Prophylactic aspirin therapy did not reduce vascular events in a study of people who had a low ankle-brachial index but no clinical evidence of cardiovascular disease, according to results of a randomized trial.
“This trial is the first to report on the effectiveness of aspirin in reducing major cardiovascular and cerebrovascular events in individuals from the general population who were free of clinical cardiovascular disease but at higher risk as identified by ABI screening,” said Dr. F. Gerald R. Fowkes of the University of Edinburgh and his associates in the Aspirin for Asymptomatic Atherosclerosis trial.
The randomized, double-blind trial involved 3,350 men and women aged 50–75 years when they were screened for a low (0.95 or lower) ankle-brachial index in 1998–2001. The subjects, all of whom were residents of central Scotland, had no clinical evidence of cardiovascular disease, but their low ABI put them at risk for coronary and cerebrovascular disease.
The study subjects were randomly assigned to receive 100 mg of enteric-coated aspirin or a placebo daily. They were followed at regular intervals for a mean of 8 years.
The primary end point—a composite of fatal or nonfatal coronary event, stroke, or revascularization procedure—was not statistically lower in subjects who took prophylactic aspirin (13.7 events per 1,000 person-years) than in those who took placebo (13.3 events per 1,000 person-years).
The secondary end point, which was angina, intermittent claudication, or transient ischemic attack in addition to the primary end point component, also did not differ between the intervention group (22.8 events per 1,000 person-years) and the placebo group (22.9 events per 1,000 person-years).
In addition, there was no significant difference in all-cause mortality between the aspirin group (12.8 deaths per 1,000 person-years) and the placebo group (13.5 deaths per 1,000 person-years).
“Although numbers were small, the trial results suggested an increased incidence of major hemorrhage and gastrointestinal ulcer, although not severe anemia, in the aspirin group, and more participants in the aspirin group than in the placebo group had fatal intracranial adverse events,” Dr. Fowkes and his colleagues wrote (JAMA 2010;303:841–8).
Given the hazard ratios and confidence intervals in the data, the study could not rule out the possibility that aspirin prophylaxis might reduce cardiovascular risk by a small degree (16%) in healthy people found to have a low ABI.
“However, extrapolating from the [nearly 29,000 people] screened for participation in our trial, a risk reduction of this order means that between 500 and 600 people from the general population would need to be screened and prescribed aspirin to prevent a single major cardiovascular event over an 8-year period,” they addd.
The British Heart Foundation and Chief Scientist's Office, Scotland funded the study. Bayer HealthCare provided the aspirin and placebo tablets as well as funds for packaging and dispensing the drugs and conducting some statistical analysis. Dr. Fowkes reported financial ties to Bayer HealthCare, Sanofi-Aventis, and Bristol-Myers Squibb.
There were 13.7 events per 1,000 person-years in patients who took aspirin vs. 13.3 events in those who took placebo.
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