Aspirin in primary cardiovascular prevention: the two faces of the coin and the importance of the Number Needed to Treat: a systematic review and meta-analysis.

Abstract

Aspirin has been an essential treatment for the primary preven-tion of cardiovascular diseases (CVD). Several randomized controlled studies do not support the routine use of aspirin, mainly due to its association with bleed-ing risk. This systematic review aims to advocate aspirin prescription based on the Number Needed to Treat (NNT) and the Number Needed to Harm (NNH). This combination provides a good measure of the effort to avoid an unfavor-able outcome, weighed against possible associated risks. A search of random-ized studies on aspirin treatment was conducted in two separate periods. Four studies from 1988-1998 and six from 2001-2018 were included in the analysis (157,060 participants). The primary endpoint was a composite outcome of Non-fatal Myocardial Infarction (NFMI), Non-fatal Ischemic Stroke (NFIS), and CV mortality. Major bleeding was a safety endpoint. We calculated the Absolute Risk Reduction (ARR%), NNT, and NNH, alongside the Relative Risk (RR) and 95% CI of each primary endpoint. The results of all included studies (10) showed a net benefit with aspirin treatment for NFMI (NNT= 259) and the composite outcome (NNT=292) with a significant relative risk reduction of 20% (p=0.003; I2= 0%) and 10% (p<0.001; I2= 0%), respectively. There was a relevant 60% in-crease in the bleeding risk (p<0.0001, NNH=208; I2= 3%). The NNT and NNH may constitute measures of efficacy and risk in clinical shared decision-making. However, it is essential to consistently establish that patients’ benefit-risk should be individualized and not represent a clinical guide for everyone.