Catenoid shape of the interventricular septum: possible cause of idiopathic hypertrophic subaortic stenosis.

Previous studies have shown that asymmetric septal hypertrophy (ASH) may occur in embryonic and malformed hearts and that muscle cell disarray is found in myocardium that contracts isometrically. To account for the characteristic ASH and septal muscle fiber disarray of idiopathic hypertrophic subaortic stenosis (IHSS), we postulated that a catenoid shape of the septum, i.e., net zero curvature, would have the mechanics required to produce IHSS. Accordingly, hearts from eight autopsied patients with IHSS were studied for curvature and thickness of free walls and septum, and they were compared to similar measurements in 80 other hearts. In all eight hearts with IHSS the septum was concave to the left in the transverse plane but convex to the left in the apex-to-base plane. Such a catenoid configuration of the septum was not observed in any of the other 80 hearts. The distinctive shape of the septum in IHSS would account for isometric contraction, since adjacent fiber tracts with opposite curvatures would develop maximum tension but would not have motion. Fiber disarray and local hypertrophy would result from such isometric contraction. Since ventricular configuration is acquired early in cardiogenesis, IHSS might therefore result from a genetic or embryonic determination of a catenoid septum.