Morphologic basis for obstruction to right ventricular outflow in hypertrophic cardiomyopathy.

The mechanism by which obstruction to right ventricular (RV) outflow occurs in patients with hypertrophic cardiomyopathy (HC) is not well understood. To clarify this issue, 5 severely symptomatic patients (aged 18 to 55 years, mean 30) with HC and marked subpulmonic obstruction (basal peak systolic pressure gradients 60 to 118 mm Hg) were studied. Four patients also had obstruction to left ventricular outflow (maximal basal or provocable pressure gradient 12 to 110 mm Hg). The RV outflow obstruction in each patient resulted from greatly hypertrophied musculature comprised of crista supraventricularis, moderator band or trabeculae. Operative resection of portions of this muscle resulted in abolition or substantial reduction of the RV outflow gradient (to 0 to 11 mm Hg) in the 3 patients with both pre- and postoperative hemodynamic studies. The left ventricular wall and ventricular septum also were massively thickened (32 to 40 mm) in each patient. These findings support the view that marked RV outflow tract obstruction in patients with HC is due to greatly hypertrophied RV muscle, and that operative resection will relieve the outflow gradients and normalize RV systolic pressure. The muscular RV hypertrophy causing obstruction appeared to constitute a primary and excessive hypertrophic process involving both ventricles.