Is the obesity paradox in cardiac surgery really a myth? Effect of body mass index on early and late clinical outcomes

ABSTRACT OBJECTIVE We aimed to investigate the obesity paradox and assess the effect of BMI on early and late clinical outcomes after cardiac surgery. DESIGN We conducted a cohort study, performing a retrospective analysis of prospectively collected data. SETTING Single institution cardiology medical center. PARTICIPANTS Consecutive patients undergoing cardiac surgery from January 2009 to January 2019. Patients were divided into 4 groups defined by body mass index (BMI): underweight (UW) (≤18,5 kg/m2): 0.5%, n=27; normal weight (NW) (18,5-25 kg/m2): 25.7%, n=1393; overweight (OW) (>25-30 kg/m2): 44.7%, n=2423; and obese (OB) (≥30 kg/m2): 29.1%, n=1576.. INTERVENTION No intervention. MEASUREMENTS AND MAIN RESULTS A multivariate analysis was used to compare clinical outcomes among the different BMI groups. Overall one year survival of BMI categories were determined by the Kaplan-Meier method and were compared using the log rank test.. We included 5419 patients. The BMI groups were significantly different regarding pre-surgical variables. Mortality according to BMI exhibited a reverse J-shaped relationship: 7,4% in UW, 5,2% in NW, 3,2% in OW, 4,3% in the OB group (P=0,016). Low cardiac output syndrome and bleeding were more frequent in the UW, whereas mediastinitis and hyperglycemia were in OB group. After adjusting for other risk factors, BMI was not an independent predictor of in-hospital mortality. One-year follow-up was completed in 95%, the analysis of long-term mortality did not show a difference between BMI categories (P log rank=0,16). Conclusion OW patients had a lower mortality and better outcomes after cardiac surgery. However, when other preoperative variables were taken into account, BMI did not have independent effect on in-hospital and one-year mortality. Keywords: Cardiac surgery, Body mass index, Obesity, Risk factors, Mortality