Echocardiography as a Research and Clinical Toolin Veterinary Medicine

D.G. ALLEN

Department of Clinical Studies, Ontario Veterinary College,University of Guelph, Guelph, Ontario Nl G 2 WI

SUMMARY

Echocardiography is the acceptedterm for the study of cardiac ultra-sound. Although a relatively new toolfor the study of the heart in man it hasalready found wide acceptance in thearea of cardiac research and in thestudy of clinical cardiac disease.Animals had often been used in theearly experiments with cardiac ultra-sound, but only recently has echo-cardiography been used as a researchand clinical tool in veterinary medi-cine. In this report echocardiographyis used in the research of anestheticeffects on ventricular function andclinically in the diagnosis of congestivecardiomyopathy in a cat, ventricularseptal defect in a calf, and pericardialeffusion in a dog. Echocardiography isnow an important adjunct to the fieldof veterinary cardiology.

R tSU M tL'echocardiographie, comme outil detravail, en recherche et en cliniqueve'trinairesL'echocardiographie correspondmaintenant au terme accepte pourl'etude des ultrasons cardiaques.Meme si cette technique represente unoutil relativement nouveau pourl'etude du coeur humain, ou l'utilisebeaucoup pour l'etude des maladiescardiaques, tant en recherche qu'enclinique. On a souvent utilise des ani-maux dans les experiences prelimi-naires, relatives aux ultrasons cardia-ques; l'emploi de l'echocardiographieen medecine veterinaire, tant enrecherche qu'en clinique, est toutefoistres recent. Le present article rapportel'utilisation de le'chocardiographie enrecherche, pour l'etude des effets delIanesthesie sur la fonction ventricu-

laire, et en clinique, pour le diagnosticde la cardiomyopathie congestive,chez un chat, d'un defaut de la cloisoninterventriculaire, chez un veau, etd'une effusion pericardique, chez unchien. L'echocardiographie constituemaintenant une addition importanteaux techniques de la cardiologieveterinaire.

I N T R O D U C T I O N

Ultrasound is defined as sound abovethe audible range. Echocardiographyuses sound waves in the order of fre-quency of greater than 20 000 Hz. Apiezoelectric crystal, in the form of atransducer, emits ultrasonic waves athigh frequency when subjected to analternating current. This same trans-ducer receives the reflected waves andforwards them to be electronicallyprocessed and displayed for interpre-tation via one of three modes, of whichthe motion (M) mode is displayed inthis paper. Patterns of cardiac motionappear as images on the M mode andcan be permanently displayed onrecording paper. Echocardiography isa safe (2), noninvasive method thatprovides quantitative information ofcardiac wall thicknesses, internal cav-ity dimensions, valve motion, ventric-ular function and the presence orabsence of intracardiac structures(3,4,5). The principal disadvantage ofthis mode of investigation is that ultra-sound propagates poorly throughgaseous or bony media. An area free oflung interface must therefore bedetermined (Figure 1). It is the pur-pose of this paper to demonstrate thevalue of echocardiography in veteri-nary medicine in both the research andclinical setting.

CARDI ACWI NDOW

FIGURE 1. Movement of the transducer (T) deli-neates the left ventricle in position T,, the mitralvalve in position T2 and the aorta: left atrium inposition T3. The lungs (stippled), liver (shaded)and cardiac window (clear) are represented.

MATERIALS AND METHODS

The Echo IV' is a multichannel physio-logical recording instrument designedto deliver high resolution recordings ofM mode echocardiograms. A singlelead electrocardiogram was usuallysimultaneously recorded for timing ofthe cardiac cycle. A 5 MHz, 6 mm non-focused transducer for use in cats or a2.5 MHz, 13 mm transducer for use inlarge dogs and calves was placed on theright hemithorax in the area of thethird, fourth or fifth intercostal spacenear the sternum where contact paste2had already been applied (Figure 2).The echocardiogram of the normal,anesthetized cat appear in Figures 3through 6. Other than for size andfunction, the echocardiogram of thenormal dog and calf are structurallysimilar to that of the cat (8,1 1).

RESULTS

Research StudyA population of ten, healthy,

'Echo IV, Echocardiograph/Simultrace Recorder, Pleasantville, New York.2Redux Gel, Hewlett Packard Co., Waltham, Massachusetts.

