Minimal important difference for 6-minute walk test distances among patients with chronic heart failure

Abstract

Background: The 6-minute walk test (6 WT) is an established tool in the assessment of endurance and prognosis in patients with chronic heart failure (CHF). For these patients there is very limited data on biological variation of 6 WT distances. We determined the minimal important difference (MID) for the 6 WT in patients with stable systolic CHF.

Methods: Two cohorts of patients with stable systolic CHF were included from the outpatients' clinic of the University of Heidelberg. In these cohorts, two 6 WT measurements were performed - in cohort 1 (n=461) 180 days and in cohort 2 (n=512) 365 days apart. Stability was defined as the absence of clinical events (3 months before the first test, between both tests, and 6 months after the second test) and stability of symptoms (NYHA) between tests. Using a standard error of measurement (SEM)-based approach, we determined the MID for both cohorts.

Results: The intraclass correlation coefficient was 0.89 at 180 days and 0.88 at 365 days. The results were consistent for groups stratified for age, gender, etiology of CHF, and individual NYHA class. The MID for the 6 WT in stable CHF patients was 35 m and 37 m between presentation and 180 and 365 days, respectively.

Conclusion: Submaximal exercise capacity as represented by the 6 WT varies little in stable CHF patients for up to 1-year intervals. The MID for changes in 6 WT values in patients with stable CHF over a period of 6 to 12 months is ~ 36 m.

Keywords: 6-minute walk-test; Biovariability; Heart failure; Minimal important difference.