Comparison of body mass index and body surface area as outcome predictors in patients with systolic heart failure

BACKGROUND: We investigated whether the 'obesity paradox' in heart failure (HF) is influenced by common confounders, and assessed if body surface area (BSA) may correlate more closely than body mass index (BMI) with prognosis. METHODS: We studied 630 systolic HF patients at their initial visit to the HF clinic. Body size was measured by BMI and BSA. The association between body indices and mortality was assessed by Cox proportional-hazard analyses. RESULTS: There were 248 deaths during mean follow-up of 39 months. A progressive inverse association of BMI and BSA tertiles (T1-T3) with mortality risk was observed (for BSA: T3, reference, T2, hazard ratio [HR] 1.41, 95% confidence interval [CI] 1.01-1.95, p = 0.04 and T1, HR = 1.78, 95% CI 1.29-2.45, p < 0.001; for BMI: T3, reference, T2, HR = 1.29, 95% CI 0.92-1.79, p = 0.13 and T1, HR = 1.66, 95% CI 1.21-2.27, p = 0.002). The obesity paradox was attenuated after multivariate adjustment, and did not persist after adjustment for age alone (for BMI: T3, reference, T2, HR = 1.13, 95% CI 0.81-1.58, p = 0.47; T1, HR = 1.30, 95% CI 0.94-1.80, p = 0.12; for BSA: T3, reference, T2, HR = 0.96, 95% CI 0.68-1.35, p = 0.82; T1, HR = 1.15, 95% CI 0.82-1.63, p = 0.42). CONCLUSIONS: BSA provides prognostic information similar to BMI in systolic HF. However, the obesity paradox of both BMI and BSA in HF may be confounded by the younger age of the obese patients.