Can. vet. J. 23: 313-316 (November 1982) 313

EC HOC AR DI OG RAP H ICA NATO MY

LEFT VENTRICL E

FIGURE 2. Movement of the transducer (T) deli-neates the left ventricle in position 1, the mitralvalve in position 2 and the aorta: left atrium inposition 3. The right ventricle (RV), interven-tricular septum (IVS), left ventricle (LV), aorta

(Ao), left atrium (LA) and chest wall (CW) are

represented.

mature cats of many breeds and eithersex were anesthetized with an intra-venous bolus ofsodium pentobarbital3at a dose of 30 mg/ kg. Indices of ven-tricular function; the percent change inminor cardiac diameter (% dD) andthe velocity of circumferential fibre

LEFT VE NTRIC L E

2 a * c o nd S

FIGURE 3. The area of the left ventricle is shown.The electrocardiogram (ECG), transducer-chestwall image (TCW), right ventricle (RV), inter-ventricular septum (IVS), left ventricle (LV), leftventricular posterior wall (LVPW), pleura-pericardium-lung (PPL), posterior chordae(PC), septal notch (SN) and anterior mitralvalve (AMV) are represented. Phases of diastole(D) and systole (S) are labelled. Tissue depth isin centimeters (cm).

-:

LV D 'LVDd

.l C~~~~A;ET

FIGURE 4. Measurements of the left ventriculdimension at end diastole (LVDd), left ventriclar dimension at systole (LVDs) interventriculseptum (IVS), left ventricular posterior wa

(LVPW) and ejection time (ET) are representeTissue depth is in centimeters (cm).

shortening (VcF), were compared wilthose same parameters obtained frounanesthetized cats (10) or via othinvasive methods of study (7,13Sodium pentobarbital has min(

MITRAL VALVE

E C G ~ ~

S ID:

T C W -

L V

LVP

P P Li

FIGURE 5. The area of the mitral valve is showThe electrocardiogram (ECG), transducer-chwall image (TCW), right ventricle (RV), intventricular septum (IVS), left ventricle (LV), Iventricular posterior wall (LVPW), pleupericardium-lung (PPL), anterior mitral va

(AMV) and posterior mitral valve (PMV);represented. Phases of systole (S) and diast(D) are labelled. Tissue depth is in centimet(cm).

:m

lar

FIGURE 6. The anterior mitral valve is labelledD, E, F, A and C according to the text (3). The Eto F slope of the anterior mitral valve, the D to Eamplitude of the anterior mitral valve and the Ato C interval of the anterior mitral valve are

presented. The P to R interval of the electro-cardiogram is labelled. Tissue depth is in centi-meters (cm).

ar effects on cardiac output, arterial pres-

all sure or peripheral resistance; however,d. significant depressions of left ventricu-

lar function, e.g. % dD and VcF are

reported (14). The depressed functionth is caused by incomplete ventricularm emptying rather than a reduction iner end diastolic size (7,14). The depres-3) sant effect of the anesthetic agent waso r consistently demonstrable echocardio-

graphically (1) and is in agreementwith other modes of investigation(13,14). Cardiac ultrasound is a reli-able technique for the study of drugeffects on cardiac physiology (6).

Animal IAn eight year old, spayed, female,

Persian cat was presented with a fourweek history of progressive dysnpea

^AV and ascites. On physical examinationthe mucous membranes of the oral cavi-ty were pale, the capillary refill was

slow, the abdomen was distended withfluid and the femoral pulse was notdetectable. Heart sounds were muffled

wn. bilaterally. Radiographically there was

lest marked pleural effusion obscuring theter- cardiac silhouette. Electrocardiographyleft demonstrated prolongation of the QRSirae complex, suggestive of left ventricularIre enlargement. There were left ventricu-ole lar premature complexes and a rapid,:ers irregular rate without evidence of P

waves suggestive of atrial fibrillation

3Somnotol, MTC Pharmaceuticals, Hamilton, Ontario.

314

MITRAL VALVE

411.

