Thirteen RCTs (12,254 participants) were included in the review. Sample sizes ranged from 60 to 4,687 patients. Fifty-three per cent of the 6,322 patients who received LMWH and were eligible for the safety endpoints received LMWH intravenously or intra-arterially. Elective PCI was undergone by 38% of the patients. The authors stated that the baseline characteristics of the groups in the trials were similar.
There were no statistically significant differences between the LMWH and unfractionated heparin groups in the number of patients who achieved efficacy endpoints or for the safety endpoint of bleeding events, although trends towards benefit with LMWH were observed for both outcomes. Some heterogeneity (Χ²=15.97, Ι²=49%) was observed across the trials for bleeding.
Patients who had LMWH intravenously or intra-arterially showed statistically significant fewer bleeding episodes compared to those with unfractionated heparin (RR 0.63, 95% CI 0.48 to 0.82, Ι²= 0%). There was a trend towards fewer deaths and myocardial infarction events in patients treated with LMWH, but this was not statistically significant. There were no significant differences between groups treated with LMWH and groups treated with unfractionated heparin in subgroup analyses of studies of patients who underwent elective or urgent PCI for the efficacy composite outcome and the safety endpoint of bleeding episodes; there was a discrepancy between the text and tables for bleed events in patients who underwent elective PCI.