Key result
Aspirin use for primary prevention reduced the incidence of major adverse cardiovascular events by 10% (RR 0.90) compared to no aspirin, but significantly increased the risk of intracranial hemorrhage and extracranial major bleeding.
Why the study?
Several large RCTs evaluating aspirin for primary prevention have been published since the 2010 Canadian antiplatelet guidelines, prompting an updated evaluation of its ischemic and bleeding effects.
Does aspirin reduce major adverse cardiovascular events in patients without known atherosclerotic cardiovascular diseases?
Meta-Analysis (n=167,587)
Does aspirin reduce major adverse cardiovascular events in patients without known atherosclerotic cardiovascular diseases?
Relative Risk: 0.9 (95% CI 0.86–0.94)
Absolute Risk Reduction: 0.4%
Number Needed to Treat: 250
Aspirin for primary prevention of cardiovascular disease yields a consistent 10% relative reduction in MACE but significantly increases major bleeding risks, supporting individualized shared decision-making rather than routine use.
Balances modest MACE reduction against major bleeding; reinforces guidelines against routine aspirin for primary prevention.
Background: Since the publication of the 2010 Canadian antiplatelet guidelines, several large randomized controlled trials (RCTs) have evaluated the role of aspirin (ASA) use in primary prevention. We evaluated the effect of ASA use, compared with no ASA, on ischemic and bleeding events in patients without known atherosclerotic cardiovascular diseases. Methods: We updated a published systematic review and meta-analysis by searching MEDLINE, Embase, and CENTRAL for the period up to March 2023. We included RCTs that enrolled patients for primary prevention of atherosclerotic cardiovascular diseases, and compared use of ASA to no ASA. We assessed risk of bias (RoB) using the Cochrane RoB tool, and certainty of evidence using the grading recommendations, assessment, development, and evaluation (GRADE) criteria. The primary efficacy outcome was major adverse cardiovascular events (MACE) (death, myocardial infarction, or stroke). The primary safety outcomes were intracranial hemorrhage and extracranial major bleeding events. We used a random-effects model to generate pooled risk ratios (RRs) and 95% confidence intervals (CIs). Results: We included 14 RCTs (n = 167,587) at overall low RoB, with a median follow-up of 5 years. Compared to no ASA, ASA use reduced the incidence of MACE (RR 0.90, 95% CI 0.86-0.94), with a higher risk of intracranial hemorrhage (RR 1.33, 95% CI 1.13-1.56) and extracranial major bleeding (RR 1.67, 95% CI 1.36-2.06). In prespecified subgroups of age, sex, and diabetes, effect estimates were consistent. Conclusions: ASA use in primary prevention is associated with a consistent reduction in MACE, but at the expense of major bleeding events. Patient values and preferences should be taken into account when considering ASA use for primary prevention.
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Laferrière et al. (2023) conducted a meta-analysis in Primary prevention of atherosclerotic cardiovascular diseases (n=167,587). Aspirin vs. No aspirin was evaluated on Major adverse cardiovascular events (MACE) (RR 0.90, 95% CI 0.86-0.94). Aspirin use for primary prevention reduced the incidence of major adverse cardiovascular events by 10% (RR 0.90) compared to no aspirin, but significantly increased the risk of intracranial hemorrhage and extracranial major bleeding.
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