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Recommendations for Standards in TransthoracicTwo-Dimensional

Echocardiography in the Dog and Cat

William P. Thomas, DVM, Cathy E. Gaber, DVM, Gilbert J. Jacobs,DVM, Paul M. Kaplan, DVM, Christophe W. Lombard, Dr Med Vet,

N. Sydney Moise, DVM, and Bradley L. Moses, DVM (TheEchocardiography Committee of The Specialty of Cardiology,

American College of Veterinary Internal Medicine)

Recommendations are presented for standardized imaging planesand display conventions for two-di- mensional echocardiography inthe dog and cat. Three transducer locations (windows) provideaccess to consistent imaging planes: the right parasternallocation, the left caudal (apical) parasternal location, and theleft cranial parasternal location. Recommendations for imagedisplay orientations are very similar to those for comparable humancardiac images, with the heart base or cranial aspect of the heartdisplayed to the examiners right on the video display. From theright parasternal location, standard views include a long-axisfour-chamber view and a long-axis left ventricular outflow view,and short-axis views at the levels of the left ventricular apex,papillary muscles, chordae tendineae, mitral valve, aortic valve,and pulmonary arteries. From the left caudal (apical) location,standard views include long-axis two-chamber and four-chamberviews. From the left cranial parasternal location, standard viewsinclude a long-axis view of the left ventricular outflow tract andascending aorta (with variations to image the right atrium andtricuspid valve, and the pulmonary valve and pulmonary artery), anda short-axis view of the aortic root encircled by the right heart.These images are presented by means of idealized line drawings.Adoption of these standards should facilitate consistentperformance, recording, teaching, and communicating results ofstudies obtained by two-dimensional echocardiography. (Journal ofVeterinary Internal Medicine 1993; 7:247-252. Copyright 0 1993 bythe American College of Veterinary Internal Medicine.)

ECHOCARDIOGRAPHY has been used for clinical and experimentalcardiac imaging and evaluation for over a decade, and has become anindispensable tool in the specialty practice of veterinarycardiology. The Spe- cialty of Cardiology of the American Collegeof Veteri-

From the Department of Veterinary Medicine, University ofCalifor- nia, Davis (Thomas), Department of Small Animal ClinicalSciences, Michigan State University (Gaber), Department ofSmallAnimal Medi- cine, University of Georgia (Jacobs), 8C Old ColonyDrive, Westford, MA (Kaplan), Department of Clinical Sciences,Cornell University (Moise), Roberts Animal Hospital, Hanover, MA(Moses), and Klinik Fur Kleine Haustiere, Tierspital derUniversitat Bern, Switzerland (Lom bard).

Accepted April 5 , 1993. Reprint requests: Dr. William P.Thomas, DVM, Dept. ofVM:Medi-

Copyright 0 1993 by the American College of Veterinary Internalcine, University of California, Davis, CA 956 16.

Medicine 089 I -6640/93/0704-0008$3.00/0

nary Internal Medicine (ACVIM) has recognized the need to adoptprofession-wide standards for nomencla- ture, display andrecording, interpretation, communica- tion, and publication ofimages obtained using this tech- nology. Accordingly, a Committeeon Echocardiogra- phy, composed of experienced veterinary cardiacultrasonographers, was formed to produce a report ofrecommendations for standards in veterinary echocardi- ography.This report, one of several to be developed by the committee,contains recommendations for standards for routine transthoracictwo-dimensional echocardiog- raphy (2DE) in the dog and cat. Theprinciples are gener- ally applicable to other species, includinghorses and other farm animals, but more study and experience willbe required before detailed recommendations can be made for thesespecies. The recommendations presented in this report have beenreviewed and approved by con- sensus of the diplomates of theSpecialty of Cardiology of

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the ACVIM and the executive committee of the Acad- emy ofVeterinary Cardiology.

Introduction

The following qualifications must be considered in using thetechniques recommended in this article:

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2.

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5.

