Association of oxygen uptake efficiency slope with other prognostic variables in heart failure

MIRIUKA S.G.; ROSS H.; WALKER M; CARSON S; DELGADO D.

Quebec, Canada

Congreso; Canadian Cardiovascular Congress; 2007

Canadian cardiovascular Society

Background: Oxygen Uptake Efficiency Slope (OUES), measured during cardiopulmonary exercise testing (CPET), has recently been proposed as an alternate way to evaluate functional capacity during exercise in heart failure (HF). OUES can be calculated without maximal exercise, a significant advantage. Previous studies have shown a promising association between OUES and outcomes in heart failure, but its overall utility of OUES in HF patients is unclear. Objectives: To assess OUES in a heart failure cohort and its relationship with clinical and laboratory prognostic variables. Methods: Consecutive heart failure patients (n=42) underwent CPET on a bicycle ergometer using a standardized ramping protocol. Breath-by-breath respiratory gas analysis was performed throughout each stage of exercise. OUES was calculated as described by the analysis of the slope of oxygen consumption (VO2) over the logarithm of ventilation (log VE). Clinical and laboratory variables were collected by chart review. Results: Mean age was 52.6±10.3 years and 31% were female; 61% were non-ischemic cardiomyopathy, 24% were in atrial fibrillation and 98% were on betablockers. Mean OUES was 21.1±7.6. Mean OUES value was significantly different across NYHA functional class (FC I (n=15)=24.4±7.2; FC II (n=14)=22.9±4.5; FC III (n=8)=14.5±7.4; FC IV (n=2)=9±2.5; p=0.001 by ANOVA). OUES was significantly and strongly correlated to peak VO2 (r=0.9, p<0.001) and VE/VCO2 slope (r=0.72, p<0.001). OUES correlated with serum sodium (r=0.48, p=0.002), creatinine (r=-0.37, p=0.02) and hemoglobin (r=0.32, p=0.047). Interestingly, OUES did not correlate with BNP levels (r=-.18, p=0.29), but BNP did correlate to VE/VCO2 slope (r=0.54, p=0.001). To assess the usefulness of OUES during submaximal exercise, OUES was calculated from the first half of the exercise (OUES50). There was a strong correlation between both methods of OUES calculation (r=0,92, p<0.001). OUES50 was also significantly different across NYHA FC (p=0.019 by ANOVA). Conclusions: OUES correlates significantly with peak VO2 and other prognostic variables in a selection of HF patients. OUES may provide useful information in those patients unable to reach anaerobic threshold. Further studies are requried to clarify its role in predicting outcomes in HF.