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 fi rst 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 mo nths after hospital discharge). We studied the influence of nine param eters on the evolution of the signal-averaged electrocardiogram: age, gender, myocardial infarction location, number of diseased coronary ve ssels, infarct-related coronary artery patency, use of thrombolytic th erapy or percutaneous transluminal coronary angioplasty in the acute p hase, left ventricular ejection fraction, and recurrence of ischemic e vents. No follow-up data were available in 15 patients. Of the remaini ng 114 patients, an ischemic event occurred in 25 (22%). The signal-av eraged electrocardiogram remained unchanged in 97 (85%) (remaining nor mal in 78 and abnormal in 19). It became abnormal in 13 (11.5%) and be came normal in 4 (3.5%). In patients with a normal SAECG-1, two factor s were associated with the change to an abnormal SAECG-2: (1) an ische mic event occurred in 11 (85%) of 13 patients whose SAECG-2 was abnorm al compared with only 13 (17%) of 78 patients whose SAECG-2 remained n ormal (p < 0.0001), and (2) 100% of patients with an abnormal SAECG-2 had an inferior myocardial infarction compared with 54% of patients wi th a normal SAECG-2 (p = 0.004). In conclusion, our findings suggest t hat in the setting of myocardial infarction, changes from an early (<4 8 hours) normal to a late (>6 months) abnormal signal-averaged electro cardiogram is highly indicative of recurrences of ischemic events and an inferior location of the myocardial infarction.