Factors influencing changes in the signal-averaged electrocardiogram within the first year after a first myocardial infarction

One hundred twenty-nine patients were prospectively studied after a first myocardial infarction. A first signal-averaged electrocardiogram (SAECG-1) was performed in the acute phase (within 48 hours after onset of symptoms) and a second one (SAECG-2) in the late phase (6 to 18 months after hospital discharge). We studied the influence of nine parameters on the evolution of the signal-averaged electrocardiogram: age, gender, myocardial infarction location, number of diseased coronary vessels, infarct-related coronary artery patency, use of thrombolytic therapy or percutaneous transluminal coronary angioplasty in the acute phase, left ventricular ejection fraction, and recurrence of ischemic events. No follow-up data were available in 15 patients. Of the remaining 114 patients, an ischemic event occurred in 25 (22%). The signal-averaged electrocardiogram remained unchanged in 97 (85%) (remaining normal in 78 and abnormal in 19). It became abnormal in 13 (11.5%) and became normal in 4 (3.5%). In patients with a normal SAECG-1, two factors were associated with the change to an abnormal SAECG-2: (1) an ischemic event occurred in 11 (85%) of 13 patients whose SAECG-2 was abnormal compared with only 13 (17%) of 78 patients whose SAECG-2 remained normal (p < 0.0001), and (2) 100% of patients with an abnormal SAECG-2 had an inferior myocardial infarction compared with 54% of patients with a normal SAECG-2 (p = 0.004). In conclusion, our findings suggest that in the setting of myocardial infarction, changes from an early (6 months) abnormal signal-averaged electrocardiogram is highly indicative of recurrences of ischemic events and an inferior location of the myocardial infarction.