Impact of high respiratory exchange ratio during submaximal exercise on adverse clinical outcome in heart failure

Background: Oxygen uptake (VO₂) at peak workload and anaerobic threshold (AT) workload are often used for grading heart failure (HF) severity and predicting all-cause mortality. The clinical relevance of respiratory exchange ratio (RER) during exercise, however, is unknown. Methods and Results: We retrospectively studied 295 HF patients (57±15 years, NYHA class I–III) who underwent cardiopulmonary exercise testing. RER was measured at rest; at AT workload; and at peak workload. Peak VO₂ had an inverse correlation with RER at AT workload (r=−0.256), but not at rest (r=−0.084) or at peak workload (r=0.090). Using median RER at AT workload, we divided the patients into high RER (≥0.97) and low RER (<0.97) groups. Patients with high RER at AT workload were characterized by older age, lower body mass index, anemia, and advanced NYHA class. After propensity score matching, peak VO₂ tended to be lower in the high-RER than in the low-RER group (14.9±4.5 vs. 16.1±5.0 mL/kg/min, P=0.06). On Kaplan-Meier analysis, HF patients with a high RER at AT workload had significantly worse clinical outcomes, including all-cause mortality and rate of readmission due to HF worsening over 3 years (29% vs. 15%, P=0.01). Conclusions: High RER during submaximal exercise, particularly at AT workload, is associated with poor clinical outcome in HF patients.