The physiologic third heart sound: Its mechanism and relation to protodiastolic gallop

Abstract

The third heart sound (S3) is thought to be caused by the abrupt deceleration of left ventricular (LV) inflow during early diastole, increased LV filling pressures, and decreased LV compliance. We sought to determine whether the ratio of early mitral inflow velocity to diastolic velocity of the mitral annulus (E/E’) could confirm the proposed mechanism of the S3.A total of 90 subjects underwent phonocardiography, echocardiography, tissue Doppler imaging, and left-sided heart catheterization.Phonocardiography detected an S3 in 21 patients (23%). Subjects with an S3 had lower ejection fraction (P = .0006) and increased E deceleration rate (P < .0001), E/E’ (P < .0001) and filling pressures (P < .0001). The phonocardiographic S3 confidence score correlated with E/E’ (r = 0.46; P < .0001) and E deceleration rate (r = 0.43, P = .0001). Of the echocardiographic variables, only E/E’ was independently associated with the S3 confidence score (P = .009), independently of invasively determined LV filling pressures (P = .001).The most important determinants of the pathologic S3 are an increased deceleration rate of early mitral inflow, elevated LV filling pressures, and abnormal compliance of the myocardium as measured by tissue Doppler imaging.