Don’t shoot the messenger: the 6-minute walk test is a useful outcome measure in exercise trials
Article Outline
To the Editor:
McKelvie et al1 report important data from their randomized, controlled trial of exercise training in chronic heart failure—the largest such trial yet reported. Disappointingly, they found no improvement in the 6-minute walk distance between the exercise and control groups, although there was a small but statistically significant increase in the symptom-limited peak oxygen uptake in the exercise group, and a nonsignificant improvement in a disease-specific quality of life measure in the exercise group.
The authors comment that the 6-minute walk test has given inconsistent results in previous trials of exercise training; the negative example that they refer to, however, showed a 20% improvement in 6-minute walk distance in the exercise group.2 This improvement failed to reach statistical significance because of the small numbers of patients—a type II error.
We believe that the authors are also wrong to conclude that the 6-minute walk test cannot be used as an alternative to peak oxygen uptake. Although it may not be as strong a predictor of mortality or transplantation as peak oxygen uptake, it still correlates significantly with New York Heart Association class, quality of life, mortality, and the need for transplantation.3 It also has considerable face validity as an index of everyday activity, which maximal exercise testing does not. It is reproducible and sensitive to changing clinical condition, even in older patients with heart failure who have comorbid disease,4 who make up the bulk of our patients in the real world, and who often cannot carry out maximal exercise testing.5
In order to realize the promise of exercise training demonstrated in physiological studies, we need to find strategies to improve adherence to training, and we need to ensure that we test our training programs on typical patients using clinically relevant outcome measures. We believe that the 6-minute walk is such a clinically relevant measure and that its use should not be abandoned in trials such as this. Instead, we should ask why the particular intervention used in the Exercise Rehabilitation Trial (EXERT) did not lead to an improvement in the 6-minute walk distance.
References
- Effects of exercise training in patients with heart failure (the Exercise Rehabilitation Trial (EXERT)). Am Heart J. 2002;144:23–30
- Nonpharmacologic therapy improves functional and emotional status in congestive heart failure. Chest. 1994;106:996–1001
- . The 6-minute walk (a simple test with clinical application). Eur Heart J. 2000;21:507–508
- Reproducibility and responsiveness of quality of life assessment and six minute walk test in elderly heart failure patients. Heart. 1998;80:377–382
- Chronic heart failure in the very elderly (clinical status, survival, and prognostic factors in 188 patients more than 70 years old). Am Heart J. 2001;142:174–180
PII: S0002-8703(03)00290-4
doi:10.1016/S0002-8703(03)00290-4
© 2003 Mosby, Inc. All rights reserved.
