Using the 6-min Walk Test to Monitor Peak Oxygen Uptake Response to Cardiac Rehabilitation in Patients With Heart Failure.

PURPOSE We examined the agreement between peak oxygen uptake (VO2peak), estimated using prediction equations from the 6-min Walk Test (6MWT), and VO2peak measured using a cardiopulmonary exercise test (CPX) to estimate change in VO2peak in patients with heart failure (HF) enrolled in cardiac rehabilitation (CR). METHODS This was secondary analysis of 54 (including 9 women) patients with HF who completed a clinical CR program. Four previously published equations using 6MWT distance were used to estimate VO2peak and were compared with a CPX at baseline, follow-up, and change using the standard and modified Bland-Altman method. Analyses were repeated for quartiles of cardiorespiratory fitness (CRF) based on measured VO2peak from the CPX. RESULTS Bland-Altman plots revealed proportional bias between all prediction equations and the measured VO2peak. The difference between methods varied by the level of CRF, with overestimation of prediction equations at greater levels of CRF and underestimation at lower levels of CRF. This poor agreement remained when comparisons were made between the estimated and measured VO2peak values at quartiles of CRF, indicating prediction equations have limited ability to predict VO2peak at any level of CRF. CONCLUSION Estimated VO2peak using 6MWT distance demonstrated poor agreement with measured VO2peak from a CPX. While distance ambulated on the 6MWT remains an important measure of physical performance in patients with HF, prediction equations using 6MWT distance are not appropriate to monitor changes in VO2peak following CR in patients with HF.