Response to Letter Regarding Article, “Physical Activity and Incidence of Atrial Fibrillation in Older Adults: The Cardiovascular Health Study”
Dr Mont and colleagues highlight prior papers suggesting that, in young and middle-aged adults, high-intensity endurance training is associated with higher risk of lone atrial fibrillation (AF). At first glance, such observations might appear inconsistent with our recent findings that greater habitual light-to-moderate physical activities are associated with significantly lower risk of new-onset AF in older adults.1 Several factors may explain these ostensibly divergent findings. First, AF is a common clinical manifestation of remarkably heterogeneous cardiac and noncardiac conditions, including coronary artery disease, valvular disease, hypertension, sleep apnea, alcohol use, pericarditis, hyperthyroidism, and genetic predisposition. Even “lone” AF has variable definitions and causes2,3 but should exclude persons with hypertension, clinical or structural cardiopulmonary disease, or age >60 years4; thus, lone AF explicitly does not exist in older adults. Consequently, pathophysiologies of lone AF, which represent ≤10% of AF cases in the population,4 may be very different from the much more common AF seen with structural heart disease, hypertension, other disorders, or aging.2,3 Thus, physical activity could increase incidence of “lone” AF in young and middle-aged adults but attenuate numerous other AF risk factors and reduce overall incidence of AF, particularly later in life when risk rises so steeply. We agree with Dr Mont et al that activity intensity may modify effects on AF, depending on the balance between acute triggering versus reduction of chronic vulnerability to AF. We found that greater leisure-time activity, more and faster walking, and moderate-intensity exercise were each associated with lower AF incidence, whereas high-intensity exercise, compared with no exercise, was unassociated with lower or higher risk. As a population-based study, the exercise intensity these older adults characterized as “high” was likely less vigorous than that seen in some younger endurance athletes. Finally, different study designs might produce divergent results. Prior reports suggesting higher AF risk with vigorous exercise or endurance training were all retrospective case-control studies or case series, which could be limited by recall bias, selection bias, or survival bias. A prospective cohort design substantially minimizes these limitations, and future prospective investigations can help confirm the direction and magnitude of associations between physical activity and AF in younger populations. Nearly 1 in 5 Americans aged ≥65 years will develop AF during the next 10 years,1 and habitual light to moderate physical activity appears to be an excellent prescription to help lower this risk.
Mozaffarian D, Furberg CD, Psaty BM, Siscovick D. Physical activity and incidence of atrial fibrillation in older adults: the Cardiovascular Health Study. Circulation. 2008; 118: 800–807.
Schoonderwoerd BA, Smit MD, Pen L, Van Gelder IC. New risk factors for atrial fibrillation: causes of ‘not-so-lone atrial fibrillation’. Europace. 2008; 10: 668–673.
Fuster V, Ryden LE, Cannom DS, Crijns HJ, Curtis AB, Ellenbogen KA, Halperin JL, Le Heuzey JY, Kay GN, Lowe JE, Olsson SB, Prystowsky EN, Tamargo JL, Wann S, Smith SC Jr, Jacobs AK, Adams CD, Anderson JL, Antman EM, Halperin JL, Hunt SA, Nishimura R, Ornato JP, Page RL, Riegel B, Priori SG, Blanc JJ, Budaj A, Camm AJ, Dean V, Deckers JW, Despres C, Dickstein K, Lekakis J, McGregor K, Metra M, Morais J, Osterspey A, Tamargo JL, Zamorano JL. ACC/AHA/ESC 2006 Guidelines for the Management of Patients with Atrial Fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients With Atrial Fibrillation): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society. Circulation. 2006; 114: e257–e354.