The progression of interstitial myocarditis to idiopathic endocardial fibroelastosis.

Diffuse interstitial mononuclear cell myocarditis of unidentified but probable viral etiology in patients with endocardial fibroelastosis (EFE) suggested a possible pathogenetic relationship. Clinical and autopsy findings were reviewed in 64 children with one or both conditions. Five had myocarditis only and 18 had idiopathic EFE only, but in 41, both lesions coexisted and demonstrated the progression of myocarditis into idiopathic EFE. Patients with myocarditis but without EFE all died within 2 weeks of the onset of symptoms. With longer survival, myocarditis subsided but EFE and myocardial hypertrophy increased progressively. Marked EFE and hypertrophy, with trivial or no residual myocarditis, occurred with survival times over 4 months. Mitral insufficiency due to ventricular dilatation and a papillary muscle displacement commonly developed with prolonged survival. The results of the study are consistent with the hypothesis that in some patients interstitial myocarditis may produce left ventricular dilatation of a duration sufficient for the development of myocardial hypertrophy and EFE. These nonspecific responses to increased expenditure of myocardial energy and increased mural tension produce ventricular compensation, but result in a marked loss of cardiac reserve. Relative mitral insufficiency perpetuates the cycle of congestive failure and diminishing cardiac reserve by causing further ventricular dilatation with consequent myocardial hypertrophy.