Oxygen Uptake Efficiency Slope (OUES) and Mortality in Chronic Heart Failure: Comparisons of Absolute and Percent-predicted Values across Different Equations

Aim: The oxygen uptake efficiency slope (OUES) is a prognostic indicator obtained from cardiopulmonary exercise testing (CPX) in chronic heart failure (CHF) patients. Although various equations exist for calculating predicted OUES, it remains unclear whether absolute or percent-predicted values offer a more accurate prognostic assessment. To investigate and compare mortality prediction in CHF patients using the OUES absolute values or the percent-predicted approach, incorporating the equations of Hollenberg, Buys, and Milani. Methods: Retrospective cohort study involving CHF patients evaluated at a tertiary university hospital between July 2013 and July 2023. All patients underwent maximal CPX and were followed in a specialized outpatient clinic. The primary outcome was all-cause mortality. To compare the prognostic accuracy between different approaches, we performed receiver operating characteristic (ROC) curve analysis and Cox proportional hazards regression. Results: A total of 1.180 patients were included, 57% male, with a mean age of 55 ± 12 years. The median follow-up was 5.0 years (IQR 3.0 to 7.2 years), resulting in 147 deaths (12.5%). The area under de curve (AUC) was 0.71 to 0.72 for males, and 0.60 to 0.63 for females, without statistical difference in the AUC between absolute and percent-predicted OUES. Different cut-offs were identified for each sex for predicting mortality and all OUES metrics remained independent predictors in multivariate models using sex and age. Conclusions: OUES, in both absolute and percent-predicted forms, demonstrated similar accuracy in predicting mortality in CHF, with sex-specific cut-offs influencing clinical assessment.