MedWire News: Chronic use of low-dose aspirin does not prevent vascular events in people with asymptomatic atherosclerotic disease detected using the ankle brachial index (ABI), study findings show.

The results of the Aspirin for Asymptomatic Atherosclerosis (AAA) study were presented during the first Hot Line clinical trials session of the 2009 European Society of Cardiology Annual Congress held in Barcelona, Spain.

Between April 1998 and December 2001, 3350 individuals with an ABI of ≤0.95 were recruited into the AAA study. The ABI is the ratio of systolic blood pressure in the ankle in relation to that in the arm. A low value is associated with an increased risk for vascular events.

After a mean follow-up of 8.2 years, no difference was found in the number of primary and secondary endpoint events in participants randomly assigned to receive 100 mg of enteric-coated aspirin or a matching placebo.

The primary endpoint was a composite of an initial fatal or nonfatal coronary event, stroke, or revascularization. This endpoint occurred in 181 (10.8%) of aspirin-treated patients and 176 (10.5%) of placebo-treated patients.

There were some minor, but again nonsignificant, differences in favor of aspirin use when individual components of the primary endpoint were considered, namely fatal stroke (0.4% vs 0.7%), nonfatal myocardial infarction (3.7% vs 4.1%) and nonfatal stroke (2.2% vs 2.3%). However, fatal coronary events and coronary or peripheral revascularization were more likely with aspirin than with placebo treatment.

All-cause mortality, a secondary endpoint, occurred in 10.5% and 11.1% of aspirin and placebo-treated patients, respectively. Major hemorrhage occurred in 2% and 1.2% of patients. Gastric ulcers were more frequent with aspirin use (0.8% vs 0.5%).

These results provide “no support for the routine use of aspirin for the prevention of vascular events in the context of ABI screening of the general population,” said Gerry Fowkes (University of Edinburgh, UK), who reported the AAA study’s results.

He noted, however, that the AAA study was only powered to detect a 25% risk reduction and that this could have missed a smaller actual reduction in cardiovascular events with aspirin use. Compliance with the study medication – this was typical of a primary prevention trial – could also have affected the findings. It is unknown whether aspirin is beneficial in a patient who has a low ABI but who is fully compliant, Fowkes said.

Carlo Patrono (Catholic University School of Medicine, Rome, Italy) commented that the AAA study results should be viewed in the context of the recent meta-analysis of aspirin trials conducted by the Antithrombotic Trialists (ATT) (Lancet 2009; 373: 1849–60).

This meta-analysis involved over 95,000 participants from six primary prevention trials of aspirin and showed a 12% proportional reduction in the percentage of serious vascular events (0·51% aspirin vs 0·57% control per year).

“Lack of statistical power does seem to be by far the most likely explanation for the null results of the AAA trial,” Patrono observed. He suggested that, until additional information is available, “a more reliable estimate of aspirin effects on particular vascular outcomes in people with asymptomatic atherosclerosis may be derived from the updated ATT meta-analysis”.

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

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