A systematic review 1 including 10 studies with a total of 4180 subjects was abstracted in DARE. The included studies contained patients with the following indications for treatment: mechanical heart valve, atrial fibrillation, coronary artery disease and high risk for cardiovascular disease. Low-dose aspirin (up to 100 mg/day) was used in 6 studies, and moderate to high doses (200 to 1000 mg/day) in 4 studies. The risk for arterial thromboembolism (myocardial infarction, unstable angina requiring hospitalisation, stroke, transient ischaemic attack or systemic embolism) was lower in patients receiving combined aspirin-OAC therapy compared with OAC therapy alone (OR 0.66, 95% CI 0.52 to 0.84; absolute risk reduction 2.5%, NNT 40). However, these benefits were limited to patients with a mechanical heart valve (OR 0.27, 95% CI 0.15 to 0.49). There was no difference in the risk for arterial thromboembolism with these treatments in patients with atrial fibrillation (OR 0.99, 95% CI 0.47 to 2.07) or coronary artery disease (OR 0.69, 95% CI 0.35 to 1.36). There was no difference in all-cause mortality with either treatment (OR 0.98, 95% CI 0.77 to 1.25).
The risk for major bleeding was higher in patients receiving aspirin-OAC therapy compared with OAC therapy alone (OR 1.43, 95% CI 1.00 to 2.02; absolute risk increase 1%, NNH 100). The subgroup analyses demonstrated a significantly greater incidence of major bleeding only in patients with a mechanical heart valve.
Comment: The quality of evidence is downgraded by imprecise results (limited study size for each comparison).
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