The imaging planes and orientations described here (the figureswere developed from canine images) are applicable to most normaldogs and cats and most animals with cardiac disease.-4 However,there may be significant individual variability related to bodyhabitus, size and location of the available imaging window, andtype and severity of disease. Fine adjust- ments of transducerposition and angulation and image plane orientations are necessaryin most ani- mals to obtain an optimal image of some cardiacstructures. The image planes and movements of the beam aredescribed using the following terms for each of the three planes ofthe body: right-left, cranial-caudal, and dorsal-ventral. Rotationof the beam is described as clockwise-counterclockwise as viewed inthe direc- tion the transducer and beam are pointed, whether theexamination is performed from the side of an upright patient, orfrom above or below a laterally recumbent patient. To maintainconsistency with standards established for human 2DE, ourrecommendations for imaging planes, display conventions, andnomenclature are very similar to those for human examination^.^Where our recommendations differ from those for human 2DE, it isacknowledged in the article. The 2DE examination, despite its valuein ascertain- ing cardiac anatomy and physiology, is notinfallible. It is most valuable when viewed as part of a completenoninvasive cardiac evaluation that includes the med- ical history,physical examination, resting electrocar- diogram, thoracicradiographs, and other appropriate laboratory tests. Indicationsfor 2DE examination should be based on findings from theseexaminations, and the results of 2DE must be interpreted in lightof other aspects of the cardiovascular evaluation. The presentrecommendations may require modifica- tions in the future, based onadditional studies and continuing clinical experience.

Patient Preparation and Positioning

Dogs and cats usually require little or no advance prepa- rationfor echocardiographic examination. Sedation is not required nordesirable except in uncooperative pa- tients. If sedation is used,the potential influence of the drug(s) on heart rate, chamberdimensions, and ventricu- lar motion compared with the unsedatedstate must be considered in the interpretation. The effects ofketamine hydrochloride on the feline M-mode echocardiogram havebeen studied, but although probably similar, the

effects of this and other sedatives on the 2DE examina- tion ofdogs and cats have not been reported. Ideally, hair is clipped overthe left and right precordial trans- ducer locations. However,satisfactory images can also be obtained in many animals by partingthe relatively thin hair coat at these points and by liberal use ofcou- pling gel.

Dogs and cats may be examined in upright (standing, sitting,sternal) or lateral recumbent positions without substantialalteration of examination technique. In most patients, however,lung interference will be minimized and image quality enhanced bypositioning the animal in lateral recumbency on a table, stand, orother device that allows transducer manipulation and examinationfrom beneath the animal.

Transducer Locations There are three general transducerlocations (win- dows) that provide access to consistent imagingplanes (Fig 1). The right parasternal location is located betweenthe right 3rd and 6th intercostal spaces (usually 4th to 5th)between the sternum and costochondral junctions. The left caudal(apical) parasternal location is located between the left 5th and7th intercostal spaces, as close to the sternum as possible. Theleft cranial parasternal loca-

Right Parasternal Window

Left Parasternal Windows

FIG. 1. Diagram of the thorax showing the approximate areas ofthe three transducer locations (windows) used for 2DE examinationin dogs and cats.

Vol. 7 . NO. 4, 1993 TRANSTHORACIC TWO-DIMENSIONALECHOCARDIOGRAPHY 249

tion is located between the left 3rd and 4th intercostal spacesbetween the sternum and costochondral junc- tions. The optimumtransducer locations vary in individ- ual animals and must bedetermined during the course of the examination. Other transducerlocations do not pro- vide consistently high-quality images, butmay be useful, especially for Doppler examination, in some animals.Although images of the heart can be obtained from a transducerlocation just caudal to the xiphoid (subcostal location), theimages often lack the clarity and anatomic detail of the right andleft intercostal locations. In most animals, because of lunginterference, it is not possible to obtain high-quality cardiacimages from a transducer lo- cation at the thoracic inlet(suprasternal notch location), although vessels in the cranialmediastinum and thoracic inlet may be visible.

Image Plane Identification

Imaging planes obtained from each transducer location are namedwith respect to their orientation with the left side of the heart,especially the left ventricle and ascend- ing aorta. A plane thattransects the left ventricle parallel to the long axis of the heartfrom apex to base is called a long-axis (longitudinal) plane. Aplane that transects the left ventricle or aorta perpendicular tothe long axis of the heart is called a short-axis plane. Individualplanes are further referred to in some cases by the region of theheart or number of chambers imaged (see below). Vari- able oblique,angled views, which are modifications of long-axis or short-axisplanes, may be necessary in indi- vidual animals to optimally imagesome structures. Stan- dardized, consistently obtainable imagingplanes for each of the three transducer locations are outlinedbelow.

