A prolonged A-H interval suggested A-V nodal involvement. 2) A prolonged duration of the His potential suggested moderate His bundle involvement. 3) Complete block distal to H appeared to reflect total disruption of both bundle branches. 4) The lesion at the penetrating portion of the His bundle could be responsible for A-H block. 5) A-H block occurred in a case of cellular infiltration in the A-V node and the His bundle, in which bilateral bundle branch showed severe fibrosis. 6) A combination of right bundle branch block, marked left axis deviation and H-V prolongation suggested trifascicular disease. 7) In case 6, there was a severe pathologic lesion at the origin of the left bundle branch, yet left bundle branch block was not indicated electrocardiographically. This study revealed a close correlation between electrophysiologic and pathologic findings in 4 out of 6 cases.
