Cardiomyopathies and specific heart muscle diseases. Definitions, terminology, classifications and new and old approaches.

Cardiomyopathies are defined as 'heart muscle diseases of unknown cause' and classified into hypertrophic, dilated and restrictive types, respectively. Hypertrophic cardiomyopathy is notable for massive ventricular hypertrophy without obvious cause, impaired diastolic and systolic function, a tendency for sudden death and a familial propensity. Dilated cardiomyopathy by contrast, demonstrates severe systolic failure progressing to congestive heart failure, with usually no familial tendency. Restrictive cardiomyopathy and diastolic heart disease represent syndromes with restriction to ventricular filling due to restrictive forces in the endomyocardium (and in constrictive pericarditis in the pericardium). The commonest cause of restrictive cardiomyopathy is endomyocardial fibrosis now usually known as hypereosinophilic endomyocardial disease. Specific heart muscle diseases are those conditions in which myocardial disease is due to a known cause: they usually produce systolic failure though occasionally a restrictive syndrome is evident. Amyloid heart disease occupies a place intermediate between cardiomyopathies and specific heart muscle diseases. The major features of the above conditions are described and current and future advances noted. Examples are the identification of the gene probably responsible for hypertrophic cardiomyopathy located on chromosome 14, and the identification of virus RNA particles in the myocardium in both myocarditis and in dilated cardiomyopathy, which strengthens the growing evidence suggesting that some cases of dilated cardiomyopathy may be due to previous myocarditis.