Image Orientation

As recommended for human examinations, the index mark on thetwo-dimensional transducer (which marks the edge of the imagingplane) should normally be ori- ented to indicate the part of thecardiac image that will appear on the right side of the imagedisplay. The trans- ducer index mark should then be pointed eithertoward the base of the heart (long-axis views) or cranially towardthe patients head (short-axis views). Because most currenttwo-dimensional echocardiographs have left- right image reversalcapability, individual examiners may prefer to reverse theorientation of the transducer index mark, especially whenperforming studies with the transducer directed upward throughholes or notches in the examination table. In these studies, manyoperators may find it easier to rotate the beam counterclockwise tochange from right intercostal long-axis to short-axis views,resulting in an index mark directed caudally in- stead ofcranially. Regardless of the orientation of the index mark,however, the general rule is that the heart

base or the cranial portion of the heart will be displayed tothe examiners right on the video display. The excep- tion to thisrule is the left caudal (apical) four-chamber view (see below).Proper image orientation can be main- tained using the right-leftimage selection switch, and regardless of the position of the indexmark, the orienta- tion of the images on the display and whenrecorded or

ABBREVIATIONS FOR FIGURES 2 THROUGH 7

RA RAu RV RVO TV PV LPA RPA CaVC VS LA LAu LV LVO LVW PM CH MVAMV PMV A 0 LC RC NC 0

Right atrium Right auricle Right ventricle Right ventricularoutflow tract Tricuspid valve Pulmonary valve Left pulmonary arteryRight pulmonary artery Caudal vena cava Ventricular septum Leftatrium Left auricle Left ventricle Left ventricular outflow tractLeft ventricular wall Papillary muscle Chorda tendineae Mitralvalve Anterior mitral valve cusp Posterior mitral valve cusp AortaLeft coronary cusp Right coronary cusp Noncoronary cusp Transducerindex mark

Long-Axis 4-Chamber View

Long-Axis LV Outflow View A

FIG. 2. Right parasternal location, long-axis views.

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FIG. 3. Right parasternal location, short-axis views. Sections Ato F show progressive views at the level ofthe apex (A), papillarymuscle (B), chorda tendineae (C), mitral valve (D), aorta (E), andpulmonary arter- ies (F), respectively (see abbreviations listabove).

printed should follow the recommendations in this arti- cle. Inaddition, the images should be displayed so that the transducerartifact and near field echoes appear at the top and the far fieldechoes toward the bottom of the display. Inversion of the image sothat the near field echoes appear at the bottom of the display (anorienta- tion favored by many pediatric cardiologists), may bepreferred by individual examiners, but is not recom- mended forroutine recording and publication of images.

Imaging Planes and Orientations For each of the three principletransducer locations there are two primary imaging planes and oneor more minor planes (also called views). The following imagingplanes can be consistently obtained in most dogs and cats:

Right Parasternal Location

With the beam plane oriented nearly perpendicular to the longaxis of the body, parallel to the long axis of the heart, and withthe transducer index mark pointing to- ward the heart base(dorsal), two views are usually ob- tained. The first is afour-chamber view with the cardiac apex (ventricles) displayed tothe left and the base (atria) to the right (Fig 2). The second,obtained by slight clock- wise rotation of the transducer and beamplane from the four-chamber view into a slightly more craniodorsalto caudoventral orientation, shows the left ventricular out- flowtract, aortic valve, and aortic root.

Long-Axis Views

Short-Axis Views

With the beam plane oriented at a small angle to the long axisof the body, perpendicular to the long axis of the

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heart, and with the transducer index mark pointing cra- nially(or cranioventrally), an orientation obtained by 90" clockwiserotation of the beam plane from the long- axis views, a series ofshort-axis views are obtained. Proper short-axis orientation isidentified by the circular symmetry of the left ventricle or aorticroot. Short-axis planes at the level of the left ventricular apex,papillary muscles, chordae tendineae, mitral valve, and aorticvalve should be obtained, respectively, by angling of the beamplane from apex (ventral) to base (dorsal). Proper short-axisalignment at the aortic valve level often re- quires additionalslight clockwise rotation of the beam plane. In some animals,further dorsal angulation allows imaging of the proximal ascendingaorta, right atrium, and right pulmonary artery. The images shouldbe dis- played with the cranial part of the image to the right andthe right heart encircling the left ventricle and aorta clockwise(right ventricular outflow tract and pulmonary valve to the right)(Fig 3).

Left Caudal (Apical) Parasternal Location

Left Apical Two-chamber Views

With the beam plane nearly perpendicular to the long axis of thebody, parallel to the long axis of the heart, and with thetransducer index mark pointing toward the heart base (dorsal), atwo-chamber view of the left heart,

Long-Axis 2-Chamber View

Long-Axis LV Outflow View

FIG. 4. Left caudal (apical) parasternal location, two-chamberviews (see abbreviations list above).

Vol. 7 . NO. 4, 1993 TRANSTHORACIC TWO-DIMENSIONALECHOCARDIOGRAPHY 25 1

4-Chamber (Inflow) View

5-Chamber (LV Outflow) View

FIG. 5. Left caudal (apical) parasternal location, four-chamberviews (see abbreviations list above).

including left atrium, mitral valve, and left ventricle, isobtained (Fig 4). Slight counterclockwise rotation of thetransducer and beam plane into a more craniodorsal to caudoventralorientation results in a long-axis view of the left ventricle,outflow tract, aortic valve, and aortic root. Both of these viewsshould be displayed with the left ventricular apex to the left andthe left atrium or aorta to the right.

