Evidence and temporality of the obesity paradox in coronary bypass surgery: An analysis of cause-specific mortality

Abstract

OBJECTIVES: We evaluated the presence of an ‘obesity paradox’ in coronary artery bypass grafting (CABG) patients, determined its time course and ascertained whether it is associated with improved cardiovascular (CV) survival versus non-CV survival. METHODS: A retrospective analysis of 3 prospectively collected databases was conducted. A fifteen-year Kaplan–Meier analysis in 7091 CABG patients was performed and repeated in 5 body mass index [BMI (kg/m2)] cohorts [Normal (18.5–24.99 kg/m2), Overweight (25–29.99 kg/m2), Obese I (30–34.99 kg/m2), Obese II (35–39.99 kg/m2) and Obese III (>_40 kg/m2)]. Mortality hazard ratios {HR [95% confidence interval (CI)]} were derived using comprehensive multivariable competing risk Cox regression, accounting for BMI categories for overall (0–15), Early (0–1), Intermediate (1–8) and Late (8–15) postoperative years, to relax the proportional hazards assumption. The regression was repeated using BMI as a continuous variable. Mortality was classified into any, CV and non-CV. RESULTS: Obese patients were younger with more comorbidities. Fifteen-year survival was improved in the Overweight and Obese I groups (P < 0.001). Adjusted 15-year mortality was reduced in the Overweight [HR (95% CI) = 0.88 (0.79–0.98)] and Obese I [HR = 0.88 (0.78–0.99)] groups driven by improved CV and non-CV survival. This trend was noted in the early (Overweight) and intermediate postoperative periods (Overweight and Obese I) with no significance in the late period. Higher mortality in the Obese III [HR = 1.28 (1.06–1.55)] group was driven by a decreased CV survival. Using BMI as a continuous variable, a BMI of 29 kg/m2 was associated with optimal survival. CONCLUSIONS: We identified a protective partial obesity paradox in the early and intermediate postoperative periods among Overweight and mildly obese (Obese I) patients with improved CV and non-CV survival. The morbidly obese (the Obese III group) had higher early and late CV mortality. © The Author(s) 2018.