Atrioventricular block in acute inferior wall myocardial infarction: harbinger of associated obstruction of the left anterior descending coronary artery.

In a prospective study 51 consecutive patients who survived the acute phase of inferior wall myocardial infarction underwent coronary arteriography. Eleven patients developed some degree of atrioventricular (AV) block in the acute phase of infarction that disappeared within a few days and was considered by electrocardiographic analysis to be located in the AV node. Patients with AV block during acute myocardial infarction had a significantly higher prevalence of left anterior descending coronary artery obstruction (91 versus 55%, p less than 0.05) than did patients without AV block and the obstruction preceded the exit of the first septal perforator branch in 73% of cases with heart block and in 30% of cases without block (p less than 0.01). The sensitivity, specificity and predictive values were 31, 95 and 91%, respectively, for the existence of left anterior descending coronary artery obstruction when AV block occurred during acute inferior myocardial infarction, and 40, 90 and 73%, respectively, for the occurrence of the coronary artery obstruction before the exit of the first septal perforator branch. Patients with inferior myocardial infarction and left anterior descending coronary artery obstruction have a sixfold greater chance of developing heart block in the acute phase of infarction than do patients with inferior infarction without such obstruction (p less than 0.05). These findings also support the observations that the proximal AV conduction system usually has a dual arterial blood supply from both the right and left anterior descending coronary arteries, and may explain the transient behavior of heart block and lack of necrosis of the AV node seen in these patients.