Randomised controlled trials (RCTs) that compared subcutaneous low-molecular weight heparins with intravenous unfractionated heparin as adjunctive therapy, in patients with acute ST-segment elevation myocardial infarction (STEMI) who received aspirin and fibrinolytic therapy, were eligible for inclusion. To be eligible the following outcomes had to be reported: death, reinfarction and bleeding in-hospital or at approximately day seven and at day 30. The follow-up period had to be from five days to three months. Trials that compared low molecular weight heparins or unfractionated heparin treated patients with untreated patients or placebo groups were excluded. Low-molecular weight heparins allowed were enoxaparin and dalteparin.
The primary outcome was the composite death from any cause or non fatal recurrent myocardial infarction in the first 30 days after randomisation. The secondary outcome was composite death from any cause, non-fatal myocardial infarction, and major bleeding (definition provided), all during index hospitalisation or at seven days.
The patients in the included trials had STEMI or left bundle branch block, mostly treated after less than six hours. Included patients' age was over 18 years; details of their sex were not provided. Enoxaparin was the low-molecular weight heparin used in all but one of the included RCTs, all of which initially administered an intravenous bolus of 30 to 40mg, with subsequent subcutaneous injections of enoxaparin for up to eight days. For the dalteparin RCT, the initial intravenous bolus was 90 IU/kg, followed by further intravenous injections for up to seven days. Comparative unfractionated heparin regimes were described and were over two to four days. The fibrinolytic therapy included tenecteplase, tissue plasminogen activator or streptokinase; all but one trial also used aspirin at a dose range of 75 to 325mg/day. Follow-up was for 30 days in the majority of the trials (range five to 90 days).
The authors did not state how many reviewers performed the study selection.