiency in a horse with a small VSD and a septal 
aneurism (arrow). The diastolic turbulent flow is directed 
from the center of the aortica valve towards the left 
ventricle. 
Contrast Echocardiography. While this may demonstrate some right-to-left shunting in diastole, with 
microbubbles appearing in the left ventricle, this is generally unnecessary for the diagnosis of VSD. If Doppler 
evaluation is not possible, a contrast study may demonstrate a filling defect at the location of the shunt (see 
Chapter 2). 
With right-to-left shunting perimembranous defects, a contrast study will demonstrate the appearance of 
microbubbles in the aortic root and ascending aorta during systole, and occasionally, within the LVOT or left 
ventricle in diastole. With muscular defects, microbubbles will often appear within the LV before appearing in the 
aorta. 
Search Result #: 2Title: Atrioventricular Valvular DysplasiaAuthor(s): Address (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24119&O=VIN 
Epidemiology 
Dysplasia of the mitral valve is most commonly seen in large breed dogs, such as Mastiffs. It has also been 
reported in Bull Terriers with or without mitral stenosis. Mitral valve dysplasia is often seen together with aortic 
subvalvular stenosis. Tricuspid valve dysplasia is most commonly reported in Labrador Retrievers where it is an 
inherited trait. There are also some anecdotal reports of tricuspid dysplasia in Borzois. Mitral and tricuspid 
malformations occur in cats mostly as part of a complex of defects referred to as endocardial cushion defects. 
We have recognized tricuspid valvular malformations in some older cats, which appear similar to tricuspid 
dysplasia in dogs. However, these cats, despite severe tricuspid regurgitation and congestive heart failure at the 
time of diagnosis, have apparently lived for over a decade without any complicationswhich is not consistent with 
severe tricuspid dysplasia. Recent studies have suggested that these cats, in fact, have a right ventricular 
cardiomyopathy with secondary remodeling of the tricuspid apparatus rather than a congenital disease. 
Pathology and Pathophysiology 
Failure of valve closure during systole results in shunting of blood from the ejecting ventricle back into its 
corresponding atrium, identical to acquired valvular insufficiency (see Chapter 6 Mitral Valve Insufficiency and 
Tricuspid Insufficiency). Consequently, both the affected ventricle and atrium enlarge to accommodate the 
regurgitant volume (i.e., eccentric hypertrophy due to volume overload). If severe enough, congestive heart 
failure develops in the dependent circulation. 
Clinical Findings 
A systolic murmur over the mitral valve or tricuspid valve can be ausculted. If severe, congestive heart failure 
develops. 
Mitral Dysplasia 
Echocardiographic Findings 
2-D echocardiography. Clinically important mitral dysplasia results in left ventricular and left atrial enlargement 
with normal wall thicknesses (i.e., eccentric hypertrophy due to volume overload) (Figure 5.21). Because this 
disease is seen mostly in large breed dogs with severe and prolonged disease, myocardial failure occurs, 
characterized by increased end-systolic ventricular dimension and decreased shortening fraction. 
Click on the image to see a larger view 
Figure 5.21. Left atrial and ventricular enlargement 
measured from a right parasternal long axis view in a 2 
year old bull mastiff with mitral dysplasia. The valve 
edges appear relatively normal compared with valves in 
patients with acquired myxomatous mitral valve disease. 
Mitral valve cusps appear largely normal but may fail to appose during systole with a visible gap between the 
valve tips. This is best appreciated in the right parasternal long-axis 4-chamber view (Figure 5.22) but can often 
be visualized in the left apical view. Occasionally, abnormally hyperechoic chordae tendineae can be visualized 
but this is an unreliable and inconsistent finding. Rarely, the valves appear grossly misshapen as is commonly 
seen with acquired valvular disease. 
Click on the image to see a larger view 
Figure 5.22. Apical 4 chamber view of the mitral valve 
in the same patient as the previous figure showing a 
lack of coaptation of the mitral valves in systole. 
