Exercise Anaerobic Threshold and Ventilatory Efficiency Identify Heart Failure Patients for High Risk of Early Death

Abstract

Background— The maximal oxygen uptake (peak V̇ o 2 ) is used in risk stratification of patients with chronic heart failure (CHF). Peak V̇ o 2 might be lower than maximally possible if exercise is stopped early because of lack of patient motivation or premature cessation by the investigator. In contrast, the anaerobic threshold (V̇ o 2 AT) and the ventilatory efficiency (V̇ e versus V̇ co 2 slope) are less subject to these influences. Thus, we compared these parameters with peak V̇ o 2 in identifying patients with CHF at increased risk for death within 6 months after evaluation. Methods and Results— We performed cardiopulmonary exercise tests with gas exchange measurements in 223 consecutive patients with CHF (114 coronary artery disease, 92 dilated cardiomyopathy, 17 others) at the Herzzentrum Ludwigshafen between 1995 and 1998. We measured peak V̇ o 2 , V̇ o 2 AT and V̇ e versus V̇ co 2 slope. We selected peak V̇ o 2 of ≤14 mL/kg per minute, V̇ o 2 AT of <11 mL/kg per minute, and V̇ e versus V̇ co 2 slope of >34 as threshold values for high risk of death. The median follow-up time was 644 days. Patients with peak V̇ o 2 of ≤14 mL/kg per minute had a >3-fold-increased risk (OR=3.4; CI, 1.3 to 9.1), with V̇ o 2 AT <11 mL/min per kg or V̇ e versus V̇ co 2 slope >34 a 5-fold increased risk for early death (OR=5.3; CI, 1.5 to 19.0; OR=4.8; CI, 1.7 to 13.8, respectively). In patients with both V̇ o 2 AT <11 mL/kg per minute and V̇ e versus V̇ co 2 slope >34, the risk of early death was 10-fold higher (OR=9.6; CI, 2.1 to 44.7). After correction for age, sex, left ventricular ejection fraction, and New York Heart Association class in a multivariate analysis, the combination of V̇ o 2 AT <11 mL/kg per minute and V̇ e versus V̇ co 2 slope >34 was the best predictor of 6-month mortality (RR=5.1, P =0.001). Conclusions— V̇ o 2 AT of <11 mL/kg per minute and slope of V̇ e versus V̇ co 2 >34, combined, better identified patients at high risk for early death from CHF than did peak V̇ o 2 and should therefore be considered when prioritizing patients for heart transplantation.