Purpose: We examined the agreement between peak oxygen uptake (V˙o2peak), estimated using prediction equations from the 6-min Walk Test (6MWT), and V˙o2peak measured using a cardiopulmonary exercise test (CPX) to estimate change in V˙o2peak 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 V˙o2peak 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 V˙o2peak from the CPX.
Results: Bland-Altman plots revealed proportional bias between all prediction equations and the measured V˙o2peak. 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 V˙o2peak values at quartiles of CRF, indicating prediction equations have limited ability to predict V˙o2peak at any level of CRF.
Conclusion: Estimated V˙o2peak using 6MWT distance demonstrated poor agreement with measured V˙o2peak 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 V˙o2peak following CR in patients with HF.