The 6-minute walk test does not reliably detect changes in functional capacity of patients awaiting cardiac transplantation
Cheetham, C., Taylor, R., Burke, V., O’Driscoll, G., Green, D. J. (2005). The 6-minute walk test does not reliably detect changes in functional capacity of patients awaiting cardiac transplantation. Journal of Heart and Lung Transplantation, 24(7), 848-853. doi:10.1016/j.healun.2004.05.012
Background: Peak oxygen consumption ((Vo2peak) is a strong independent predictor of prognosis in patients with severe chronic heart failure (CHF) and is used to guide optimal timing of transplantation. However, its assessment is relatively expensive and time-consuming and requires sophisticated equipment and highly trained personnel. The purpose of this study was to determine whether changes in 6-minute walk test (6WT) distance, a simple, inexpensive potential alternative measure of functional capacity, can predict changes in Vo2peak in patients with severe CHF.
Methods: Sixteen subjects (ejection fraction 23 ± 2%, Vo2peak 16.2 ± 1.1 ml kg −1min−1) underwent repeated 6WT and Vo2peak assessments that included familiarization and 4 serial measures, 6 weeks apart (baseline and at Weeks 6, 12 and 18). Analysis compared baseline performance with each subsequent testing occasion.
Results: At baseline, mean (± SE) VO2peak was 16.3 ± 1.1 ml kg−1 min−1 and 6WT distance was 458 ± 21 m. 6WT and V̇o2peak were strongly correlated at all timepoints (average r = 0.82; all p < 0.05). However, mixed model analysis, assessing the capacity of the changes seen in 6WT to predict changes in V̇o2peak, showed no statistical significance (F = 0.11; p = 0.74).
Conclusions: The 6WT is commonly used to assess functional capacity in patients with heart failure. This study demonstrates that, despite a strong cross-sectional correlation with Vo2peak, changes in the 6WT are not a reliable predictor of changes in Vo2peak within patients. Therefore, the 6WT has limited utility as a serial measure to assess changes in the clinical status of patients with severe heart failure.