Maximum Daily 6 Minutes of Activity: An Index of Functional Capacity Derived from Actigraphy and Its Application to Older Adults with Heart Failure

OBJECTIVES: To compare the correlation between the maximum 6 minutes of daily activity (M6min) and standard measures of functional capacity in older adults with heart failure (HF) with that in younger subjects and its prognostic utility. DESIGN: Prospective, cohort study. SETTING: Tertiary care, academic HF center. PARTICIPANTS: Sixty, ambulatory, adults, New York Heart Association (NYHA) Class I to III, stratified into young (50.9 +/- 9.4) and older cohorts (76.8 +/- 8.0). MEASUREMENTS: Correlation between M6min and measures of functional capacity (6-minute walk test; 6MWT) and peak oxygen consumption (VO(2)) according to cardiopulmonary exercise testing in a subset of subjects. Survival analysis was employed to evaluate the association between M6min and adverse events. RESULTS: Adherence to actigraphy was high (90%) and did not differ according to age. The correlation between M6min and 6MWT was higher in subjects aged 65 and older than in those younger than 65 (correlation coefficient (r=0.702, P<.001 vs r=0.490, P=.002). M6min was also significantly associated with peak VO(2) (r=0.612, P=.006). During the study, 26 events occurred (2 deaths, 10 hospitalizations, 8 emergency department visits, and 6 intercurrent illnesses). The M6min was significantly associated with subsequent events (hazard ratio=2.728, 95% confidence interval=1.10-6.77, P=.03), independent of age, sex, ejection fraction, NYHA class, brain natriuretic peptide, and 6MWT. CONCLUSION: The high adherence to actigraphy and association with standard measures of functional capacity and independent association with subsequent morbid events suggest that it may be useful for monitoring older adults with HF.