Exercise testing to predict outcome in idiopathic versus associated pulmonary arterial hypertension

We tested the ability of exercise testing to predict not only survival, but also time to clinical worsening (TTCW) in idiopathic versus associated pulmonary arterial hypertension (PAH). 136 patients with PAH (85 idiopathic and 51 with associated conditions) underwent cardiopulmonary exercise testing and a 6-min walk test. Death or transplantation, and clinical worsening events were recorded. 32 patients died and four had lung transplantation. In a univariate analysis, PAH patients survival was associated with oxygen uptake (V'(O(2))) at peak exercise and at the anaerobic threshold, ventilatory equivalent for carbon dioxide (minute ventilation (V'(E))/carbon dioxide production (V'(CO(2))) at the anaerobic threshold ((at))), V'(E)/V'(CO(2)) slope and distance walked. TTCW was associated with peak V'(O(2)) and V'(O(2),at), V'(E)/V'(CO(2),at), end-tidal carbon dioxide tension measured at the anaerobic threshold, peak oxygen pulse, increase in oxygen pulse and distance walked. In a multivariable analysis, distance walked and V'(E)/V'(CO(2),at) predicted survival, and only peak V'(O(2)) predicted TTCW. The receiver operating characteristic curve-derived cut-off values were 305 m for the 6-min walk distance, 54 for V'(E)/V'(CO(2),at) and 11.6 mL·kg(-1)·min for peak V'(O(2)). In the subgroup with associated PAH, no variable independently predicted either survival or clinical worsening. We conclude that several exercise variables predict survival and clinical stability in idiopathic PAH. Exercise variables are less accurate predictors of outcome in associated PAH.