M-mode echocardiography. M-mode imaging reveals increased left ventricular diastolic dimensions and 
increased left atrial dimensions and LA/Ao with clinically significant dysplasia. Systolic dimensions are often also 
enlarged due to myocardial failure resulting in a decrease in shortening fraction (Figure 5.23). E-point septal 
separation (EPSS) may be increased as myocardial failure develops. 
Click on the image to see a larger view 
Figure 5.23. Transventricular M-mode image in a dog 
with mitral dysplasia and myocardial insufficiency. Left 
ventricular contractility is reduced as evidenced by 
increased end-systolic dimensions. 
Spectral Doppler. Pulsed-wave Doppler examination of the mitral valve from the left apical 4-chamber view 
shows increased passive inflow (tall E-wave) with the sample volume positioned in the left ventricle, and a high-
velocity turbulent flow in the left atrium during ventricular systole when the sample volume is positioned in the left 
atrium. Continuous-wave Doppler in the same view shows a high-velocity systolic jet away from the transducer 
(i.e., from the left ventricle to the left atrium). The velocity of the jet is generally >5m/s. Spectral Doppler 
interrogation of the mitral valve should not be performed from the right side as inaccurate measures of velocity 
will be obtained. 
Color Doppler. Color Doppler interrogation of the mitral valve in the right parasternal long-axis or short-axis view 
or left apical views demonstrates a regurgitant jet similar to that seen with acquired mitral valve disease. 
Tricuspid Dysplasia 
Echocardiographic Findings 
2-D echocardiography. The right ventricular and right atrial are enlarged (i.e., eccentric hypertrophy due to 
volume overload) with normal wall thicknesses. In cases of severe tricuspid dysplasia, the right atrium often 
occupies the majority of the image in most views and rotates the axis of the heart so that standard views are 
difficult to obtain. Often, the left ventricle appears small in severe cases because of decreased preload to the left 
heart and the relative enormity of the right heart (Figure 5.24). 
Click on the image to see a larger view 
Figure 5.24. Severe tricuspid dysplasia in a Labrador 
retriever. The left ventricular diameter appears much 
smaller than the right ventricular diameter. Additionally, 
the tricuspid edges appear abnormally shaped and 
positioned (arrow). 
Tricuspid valve cusps appear abnormal in most cases. Most commonly, the septal cusp of the tricuspid valve 
appears tethered to the septum by very short dysplastic chordae tendineae. The non-septal cusp usually appears 
as a "sail" leaflet, which is enlarged, but unable to close the tricuspid orifice during systole. It is also attached to 
short chordae. In many cases of tricuspid dysplasia, there is virtually no difference between the systolic and 
diastolic orifice (Figure 5.25 and 5.26). 
Click on the image to see a larger view 
 
Figure 5.25. Tricuspid dysplasia in a Golden retriever. The septal cusp appears tethered and restricted from closing 
(arrow). The papillary muscle attached to the elongated free-wall cusp appears prominent. Echocardiographic image 
(A) and schematic representation (B). 
 
Figure 5.26. Severe tricuspid dysplasia in a Labrador retriever. The right atrium occupies most of the image 
distorting the standard projection. The septal border of the tricuspid valve is prevented from closing, and the left 
heart is small because of reduced right ventricular cardiac output. Echocardiographic image (A) and schematic 
representation (B). 
M-mode echocardiography. M-mode imaging reveals variably increased right ventricular diastolic dimensions and 
increased right atrial dimensions. 
Spectral Doppler. Pulsed-wave Doppler examination of the tricuspid valve from the left apical 4-chamber view or 
right parasternal long-axis view shows increased passive inflow (tall E-wave) during diastole and turbulent flow in 
the right atrium during ventricular systole. Continuous-wave Doppler in the same view shows a moderate-velocity 
systolic jet away from the transducer (i.e., from the right ventricle to the right atrium). Velocity of the jet is 
generally 2.5-3m/s (reflective of a transvalvular pressure gradient of 25-36mmHg). 
Color Doppler. Color Doppler interrogation of the tricuspid valve in the right parasternal long-axis view 
demonstrates a regurgitant jet, similar to that seen with acquired tricuspid valve disease, but often much larger 
(Figure 5.27). 
