Dilated cardiomyopathy - Disorders of the myocardium

Dilated cardiomyopathy

Definition

Progressive ventricular dilatation with normal coronary arteries.

Aetiology

Most cases are idiopathic but are often assumed to follow an undiagnosed viral myocarditis. The commonest identifiable cause is high alcohol intake. Other factors:

Genetic: Single gene mutations and skeletal muscular dystrophies.

Familial: 30% of cases have relatives with left ventricular dysfunction or enlargement.

There is an association with chronic infective, toxic or

immune myocarditis.

Many systemic diseases may cause the clinical features of dilated cardiomyopathy, e.g. ischaemic heart disease, amyloidosis, metabolic diseases, haemochromatosis and systemic lupus erythematosus.

Pathophysiology

The dilatation of the heart results in impaired contraction especially affecting the left ventricle. Left ventricular failure causes an elevated enddiastolic pressure with resultant increase in pressure within the pulmonary circulation and eventually right-sided heart failure. The dilatation also results in a functional regurgitation at the tricuspid and/or mitral valves (valve ring dilation).

Clinical features

Symptoms are dependent upon the degree of cardiac failure. Patients tend to present with dyspnoea and orthopnoea, which may be acute or of more insidious onset.

On examination, the JVP is raised possibly with a systolic pressure wave (cv wave) due to tricuspid regurgitation, and the blood pressure is low. Tachycardia is common and low perfusion results in peripheral vascular shutdown (small thready pulse, cold extremities and peripheral cyanosis). Auscultation may reveal a gallop rhythm (tachycardia with third heart sound due to rapid ventricular filling) and the pansystolic murmurs of mitral and tricuspid regurgitation. Ankle and/or sacral oedema, mild hepatomegaly and jaundice, due to hepatic congestion or tricuspid regurgitation, and ascites are signs of right-sided heart failure.

Macroscopy/microscopy

The ventricles are dilated (left more than right), the chamber walls are thin and the muscle poorly contractile. Fibrosis tends to occur in the dilated myocardium with a cellular infiltration especially T lymphocytes.

Complications

Atrial fibrillation is common, particularly in alcoholic cardiomyopathy, and bouts of ventricular tachycardia may occur. Mural thrombosis may occur in either ventricle with the associated risk of systemic embolisation.

The impaired cardiac output leads to failure to perfuse the kidneys and hence secondary renal failure.

Investigations

Chest X-ray shows cardiac enlargement with signs of pulmonary oedema including upper lobe vein diver-sion, Kerley B lines and may show pleural effusions.

ECG usually shows sinus tachycardia or atrial fibrillation, there may be nonspecific T wave changes.

Echo reveals ventricular dilation, poor contractility and will demonstrate any valvular regurgitation.

Cardiac catheterisation may be needed to exclude coronary artery disease, as this may present similarly without any history of angina or myocardial infarct.

Patients should also have an ESR, creatine kinase, viral serology, U&Es, LFTs and calcium, iron studies and thyroid function tests to help identify the underlying cause.

Management

General measures include bed rest, fluid restriction and quitting alcohol.

Treat arrhythmias (digoxin especially useful in atrial fibrillation) and commence treatment for cardiac failure  with care as it may cause hypotension.

Patients with atrial fibrillation, a history of thromboembolic disease or a presence of intracardiac thrombous should be anticoagulated. Severe cases may benefit from anti-coagulation without other risk factors.

Prognosis

The prognosis is very poor. Young patients may be treated with cardiac transplantation.