Effect of body mass index on outcomes after cardiac surgery: is there an obesity paradox?

Abstract

Background: Numerous studies have documented an obesity paradox in which overweight and obese people with cardiovascular disease have a better prognosis compared with patients with normal body mass index (BMI). This study sought to quantify the effect of BMI on clinical outcomes after cardiac surgery and investigate the obesity paradox.

Methods: A concurrent cohort study of 2,440 consecutive patients undergoing cardiac surgery (coronary artery bypass grafting [CABG], valve, or CABG and valve surgery) from January 2004 to December 2008 was carried out. The patients were divided into three groups on the basis of BMI: normal weight (BMI 18.5 to 24.9; n=556; 23%), overweight (BMI 25.0 to 29.9; n=965; 39%), and obese (BMI≥30; n=919; 38%). Multivariable analyses and propensity score matching were used to compare the early and late clinical outcomes among the different BMI groups.

Results: Overweight patients had a lower operative mortality (odds ratio, 0.4; 95% confidence interval, 0.2 to 0.9; p=0.031) compared with normal BMI patients. Obese patients had a comparable risk for operative mortality (odds ratio, 0.8; 95% confidence interval, 0.4 to 1.6; p=0.47) compared with normal-weight patients. Actuarial 5-year survival was better for the overweight (hazard ratio, 0.5; 95% confidence interval, 0.4 to 0.8; p=0.002) and comparable for the obese (hazard ratio, 0.9; 95% confidence interval, 0.5 to 1.4; p=0.49) groups compared with the normal-weight patients.

Conclusions: Overweight patients have better early hospital outcomes and improved survival after cardiac surgery compared with normal BMI patients, supporting the obesity paradox.