Six-Minute Walk Test as a Prognostic Tool in Stable Coronary Heart Disease: Data From the Heart and Soul Study
Does a 6-minute walk test (6MWT) provide prognostic information among patients with stable coronary heart disease (CHD)?
Data for the present analysis were from the Heart and Soul Study, a prospective cohort study designed to investigate the effects of psychosocial factors on health outcomes in patients with stable CHD. Patients were eligible if they had at least one of the following: history of myocardial infarction, angiographic evidence of at least 50% stenosis in at least one coronary vessel, evidence of exercise-induced ischemia by treadmill electrocardiogram or stress nuclear perfusion imaging, or a history of coronary revascularization. From September 11, 2000, through December 20, 2002, participants were enrolled from 12 outpatient clinics in the San Francisco bay area. 6MWT distance treadmill exercise capacity was measured; participants were followed for a median of 8.0 years. The primary outcome of interest was a composite outcome of cardiovascular (CV) events including heart failure, myocardial infarction, and death.
Of the 556 participants who provided data on the 6MWT and treadmill testing, 218 (39.2%) experienced CV events during the follow-up period. Patients in the lowest quartile of 6MWT distance (87-419 m) had 4 times the rate of events as those in the highest quartile (544-837 m) (unadjusted hazard ratio [HR], 4.29; 95% confidence interval [CI], 2.83-6.53; p < 0.001). Each standard deviation decrease in 6MWT distance (104 m) was associated with a 55% higher rate of CV events (age-adjusted HR, 1.55; 95% CI, 1.35-1.78). After adjustment for traditional risk factors and cardiac disease severity measures including ejection fraction, each standard deviation decrease in 6MWT was associated with a 30% higher rate of CV events (HR, 1.30; 95% CI, 1.10-1.53). When added to traditional risk factors, the 6MWT resulted in category-free net reclassification improvement of 39% (95% CI, 19%-60%). The discriminative ability of the 6MWT was similar to that of treadmill exercise capacity for predicting CV events (c-statistics both 0.72; p = 0.29).
The investigators concluded that distance walked on a 6MWT predicted CV disease events in patients with stable CHD. The addition of a simple 6MWT to traditional risk factors improved risk prediction and was comparable with treadmill exercise capacity.
These findings suggest a 6MWT is a low-cost effective predictor of CV disease events among patients with stable heart disease. The next question is whether interventions to improve physical activity resulting in improved 6MWT distance would translate into reductions in CV disease events.
Keywords: Myocardial Infarction, Coronary Artery Disease, Follow-Up Studies, Risk Factors, Electrocardiography, Heart Diseases, Prognosis, Incidence, Walking, San Francisco, Motor Activity, Neuroblastoma, Exercise Test
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