Aspirin in primary prevention still unclear

The jury is still out on whether aspirin has a role to play in the prevention of cardiovascular events in people at moderate risk, late breaking results from the ARRIVE study reveal.

Presented by Professor J Michael Gaziano of the Brigham and Women’s Hospital, Boston, Massachusetts in a Hot Line session at the ESC congress this week, the study is the first RCT to explore the efficacy and safety of aspirin in the ‘average risk’ patient population (10-year risk of a first acute cardiovascular event of 10 to 20%).

Patients were randomised to either 100 mg enteric coated aspirin or placebo.  Median follow-up was 60 months and the primary endpoint was time to first occurrence of a composite of cardiovascular death, myocardial infarction, stroke, unstable angina and transient ischaemic attack.

In the intention-to-treat analysis, a primary cardiovascular event occurred in 4.29% of participants allocated daily aspirin vs 4.48% of participants allocated placebo (hazard ratio [HR] 0.96; 95% confidence intervals [CI] 0.81–1.13; p=0.60).

However, there was an unexpectedly low number of cardiovascular events that occurred overall, a finding that was probably reflective  of contemporary risk management strategies, making the study more representative of a low-risk population.

“The role of aspirin in primary prevention among patients at moderate risk could therefore not be addressed,” the researchers wrote in the study which was  published in The Lancet simultaneously.

The risk of total and non-fatal MI (HR 0.53; 95% CI 0.36–0.79; p=0.0014 and HR 0.55; 95% CI 0.36–0.84; p=0.0056, respectively) was reduced by aspirin in the per-protocol analysis, and the relative risk reduction of MI in the aspirin group was 82.1% for those aged 50–59 years.

“Those who took aspirin tended to have fewer heart attacks, but there was no effect on stroke. As expected, the rate of gastrointestinal bleeding was higher in the aspirin group, but there was no difference in fatal bleeding events between groups,”  Prof. Gaziano said.

Although mostly mild, gastrointestinal bleeds occurred twice as often in the aspirin group than the placebo group (0.97% vs 0.46%, respectively; HR 2.11; 95% CI 1.36–3.28; p=0.0007).

The researchers said that while ARRIVE aimed to add relevant information about the cardiovascular benefits and bleeding risks of aspirin among people at moderate cardiovascular risk, it highlighted some of the challenges of doing long-term prevention studies in the current era.

“Findings from ARRIVE are generally consistent with many other studies that tended to show aspirin’s ability to lower the risk of first non-fatal myocardial infarction without affecting the risk of total stroke. With respect to safety, as expected, rates of gastrointestinal bleeding events and some other minor bleeding events were higher in the aspirin treatment group, but there was no difference in the incidence of fatal events”.

“The use of aspirin remains a decision that should involve a thoughtful discussion between a clinician and a patient, given the need to weigh the cardiovascular as well as possible cancer prevention benefits against the bleeding risks, patient preferences, cost, and other factors,” they concluded.

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