Cardiomyopathy is a group of diseases with primary, usually diffuse, involvement of the myocardium. The myocardial disease is not secondary to ischaemic, valvular, congenital or pericardial disease. Although extensive ischaemic insult to the myocardium has been called ischaemic cardiomyopathy, there is some debate whether this entity should be included under the term cardiomyopathy. Many cardiomyopathies have no recognized aetiology. Several classifications have been proposed. A clinical functional classification consists of:
- dilated (formerly called congestive) cardiomyopathy, characterized by dilated left ventricle with diffuse myocardial hypokinesis;
- hypertrophic, characterized by symmetrical or asymmetrical ventricular hypertrophy disproportionate to or without pressure load; and
- restrictive cardiomyopathy, characterized by diastolic impairment of the ventricles. Some dilated cardiomyopathies have a known cause such as alcoholic, postviral, ischaemic, and adriamycin-dilated cardiomyopathies. The cardiomyopathies have also been characterized as:
- primary, for which the cause is usually unknown and is not part of a systemic disease; and
- secondary, in which the cause of the cardiomyopathy is part of a generalized systemic disease, such as sarcoidosis or amyloidosis.
Some of the secondary cardiomyopathies are also called infiltrative cardiomyopathies since they are caused by extensive infiltration of pathological cells or substances into the myocardium such as amyloidosis, haemochromatosis, sarcoidosis, glycogen storage disease, etc. The diagnosis of a specific cause of a cardiomyopathy is now facilitated by percutaneous transvenous (right ventricular) or transarterial (left ventricular) endomyocardial biopsy.
Plain radiograph in dilated cardiomyopathy typically demonstrates substantial cardiomegaly with or without signs of pulmonary venous hypertension (Fig.1). In hypertrophic cardiomyopathy, the heart size is usually normal but cardiomegaly may be present in patients with severe hypertrophy or late in the course of the disease when myocardial failure ensues. In restrictive cardiomyopathy, the X-ray demonstrates little or no cardiomegaly. Because of high ventricular filling pressures, the atria may be enlarged and signs of pulmonary venous hypertension may be prominent.
Cardioangiography in dilated cardiomyopathy demonstrates increase in left ventricular (LV) end-diastolic and end-systolic volumes and decrease in stroke volume and ejection fraction. There is diffuse hypokinesis and frequently mild to moderate mitral regurgitation. In hypertrophic cardiomyopathy cardioangiography frequently shows reduced LV volumes and increased ejection fraction. The ventricular shape is frequently abnormal with enlarged papillary muscles, eccentric hypertrophy of the upper ventricular septum and cavity obliteration at end systole. A lucent line in the LV outflow region is observed in the obstructive form, due to apposition of the anterior leaflet of the mitral valve with the hypertrophied septum during systole. In addition, anterior motion of the mitral valve may be evident during systole. Mild to moderate mitral regurgitation is sometimes present. In restrictive cardiomyopathy, the angiogram may show normal or increased ventricular volumes and sometimes symmetrically thick left ventricular myocardium. Amyloid heart disease not uncommonly causes symmetrically thickened myocardium. Systolic contraction of the left ventricle may be normal or mildly reduced. However, the diastolic filling pattern is abnormal, consisting of rapid filling in early diastole followed by a plateau with little filling in late diastole. The filling pattern is similar in constrictive pericarditis so the two diseases cannot usually be distinguished by angiography. Endomyocardial biopsy may be the only method for providing a definitive diagnosis.
Echocardiography in dilated cardiomyopathy displays increased size of the LV cavity, and normal thickness of the LV myocardium. The LV cavity has a spherical shape and may contain mural thrombus. Doppler echocardiography frequently identifies mild to moderate mitral regurgitation. In hypertrophic cardiomyopathy, echocardiography shows increased LV mass and wall thickness, and usually reduced LV volume. The hypertrophy may be symmetrically or asymmetrically distributed in the LV. In asymmetric septal hypertrophy (ASH) the wall thickening is localized or more severe in the basal septum. Variant forms of asymmetric hypertrophy may show the most severe hypertrophy at the apical or mid portion of the LV. In the obstructive form, the echocardiogram demonstrates systolic anterior motion (SAM) of the anterior mitral valve leaflet. Doppler and colour flow mapping may display mitral regurgitation.
In restrictive cardiomyopathy echocardiography is frequently nondiagnostic. Amyloid cardiomyopathy may be identified by demonstrating symmetric wall thickening and reduced contractile function. Increased reflectance of the myocardium may be caused by amyloid deposition.
Electron beam CT (EBCT) and magnetic resonance imaging (MRI) may also be used in the evaluation of cardiomyopathies by providing precise measurements of LV volumes and mass. In hypertrophic cardiomyopathy, both techniques demonstrate the severity and distribution of hypertrophy of the left ventricle and less frequently in the right ventricle (Fig.2). MRI has also demonstrated variant forms of hypertrophic cardiomyopathy. In restrictive cardiomyopathy, both CT and MRI can be used to indicate normal pericardial thickness (< 4mm) and thereby exclude the primary differential diagnosis, constrictive pericarditis. For specific types of cardiomyopathy, see cardiomyopathy alcoholic, cardiomyopathy amyloid, cardiomyopathy dilated, doxorubicin, cardiomyopathy Duchenne muscular dystrophy, haemochromatosis cardiac involvement, cardiomyopathy hypertrophic, cardiomyopathy infiltrative, cardiomyopathy restrictive, cardiomyopathy secondary.
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