The NHS Choices 'Behind the Headlines' service has assessed a trial presented at the recent European College of Cardiology Conference that found no benefit in prescribing low-dose aspirin to people with atherosclerosis but no overt cardiovascular disease: this study has generated significant media interest.

'Behind the Headlines' briefly describes the trial (Aspirin for Asymptomatic Atherosclerosis, AAA study): this has not yet been published and details are only available from the conference abstract. It involved 3,350 people (of 28,980 screened) who had no overt cardiovascular disease but had a reduced ankle-brachial index (ABI, the ratio of systolic BP at the ankle to that in the arm and an indicator of sub-clinical atherosclerosis). They were randomised to aspirin 100mg daily or placebo and followed-up every six months. Primary endpoint was a composite of initial fatal or nonfatal coronary event or stroke or revascularisation.

After a mean of 8.2 years follow-up, 357 participants had a primary endpoint event, with no significant difference between active and placebo groups (181 vs. 176 events; hazard ratio [HR] 1.03; 95% CI 0.84 to 1.27). There were also no significant differences in the secondary endpoints studied, including major bleeding requiring hospitalisation (2% aspirin vs. 1.2% placebo; HR 1.71, 95% CI 0.99 to 2.97). Overall compliance with medication was relatively low (60%).

The authors conclude that in the context of screening by ABI, routine low-dose aspirin for people with atherosclerosis but no clinical cardiovascular disease cannot be supported.

An accompanying commentary notes that the study would have been underpowered to detect a benefit at the level found for low-dose aspirin in a recent large meta-analysis of primary prevention trials (12% relative reduction), although the 95% CI overlaps this. The commentator suggests that this lack of power, together with the low compliance, may explain the null finding. He also suggests other possible explanations.