Left Apical Four-Chamber Views

With the beam plane placed into a left-caudal to right- cranialorientation and then directed dorsally toward the heart base, andwith the transducer index mark pointing caudally and to the left, afour-chamber view of the heart may be obtained (Fig 5) . Note thatthis is the only view in which the transducer index mark ispointing caudally and to the left, opposite the normal convention.De- pending on the exact location of the caudal (apical) win- dow,the appearance of this view varies between animals more than mostother views. The image should show the ventricles in the near fieldclosest to the transducer and the atria in the far field, with theheart oriented verti- cally. The left heart (left ventricle, mitralvalve, and left atrium) should appear to the right and the rightheart to .

the left on the screen. In some animals, especially cats, theavailable window allows imaging through the lateral leftventricular wall, rather than the apex, resulting in an imagetilted horizontally (apex to the upper left, base to the lowerright). Slight cranial tilting of the beam from the four-chamberview brings the left ventricular outflow region into view, and insome animals it is possible to simultaneously image all fourcardiac chambers, both atrioventricular valves, the aortic valve,and proximal aorta (sometimes referred to as a five-chamberview).

Left Cranial Parasternal Location

Long-Axis Views

With the beam plane oriented approximately parallel to the longaxis of the body and to the long axis of the heart, and with thetransducer index mark pointing cranially, a view of the leftventricular outflow tract, aortic valve, and ascending aorta isobtained (Fig 6, view 1). The image is displayed with the leftventricle to the left and the aorta to the right. This view, whichis similar to the

Lonq-Axis View 1

Long-Axis View 2

Long-Axis View 3

FIG. 6. Left cranial parasternal location. long-axis views (seeabbrevia- tions list above).

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FIG. 7. Left cranial parasternal location, short-axis view atthe level of the aortic root, showing the right ventricular inflowand outflow tracts (see abbreviations list above).

two-chamber outflow view obtained from the left caudal (apical)location (Fig 4), shows the right ventricular out- flow tract,aortic valve, and ascending aorta better than the correspondingcaudal (apical) view. From this beam orientation, angling of thebeam ventral to the aorta pro- duces an oblique view of the leftventricle and the right atrium, tricuspid valve, and inflow regionof the right ventricle (view 2). In this view the left ventricle isdis- played to the left and the right auricle to the right. An-gling of the transducer and beam plane dorsal to the aorta producesa view of the right ventricular outflow tract, pulmonary valve, andmain pulmonary artery (view 3).

Short-Axis View

With the beam plane oriented approximately perpendic- ular tothe long axis of the body and to the long axis of

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the heart, and with the transducer index mark pointing dorsally,an orientation obtained by 90" clockwise beam rotation from thelong-axis views, a short-axis view of the aortic root encircled bythe right heart is obtained (Fig 7). The image, which is similar tothe short-axis view at the aortic valve level obtained from theright side (Fig 3), is displayed with the right heart encirclingthe aorta clock- wise, with the right ventricular inflow tract tothe left and the outflow tract and pulmonary artery to theright.

The Specialty of Cardiology of the ACVIM and the Academy ofVeterinary Cardiology recommend adop- tion of these imagingstandards for the performance, dis- play, recording, andpublication of transthoracic 2DE images in dogs and cats. Inverbal, visual, and writ- ten communications (includingpublications), images should be identified by transducer location(right, left caudal, left cranial), major beam plane orientation(long- axis, short-axis, angled/oblique), and minor beam planeorientation (four-chamber, two-chamber, outflow, in- flow, etc.).Adoption of these standards should facilitate consistentperformance, recording, teaching, and com- municating results ofstudies obtained by 2DE.

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cardiography in the normal cat. Vet Radiol 1985; 26:149-158. 2.Thomas WP. Two-dimensional, real-time echocardiography in

the dog. Technique and anatomic validation. Vet Radiol 1984;2550-64.

3. O'Grady MR, Bonagura JD, Powers JD, et al. Quantitativecross- sectional echocardiography in the normal dog. Vet Radiol

4. Moise NS. Echocardiography. In: Fox PR, ed. Canine and FelineCardiology. New York: Churchill Livingstone, 1988; 1 13- 156.

5. Henry WL, DeMaria A, Gramiak R, et al. Report ofthe AmericanSociety of Echocardiography committee on nomenclature and standardsin two-dimensional echocardiography. Circulation 1980; 62:2 12-217.

1986; 27:34-49.