title: Clinical effects of anticoagulant therapy in suspected acute myocardial infarction: systematic overview of randomised trials.
abstract: OBJECTIVE
  Most randomised trials of anticoagulant therapy for suspected acute myocardial infarction have been small and, in some, aspirin and fibrinolytic therapy were not used routinely. A systematic overview (meta-analysis) of their results is needed, in particular to assess the clinical effects of adding heparin to aspirin.
  
  
  METHODS
  Computer aided searches, scrutiny of reference lists, and inquiry of investigators and companies were used to identify potentially eligible studies. On central review, 26 studies were found to involve unconfounded randomised comparisons of anticoagulant therapy versus control in suspected acute myocardial infarction. Additional information on study design and outcome was sought by correspondence with study investigators.
  
  
  METHODS
  Patients with suspected acute myocardial infarction.
  
  
  METHODS
  No routine aspirin was used among about 5000 patients in 21 trials (including half of one small trial) that assessed heparin alone or heparin plus oral anticoagulants, and aspirin was used routinely among 68,000 patients in six trials (including the other half of one small trial) that assessed the addition of intravenous or high dose subcutaneous heparin.
  
  
  METHODS
  Death, reinfarction, stroke, pulmonary embolism, and major bleeds (average follow up of about 10 days).
  
  
  RESULTS
  In the absence of aspirin, anticoagulant therapy reduced mortality by 25% (SD 8%; 95% confidence interval 10% to 38%; 2P = 0.002), representing 35 (11) fewer deaths per 1000. There were also 10 (4) fewer strokes per 1000 (2P = 0.01), 19 (5) fewer pulmonary emboli per 1000 (2P < 0.001), and non-significantly fewer reinfarctions, with about 13 (5) extra major bleeds per 1000 (2P = 0.01). Similar sized effects were seen with the different anticoagulant regimens studied. In the presence of aspirin, however, heparin reduced mortality by only 6% (SD 3%; 0% to 10%; 2P = 0.03), representing just 5 (2) fewer deaths per 1000. There were 3 (1.3) fewer reinfarctions per 1000 (2P = 0.04) and 1 (0.5) fewer pulmonary emboli per 1000 (2P = 0.01), but there was a small non-significant excess of stroke and a definite excess of 3 (1) major bleeds per 1000 (2P < 0.0001).
  
  
  CONCLUSIONS
  The clinical evidence from randomised trials dose not justify the routine addition of either intravenous or subcutaneous heparin to aspirin in the treatment of acute myocardial infarction (irrespective of whether any type of fibrinolytic therapy is used).
authors.affiliation: BHF/MRC/ICRF Clinical Trial Service Unit, University of Oxford.
authors.forename: R
authors.initials: R
authors.lastname: Collins
authors.forename: S
authors.initials: S
authors.lastname: MacMahon
authors.forename: M
authors.initials: M
authors.lastname: Flather
authors.forename: C
authors.initials: C
authors.lastname: Baigent
authors.forename: L
authors.initials: L
authors.lastname: Remvig
authors.forename: S
authors.initials: S
authors.lastname: Mortensen
authors.forename: P
authors.initials: P
authors.lastname: Appleby
authors.forename: J
authors.initials: J
authors.lastname: Godwin
authors.forename: S
authors.initials: S
authors.lastname: Yusuf
authors.forename: R
authors.initials: R
authors.lastname: Peto
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use*; D001241:Aspirin / Q000008:administration & dosage / Q000627:therapeutic use*; D002561:Cerebrovascular Disorders / Q000517:prevention & control; D004359:Drug Therapy, Combination; D006493:Heparin / Q000008:administration & dosage / Q000627:therapeutic use*; D006801:Humans; D009203:Myocardial Infarction / Q000188:drug therapy*; D011655:Pulmonary Embolism / Q000517:prevention & control; D016032:Randomized Controlled Trials as Topic; D012008:Recurrence; D016019:Survival Analysis; D016896:Treatment Outcome
chemical_list: D000925:Anticoagulants; D006493:Heparin; D001241:Aspirin