Recommendations for Standards in Transthoracic Two-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 (The Echocardiography Committee of The Specialty of Cardiology,

American College of Veterinary Internal Medicine)

Recommendations are presented for standardized imaging planes and display conventions for two-di- mensional echocardiography in the dog and cat. Three transducer locations (windows) provide access to consistent imaging planes: the right parasternal location, the left caudal (apical) parasternal location, and the left cranial parasternal location. Recommendations for image display orientations are very similar to those for comparable human cardiac images, with the heart base or cranial aspect of the heart displayed to the examiners right on the video display. From the right parasternal location, standard views include a long-axis four-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-chamber views. From the left cranial parasternal location, standard views include a long-axis view of the left ventricular outflow tract and ascending aorta (with variations to image the right atrium and tricuspid valve, and the pulmonary valve and pulmonary artery), and a 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 consistent performance, recording, teaching, and communicating results of studies obtained by two-dimensional echocardiography. (Journal of Veterinary Internal Medicine 1993; 7:247-252. Copyright 0 1993 by the American College of Veterinary Internal Medicine.)

ECHOCARDIOGRAPHY has been used for clinical and experimental cardiac imaging and evaluation for over a decade, and has become an indispensable tool in the specialty practice of veterinary cardiology. The Spe- cialty of Cardiology of the American College of Veteri-

From the Department of Veterinary Medicine, University of Califor- nia, Davis (Thomas), Department of Small Animal Clinical Sciences, Michigan State University (Gaber), Department ofSmall Animal Medi- cine, University of Georgia (Jacobs), 8C Old Colony Drive, Westford, MA (Kaplan), Department of Clinical Sciences, Cornell University (Moise), Roberts Animal Hospital, Hanover, MA (Moses), and Klinik Fur Kleine Haustiere, Tierspital der Universitat 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 Internal cine, 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 adopt profession-wide standards for nomencla- ture, display and recording, interpretation, communica- tion, and publication of images obtained using this tech- nology. Accordingly, a Committee on Echocardiogra- phy, composed of experienced veterinary cardiac ultrasonographers, was formed to produce a report of recommendations for standards in veterinary echocardi- ography. This report, one of several to be developed by the committee, contains recommendations for standards for routine transthoracic two-dimensional echocardiog- raphy (2DE) in the dog and cat. The principles are gener- ally applicable to other species, including horses and other farm animals, but more study and experience will be required before detailed recommendations can be made for these species. The recommendations presented in this report have been reviewed and approved by con- sensus of the diplomates of the Specialty of Cardiology of

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

Introduction

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

1.

2.

3.

4.

5.

The imaging planes and orientations described here (the figures were developed from canine images) are applicable to most normal dogs and cats and most animals with cardiac disease.-4 However, there may be significant individual variability related to body habitus, size and location of the available imaging window, and type and severity of disease. Fine adjust- ments of transducer position and angulation and image plane orientations are necessary in most ani- mals to obtain an optimal image of some cardiac structures. The image planes and movements of the beam are described using the following terms for each of the three planes of the body: right-left, cranial-caudal, and dorsal-ventral. Rotation of the beam is described as clockwise-counterclockwise as viewed in the direc- tion the transducer and beam are pointed, whether the examination is performed from the side of an upright patient, or from above or below a laterally recumbent patient. To maintain consistency with standards established for human 2DE, our recommendations for imaging planes, display conventions, and nomenclature are very similar to those for human examination^.^ Where our recommendations differ from those for human 2DE, it is acknowledged in the article. The 2DE examination, despite its value in ascertain- ing cardiac anatomy and physiology, is not infallible. It is most valuable when viewed as part of a complete noninvasive cardiac evaluation that includes the med- ical history, physical examination, resting electrocar- diogram, thoracic radiographs, and other appropriate laboratory tests. Indications for 2DE examination should be based on findings from these examinations, and the results of 2DE must be interpreted in light of other aspects of the cardiovascular evaluation. The present recommendations may require modifica- tions in the future, based on additional studies and continuing clinical experience.

Patient Preparation and Positioning

Dogs and cats usually require little or no advance prepa- ration for echocardiographic examination. Sedation is not required nor desirable except in uncooperative pa- tients. If sedation is used, the potential influence of the drug(s) on heart rate, chamber dimensions, and ventricu- lar motion compared with the unsedated state must be considered in the interpretation. The effects of ketamine hydrochloride on the feline M-mode echocardiogram have been studied, but although probably similar, the

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

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

Transducer Locations There are three general transducer locations (win- dows) that provide access to consistent imaging planes (Fig 1). The right parasternal location is located between the 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 and 7th intercostal spaces, as close to the sternum as possible. The left cranial parasternal loca-

Right Parasternal Window

Left Parasternal Windows

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

Vol. 7 . NO. 4, 1993 TRANSTHORACIC TWO-DIMENSIONAL ECHOCARDIOGRAPHY 249

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

Image Plane Identification

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

Image Orientation

As recommended for human examinations, the index mark on the two-dimensional transducer (which marks the edge of the imaging plane) should normally be ori- ented to indicate the part of the cardiac image that will appear on the right side of the image display. The trans- ducer index mark should then be pointed either toward the base of the heart (long-axis views) or cranially toward the patients head (short-axis views). Because most current two-dimensional echocardiographs have left- right image reversal capability, individual examiners may prefer to reverse the orientation of the transducer index mark, especially when performing studies with the transducer directed upward through holes or notches in the examination table. In these studies, many operators may find it easier to rotate the beam counterclockwise to change from right intercostal long-axis to short-axis views, resulting in an index mark directed caudally in- stead of cranially. 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 to the examiners right on the video display. The excep- tion to this rule is the left caudal (apical) four-chamber view (see below). Proper image orientation can be main- tained using the right-left image selection switch, and regardless of the position of the index mark, the orienta- tion of the images on the display and when recorded or

