J Vet Clin 29(3) : 242-246 (2012)

242

Restrictive Cardiomyopathy in a Korean Domestic Short-haired Cat

Hyo-Seung Nam, Suk-Hee Han, Ran Choi, Seung-Gon Lee and Changbaig Hyun1

Section of Small Animal Internal Medicine, College of Veterinary Medicine, Kangwon National University, Chuncheon 201-100, Korea

(Accepted: June 11, 2012)

Abstract : A 3-year-old castrated male Korean domestic short-haired cat (weighing 5.2 kg) was referred to the KangwonNational University Veterinary Teaching Hospital, with primary complaints of ascites, pleural effusion and respiratorydistress. Diagnostic studies revealed marked chylous and hemorrhagic pleural effusion, cardiomegaly, restrictive fillingpattern of transmitral flow and mitral annular tissue Doppler profiles and minimally thickened left ventricular freewall. Based on the echocardiographic findings, the case was tentatively diagnosed as restrictive cardiomyopathy. Thecase was treated with removal of pleural effusion and medical therapy including furosemide, enalapril, sildenafil,clopidogrel. This is the first case report of restrictive cardiomyopathy in Korea.

Key words : restrictive cardiomyopathy, RCM, pleural effusion, cat.

Introduction

Feline restrictive cardiomyopathy (RCM) is a form of car-

diomyopathy characterized by severely impaired diastolic

filling associated with increased ventricular stiffness, and rel-

atively normal left ventricular dimensions and systolic func-

tion. RCM has also been called intermediate cardiomyopathy

and endomyocardial fibrosis (1,6). Although rhythmicity and

contractility of the heart may be preserved, the myocardial

function can be limited due to inadequate ventricular filling

from the stiffness of the heart chambers (atria and ventricles).

It causes the reduction of preload and end-diastolic volume

and thus increases venous return causing pulmonary hyperten-

sion (6). With time, the cat can develop marked diastolic dys-

function and eventually heart failure. If untreated, cats with

RCM often develop the following characteristics: Biatrial

enlargement, thickened LV walls (with normal chamber size),

thickened RV free wall (with normal chamber size), elevated

right atrial pressure (> 12 mmHg), moderate pulmonary hyper-

tension, normal systolic function, poor diastolic function (5,6).

Clinical manifestations and therapeutic strategy are similar

to feline hypertrophic cardiomyopathy. This case report has

firstly describes a rare case of feline RCM in Korea.

Case

A 3-year-old castrated male Korean domestic short-haired

(DSH) cat presented to the VTH of Kangwon National Uni-

versity clinic with primary complaints of ascites, pleural effu-

sion and respiratory distress. The cat was referred for episodic

dyspnea and clinical findings consisted of low systolic blood

pressure, tachycardia, recurrent chylous pleural effusion,

ascites and the presence of a gallop rhythm on auscultation.

On the physical examination at our clinic, auscultation of

the thorax revealed a heart rate of 220 beats per minute and

moderate tachypnea (60 breaths per minute). A grade III/VI

systolic left and right sided murmur with S4 gallop sound

was present (after removal of ascites and pleural effusion).

No arrhythmia was noted. Increased bronchovesicular sounds

and occasional crackles were auscultated. The systolic blood

pressure measured by Doppler method was ~110 mmHg. No

other abnormalities were detected on physical examination,

except weak femoral pulse. A routine hemogram and serum

biochemistry profile revealed no significant abnormalities

except for an elevated urea (suggestive of prerenal azotemia,

34 mg/dL), reduced albumin (2.4 g/dL) and total protein (5.3

g/dL) and haemoconcentration. Urinalysis showed no abnor-

malities. The 12-lead surface ECG showed no particular

abnormalities except sinus tachycardia (220-250 bpm).

Because the cat was dyspneic due to severe pleural effu-

sion, emergency thoracocentesis was performed at the right

hemithorax. About 400 mL milky pink pleural fluid was re-

moved. After removal of pleural effusion, the respiration of

cat was much improved and stabilized. Analysis of pleural

effusion revealed chylous modified transudate (consisting of

small lymphocytes and red blood cells). Thoracic radiography

was then taken. There is severe cardiomegaly and left atrial

dilation seen on lateral and ventrodorsal projections (Fig 1).

