Abstract 3001: Percent-Predicted Oxygen Uptake Efficiency Slope Prognostically Outperforms the Actual Value in Patients With Heart Failure
Introduction: The oxygen uptake efficiency slope (OUES) is a newer maker of ventilatory efficiency with potential prognostic value in patients with heart failure (HF). Like peak oxygen consumption (VO2), the OUES is modulated by age and sex, creating the potential for the utility of a percent-predicted expression.
Hypothesis: We hypothesize that a percent-predicted expression of the OUES will provide superior prognostic resolution compared to the actual value in a group of patients with HF.
Methods: Three hundred and seventy two patients with HF (Age: 59.2±14.9 years, ejection fraction: 36.4±16.4%, 64% male, 37% ischemic HF) underwent cardiopulmonary exercise testing (CPX) to determine peak oxygen consumption (VO2) and ventilatory efficiency (VE/VCO2 slope and OUES). Percent-predicted OUES values were calculated using previously published equations. Subjects were subsequently tracked for major cardiac events for three years.
Results: Mean values for peak VO2, the VE/VCO2 slope, the OUES and percent-predicted OUES were 15.8±6.0 mlO2•kg−1•min−1, 34.0±8.7, 1.7±0.85 and 71.4±27.4%, respectively. There were 79 (69 deaths, 9 transplants and 2 LVAD implantations) major cardiac events. Receiver operating characteristic curve analysis revealed area under the curve was greater for the percent-predicted OUES expression (area: 0.70, 95% CI: 0.63– 0.76, p<0.001) compared to the actual value (area: 0.66, 95% CI: 0.60 – 0.73, p<0.001). Two separate multivariate Cox regression analyses demonstrated the VE/VCO2 slope (Chi-square: 47.7, p<0.001) was the strongest prognostic maker while peak VO2 was removed in both instances (Residual chi-square: 0.62, p=0.40). While the actual OUES value was removed from the multivariate regression (Residual chi-square: 0.92, p=0.34), percent-predicted OUES adding prognostic value to the VE/VCO2 slope and was retained (Residual chi-square: 6.3, p=0.01).
Conclusions: The VE/VCO2 slope is poorly related to age and sex, lending to its robust prognostic value when expressed as an actual value. Conversely, a percent-predicted expression of the OUES, a variable whose actual value is influenced by age and sex, may bolster prognostic power and justify its clinical consideration in the HF population undergoing CPX.