HYPERTROPHIC CARDIOMYOPATHY

Hypertrophic cardiomyopathy is a primary myocardial disorder of unknow n cause with diverse clinical manifestations due to unimpaired, someti mes hyperkinetic, systolic left ventricular ejection function with or without outflow tract obstruction and/or diastolic dysfunction from im paired ventricular relaxation. Autosomal dominant genetic transmission is common, with sporadic occurrence in, at most, half of the cases. M olecular genetic analysis demonstrates abnormal myosin heavy-chain gen e expression in some families. Asymmetrical left ventricular hypertrop hy occurs with disproportional thickening of the anterior basal septum compared with the free wall. Extensive and widespread myocardial fibe r disarray is common. A systolic pressure gradient across the left ven tricular outflow tract may be present at rest, can be induced as with isoproterenol, or may be absent. The clinical picture and prognosis ar e greatly affected by the common diastolic dysfunction of impaired ven tricular relaxation due to increased stiffness. Although hypertrophic cardiomyopathy may be recognized in infancy, clinical signs usually be gin in adolescence or young adult years. Presenting symptoms are dyspn ea, fatigue, chest pain, syncope, or sudden death. Infants may present for evaluation because of a family history, the auscultation of an as ymptomatic murmur, or, less frequently, because of an arrhythmia or co ngestive heart failure. The echocardiogram is the most useful tool for monitoring the evolution of the disease and results of treatment. Sig nificant diagnostic features are left ventricular hypertrophy, asymmet ric septal hypertrophy, and systolic anterior motion of the anterior m itral leaflet. Doppler echocardiographic studies can quantify the degr ee of outflow tract obstruction and are useful to evaluate therapy. In dices of diastolic left ventricular dysfunction are demonstrable, incl uding wall motion abnormalities, prolongation of early diastolic peak velocity of flow across the mitral valve, flow deceleration and relaxa tion times, and a decreased mitral E:A flow ratio. Hemodynamic evaluat ion by cardiac catheterization is used less often today because of the usefulness of echocardiagraphic studies. Holter 24- to 48-hour electr ocardiographic monitoring is advised to identify patients with ventric ular tachycardia who have a risk of sudden and unexpected death. In al l age-groups, however, and especially in children, the absence of vent ricular arrhythmia in no way excludes the possibility of sudden death. Beta-Adrenergic blocking medications have been the primary medical tr eatment for hypertrophic cardiomyopathy for many years, but these agen ts do not appear to change the natural history of the condition or pre vent sudden death. Verapamil, the most widely used calcium channel blo cker in hypertrophic cardiomyopathy, appears to improve symptoms and e xercise capacity. Amiodarone, which suppresses ventricular tachycardia , may prevent sudden death. Surgical therapy for hypertrophic cardiomy opathy is considered elsewhere in this issue of Progress in Pediatric Cardiology.