ASA effective in secondary prevention of vascular disease, uncertain in primary prevention

Clinical Question

Is aspirin effective in the primary or secondary prevention of vascular disease?

Bottom Line

Aspirin is effective in the primary and secondary prevention of vascular events. However, in primary prevention, the rate of bleeding complications nearly offsets the benefits. (LOE = 1a)

Reference

Antithrombotic Trialists' (ATT) Collaboration, Baigent C, Blackwell L, Collins R, et al. Aspirin in the primary and secondary prevention of vascular disease: collaborative meta-analysis of individual participant data from randomised trials. Lancet 2009;373(9678):1849-1860.  [PMID:19482214]

Study Design

Meta-analysis (randomized controlled trials)

Funding

Government

Setting

Various (meta-analysis)

Synopsis

The authors of this collaborative project pooled patient-level data from randomized trials comparing aspirin with no aspirin (or other antiplatelet drugs) for the primary and secondary prevention of vascular occlusive disease (myocardial infarction, coronary heart disease mortality, stroke, and other vascular events). For primary prevention studies to be eligible, they had to have enrolled more than 1000 patients without diabetes and reported at least 2 years of follow-up. The authors report that they looked for unpublished studies but found none. When the individual data were pooled, the authors used intention-to-treat analysis to assess the outcomes. The authors identified 6 primary prevention trials with 95,000 patients, and 16 secondary prevention trials with 17,000 patients. In the primary prevention studies, 0.51% of patients taking aspirin had a vascular event each year compared with 0.57% of control patients. One would need to treat 1560 for 1 year to prevent 1 event (95% CI, 1004 - 3460). In the primary prevention trials, the annual rate of serious extracranial bleeding complications was 0.1% in patients taking aspirin and 0.07% in control patients (number needed to treat to harm [NNTH] = 2840; 2030 - 4710). In the secondary prevention studies, the annual rate of any vascular event was 6.7% in patients taking aspirin and 8.2% in control patients (number needed to treat = 73; 53 - 115). In the secondary prevention trials, the annual rate of major extracranial bleeding was 0.11% in the patients taking aspirin and 0.03% of control patients (NNTH = 1265; 743 - 3280).
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