Hypertrophic cardiomyopathy is a primary myocardial disorder of unknown cause with diverse clinical manifestations due to unimpaired, sometimes hyperkinetic, systolic left ventricular ejection function with or without outflow tract obstruction and/or diastolic dysfunction from impaired ventricular relaxation. Autosomal dominant genetic transmission is common, with sporadic occurrence in, at most, half of the cases. Molecular genetic analysis demonstrates abnormal myosin heavy-chain gene expression in some families. Asymmetrical left ventricular hypertrophy occurs with disproportional thickening of the anterior basal septum compared with the free wall. Extensive and widespread myocardial fiber disarray is common. A systolic pressure gradient across the left ventricular outflow tract may be present at rest, can be induced as with isoproterenol, or may be absent. The clinical picture and prognosis are greatly affected by the common diastolic dysfunction of impaired ventricular relaxation due to increased stiffness. Although hypertrophic cardiomyopathy may be recognized in infancy, clinical signs usually begin in adolescence or young adult years. Presenting symptoms are dyspnea, fatigue, chest pain, syncope, or sudden death. Infants may present for evaluation because of a family history, the auscultation of an asymptomatic murmur, or, less frequently, because of an arrhythmia or congestive heart failure. The echocardiogram is the most useful tool for monitoring the evolution of the disease and results of treatment. Significant diagnostic features are left ventricular hypertrophy, asymmetric septal hypertrophy, and systolic anterior motion of the anterior mitral leaflet. Doppler echocardiographic studies can quantify the degree of outflow tract obstruction and are useful to evaluate therapy. Indices of diastolic left ventricular dysfunction are demonstrable, including wall motion abnormalities, prolongation of early diastolic peak velocity of flow across the mitral valve, flow deceleration and relaxation times, and a decreased mitral E:A flow ratio. Hemodynamic evaluation by cardiac catheterization is used less often today because of the usefulness of echocardiagraphic studies. Holter 24- to 48-hour electrocardiographic monitoring is advised to identify patients with ventricular tachycardia who have a risk of sudden and unexpected death. In all age-groups, however, and especially in children, the absence of ventricular arrhythmia in no way excludes the possibility of sudden death. Beta-Adrenergic blocking medications have been the primary medical treatment for hypertrophic cardiomyopathy for many years, but these agents do not appear to change the natural history of the condition or prevent sudden death. Verapamil, the most widely used calcium channel blocker in hypertrophic cardiomyopathy, appears to improve symptoms and exercise capacity. Amiodarone, which suppresses ventricular tachycardia, may prevent sudden death. Surgical therapy for hypertrophic cardiomyopathy is considered elsewhere in this issue of Progress in Pediatric Cardiology.
