Valvular heart disease is a condition that impairs the normal function of cardiac valves and often requires surgical intervention to improve patient outcomes. Body mass index (BMI) is a widely used international standard for assessing body fatness and overall health status. Significant changes in BMI are positively correlated with the incidence of metabolic syndrome and cardiovascular and cerebrovascular diseases, and both excessively high and low BMI may increase the risk of postoperative complications. This study aims to investigate the association between BMI and the perioperative period in patients with valvular heart disease.

This retrospective study used data from the INSPIRE database and included 972 patients undergoing cardiac valve surgery. Patients were classified into four BMI categories: underweight (<18.5 kg/m²), normal weight (18.5 kg/m²≤BMI<24.0 kg/m²), overweight (24.0 kg/m²≤BMI<28.0 kg/m²), and obese (BMI≥28.0 kg/m²). Logistic regression models were employed to assess the association between BMI and in-hospital mortality. Model discrimination was evaluated using the area under the receiver operating characteristic curve (AUC). Restricted cubic spline (RCS) regression was applied to explore potential non-linear associations between BMI and mortality risk.

Multivariable logistic regression analysis identified cardiopulmonary bypass time, serum albumin, activated partial thromboplastin time, serum creatinine, body mass index (BMI), and continuous renal replacement therapy (CRRT) as independent predictors of postoperative mortality following cardiac valve replacement. Each 1-unit increase in BMI was associated with an 11% reduction in mortality risk (OR=0.89, 95% CI: 0.81–0.99, P=0.027). Receiver operating characteristic (ROC) curve analysis demonstrated that the combined model incorporating these variables achieved high predictive accuracy (AUC=0.857, 95% CI: 0.795–0.920), with a sensitivity of 80.36% and a specificity of 80.57%. Restricted cubic spline analysis revealed a significant non-linear association between BMI (kg/m²) and mortality, with two inflection points at 23.41 kg/m² and 29.69 kg/m². For BMI<23.42, mortality risk increased with decreasing BMI; for 23.42≤BMI<29.69, risk declined to its lowest level; and for BMI≥29.69, mortality risk tended to rise again.

Low BMI is strongly associated with perioperative mortality after cardiac valve surgery, and serves as a potential predictor of mortality risk.