Stopping aspirin may increase risk of cardiovascular events

According to a Swedish population-based cohort study published in the journal Circulation (2017;136:1183–92), discontinuation of long-term, low-dose aspirin can increase the risk of cardiovascular events.

Investigators examined a cohort of 601,527 users of low-dose (75–160mg daily) aspirin for primary or secondary prevention of cardiovascular disease from the Swedish prescription register. The study included only patients who had taken aspirin continuously with high adherence (≥80%) during the first observed year of treatment. Cardiovascular events were identified using inpatient and cause-of-death registers, excluding outcomes occurring within the first three months of major bleeding or a surgical procedure.

After a median follow-up of three years, a total of 62,690 cardiovascular events occurred. Patients who discontinued aspirin during the follow-up period had a 37% higher rate of cardiovascular events (hospitalisation for myocardial infarction, stroke or cardiovascular death) than those who continued taking it (adjusted hazard ratio 1.37, 95%CI 1.34–1.41). This, the authors say, corresponds to an additional cardiovascular event per year in one in 74 patients who discontinued aspirin. Aspirin discontinuation appeared to be particularly unsafe in patients with existing cardiovascular disease, with an additional cardiovascular event per year in one in every 36 secondary prevention patients who discontinued aspirin, compared with one in every 146 primary prevention patients. The risk increased shortly after discontinuation of aspirin and did not appear to diminish over time.

The authors conclude that good adherence to low-dose aspirin treatment in the absence of major surgery or bleeding is likely to be an important treatment goal. However, they acknowledge the limitations of the study, including the possibility of confounding because it was an observational study and not a randomised trial; there was no access to important physical patient characteristics such as smoking status, blood pressure and lipid levels, nor were the reasons for discontinuation of aspirin recorded.

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