First heart sound in atrial septal defect.

This is a retrospective study of 25 patients with secundum-type of ASD, confirmed by catheterization and angiocardiography. As controls, 25 normal subjects of matching age were studied. The phonocardiograms and carotid pulses of the 2 groups were recorded and compared. Special attention was paid to the interval between the 2 main components (Ia and Ib) of the first heart sound, to the amplitude of both Ia and Ib, and to the relationship between carotid upstroke and first heart sound. All intervals between sound components of the patients with ASD were found similar to those of the controls. No increase in amplitude of Ib could be documented. The amplitude of the first heart sound relative to that of the second sound (measured from the ratio I/IIA) was similar to that of the controls, Finally, a slight precedence of aortic valve opening (obtained from the carotid upstroke time minus transmission time) over the second component of the first sound (Ib) was found both in ASD and in controls. In view of these facts, a tricuspid contribution to the mechanism of the b component of the first heart sound appears highly unlikely. On the other hand, this component seems closely related to the dynamic events (blood acceleration and walls deceleration in the aortic root) that follow the aortic valve opening.