Cardiomyopathies

Cardiomyopathy is disease of the heart muscle that results in abnormal cardiac function. In its broadest sense this includes what has been termed primary or idiopathic cardiomyopathies, which couldn't be attributed to a specific cause.
The secondary or specific cardiomyopathies are often associated with disease involving other organs (e.g. sarcoidosis, amyloidosis, systemic lupus erythematosus, systemic sclerosis and polyarteritis nodosa), or with specific cardiac abnormalities (e.g. hypertension, ischaemic heart disease, valvular dysfunction or abnormalities of the pericardium). Cardiomyopathy is also associated with Duchenne muscular dystrophy.¹

This article deals with the idiopathic or primary cardiomyopathies, though there is a certain amount of crossover between the groups. The degree of cardiac dysfunction ranges from lifelong symptomless forms to major health problems such as progressive heart failure, arrhythmia, thromboembolism and sudden cardiac death.² The World Health Organisation classifies cardiomyopathies into 5 groups:

• Dilated cardiomyopathy: commonest form, (synonym congestive cardiomyopathy). The left or both ventricles are dilated with impaired contraction. Causes include: ischaemia, alcoholic, toxic, thyroid disorders, valvular, familial/genetic and idiopathic.
• Hypertrophic obstructive cardiomyopathy: 2nd commonest; estimated adult prevalence is 1:500, with left and/or right ventricular hypertrophy. Usually familial (autosomal dominant).
• Restrictive cardiomyopathy: rare; estimated prevalence between 1:1000 and 1:5000, with restrictive filling and reduced diastolic filling of one/both ventricles and normal or near normal systolic function. Causes include: amyloidosis, endomyocardial fibrosis, and idiopathic.
• Arrhythmogenic right ventricular cardiomyopathy: with fibro-fatty replacement of right ventricular myocardium, Uhl's anomaly (parchment heart). Cause is unknown; familial form is usually autosomal dominant with incomplete penetrance but may be recessive, e.g. Naxos disease (autosomal recessive family from the Greek Island).
• Unclassified: with no typical features of the above. Causes include: fibroelastosis, non-compacted myocardium, systolic dysfunction with minimal dilatation, mitochondrial diseases.

Hypertrophic Cardiomyopathy, Dilated Cardiomyopathy, Restrictive Cardiomyopathy and Arrhythmogenic Right Ventricular Cardiomyopathy are each discussed in separate articles.

• In contrast to coronary heart disease having a higher incidence in the elderly, cardiomyopathies can occur at younger ages. Therefore cardiomyopathy should be suspected in any young person presenting with a heart failure, arrhythmias or thromboembolism.²
• A familial cause has been shown in 50% of patients with hypertrophic cardiomyopathy, 35% with dilated, and 30% with arrhythmogenic right ventricular cardiomyopathy. Restrictive cardiomyopathy is usually not familial.

• Coronary artery disease.
• Mitral valve disease.
• Athlete's heart: prolonged isometric training may produce heart changes resembling some features of hypertrophic cardiomyopathy.
• Amyloidosis.
• Hypertensive heart disease: severe, chronic systolic and diastolic hypertension.
• Valvular and subvalvular aortic stenosis.
• Infundibular pulmonary stenosis.
• Ventricular septal defect.
• Constrictive pericarditis.

• Blood tests: full blood count, ESR, renal function, electrolytes, liver function, cardiac enzymes and thyroid function tests.
• Chest x-ray.
• ECG: a normal electrocardiogram is uncommon in any form of cardiomyopathy.
• Transthoracic doppler echocardiography: can confirm the diagnosis of hypertrophic cardiomyopathy, help distinguish between restrictive cardiomyopathy and constrictive pericarditis, exclude valvular heart disease, and assess the severity of ventricular dysfunction in dilated cardiomyopathies.
• Beta-natriuretic peptide has a potential role as a test for ventricular dysfunction.
• Non-invasive stress testing is recommended only for patients who have a high probability of underlying ischaemic heart disease, prior myocardial infarction, or extensive hibernating myocardium or for evaluation for possible heart transplantation.
• Cardiac catheterisation can help in excluding coronary artery disease as the cause of the dilated cardiomyopathy and in distinguishing restrictive cardiomyopathy from constrictive pericarditis.
• Magnetic resonance imaging: may help distinguish between constrictive disease and restrictive cardiomyopathy.
• Right ventricular endomyocardial biopsy is occasionally used to distinguish between myocarditis and idiopathic dilated cardiomyopathy. A normal result does not rule out cardiomyopathy.

• Treatment options are symptomatic and mainly directed towards treatment of heart failure and prevention of thromboembolism and sudden death.
• Identification of patients with high risk for major arrhythmic events is important because implantable cardioverter defibrillators can prevent sudden death.
• All patients with cardiomyopathy require a thorough cardiological assessment of functional capacity, cardiac function and risk of serious arrhythmia.
• Patients with hypertrophic obstructive cardiomyopathy (HOCM) may be treated by surgical or non-surgical myectomy. Non-surgical reduction involves injecting alcohol into the heart via a catheter inserted into the femoral artery. This destroys part of the muscle in the septum, which then becomes thinner.³