94a. r,149.-.4 ..-M

P R

E F

.1,1VOR .. .11"7

I Irs. " %%_

I-I

RV

FIGURE 7. Echocardiogram ofa Persian cat withcongestive cardiomyopathy. The right ventricle(RV), interventricular septum (IVS), left ventri-cle (LV), left ventricular posterior wall (LVPW),pleurapericardium-lung (PPL) and pericardialeffusion (PE) are labelled.

(12). The echocardiograms (Figures 7and 8) represent the heart at the level ofthe left ventricle and mitral valverespectively. Notable left ventricularechographic findings include a dilatedleft ventricular diastolic dimension(2.05 cm), normal 1.48 ± 0.26 cm andenlarged systolic dimension (1.79 cm)normal 0.88 + 0.24 cm, paradoxical orasynchronous motion of the septumand left ventricular wall and pericardialeffusion (9) (Figure 7). Ventricularfunction as judged by the percentchange in minor diameter (% dD) andvelocity of circumferential fibre short-ening (VcF) was depressed 12.7% and1.24 cm/ second respectively. Thesevalues are compared with normalvalues of 41 ± 7.3% and 2.86 +0.78 cm/second respectively. The Awave was not demonstrable on theanterior mitral valve. This finding canbe found in atrial fibrillation (3) (Figure8). A diagnosis ofcongestive cardiomyo-

14V~ ~ ~~-

F IGURE 8. Echocardiogram of a Persian cat withcongestive cardiomyopathy. The right ventricle(RV), interventricular septum (IVS) and ante-rior mitral valve (AMV) are labelled. No A waveis evident on the AMV.

VW _--:--' LV%

% - .* AM

FIGURE 9. Echocardiogram of a Jersey calf with a right sided systolic murmur. The right ventricle(RV), interventricular septum (IVS), left ventricle (LV), anterior mitral valve (AMV) and leftventricular posterior wall (LVPW) are labelled. Note the drop out of septal echoes. (S).

pathy was made on the basis of thesefindings.

Animal 2A ten day old, male, Jersey calf was

referred for evaluation of a cardiacmurmur. The murmur was a Grade3/5 harsh, systolic murmur loudest onthe right hemithorax at the fourthintercostal space near the sternum.Physical examination also revealedthe presence of wry tail, a congenitaldevelopmental abnormality of thesacral spine. An echocardiographicscan or a continuous sweep from thearea of anterior mitral valve to the areaof the aorta and left atrium (Figure 2)demonstrated a consistent dropout ofinterventricular septal echoes in thearea just cranial to the anterior mitralvalve (Figure 9). Ventricular septaldefect was diagnosed and the calf waseuthanized. At postmortem a 2 cm sizedefect was demonstrated in the area ofthe membranous interventricularseptum.

Animal 3A seven year old, male, Great Dane

was presented with a history of dysp-nea, anorexia and progressive weak-ness of two weeks duration. The dogwas dull and lethargic. A physicalexamination demonstrated palemucous membranes, a weak pulse anda pulse deficit. Heart sounds weremuffled. Radiographically the cardiac

silhouette was obscured by pleuraleffusion. Electrocardiographicallythere was left atrial enlargement andoccasional left ventricular prematurecontractions. Echocardiographically,paradoxical or asynchronous motionof the interventricular septum and leftventricular posterior wall, and a largepericardial effusion were noted (Fig-ure 10). A diagnosis of giant breedcardiomyopathy with pericardial andpleural effusion was diagnosed (3).

DISCUSSIONThis paper illustrates some of the usesof echocardiography in veterinarymedicine. As a research tool it hasproven useful in the evaluation ofanesthetic agents on ventricular func-tion. More importantly it is a non-invasive investigative tool and there-fore does not introduce the possibilityof error caused by the presence of aninstrument used for intracardiac study(14). Cardiac ultrasound may also beused to evaluate the effects of otherchemicals on cardiac function (6).

In animal 1 and animal 3 it wasimpossible to evaluate the cardiacshadow radiographically because ofthe presence of a pleural effusion.Echocardiography has successfullydemonstrated congestive cardio-myopathies with pericardial effusionin both cases. Similarly ultrasoundcould be used to differentiate betweena dilated heart and a heart with peri-

315

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.,Iw rAli'.2z.-Jl -"--14.

