Arrhythmogenic Right Ventricular Cardiomyopathy - Feline Cardiomyopathies

Overview

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is a rare form of cardiomyopathy in cats and is more commonly seen in humans and dogs. ARVC is characterised by fibrofatty infiltration replacement of cardiomyocytes predominantly in the right ventricle and right atrium; this may also effect the left ventricle to a lesser degree in some cases. Pathophysiological sequelae include severe right ventricular myocardial failure, life-threatening ventricular arrhythmias and sudden death.

Aetiology

Little is known about he cause of ARVC in cats. In humans and Boxer dogs, ARVC is caused by mutations in various components of the desmosome (necessary for cell-cell adhesion). The resultant loss of mechanical coupling predisposes to arrhythmias.

Pathophysiology

Reduced myocardial contractility predominantly involves the right ventricle. This results in reduced stroke volume and increased ventricular filling pressure due to increased end-systolic ventricular diameter. This eventually leads to congestive heart failure (CHF).

Clinical Signs

Signalment

There is no breed or sex predilection. Mean age at the time of diagnosis was 7.3 +/- 5.2 years in one case series of 11 cats.

Physical Examination

The majority of cats present with signs referable to right-sided CHF. Other clinical findings include:

• Soft right parasternal pansystolic murmur, due to tricuspid regurgitation
• Syncope
• Lethargy
• Anorexia

Right-sided Congestive Heart Failure

• Tachypnoea
• Jugular vein distension, jugular pulses
• Hepatojugular reflux
• Ascites
• Hepatomegaly

Arrhythmias

Cats with ARVC may present with arrhythmias including ventricular tachycardia, atrial fibrillation, atrial standstill, supraventricular tachycardia, ventricular premature complexes, right bundle branch block and AV block.

Diagnosis

Radiography

Marked right sided cardiomegaly is found in all cats with ARVC. Pleural effusion is the most common manifestation of right-sided CHF in these cats. Other findings consistent with right-sided CHF include ascites and dilation of the caudal vena cava.

Echocardiography

Echocardiography is essential for diagnosis and must exclude other diseases with predominantly right heart pathology, such as atrial septal defect (ASD), cor pulmonale and tricuspid dysplasia.

Marked right ventricular eccentric hypertrophy (increased end-diastolic diameter) and right atrial dilation are the most readily recognised abnormalities in ARVC. There may be right ventricular aneurisms and abnormal muscle trabeculations in the right ventricular apex. Increased right ventricular diastolic pressure leads to the interventricular septum bowing and flattening (paradoxical septal motion).

There may be left atrial dilation in some cats with ARVC because end-stage disease may also effect the left ventricle and left atrium.

Two Dimensional and M-mode

• Right ventricular dilation +/- aneurismal thinning (thinning of the myocardial wall, usually at the apex)
• Right ventricular hypokinesia
• Right atrial enlargement

Doppler

• Mild tricuspid regurgitation

Differential Diagnoses

The main differential for ARVC in cats is tricuspid dysplasia, which causes severe volume overload to the right ventricle and right atrium. Colour flow doppler interrogation of the tricuspid valve in ARVC often reveals a mild central jet of tricuspid regurgitation secondary to annular dilation. The tricuspid valve appeas structurally normal. In comparison, a cat with tricuspid dysplasia would have significant tricuspid regurgitation and a structurally abnormal tricuspid valve with clubbed, thickened leaflets and a short, thickened chordae tendinae combined with abnormal papillary muscles. The distinction is important because prognosis for ARVC is grave compared with tricuspid dysplasia.

Electrocardiography (ECG)

Ventricular arrhythmias are common in cats with ARVC and can lead to syncope or sudden death. The arrhythmias are caused by macroreentrant circuits that develop in regions of fibrofatty replacement of cardiomyocytes.

• Ventricular premature complexes (VPCs)
• Ventricular tachycardia
• Atrial fibrillation
• Right bundle branch block

Treatment

Positive inotropes, such as pimobendan, may be required to treat severe right ventricular myocardial failure. Congestive heart failure is treated with furosemide and an ACE inhibitor such as Benezepril. Anticoagulant therapy is almost always indicated because cats with ARVC often have marked right atrial dilation which puts them at high risk of pulmonary thromboembolism.

Antiarrhythmic therapy may be necessary for treatment of severe ventricular or supraventricular tachyarrhythmias.

Prognosis

Prognosis for cats with ARVC is grave. In one case series of 12 cats with ARVC, 75% of cats died or where euthanised due to right heart failure or thromboembolism with a median survival time of 1 month in CHF cases.

References

• Fox PR et al. Spontaneous occurence of arrhythmogenic right ventricular cardiomyopathy in the domestic cat: a new animal model of human disease. Circulation, 102:1863, 2000