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Trial casts doubt on aspirin guidance

By Nigel Praities

Use of aspirin for primary prevention of cardiovascular disease has been dealt what could prove a fatal blow, after a major new trial found no evidence that it was beneficial.

The Aspirin for Asymptomatic Atherosclerosis, or AAA, study found prescribing aspirin to patients identified as at high risk of vascular events through screening could not be justified when weighed against the raised risk of internal bleeding.

The research, presented at the European Society of Cardiology's annual congress in Barcelona this week, adds to the results of a recent meta-analysis published in The Lancet that also questioned use of aspirin for primary prevention.

The findings prompted the Joint British Societies to pledge to look again at its guidance recommending aspirin for primary prevention in high-risk and diabetic patients.

Researchers found no statistically significant difference in fatal or non-fatal coronary events, strokes or revascularisations between patients with asymptomatic atherosclerosis taking 100mg aspirin a day for eight years and those on placebo.

The study recruited 28,980 Scottish men and women aged 50 to 75 who were free of clinically evident cardiovascular disease. The ankle brachial index of all patients was measured, and the 3,350 with an index of 0.95 or lower were then randomised to once-daily 100mg aspirin or placebo.

Aspirin treatment resulted in a surprise 3% increase in the risk of a coronary event, stroke or revascularisation compared with placebo, although this was not statistically significant.

Major haemorrhages were more commonly seen in the aspirin group, with 34 cases requiring hospitalisation, compared with 20 in the placebo group.

Study leader Professor Gerry Fowkes, professor of epidemiology at the University of Edinburgh, said the results showed aspirin had ‘absolutely no effect'.

He added: ‘More haemorrhages were observed in the aspirin than in the placebo group. There is no support for the use of aspirin for the prevention of vascular events in a screened population.'

Dr Iain Simpson, vice-president of the British Cardiovascular Society, told Pulse: ‘The JBS2 guidelines now look out of date. These new trials will be considered as part of the new JBS3 guidelines. This needs looking at with some urgency.'

The results prompted an immediate riposte by aspirin enthusiasts.

Professor Carlo Patrono, professor of pharmacology at the University of Rome, said the study was underpowered: ‘The sample size would have to be about four times larger to achieve the intended power. Lack of statistical power seems by far the most likely explanation for the null results.'

Professor Patrono claimed a forthcoming analysis from the Oxford Clinical Research Trials Unit, including the AAA study result, suggested there still was a positive effect from aspirin when used in primary prevention.

The AAA study

The study recruited 3,350 men and women aged 50 to 75 years who were free of clinically evident cardiovascular disease in central Scotland with an ankle brachial index of ≤0.95 ABI. Participants were followed up for a mean of 8.2 years

Coronary event or stroke, or revascularisation occurred in 357 participants had a primary endpoint event, a rate of13•5 per 1000 person years, compared with 181 in the aspirin group and 176 in the placebo group.

A vascular event occurred in 578 participants, but again no statistically significant difference was found between the aspirin and placebo groups, at 288 versus 290 events respectively.

All-cause mortality was similar in both groups at 176 v 186 deaths. An initial event of major bleeding requiring admission to hospital occurred in 34, or 2% of subjects in the aspirin group and 20, or 1.2% of the placebo group.

Aspirin use for primary prevention was found to have 'absolutely no effect' Aspirin use for primary prevention was found to have 'absolutely no effect'

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