Idiopathic hypertrophic subaortic stenosis and ventricular preexcitation.

Two patients who had idiopathic hypertrophic subaortic stenosis (IHSS) and type A ventricular preexcitation were studied and showed variations of the subvalvular flow gradients. The increase in subvalvular gradient, occurring at a time when preexcitation developed, was associated with significant increase of the systolic murmur and the systolic anterior motion of the mitral valve. In patient 1, the significant increase in subvalvular gradient during ventricular preexcitation was also confirmed by catheterization of the left side of the heart. The increase of the gradient with the development of the ventricular preexcitation was apparently due to decreased end-diastolic volume. The importance of ventricular volume considered as a variable affecting outflow tract gradient in idopathic hypertrophic subaortic stenosis is emphasized.