The 6-minute walk test may improve cardiovascular risk prediction in patients with stable coronary heart disease, researchers found.

Even after adjustment for traditional cardiovascular risk factors and measures of cardiac disease severity, each standard deviation decrease in walk distance was associated with a 30% greater risk of MI, heart failure, or death (HR 1.30, 95% CI 1.10 to 1.53), according to Alexis Beatty, MD, of the University of California San Francisco, and colleagues.

And adding the 6-minute walk distance to traditional risk factors improved a predictive model, with the C statistic increasing from 0.69 to 0.72 (P=0.04), the researchers reported online in Archives of Internal Medicine.

“Given the greater ease and lesser cost of the 6-minute walk test compared with cardiovascular stress testing, I would recommend that physicians interested in improving their patients’ level of fitness use the [test] as a means of getting the patient started on regular exercise,” David Nash, MD, of the SUNY Upstate Medical Center in Syracuse, wrote in an accompanying comment. “Once the patients become familiar with the ease and safety of the 6-minute walk test, they can be encouraged to repeat the [test] more frequently, even on a daily basis,” he wrote. “It is then possible to lengthen the walk at appropriate intervals.” The 6-minute walk test has been shown to predict cardiovascular events in patients with heart failure, pulmonary hypertension, and pulmonary disease, but its prognostic value in patients with stable coronary heart disease had remained unknown. To explore the issue, Beatty and colleagues examined data from 556 outpatients with stable coronary heart disease who were enrolled in the Heart and Soul Study. All underwent a 6-minute walk test and treadmill exercise testing from Sept. 11, 2000, through Dec. 20, 2002. Through a median of 8 years of follow-up, 39.2% of the patients met the composite cardiovascular endpoint that included heart failure, MI, or death from cardiovascular events, including heart failure, MI, and all-cause death. The rate was about 62% among patients in the lowest quartile for 6-minute walk distance (285 feet to 1,375 feet) and about 22% for those in the highest quartile (1,785 feet to 2,746 feet). The difference was significant at P<0.001. Each standard deviation decrease in the 6-minute walk test (341 feet) was associated with a greater risk of the composite endpoint and each of the individual components, even after adjustment for traditional risk factors. Adding the 6-minute walk distance to those risk factors resulted in a category-free net reclassification improvement of 39.3% and an integrated discrimination improvement of 4.1%. The discriminative ability of the test was similar to that of the treadmill exercise test. Both yielded a C statistic of 0.72. "Treadmill exercise testing will remain the preferred modality for evaluating patients with suspected ischemia," according to Beatty and colleagues. "However, for stable outpatients undergoing testing for prognosis, the 6-minute walk test offers potential advantages." Those include the simplicity of the test, which requires a hallway with distance markings and a stopwatch, the generally mild adverse events resulting from the self-paced nature of the test, and the lower cost. "The 2012 Medicare Physician Fee schedule reports a payment for the 6-minute walk test of $59.91 compared with cardiovascular stress testing at $88.50 (plus $208 to $503 for imaging)," the authors noted. They acknowledged that the study was limited by potential selection bias, the inclusion of mostly male participants, and the exclusion of patients who could not walk at least one block. Beatty is supported by the National Heart, Lung, and Blood Institute. The Heart and Soul Study was supported by a grant from the Department of Veterans Affairs (Epidemiology Merit Review Program); a grant from the National Heart, Lung, and Blood Institute; and grants from the Robert Wood Johnson Foundation (Generalist Physician Faculty Scholars Program), the American Federation for Aging Research (Paul Beeson Faculty Scholars in Aging Research Program), the Ischemia Research and Education Foundation, and Nancy Kirwan Heart Research Fund.