Usefulness of the signal-averaged electrocardiogram for evaluating the block site of right bundle branch block following surgical correction of a congenital heart disease.

It is important to distinguish proximal right bundle branch block (RBBB) from distal RBBB because patients with both proximal RBBB and left bundle branch block may progress to a late atrioventricular conduction disturbance. Signal-averaged electrocardiograms (SAECGs) were investigated in 35 patients with RBBB following surgical correction of tetralogy of Fallot or ventricular septal defect in order to determine the block site of RBBB noninvasively using a SAECG. The site of RBBB was first identified by a body surface map; 12 patients had proximal RBBB (group 1), and 23 had distal RBBB (group 2). The control groups consisted of 8 patients with RBBB without congenital heart disease (group 3) and 20 normal subjects (group 4). The mean of the filtered QRS duration in the group 1 patients was significantly longer than in the other 3 groups (p < 0.01). The number of fragmented signals in group 1 was significantly greater than that in the other 3 groups (p < 0.01). A filtered QRS pattern was divided into 4 different types (whole, early, late, and normal) according to the successive fragmented signals; the "whole" type was the most common in group 1 (83%). SAECG is successful in identifying those patients with proximal RBBB according to the following indices: a filtered QRS duration equal to or longer than 160 msec, a fragmented signal number greater than 10 and a "whole" type filtered QRS pattern. In conclusion, SAECG is a useful tool for distinguishing proximal RBBB from distal RBBB.