Naturally occurring cardiomyopathy in the Doberman pinscher: A possible large animal model of human cardiomyopathy?

JACC Vol. 16. No. I July 1990:20&-6

200

MARK L. SMUCKER, MD, FACC, SANJIV KAUL, MD, FACC, JERRY A. WOOD JAMES C. KEITH, DVM, PHD, SCOTT A. MANNING, PA, JOSEPH A. GASC Charlottesville and Blacksbrrrg, Virginia

Currentlythere is no largeanimal model of dilated cardiomyopathy.The smaller animal models of cardiomyopathy, such as the Syrian hamster, cannot be studied with echo. cardiography and cardllc catheterization, and the relevance of these models to human dilated cardiomyopathy is open to question. On the sis of some initial observations in Doberman pinschers, it was speculated that these dogs could have otxult left ventricular dysfunction. Accordingly, studies were performed in 46 apparently healthy Doberman p&hers and in 41 mongrel dogs: two.dimensional echo. cardiography (Jo dogs ln each group), cardiac catheteriza= tion (16 Doberman pinschers and 12 mongrels) and corouary blood Row studies (I3 Doberman pinschers and 6 mongrels). In the awake, uusedated dogs studied with

Currently there is no large animal model of dilated cardiomyopathy. Small animals such as Syrian hamsters have conventionally been used to study the pathophysiology of dilated cardiomyopathy(l-3). However, it is not possible to study these animals using clinically applicable tools such as cardiac catheterizationor echocardiographyand their significance as models of human cardiomyopathy is open to question. In our experimental work using dogs we noted that some large dogs tended to have reduced global left ventricular function at rest. Review of the veterinary studies (4-U) revealed that dilated cardiomyopathy is especially common

From the Division of Cardiology, Department of Internal Medicine. University of Virginia School of Medicine. Charlottesville. Virginia and the Departments of Small Animal Clinical Sciences and Veterinary Biosciences. the Virginia-Maryland Regional College of Veterinary Medicine. Virginia Polytechnic Institute. Blacksburg. Virginia. This study was presented in part at the Annual National Scientific Session of the American Federation for Clinical Research. May 1988. Washington. D.C. It was supported in part by a grant in aid fmm the American Heart Association (Virginia Affiliate). Glen Allen. Virginia and by the David A. Greiner Heart Valve Research Fund, Charlottesville, Virginia. Dr. Kaul is a recipient of a Clinical Investigator Award fKO8-HLO1833) and of a FIRST Award tR29-HI383451 from the National Institutes of Health, Bethesda, Maryland. Address Sanjiv Kaul. MD. Box 158. Division of Cardiology. University of Virginia School of Medicine, Charlottesville. Virginia 22908. 01~

by the American College of Cardiology

going cardiac catbeteruta

reserve were similar in the two groups. It is concluded that apparently schers have occult left ventricular may serve as a large animal mode athy and should not be used experi cardiac physiology. (./ Am Coil Cardiol1990;16:200-6)

in large-breed dogs and is frequently reported in Doberman pinschers. This finding may have important implication:: I) The Doberman pinscher may be a potential model of human cardiomyopathy. 2) Some presumably healthy laboratory animals supplied by dog pounds for cardiovascular research may have occult left ventricular dysfunction that, if undetected, might produce errors in the results obtained in these studies. We therefore undertook the present study to determine whether Doberman pinschers have occult left ventricular dysfunction. We chose mongrel dogs as controls because we have not noted dilated cardiomyopathy in mongrel dogs studied in our experimental echocardiography laboratory (16-18)and because genetic factors may play a role in canine cardiomyopathy making mongrel dogs less susceptible to cardiomyopathy than purebred animals (12.14).

