Clinical and Anatomic Implications of Intraventricular Conduction Blocks

The electrocardiogram in 480 patients with acute myocardial infarction showed right bundle-branch block (RBBB) with normal QRS axis in 18 patients (3.7%), left bundle-branch block (LBBB) in 31 (8%), RBBB and left anterior hemiblock (LAH) in 23 (4.8%), RBBB and left posterior hemiblock (LPH) in four (1%), LAH alone in 20 (4%), LPH in one (0.2%), and no evidence of intraventricular conduction (I-V) disturbance in 383 (80%). Eighteen of the 97 patients with I-V block showed 10 A-V block, and seven of the 18 (39%) showed abrupt progression to high-grade A-V block, while only six of 79 (8%) without 10 A-V block showed similar progression. Cause of death in patients witlr I-V block was cardiac failure and/or shock in 92%; only three instances of primary asystole occurred. The incidence of complete heart block was higher in the I-V disease group (15%) than in the group without block (5%), but not significantly. Patients with LAH or RBBB and LAH usually had occlusion of the left anterior descending artery with extensive septal infarction, while patients with RBBB or LBBB had a more variable pattern of vessel involvement. Presence of I-V block in patients with acute myocardial infarction implies a hectic clinical course with poor prognosis, but does not justify prophylactic temporary transvenous intracardiac pacing except perhaps in the subgroup with associated 10 A-V block.