Key result
Female sex linked to ~36% higher CABG operative mortality, largely mediated by intraoperative anemia.
Why the study?
Women undergoing CABG have higher operative mortality than men, motivating an evaluation of the relationship between intraoperative anemia, CABG operative mortality, and sex.
Does intraoperative anemia mediate the association between female sex and higher operative mortality in patients undergoing isolated primary CABG?
Cohort (n=1,434,225)
Yes
Does intraoperative anemia mediate the association between female sex and higher operative mortality in patients undergoing isolated primary CABG?
Intraoperative anemia mediates 38.5% of the excess operative mortality risk in women undergoing CABG, suggesting that avoiding nadir hematocrit values below 22.0% may reduce sex disparities in surgical outcomes.
Answers are grounded in this paper and cite their sources.
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Captured external expert commentary on this paper, strongest first. Original sources are linked where available.
“While this study does not establish causation, it does demonstrate a distinct association between intraoperative anemia and female CABG mortality. We knew that anemia was a risk factor in general for cardiac surgery outcomes, but we were surprised that it explained nearly 40% of the excess CABG mortality in women. That was a striking finding.”
Intraoperative anemia mediates much of women's excess CABG mortality; leaves open whether avoiding hematocrit <22% narrows sex disparities.
BACKGROUND Women undergoing coronary artery bypass grafting (CABG) have higher operative mortality than men. OBJECTIVES The purpose of this study was to evaluate the relationship between intraoperative anemia (nadir intraoperative hematocrit), CABG operative mortality, and sex. METHODS This was a cohort study of 1,434,225 isolated primary CABG patients (344,357 women) from the Society of Thoracic Surgeons Adult Cardiac Surgery Database (2011-2022). The primary outcome was operative mortality. The attributable risk (AR) (the risk-adjusted strength of the association of female sex with CABG outcomes) for the primary outcome was calculated. Causal mediation analysis derived the total effect of female sex on operative mortality risk and the proportion of that effect mediated by intraoperative anemia. RESULTS Women had lower median nadir intraoperative hematocrit (22.0% [Q1-Q3: 20.0%-25.0%] vs 27.0% [Q1-Q3: 24.0%-30.0%], standardized mean difference 97.0%) than men. Women had higher operative mortality than men (2.8% vs 1.7%; P < 0.001; adjusted OR: 1.36; 95% 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, 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 <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.
Harik et al. (2024) conducted a cohort in Isolated primary coronary artery bypass grafting (CABG) (n=1,434,225). Female sex and intraoperative anemia (nadir intraoperative hematocrit) vs. Male sex was evaluated on Operative mortality (OR 1.36, 95% CI 1.30-1.41, p=<0.001). Female sex was associated with higher CABG operative mortality (2.8% vs 1.7%; aOR 1.36; 95% CI 1.30-1.41), with 38.5% mediated by intraoperative anemia.