Isometric Cardiac Contraction

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Abstract
The bizarre septal architecture of idiopathic hypertrophic subaortic stenosis (IHSS) may be secondary to a small systolic cavity with late systolic isometric contraction. We examined ventricular muscle for IHSS-type muscle-fiber disarray in infant hearts in which isometric contraction would occur during development — namely, pulmonary or aortic-valve atresia with intact ventricular septum and normal atrioventricular valves. Fifteen patients with aortic atresia and 10 with pulmonary atresia were compared to 25 normal controls of matched age and heart weight. Aortic atresia showed disorganization of muscle-fiber alignment of left ventricle, particularly septum, and intramural coronary-artery changes virtually identical to IHSS. Pulmonic atresia had similar right ventricular disarray and vessel changes, again most marked in the septum. Thus, cardiac muscle-cell disorientation similar to IHSS occurs in infant ventricles with out-flow-tract obstruction. This IHSS-type myocardial-fiber disarray may result from altered wall stresses related to isometric systolic contraction. (N Engl J Med 296:135–139, 1977)