Hypertrophic cardiomyopathy presenting before 2 years of age in 13 patients.

Thirteen patients with hypertrophic cardiomyopathy (HCM) who presented by 2 years of age were evaluated. All had been referred because of a heart murmur. Four had positive family histories for HCM and 2 had congestive heart failure. Cardiothoracic ratios ranged from 0.43 to 0.70 (mean 0.56). In 12 cases, electrocardiograms showed abnormal Q waves, ventricular hypertrophy, or aberrant rhythms. Resting peak systolic pressure differences ranged from 0 to 92 mm Hg (mean 21.1) across the right ventricular outflow tract, and from 0 to 112 mm Hg (mean 36) across the left ventricular outflow tract (LVOT). Cardiac angiography showed evidence of asymmetric septal hypertrophy (ASH) in all patients, LVOT obstruction in 3, and aortic and mitral insufficiency in 1. Six patients received no therapy, 6 were treated with propranolol, and 3 were treated with left ventricular myomectomy. During follow-up (mean 6.1 years), no patient died and 10 became or remained asymptomatic. The apparently favorable clinical course observed in these patients during this period of follow-up may be related to early treatment, made possible by the early diagnosis.