Aspirin does not reduce CV events in persons with low ankle-brachial index

Aspirin does not reduce cardiovascular events in asymptomatic persons with low ankle-brachial index, according to a recent study.

Researchers in Scotland conducted the Aspirin for Asymptomatic Atherosclerosis trial, an intention-to-treat randomized, double-blind placebo-controlled trial involving 3,350 Scottish men and women 50 to 75 years of age who had no clinical coronary artery disease but had a low ankle-brachial index (ABI) on screening. Participants were assigned to receive 100 mg of enteric-coated aspirin per day or placebo. The study's primary end points included initial fatal or nonfatal coronary event, stroke or revascularization; secondary end points were all initial vascular events, including angina, intermittent claudication or transient ischemic attack, and all-cause mortality. The study results appear in the March 3 Journal of the American Medical Association.

Study participants were followed for a mean of 8.2 years. During that time, 357 had a coronary event, stroke or revascularization, with no statistically significant difference between the aspirin and placebo groups (13.7 events per 1,000 person-years vs. 13.3 events per 1,000 person-years; hazard ratio [HR], 1.03; 95% CI, 0.84 to 1.27). Likewise, no statistically significant difference was seen between groups in the 578 participants who experienced an initial vascular event (22.8 events per 1,000 person-years vs. 22.9 events per 1,000 person-years; HR, 1.00; 95% CI, 0.85 to 1.17). All-cause mortality was also similar in the aspirin and placebo groups (176 deaths vs. 186 deaths; HR, 0.95; 95% CI, 0.77 to 1.16). Thirty-four participants in the aspirin group and 20 in the placebo group had major hemorrhage requiring hospital admission (2.5 per 1,000 person-years vs. 1.5 per 1,000 person-years; HR, 1.71; 95% CI, 0.99 to 2.97).

The authors acknowledged that their study had a limited power to detect a small aspirin effect, that the study population included many more women than men (approximately 70% vs. approximately 30%), and that overall rates of cardiovascular and cerebrovascular events were low. They questioned whether a larger trial in this area would be warranted, given that the number of events prevented was small and that aspirin therapy can have harmful side effects. The authors concluded that aspirin did not reduce cardiovascular events in asymptomatic persons with a low ABI, but did not rule out the possibility that other interventions in this population, such as statins, may be helpful.

“These data do not support recommendations for ABI screening in an effort to ultimately reduce CVD event rates in patients at risk for peripheral artery disease,” an accompanying editorial said. “Future studies using different markers of increased risk are needed, including the ABI, to address whether therapeutic or lifestyle modifications affect outcomes among patients identified by those markers.”