Idiopathic hypertrophic subaortic stenosis. III. Analysis of the myocardial fibre shortening of the free left ventricular wall by means of geometric models.

Left ventricular cineangiographic data from 4 patients with idiopathic hypertrophic subaortic stenosis (IHSS) and 10 control patients have been analysed by means of geometric models. The myocardial fibre shortening of the free left ventricular wall in IHSS has been compared with the fibre shortening of the left ventricular wall in the control group. During the first half of systole, the fibre shortening occurs equally fast in the two groups, but during the second half it lags clearly behind in the IHSS group. The stroke volume is ejected much faster in the IHSS group and the ejection fraction is much higher. This is caused by several factors related to both functional and anatomic derangements of the left ventricle and the interventriclar septum: (1) A hypertrophic septum contracting isometrically with no persisting concavity away from the left ventricular cavity, acting as a suspender, and the posterior wall encroaching upon the septum in a slit-like manner. (2) Some increase in septal thickness narrowing the ventricular cavity. (3) A hypertrophic nonseptal ventricular wall. (4) A long ventricular cavity relative to the width. (5) A shallow left ventricular cavity. (6) A somewhat smaller EDV than normal.