Complete right bundle branch block and acute myocardial infarction an ominous sign.

Complete right bundle branch block associated with a normal QRS axis and a normal PR interval was observed in 2.8 percent of 500 consecutive acute myocardial infarction patients admitted to the coronary care unit of a community teaching hospital. This experience and a review of the literature reveals that this unifascicular block complicating acute myocardial infarction is typically associated with (1) an elderly patient population, (2) a hospital mortality rate in excess of 50 percent, and (3) a "new" onset complete right bundle branch block which carries a higher mortality than when this electrocardiographic pattern preexists the acute infarction.