Intraoperative, intracardiac echocardiography during left ventriculomyotomy and myectomy for hypertrophic subaortic stenosis.

In 15 patients undergoing left ventriculomyotomy and myectomy for idiopathic hypertrophic subaortic stenosis (IHSS), the thickness of the interventricular septum was measured before and after muscle resection by means of a modified sternal-notch pediatric ultrasound transducer. Preoperative and intraoperative measurements by echogram were highly correlated (r = 0.92, P = 0.6), and accurately predicted the dimensions of the excised bar of muscle (r = 0.98, P = 0.6). The mean depth of the trough created at operation was 9.7 +/- 0.8 mm, and the mean thickness of the septum remaining was 14.3 +/- 0.9 mm. When studied 6 months postoperatively, all surviving patients were functionally improved, and none had a pressure gradient when studied in the resting state. However, two-thirds of the patients had residual provocable gradients (decreased by 70% from those preoperatively). Intraoperative echogram measurements failed to correlate with the presence or extent of the postoperative provocable gradients. Intraoperative echocardiography provides imaging of dimensions otherwise unavailable, and may help define the characteristics of the myectomy that result in uniform symptomatic and hemodynamic benefit.