[Proceedings: Right bundle-branch block without a wide split of the 2nd sound]

In a series of 38 complete right bundle branch blocks (RBBB) (17 "idiopathic" and 21 cardiopathies), auscultation and phonocardiograms disclosed a normal split second heart sound (S2 = A2-P2 less than or equal to 0.045 sec) in 27 and a wide split S2 (A2-P2 greater than or equal to 0.06 sec) in only 11 cases. Analysis of the initial and terminal vectors constructed from ECGs recorded at 250 mm/sec shows no valid correlation between a transseptal mode of depolarization of the right ventricle and the presence of either a normal or wide split of the 2nd heart sound. A review of the mechanisms generating the 2nd sound and discussion of the additional factors which may influence the duration of A2-P2 in RBBB (start of activation, length and quality of right ventricular systole, impedance of pulmonary arterial bed, possible delay of 2nd aortic sound) explain why wide splitting of the 2nd sound in RBBB is the exception rather than the rule.