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

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Abstract
Postoperative right bundle branch block (RBBB) may be produced by conduction block at any of several sites. 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 8 patients right bundle branch (RBBB) 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 5 patients RBB conduction was interrupted distally in the area of the moderator band. RV activation in these patients was delayed at most sites but the apical septal sites were activated normally. In 7 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. At least 3 distinct types of postoperative RBBB exist and can be identified by differences in RV activation.