A cardiopulmonary exercise testing score for predicting outcomes in patients with heart failure

Objective: The aim of this study is to evaluate the predictive accuracy of a cardiopulmonary exercise test (CPX) score. Background: Cardiopulmonary exercise test responses, including peak VO₂, markers of ventilatory inefficiency (eg, the VE/VCO₂ slope and oxygen uptake efficiency slope [OUES]), and hemodynamic responses, such as heart rate recovery (HRR) and chronotropic incompetence (CRI) are strong predictors of outcomes in patients with heart failure (HF). However, there is a need for simplified approaches that integrate the additive prognostic information from CPX. Methods: At 4 institutions, 710 patients with HF (568 male/142 female, mean age 56 ± 13 years, resting left ventricular ejection fraction 33 ± 14%) underwent CPX and were followed for cardiac-related mortality and separately for major cardiac events (death, hospitalization for HF, transplantation, left ventricular assist device implantation) for a mean of 29 ± 25 months. The age-adjusted prognostic power of peak VO₂, VE/VCO₂ slope, OUES (VO₂ = a log₁₀VE + b), resting end-tidal carbon dioxide pressure (PetCO₂), HRR, and CRI were determined using Cox proportional hazards analysis, optimal cutpoints were determined, the variables were weighted, and a multivariate score was derived. Results: There were 175 composite outcomes. The VE/VCO₂ slope (≥34) was the strongest predictor of risk and was attributed a relative weight of 7, with weighted scores for abnormal HRR (≤6 beats at 1 minute), OUES (>1.4), PetCO₂ (2 (≤14 mL kg^-1 min^-1) having scores of 5, 3, 3, and 2, respectively. Chronotropic incompetence was not a significant predictor and was excluded from the score. A summed score >15 was associated with an annual mortality rate of 27% and a relative risk of 7.6, whereas a score