Animals studied. The animals studied included 30 Do man pinschers that were privately owned and 57 dogs Doberman pinschers and 41 mongrels) obtained by the University of Virginia vivarium from federally licensed dog pounds. The protocol was approved by the University of 0735-1097/90/$3.50

JAW Vol. 16. No. I July l990:2QO-6

e was rrcor

ransducer was used to obtain images that were recorde deotdpe with a commercially available recorder (Panasonic NV 8950). T/E recorded images were rcviesrt~d hy (1 s id obserW resentative who wm not aware of ehe Arced olrhe dog. images from the parasternal long- and short-axis views (the 1:transferred to an latter at the mid~~illary muscle le system, Kontron off-line image analysis computer Electronic) (20). The end-diastolic left ve~tr~c~~ar size was of the measured from the long-axis view just kness mitral leaflets (19). End-diastolic and or wall were meaof the interventricu~ar septum and iews from which sured from both long- and short average values of wall thickness were calculated. Percent systolic thickening was calculated using the equation (20) percent thickening I- [(end-systolic thickness - enddiastolic thicknessllend-diastolic thickness] x IOO. Cardiac catheterization was performed in 16 Doberman pinschers and 12 mongrel dogs under general anesthesia with use of either nitrous oxide and fentanyl(14 Dobermans, 7 mongrels) or isollurane (3 Dobermans, 4 mongrels) during mechanical ventilation with a dual-phase control pump (Harvard Apparatus). Arterial blood gases were obtained at regular intervals throughout the catheterization. Physiologic pi-l. Po2. and Ro2 levels were maintained by ventilator adjostmel~t or by administration of sodium bicarbonate, or both. A balloon flotation catheter was inserted through the left femoral vein and advanced into the pulmonary artery. A 51; pigtail catheter was introduced into the right femoral artery and a modified 8F Gensini catheter was inserted in the left femoral artery. The dogs were positioned on their left sides and right heart and aortic pressures were recorded using

allowed tc; recover for a mi~imMm of 48 ~~tb~t~~.l~~t~~i~ before bloo They were anesthetized wit

physiologic range. A thoracotorny was performed in the fifth left intercostal space and the pericardium was opened. A cannula was posittoncd in the lrtt atrial appendage for injection of 5 &i of I I to I3 pm radiolabeled microspheres (Dupont). injections of microspheres were performed in each dog: baseline and durrng intravenous infusion of adenosine at a rate of 4.7 pm/kg per min. which produces maximal coronary vasoddation (22). microsphere:, were use ruthenium-~03, c order cernuu-141, tin scaardium-4n. Prior to injection into the left atri of microspheres was dilute normal saline solution co Immedidtely before injecti sphcrc suspension was agitated vigorously back and forth between two 6 ml syringes connected by a stopcock, a ploccdurc thcit produces excellent dispersion of the micro-

202

JACC Vol. 16. No. 1 July 159&200-6

SMUCKER ET AL. CARDIOMYOPATHY IN DOBERMAN PINSCHERS

Table1. Echocardiographic Data(meanvalues+ I SD) EDDllO kg EDD HeartRate Weight (mdl0 kg) (min-‘) (mm) (kn) _ DOhllilllS

(n = 30)

Mongrels (n = 31) p value

33 +8

24 *5 0.0001

107 221

119 rl6 0.01

43 ?6

38 +4 o.ooo2

13.9 23.3

16.5 23.3 0.003

EDWT

(mm)

EDWTIlO

9.9

3.i

21.0

20.8

9.4 kO.9 0.05

kg

(mm/IO kg)

Syst Th

(mm) 2.7 20.6

4.1

3.4

20.8

+0.9 0.001

0.0001

Nor Th (mm/l0 kg)

%Th

0.9 20.4

28 27

1.5 to.5 O.O@Ol

36 +I0 o.OBO3

EDD = left ventricular end-diastolic diameter; EDWT = left ventricular end-diastolic wall thickness: Nor Th = systolic thickening normalized to body mass; Syst Th = left ventricular systolic thickening; Th = systolic left ventricular wall thickening.

