(Updated at bottom)– The 6-minute walk test (6MWT) can improve risk prediction in people with stable coronary disease, according to a new study published in Archives of Internal Medicine. The 6MWT may also be cost-effective and, in addition, may help physicians motivate their patients to exercise, suggest the authors.
Alexis Beatty and colleagues performed a 6MWT and a treadmill exercise test in 556 people with stable coronary heart disease. After a median followup of 8 years, cardiovascular (CV) events had occurred in 39.2% of the study participants.
Compared to people in the highest quartile of walking distance (544-837 m), people in the lowest quartile of walking distance (87-419 m) had 4 times the risk of a CV event during followup.
- Unadjusted hazard ratio: 4.29, CI 2.83-6.53, p < .001
After adjustment for other factors, each 104 m decrease in walking distance (1 standard deviation) was associated with a 30% increase in CV events (HR 1.30,CI 1.10-1.53). The 6MWT was similar to the treadmill exercise test in predicting CV events.
The authors wrote that treadmill testing is still preferable for evaluating patients with suspected ischemia, but they noted a number of advantages of the 6MWT in stable patients:
The 6MWTcan be conducted with little equipment other than a hallway marked for distance and a stopwatch. Due to the self-paced nature of the test, adverse events of chest pain, dyspnea, or musculoskeletal pain are usually mild; serious adverse events have not been described. Furthermore, the 6MWT is less expensive than treadmill exercise testing, especially if stress testing is bundled with imaging that may be unnecessary.
Furthermore, the 6MWT can be used to motivate patients to exercise:
Despite evidence demonstrating the efficacy of exercise-based rehabilitation in patients with CHD for reducing mortality, most patients do not participate in cardiac rehabilitation or achieve recommended levels of physical activity. There is a need for improved strategies to identify patients at the greatest risk of cardiovascular events and to motivate patients and physicians to address physical activity as a modifiable risk factor. Repeated measurement of the 6MWT could be used as a simple office-based tool to monitor exercise capacity and motivate patients to achieve appropriate levels of physical activity. Although we demonstrated that the 6MWT can predict cardiovascular events in stable CHD, its use for improving prognosis merits further study.
In an accompanying comment, David Nash agrees with the investigators and recommends “that physicians interested in improving their patients’ level of fitness use the 6MWT as a means of getting the patient started on regular exercise. Once the patients become familiar with the ease and safety of the 6MWT, they can be encouraged to repeat the 6MWT more frequently, even on a daily basis. It is then possible to lengthen the walk at appropriate intervals.”
Perhaps I’m overreacting but I think this is a great paper in its own modest way. Unlike so many of the studies I write about I can’t find even a hint of bias, distortion, or gamesmanship. The authors proposed a promising hypothesis, carefully analyzed their results without resorting to data dredging or statistical trickery, and reported the results in a clear and concise manner, always keeping in mind the practical, real-world effect of their work. The authors are academics but this does not appear to be a paper written solely to placate a sponsor, gain publication credit, or display intellectual fireworks.
The absence of any commercial interest or motivation is particularly refreshing, except insofar as the subject of the paper, the 6-minute walk test, may actually save money by offering an inexpensive alternative for suitable patients to the more expensive treadmill exercise tests (and the much more expensive imaging procedures that so often accompany treadmill tests). Further, as the authors and the editorialist observe, the 6-minute walk tests has a rare virtue, in that it secretly performs double duty, not only improving prognostication but supporting the much-needed therapeutic task of starting and encouraging patients to exercise.
These facts shouldn’t be remarkable or unusual in any way. It’s a sad commentary on so much of the medical literature that they are.
Update– Perhaps it’s belaboring the obvious, but I think we should ask why there aren’t more studies like this, and why professional societies and other institutions don’t offer more CME activities to assist physician implementation of these kinds of strategies in clinical practice. Successful introduction of an exercise program in a population at high risk for CV events would almost certainly have a greater impact on outcomes than the various strategies that have been the subject of the myriad ongoing debates in the cardiology community involving drugs versus devices, more drugs versus less drugs, drug A versus drug B, drug A + B versus drug A + B+ C, device X plus drug A versus device Y plus drug B, etc etc ad nauseum.
Imagine if we could devote even a small portion of the intellectual energy and practical resources now devoted to drug and device development to research in exercise and nutrition. The common response to advocates of lifestyle-based therapies is that they don’t work in most people. But remember: the vast majority of drugs don’t work either, and even the most successful drugs and devices require an enormous concentration of resources to bring them successfully to market. Wouldn’t it be great if we could try the same thing with something as simple as exercise?