A MET a Day Keeps Arrhythmia at Bay: The Association Between Exercise or Cardiorespiratory Fitness and Atrial Fibrillation

Abstract

Medical scholars have long regarded exercise as critical to successful maintenance of health and avoidance of disease.1O'Keefe J.H. Franklin B. Lavie C.J. Exercising for health and longevity vs peak performance: different regimens for different goals.Mayo Clin Proc. 2014; 89: 1171-1175Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar Expanding on this concept, the contemporary practice of medicine requires that we be able to offer patients definitions of what is specifically meant by “exercise” and, indeed, by “health.” Over the past several decades, research into atrial fibrillation has suggested that it may be an epidemiological inevitability—ie, an event a substantial proportion of people will experience at some juncture of their lives. However, increasingly, research data have suggested that, in fact, this perceived “inevitability” may be one created by ourselves—by lifestyle choices, obesity, poor fitness, and diet. Several investigators have specifically focused on the role of exercise and physical fitness in the pathogenesis of atrial fibrillation. However, the data in this regard have often been conflicting, and thus practitioners of medicine are required to reconcile those conflicts to identify best clinical advice for their patients. In this issue of Mayo Clinic Proceedings, Faselis et al2Faselis C. Kokkinos P. Tsimploulis A. et al.Exercise capacity and atrial fibrillation risk in veterans: a cohort study.Mayo Clin Proc. 2016; 91: 558-566Google Scholar report an inverse association between the exercise capacity of military veterans and the likelihood of development of atrial fibrillation over long-term follow-up. These data suggest that better exercise capacity serves as a protective measure against atrial fibrillation. However, this suggestion that physical fitness confers benefit appears at first glance to counter prior data that participating in long-term, high-intensity physical activity is associated with increased arrhythmia risk. It is important that we attempt to understand the fundamental differences among the various research results, such that any reconciliation can be used to provide appropriate prescription for our patients. Specifically, our interpretation and speculative synthesis should account for a pathophysiologic difference between cardiorespiratory fitness in the broader population vs high-intensity physical activity among elite athletes and recognize that extremes of exercise—ie, too little or too much exercise—may impact atrial fibrillation risk. There is an established body of literature supporting the concept that endurance exercise, particularly in elite athletes and military personnel, increases the risk of atrial fibrillation.3Baldesberger S. Bauersfeld U. Candinas R. et al.Sinus node disease and arrhythmias in the long-term follow-up of former professional cyclists.Eur Heart J. 2008; 29: 71-78Crossref PubMed Scopus (245) Google Scholar, 4Karjalainen J. Kujala U.M. Kaprio J. Sarna S. Viitasalo M. Lone atrial fibrillation in vigorously exercising middle aged men: case-control study.BMJ. 1998; 316: 1784-1785Crossref PubMed Scopus (257) Google Scholar, 5Mont L. Tamborero D. Elosua R. et al.Physical activity, height, and left atrial size are independent risk factors for lone atrial fibrillation in middle-aged healthy individuals.Europace. 2008; 10: 15-20Crossref PubMed Scopus (209) Google Scholar, 6Elosua R. Arquer A. Mont L. et al.Sport practice and the risk of lone atrial fibrillation: a case-control study.Int J Cardiol. 2006; 108: 332-337Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar, 7Heidbüchel H. Anné W. Willems R. Adriaenssens B. Van de Werf F. Ector H. Endurance sports is a risk factor for atrial fibrillation after ablation for atrial flutter.Int J Cardiol. 2006; 107: 67-72Abstract Full Text Full Text PDF PubMed Scopus (133) Google Scholar, 8Molina L. Mont L. Marrugat J. et al.Long-term endurance sport practice increases the incidence of lone atrial fibrillation in men: a follow-up study.Europace. 