MedWire News: Results of the Aspirin for Asymptomatic Atherosclerosis (AAA) trial show that aspirin does not reduce the risk for cardiovascular events in individuals with subclinical atherosclerosis as identified by a low ankle brachial index (ABI).

The findings were originally reported at the European Society of Cardiology annual meeting last September and reported by MedWire News at the time, and now appear in print in the Journal of the American Medical Association.

The study included 28,980 men and women aged 50 to 75 years living in central Scotland, UK, and found no difference in the primary outcome of a composite of fatal or nonfatal coronary event, stroke, or revascularization between those randomly assigned to aspirin 100 mg daily and those assigned to placebo.

Writing in a related editorial, Jeffrey Berger (New York University School of Medicine, USA) discussed what the trial means for aspirin use in primary prevention.

He reasoned: “Although the population studied had subclinical atherosclerosis as determined by the ABI, participants had no previous history of cardiovascular disease (CVD) events. Thus the goal remains the same – prevention of a first cardiovascular event.”

In this context, the findings are consistent with those of previous primary prevention trials, Berger said.

A remaining possibility for the failure of aspirin to reduce cardiovascular events in patients without clinically established, or subclinical, CVD is that the majority of participants are at low absolute risk for CVD. Even in AAA, despite an ABI cutoff of 0.95 or less being an inclusion criterion, the event rate was still low (60% of predicted) and the extension of follow-up from 5.0 to 9.5 years to capture more events was likely hampered by decreasing adherence and an increase in crossovers, Berger said.

Furthermore, the trial was powered to detect a 25% difference for the primary outcome, which “may have been somewhat ambitious.”

Other issues such as the use of an enteric-coated aspirin in the trial and its addition to standard medical therapy may have impacted on the results, Berger added.

Future studies should perhaps consider the individual patient’s nascent platelet reactivity as an inclusion criterion, rather than concentrating on overall CVD risk, he suggested.

“Because individuals with increased platelet activity are at greater cardiovascular risk, and because aspirin decreases platelet activity, perhaps measuring platelet activity in individuals without CVD may help to identify a high-risk group that would benefit from preventive therapy,” explained Berger.

“Only adequately powered trials would provide the answer.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

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AAA study finds no benefit of aspirin in asymptomatic atherosclerosis