Exercise performance after septal myotomy and myectomy in patients with obstructive hypertrophic cardiomyopathy.

The effect of left ventriculomyotomy and myectomy on exercise capacity and cardiac function in patients with obstructive hypertrophic cardiomyopathy has not previously been determined. In this study, 29 patients were evaluated during graded treadmill exercise before and after operation. Postoperatively, 27 of 29 patients reported symptomatic improvement and had greatly reduced left ventricular outflow gradient. Twenty-five of 28 patients (89 percent) attained higher exercise levels after operation, and this was accompanied by an increase in total body oxygen consumption from 16 to 21 ml/min per kg (P less than 0.005). A significant increase in cardiac index during maximal exercise also accompanied this improved exercise performance (5.0 to 5.7 liters/min per m2, P less than 0.05). The increase in maximal cardiac index was associated with greater desaturation of mixed venous blood (34 to 24 percent, P less than 0.02) in patients with preoperative angina. At a given level of mixed venous oxygen saturation (30 percent), overall mean cardiac index was higher postoperatively (4.6 to 5.2 liters/min per m2, P less than 0.05). These results suggest that, although several mechanisms probably contribute to symptomatic improvement after myotomy and myectomy, enhanced cardiac performance plays an important role in the majority of patients.