Rethinking the role of sex and body size in mortality after coronary artery bypass grafting: a retrospective cohort study

OBJECTIVE: Female sex and smaller body size have been associated with increased mortality after coronary artery bypass grafting. Whether these factors represent independent determinants or markers of correlated vulnerability remains uncertain. METHODS: We performed a retrospective, single-centre cohort study of adults undergoing non-emergent isolated coronary artery bypass grafting at Amsterdam UMC between January 2000 and April 2021. We examined whether body surface area explained the association between sex and all-cause mortality within one year by sequentially adding body surface area and other clinical covariates to Cox proportional hazards regression models. RESULTS: Among 6,411 patients, 1,261 (20%) were female, and 192 patients (3.0%) died within one year. Female patients and patients with lower body surface area were older and had lower haemoglobin levels. Crude 1-year mortality was numerically higher in female patients than male patients (3.4% vs 2.9%) and in lower versus higher body surface area patients (3.6% versus 2.4%). After adjustment for age, estimated glomerular filtration rate and haemoglobin level, female sex and increasing body surface area were associated with a lower hazard of all-cause mortality. CONCLUSIONS: Crude one-year mortality was higher in female patients and in patients with lower body surface area. After adjustment, female sex and increasing body surface area were both associated with a lower mortality hazard, suggesting that the crude sex difference partly reflects differences in body size and clinical risk profile.