The "sigmoid septum". Variation in the contour of the left ventricular outt.

Fifty human hearts were studied for the shape of the left ventricular septum. In certain normal hearts, the base of the ventricular septum may bulge prominently into the outflow tract of the left ventricle. Such hearts have been referred to as having a sigmoid ventricular septum. It was shown that the sigmoid septum of some degree occurred in 24 of 44 apparently normal hearts from adults. The incidence of sigmoid septum increases with age. Classically, hearts with sigmoid septum are not hypertrophied.It is postulated that the condition develops as the result of physiologic decreases in cardiac output which occurs in aging people. This decrease in output leads, in turn, to a shrinking of the left ventricular cavity. The sigmoid septum probably does not result in obstruction to the outflow tract of the left ventricle but, because of its close relationship to the mitral valve, may become obstructive when the mitral valve is replaced by an artificial ball valve.