Peak oxygen uptake better predicts outcome than submaximal respiratory data in heart transplant candidates

Abstract

Background - Many studies have focused on the prognostic power of peak oxygen uptake (V̇O2) in patients with chronic heart failure, but maximal exercise testing is not without risk. The purpose of the present study was, therefore, to assess the prognostic significance of the steepness of changes in ventilation and carbon dioxide output (V̇CO2) during submaximal exercise in comparison with V̇O2. Methods and Results - The study population consisted of 284 adult heart transplant candidates who performed a graded maximal bicycle ergometer test with respiratory gas analysis. Using the respiratory data up to a gas exchange ratio of 1.0, 3 submaximal slopes were calculated in each patient. During follow-up (median, 1.33 years), 57 patients died and 149 had ≥1 cardiovascular event. When using Cox proportional hazards analysis, both peak V̇O2 and submaximal respiratory slopes predicted outcome before and after accounting for age, sex, and body mass index. However, whereas the prognostic power of peak V̇O2 was independent of submaximal respiratory data, the prognostic significance of the slopes was lost after controlling for peak V̇O2. Stepwise regression analysis even selected peak V̇O2 as an independent prognostic index among the following factors: cause of heart failure, ejection fraction, pulmonary vascular resistance, natremia, and the forced expiratory volume in 1 s. Conclusions - Respiratory data during submaximal exercise are significant predictors of outcome in patients with chronic heart failure, but their prognostic power is inferior to that of peak V̇O2. However, these data may be useful when maximal exercise is contraindicated or not achievable.