spheres (24). When hemodynamic status was stable, duplicate continuous arterial blood withdrawalswere begun and the microspheres were injected 15 s later. The arterial withdrawalswere continued for a total of 90 s. At the end of each experiment the dogs were killed by applying an electrical stimulus to the right ventricle, and the heart was removed. The left ventricle was divided into four to five sections from base to apex. Transmurai samples were taken from each layer and each sample was divided into epicardial, midwali and endocardiai sections of approximately equal weight. Each of these subsegments was weighed and counted for 500 s in a well counter with a multichannel analyzer (Auto-gamma scinriiiation counter, Packard) (25). The arterial blood samples and pure isotope samples were counted in similar fashion. Myocardial bloodj?ow (mllmin) was calculated as (Cm x Qm)/Cr, where Cm = tissue counts (counts/min), Qm = withdrawalrate of arterial samples (milmin)and Cr = counts in reference arterial sample (countslmin) (23). Flow/g of tissue was calculated by dividing blood flow by the sample weight. Transmurai, endocardial and epicardial flow determinations were made. Endocardiailepicardiai blood flow ratios were calculated by dividing the endocardiai flow by the epicardialflow. Coronary vascular resistance was calculated by dividing the difference between mean aortic pressure and mean left atrial pressure by transmurai myocardiai blood flow. Statisticalmethods. Data were compiled and analyzed on a minicomputer (VAX 8200, DigitalEquipment) using commerciallyavailablesoftware (RSII, BBN Software Products) (26).Continuous variables were expressed as mean values + 1 SD and the Doberman pinschers and mongrels were compared by using the Student’s t test with pooled variance. Categoric variables were expressed as proportions and the two groups of dogs were compared by means of the chisquare test. Differences between groups were considered significantat p < 0.05 (two-sided).

Results ~~orardiography (Table I, Fig. 1). The Doberman pin-

schers were significantlylarger than the mongrel dogs (p = 0.0001)and their heart rate was significantly slower (p = 0.01). The left ventricular end-diastolic dimension was significantlylarger in the Dobermans than in the mongrels (p = 0.002), but not when end-diastolic dimension was normaiized for body mass. The left ventricl;“arwall thickness was slightlygreater in the Dobermans than in the mongrels, but it was thinner in the Dobermans when normalized for body mass (p = O.OOOi). Absolute ventricular wall systolic thickening was lower in the Dobermans than in the mongrels (p = 0.001)as was wail thickening normalized for body mass (p = 0.0001).The percent systolic left ventricular wail thickening was also lower in the Dobermans (p = 0.0003).Assuming a “normal” percent wail thickening of ~2% (13), 15(50%)of the 30 Dobermans and 7 (23%) of the 31 mongrels had impaired left ventricular systolic wail thickening (p = 0.03).

Figure1. Mean left ventricularwail thicknessat end-diastoleand left ventricularsystolicwallthickeningin mongrels and Doberman pinschers on two-dimensional echocardiography. The dimensions have been normalized for body mass. The left ventricular walls are thinner (p = 0.0001)in Dobermans and thicken less during systole as compared with mongrels (p = 0.0001). 61

PERCENT THICKENING END-DIASTOLIC THICKNESS

Weight

LVESV Id) 2Y12

io

+I8

2714

+3

27 r8

139 231

29115 +_4/4

a.81

O.OOlII

0.I110.21

Dobermans

28

(n = 16)

+5

Mongrels (n = 12) P value

Heart Rate IO1

LVEDP = left venlricular end-diasdic ventricular end-systolic pressure; LVESV pressure.

13

LVEDV Wll)

LVEF

I26

50

17

0.38

27

?18

214

219

+0.11

13 28

14 +-5

150 +_2?

3: s_12

31 k-20

0.63 kO.09

0.25

0.62

0.006

0.001

I.0

0.0001

pressure: LVEDV = left ventricu!ar end-diastolic volume; LVEF = left ventricular ejection fraction; LVESP = left = left venlricular end-systolic volume: PA = pulmonary artery pressure: PCWP = pulmonary capillary wedge

A nary vasodi$ation, caus to fall substantially in both e was no difference in regio ow or coronary vascular resist

with dilated cardiomyopathy. in these reports are similar to

systolic performance,

tistically significant, the heart rate tende s. There was no Doberman pinschers than in the mo difference in the systemic pressures, nary blood flow or coronary vascular resistance between

Figure 2. Cineangiographic left ventricular ejection fraction in mongrels and Doberman pinschers. Dobermans had a lower mean with mongrels. ejection fraction

* p -

*

current study indicate that global left ventricular function is matic and apparently healthy ently reduced in asy are similar in both awake and of this breed. The re

Figure 3. Cineangiographically derived mean left ventricular volumes in mongrels and Doberman pinschers. The end-systolic volume is higher (p = 0.001) and the stroke volume is lower (p = 0.001) in the Dobermans.

c.001

STROKE VOLUME

a ENID-SVSTOI VOLUME

e 0.00

MONGRELS 67 - 12)

