Extent of early ST segment elevation resolution: a strong predictor of outcome in patients with acute myocardial infarction and a sensitive measure to compare thrombolytic regimens. A substudy of the International Joint Efficacy Comparison of Thrombolytics (INJECT) trial.

OBJECTIVES

This study was undertaken to assess prospectively the prognostic power of early ST segment elevation resolution in a large cohort of patients with myocardial infarction and to test the value of differences in ST segment resolution as a surrogate end point.

BACKGROUND

Previous studies revealed that the use of two cutoff points for three groups of ST segment resolution within 3 h after the start of thrombolysis is most effective in predicting outcome.

METHODS

The International Joint Efficacy Comparison of Thrombolytics (INJECT) trial compared mortality in 6,010 patients randomized to receive either reteplase or streptokinase. The 1,909 German patients form the basis of this substudy. The three groups of ST segment resolution were defined as complete (> or = 70%), partial (70% to 30%) and no resolution (< 30% to > or = 0%).

RESULTS

In 1,398 patients presenting < or = 6 h from onset of acute myocardial infarction, the 35-day mortality rate for complete, partial and no ST segment resolution was 2.5%, 4.3% and 17.5%, respectively (p < 0.0001). Peak creatine kinase levels (fraction of normal) were 9.8, 13.4 and 14.0, respectively (p < 0.0001). When baseline characteristics were included, ST segment resolution was the most powerful independent predictor of 35-day mortality. The proportion of patients with complete ST segment resolution was larger, and that with no ST segment resolution smaller, with reteplase than with streptokinase (p = 0.006).

CONCLUSIONS

No ST segment resolution, indicating failed thrombolysis, predicts very high early mortality, whereas complete resolution is associated with a small infarct area and low mortality. Partial ST segment resolution also predicts larger infarct areas, but early mortality is relatively low. Different extents of ST segment resolution may serve as a sensitive surrogate end point in clinical trials.