Postoperative right bundle branch block: identification of three levels of block.

It has been postulated that postoperative right bundle branch block (RBBB) may be produced by conduction block at any of several sites. In this study the site of block and resultant pattern of ventricular activation were documented in 20 patients in whom RBBB developed during repair of congenital cardiac defects. Intraoperative epicardial and endocardial mapping and recording from the right ventricular specialized conduction system were performed before and after repair in each patient. In eight patients right bundle branch (RBB) conduction was interrupted proximally in the area of the ventricular septal defect. Right ventricular (RV) activation in these patients was delayed at all sites. In five patients RBB conduction was interrupted distally in the area of the moderator band. RV activation in these patients was delayed at most sites; however, the apical septal sites were activated normally. In seven patients, RBB conduction was interrupted terminally in the area of the terminal fascicular network. In these patients RV activation was delayed only in basilar areas. We conclude that at least three distinct types of postoperative RBBB exist and can be identified by differences in RV activation.