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Aspirin in healthy people
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A large body of evidence has shown that daily use of low-dose aspirin can reduce the risk of a first CVD event. For example, aspirin can reduce the risk of a first heart attack by as much as 23% to 32%, and the combined risk of heart attack, ischemic stroke or vascular death by 12% to 15%. As a result, the broader, appropriate use of aspirin could help prevent a significant number of the estimated 32 million heart attacks that occur each year worldwide, and this approach could be cost effective.
So what will the impact of the Aspirin for Asymptomatic Atherosclerosis Trial (AAAT), published earlier this year, which failed to demonstrate a significant benefit in a population at low risk of having a cardiac event? Several consumer news media outlets used the study results to warn healthy individuals to reconsider the use of aspirin if they are not at risk for a heart attack, and reported that the study suggested the risks of internal bleeding associated with aspirin outweighed its potential advantages in healthy people. The reality is that these findings — and this message — are not news at all. The medical establishment around the world has never suggested that healthy people at low CV risk use low-dose aspirin to prevent a heart attack or other cardiac event. International guidelines, based upon a wealth of study data, support the use of daily low-dose aspirin for individuals at moderate-to-high risk of a first event. This recent study simply reaffirms that aspirin should only be used for moderate- to high-risk individuals.
It is also important to note that the study was not conducted in “healthy people,” but rather a group that had asymptomatic mild vascular disease who were at low risk for a first CV event. Furthermore, the study was designed to compare the effects of low-dose aspirin (100 mg daily) vs. placebo on CV events in patients with asymptomatic atherosclerosis. Using a screening technique known as ankle brachial index (ABI) that compares BP in the ankle and the arm, study participants were those whose ABI was slightly lower than normal, and below the cut-off to define high risk in a number of studies. No other standard CV risk factors (such as family history, smoking, obesity, high BP) were required for study entry, which resulted in the baseline risk in the trial being lower than anticipated (1.36% per year), which is below today’s accepted threshold for primary prophylaxis with aspirin.
As a result, it turned out in the trial that the actual occurrence of events such as MI or stoke was much lower than predicted when the study was initially designed over the eight years, even though asymptomatic atherosclerosis is associated with an increased lifetime risk for CV events. Because of this lower-than-expected occurrence, not enough people were included in the study to allow the preventative effects of low-dose aspirin to be seen. Furthermore, the rate of compliance among those in the study was only about 60%, indicating that on average, on as many as 4 days out of 10, patients did not take their low-dose aspirin as directed. Under these circumstances, it is hard to know whether low-dose aspirin would be effective in people identified only by ankle-brachial index.
Despite these study limitations, there was still an indication of positive effects of low-dose aspirin consistent with previous research. For example, there were fewer non-fatal MIs in the aspirin group. Also, the number of ischemic strokes was lower. In terms of safety, the occurrence of major bleeding — a potential side-effect of aspirin — was rare and not significantly different between the aspirin and placebo groups.
The bottom line is that it is not at all surprising that a study of a lower-risk population failed to support the use of low-dose aspirin in preventing first CVD events. In fact, AAAT adds to the rich body of research evaluating the safety and effectiveness of low-dose aspirin in preventing a first CVD event by reaffirming the important position that low-aspirin should be used in appropriate, moderate- to high-risk patients.
Freek Verheugt, MD, PhD, is a cardiologist at University Hospital Nijmegen in Nijmegen, the Netherlands.
For more information:
- Eidelman R. Arch Int Med. 2003;163(17):2006-2010.
- Bartolucci A. Am J Cardiol. 2006;98(6):746-750.
- ATT collaboration. Lancet. 2009;373(9678):1849-1860.
- WHO. Integrated Management of Cardiovascular Risk. 2002. PDF. Accessed March 03, 2010.
- Fowkes F. JAMA. 2010;303(9):841-848.