Cardiovascular disease (CVD), including heart attack and stroke is the leading cause of death in the United States.1 The lifetime risk of developing coronary heart disease (CHD) after 40 years of age is 49% for men and 2% for women.2 Aspirin therapy is frequently recommended to patients for the prevention of vascular events. Many guidelines recommend using aspirin for primary prevention in patients that have a moderate or higher CHD risk. The use of aspirin for secondary prevention has been well established and the benefits substantially exceed the risks. However, the balance of risks and benefits is not as clear in ASA’s use for primary prevention.3
The Antithrombotic Trialists’ Collaborators performed a meta-analysis on six primary prevention trials and sixteen secondary prevention trials that examined long-term aspirin therapy to no aspirin therapy (with no other antiplatelet drug in either group) as primary and secondary prevention.3 The primary outcomes assessed were serious vascular events (MI, stroke, or vascular death), major coronary event, any stroke, death from any cause, and major extracranial bleed. The primary prevention analysis included 95,000 individuals at low risk for vascular disease and the secondary prevention analysis included 17,000 individuals at high average risk. The primary prevention group included patients without known occlusive disease. The secondary prevention group included patients with previous MI, stroke, or transient cerebral ischemia.
In the primary prevention trials 1671 serious vascular events occurred during a 330,000 person-years in people allocated aspirin compared with 1883 events during a 330,000 person-years in those allocated a control. This small absolute risk reduction (only 0.07% per year) represents a 12% proportional reduction (rate ratio [RR] 0.88 95% CI 0.82-0.94 p=0.0001). The reduction seemed similar in men and women and was not statistically significant between those with predicted 5-year risk of coronary heart disease less than 2.5%, 2.5-5%, 5-10% or 10% or more. The proportional risk reduction did not differ between the primary and secondary groups, but the absolute risk reduction was smaller in the primary prevention group when compared to the secondary prevention group.
Major coronary events and strokes accounted for the majority of serious vascular events therefore, analysis on these outcomes were assessed separately. In the primary prevention trials patients on aspirin had an 18% proportional reduction in major coronary events, but only a small absolute risk reduction (0.28% vs 0.34% per year; RR 0.82 95% CI 0.75-0.90 p=0.001). The majority of this decrease was from a 23% proportion reduction in non-fatal MI. There was not a clear reduction in mortality from CHD.
The primary prevention analysis for ischemic stroke suggested a greater proportional risk reduction in women than in men. However, the secondary prevention analysis did not demonstrate the same suggestion. Aspirin decreased the incidence of ischemic stroke and increased the incidence of hemorrhagic stroke for both the primary and secondary prevention groups. In addition, aspirin reduced the aggregate of all strokes when used as secondary prevention.
Clinical trials have proven that the benefits ...