2008; 10: 618-623Crossref PubMed Scopus (248) Google Scholar, 9Aizer A. Gaziano J.M. Cook N.R. Manson J.E. Buring J.E. Albert C.M. Relation of vigorous exercise to risk of atrial fibrillation.Am J Cardiol. 2009; 103: 1572-1577Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar This evidence appears contrary to expectations that exercise is assumed to have a beneficial effect on prevention of cardiac diseases and mortality. Specifically, it is initially difficult to reconcile how exercise-related improvements in general cardiovascular health may actually increase the risk of atrial fibrillation. In order to gain insights, a deeper understanding of underlying pathophysiology is critical. An important pathophysiologic underpinning of atrial fibrillation is that of autonomic dysregulation. Historically, atrial fibrillation has often been regarded, at least in part, as a result of abnormal autonomic tone, occurring as a result of sympathetic/parasympathetic mismatch.10Kapa S. Mears J.A. Asirvatham S.J. The autonomic ether: emerging electrophysiologic associations.Indian Heart J. 2011; 63: 333-340PubMed Google Scholar Coumel et al11Coumel P. Attuel P. Lavallée J. Flammang D. Leclercq J.F. Slama R. The atrial arrhythmia syndrome of vagal origin.Arch Mal Coeur Vaiss. 1978; 71 ([in French]): 645-656PubMed Google Scholar first coined the concept of “vagal atrial fibrillation,” with subsequent data suggesting that atrial fibrillation may occur because of sudden shifts between high sympathetic and high vagal tone.10Kapa S. Mears J.A. Asirvatham S.J. The autonomic ether: emerging electrophysiologic associations.Indian Heart J. 2011; 63: 333-340PubMed Google Scholar However, atrial fibrillation is, in fact, a heterogeneous disease process likely influenced by multiple factors, including neural, structural (eg, left atrial size), hemodynamic (eg, left atrial stretch in the setting of hypertension or diastolic dysfunction), and electrical (eg, varied conduction patterns throughout the atrial myocardium due to patchy fibrosis) pathology. Although the contribution of exercise to this milieu is thought to be related to altered autonomic tone, it may in fact be that different forms of exercise alter atrial fibrillation risk through a spectrum of direct and indirect cardiovascular effects not solely related to those of the autonomic nervous system. Specifically, exercise has been found to result in ventricular hypertrophy, which, in turn, may cause some element of diastolic dysfunction and increased left atrial stretch, culminating in atrial fibrillation.12McClean G. George K. Lord R. et al.Chronic adaptation of atrial structure and function in elite male athletes.Eur Heart J Cardiovasc Imaging. 2015; 16: 417-422Crossref PubMed Scopus (33) Google Scholar The epidemiological data on atrial fibrillation risk and exercise have largely been obtained in endurance athletes (ie, elite athletes) and active military personnel.3Baldesberger S. Bauersfeld U. Candinas R. et al.Sinus node disease and arrhythmias in the long-term follow-up of former professional cyclists.Eur Heart J. 2008; 29: 71-78Crossref PubMed Scopus (245) Google Scholar, 4Karjalainen J. Kujala U.M. Kaprio J. Sarna S. Viitasalo M. Lone atrial fibrillation in vigorously exercising middle aged men: case-control study.BMJ. 1998; 316: 1784-1785Crossref PubMed Scopus (257) Google Scholar, 5Mont L. Tamborero D. Elosua R. et al.Physical activity, height, and left atrial size are independent risk factors for lone atrial fibrillation in middle-aged healthy individuals.Europace. 2008; 10: 15-20Crossref PubMed Scopus (209) Google Scholar, 6Elosua R. Arquer A. Mont L. et al.Sport practice and the risk of lone atrial fibrillation: a case-control study.Int J Cardiol. 2006; 108: 332-337Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar, 7Heidbüchel H. Anné W. Willems R. Adriaenssens B. Van de Werf F. Ector H. Endurance sports is a risk factor for atrial fibrillation after ablation for atrial flutter.Int J Cardiol. 2006; 107: 67-72Abstract Full Text Full Text PDF PubMed Scopus (133) Google Scholar, 8Molina L. Mont L. Marrugat J. et al.Long-term endurance sport practice increases the incidence of lone atrial fibrillation in men: a follow-up study.Europace. 2008; 10: 618-623Crossref PubMed Scopus (248) Google Scholar, 9Aizer A. Gaziano J.M. Cook N.R. Manson J.E. Buring J.E. Albert C.M. Relation of vigorous exercise to risk of atrial fibrillation.Am J Cardiol. 