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

Background-Many studies have focused on the prognostic power of peak oxygen uptake ((V)over dotO(2)) in patients with chronic heart failure, but maxim al exercise testing is not without risk. The purpose of the present study w as, therefore, to assess the prognostic significance of the steepness of ch anges in ventilation and carbon dioxide output ((V)over dotCO(2),) during s ubmaximal exercise in comparison with (V)over dotO(2). Methods and Results-The study population consisted of 284 adult heart trans plant candidates who pet-formed a graded maximal bicycle ergometer test wit h 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 greater than o r equal to 1 cardiovascular event. When using Cox proportional hazards anal ysis, both peak (V)over dotO(2) and submaximal respiratory slopes predicted outcome before and after accounting for age, sex, and body mass index. How ever, whereas the prognostic power of peak iio, was independent of submaxim al respiratory data, the prognostic significance of the slopes was lost aft er controlling for peak (V)over dotO(2),. Stepwise regression analysis even selected peak (V)over dotO(2), as an independent prognostic index among th e following factors: cause of heart failure, ejection fraction, pulmonary v ascular resistance, natremia, and the forced expiratory volume in 1 s. Conclusions-Respiratory data during submaximal exercise are significant pre dictors of outcome in patients with chronic heart failure, but their progno stic power is inferior to that of peak (V)over dotO(2) However, these data may be useful when maximal exercise is contraindicated or not achievable.