Intensity and daily reliability of the six-minute walk test in moderate chronic heart failure patients

Objective: To assess the intensity and daily reliability of the six-minute walk test (6MWT) in patients with moderate chronic heart failure (CHF). Design: Evaluation of testing protocol. Setting: Hospitalized care. Participants: CHF patients under optimal drug treatment (CHF-D, n = 12) or optimal drug treatment plus multisite cardiac pacing (CHF-P, n = 12). Interventions: Not applicable. Main Outcome Measures: Peak values of oxygen uptake (Vo(2)) and heart rate during a symptom-limited, treadmill exercise test and Vo(2), heart rate, and distance during 2 6MWT sessions (morning and afternoon). The 6MWT intensity was estimated by the ratio (%) of Vo(2) and heart rate values measured at the end of this test in relation to the respective peak values obtained during the treadmill exercise test. Results: Subjects' Vo(2) and heart rate during the 6MWT were lower (P < .001) and were about 90% of the peak values (Vo(2): CHF-D, 90.5% +/- 11.1%; CHF-P, 93.0% +/- 13.2%; heart rate: CHF-D, 90.6% +/- 6.6%; CHF-P, 91.4% +/- 9.6%). The distance walked during both 6MWT sessions did not differ significantly, with low coefficients of variation (less than or equal to 2.0%) and high intraclass correlation coefficients (greater than or equal to .98). In CHF-D only, the patients' Vo(2) and heart rate were significantly (P< 0.1, P < .05, respectively) higher during the afternoon session. Conclusions: Despite an intensity significantly lower but close to that of the symptom-limited exercise test, the 6MWT was well tolerated in both CHF groups. In these populations, the 6MWT is reliable on a daily basis, for the distance walked. However, for assessing Vo(2) and heart rate values in CHF-D patients, the 6MWT must always be performed at the same time of day.