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New study challenges aspirin guidelines for patients at risk of atherosclerotic cardiovascular disease

A new study challenges the ‘one size fits all’ approach to current aspirin guidelines for patients at risk of atherosclerotic cardiovascular disease (ASCVD).

The findings of three trials published in 2018 (ASPREE, ASCEND and ARRIVE), which assessed the effects of starting aspirin therapy versus a placebo on ASCVD outcomes in aspirin-naive adults, resulted in guidelines no longer recommending low-dose aspirin for the primary prevention of ASCVD.

The amended guidelines were motivated by findings showing an increased risk of significant bleeding for patients taking aspirin across the three trials; however, questions remain for patients who were already taking aspirin before the trials.

In a meta-analysis of a subset of the trial results, researchers from the University of Galway found that people who had been previously taking aspirin but had chosen to stop without consultation with their doctor faced a 28% increased risk of ASCVD.

The findings are published in the journal Circulation, and, in the absence of further data, the researchers suggest that patients already safely treated with low-dose aspirin for primary prevention of ASCVD can continue to do so.

The three original randomised trials involved over 47,140 patients from 10 countries, including the US, the UK and Australia.

In a previously published subgroup analysis, the ASPREE trial authors studied 1,714 participants taking aspirin at least twice weekly before enrolment.

In a randomised analysis, those who stopped taking aspirin and took a placebo had a trend to increased risk for ASCVD events compared with continuing aspirin (55 of 841 [6.5%] versus 44 of 873 [5.0%]). However, the findings have limitations since they were based on a small sample size of 99.

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In the present investigation, trial-level meta-analyses were performed to study the subgroup of participants taking aspirin at baseline in both the ASPREE and ASCEND trials (n=7,222).

Data from the subset of patients revealed that there was a higher risk of both fatal or non-fatal ASCVD among baseline users who were randomised to stop aspirin and take a placebo versus those randomised to continue aspirin (450 of 3,609 [12.5%] versus 374 of 3,613 [10.4%]).

The hazard ratios in both subset meta-analyses (1.32 for the ASPREE data and 1.21 for the ASPREE and ASCEND combined analysis) suggest that although there is a potential trend towards increased risk for ASCVD events among those who stopped taking aspirin, the results are not statistically significant.

The Galway researchers found the difference in the risk of major bleeding was not statistically significant between baseline aspirin users randomised to discontinue aspirin and those who continued (123 out of 3609 [3.4%] versus 142 out of 3613 [3.9%]; hazard ratio, 0.86).

Professor John W. McEvoy from the University of Galway said the ‘results are hypothesis-generating’ and challenge the ‘one size fits all’ guidelines.

He said: ‘Our findings of the benefit of aspirin in reducing heart disease or stroke without an excess risk of bleeding in some patients could be due to the fact that adults already taking aspirin without prior bleeding problems are inherently lower risk for a future bleeding problem from the medication. Therefore, they seem to get more of the benefits of aspirin with less of the risks.’

Professor McEvoy explained that more research was needed but added: ‘Until further evidence becomes available, it seems reasonable that persons already safely treated with low-dose aspirin for primary prevention may continue to do so unless new risk factors for aspirin-related bleeding develop.’

A study published in March 2023 found that the benefits of aspirin use in myocardial infarction are offset by statin use in patients without ASCVD.

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