Exercise ventilation inefficiency and cardiovascular mortality in heart failure: the critical independent prognostic value of the arterial CO2 partial pressure

Aims In chronic heart failure (CHF) patients, the ventilation (Ve) needed to eliminate metabolically produced CO2 during exercise (i.e. the Ve/Vco2 slope) is a strong prognosticator. Ve/Vco2 slope determinants are the dead space–tidal volume (Vd/Vt) ratio and the arterial CO2 partial pressure (Paco2). We aimed at defining the respective prognostic role of these two variables. Methods and results One hundred and twenty-eight stable CHF patients (average left ventricular ejection fraction 34±10%) underwent cardiopulmonary exercise testing and blood gas analysis. The prognostic relevance of the Ve/Vco2 slope, Vd/Vt, and Paco2 at peak exercise was evaluated by the Kaplan–Meier approach with log-rank testing and by multivariate Cox regression analysis. During a mean period of 31.3±20 months, 24 patients died from cardiac causes. In univariate analysis, predictors of death included the use of anti-aldosterone drugs, low peak Vo2, peak Ve/Vo2, peak Paco2 and high Ve/Vco2 slope, and peak Vd/Vt. Multivariate analysis identified a low peak Paco2 (