TIMI Risk Index and the Benefit of Enoxaparin in Patients with ST-Elevation Myocardial Infarction

Purpose The purpose of the study was to evaluate the cause of death, risk of nonfatal complications, and relative outcomes with an enoxaparin versus unfractionated heparin strategy in ST-elevation myocardial infarction stratified using the Thrombolysis in Myocardial Infarction (TIMI) Risk Index (TRI). Methods We evaluated 30-day outcomes in 19,941 patients with ST-elevation myocardial infarction treated with fibrinolysis and unfractionated heparin or enoxaparin. Patients were categorized on the basis of prespecified ranges of the TRI [heart rate × (age/10)2/systolic blood pressure]. Results There was a strongly graded increase in 30-day mortality with increasing TRI (1.2%-20.7%, P <.0001). The proportion of deaths due to mechanical causes (congestive heart failure, shock, and myocardial rupture) increased progressively with the TRI. There also was a significant positively graded association between the TRI and nonfatal heart failure or shock (0.4%-4.4%, P <.0001). In contrast, death resulting from recurrent ischemic events predominated in the lowest TRI group. The relative reduction in death/myocardial infarction with the enoxaparin strategy appeared inversely graded with the TRI. There was a 38% reduction in the lowest risk group (relative risk 0.62, 95% confidence interval 0.45-0.86) and a decrease in the relative benefit of enoxaparin with increasing risk index. Conclusions The TRI was a strong predictor of all-cause mortality in a broad population, with a positive association with the risk of death due to mechanical complications and an inverse association with deaths due to recurrent ischemia. The enoxaparin strategy was superior to unfractionated heparin in a majority of patients with ST-elevation myocardial infarction, except for the group at the highest risk for severe mechanical complications, in whom the 2 anticoagulant strategies showed similar results.