Objectives: To investigate the relationship between body mass index (BMI) and early outcomes, and specific types of morbidities associated with low and high BMI, in patients undergoing coronary artery bypass grafting. Methods: This was a retrospective study on isolated coronary artery bypass grafting patients (aged ≥60 years) between 2008 and 2017 in the Japan Cardiovascular Surgery Database. The primary end point was defined as operative mortality. The secondary end point was combined morbidity (ie, operative mortality, reoperation for bleeding, stroke, new onset of hemodialysis, mediastinitis, and prolonged ventilation). Patient characteristics and outcomes were compared among BMI groups. Spline curves were fit between BMI and outcomes. Multivariable logistic regression models with categorized BMI and generalized additive models with spline-transformed BMI were used to estimate and visualize the effect of BMI adjusted for other covariates. Results: A total of 96,058 patients were included in the analysis. Low (<18.5) and high (≥30) BMI were both associated with a higher risk of mortality (low: adjusted odds ratio, 1.34; 95% confidence interval, 1.16-1.54; P <.0001, and high: adjusted odds ratio, 2.10; 95% confidence interval, 1.70-2.59; P <.0001) and combined morbidity (low: adjusted odds ratio, 1.18; 95% confidence interval, 1.08-1.29; P =.0002 and high: adjusted odds ratio, 1.82; 95% confidence interval, 1.63-2.03; P <.0001). Low and high BMI were associated with different types of morbidities. In models using spline transformation, the deviation of BMI from a proximately 21 to 23 was proportionally associated with increased risk. Conclusions: In patients undergoing coronary artery bypass grafting, low and high BMI were risk factors of mortality associated with different types of morbidities, which may warrant tailored preventive approaches.
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