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 (<33 mm Hg), and peak VO2 (≤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 <5 was associated with a mortality rate of 0.4%. The composite score was the most accurate predictor of cardiovascular events among all CPX responses considered (concordance indexes 0.77 for mortality and 0.75 for composite outcome composed of mortality, transplantation, left ventricular assist device implantation, and HF-related hospitalization). The summed score remained significantly associated with increased risk after adjusting for age, gender, body mass index, ejection fraction, and cardiomyopathy type. Conclusion: A multivariable score based on readily available CPX responses provides a simple and integrated method that powerfully predicts outcomes in patients with HF.