Efficacy and safety of unfractionated heparin versus enoxaparin:: a pooled analysis of ASSENT-3 and -3 PLUS data

Background: The optimal antithrombotic therapy to accompany tenecteplase in cases of acute ST-segment elevation myocardial infarction (STEMI) remains unclear. We undertook a prespecified pooled analysis of data from the ASSENT-3 and ASSENT-3 PLUS trials. Methods: We created a combined database of the 2040 and 818 patients who received enoxaparin in ASSENT-3 and ASSENT-3 PLUS, respectively, and compared them with the 2038 and 821 patients who received unfractionated heparin. Results: The primary efficacy end point, a composite of 30-day mortality, reinfarction or refractory ischemia, was 16.0% with enoxaparin versus 12.2% with unfractionated heparin (p < 0.001); the efficacy plus safety (intracranial hemorrhage [ICH] or major systemic bleeding) end point, 18.0% versus 15.0% (p = 0.003). The 1049 patients urgently revascularized had greater benefit from enoxaparin (15.4% v. 10.1%, p = 0.013), yet the excess in major systemic bleeding evident with enoxaparin (3.3% v. 2.4%, p = 0.01) was largely confined to the 3492 patients without or before revascularization. Although ICH rates in the groups were similar (1.3% v. 0.9%, p = 0.26), an excess of ICH occurred among those administered enoxaparin during the ASSENT-3 PLUS trial (6.7% v. 0.8%, p = 0.013), especially among women over 75 years of age. Interpretation: These data demonstrated the benefit of enoxaparin used in conjunction with tenecteplase, but raised caution about its prehospital use to treat STEMI in elderly women.