Effects of Respiratory Exchange Ratio on the Prognostic Value of Peak Oxygen Consumption and Ventilatory Efficiency in Patients With Systolic Heart Failure

Objectives The purpose of this analysis was to evaluate the prognostic characteristics of peak oxygen consumption (Vo(2)) and the minute ventilation/carbon dioxide (VE/Vo(2) ) slope of different peak respiratory exchange ratios (RERs) obtained from cardiopulmonary exercise testing in patients with heart failure (HF). Background For patients with HF, peak Vo(2) and the VE/VCo2 slope are used for assessing prognosis. Peak Vo(2) is assessed in association with peak RER >= 1.10, indicating maximal effort and prognostic sensitivity. Conversely, the VE/VCo2 slope provides effort-independent prognostic discrimination. Methods Patients with HF scheduled to undergo cardiopulmonary exercise testing were enrolled. Patients were subclassified by peak RER (RER < 1.00, RER 1.00 to 1.04, RER 1.05 to 1.09, RER >= 1.10) and followed for up to 3 years for major cardiac-related events (death, left ventricular assist device implantation, or cardiac transplantation). Results Included were 1,728 patients with HF (75% males; 40% ischemic etiology; age: 55 +/- 14 years; left ventricular ejection fraction: 28 +/- 10%). Two hundred seventy major events occurred, with no proportional differences across the RER subgroups. Multivariate Cox regression analysis indicated that the VE/VCo2 slope and peak Vo(2) remained prognostic within each subgroup; the VE/VCo2 slope remained the strongest predictor. Receiver-operating characteristic analysis demonstrated equitable prognostic cutoffs for the VE/VCo2 slope (range: 34.9 to 35.7; area under the curve [AUC] range: 0.69 to 0.75) and peak Vo(2) (range: 13.8 to 14.0 ml$ kg(-1)$ min(-1); AUC range: 0.68 to 0.75). Conclusions Peak Vo(2) provided a sensitive assessment of prognosis in patients with HF in all RER subgroups. The VE/VCo2 slope provided greater prognostic discrimination in all RER subgroups. Clinical consideration may be warranted for patients with low RER, low peak Vo(2), and an elevated VE/VCo2 slope. (J Am Coll Cardiol HF 2013; 1: 427-32) (C) 2013 by the American College of Cardiology Foundation