Histopathology of heart block complicating acute myocardial infarction. Correlation with the His bundle electrogram

Histopathological studies of the conduction system were related to His bundle electrogram recordings in seven patients with acute myocardial infarction and atrioventricular (A-V) conduction disturbances. The three patients with inferior infarctions had normal width QRS complexes and delay or block of the impulses above the His bundle. Recent ischemic changes were present in the A-V node in two cases and in the distal conduction system in all three cases. In the four patients with antero-septal infarction and right bundle branch block (RBBB), either the H-V interval was prolonged or block was present below the H spike. The A-H interval was normal in each of these cases, and the A-V node was not affected by the recent infarction. The right bundle branch was involved in all four of these cases and two patients also had involvement of the left bundle branch. In general there was a good correlation between the sites of heart block as defined by the His bundle electrogram and the histopathological analysis of the cardiac conduction system.