Abstract 3806: Effect of Risk on the Benefit of Enoxaparin versus Unfractionated Heparin in Patients with ST-Elevation Myocardial Infarction in the ExTRACT-TIMI 25 Trial
BACKGROUND: Enoxaparin (Enox) decreases the rate of death and non-fatal recurrent myocardial infarction (MI) compared to unfractionated heparin (UFH) in patients (pts) receiving fibrinolysis for ST-elevation MI (STEMI). In a prespecified analysis, we investigated the benefit of Enox after stratifying for baseline risk using the TIMI Risk Index (TRI), a previously validated risk assessment tool in STEMI.
METHODS: We evaluated 30-day outcomes in 20,479 pts with STEMI treated with fibrinolysis and UFH or Enox in the ExTRACT-TIMI 25 Trial. Pts were categorized based on pre-specified ranges of the risk index (groups 1–5).
RESULTS: The TRI demonstrated a strongly graded increase in 30-day death/MI with rising risk index (P-trend<0.0001). A higher TRI was associated with longer time from sx onset to fibrinolysis (p<0.0001) and more heart failure at presentation (p<0.0001). The relative risk reduction (RRR) of Enox appeared inversely graded with the TRI. There was a 38% reduction in death/MI in the lowest risk group (RR 0.62, 95%CI 0.45– 0.86) while there was a progressive decrease in the relative benefit of Enox vs UFH (Figure⇓) with increasing risk index (P-interaction<0.01). However, the absolute risk difference (ARD) between treatment arms was similar across TRI groups, with the exception of group 5 in which no difference was observed. This pattern persisted when restricted to pts aged <75 yrs.
CONCLUSIONS: We observed a pattern of increasing relative benefit of Enox with decreasing baseline risk. Pts in the highest TIMI Risk Index group are more likely to present with heart failure and have larger completed infarctions, possibly mitigating the reduction in recurrent MI with Enox.