Abstract 82: Six-Minute Walk Test as a Prognostic Tool in Patients with Stable Coronary Heart Disease: Data from the Heart and Soul Study

Abstract

Background: The prognostic value of the six-minute walk test (6MWT) in patients with stable coronary heart disease (CHD) is unknown. We sought to determine the ability of the 6MWT to predict cardiovascular events in patients with stable CHD. Methods: We measured 6MWT distance and treadmill exercise capacity in 555 outpatients with stable CHD between September 2000 and December 2002. Participants were followed for an average of 6.8 years for cardiovascular events (heart failure, myocardial infarction, and death). Results: Patients in the lowest quartile of 6MWT distance (87-419 meters) experienced cardiovascular events at 4 times the rate of patients in the highest quartile (544-837 meters) (62% vs. 22%, unadjusted HR 4.26, 95%CI 2.80-6.48, p<0.0001) (see Figure). Each standard deviation (SD) decrease in 6MWT distance (104 meters) was associated with an 86% higher rate of heart failure (age-adjusted HR 1.86, 95%CI 1.51-2.30), a 47% higher rate of myocardial infarction (age-adjusted HR 1.47, 95%CI 1.15-1.89), a 54% higher rate of death (age-adjusted HR 1.54, 95%CI 1.32-1.80), and a 55% higher rate of any event (age-adjusted HR 1.55, 95%CI 1.35-1.78). After adjustment for traditional risk factors and cardiac disease severity measures (ejection fraction, inducible ischemia, diastolic dysfunction, NT-proBNP, and CRP), each SD decrease in 6MWT remained associated with a 28% higher rate of cardiovascular events (HR 1.28, 95%CI 1.08-1.51). When added to the Framingham Risk Score, the 6MWT resulted in category-free net reclassification improvement of 48% (95%CI 32% - 66%). The discriminative ability of 6MWT was similar to treadmill exercise capacity for predicting cardiovascular events (c-statistics 0.70 vs. 0.70, p=0.97). Conclusions: Distance walked on 6MWT predicted cardiovascular events in patients with stable CHD. The addition of 6MWT to traditional risk factors improved risk prediction and was comparable to treadmill exercise capacity.