Assessment and Significance of ST-Segment Changes Detected by Ambulatory Electrocardiography After Acute Myocardial Infarction

This study assessed the prognostic value of ST-segment changes detected by ambulatory electrocardiographic monitoring during the early in-hospital period after acute myocardial infarction. New methods for defining the ST-segment reference level and for measuring ST segment elevation were used. ST-segment depression was defined as a change in ST level by ≥0.1 mV 80 ms after the J point, elapsing ≥1 minute. ST-segment elevation was defined as a deviation by ≥15 mV, elapsing ≥1 minute, and measured at the J point. An interval of ≥2 minutes was required before another discrete episode was counted. Four ST-segment reference levels were automatically calculated: (1) “isoelectric,” (2) “nearest to normal,” (3) “24-hour median,” and (4) “first-hour median.” During a mean follow-up period of 3 years (mean 36 ± 15 months), 47 cardiac events occurred in 38 patients: 18 deaths, 9 nonfatal reinfarctions, and 20 revascularization procedures. More deaths occurred in patients with than without ST elevation–24-hour median (22% vs 5%, p = 0.03), and in patients with than without 51 depression–isoelectric (61% vs 32%, p = 0.02), and in patients with than without ST-depression–24-hour median (61%vs 23%, p = 0.003). “All cardiac events” (deaths, infarctions, or revascularization procedures) occurred more often in patients with than without ST depression–isoelectric (55% vs 22%, p = 0.003), and in patients with than without S1-depression–24-hour median (47% vs 17%, p = 0.004). Sensitivity, specificity, and accuracy of ST depression/elevation–24-hour median to assess mortality were 78%, 71%, and 73%, respectively. These values were higher than those obtained by either ST depression or ST elevation alone, measured from the isoelectric line. Survival time was best predicted by ST depression/elevation–24-hour median (p = 0.0001, 41% difference between groups, 95% confidence intervals [CI] 8% to 66%). The same was true for cumulative survival free of reinfarction (p = 0.0005, 34% difference between graups, 95% CI3% to 71%) and of all cardiac events (p = 0.0004, 42% difference between groups, 95% CI l% to 69%). In a multivariate regression analysis, ST depression/elevation–24-hour median was the strongest variable predicting mortality (p <0.001, hazards ratio 6.3), and the only variable predicting reinfarctions (p <0.01, hazards ratio 4.25) and sudden deaths (p <0.05, hazards ratio 5.1). Thus, these findings illustrate the prognostic value of ST-segment changes detected with ambulatory electrocardiographic monitoring during the early in-hospital period after acute myocardial infarction, according to the new diagnostic criteria.