000ERU&NS (n - 16)

204

JACC Vol. 16. No. 1 July 1%‘0:20&-6

SMUCKER ET AL. CARDIOMYOPATHY IN DOBERMAN PINSCHERS

Table 3. Coronary Blood Flow Data (mean values + I SD) Conlrol Doberman (n = i3) HR (min-‘1 LAP (mm Hg) AoP (mm Hg) CO (litewmin-‘1

127 i: 24 1+4 107 + 31 3.9 f I.4

CBF (ml*gmin-‘1 Endo Epi Trans Endolepi CVR (mm Hgmiaml-‘1

I.3 1.2 1.2 I.1

--em-

+ 0.6 + 0.6 + 0.6 rt: 0.2

99246

Adenosine --_~

.Mongrel (n = 6)

Qoberman (n = 13)

Mongrel (n = 6)

143 d I4 926 104 + 21 3.0 f 0.8

I25 + 20 724 59 f 21 4.3 2 1.2

I41 + I3 723 52 + 22 3.3 d I.5

1.2 I.1 I.2 I.1

f f f f

0.3 0.3 0.3 0.1

85 e 21

2.5 3.4 3.1 0.68

5 5 f f

2.2 2.2 2.3 0.21

21 +8

1.9 1.4 2.2 0.72

+ t * =

1.3 1.3 1.3 0.16

21 +8

AoP = mean aortic pressure; CBF = coronary blood flow; CO = cardiac output: CVR = coronary vascular resislance ([AoP-LAPjltransmwal blood flow); Endo = endocardial;Epi = epicardial: HR = heart rate; LAP = mean left atrial pressure; Tram = bansmural.

anesthetized states and are not associated with any changes in rest coronary blood flow or in coronary blood flow reserve. Our data suggest that Dobermans deserve further investigation, especially in natural history studies and histopathologic studies, as potential large animal models of dilated cardiomyopathy. Our results also indicate that these dogs should not be used in experimental studies designed to assess left ventricular function. Clinicalfeatures.Doberman pinschers may be the breed of dogs most frequently afflicted with dilated cardiomyopathy (4,12-U). Both clinical and histologic evidence of cardiomyopathy has been demonstrated in these dogs (15). They present with weight loss, anorexia, weakness, general debilitation,exerciseintolerance, dyspnea, orthopnea, tachypnea, ascites, rhythm disturbances, syncope and sudden death (4). Signs develop over days to weeks, probably depending on the owner’s recognition of them. The expected life span after the onset of heart failure is only 6 to 12months (4,12). Cardiomyopathy is most frequently manifested in dogs aged 2 to 9 years (mean approximately5 years) (6,12). Because these clinicalfeatures are similarto those of human cardiomyopathy, Dobermans may serve as an experimental model of human cardiomyopathy. Globalleft ventricularfunction. In a study (13)of Doberman pinschers, echocardiography was performed in six clinically normal dogs and nine dogs with cardiomyopathy. The percent wallthickening was 37 ?r 4% in the normal dogs and 15 f 5% in the dogs with cardiomyopathy. The mean percent systolic thickening of 28% in the clinically healthy privately owned Doberman pinschers in our study was midwaybetween that of the normal and symptomatic dogs in that study (13). Furthermore, half of the privately owned apparently healthy Dobermans in our study had definite systolic left ventricular dysfunction by echocardiography. There are few invasive hemodynamic studies in canines

with cardiomyopathy. A study (28) of 13 dogs with severe congestive heart failure (including 8 Doberman pinschers) reported a heart rate of 174 2 34 min- ’ and pulmonary artery wedge pressure of 23 + 8 mm Hg. The left ventricular ejection fraction in our clinically healthy Dobermans was as low as those in previous reports of dogs with congestive heart failure (5,6,9) but was unaccompanied by tachycardia or elevated left heart fillingpressures. The systolic dysfunction we observed in the Dobermans at catheterization was not due to differingafterloads because these dogs had lower peak and end-systolic pressures than did the mongrel dogs despite higher end-systolic volume and lower ejection fraction. It was also not due to the effects of anesthesia during catheterization because systolic dysfunction was apparent in awake, unsedated Dobermans during echocardiography, although to a lesser degree. We also used nonionic contrast medium for ventriculography to minimize the effect of the contrast agent on left ventricular function. The poorer left ventricular function noted during catheterization compared with that during echocardiography may be related, in part, to early disease in pound dogs compared with those privately owned. It is possible that the Dobermans obtained from the pounds had early manifestations of disease such as a decrease in exercise tolerance and had therefore been abandoned. Coronarybled flow studies. We are not aware of any previous coronary blood flow studies in dogs with occult left ventricular dysfunction. Our data suggest that vascular abnormalities are not important in the early stages of the pathophysiology of the systolic dysfunction observed in Doberman pinschers. Both the rest coronary blood flow and the coronary blood flow reserve were normal in the Dobermans evaluated in this study. However, the coronary vasculature may become involved as the disease progresses and may be abnormal in symptomatic dogs.

