[Changes in high amplification ECG during the 2 years following the acute phase of myocardial infarction]

Late potentials have been reported 1 to 15 days after the onset of myocardial infarction but the evolution during long-term follow-up is not so well known. In order to determine if the signal averaged electrocardiogram remained stable or if it was necessary to repeat the investigation during a period of 2 years, 90 patients underwent 2 recordings on average 3 weeks after the onset of the infarct and then 2 years later. After the first recording, 16 patients (18%) had late potentials. The second recording was performed under the same conditions by the same operator. Globally, the signal averaged electrocardiogram recorded by Simson's method remained remarkably stable (83/90). It was rare to observe late potentials occurring for the first time after the initial recording (4 cases, 5%) in this study. It was more common to observe their disappearance (3 cases, 19%). No explanation could be found except in one case. These possible long-term changes in the signal averaged electrocardiogram suggest that the investigation should only be repeated in patients with abnormalities on the initial recording. Some authors have reported a better prognosis in patients in whom late potentials disappeared but this was not verified in this study.