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

Abstract

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 in- terrupted 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.THE ELECTROCARDIOGRAPHIC PATTERN of right bundle branch block (RBBB) appears frequently after open heart surgery for correction of congenital malformations.This RBBB pattern often results from disruption of the right ventricular specialized conduction system during right ventriculotomy or infundibular resection,1-3 but may also occur after transatrial repair of ventricular septal defects in which neither right ventriculotomy nor in- fundibular resection is performed.4-6It has therefore been postulated that the postoperative RBBB pattern may be produced by conduction block at any of several sites along the course of the bundle of His or right bundle branch (RBB).27The present study was performed to identify the sites of block and consequent patterns of ventricular activation during RBBB produced during repair of congenital cardiac defects. Materials and MethodsTwenty patients who underwent total repair of either tetralogy of Fallot (12 patients), ventricular septal defect (three patients), complete atrioventricular (AV) canal (three patients) or double outlet right ven- tricle (two patients) were studied during cardiac sur- From the Cardiovascular Section, Departments of Medicine and