High incidence of myocarditis by endomyocardial biopsy in patients with idiopathic congestive cardiomyopathy.

Thirty-five patients with unexplained congestive heart failure were evaluated with endomyocardial biopsy. Utilizing microscopic, ultrastructural and immunofluorescent studies, samples were classified as exhibiting either no inflammation (cardiomyopathy) or active lymphocytic myocarditis, grade I to IV. Twenty-two (63%) of the patients had inflammatory changes. Of these 22 patients, 18 had low grade I or II inflammation, 7 were treated with immunosuppressive agents with improvement in 5 and stabilization in 1. One patient died of progressive congestive heart failure. Three of four patients with high grade III or IV myocarditis died after a fulminant course. The results suggest that inflammatory myocarditis may be more common than previously suspected and add evidence that there may be ongoing inflammation in many cases of congestive cardiomyopathy.