Atrioventricular Block in Acute Myocardial Infarction

¹ Field Epidemiology Research Section, National Heart and Lung Institue, National Institutes of Health, Bethesda; Holy Cross Hospital of Silver Spring, Maryland

One hundred thirty-four patients with acute myocardial infarction complicated by various degrees of A-V block are presented. First degree block was seen in 11.8 percent of all myocardial infarction patients; one-third of these—many with a P-R interval of 0.24 seconds or more—progressed to a higher level of block. Those with first degree block only had an equal incidence of anterior and inferior sites of infarction; block often persisted throughout the hospital course and the mortality rate was 18.3 percent, which did not differ from that of nonblock patients. Some myocardial infarction patients (4.8 percent) demonstrated second-degree block. Those who did not progress had a mortality rate of 41.4 percent. Not uncommonly, this block was associated with congestive heart failure, hypotension or digitalis toxicity. Onset of block tended to be delayed until the third hospital day, possibly because of the development of digitalis toxicity. Inferior myocardial infarction was more common than anterior. Type I block (Wenckebach) occurred much more frequently than type II. Complete heart block occurred in 45 (5.9 percent) of myocardial infarction patients with a mortality rate of 64.4 percent. Fifty-three percent of the patients were in shock at the time complete block was discovered. Onset of block and death were early phenomena and duration was brief. Eight of the 45 had anterior myocardial infarction, but only one survived.