Association of obesity and survival in systolic heart failure after acute myocardial infarction: potential confounding by age

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Abstract
Aims To determine the association between obesity and outcomes in post‐acute myocardial infarction (AMI) patients with systolic heart failure (HF). Methods and results Of the 6632 Eplerenone Post‐Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS) participants, 6611 had data on baseline body mass index (BMI) and 6561 had BMI ≥ 18.5 kg/m2. Of these, 1573 were obese (BMI ≥ 30 kg/m2) and 4988 were non‐obese (BMI 18.5–29.9 kg/m2). Propensity scores for obesity, estimated for each patient, were used to assemble a cohort of 1519 pairs of obese and non‐obese patients who were balanced on 65 baseline characteristics. All‐cause mortality occurred in 13.7 and 13.8% of matched obese and non‐obese patients, respectively, during 16 months of median follow‐up [matched hazard ratio (HR) for obesity 0.98; 95% confidence interval (CI) 0.79–1.21; P = 0.831]. Before matching, the obese group was younger (mean age, 62 vs. 64 years; P < 0.0001) and had more women (37 vs. 26%; P < 0.0001). The paradoxical pre‐match association between obesity and reduced mortality (unadjusted HR 0.82; 95% CI 0.70–0.95; P = 0.008) disappeared when adjusted for age alone (age‐adjusted HR 0.91; 95% CI 0.78–1.06; P = 0.206) but not for gender alone (gender‐adjusted HR 0.79; 95% CI 0.68–0.92; P = 0.003). Obesity had no association with mortality in 1573 pairs of age‐matched obese and non‐obese patients (age‐adjusted HR 0.94; 95% CI 0.77–1.13; P = 0.484). Conclusion In post‐AMI patients with systolic HF, obesity provides no independent intrinsic survival benefit. The paradoxical unadjusted survival associated with obesity is largely explained by the younger age of obese patients.