Abstract 4865: The Amplitude Ratio of the First to Second Heart Sound Mirrors Left Ventricular Systolic Function
Background: In animal studies, the amplitude of the mitral component of the first heart sound (S1) is proportional to the rate of left ventricular pressure rise (dP/dt). To develop a clinical application for this property, we tested the hypothesis that the relative amplitudes of S1 and S2 (aortic component of second heart sound) represent left ventricular dP/dt and ejection fraction (EF) in humans.
Methods: Phono-electrocardiographic recordings using a digital hand-held device (HD Medical Group Ltd) followed by an echocardiogram were performed within two hours of a clinically indicated cardiac catheterization. Left ventricular dP/dt was estimated by intracardiac manometer or Doppler echocardiogram, left ventricular EF was measured by biplane 2D. The largest positive to negative deflections of the first and second heart sound components were defined as S1 and S2. The ratios of S1 to S2 (S1/S2) were obtained from the right upper sternal border (RUSB), left upper sternal border (LUSB) and apical area. Normal EF and dP/dt were defined as ≥ 55% and ≥ 1000 mmHg/s respectively.
Results: We studied 61 patients with dP/dt ranging from 400 to 2850 mmHg/sec, EF ranging from 11 to 78 %. Body mass index, P-R interval, pulmonary or systemic blood pressure were not different between the normal and reduced EF or dP/dt groups. Compared with the group with reduced dP/dt or EF, the median S1/S2 at LUSB and RUSB were significantly higher in those with normal dP/dt (1.52 vs 0.78 for LUSB; 1.31 vs 0.75 for RUSB, p<0.05) or EF (1.44 vs 0.95 for LUSB; 1.65 vs 0.83 for RUBS, p<0.05). On receiver operating curve analysis, S1/S2 at LUSB and RUSB, had significant discriminative values for detecting normal dP/dt (AUC = 0.82 for LUSB, 0.74 for RUSB) and EF (AUC = 0.72 for LUSB, 0.68 for RUSB). The sensitivity and specificity of S1/S2 ≥1 for detecting normal left ventricular systolic function (normal dP/dt or EF) were 72– 80% and 57–71% respectively.
Conclusion: This study demonstrated that S1, corrected for S2, mirrors left ventricular systolic function. A ratio of S1 to S2 of ≥1 is a useful indicator of normal left ventricular systolic function defined by dP/dt ≥1000 mmHg/s or EF ≥55%. Digital phonocardiography appears promising as an adjunctive bed-side tool for assessing left ventricular systolic function.