SPECIAL COMMUNICATIONS: Letters to the Editor-in-Chief
We recently read with interest the article published by Maldonado-Martin et al. (6), who stated that the 6-min walk test (6-MWT) "does not accurately predict functional capacity in older heart failure patients." In our opinion, several methodological limitations should be appreciated in the context of this study in elderly patients with chronic heart failure (CHF).
The authors' choice of walk test protocol deserves closer attention. No patient encouragement was provided during the 6-MWT. The seminal paper by Guyatt et al. (3) reported that if CHF patients are encouraged, they are able to walk significantly further. The American Thoracic Society (2) stated that "standardized phrases for encouragement must be used during the test" because encouragement significantly increases distance walked.
Measures of cycle ergometer exercise intolerance could be adversely affected by workload selection. Maldonado-Martin reported an initial workload of 12.5 W for 2 min, followed by 25 W for 3 min, and 25-W increments in 3-min stages until volitional fatigue. Other investigators (1), including our laboratory (Academic Cardiology, University of Hull, UK), have found that an initial unloaded cycle phase followed by smaller workload increments (10-15 W·min−1) improves patient compliance with exercise to volitional exhaustion.
Rostagno and coworkers (7) estimated that one in three patients with CHF were unable to perform a cardiopulmonary exercise test (CPET) successfully as defined by an RER ≥ 1.10. In our heart failure clinic, in which the majority of patients suffer from LVSD and are older than 70 yr of age, the figure is closer to one in two. CHF is a condition that often coexists with other morbidities such as osteoarthritis, diabetes, and COPD, among others. These, combined with other cognitive factors and protocol selection affect a patient's ability to perform a CPET successfully. Consequently, it was interesting to read that Maldonado-Martin had excluded "any other condition limiting exercise duration." The authors may have effectively excluded the "more representative" elderly CHF patients from their study. It was not surprising, therefore, that the mean 6-MWT distance (432-447 m) was higher than those typically reported in similar trials.
The 6-MWT is a self-paced test that measures submaximal exercise capacity. We have recently shown that elderly CHF patients perform the 6-MWT below the VT (5). The 6-MWT is a reproducible test in CHF patients with no changes in symptoms after 12 months (4). Further, changes in 6-MWT performance were sensitive to changes in symptom severity. Corresponding CPET data have yet to be reported.
In summary, the decision to ask an elderly patient with CHF to perform a CPET should not be taken lightly, because of the physical and psychological stress involved in testing to volitional exhaustion and/or limiting dyspnea. Maldonado-Martin et al. suggested that direct measurements of peak oxygen consumption and ventilatory threshold should be preferred outcome measures when an accurate determination of functional capacity is required. In our opinion, these tests should be viewed as complementary in that they assess different aspects of functional status, and there are reasons to use one test over another, depending on clinical requirements. For the foreseeable future, the 6-MWT will remain the pragmatic test of choice for assessing submaximal exercise tolerance in elderly CHF patients.
Carnegie Research Institute
Leeds Metropolitan University
Beckett's Park Campus
Leeds LS6 3QS
1. Agostoni, P., R. Pellegrino, C. Conca, J. R. Rodarte, and V. Brusasco. Exercise hyperpnea in chronic heart failure: relationships to lung stiffness and expiratory flow limitation. J. Appl. Physiol.
2. American Thoracic Society. Guidelines for the six-minute walk test. Am. J. Respir. Crit. Care Med.
3. Guyatt, G. H., S. O. Pugsley, M. J. Sullivan, et al. Effect of encouragement on walking test performance. Thorax
4. Ingle, L., R. J. Shelton, A. S. Rigby, S. Nabb, A. L. Clark, and J. G. Cleland. The reproducibility and sensitivity of the 6-min walk test in elderly patients with chronic heart failure. Eur. Heart J.
5. Ingle, L., M. Wilkinson, S. Carroll, C. Boyes, J. G. F. Cleland, and A. L. Clark. Cardiorespiratory requirements of the 6-min walk test in patients with and without left ventricular systolic dysfunction. Int. J. Sports Med.
6. Maldonado-Martin, S., P. H. Brubaker, L. A. Kaminsky, J. B. Moore, K. P. Stewart, and D. W. Kitzman. The relationship of 6-min walk to V˙O2peak
and VT in older heart failure patients. Med. Sci. Sports Exerc.
7. Rostagno, C., G. Olivo, M. Comeglio, et al. Prognostic value of 6-minute walk corridor test in patients with mild to moderate heart failure: comparison with other methods of functional evaluation. Eur. J. Heart Fail.