1. The benefit of daily aspirin varied dramatically depending on whether one cardiovascular disease event was equivalent to one or two bleeding events
2. Subgroups that tended to benefit more from aspirin treatment included patients with cardiovascular disease risk factors such as hyperlipidemia, hypertension, diabetes, smokers) and those with lower bleeding risk factors.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Aspirin reduces the risk of cardiovascular disease (CVD) in at-risk patients while increasing the risk of bleeding, but it is unclear if aspirin benefits outweigh the risks in patients without known CVD. This study found that when a CVD event was considered equivalent to 2 major bleeding events, net benefits of aspirin increased to 21% of women and 41% of men. Patients with more CVD risk factors (including hyperlipidemia, hypertension, diabetes, smokers) and those with lower bleeding risk factors benefited more from aspirin treatment. Despite the significance of these results, one limitation of this study was the generalizability of findings given that the study took place in a New Zealand primary care setting. Further, because the study design incorporated hemorrhagic stroke as an outcome for CVD and bleeding risk scores, the true proportion of patients who experienced a net benefit may be higher than reported. Future studies should further compare the threshold of CVD risk above which aspirin is beneficial to the threshold of bleeding risk above which aspirin is harmful. To help make these decisions at present, it is important for both the clinician and patient to discuss the risks and benefits of aspirin to decide what is best for them.
In-Depth [systematic review and meta-analysis]: This New Zealand study was a systematic review of 245,028 New Zealand residents from January 2012 to December 2016 without established CVD, including ages 30 to 79 years (43.6% women). Researchers conducted a risk-benefit analysis of aspirin use in patients without CVD. The net effect of aspirin was calculated by subtracting the number of prevented CVD events from the number of major bleeds likely to be caused over 5 years. CVD and bleeding risk were calculated using models validated in PREDICT cohort data, a web-based program integrated with New Zealand’s electronic primary care practice systems. Patients were excluded if they were outside of the age range, had a history of CVD, CHF, atrial fibrillation, CKD, diabetes, intracranial bleeding, or those receiving an anti-thrombotic agent in the past 6 months. When a hospitalization or death from a CVD event and major bleed are considered equivalent, the net benefit from aspirin ranged from 0.0% to 28.5% in women and 0.1% to 50% among men (using the upper and lower limits of 95% CIs). Greater net benefits were seen in subgroups that were older, current smokers, had diabetes, or were receiving blood pressure or lipid lowering medication. If 1 CVD event was considered equivalent to 2 major bleeds, the net benefit from aspirin increased to 0.1% to 60% in women and 1.9% to 77.9% among men, using the upper and lower limits of 95% CIs and not point estimates. Greater net benefits were seen in patients with a lower baseline bleeding risk and non-current smokers.
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