The amplitude ratio of the first to second heart sound is reduced in left ventricular systolic dysfunction.

In animal studies, the amplitude of the first heart sound (S1) is proportional to the rate of left ventricular pressure rise (LV dP/dt). To develop a clinical application for this property, we performed phono-electrocardiographic recordings using a digital hand-held device followed by an echocardiogram within 2 hours of a clinically indicated cardiac catheterization. Compared with the group with reduced dP/dt (<1000 mm Hg/s) or ejection fraction (EF) (<55%), the median S1/S2 detected at the cardiac base was higher in those with normal dP/dt or EF. On ROC analysis, S1/S2 significantly discriminated normal from reduced dP/dt and EF. This study demonstrated that S1, corrected for S2, is decreased in patients with impaired LV systolic function. Digital phonocardiography appears promising as an adjunctive bedside tool for evaluating left ventricular systolic function.