Click on the image to see a larger view 
Figure 5.27. Color Doppler image from the same 
subject as in Figure 5. 26. Turbulent systolic flow can be 
seen across the tricuspid valve. 
Search Result #: 3Title: Aortic Valve DysplasiaAuthor(s): Address (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24120&O=VIN 
Epidemiology 
This is rare defect. The author has identified a high incidence of aortic valve malformations in a family of Sussex 
Spaniels. It is commonly identified in horses. 
Pathology and Pathophysiology 
In most cases seen by the author, aortic valve dysplasia results from abnormal division of the aortic cusp, 
producing a bicuspid or quadricuspid valve. These valves often have a failure of coaptation at the commissural 
fornices with resultant aortic regurgitation. The severity of the regurgitation determines the hemodynamic 
consequences. If severe, congestive heart failure and myocardial failure develop. Rarely, valvularstenosis may 
be observed. 
Clinical Findings 
A diastolic murmur over the aortic valve can sometimes be ausculted. If severe, a bounding arterial pulse may be 
present. Pulmonary edema may develop if severe. If stenosis exists, a systolic murmur may be ausculted. 
Echocardiographic Findings 
2-D echocardiography. Left ventricular enlargement occurs proportional to the aortic insufficiency. If severe, left 
atrial enlargement follows because of increased left ventricular diastolic pressures. Also, if severe, myocardial 
failure develops characterized by decreased contractility and increased end systolic dimensions. Abnormal valve 
morphology is best identified in the right parasternal short-axis view or left cranial short-axis view. Occasionally, 
the commissural failure of coaptation can be seen in this view. 
M-mode echocardiography. Left ventricular dimensions in diastole and eventually systole increase due to 
increased preload and ultimately myocardial failure. Consequently, shortening fraction may initially be increased 
and progressively decrease over time as the condition progresses. The left atrium and LA/Ao may be enlarged. 
Occasionally, unusual morphology of the aortic valve in the right-parasternal short-axis view can be detected 
along with diastolic aortic valve flutter. 
Examination of the mitral valves (usually in the right parasternal short-axis view) often demonstrates diastolic 
mitral valve flutter. This occurs because the regurgitant jet hits the open septal mitral cusp during diastole 
causing it to vibrate (Figure 5.28, also Box 2.6, Chapter 2). E-point-to-Septal Separation (EPSS) may be 
increased for the same reason. 
Click on the image to see a larger view 
Figure 5.28. M-mode tracing from a dog with aortic 
valve dysplasia and valvular insufficiency in which it is 
possible to observe diastolic flutter of the septal border 
of the mitral valve (arrow). 
Spectral Doppler. Continuous-wave Doppler of the left ventricular outflow tract from the left apical 5-chamber 
view shows a high-velocity regurgitant diastolic jet towards the transducer (i.e., from the aorta to the left 
ventricle). Early diastolic peak velocity approaches 5m/s. With mild-moderate insufficiency, the jet assumes a 
relatively square shape with little change in peak velocity from early to late diastole (Figure 5.29). With severe 
insufficiency, the jet velocity decreases through diastole due to a decrease in transvalvular pressure gradient, 
both from a decrease in aortic diastolic pressure and increase in left ventricular diastolic pressure. Thus, the 
slope of the velocity profile can be used to estimate the severity of the insufficiency. 
Click on the image to see a larger view 
Figure 5.29. Continuous wave Doppler tracing through 
the aortic valve of a dog with aortic dysplasia and 
insufficiency. The figure shows a high velocity diastolic 
flow, with a flat plateau shape throughout diastole, 
indicative of mild disease. 
Pulsed-wave Doppler of the left ventricular outflow tract during systole may demonstrate laminar flows with 
increased peak velocity because of the increased stroke volume from the left ventricle. If stenosis co-exists, 
turbulent flow may be observed. 
Color Doppler. Color Doppler examination of the aortic valve shows a regurgitant jet of variable size depending 
on the degree of insufficiency. The jet may originate at the center point of the valve closure or from the fornices of 
the affected commissures along the wall of the aorta (Figure 5.30). 
