Abstract 005: Six-Minute Walk Test Predicts Heart Failure, Myocardial Infarction, and Death in Patients with Stable Ischemic Heart Disease: Data from the Heart and Soul Study

Abstract

Background: The six-minute walk test (6MWT) is commonly used to assess functional exercise capacity in patients with heart or lung disease. However, its ability to predict events in patients with stable ischemic heart disease (IHD) is unknown. Methods: We measured 6MWT distance and treadmill exercise capacity in 556 outpatients with stable IHD between September 2000 and December 2002. Participants were followed for an average of 7.7 years to determine cardiovascular (CV) events (myocardial infarction, heart failure, or death). We used Cox proportional hazards models to evaluate 6MWT distance and treadmill exercise capacity as predictors of subsequent events. Results: Among the 556 patients, there were 82 heart failure hospitalizations, 63 myocardial infarctions, and 184 deaths from any cause. Patients in the lowest quartile of 6MWT distance (284-1375 ft) were 3 times as likely as patients in the highest quartile (1786-2746 ft) to experience CV events (62% vs. 22%, age-adjusted HR 3.15, 95%CI 1.98-5.03, p<0.0001). Each standard deviation (SD) decrease in 6MWT distance (342 ft) was associated with an 86% greater risk of heart failure (age-adjusted HR 1.86, 95%CI 1.51-2.31, p<0.0001), a 47% greater risk of myocardial infarction (age-adjusted HR 1.47, 95%CI 1.15-1.89, p=0.002), a 54% greater risk of death (age-adjusted HR 1.54, 95%CI 1.32-1.80, p<0.0001), and a 55% greater risk of any event (age-adjusted HR 1.55, 95%CI 1.35-1.78, p<0.0001). After adjustment for traditional risk factors and measures of cardiac disease severity (left ventricular ejection fraction, inducible ischemia, diastolic dysfunction, NT-proBNP and CRP), each SD decrease in 6MWT remained associated with a 38% greater risk of CV events (HR 1.38, 95%CI 1.10-1.74, p=0.005). 6MWT distance was similar to treadmill exercise capacity for predicting CV events (age-adjusted c-statistics 0.72 vs. 0.71, p=0.73 for comparison). Conclusions: Distance walked on 6MWT is as good as treadmill exercise capacity for predicting CV events in patients with stable IHD.