Systematic reviewThe 6-minute walk test in outpatient cardiac rehabilitation: validity, reliability and responsiveness—a systematic review
Section snippets
Background
Measurement of oxygen consumption during cardiopulmonary exercise testing is the gold standard for determining baseline functional capacity, training intensity and cardiovascular risk, and for evaluating training outcomes in patients undergoing cardiac rehabilitation [1]. However, the 6-minute walk test (6MWT) is often recommended [2], [3], [4] to estimate functional exercise capacity in patients undergoing cardiac rehabilitation, rather than subjecting patients to an exercise stress test. The
Data sources
The first author conducted searches of OvidMEDLINE (January 1948 to March 2011), CINAHL and SPORTdiscus (January 1997 to April 2011), EMBASE (January 1980 to April 2011), Cochrane Reviews (current) and Cochrane Clinical Trials (current) databases using the search terms in Box A (see supplementary online material). The ‘date of publication’ limitation varied between the databases due to availability of library access.
Eligibility criteria
Trials using 6MWTs in subjects with coronary artery disease undergoing cardiac rehabilitation on an outpatient basis were included. Clinical trials and observational studies that described repeated 6MWTs, that compared 6MWDs with established reference tests, and that examined 6MWDs before and after cardiac rehabilitation were included. Trials that were not available as full-text articles, not in the English language, and in populations other than patients undergoing cardiac rehabilitation on an
Study appraisal and synthesis methods
The first author screened titles and abstracts of the identified articles for duplicates, and adherence to inclusion and exclusion criteria. The reference lists of the included articles were scanned for potentially relevant studies. The first author extracted and tabulated the data from the included articles under the categories of reliability, validity and responsiveness, and the third author confirmed this process.
In order to assess the quality of the extracted articles for reliability,
Results
The search yielded 175 acceptable articles. Fig. 1 outlines the flow of article selection for analysis and the reasons for exclusions. The size of study cohorts varied, with large subject numbers in retrospective studies [6], [28], [29], [30] and smaller numbers in prospective trials [7], [11], [31], [32]. One article described a prospective study and made comparisons retrospectively with data from patient files [10].
Table 1 shows the quality appraisal of the included articles. Some studies
Discussion
The 6MWT is a common outcome measure in cardiac rehabilitation; however, to the authors knowledge, this is the first study to systematically review the reliability, validity and responsiveness of the 6MWT in patients undergoing cardiac rehabilitation. A meta-analysis found strong evidence that the 6MWT is responsive to change in clinical status following cardiac rehabilitation, and found a grouped estimate of the mean difference in 6MWD following cardiac rehabilitation of 60.43 m (95% CI 54.57
Limitations
Although an extensive search of the databases was conducted, it could be that relevant articles were missed by refining the search question to ensure capture of studies in patients undergoing cardiac rehabilitation on an outpatient basis and exclusion of those in other populations. Furthermore, in reviewing the titles in the reference lists of retrieved full-text articles for the terms ‘6MWT’, ‘6MWD’ and ‘outpatient cardiac rehabilitation’, relevant articles may have been excluded. The study
Conclusion and implications of key findings
This review found that the 6MWT is suitable for outcome assessment before and after cardiac rehabilitation, despite a learning effect of 2% to 8% with repeated tests. In order to allow comparison of programme effectiveness, this review found an estimated change in 6MWD following cardiac rehabilitation of 60.4 m, with a median effect size of 0.65.
The evidence for validity against symptom-limited and ventilatory threshold exercise tests and against quality-of-life-measurements remains
Acknowledgements
The authors would like to acknowledge Leanne Bisset for her expert advice in the review of the manuscript, and Ian Yang for his expert advice and assistance with the meta-analysis.
Funding: Grant from Queensland Health Community Rehabilitation Workforce Project: Community Rehabilitation Research Scheme (letter dated 24/6/07).
Conflict of interest: None declared. The Prince Charles Hosptial Ethics Committee approval number: 2760
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