The ventrodorsal view shows marked cardiomegaly with bi-

atrial dilation (valentine heart; Fig 1A). The lateral view

shows mild patchy interstitial infiltrates, especially around

hilar region, loss of cardiac silhouette due to pleural effusion

as well as marked left atrial dilation which are consistent

with left sided heart failure (Fig 1B).

1Corresponding author.E-mail : hyun5188@kangwon.ac.kr

Restrictive Cardiomyopathy in a Korean Domestic Short-haired Cat 243

An echocardiogram was then performed. Marked right and

left atrial enlargement was noted on B-mode right paraster-

nal 4 chamber view (Fig 2C). The left atrial to aortic ratio was

3.1:1 (reference range 1.25 ± 0.18) with the left atrium mea-

sured at 2.39 cm and the aorta at 0.77 cm (Fig 2B). Border-

line increase of diastolic left ventricular free wall (0.72 cm,

Fig 1. Thoracic radiography of this case taken after removal of pleural effusion. There is severe cardiomegaly and left atrial dilation seen

on lateral (A) and ventrodorsal (B) projections. The lateral view shows mild patchy interstitial infiltrates, especially around hilar region,

loss of cardiac silhouette due to pleural effusion as well as marked left atrial dilation which are consistent with left sided heart failure.

The ventrodorsal view shows marked cardiomegaly with bi-atrial dilation (valentine heart).

Fig 2. The 2D-echocardiography of this case. A, D: Borderline increase of diastolic left ventricular free wall (0.72 cm, under 0.6 cm con-

sidered normal) and interventricular septal thickness (0.59 cm, under 0.6 cm considered normal) were noted on B and M-mode right

parasternal short axis views. Interestingly, the echogenecity of left/right ventricular endocardium was markedly increased, suggesting

endocardial fibrosis. B: The left atrial to aortic ratio was 3.1:1 (reference range 1.25 ± 0.18) with the left atrium measured at 2.39 cm and

the aorta at 0.77 cm. C: Marked right and left atrial enlargement was noted on B-mode right parasternal 4 chamber view.

244 Hyo-Seung Nam, Suk-Hee Han, Ran Choi, Seung-Gon Lee and Changbaig Hyun

under 0.6 cm considered normal) and interventricular septal

thickness (0.59 cm, under 0.6 cm considered normal) were

noted on B and M-mode right parasternal short axis views

(Fig 2A and 2D). Interestingly, the echogenecity of left/right

ventricular endocardium was markedly increased, suggesting

endocardial fibrosis (Fig 2C). Systolic anterior motion of the

mitral valve was present. A regurgitant jet through the mitral

valve and tricuspid valve had a peak velocity of 4.21 m/s

(pressure gradient ~70 mmHg) and 2.92 m/s (pressure gradi-

ent ~35 mmHg), correlating with an increased left and right

atrial pressure (normal 0-5 mmHg in diastole). The pulse

wave Doppler interrogation of the mitral inflow revealed a

typical restrictive filling pattern including increased early

diastolic filling velocity (2.85 m/s), a decreased atrial filling

velocity (0.54 m/s), increased E:A ratio (4.42), shortened

deceleration time (32 ms), and decreased isovolumic relax-

ation time (IVRT, 23 ms) (Fig 3A). Tissue Doppler imaging

(TDI) echocardiography revealed diastolic dysfunction evi-

denced by reduced early diastolic mitral annular velocity and

reversal of early to late diastolic velocities (Fig 3B). These

Fig 3. Transmitral flow profiles and tissue Doppler profiles at mitral annulus. A: The pulse wave Doppler interrogation of the mitral inflow

revealed a typical restrictive filling pattern including increased early diastolic filling velocity (2.85 m/s), a decreased atrial filling velocity

(0.54 m/s), increased E:A ratio (4.42), shortened deceleration time (32 ms), and decreased IVRT (23 ms). B: Tissue Doppler imaging (TDI)

echocardiography revealed diastolic dysfunction evidenced by reduced early diastolic mitral annular velocity and reversal of early to late

diastolic velocities, IVRT = Isovolumic relaxation time.

