Electrophysiologic and Pathologic Correlations in Two Cases of Chronic

This study concerns two cases of chronic 20 atrioventricular (A-V) block with left bundle branch block (LBBB). Pathological studies included serial section of the conduction systems. Case 1 had type I 20 block with LBBB. Electrophysiological studies revealed type I 20 block proximal to the His bundle recording site and a prolonged H-V interval (60 msec). Pathologically there was a moderate to marked fibrosis of the ap-proaches to the A-V node and of the A-V node, marked fibrosis of the left bundle branch, and moderate in-volvement of the right bundle branch. The changes proximal to the His bundle were more marked than the changes distal to this bundle. Case 2 had type II and 2:1 20 A-V block with LBBB. Electrophysiologically the site of block was distal to the His bundle recording site, and there was a prolonged A-H interval (145 msec). Pathologically there was marked fibrosis of the A-V node and severe involvement of both bundle branches. The changes distal to the His bundle were more severe than the changes proximal to the His bun-dle. This study reveals that the electrophysiologic data more closely approximated the pathologic findings than did surface electrocardiographic data alone. It also emphasizes that there may be multiple sites of dis-ease in chronic 20 block with bundle branch block. RECENT STUDIES from our laboratories hav