Arrhythmogenic right ventricular cardiomyopathy and fatty replacement of the right ventricular myocardium: are they different diseases?

BACKGROUND The relationship between arrhythmogenic right ventricular cardiomyopathy (ARVC) and pure fat replacement of the right ventricle is unclear. METHODS AND RESULTS Myocardial thickness, epicardial fat thickness, percent fibrosis, and intramyocardial fat infiltration were measured in 16 sections each from 25 hearts with typical (fibrofatty) ARVC, 7 hearts with fat replacement of the right ventricle without fibrosis (FaRV), and 18 control hearts from patients who died of noncardiac causes. Patients with fibrofatty ARVC were younger than those with FaRV (31+/-14 versus 44+/-13 years, P=.02), more likely to have a history of arrhythmias or a family history of premature sudden death (56% versus 0%, P=.01), more likely male (80% versus 29%, P=.02), and less likely to have coexisting conditions that might have predisposed to sudden death (12% versus 86%, P<.001). Fibrofatty ARVC was characterized by right ventricular myocardial thinning, fat infiltration of the anterobasal and posterolateral apical right ventricle, subepicardial left ventricular fibrofatty replacements (64%), myocyte atrophy (96%), and lymphocytic myocarditis (80%). FaRV showed normal or increased myocardial thickness, a diffuse increase in intramyocardial and epicardial fat, little inflammation, and an absence of myocardial atrophy. Intramyocardial fat was frequently seen in normal hearts, especially in the anteroapical region, but was less extensive than in fibrofatty ARVC and FaRV. CONCLUSIONS ARVC is a familial arrhythmogenic disease characterized by fibrofatty replacement of myocytes with scattered foci of inflammation. Fat infiltration per se is probably a different process that should not be considered synonymous with ARVC.