.-$Eft

i J sXt

.. ir 7 fWP

FIGURE 10. Echocardiogram of a Great Dane with cardiomyopathy. Labelling is the same as inFigure 7.

cardial effusion only (3). The tech-nique also evaluates the heart's abilityto compensate for the disease on thebasis of the % dD and VcF (3,4,5).Lower than normal values suggestdepressed ventricular function. Inanimal 2 a ventricular septal defectwas revealed. Unfortunately false pos-itive and false negative results mayoccur in the evaluation of ventricularseptal defects (3). To reduce this errora solution of indocyaninegreen may berapidly injected via an intracardiaccatheter in the left ventricle to createmicrobubbles. These may be visual-ized echocardiographically as theyappear first within the left ventricleand then within the right ventricle thusconfirming the presence of a septaldefect (3).

Cardiac ultrasonography is not onlyuseful in the diagnosis of cardiacpathology, but also to evaluate theresponse to treatment, medically orsurgically (3). Thus with successfultreatment of congestive cardiomyo-

pathy one might expect: ventriculardimensions to decrease to near normalsize and indices of ventricular func-tion, e.g. % dD and VcF, to increase tonear normal values.The current high cost of an echo-

cardiographic unit limits its scope tothat of a teaching institution, but as itsusefulness becomes more widely rec-ognized it should become more readilyavailable at a lower cost and will ulti-mately be included in all completecardiovascular examinations thatwarrant its use.

ACKN OWL EDG M ENTS

The author wishes to thank Drs. A.McKinnon, W. Hollingshead and C.Hunt for their cooperation in the clini-cal cases.

REFER ENCES

1. ALLEN, D.G. Echocardiographic study of the

anesthetised cat. Can. J. comp. Med. 46:115-122. 1982.

2. BAKER, M.L. and G.V. DALRYMPLE. Biologicaleffects of diagnostic ultrasound. A Review.Radiology 126: 479-483. 1978.

3. FEIGENBAUM, H. Echocardiography. 2ndEdition. pp. 1-340. Philadelphia: Lea &Febiger. 1976.

4. FORTUIN, N.J., W.P. HOOD and E. CRAIGE. Eva-luation of left ventricular function by echo-cardiography. Circulation 46: 26-35. 1972.

5. GUTGESELL, H.P., M. PAQUET, D.F. DUFF andD.G. McNAMAR. Evaluation of left ventricularsize and function by echocardiography.Results in normal children. Circulation 56:457-462. 1977.

6. HIROTA, Y.S. MICHIHIRO, K. HORI and T.TAKATSU. Dynamic echoventriculography.Noninvasive assessment of nitroglycerin,phenylephrine, isoproterenol and propa-nolol on the human cardiovascualr system.Jap. Heart J. 19: 719-731. 1978.

7. MERIN, R.G. Effect of anesthetics on theheart. Surg. Clin. N. Am. 55: 759-774. 1975.

8. PIPERS, F.S., J.D. BONAGURA, R.L. HAMLIN andM. KITTLESON. Echocardiographic abnor-malities of the mitral valve associated withleft side heart diseases in the dog. J. Am. vet.med. Ass. 176: 580-586. 1981.

9. PIPERS, F.S. and R.L. HAMLIN. Clinical use ofechocardiography in the domestic cat. J.Am. vet. med. Ass. 176: 57-61. 1980.

10. PIPERS, F.S., V. REEF and R.L. HAMLIN. Echo-cardiography in the domestic cat. Am. J.vet. Res. 40: 882-886. 1979.

11. PIPERS, F.S., D.M. RINGsand B.L. HULL. Echo-cardiographic diagnosis of endocarditis inthe bull. J. Am. vet. med. Ass. 172: 1313-1316. 1978.

12. TILLEY, L.P. Essentials of Canine and FelineElectrocardiography. pp. 224-225. St.Louis: C.V. Mosby Co. 1979.

13. URTHALER, F., B.L. KRAMES and T.N. JAMES.Selective effects of pentobarbital on auto-maticity and conduction in the intact canineheart. Cardiovascular Research 8: 46-57.1974.

14. VATNER, S.F. and E. BRAUNWALD. Cardiovas-cular control mechanisms in the consciousstate. New Engl. J. Med. 6: 970-976. 1975.

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