2009; 103: 1572-1577Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar Furthermore, most studies fall into 1 of 3 distinct patterns: (1) controlled studies of participants involved in high-intensity exercise (ie, engaged in competitive sports, endurance athletes), (2) population-based cohort studies in which exercise levels are studied by survey, and (3) studies of effect on level of cardiorespiratory fitness as assessed by exercise testing.3Baldesberger S. Bauersfeld U. Candinas R. et al.Sinus node disease and arrhythmias in the long-term follow-up of former professional cyclists.Eur Heart J. 2008; 29: 71-78Crossref PubMed Scopus (245) Google Scholar, 4Karjalainen J. Kujala U.M. Kaprio J. Sarna S. Viitasalo M. Lone atrial fibrillation in vigorously exercising middle aged men: case-control study.BMJ. 1998; 316: 1784-1785Crossref PubMed Scopus (257) Google Scholar, 5Mont L. Tamborero D. Elosua R. et al.Physical activity, height, and left atrial size are independent risk factors for lone atrial fibrillation in middle-aged healthy individuals.Europace. 2008; 10: 15-20Crossref PubMed Scopus (209) Google Scholar, 6Elosua R. Arquer A. Mont L. et al.Sport practice and the risk of lone atrial fibrillation: a case-control study.Int J Cardiol. 2006; 108: 332-337Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar, 7Heidbüchel H. Anné W. Willems R. Adriaenssens B. Van de Werf F. Ector H. Endurance sports is a risk factor for atrial fibrillation after ablation for atrial flutter.Int J Cardiol. 2006; 107: 67-72Abstract Full Text Full Text PDF PubMed Scopus (133) Google Scholar, 8Molina L. Mont L. Marrugat J. et al.Long-term endurance sport practice increases the incidence of lone atrial fibrillation in men: a follow-up study.Europace. 2008; 10: 618-623Crossref PubMed Scopus (248) Google Scholar, 9Aizer A. Gaziano J.M. Cook N.R. Manson J.E. Buring J.E. Albert C.M. Relation of vigorous exercise to risk of atrial fibrillation.Am J Cardiol. 2009; 103: 1572-1577Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar, 13Frost L. Frost P. Vestergaard P. Work related physical activity and risk of a hospital discharge diagnosis of atrial fibrillation or flutter: the Danish Diet, Cancer, and Health Study.Occup Environ Med. 2005; 62: 49-53Crossref PubMed Scopus (43) Google Scholar, 14Everett B.M. Conen D. Buring J.E. Moorthy M.V. Lee I.M. Albert C.M. Physical activity and the risk of incident atrial fibrillation in women.Circ Cardiovasc Qual Outcomes. 2011; 4: 321-327Crossref PubMed Scopus (81) Google Scholar, 15Mozaffarian D. Furberg C.D. Psaty B.M. Siscovick D. Physical activity and incidence of atrial fibrillation in older adults: the Cardiovascular Health Study.Circulation. 2008; 118: 800-807Crossref PubMed Scopus (335) Google Scholar, 16Grundvold I. Skretteberg P.T. Liestøl K. et al.Importance of physical fitness on predictive effect of body mass index and weight gain on incident atrial fibrillation in healthy imaged men.Am J Cardiol. 2012; 110: 425-432Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar, 17Qureshi W. Alirhayim Z. Blaha M.J. et al.Cardiorespiratory fitness and risk of incident atrial fibrillation: results from the Henry Ford Exercise Testing (FIT) Project.Circulation. 2015; 131: 1827-1834Crossref PubMed Scopus (131) Google Scholar, 18Pathak R.K. Elliott A. Middeldorp M.E. et al.Impact of CARDIOrespiratory FITness on arrhythmia recurrence in obese individuals with atrial fibrillation: the CARDIO-FIT Study.J Am Coll Cardiol. 2015; 66: 985-996Abstract Full Text Full Text PDF PubMed Scopus (333) Google Scholar Table 1 summarizes studies to date regarding exercise and atrial fibrillation risk, and Table 2 summarizes studies of fitness levels and their impact on atrial fibrillation risk.Table 1Studies of Exercise and Atrial Fibrillation RiskReference, yearPopulationExercise levelAtrial fibrillation riskIncreased risk Baldesberger et al,3Baldesberger S. Bauersfeld U. Candinas R. et al.Sinus node disease and arrhythmias in the long-term follow-up of former professional cyclists.Eur Heart J. 2008; 29: 71-78Crossref PubMed Scopus (245) Google Scholar 2008Former professional cyclists (n=134) vs controls (n=62)HighIncreased (10% vs 0%) Karjalainen et al,4Karjalainen J. Kujala U.M. Kaprio J. Sarna S. Viitasalo M. Lone atrial fibrillation in vigorously exercising middle aged men: case-control study.BMJ. 1998; 316: 1784-1785Crossref PubMed Scopus (257) Google Scholar 1998Top-level veteran orienteers (n=300) vs controls (n=495)HighIncreased (5.3% vs 0.9%) Mont et al,5Mont L. Tamborero D. Elosua R. et al.Physical activity, height, and left atrial size are independent risk factors for lone atrial fibrillation in middle-aged healthy individuals.Europace. 