Catenoidal shape of the interventricular septum in idiopathic hypertrophic subaortic stenosis: Two dimensional echocardiographic confirmation

A catenoid is a curved surface with the property of net zero curvature at all points. Morphologic observations have suggested that the interventricular septum in idiopathic hypertrophic subaortic stenosis has a catenoid shape, (that is, concave to the left in the transverse plane and convex to the left in the sagittal plane). To determine if such a septal configuration is present in living patients, six patients with clinically diagnosed idiopathic hypertrophic subaortic stenosis were studied with phased array two dimensional echocardiography, and left ventricular wall segment curvature, thickness and motion were compared with values in six patients with left ventricular hypertrophy secondary to long-standing systemic hypertension, and in six normal subjects. A curvature thickness index was determined from the echocardiographic image for systole and diastole as: curvature thickness index equals segment thickness times the sum of curvatures in the transverse and sagittal planes. In all six patients with idiopathic hypertrophic subaortic stenosis the septum had a catenoidal configuration and showed significantly less (p < 0.05) septal change in the curvature thickness index during the cardiac cycle than it did in the control groups. In contrast, the left ventricular free wall had significantly greater (p < 0.05) change of curvature thickness index over the cardiac cycle in patients with idiopathic hypertrophic subaortic stenosis. The hyperkinetic free wall motion seemed to account in part for systolic anterior motion of the anterior mitral leaflet as part of the displacement of the entire mitral apparatus. The catenoid shape of the septum observed in idiopathic hypertrophic subaortic stenosis may account for asymmetric hypertrophy and septal immobility, because a ventricular segment with net zero curvature would develop internal tension but have isometric contraction.