Conduction disturbances in acute myocardial infarction: incidence, site-wise relationship and the influence on in-hospital prognosis.

The study was designed to assess the incidence of conduction disturbances, the relationship of the site of infarction with the type of conduction disturbances and the influence of conduction disturbances on the in-hospital prognosis. One hundred consecutive patients (M:F = 89:11) with a age range of 35-60 years with the history of first attack of acute myocardial infarction were included in the study. There were 45 anterior, 43 inferior and 12 combined anterior and inferior myocardial infarction patients. 44 of the patients had some type of conduction disturbances (Group A) and 56 had none (Group B). Inferior myocardial infarction patients showed higher incidence of conduction disturbances than anterior myocardial infarction (56.8% and 31.8% respectively) (Odd's ratio 2.98, 95% ci 1.14 to 7.9). Conduction disturbances were mostly (92%) atrio-ventricular in inferior myocardial infarction and mostly (72%) intraventricular in anterior myocardial infarction. Of the 13 cases of complete atrioventricular block, 8 had inferior, 2 anterior and 3 combined anterior and inferior infarction. In inferior infarction, complete atrioventricular block developed gradually through 1 degree and 2 degrees atrioventricular block but in the anterior infarction it developed suddenly. Patients with conduction disturbances developed more complications (84%) than those without conduction disturbances (54%). Mortality rate was higher in Group A (25%) than in Group B (3.6%) (Odd's ratio 9.0, 95% ci 1.76 to 86.73) with a overall rate of 13%. Mortality rate was higher in anterior myocardial infarction (50%) than in inferior myocardial infarction (25%) when complicated by complete atrioventricular block. It was concluded that conduction disturbances are predominantly atrioventricular in inferior and intra-ventricular in anterior MI; conduction disturbances are associated with increased risk of complications and death. Anterior location of MI may have an independent risk attribute.