2008; 10: 15-20Crossref PubMed Scopus (209) Google Scholar 2008Patients (n=107) vs healthy volunteers (n=107)Moderate to highIncreased, dose dependent with more hours, heavier exertion (odds ratio, 15) Elosua et al,6Elosua R. Arquer A. Mont L. et al.Sport practice and the risk of lone atrial fibrillation: a case-control study.Int J Cardiol. 2006; 108: 332-337Abstract Full Text Full Text PDF PubMed Scopus (199) Google Scholar 2006Sports competitors (n=60) vs controls (n=109)HighIncreased (odds ratio, 3) Heidbüchel et al,7Heidbüchel H. Anné W. Willems R. Adriaenssens B. Van de Werf F. Ector H. Endurance sports is a risk factor for atrial fibrillation after ablation for atrial flutter.Int J Cardiol. 2006; 107: 67-72Abstract Full Text Full Text PDF PubMed Scopus (133) Google Scholar 2006Endurance athletes (n=31) vs controls (n=106) with history of CTI flutterHighIncreased (odds ratio, 1.8) Molina et al,8Molina L. Mont L. Marrugat J. et al.Long-term endurance sport practice increases the incidence of lone atrial fibrillation in men: a follow-up study.Europace. 2008; 10: 618-623Crossref PubMed Scopus (248) Google Scholar 2008Marathon runners (n=252) vs controls (n=305)HighIncreased (odds ratio, 8.8) Aizer et al,9Aizer A. Gaziano J.M. Cook N.R. Manson J.E. Buring J.E. Albert C.M. Relation of vigorous exercise to risk of atrial fibrillation.Am J Cardiol. 2009; 103: 1572-1577Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar 2009Physicians engaging in exercise (n=16,921)Moderate to highIncreased in young men and joggers (odds ratio, ∼1.5-1.7), decreased with increasing ageNo effect Frost et al,13Frost L. Frost P. Vestergaard P. Work related physical activity and risk of a hospital discharge diagnosis of atrial fibrillation or flutter: the Danish Diet, Cancer, and Health Study.Occup Environ Med. 2005; 62: 49-53Crossref PubMed Scopus (43) Google Scholar 2005Population based (n=38,000)Light to moderate (work related)No effect Everett et al,14Everett B.M. Conen D. Buring J.E. Moorthy M.V. Lee I.M. Albert C.M. Physical activity and the risk of incident atrial fibrillation in women.Circ Cardiovasc Qual Outcomes. 2011; 4: 321-327Crossref PubMed Scopus (81) Google Scholar 2011Women (n=34,759)Moderate by MET hours per weekNo effect (after accounting for BMI)Reduced risk Mozaffarian et al,15Mozaffarian D. Furberg C.D. Psaty B.M. Siscovick D. Physical activity and incidence of atrial fibrillation in older adults: the Cardiovascular Health Study.Circulation. 2008; 118: 800-807Crossref PubMed Scopus (335) Google Scholar 2008Population based (n=5446)Light to moderateReduced risk (odds ratio, 0.72) with moderate; no effect with high intensityBMI = body mass index; CTI = cavotricuspid isthmus; MET = metabolic equivalent task. Open table in a new tab Table 2Studies of Fitness Level and Atrial Fibrillation RiskReference, yearPopulationFitness levelAtrial fibrillation riskGrundvold et al,16Grundvold I. Skretteberg P.T. Liestøl K. et al.Importance of physical fitness on predictive effect of body mass index and weight gain on incident atrial fibrillation in healthy imaged men.Am J Cardiol. 2012; 110: 425-432Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar 2012Middle-aged men (n=2014)Greater than population meanReduced risk by 23% when “fit” (ie, better than mean)Qureshi et al,17Qureshi W. Alirhayim Z. Blaha M.J. et al.Cardiorespiratory fitness and risk of incident atrial fibrillation: results from the Henry Ford Exercise Testing (FIT) Project.Circulation. 