Overweight is associated with better one-year survival in elderly patients after cardiac surgery: a retrospective analysis of the MIMIC-III database

BACKGROUND: The relationship of body mass index (BMI) to short- and long-term outcomes after cardiac surgery remains controversial, and the dose-response relationship between BMI and mortality in patients receiving cardiac surgery is unclear. Furthermore, the influence of age, concomitant disease, and types of surgery on the prognostic role of BMI has yet to be determined. METHODS: A retrospective cohort study with 6,473 adult patients receiving cardiac surgery was conducted using the Multiparameter Intelligent Monitoring in Intensive Care (MIMIC-III) database. Multivariate Cox proportional hazard analysis and multivariate logistic regression analysis were used to assess the association of BMI with 1-year and in-hospital mortality. Restricted cubic regression splines were used to evaluate the effect of BMI as a continuous variable and to determine appropriate cut points. Subgroup analyses were performed based on age, hypertension and types of surgery. RESULTS: The baseline characteristics of patients differed between BMI categories. On multivariable analysis, overweight patients (BMI 25–30 kg/m(2)) had a lower 1-year mortality [hazard ratio (HR) =0.660, 95% confidence interval (CI): 0.516–0.843, P=0.001] when compared with normal weight patients (BMI 18.5–25 kg/m(2)). For patients with BMI <30 kg/m(2), each 1 kg/m(2) BMI increase was independently associated with a significant decrease in the 1-year mortality risk (HR =0.936, 95% CI: 0.899–0.975, P=0.002), while in patients with BMI ≥30 kg/m(2), an increase in BMI did not increase the 1-year mortality risk (HR =1.032, 95% CI: 0.998–1.067, P=0.064). Subgroup analyses suggested the protective effect of overweight on post-cardiac surgery survival was confined to patients with advanced age (>60 years), hypertension and those undergoing isolated coronary artery bypass grafting (CABG). CONCLUSIONS: Overweight was associated with better 1-year survival in patients after cardiac surgery when compared to normal weight. The protective effect of overweight on post-cardiac surgery survival was confined to elderly patients (>60 years).