Th first degree atrioventricular block occurred in 65 cases, and second degree atrioventricular block with Wenckebach periodicity in 13. There were 9 cases of third degree atrioventricular block with nomal QRS complexes causing Adams-Stokes attacks which represented 2.9% of all conduction disturbances. It occurred equally in both sexes and predominantly after 6th decade of life.

There were 99 cases of complete right bundle branch block(RBBB) and 12 cases of complete left bundle branch block(LBBB). The latter were mainly associated with significant heart diseases.

As for the intraventricular conduction defects other than the simple bundle branch blocks, the findings were as follows;

1. Simple hemiblocks were found in 92 cases or 0.73% of total series and 29.3% of all conduction disturbances. Left anterior hemiblock(LAH) occurred 3 times more frequently than left posterior hemiblock(LPH).

2. Partial bilateral bundle branch block(BBBB) were found in 25 cases representing 0.2% of the total series and 8.0% of all conduction disturbances. Among the 25 cases of BBB, 11 had RBBB plus LAH, 10 RBBB plus LPH, 1 LBBB plus first degree A-V block, and 3 LBBB of diphtheritic cardic involvement. Trifascicular heart block causing Adams-Stokes attacks occurred in 9 of the 25 cases resulting in death in 7 cases. The underlying diseases were ischemic heart disease, hypertensive heart disease, congenital heart disease and diphtheritic carditis.

This report represents the first electrocardiographical documentation of occurrence of trifascicular heart block progressing from BBBB in Korea.