Cardiomyopathy: a necessary revision of the WHO classification.

The classification of myocardial disease proposed by the WHO/ISFC task force in 1980 distinguishes specific heart muscle diseases from myocardial diseases of unknown origin, termed cardiomyopathies, and differentiated into the dilated, hypertrophic and restrictive forms. This last group includes endomyocardiofibrosis and fibroblastic parietal endocarditis. In more recent years, two new forms of heart muscle disease have been recognized: so-called "primary" restrictive cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy. Primary restrictive cardiomyopathy is characterized anatomically by normally sized, non-hypertrophic ventricles with dilated atria, and functionally by impaired diastolic compliance due to myocardial stiffness. The clinical picture is that of chronic congestive heart failure; histology shows interstitial fibrosis and myocardial disarray, but not hypereosinophilia. In arrhythmogenic right ventricular cardiomyopathy, the myocardium of the right ventricular free wall is substituted by fibrous and/or adipose tissue, which results in regional dynamic alterations and ominous ventricular arrhythmias. The left ventricle is usually spared. Both forms should be classified as heart muscle diseases of unknown origin, and kept clearly distinct from the other cardiomyopathies listed in the WHO classification.