August 9th, 2012
Go For a Walk: Can Six-Minute-Walk Distance Predict CV Events?
Alexis L Beatty, MD and John Ryan, MD
In this post, Alexis Beatty discusses her Archives of Internal Medicine study, which found that the Six Minute Walk Test (6MWT) improves risk prediction in people with stable coronary heart disease (CHD). CardioExchange’s John Ryan follows up with questions for Beatty about the test.
We have a number of simple tools for predicting risk of a first CHD event. However, our arsenal of tools for predicting risk of secondary events in patients with stable CHD is not as well-stocked. In our recent study we investigated whether the 6MWT — a simple test of functional exercise capacity measuring the distance a person can walk in six minutes — could predict cardiovascular events in a cohort of 556 outpatients with stable CHD enrolled in the Heart and Soul Study, a prospective cohort study at the San Francisco Veterans Affairs Medical Center and University of California, San Francisco.
Those who walked the shortest distance in six minutes (87–419 m) were significantly more likely to have a cardiovascular event (myocardial infarction, heart failure, or death) than those who walked the longest distance in six minutes (544–837 m; 62% vs. 22%). When we compared the improvement in risk prediction with the 6MWT to the improvement in risk prediction with Treadmill Exercise Capacity, we found that the tests were comparable. Thus, the 6MWT may be a simple, inexpensive, and useful tool for determining prognosis in outpatients with stable CHD.
While the results may not be immediately generalizable to all populations (our study had mostly males and we only performed the 6MWT in participants who thought they could walk for six minutes without symptoms), they suggest the potential for the 6MWT to be employed in clinical practice. Also, it would be interesting to see if improving the distance achieved during the 6MWT over time would result in better outcomes.
Ryan: What limited the patients from walking further during their 6MWT test? If they developed fatigue or dyspnea, how confident are we that these symptoms were not an anginal equivalent in this population with stable CHD?
Beatty: Participants who did not think that they could walk for six minutes without having symptoms such as dyspnea or chest pain were not administered the 6MWT in our study. Few patients were limited by chest pain, shortness of breath, or musculoskeletal pain. It is possible that symptoms experienced with a walking test could be an anginal equivalent.
Ryan: Under what circumstances would you recommend a patient with stable CHD be referred for the 6MWT instead of standard stress testing?
Beatty: If the goal is to determine prognosis or functional exercise capacity in a stable patient, then the 6MWT may be preferrable to standard stress testing. If the goal is to diagnose ischemia, standard stress testing would be appropriate and the 6MWT would not be recommended.
Would you perform the 6MWT in your outpatients with stable CHD?
4 Responses to “Go For a Walk: Can Six-Minute-Walk Distance Predict CV Events?”
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How did you tease out those patients who were simply in poor condition? or those with conditions such as obesity or being overweight, COPD/ILD, or venous insufficiency or other chronic vascular disorders?
Some of the participants did have lung disease (17%, including asthma, COPD, and other chronic lung disease) and peripheral arterial disease (7%). The average BMI in our study was around 28. In our primary analysis, we adjusted for the presence of these conditions when looking at the association between 6MWT and cardiovascular events.
It is difficult to say whether we are just picking up people in poor condition. We excluded participants from the main study who didn’t think they would be able to walk one block, and we did not perform the 6MWT in participants who thought they couldn’t walk for six minutes without chest pain, shortness or breath, or other significant symptoms. If you compare the people who didn’t perform the 6MWT because of these exclusions to the people who did perform the 6MWT, the excluded people had similar event rates to the people in the lowest quartile of 6MWT performance.
As a respiratory physician I have daily experience with the 6MWT. For patients with significant comorbidities, i.e. COPD, coxarthrosis, low back pain, pad etc the test is not appropriate.
A proper 6 MWT needs a specially educated nurse for 30 min.
The repeatibility is poor
Patients with a 6 MWT with 800 m are athlets.
One think that has not been mentioned is the use of the the 6MWT as part of a focused attempt to improve patient compliance. Adherence to medication, diet, exercise, non smoking and medication is notoriously low in our society. The 6 MWT can be utilized to encourage group meetings where the goup can benefit form a trained speaker, someone who can motivate the laggards, and improve overall adherence. I have read that poor adherence results in 90,00 deaths and $300 Billion dolars in total expenditures. Even if the numbers may be hard to prove, there is little doubt that we can all do a better job.
Let me hear from you.
David T Nash MD Clinical Professor of Medicine