JACC Vol. 06, No. I July

I :200-6

Y in

breed and cardiac e acknowledge the technical assistance of John . Evett and Cindy Pi&us, Eugene Wright. Jr., DVM and Kenneth Marcellus, DV acquisition and care oftbe animals obtained through the University of Virginia vivarium and Luiz Bellardinelli. D for his helpful insights.

in humans. lin addition, the disease process i

seen in human cardiomyopathy. We believe that further investigation into systolic dysfunction in Doberman pinschers is warranted to assess the feasibility of developing a large animal model of cardio gest that Dobermans sho models designed to study Li lions. There are several limitations to this study: 1) Although our study demonstrates that occult cardiomyopathy is frequent in Doberman pinschers, its design does not examine the relation between decreased ejection fraction or percent systolic left ventricular wall thickening and the syndrome of congestive heart failure. This issue must be addressed before the Doberman can be used as a canine model of human cardiomyopathy. 2) Even though this study demonstrates frequent systolic dysfunction in apparently healthy Dobermans, it does not examine the incidence of the clinical syndrome of heart failure or time course over which it develops in these dogs. 3) The Dobermans studied by echocardiography were larger than the mongrel control dogs and were larger than the Dobermans undergoing cardiac catheterization. The probable reason is that these privately owned dogs were better cared for than those obtained from pounds. Like previous authors (18,19,21),we have normalized dimensional data for body mass or body surface area. Although apparent abnormalities in some variables such as the left ventricular end-diastolic dimension are no longer abnormal when normalized for body mass, both absolute and percent left ventricular systolic thickening were significantly

I. Sievers R. Wrmiey WW. James T. Wikman-Coffelt J. Energy levels al systole vs diastole in normal hamster hearts vs myopathic hamster hearts. Circ Res 1985:53:759-66.

2. Camacho SA. W&man-Co@elt

J. Wu ST. et al. Improvement in myocardial performance without a decrease in high-energy phosphate metabolites after isoproterenol in Syrian cardiomyopathic hamsters. Circulation 1988:77:712-c).

3. Buser PT. Camacho SA. Shao TW. et al. The effect of dobutamine on myocardial performance and high-energy phosphate metabolism at different stages of heart failure in cardiomyopathic hamsters: a 3’P MRS study. Am Heart J 1989;117:86-91. 4. Hill BL. Canine idiopathic congestive cardiomyopathy. Continuing Education 1981:3:615-20.

Compendium on

5. Tilley LP, Liu S-K. Cardiomyopathy in the dog. In: Roy P-E. Ron: G, eds. Recent Advances in Studies on Cardiac Structure and Metabolism. The Metabolism of Contraction. Vol. IO. Baltimore: Univer,ity Park Press, 1975:41-53. 6. Liu S-K. Tilley LP. Animal models of primary myocardial disease. Yale J Biol Med 1980:53:191-211. I. Van Vleet JF. Ferrans VJ. Weirich WE. Pathologic alterations in congestive cardiomyopathy of dogs. Am J Vet Res 1981:42:416-24. 8. Lippert AC. Twardock AR, Gelberg HB. Nuclear angiography in a dog with congestive cardiomyopathy. J Am Vet Med Assoc 1986:188:525-7. 9. Lord PF. Left ventricular volumes of diseased canine heart: congestive cardiomyopathy and volume overload (patent ductus arteriosus and primary mitral valvular insufficiency). Am J Vet Res 1974:35:493-501. IO. Kittleson MD. Eyster GE. Knowlen 66, Olivier NB, Anderson LK. Efficacy of digoxin administration in dogs with idiopathic congestive cardiomyopathy. J Am Vet Med Assoc 1985;186:162-5.

