Six-Minute Walk Test as a Prognostic Tool in Stable Coronary Heart Disease

Abstract

The prognostic value of the 6-minute walk test (6MWT) in patients with stable coronary heart disease is unknown. We sought to determine whether the 6MWT predicted cardiovascular events in ambulatory patients with coronary heart disease. We measured 6MWT distance and treadmill exercise capacity in 556 outpatients with stable coronary heart disease from September 11, 2000, through December 20, 2002. Participants were followed up for a median of 8.0 years for cardiovascular events (heart failure, myocardial infarction, and death). Cardiovascular events occurred in 218 of 556 participants (39.2%). 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, 4.29; 95% CI, 2.83-6.53; P < .001). Each SD decrease in 6MWT distance (104 m) was associated with a 55% higher rate of cardiovascular events (age-adjusted hazard ratio, 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, amino-terminal portion of the prohormone of brain-type natriuretic peptide, and C-reactive protein), each SD decrease in 6MWT was associated with a 30% higher rate of cardiovascular events (hazard ratio, 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 cardiovascular events (C statistics both 0.72; P = .29). Distance walked on the 6MWT predicted cardiovascular events in patients with stable coronary heart disease. The addition of a simple 6MWT to traditional risk factors improved risk prediction and was comparable with treadmill exercise capacity.