Fig 4. Myocardial strain exam (Bull’s eye) of this case showed moderated myocardial dyssynchrony while the left ventricle contracts

and relaxes.

Restrictive Cardiomyopathy in a Korean Domestic Short-haired Cat 245

findings were consistent with restrictive cardiomyopathy

(RCM) due to either endomyocardial fibrosis or endomyocar-

dial fibroelastosis. Furthermore, myocardial strain exam (Bull’s

eye) of this case showed the cat was suffering moderate myo-

cardial dyssynchrony while the left ventricle contracted and

relaxed (Fig 4).

The cat was medicated with furosemide (2 mg/kg q12h,

PO, Lasix, Handok, Korea), enalapril (0.5 mg/kg, q12h, PO,

Poonglim, Korea), spironolactone (1 mg/kg, q12h, PO, Aldac-

tone, USA) for controlling pleural effusion and pulmonary

edema, sildenafil (1 mg/kg, q12h, PO, Viagra, Pfizer, USA) and

pimobendan (0.25 mg/kg, q12h, PO, Vetmedin, Boehringer

Ingelheim, Germany) for reducing the resistance of pulmonary

vasculature and improving systolic function, and clopidogrel

(16.5 mg/head, q24h, PO, Unimed, Korea) for minimizing the

risk of thromboembolism. The cat was then released with

advice of moderate salt restriction.

Two week after the first visit, the cat re-presented for the

follow-up study. There was no further accumulation of pleu-

ral effusion and pulmonary edema. The cat is more active

and healthy, although the echocardiographical findings were

not much different from the first presentation. The cat was

released again with the same medication. The cat is still alive

and is currently being checked regularly (~8 months after the

first visit, to date).

Discussion

Diagnosis of RCM is challenging in routine diagnostic

imaging study (7). Based on the definition of RCM in human

literatures, human RCM is characterized by restrictive filling

and reduced diastolic volume of either or both ventricles with

normal or near-normal systolic function and wall thickness

(6). According to veterinary literatures, feline RCM is a rare

type of myocardial disease characterized by abnormal dias-

tolic function, normal to mildly increased left ventricular wall

thickness, and normal to mildly reduced systolic function

(1,6,7). Histopathologically, RCM is characterized by infiltra-

tion of the endocardium, subendocardium, or myocardium by

fibrous tissue or another component and causes impaired

ventricular diastolic compliance (i.e., stiffness is increased, 6,

7). Although specific causes, such as amyloidosis and eosi-

nophilic infiltration have been identified as causes of RCM,

specific causes for feline RCM have not been clearly defined,

to date (5). In the past, the definitive diagnosis can be only

made by histopathology revealing ventricular or endocardial

fibrosis.

However, recent development of echocardiographic tech-

nologies (i.e. tissue Doppler on mitral annulus, transmitral

profiles on PW Doppler and radial strain exam) enables us to

identify RCM in cats without the use of invasive diagnostic

procedures to directly measure left ventricular diastolic func-

tion. Echocardiographic diagnostic criteria RCM is revealing

a typical restrictive filling pattern seen on PW Doppler inter-

rogation of the mitral inflow (1,5). A restrictive filling pattern

is generally observed if there is severe diastolic impairment

leading to markedly elevated left atrial pressure and a high

left atrial-to-LV diastolic pressure gradient. It is characterized

by an increased early diastolic filling velocity (> 1 m/s), a

decreased atrial filling velocity (< 0.4 m/s), increased E:A

ratio (> 2), shortened deceleration time (normal is 59 ± 14

ms), and decreased IVRT (normal is 55 ± 13 ms) (1,5). Also

cats with RCM can have reduced early diastolic (e’) mitral

annulus velocity indicative of diastolic dysfunction. In this

case, the cat showed a typical restrictive filling pattern on PW

and tissue Doppler study. Furthermore the cat had moderate

mitral and tricuspid regurgitation without any evidence of

valvular degeneration. Strain echocardiography also revealed

moderate myocardial dyssynchrony due to impaired ventricu-

lar function. The hyperechoic endocardium on the 2D echocar-

diography strongly suggested endocardial fibrosis in this cat.