I I. McKinney B. Pathology of the Cardiomyopathies.

London: Butterworth,

1974~523-72. 12. Thomas

WP. Myocardial

diseases of the dog. In: Bonagura

JD. ed.

206

SMUCKER ET AL. CARDIOMYOPATHY

JACC Vol. 96, No. 1 IN DOBERMAN

July P990:200-6

PINSCHERS

Contemporary Issues in Small Animal Practice. Vol. 7. Cardiology. York: Churchill Livingstone. 1987:117-53. 13. Calvert CA, Chapman WL, Toal RL. Congestive cardiomyopathy Doberman pinscher dogs. J Am Vet Med Assoc 1982:181:598-%2. 14. Calvert CA. Dilated congestive cardiomyopathy in Doberman Compendium on Continuing Education. 1980;8:417-30.

secondary to idiopathic dilamd cardi~my~~al~y. 690-5.

New in

pinschers.

Effects of selectively altering collateral driving pressure on regional perfusion and function in occluded coronary bed in the dog. Circ Rcs 1987;61:77-85. 17. Kaul S, Pandian NG. Gillam LD. Newell JB, Okada RD. Weyman AE. Contrast echocardiography in acute myocardial ischemia. HI. An in vivo comparison of the extent of abnormal wall motion with the area at risk for necrosis. J Am Call Cardiol 1986;7:383-92. 18. Oliner C, Kelly P, Oliner J. Glasheen W, Kaul S. A model to predict regional myocardial flow-function relationships (abstr). Circulation 1987; 76(suppl IVJ:lV-95. 19. O’Crady MR. Bonagura JD. Powers JD. Herring DS. Quantitative cross-sectional echocardiography in the normal dog. Vet Radio1 1986;27: 34-49. 20. Keller MW, Glasheen W. Teja K. Gear S. Kaul S. Myocardial contrast echocardiography without significant hemodynamic effects or reactive hyperemia: a major advantage in the imaging of regional myocardial perfusion. J Am COB Cardiol 1988;12: 1039-47. 21. Smucker ML, Sanford CF. Lipscomb KM. Effects of hydralazine on pressure-volume and stress-volume relations in congestive heart failure

198.5;56:

22. Gascho JA, Mueller TM, Eastbam C, Marcus ML. Effects of vohnue overload hypertrophy on coronary circulation in awake dogs. Cardiovasc Res 1982:16:288-92.

23. Heyman

MA, Payne BD, Hoffman HE, Rudolph AM. Blood Bow measurements with radionuclide-labeled particles. Prog Cardiovasc Dis 1977;20:55-79.

15. Hazlett MJ. Maxie MG. Alien DG. Wilcox BP. A retrosoective study of heart disease in Doberman pinscher dogs. Can Vet J 1983;24:205-10:

16. Kaul S, Pandian NG. Guerrero JL, Gillam LD. Gkada RD. Weyman AE.

Am J Cardioi

24. Ciascho JA. Lesnefskv EJ. eller GA. Effects of acute left anterior descending occlusion on regional myocardiaf blood Row and W.-I! thickening in the presence of a circu Am J Cardiol 1984;54:399-406. 25, Kaul S, Kelly P. Ohner JD. Glasheen Assessment of regional myocardial Moo two-dimensional echocardiography. J Am Cob Cardiol 1989;13:468-82. 26. RS/I User’s Guide. Book 2. Cambridge: 202-14.

BBN Software Products. 1984:

27. Lord PF. Carmichael IA, Tashjian RJ. Left ventricular volume measurements by single plane cineangiocardiograptly: hemodynamic study of normal canine left ventricle. Am J Vet Res 1970;31:2031-43. 28. Kittleson MD, Johnson LE. Pion PD. The acme hemodynamic milrinone in dogs with severe idiopathic myocardial failure. J Vet fntern Med 1987;1:121-7. 29. Ricci DR. &lick AE, Alderman EL. et al. Role of tachyca inotropic stimulus in man. J Clin fnvest 1979:63:695-703. 30.