Effects of late (1 to 30 days) reperfusion after acute myocardial infarction on the signal-averaged electrocardiogram

Early reperfusion (4 to 6 hours) after acute myocardial infarction reduces mortality and reduces the incidence of late potentials on a signal-averaged electrocardiogram (SAECG). Recent reports suggest that reperfusion accomplished after >6 hours also may reduce mortality. The effect of such later reperfusion on the SAECG is not known. We hypothesized that reperfusion by angioplasty accomplished >24 hours after onset of infarction would reduce late potentials and improve the parameters on the SAECG. Forty-one patients with a totally occluded infarct-related artery 12 ± 8 days after infarction underwent attempted angioplasty. SAECG, echocardiography and thallium-201 imaging were performed before and 1 month after attempted angioplasty. Angioplasty resulted in successful reperfusion in 32 patients and was unsuccessful in 9. No change in the incidence of late potentials occurred after successful reperfusion (13 of 32 patients before and 13 of 32 patients 1 month later) or after unsuccessful reperfusion (6 of 9 patients before and 5 of 9 patients 1 month later). Among patients with successful reperfusion, no significant change occurred in the QRS duration or the terminal signal duration <40 μV. The terminal root-mean-square voltage in microvolts improved significantly at 1 month (31 ± 25 before to 38 ± 29 after, p = 0.004). Twenty-two of 32 patients with successful reperfusion had improved wall motion in the infarct zone at 1 month. Despite an improvement in function in these patients, no change in the incidence of late potentials occurred by 1 month. Among patients with successful reperfusion, those without late potentials at baseline had improved wall motion to a greater extent than those with late potentials (change in wall motion score, 1.5 ± 0.9 vs 0.6 ± 0.8, p = 0.009). It is concluded that late reperfusion after acute myocardial infarction has little effect on the SAECG, and a normal SAECG in patients with a totally occluded artery after infarction may signify the presence of viable myocardium.