Differential associations between body mass index and outcomes after elective adult cardiac surgery: A linked data cohort study

Abstract

This study assessed the relationships between body mass index (BMI) and different outcomes after adult cardiac surgery by linking detailed preoperative comorbidity data with the long-term mortality and morbidity outcomes of 2131 consecutive patients who had elective cardiac surgery at a major cardiac surgical hospital in Western Australia. Patients with a high BMI had more comorbidities and were more likely to have had coronary artery bypass grafting than valve surgery. A total of 143 patients (6.7%) died during a median follow-up period of 30 months. The major causes of death were congestive heart failure (25.9%), myocardial infarction (14.7%), infection (23.8%) and cancer (13.9%). BMI had no association with long-term mortality, after adjusting for important confounders including the Charlson Comorbidity Index. BMI had a relatively linear relationship with the risk of new-onset atrial fibrillation (odds ratio 1.05 per point increment, 95% confidence interval 1.03 to 1.05) and venous thromboembolism (odds ratio 1.20, 95% confidence interval 1.14 to 1.26). BMI was the second most important predictor after age and accounted for 22% of the variability in the risk of atrial fibrillation. BMI had an inverse relationship with the risk of requiring allogeneic blood transfusion, postoperative intraaortic balloon pump, or surgical re-exploration. In summary, BMI had differential associations with different short- and long-term outcomes after elective adult cardiac surgery. After adjusting for important confounders including the presence of cancers, we did not observe any 'obesity paradox' and patients with a high BMI were not associated with an increased probability of long-term survival.