Idiopathic Hypertrophic Subaortic Stenosis

While considerable information concerning the hemodynamic and angiographic features of idiopathic hypertrophic subaortic stenosis (IHSS) is available, data concerning the natural history of the disease are limited. The clinical courses of 126 patients with hemodynamically documented IHSS, examined repeatedly for up to 12 years, were analyzed. The older patients tended to be more severely symptomatic. Although the course was extremely variable, the patients who were asymptomatic initially tended to remain so, while those who were more disabled generally deteriorated, died, or improved spontaneously. Bacterial endocarditis occurred in three patients. Ten patients died as a consequence of the natural history of IHSS; six of these deaths were unexpected. Sudden deaths occurred usually in patients with no or mild obstruction, and in patients with both the familial and sporadic forms of the disease. Atrial fibrillation was observed in 8% of the patients, and abnormalities of atrioventricular conduction, in 30%. Absence of voltage criteria for left ventricular hypertrophy occurred more frequently in asymptomatic patients, those with mild obstruction, and those with familial IHSS. Pulmonary hypertension occurred in one third of the patients, and was associated with considerable clinical disability. Obstruction to right ventricular outflow occurred in eight patients (15%), two of whom had no associated obstruction to left ventricular outflow.