2015; 131: 1827-1834Crossref PubMed Scopus (131) Google Scholar 2015Population based (n=64,561)Increasing levels of fitness based on METsOne higher MET achieves 7% reduced riskPathak et al,18Pathak R.K. Elliott A. Middeldorp M.E. et al.Impact of CARDIOrespiratory FITness on arrhythmia recurrence in obese individuals with atrial fibrillation: the CARDIO-FIT Study.J Am Coll Cardiol. 2015; 66: 985-996Abstract Full Text Full Text PDF PubMed Scopus (333) Google Scholar 2015Consecutive obese patients (n=1415)Exercise program, assessment of METsFitness gain of ≥2 METs = 83% freedom vs 29% freedom in fitness gain <2 METsFaselis et al,2Faselis C. Kokkinos P. Tsimploulis A. et al.Exercise capacity and atrial fibrillation risk in veterans: a cohort study.Mayo Clin Proc. 2016; 91: 558-566Google Scholar 2016Military veterans (n=5962)Levels of fitness based on METs (9 being highest)High levels of fitness have reduced risk (odds ratio, 0.37)MET = metabolic equivalent task. Open table in a new tab BMI = body mass index; CTI = cavotricuspid isthmus; MET = metabolic equivalent task. MET = metabolic equivalent task. Overall, the data appear to suggest that high levels of frequent exertional activity (eg, endurance athletics) carry some increased risk of atrial fibrillation, although activity in general (ie, daily light to moderate physical activity) has either no effect on risk or perhaps even a reduced risk. This finding is counter to the results of studies of cardiorespiratory fitness that suggest that either a better initial fitness level or improvement in the level of fitness over time carries protective benefits against atrial fibrillation. However, one critical difference between these 2 concepts is that while studies based on exercise depended on self-reporting of activity levels, studies based on fitness level typically employed objective standards to measure cardiorespiratory fitness. The vast majority of published studies have found beneficial effects of physical activity on long-term cardiovascular risk.1O'Keefe J.H. Franklin B. Lavie C.J. Exercising for health and longevity vs peak performance: different regimens for different goals.Mayo Clin Proc. 2014; 89: 1171-1175Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar In fact, light to moderate physical activity can improve diabetes mellitus control, cholesterol levels, body mass index, coronary disease risk, and symptoms associated with heart failure. However, at high levels of aerobic activity, deleterious effects on the heart have also been reported. Elevation of serum troponin concentrations (eg, in marathon runners), decreased right ventricular function, and other effects have been clearly associated with high-level endurance exercise.19Shave R. Baggish A. George K. et al.Exercise-induced cardiac troponin elevation: evidence, mechanisms, and implications.J Am Coll Cardiol. 2010; 56: 169-176Abstract Full Text Full Text PDF PubMed Scopus (319) Google Scholar, 20Elliott A.D. La Gerche A. The right ventricle following prolonged endurance exercise: are we overlooking the more important side of the heart? a meta-analysis.Br J Sports Med. 2015; 49: 724-729Crossref PubMed Scopus (68) Google Scholar Although the effects of exercise on autonomic tone wherein parasympathetic/vagal tone is increased would seem to universally offer cardiac benefits, it may be that there does exist a subtype of vagal atrial fibrillation that, in the setting of a profound predominance of vagal tone, predisposes some individuals to atrial fibrillation. It has long been recognized that individuals who engage in endurance exercise have higher parasympathetic tone, less sympathetic outflow at times of peak exercise, and lower heart rates at rest.21Winder W.W. Hagberg J.M. Hickson R.C. Ehsani A.A. McLane J.A. Time course of sympathoadrenal adaptation to endurance exercise training in man.J Appl Physiol Respir Environ Exerc Physiol. 