Although the thickness of left ventricular free wall was slightly

thicker than 6 mm, left and right atrial size was remarkably

increased. Those echocardiographic findings strongly indicated

restrictive cardiomyopathy without histopatholgical exam.

Other diagnostic findings known in literatures are similar to

other cardiomyopathy causing diastolic dysfunction (e.g.

HCM) (3). Over half (55%) of cats were present with clinical

signs of dyspnea (3). However, fewer cats may have abnormal-

ities on cardiac auscultation (cardiac murmur in 36% affected

cats, S4 gallop in 23%, arrhythmias in 12%) (3). Typical find-

ings on thoracic radiography are cardiomegaly including left

atrial dilation or biatrial dilation (73% in affected cats), pleural

effusion (55%), pulmonary edema (41%) and ascites (23%).

Chylous modified transudate of pleural effusion is also com-

mon in cats with heart failure as noticed in this study. Pulmo-

nary venous distension and/or dilated caudal vena cava can

be also occurred secondary to heart failure. In this case, the cat

showed typical findings in clinical manifestations and thoracic

radiography. However, these findings can not be discrimina-

tive form other type of feline cardiomyopathies.

Unfortunately, no specific treatment toward RCM has dis-

covered to date. Because most cats diagnosed with RCM have

clinical signs associated with congestive heart failure (CHF),

therapeutic strategy should be directed to lessen edema forma-

tion (i.e. pulmonary edema, pleural effusion), to prevent activa-

tion of rennin-angiotensin-aldosterone system (RAAS) and

sympathetic nervous system (SNA), to improve diastolic and

systolic function of left ventricle, and to minimize risk of

thromboembolism (1,2,4). In this case, furosemide and spirono-

lactone was used to lessen fluid retention. Enalapril was used

to prevent activation of RAAS. Furthermore, sildenafil and

pimobendan were used for reducing the resistance of pulmo-

nary vasculature and improving systolic function. Lastly, clo-

pidogrel was added into the prescription for minimizing the

risk of thromboembolism. Generally the affected cat can only

survive for 3-4 months after showing overt clinical signs of

fluid retention (8).

To our best knowledge, this case is the first report describ-

ing feline RCM in Korea.

246 Hyo-Seung Nam, Suk-Hee Han, Ran Choi, Seung-Gon Lee and Changbaig Hyun

Acknowledgments

This study was supported by Institute of Veterinary Sci-

ence, Kangwon National University.

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Jones TJ, Wotton PR. Feline idiopathic cardiomyopathy: a

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In: Kittleson, M. D. and Kienre, R. D. (eds) Small Animal

Cardiovascular Medicine. Mosby, St. Louis. pp. 363-369.

7. Stalis IH, Bossbaly MJ, Vanwinkle TJ. Feline endomyocarditis

and left-ventricular endocardial fibrosis. Vet Pathol 1995; 32:

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failure: a meta-analysis. Int J Cardiol 2007; 116: 70-77.

코리안 숏헤어 고양이의 제한성 심근병증

남효승·한숙희·최란·이승곤·현창백1

강원대학교 수의과대학 소동물내과교실

요 약 : 3살된 코리안 숏헤어 고양이(몸무게 5.2 kg)가 복수, 흉수, 호흡곤란으로 인해 강원대학교 수의과대학병원에

진료의뢰 되었다. 진단검사상, 유미성 흉수와 출혈성 복수, 심장비대, PW 도플러 초음파와 TDI 초음파의 restrictive

filling pattern, 미비하게 비대된 좌심실 자유벽이 관찰되었다. 심장초음파 진단소견을 토대로 제한성 심근병증으로 잠

정진단 내리게 되었다. 본 환자는 흉수를 제거하고 furosemide, enalapril, sildenafil, clopidogrel을 포함한 약물치료를

하였다. 이것은 국내에서 처음으로 발표하는 제한성 심근병증의 증례이다.

주요어 :제한성 심근병증, RCM, 흉수, 고양이