Higher Mortality in Women After Coronary Artery Bypass: Meta-analysis and Bias Analysis of Confounding

Some studies suggest that the observed higher mortality in women compared with men after coronary artery bypass grafting (CABG) is due to confounding. Our meta-analysis aimed to (1) summarize the effect of sex on mortality after CABG and (2) identify whether unmeasured confounding likely explains the apparent higher mortality in women.

We searched MEDLINE, Embase, and CENTRAL databases for studies examining sex and 30-day mortality after CABG. We used random-effects meta-analysis to estimate the summary odds ratio (OR) of mortality in women versus men using (1) unadjusted study results and (2) adjusted study results. Available confounders data from included studies were identified. Using the OR of measured confounders and the risk of death to inform unmeasured confounding effects, we performed bias analysis simulation to correct potential unmeasured confounding in the summary OR.

From 7,138 retrieved studies, 112 were included (N = 5,008,262 patients); 25 studies reported adjusted OR (N = 770,450 patients). Overall 30-day mortality was 4.9% in women versus 3.3% in men. The unadjusted summary OR (1.81; 95% confidence interval, 1.72-1.91) and adjusted summary OR (1.40, 95% confidence interval, 1.35-1.45) demonstrated women had an increased risk for 30-day mortality compared with men. Simulations correcting for unmeasured confounding mostly ranged from 1.05 to 1.80, which supports a higher risk for death in women after CABG.

The findings of this review suggest that confounding is unlikely to account for the increased risk for mortality in women after CABG and that biological factors have a causal effect.