A phonocardiographic study of right bundle branch block, with special reference to the second heart sound.

The second heart sounds in 29 cases with right bundle branch block, mainly surgically induced, were studied. Three general types of the second sound were classified. Eleven cases revealed wide splitting of the second sound (0.05 sec. or more), and 14 cases showed narrow splitting less than 0.05 sec.), while 4 cases showed a single 2nd heart sound throughout the respiratory cycle. Ten cases revealed a respiratory change in the splitting, and 14 cases showed fixed splitting. The cases with a widely split 2nd sound revealed fixed splitting except in 2 cases. Among the cases with narrow splitting, 8 cases (57%) showed respiratory change. All cases with a QRS duration of 0.14 sec. or more revealed fixed splitting. A Valsalva maneuver was performed in 18 cases with RBBB. Five cases showed a widening of the split 2nd sound immediately following the release of Valsalva maneuver and then the IIA-IIP interval decreased, but in only 2 cases did the IIA-IIP interval merge into single sound. In 13 cases the IIA-IIP interval remained unchanged throughout the Valsalva maneuver. No correlation was found between splitting of the second heart sound and the type of vectorcardiogram in RBBB. The mechanism of these observations was discussed.