Prognostic value of a new cardiopulmonary exercise testing parameter in chronic heart failure: oxygen uptake efficiency at peak exercise — comparison with oxygen uptake efficiency slope

A growing body of evidence shows the prognostic value of oxygen uptake effi ciency slope (OUES), a cardiopulmonary exercise test (CPET) parameter derived from the logarithmic relationship between O2 consumption (VO2) and minute ventilation (VE) in patients with chronic heart failure (CHF). Objective: To evaluate the prognostic value of a new CPET parameter — peak oxygen uptake effi ciency (POUE) — and to compare it with OUES in patients with CHF. Methods: We prospectively studied 206 consecutive patients with stable CHF due to dilated cardiomyopathy — 153 male, aged 53.3±13.0 years, 35.4% of ischemic etiology, left ventricular ejection fraction 27.7±8.0%, 81.1% in sinus rhythm, 97.1% receiving ACE-Is or ARBs, 78.2% beta-blockers and 60.2% spironolactone — who performed a fi rst maximal symptom-limited treadmill CPET, using the modified Bruce protocol. In 33% of patients an cardioverter- defi brillator (ICD) or cardiac resynchronization therapy device (CRT-D) was implanted during follow-up. VO 2, percentage of predicted peak VO2, VE/VCO2 slope, OUES and POUE were analyzed. OUES was calculated using the formula VO2 (l/min) = OUES (log10VE) + b. POUE was calculated as pVO2 (l/min) / log10peakVE (l/min). Correlation coeffi cients between the studied parameters were obtained. The prognosis of each variable adjusted for age was evaluated through Cox proportional hazard models and R2 percent (R2%) and V index (V6) were used as measures of the predictive accuracy of events of each of these variables. Receiver operating characteristic (ROC) curves from logistic regression models were used to determine the cut-offs for OUES and POUE. Results: pVO2: 20.5±5.9; percentage of predicted peak VO2: 68.6±18.2; VE/VCO2 slope: 30.6±8.3; OUES: 1.85±0.61; POUE: 0.88±0.27. During a mean follow-up of 33.1±14.8 months, 45 (21.8%) patients died, 10 (4.9%) underwent urgent heart transplantation and in three patients (1.5%) a left ventricular assist device was implanted. All variables proved to be independent predictors www.revportcardi ol.org ISSN 0870-2551