Infantile hypertrophic cardiomyopathy with QT prolongation.

An infant who died at 5 months with hypertrophic cardiomyopathy accompanied by QT prolongation was examined at autopsy. At the age of 16 days, serum IgM level was elevated (226 mg/dl). Microscopic examination revealed characteristics of hypertrophic cardiomyopathy with myocardial cell hypertrophy with disarray and healed myocarditis with patchy fibrosis and mononuclear cell infiltration. The histological findings were compatible with those of postmyocarditic cardiomegaly developing during the fetal period.