Prognostic value of time-related changes of cardiopulmonary exercise testing indices in stable chronic heart failure: a pragmatic and operative scheme

Abstract

Although peak oxygen consumption (VO2) is an objective measurement of functional capacity linked to survival, most clinicians use clinical history to monitor changes over time of functional disability. The aim was to verify the prognostic value of time-related changes (Delta) of symptom-limited cardiopulmonary exercise testing (CPX) indices in stable chronic heart failure (CHF). We studied 231 stable CHF patients (200 men) with left ventricular ejection fraction (LVEF) of 24 +/- 8% and peak VO2 of 14.3 +/- 8 ml/kg per min, who performed two symptom-limited CPX over time. The two incremental CPX were separated by a mean interval of 258 +/- 42 days; 59 (26%) suffered cardiovascular death or underwent urgent heart transplantation during the follow-up (1167 +/- 562 days). Peak VO2, LVEF (measured at second evaluation), Deltapeak VO2 and DeltaNYHA (New York Heart Association classification) were selected as independent predictors in the total population, and LVEF, Deltapeak VO2, and NYHA in patients with peak VO2 of 14 ml/kg per min or less (106 patients); no Delta parameter was selected in patients with preserved exercise tolerance. Survival analysis was performed taking into consideration the inter-test variability of peak VO2 (6%): true fall: more than 6% decrease, decline within the measurement variability; less than 6% decrease, improvement within the measurement variability; less than 6% increase and true rise; more than 6% increase: total mortality rate was 51, 23, 19 and 14% (P < 0.0001), respectively. Deltapeak VO2 is a useful outcome index; a combination of static (single) and time-related functional variables can enhance the prognostication process in stable CHF patients.