The contribution of tricuspid valve closure to the first heart sound. An intracardiac micromanometer study.

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Abstract
The sound-pressure correlates of the second high frequency component of a split first heart sound (S1) were investigated in 27 patients. An external phonocardiogram was recorded with high fidelity sound and pressure from the left and right atria in 21 patients, from the pulmonary artery in 14 of these, and from the central aorta in 11. In the remaining six patients, high fidelity recordings from the central aorta and right-sided chambers were obtained with an external phonocardiogram. The external component of S1 that coincided with a left atrial C wave and "internal sound" was defined as M1. In those cases where the left atrial pressure was not recorded, this component could be identified by a low frequency transient in the central aortic pressure trace. The other external high frequency component of S1 that was synchronous with a separate right atrial C wave and "internal sound" was defined as T1; with two exceptions, M1 preceded T1. The two exceptions which caused reversal of this order, so that T1 preceded M1, were due to chronic left bundle branch block and mitral stenosis. In both cases, T1 was shown to be distinctly separated from the upstroke of pressure rise in the central aorta. This finding was also demonstrated in three cases of right bundle branch block and one case with aortic valvular disease. The usual asynchrony of ventricular contraction was altered by induction of ventricular premature systoles; the separation of externally identifiable M1 and T1 components and their internal markers was predictably altered by this maneuver. The occurrence of T1 was variable in relation to the upstroke of the pulmonary artery pressure, which suggests that it is not related to pulmonic ejection. It is concluded that micromanometrically recorded right and left atrial C waves can serve as markers for externally recordable M1 and T1 components of the first heart sound. In addition, T1 is frequently an externally recordable and audible event.