Incident atrial fibrillation in relation to disability-free survival, risk of fracture, and changes in physical function in the Cardiovascular Health Study

Abstract

Background: Atrial fibrillation (AF) is common in older adults and associated with an increased risk of stroke, heart failure, dementia, and death, but important gaps remain in our understanding of the physical and functional consequences of AF. The aim of this study was to investigate the associations of incident AF with disability-free survival, risk of fracture, and changes in gait speed and grip strength in the Cardiovascular Health Study (CHS), a population-based longitudinal cohort study of adults aged 65 years and older. Methods: The study population included up to 4462 CHS participants enrolled in fee-for-service Medicare, followed between 1991 and 2009. Individuals with prevalent AF or a history of stroke or heart failure at baseline were excluded. Incident AF during cohort follow-up was identified by annual study electrocardiogram (ECG), hospital discharge diagnosis, or AF diagnosis in Medicare inpatient, outpatient, or physician service claims. Disability-free survival was defined as survival free of Activities of Daily Living (ADL) disability. ADLs were self-reported at annual clinic visits or via telephone interview. Fracture (defined as fractures of the hip, distal forearm, pelvis, or humerus) was identified by hospital discharge diagnosis or Medicare claims. Gait speed (time to walk 15 feet, converted to meters per second) and grip strength (in kilograms) were assessed at annual clinic visits. We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals for the associations of incident AF with disability-free survival and the risk of fracture. Linear mixed effects models were used to examine incident AF and one-year change in grip strength and gait speed. All estimates were adjusted for baseline age sex, race, clinic, education, body mass index, smoking, baseline self-reported physical activity, and time-varying hypertension, use of anti-hypertensive medications, coronary heart disease, and diabetes. Estimates for the associations of incident AF with disability-free survival were further adjusted for interim stroke and heart failure. Results: Incident AF was associated with decreased disability-free survival (HR for death or ADL disability=1.71, 95% CI 1.55, 1.90, HR for ADL disability=1.36, 95% CI 1.18, 1.58) compared to individuals without incident AF, and this association persisted after adjustment for stroke and heart failure (HR for death or ADL disability=1.50, 95% CI 1.34, 1.66, HR for ADL disability=1.24, 95% CI 1.07, 1.44). Incident AF was not associated with changes in gait speed (estimated one-year change in subjects without AF = -0.011 m/s; with incident AF = -0.013 m/s; difference = -0.002 m/s, 95% CI -0.006, 0.003) or grip strength (estimated one-year change in subjects without AF = -0.47 kg; with incident AF = -0.48 kg; difference = -0.01 kg, 95% CI -0.13, 0.10). Individuals with incident AF were not at higher risk of fracture (adjusted HR=0.97, 95% CI 0.77, 1.21) or hip fracture (adjusted HR=1.09, 95% CI 0.83, 1.42). Conclusion: The results of this study suggest that incident AF is a risk factor for disability in older adults. However, incident AF does not appear to be a risk factor for fracture and does not appear to accelerate declines in gait speed or grip strength. Additional research is needed to understand the potential mechanisms through which AF influences disability and to examine whether prevention or treatment of AF can reduce the burden of disability in the elderly.