The first heart sound in atrial septal defect with reference to atrioventricular valve motion and hemodynamics.

To clarify the characteristics of the first heart sound in atrial septal defect (ASD) and its pathophysiological basis, 17 patients with ASD associated with incomplete right bundle branch block (IRBBB) and 7 with isolated IRBBB were studied using phonoechocardiography and Doppler echocardiography. Fifteen of the 17 ASD patients also were studied following surgical closure of the defect. Indices were compared among the preoperative ASD, postoperative ASD, and IRBBB groups including: P-Q intervals, loudness of the mitral and tricuspid component of the first heart sound (IM, IT), end-diastolic closing excursions of the mitral and tricuspid valves (Mx, Tx), and mitral and tricuspid inflow velocities during early diastole and atrial contraction. There were no significant differences in the P-Q intervals among these 3 groups. IM was attenuated, and IT was accentuated in ASD compared with IRBBB. Postoperatively, IM was augmented in all but 1 patient and IT was attenuated in all patients. Mx was significantly smaller, and Tx was significantly larger in ASD than in IRBBB. Postoperatively, Mx was significantly increased and Tx was significantly reduced; the maximal mitral inflow velocity during atrial contraction was increased while the maximal tricuspid inflow velocity was significantly reduced. Thus, the first heart sound in ASD is characterized by an attenuated mitral component and an accentuated tricuspid component. Hemodynamic alterations and consequent changes in closing energies of the atrioventricular valves probably account for these features.