1978; 45: 370-374PubMed Google Scholar However, interestingly, increased vagal tone has also been conversely suggested to reduce atrial fibrillation risk. Thus, instead it may be that net sympathetic-parasympathetic balance and sudden shifts in that balance contribute more to the genesis of atrial fibrillation than increased vagal tone alone.10Kapa S. Mears J.A. Asirvatham S.J. The autonomic ether: emerging electrophysiologic associations.Indian Heart J. 2011; 63: 333-340PubMed Google Scholar The more active the individual, the more profound the parasympathetic dominance may be. However, how much more incrementally “fit” the endurance athlete is than the light to moderate daily exerciser and how this difference in fitness translates into differences in sympathovagal balance is less clear. It is possible that at extreme levels of exercise, physiologic benefits initially achieved with improved autonomic tone and fitness may reverse and lead to pathologic effects thereby increasing arrhythmia risk. What is more likely is that exercise does not carry a dose-dependent benefit at higher levels, but the net benefit actually declines at some point and eventually increases arrhythmia risk (Figure). The combination of autonomic, structural, and hemodynamic effects with high-level endurance exercise may impart some of this increased risk of arrhythmias. However, it is not well established at what level of exercise this risk increases and whether there is an “optimal” exercise regimen to avoid falling on the “wrong” end of the risk-to-benefit curve. Patients who engage in endurance exercise generally are younger and have fewer cardiovascular risk factors than those who do not. Thus, even though there is an increased risk of atrial fibrillation associated with higher-level endurance exercise, whether individuals who engage in endurance exercise should be treated more aggressively for thromboembolic risk is unclear. In fact, studies to date suggest that patients who engage in endurance exercise have a lower long-term risk of stroke.22Lee C.D. Folsom A.R. Blair S.N. Physical activity and stroke risk: a meta-analysis.Stroke. 2003; 34: 2475-2481Crossref PubMed Scopus (595) Google Scholar There is a lack of studies on whether those who engage in endurance exercise and have development of atrial fibrillation necessarily have an increased stroke risk compared with the general population. This issue is a particularly appealing focus for future research given the former group's overall lower likelihood of other stroke risk factors such as diabetes mellitus, atherosclerotic disease, and hypertension. Further study is needed to better understand if this subtype of atrial fibrillation associated with endurance exercise is as equally pathologic as atrial fibrillation that occurs in relatively more sedentary, obese, and older cohorts. Also appearing in the current issue of Mayo Clinic Proceedings, Chao et al23Chao T.-F. Liu C.-J. Tuan T.-C. et al.Impact on outcomes of changing treatment guideline recommendations for stroke prevention in atrial fibrillation: a nationwide cohort study.Mayo Clin Proc. 2016; 91: 567-574Google Scholar report on the relationship between changing treatment guidelines for stroke prevention vs patient outcomes. On the basis of their findings, evolving guidelines are resulting in anticoagulation being recommended in significantly more patients with atrial fibrillation. In turn, following these guidelines has resulted in improved patient outcomes. Thus, as evidence and guidelines serve to further refine exactly who requires anticoagulation, consideration of specific cohorts who may reflect a different “subtype” of atrial fibrillation (eg, exercise-associated atrial fibrillation) will need to be considered. For now, however, clinician and patient adherence to guideline recommendations for anticoagulation (even if questions arise about the cause of a specific patient's atrial fibrillation) is most likely to optimize patient outcomes. There are 2 critical limitations to existing studies of the association between physical activity, fitness, and atrial fibrillation. First, most studies depend on resting electrocardiograms and not more intensive ambulatory monitoring (eg, employing continuous loop recorders). This type of limitation is present in the study by Faselis et al.2Faselis C. Kokkinos P. Tsimploulis A. et al.Exercise capacity and atrial fibrillation risk in veterans: a cohort study.Mayo Clin Proc. 2016; 91: 558-566Google Scholar It is possible that patients who are more likely to engage in high levels of physical activity are also engaged in the health care system for regular physical examinations and are consequently monitored more closely. In turn, those who have better cardiorespiratory fitness but are not