Operative Treatment in Idiopathic Hypertrophic Subaortic Stenosis

Operations designed to relieve obstruction to left ventricular outflow were carried out in 25 patients with idiopathic hypertrophic subaortic stenosis (IHSS). All of the patients were symptomatic and 23 were in functional classes III or IV. Preoperatively, a systolic pressure gradient within the left ventricle was demonstrated in every patient (average, 102 mm Hg), and the average left ventricular end-diastolic pressure was 19 mm Hg. Six patients had pulmonary hypertension. During cardiopulmonary bypass, the outflow tract of the left ventricle was exposed through an aortotomy. In five early patients only ventriculomyotomy was carried out, but in all subsequent operations myotomy was combined with a limited resection of the hypertrophied muscular tissue. One patient died, apparently of arrhythmia, on the eighth postoperative day, and another 8 months after operation following cerebral thrombosis. In two other patients complete heart block was produced, and they have implanted pacemakers. Twenty-one of the 23 surviving patients have been followed for periods of 1 to 8 years; 15 are asymptomatic (class I). Six patients have mild residual limitation of activity (class II), but none has had congestive heart failure or syncope postoperatively, and only one experiences significant angina. Left heart catheterization has been performed on one or more occasions after operation in all 21 patients. In 19, no systolic pressure gradient was evident within the left ventricle under resting conditions, and in the other two patients, gradients of 11 and 8 mm Hg were recorded. The left ventricular end-diastolic pressure was lower in 16 of the 17 patients in whom it was abnormally elevated preoperatively, and in nine of them it was normal. The pulmonary arterial pressure was normal postoperatively in all patients who had severe pulmonary hypertension.