Pathological Extent of Interventricular Septal Infarction in Patients with Acute Anteroseptal Myocardial Infarction with and without Right Bundle Branch Block.

The purpose of the present study is to elucidate the difference in extent of myocardial infarction (MI) between those cases with and those without right bundle branch block (RBBB) occurring during the course of acute MI. We examined postmortem hearts from 20 patients with acute anteroseptal MI; 10 with (group A) and 10 without RBBB (group B). The extent of MI was studied pathologically in the interventricular septum (IVS) and reconstructed. The longitudinal extent of MI did not distinctly differ between groups A and B. In 5 hearts of group B, the anterior limit of the MI extended as high, or as close to the cardiac base, as in group A hearts. Transmural MI was relatively common and seen more frequently in group A than in group B. However, the MI did not always extend evenly to the left and right ventricular sides in the IVS. Left-sided predominance in extent of the MI was more frequently observed in group B than in group A. Right-sided predominance in the extent of septal MI was relatively rare and was seen in 5 cases at the portion where the right bundle branch came down. Four of these were group A patients. Thus, involvement of the right bundle branch might partly depend on the unevenness of the mural extent of the MI as well as the height of extension of the MI in the IVS.