Introduction: Peak oxygen consumption (peak VO2) is an established indicator in patients with chronic heart failure (HF), though it is effort-dependent and highly influenced by patient motivation. Respiratory exchange ratio (RER) reflects exercise-induced metabolic acidosis and is used as an objective index of effort adequacy in cardiopulmonary exercise testing (CPET). However, little is known about the clinical relevance of RER during submaximal exercise level in HF patients. The aim of this study is to investigate the prognostic value of RER at submaximal level, especially at anaerobic threshold (AT) in patients with HF.
Methods and Results: We studied 261 HF patients (58 ± 15 years, NYHA class I - III) who underwent a CPET. According to the median value of AT RER (0.97), we divided into two groups; high AT RER and low AT RER (Fig. 1). Propensity score matching was then conducted to adjust for age, gender, and NYHA class between groups using a multivariate logistic regression model (c-statics 0.65). After propensity score matching, peak VO2 tended to be lower in high AT RER than low AT RER group (14.7 ± 4.0 vs. 16.2 ± 4.6 mL/kg/min, P = 0.06). The Kaplan-Meier analysis revealed that high AT RER predicted worse composite outcomes (all cause death and HF readmission) over 3 years (Fig. 2).
Conclusions: Elevated submaximal RER predicts adverse clinical outcomes in HF patients, suggesting that energy release from enhanced anaerobic metabolism might lead to exercise intolerance and poor prognosis. Submaximal RER could be a novel prognostic marker in HF patients who fail to achieve a maximal effort.