Body Mass Index, Muscle Mass, and All-Cause Mortality in Patients With Acute Heart Failure: The Obesity Paradox Revisited

BACKGROUND AND OBJECTIVES: Lower body mass index (BMI) is considered a poor prognostic factor in patients with heart failure (HF). We aimed to investigate the clinical impact of BMI on the risk of mortality in patients with acute HF (AHF) across various phenotypes. METHODS: We retrospectively identified 4,146 registry patients with AHF and BMI data. The study population was categorized according to the WHO Asia-Pacific BMI classification: BMI <18.5 kg/m(2) (underweight; n=418), BMI 18.5–23 kg/m(2) (ideal; n=1,620), BMI 23–25 kg/m(2) (overweight; n=828), BMI 25–30 kg/m(2) (obesity I; n=1,047), and BMI ≥30 kg/m(2) (obesity II; n=233). The risk of all-cause mortality was compared between these 5 groups. RESULTS: During a median follow-up of 32 months, 1,732 patients (41.8%) died. Compared to patients with obesity II, those with overweight, ideal BMI or underweight status had a higher risk of mortality (overweight: hazard ratio [HR], 1.606; 95% confidence interval [CI], 1.016–2.539; p=0.042) (ideal BMI: HR, 1.744; 95% CI, 1.112–2.734; p=0.015) (underweight: HR, 2.729; 95% CI, 1.686–4.417; p<0.001). Higher risk of mortality among patients with lower BMI was observed regardless of age, sex, hypertension, diabetes, ischemic heart disease, atrial fibrillation, and HF phenotype. Furthermore, low muscle index (total muscle mass/height(2)), calculated using serum cystatin C data in a subset of 579 patients, was associated with higher mortality risk. CONCLUSIONS: A lower BMI is associated with a higher risk of mortality in patients with AHF. This obesity paradox is observed in AHF regardless of comorbidities and HF phenotype.