engaged in sports or higher-level athletics may be healthier and thus utilize the health care system less, and thus are not monitored as closely. Therefore, although most data suggest that endurance athletes have a greater risk of atrial fibrillation and those with better cardiorespiratory fitness have lower risk, these important limitations should be accounted for. Another important point is the difference between cardiorespiratory fitness and physical exertion. It is a natural assumption confirmed by prior studies that those with better cardiorespiratory fitness likely engage in more physical activity.24DeFina L.F. Haskell W.L. Willis B.L. et al.Physical activity versus cardiorespiratory fitness: two (partly) distinct components of cardiovascular health?.Prog Cardiovasc Dis. 2015; 57: 324-329Abstract Full Text Full Text PDF PubMed Scopus (182) Google Scholar However, whether research focuses on the higher levels of fitness or on physical activity, the nature of the fitness-activity correlation remains unclear. Measurements of fitness involve studies that require incrementally more challenging, short (3-minute) bursts of aggressive exertion. The total time to reach the “high” metabolic equivalent task (MET) of 9.3 mentioned by Faselis et al, for example, requires less than 9 minutes on a standard Bruce treadmill protocol. However, endurance athletes are often engaged in prolonged (ie, several hours) high-level aerobic activity. Thus, when considering patients with high levels of fitness, comparing risk with that of endurance athletes in prior studies may not be reasonable. Pathak et al18Pathak R.K. Elliott A. Middeldorp M.E. et al.Impact of CARDIOrespiratory FITness on arrhythmia recurrence in obese individuals with atrial fibrillation: the CARDIO-FIT Study.J Am Coll Cardiol. 2015; 66: 985-996Abstract Full Text Full Text PDF PubMed Scopus (333) Google Scholar reported that gains of 2 METs or more in fitness correlated with a reduction in atrial fibrillation risk when participants used a regimented exercise program characterized by (1) exercising 3 to 5 days per week and (2) low- to moderate-intensity exercise that was partly based on heart rate monitoring and matched to age and ability. This regimen is fundamentally different from the physical activity level targeted by endurance athletes. Thus, a reasonable interpretation from published data is that although high-level endurance exercise may have some deleterious effects and lead to an increased risk of atrial fibrillation, low to moderate regular physical activity aimed at maintaining a high level of cardiorespiratory fitness is protective. At what point further increase in levels of physical activity no longer confers benefit, but instead increases risk, is unclear. On the basis of a reasoned mechanistic understanding as well as observational and prospective data, it is clear that improvements in population-wide cardiorespiratory fitness likely reduce the risk of atrial fibrillation. However, it is unclear at what point further increasing the levels of physical exertion may result in a diminution of benefit and perhaps even increase the risk of atrial fibrillation. Current data, when interpreted in aggregate, suggest that physicians should recommend that most patients participate in light to moderate physical activity aimed toward achieving a reasonably high exertional capacity/cardiorespiratory fitness level when the goals are the prevention of atrial fibrillation and maintenance of long-term cardiovascular health. Exercise Capacity and Atrial Fibrillation Risk in Veterans: A Cohort StudyMayo Clinic ProceedingsVol. 91Issue 5PreviewTo assess the association between exercise capacity and the risk of developing atrial fibrillation (AF). Full-Text PDF Impact on Outcomes of Changing Treatment Guideline Recommendations for Stroke Prevention in Atrial Fibrillation: A Nationwide Cohort StudyMayo Clinic ProceedingsVol. 91Issue 5PreviewTo investigate the impact on outcomes of changing treatment guideline recommendations by comparing the proportion of patients with atrial fibrillation (AF) recommended oral anticoagulants (OACs) under the 2011 and 2014 American College of Cardiology/American Heart Association (ACC/AHA) guidelines. Full-Text PDF