The 6-min walk and peak oxygen consumption in advanced heart failure: Aerobic capacity and survival

Background This study sought to determine to what extent the 6-min walk (6MW) distance in advanced heart failure predicts aerobic capacity and provides comparable information regarding survival. Peak oxygen uptake (VO2) and the 6MW both describe function and predict outcome over a wide range of heart failure, but their determinants and implications may differ within a narrower clinical spectrum. This study compared 6MW with aerobic capacity both at peak exercise and during low-level cycling. Methods and Results Both the 6MW and symptom-limited cycle ergometry were performed by 307 patients of whom 264 patients additionally performed 6 min of 20-W cycling to estimate aerobic capacity during sustained low-level activity. In the first 198 patients, multivariate analysis of survival was performed with the 6MW and peakVO(2). Patients achieved the 6MW of 393 +/- 104 m and peakVO(2) of 14 +/- 5 mL/kg per minute. Although low peak VO2 was more likely with the shorter 6MW, the relation was weak within peakVO(2) range of 10 to 20 mL/kg per minute (n = 213, 69% of patients, r = 0.28). During 20-W exercise, VO2 was 9.2 +/- 2.0 mL/kg per minute, with respiratory exchange ratio poorly correlated with the 6MW. in contrast to peakVO(2), the 6MW in meters did not predict survival. Division into short, medium, and long walks, however, supplemented simple clinical description. Conclusions Although helpful in broader populations for identification of patients with obvious clinical compromise, the 6MW distance is not a surrogate for peak VO2 in assessing aerobic capacity or prognosis for individuals with advanced heart failure.