Exercise anaerobic threshold and ventilatory efficiency identify heart failure patients for high risk of early death

Abstract

Background - The maximal oxygen uptake (peak V̇O2) is used in risk stratification of patients with chronic heart failure (CHF). Peak V̇O2 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 (V̇O2AT) and the ventilatory efficiency (V̇E versus V̇CO2 slope) are less subject to these influences. Thus, we compared these parameters with peak V̇O2 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 V̇O2, V̇O2AT and V̇E versus V̇CO2 slope. We selected peak V̇O2 of ≤14 mL/kg per minute, V̇O2AT of <11 mL/kg per minute, and V̇E versus V̇CO2 slope of >34 as threshold values for high risk of death. The median follow-up time was 644 days. Patients with peak V̇O2 of ≤14 mL/kg per minute had a >3-fold-increased risk (OR= 3.4; CI, 1.3 to 9.1), with V̇O2AT <11 mL/min per kg or V̇E versus V̇CO2 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 V̇O2AT >11 mL/kg per minute and V̇E versus V̇CO2 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 V̇O2AT <11 mL/kg per minute and V̇E versus V̇CO2 slope >34 was the best predictor of 6-month mortality (RR=5.1, P=0.001). Conclusions - V̇O2AT of <11 mL/kg per minute and slope of V̇E versus V̇CO2 >34, combined, better identified patients at high risk for early death from CHF than did peak V̇O2 and should therefore be considered when prioritizing patients for heart transplantation.