Echocardiographic observations on the mechanism of production of the second heart sound.

This investigation was designed to determine the echocardiographic correlates of the aortic and pulmonary components of the second heart sound. Simultaneous recordings of the ECG, phonocardiogram, carotid pulse tracing and the echocardiogram of the aortic valve were made in 54 patients. The tracings were recorded at a paper speed of 100 mm/sec, with 20 msec time lines. Aortic valve closure (AVC) on the echocardiogram occurred before the onset of the aortic component of the second heart sound (A2) in all but two patients. The mean AVC-to-A2 interval was 12 msec with a range of 5 to 25 msec. Simultaneous recordings of the pulmonary valve echocardiogram, ECG, phonocardiogram and carotid pulse tracing were made in 14 patients. Pulmonary valve closure (PVC) on the echocardiogram preceded the pulmonary component of the second sound (P2) in all patients. The mean PVC-2 interval was 60 msec with a range of 30 to 75 msec. We conclude that aortic valve closure and pulmonary valve closure are not directly responsible for the genesis of the second heart sound (S2). These observations are consonant with the theory that S2 is caused by deceleration of columns of blood resulting from semilunar valve closure, throwing the cardiohemic system into vibration.