ELECTROPHYSIOLOGY Resting Heart Rate and Incident Atrial Fibrillation in the Elderly WESLEY T. O’NEAL, M.D., M.P.H.,* MOHAMED F. ALMAHMOUD, M.D.,† and ELSAYED Z. SOLIMAN, M.D., M.SC., M.S.†,‡ From the *Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina; †Department of Internal Medicine, Section on Cardiology, Wake Forest School of Medicine, Winston-Salem, North Carolina; and ‡Department of Epidemiology and Prevention, Epidemiological Cardiology Research Center (EPICARE), Wake Forest School of Medicine, Winston-Salem, North Carolina Background: Alterations in autonomic tone and/or sinus node dysfunction are common with aging. We hypothesized that older persons with low or high heart rates represent a population with subclinical abnormalities who are more likely to develop atrial fibrillation (AF). Methods: A total of 5,226 participants aged 65 years or more (85% white; 42% male) with complete data from the Cardiovascular Health Study were used in this analysis. AF cases were identified during the yearly study electrocardiograms, participant history of a physician diagnosis, or by hospitalization data. Cox regression was used to compute hazard ratios (HR) and 95% confidence intervals (CI) for the association between resting heart rate and incident AF using clinically relevant categories (heart rate 60 beats/min, 60< heart rate beats/min 90 beats/min (reference), heart rate >90 beats/min) and as a continuous variable per 5 beats/min decrease. Results: Over a median follow-up of 12.7 years, a total of 532 (10.2%) participants developed AF. In a multivariable Cox regression analysis, heart rates 60 beats/min (HR = 1.3, 95% CI = 1.1, 1.5), but not >90 beats/min (HR = 1.1, 95% CI = 0.52, 2.3), were associated with an increased risk of AF. Additionally, heart rate per 5 beats/min decrease was associated with an increased risk of AF (HR = 1.06, 95% CI = 1.01, 1.1). The results were consistent in subgroup analyses stratified by age, sex, race, and baseline cardiovascular disease. Conclusion: In the elderly, low heart rates are associated with an increased risk of AF. Potentially, underlying alterations in autonomic tone and/or subclinical sinus node dysfunction manifested as slow heart rate predispose to AF. (PACE 2015; 38:591–597) heart rate, atrial fibrillation, epidemiology Introduction Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice and its prevalence increases with age and among those with diabetes, hypertension, prior myocardial infarction, and heart failure. 1–3 The prevalence Authors Wesley T. O’Neal and Mohamed F. Almahmoud contributed equally in the writing of this manuscript. This manuscript was prepared using CHS research materials obtained from the NHLBI Biologic Specimen and Data Repository Information Coordinating Center and does not necessarily reflect the opinions or views of the CHS or the NHLBI. Disclosures: The authors report no disclosures or sources of funding. Address for reprints: Wesley T. O’Neal, M.D., Department of Internal Medicine, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157. Fax: 336-716- 2273; e-mail: woneal@wakehealth.edu Received October 9, 2014; revised December 3, 2014; accepted January 4, 2015. doi: 10.1111/pace.12591 of AF is projected to double by the year 2050 due to a higher predilection for older adults and the expected growth in this population. 1,4 With the increased burden that AF will place on the healthcare system, the identification of AF risk factors is of paramount importance to detect and treat this arrhythmia in order to prevent complications such as stroke. 5,6 Among patients who are treated for hyperten- sion, a higher incidence of AF has been observed among individuals with higher compared with lower heart rates. 7 In contrast, healthy male endurance athletes who have lower heart rates have been shown to have increased rates of AF than those who have higher heart rates. 8–10 Alterations in autonomic tone and/or sinus node dysfunction, which are common with aging, possibly predispose to AF. Therefore, older persons with low or high heart rates may represent a population more likely to develop AF. To our knowledge, the association between resting heart rate and incident AF has not been examined in the elderly. The purpose of this study was to ©2015 Wiley Periodicals, Inc. PACE, Vol. 38 May 2015 591