A systematic review 1 included 12 studies with a total of 26 831 subjects with ST-elevation myocardial infarction (STEMI). The studies compared low-molecular weight heparin (LMWH) to placebo or unfractionated heparin (UFH) in conjunction with thrombolysis. Enoxaparin was statistically superior to placebo regarding medium-term death, reinfarction and angina rate in 2 RCTs. It was also superior to UFH for in-hospital and medium-term occurrence of death, reinfarction and angina in 2 RCTs. Study results varied regarding infarct-related artery (IRA) patency rates. One trial reported a higher incidence of intracranial haemorrhage, twice that obtained with UFH. One RCT found that dalteparin was superior to placebo on left ventricular thrombosis and arterial thromboembolism on day 9, with no effects on the reinfarction or mortality rates; however, dalteparin was associated with a higher risk of major and minor bleedings. A second RCT found no significant effect on Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow in the infarct related artery (IRA), but TIMI 0 to 3 flow and its combination with intraluminal thrombus were significantly less frequent in the dalteparin group; the rate of clinical events were also lower in the dalteparin group compared with placebo. Compared with UFH, dalteparin had no significant effect on clinical events and on the IRA late patency, but less thrombus.
An RCT 2 included 483 subjects with STEMI presenting <6 hours from symptom onset. Full-dose tenecteplase (TNK) and either unfractionated heparin (UFH) or enoxaparin, or half-dose TNK plus abciximab and either UFH or enoxaparin were compared. With full-dose TNK and UFH, the rate of TIMI 3 flow at 60 minutes was 52% and was 48% to 51% with enoxaparin. Using combination therapy, the rate of TIMI 3 flow was 48% with UFH and 47% to 58% with enoxaparin. The rate of TIMI 3 flow among all UFH patients was 50% and 51% among enoxaparin patients. Death/recurrent MI in 30 days occurred in the full-dose TNK group in 15.9% of patients with UFH and 4.4% with enoxaparin (P=0.005). In the combination therapy group, the rates were 6.5% with UFH and 5.5% with enoxaparin. The rate of major hemorrhage with full-dose TNK was 2.4% with UFH and 1.9% with enoxaparin, and with combination therapy, it was 5.2% with UFH and 8.5% with enoxaparin.
Another RCT 3 included 20 506 subjects with STEMI who were scheduled to undergo fibrinolysis to receive enoxaparin throughout the index hospitalization or weight-based UFH for at least 48 hours. The primary end point (death or nonfatal recurrent MI through 30 days) occurred in 12.0% in the UFH group and 9.9% in the enoxaparin group (p<0.001). Nonfatal reinfarction occurred in 4.5% in UFH group and 3.0% in enoxaparin group (p<0.001); 7.5% of patients given UFH died, as did 6.9% of those given enoxaparin (p=0.11). The composite of death, nonfatal reinfarction, or urgent revascularization occurred in 14.5% in UFH group and 11.7% in enoxaparin group (p<0.001); major bleeding occurred in 1.4% and 2.1%, respectively (p<0.001). The composite of death, nonfatal reinfarction, or nonfatal intracranial hemorrhage (a measure of net clinical benefit) occurred in 12.2% of patients given UFH and 10.1% of those given enoxaparin (p<0.001).
Comment: The quality of evidence is downgraded limitations in review quality.
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