ABBREVIATIONS FOR FIGURES 2 THROUGH 7

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

Right atrium Right auricle Right ventricle Right ventricular outflow tract Tricuspid valve Pulmonary valve Left pulmonary artery Right pulmonary artery Caudal vena cava Ventricular septum Left atrium Left auricle Left ventricle Left ventricular outflow tract Left ventricular wall Papillary muscle Chorda tendineae Mitral valve Anterior mitral valve cusp Posterior mitral valve cusp Aorta Left coronary cusp Right coronary cusp Noncoronary cusp Transducer index mark

Long-Axis 4-Chamber View

Long-Axis LV Outflow View A

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

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Short-Axis Views

THOMAS

FIG. 3. Right parasternal location, short-axis views. Sections A to F show progressive views at the level ofthe apex (A), papillary muscle (B), chorda tendineae (C), mitral valve (D), aorta (E), and pulmonary arter- ies (F), respectively (see abbreviations list above).

printed should follow the recommendations in this arti- cle. In addition, the images should be displayed so that the transducer artifact and near field echoes appear at the top and the far field echoes toward the bottom of the display. Inversion of the image so that the near field echoes appear at the bottom of the display (an orienta- tion favored by many pediatric cardiologists), may be preferred by individual examiners, but is not recom- mended for routine recording and publication of images.

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

Right Parasternal Location

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

Long-Axis Views

Short-Axis Views

With the beam plane oriented at a small angle to the long axis of 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" clockwise rotation of the beam plane from the long- axis views, a series of short-axis views are obtained. Proper short-axis orientation is identified by the circular symmetry of the left ventricle or aortic root. Short-axis planes at the level of the left ventricular apex, papillary muscles, chordae tendineae, mitral valve, and aortic valve should be obtained, respectively, by angling of the beam plane from apex (ventral) to base (dorsal). Proper short-axis alignment at the aortic valve level often re- quires additional slight clockwise rotation of the beam plane. In some animals, further dorsal angulation allows imaging of the proximal ascending aorta, right atrium, and right pulmonary artery. The images should be dis- played with the cranial part of the image to the right and the 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 the body, parallel to the long axis of the heart, and with the transducer index mark pointing toward the heart base (dorsal), a two-chamber view of the left heart,

Long-Axis 2-Chamber View

Long-Axis LV Outflow View

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

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

4-Chamber (Inflow) View

5-Chamber (LV Outflow) View

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

including left atrium, mitral valve, and left ventricle, is obtained (Fig 4). Slight counterclockwise rotation of the transducer and beam plane into a more craniodorsal to caudoventral orientation results in a long-axis view of the left ventricle, outflow tract, aortic valve, and aortic root. Both of these views should be displayed with the left ventricular apex to the left and the left atrium or aorta to the right.

Left Apical Four-Chamber Views

With the beam plane placed into a left-caudal to right- cranial orientation and then directed dorsally toward the heart base, and with the transducer index mark pointing caudally and to the left, a four-chamber view of the heart may be obtained (Fig 5) . Note that this is the only view in which the transducer index mark is pointing 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 most other views. The image should show the ventricles in the near field closest to the transducer and the atria in the far field, with the heart oriented verti- cally. The left heart (left ventricle, mitral valve, and left atrium) should appear to the right and the right heart to .

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

Left Cranial Parasternal Location

Long-Axis Views

With the beam plane oriented approximately parallel to the long axis of the body and to the long axis of the heart, and with the transducer index mark pointing cranially, a view of the left ventricular outflow tract, aortic valve, and ascending aorta is obtained (Fig 6, view 1). The image is displayed with the left ventricle to the left and the aorta to the right. This view, which is similar to the

Lonq-Axis View 1

Long-Axis View 2

Long-Axis View 3

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

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FIG. 7. Left cranial parasternal location, short-axis view at the level of the aortic root, showing the right ventricular inflow and 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 corresponding caudal (apical) view. From this beam orientation, angling of the beam ventral to the aorta pro- duces an oblique view of the left ventricle and the right atrium, tricuspid valve, and inflow region of the right ventricle (view 2). In this view the left ventricle is dis- played to the left and the right auricle to the right. An- gling of the transducer and beam plane dorsal to the aorta produces a view of the right ventricular outflow tract, pulmonary valve, and main pulmonary artery (view 3).

Short-Axis View

With the beam plane oriented approximately perpendic- ular to the 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 the long-axis views, a short-axis view of the aortic root encircled by the right heart is obtained (Fig 7). The image, which is similar to the short-axis view at the aortic valve level obtained from the right side (Fig 3), is displayed with the right heart encircling the aorta clock- wise, with the right ventricular inflow tract to the left and the outflow tract and pulmonary artery to the right.

The Specialty of Cardiology of the ACVIM and the Academy of Veterinary Cardiology recommend adop- tion of these imaging standards for the performance, dis- play, recording, and publication of transthoracic 2DE images in dogs and cats. In verbal, visual, and writ- ten communications (including publications), 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 plane orientation (four-chamber, two-chamber, outflow, in- flow, etc.). Adoption of these standards should facilitate consistent performance, recording, teaching, and com- municating results of studies 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. Quantitative cross- sectional echocardiography in the normal dog. Vet Radiol

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

5. Henry WL, DeMaria A, Gramiak R, et al. Report ofthe American Society of Echocardiography committee on nomenclature and standards in two-dimensional echocardiography. Circulation 1980; 62:2 12-2 17.

1986; 27:34-49.