Click on the image to see a larger view 
 
 
Figure 5.30. Color Doppler image of a dysplastic aortic valve can allow visualization of either a centrally directed 
regurgitant jet (A) or an eccentric jet (B). In B, two regurgitant jets secondary to a quadricuspid aortic valve can be 
seen directed along the septal border of the mitral valve. 
Search Result #: 4Title: Cor TriatriatumAuthor(s): Address (URL): 
http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=ECHO2007&PID=24121&O=VIN 
Epidemiology 
There are no obvious predispositions to this condition. Cor triatriatum Dexter (CTD) has been recorded only in 
dogs, while Cor Triatriatum Sinister (CTS) has been documented only in cats. 
Pathology and Pathophysiology 
CTD and CTS arise from abnormalities of development of the sinus venosus valve which is largely an embryonic 
and fetal structure that regresses with septation of the atria. Thus, they are defects of septation; however, they do
not result in typical shunting lesions but rather act as obstructive lesions. In some cases, where the valve fails to 
regress, it forms an obstruction to atrial inflow from either the caudal vena cava (CTD) or from the pulmonary 
veins (CTS). CTS is very difficult to distinguish from supravalvular mitral stenosis so both conditions will be 
addressed here as CTS. 
Obstruction of inflow increases hydrostatic pressure in the dependent circulation (systemic abdominal venous 
circulation with CTD; pulmonary venous circulation with CTS) and, if severe, ultimately results in congestive heart 
failure. Cats with CTS often have no evidence of CHF for several years despite having the increased pulmonary 
venous pressures from birth. This is thought to be due to development of compensatory (secondary) pulmonary 
artery hypertension as a protective mechanism which reduces pulmonary blood flow. On the other hand, most 
dogs with CTD develop ascites within a few months. 
CTD necessitates shunting of venous blood around the obstruction, so collateral venous drainage develops, often 
through the vertebral or azygous veins. The persistent sinus venosus valve in CTD can incorporate the coronary 
sinus (venous return from the coronary circulation) resulting in dilation of the main coronary vein. The persistent 
sinus venosus valve can be perforate or imperforate. 
CTS often has a concurrent atrial septal defect or patent foramen ovale resulting in left-to-right shunting. 
Echocardiography 
2-D echocardiography. CTD is often not visualized in the standard right-parasternal long axis views because the 
partition is too caudal. It can be seen in the right-parasternal short axis view as a three-chambered atrial cluster. 
Occasionally, the opening between the caudal and cranial atrial chambers can be seen. The caudal vena cava is 
distended. The right ventricle is often small, as is the left heart, due to decreased preload (Figure 5.31). 
CTD can also be visualized from the left cranial right-ventricular/right-atrial view (Figure 5.32). 
Click on the image to see a larger view 
 
Figure 5.31. 2D image from the right parasternal short 
axis view in a dog with cor triatriatum dexter. The right 
atrium is divided into 2 chambers: a cranial chamber 
Figure 5.32. Visualization of cor triatriatum dexter in a 
dog, from the left cranial view optimized for the tricuspid 
valve. At the bottom of the image, two right atrial 
(RA1) and a caudal chamber (RA2). A perforation in the 
dividing septum is indicated by the arrow. 
chambers (RA1 and RA2) separated by a membrane can 
be seen (arrow). 
Additionally, if the coronary sinus is obstructed, a dilated coronary vein can be seen circling around the back of 
the left atrium along the atrioventricular groove. This often looks like a persistent cranial vena cava (see above). 
CTS is usually visualized from the right parasternal long axis or short axis view. It can also be seen in the left 
cranial short-axis view. Supravalvular mitral stenosis is lower in the atrium than a true CTS and both of these 
types of lesions are seen as a shelf across the atrium just above the mitral annulus. 
M-mode. There is no benefit from M-mode evaluation of these conditions. 
Spectral Doppler. Careful interrogation of the right atrium with a perforate CTD can reveal turbulent continuous 
flow from the caudal chamber to the cranial chamber. (Note, the flow