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To study the dynamics of signal-averaged ECG and late potentials (LP) in the first month of myocardial infarction (MI) and the impact of coronary reperfusion on them, examinations were made of 98 patients with primary myocardial infarction, in 69 of whom coronary reperfusion was achieved. LP was found to be detectable just in the first hours of MI, their stabilization (steady-state appearance or cessation) mainly occurred at day 3 of the onset. LP detection at this time allowed them to be predicted before the patients' discharge (70% sensitivity and 95% specificity, 82% predictive value in the first 24 hours of MI, LPs are characterized by more instability than those in the subsequent period of the patients' hospitalization. Thrombolytic therapy and coronary artery patency have no impact on the frequency of LP recording and parameters of signal-averaged ECG. No significant difference was found in the frequency of recording LP in anterior and inferior MI before discharge. The frequency of LP recording does not depend on the sex and age of a patient, the maximum creatine phosphokinase levels, and the presence of postinfarction angina pectoris and heart failure.

The dynamics of signal-averaged ECG and late potentials was studied in 19 patients with coronary heart disease during spontaneous anginal episodes. Baseline late potentials were observed in 9 (45%) patients, they remaining in all during and after anginal episodes. The occurrence of new late potentials was recorded in none of them. There were no significant differences in some parameters of signal-averaged ECG before, during, and after an anginal episode, though the duration of low-amplitude signals tended to increase at the end of the QRS complex and the mean square amplitude of late 40 msec of QRS complex decreased during transient myocardial ischemia. The differences did not achieve their statistical significance. It was concluded that transient myocardial ischemia during spontaneous anginal episodes failed to lead to the appearance of a substrate for the occurrence of late potentials.