CARDIOMYOPATHY

Cardiomyopathies comprise a group of diseases of the myocardium that affect the mechanical (hypertrophic, arrhythmogenic right ventricular, dilated and restrictive cardiomyopathy) or electrical function (conduction system disease and ion channelopathies, e.g. long QT syndrome) of the heart. Diagnosis of myocardial disease is usually by imaging (echocardiogram and cardiac MR).

Hypertrophic cardiomyopathy (HCM)

HCM is characterized by marked ventricular hypertrophy in the absence of abnormal loading conditions such as hypertension and valvular disease. There is usually disproportionate involvement of the interventricular septum. The hypertrophic non-compliant ventricles impair diastolic filling, so that stroke volume is reduced. Most cases are familial, autosomal dominant, and caused by mutations in genes encoding sarcomeric proteins, e.g. troponin T and β-myosin. It is the most common cause of sudden cardiac death in young people.

Clinical features

Patients may be symptom-free (and detected through family screening) or have breathlessness, angina or syncope. Complications include sudden death, atrial and ventricular arrhythmias, thromboembolism, infective endo-carditis and heart failure. The carotid pulse is jerky because of rapid ejection and sudden obstruction to the ventricular outflow during systole. An ejection systolic murmur occurs because of left ventricular outflow obstruction, and the pansystolic murmur of functional mitral regurgitation may also be heard.

Investigations

■ ECG is almost always abnormal. A pattern of left ventricular hypertrophy with no discernible cause is diagnostic.

■ Cardiac imaging shows ventricular hypertrophy (on echo and MR) and fibrosis (on MR).

■ Genetic analysis may confirm the diagnosis and provide prognostic information.

Management

Amiodarone reduces the risk of arrhythmias and sudden death. Individuals at highest risk are fitted with an implantable cardiac defibrillator. Chest pain and dyspnoea are treated with β-blockers and verapamil. In selected cases outflow tract gradients are reduced by surgical resection or alcohol ablation of the septum, or by dual-chamber pacing.

Dilated cardiomyopathy (DCM)

DCM is characterized by a dilated left ventricle which contracts poorly. Inheritance is autosomal dominant in the familial disease.

Clinical features

Shortness of breath is usually the first complaint; less often patients present with embolism (from mural thrombus) or arrhythmia. Subsequently there is progressive heart failure with the symptoms and signs of biventricular failure.

Investigations

■ Chest X-ray may show cardiac enlargement.

■ ECG is often abnormal. The changes are non-specific and include arrhyth-mias and T-wave flattening.

■ Cardiac imaging shows dilated ventricles with global hypokinesis. Cardiac MR may show other aetiologies of left ventricular dysfunction, e.g. previ-ous myocardial infarction.

Other tests such as coronary angiography, viral and autoimmune screen and endomyocardial biopsy may be needed to exclude other diseases (Table 10.15) that present with the clinical features of DCM.

Management

Heart failure and atrial fibrillation are treated in the conventional way (pp. 440, 429). Cardiac resynchronization therapy and implantable cardiac defi-brillators are used in patients with NYHA III/IV grading. Severe cardiomyopa-thy is treated with cardiac transplantation.

Primary restrictive cardiomyopathy

The rigid myocardium restricts diastolic ventricular filling and the clinical features resemble those of constrictive pericarditis (see later). In the UK the most common cause is amyloidosis. The ECG, chest X-ray and echocardio-gram are often abnormal, but the findings are non-specific. Diagnosis is by cardiac catheterization, which shows characteristic pressure changes. An endomyocardial biopsy may be taken during the catheter procedure, thus providing histological diagnosis. There is no specific treatment and the prog-nosis is poor, with most patients dying less than a year after diagnosis. Cardiac transplantation is performed in selected cases.

Arrhythmogenic right ventricular cardiomyopathy

There is Progressive fibro-adipose replacement of the wall of the right ven-tricle. The typical presentation is ventricular tachycardia or sudden death in a young man.

Table 10.15 Heart muscle disease presenting with features of dilated cardiomyopathy

Ischaemia

Hypertension

Congenital heart disease

Peripartum cardiomyopathy

Iníections, e.g. cytomegalovirus, HIV

Alcohol excess

Muscular dystrophy

Amyloidosis

Haemochromatosis