Abstract 12145: Intraoperative Anemia Mediates Sex Disparity in Operative Mortality After Coronary Artery Bypass Grafting

Abstract

Introduction: Women undergoing coronary artery bypass grafting (CABG) have higher mortality compared with men, yet its drivers are unclear. Hypothesis: The association of female sex with the risk of operative mortality after CABG may be mediated by intraoperative anemia. Aim: To investigate the relationship between sex, intraoperative anemia, and operative mortality. Methods: Retrospective cohort study of 1,434,225 isolated primary CABG patients (344,357 women) from the Adult Cardiac Surgery Database of the Society of Thoracic Surgeons (2011-2022). The primary outcome was operative mortality. The attributable risk (AR, quantifying the risk-adjusted strength of the association of female sex with CABG outcomes) was calculated. Causal mediation analysis adjusted for 42 baseline risk factors was used to derive the total effect of female sex on mortality risk and the proportion of that effect mediated by intraoperative anemia (nadir hematocrit). Spline regression evaluated the relationship of operative mortality and nadir intraoperative hematocrit. Results: Women had lower median preoperative hematocrit (36.9%, interquartile range [IQR] 33.3-40.0 vs 41.0% [37.4-44.0], standardized mean difference [SMD] 74.0%) and nadir intraoperative hematocrit (22.0% [20.0-25.0] vs 27.0% [24.0-30.0], SMD 97.0%) compared with men. Women had higher operative mortality than men (2.8% vs 1.7%, p<0.001, adjusted odds ratio 1.36, 95% confidence interval [CI] 1.30-1.41). The AR of female sex for operative mortality was 1.21 (95% CI 1.17-1.24). After adjusting for nadir intraoperative hematocrit, the AR was reduced by 43% (1.12, 95% CI 1.09-1.16). Intraoperative anemia mediated 38.5% of the increased mortality risk associated with female sex (95% CI 32.3-44.7%). Spline regression showed a stronger association between operative mortality and nadir intraoperative hematocrit at hematocrit values below 22.0% (p<0.001). Conclusions: The association of female sex with increased CABG operative mortality is mediated to a large extent by intraoperative anemia. Avoiding nadir intraoperative hematocrit values below 22.0% may reduce sex differences in CABG operative mortality.