The effect of infarct size on atrioventricular and intraventricular conduction disturbances in acute myocardial infarction.

The effect of infarct size estimated from serial CK-MB isoenzyme determinations on the incidence of atrioventricular and intraventricular conduction disturbances was examined in 250 patients suffering their first myocardial infarction. The size of the infarct was significantly greater (P less than 0.001) in 72 patients with conduction disturbances than in 178 without conduction defects (54 +/- 29 vs. 35 +/- 22 CK-MB gEq). The largest size was observed in 10 patients with bifascicular block (71 +/- 38 CK-MB gEq). Within the group of patients with intraventricular conduction disturbances, the size of the infarct was significantly greater (P less than 0.01) when localized inferiorly rather than anteriorly (91 +/- 10 vs. 58 +/- 27 CK-MB gEq). The size in those patients with complete atrioventricular block and anterior infarction was larger than in those with an inferior lesion (76 +/- 21 vs. 52 +/- 33 CK-MB gEq). The size in those patients with inferior infarction and complete block was significantly greater (P less than 0.05) than in patients with similarly positioned infarction without conduction disturbances (52 +/- 33 vs. 35 +/- 22 CK-MB gEq). There was no significant difference in the size of infarct when inferior infarction was complicated by first- and second-degree block in comparison to those without conduction defects (38 +/- 23 vs. 35 +/- 22 CK-MB gEq). A correlation was observed between the size of infarction and the incidence of conduction disturbances (P less than 0.001); the greater the size the higher the incidence of conduction disturbances.