Atrial fibrillation

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Atrial fibrillation is a relatively uncommon disorder (albeit the most common form of cardiac arrhythmia) for which the main lifestyle risk factors are obesity, metabolic syndrome, high pulse pressure, high blood pressure and hypertension, atherosclerosis, sleep apnea, long-term alcohol consumption, stress, and certain personality traits. Large amounts of life-time endurance exercise are predictive of an increased risk of atrial fibrillation, although lower intensities and amounts do not appear to have the same association. Exercise may be beneficial only as supervised by a medical professional.

CONTENTS


What is atrial fibrillation?

Atrial fibrillation is a common form of cardiac arrhythmia that often leads to an increased and/or irregular heartbeat and/or low blood pressure. This altered heart rhythm makes the heart less efficient at moving blood around the body. It is thought to arise as a result of abnormal electrical impulses firing in the atria, which override the natural pacemaker of the heart and consequently lead to an irregular pulse rate. The general symptoms of atrial fibrillation include tiredness, breathlessness, dizziness and chest pain (angina). While atrial fibrillation occurs commonly following cardiac surgery, the exact causes and underlying pathology are poorly understood.

Atrial fibrillation is often classified as being permanent (rather than transient). Permanent atrial fibrillation describes the scenario in which a regular heart rhythm cannot be sustained after cardioversion (a procedure by which heart rhythm is medically restored either by the use of electricity or pharmaceutical remedies) or simply when such treatments are not applied, which leads to the continuing presence of atrial fibrillation. Commonly-provided treatments for patients with permanent atrial fibrillation include medications to control heart rate and anticoagulant agents (see Camm et al.). However, exercise is not typically prescribed.

Atrial fibrillation is often classified as being lone (rather than in combination with cardiovascular disease). This type of atrial fibrillation is thought to be most commonly found in endurance athletes. However, some researchers have challenged the idea that lone atrial fibrillation even exists (see Potpara), noting that as diagnostic tools for cardiovascular disease have improved, the prevalence of this type of atrial fibrillation has reduced. Moreover, the definition of lone atrial fibrillation was originally produced long before the current wave of research into cardiovascular disease. This likely means that studies of varying ages use slightly different meanings to the definition (Wyse et al.). Nevertheless, lone atrial fibrillation as defined today has been reported to have a favourable long-term prognosis (Potpara et al.) in comparison with atrial fibrillation in conjunction with other cardiovascular disease.

What is the prevalence of atrial fibrillation?

The following studies have assessed the prevalence of atrial fibrillation

Study Population Prevalence
Heeringa et al. European individuals aged <55 years 5.5%
Heeringa et al. European individuals aged 55 – 59 years 0.7%
Heeringa et al. European individuals aged >85 years 17.8%
Stewart et al. Scottish individuals aged 45 – 64 years 0.65%
Go et al. Californian adults aged >20 years 0.95%
Go et al. Californian adults aged 20 – 50 years 0.1%
Go et al. Californian adults aged >80 years 9.0%
Furberg et al. US males aged >65 years 6.2%
Furberg et al. US females aged >65 years 4.8%
Feinberg et al. US males aged >40 years 2.3%
Feinberg et al. US males aged >65 years 5.9%

Based on the above studies, it seems that the prevalence of atrial fibrillation ranges widely from around 0.65% – 17.8% and increases quickly with advancing age, although gender and ethnicity may also play a role. Other differences between studies are likely to reflect the measurement methods and the definitions of atrial fibrillation used.

What is the incidence of atrial fibrillation?

The following studies have assessed the incidence of atrial fibrillation:

Study Population Incidence
Heeringa et al. European individuals aged <55 years 9.9 per 1000 person-years
Heeringa et al. European individuals aged 55 – 59 years 1.1 per 1000 person-years
Heeringa et al. European individuals aged 80 – 84 years 20.7 per 1000 person-years
Stewart et al. Scottish individuals aged 45 – 64 years 6.5 cases per 1000 examinations
Psaty et al. US adults aged >65 years 19.2 per 1000 person-years
Psaty et al. US males aged 65 – 74 years 17.6 per 1000 person-years
Psaty et al. US males aged 75 – 84 years 42.7 per 1000 person-years
Psaty et al. US females aged 65 – 74 years 10.1 per 1000 person-years
Psaty et al. US females aged 75 – 84 years 21.6 per 1000 person-years

Based on the above studies, it seems that the incidence of atrial fibrillation ranges widely from around 1.1 – 42.7 per 1,000 person-years and increases quickly with advancing age. Other differences between studies are likely to reflect the measurement methods and the definitions of atrial fibrillation used.

What are the prognostic markers for atrial fibrillation?

Some researchers have identified that signal-averaged electrocardiogram (ECG) can be used to anticipate the risk of atrial fibrillation, as set out in the table below:

Study Approach Finding
Guidera and Steinberg The researchers assessed the ability of the signal-averaged electrocardiogram (ECG) to detect delayed atrial activation in patients with a history of atrial fibrillation. They therefore reviewed 12-lead and signal-averaged ECGs from 15 patients with a history of atrial fibrillation and 15 age- and disease-matched controls with no history of atrial fibrillation. The researchers reported that the P wave duration by standard ECG was not significantly different between the two groups of subjects. However, they also reported that mean unfiltered and filtered P wave durations were longer in patients with atrial fibrillation than in controls. The researchers found that when using a vector composite of filtered orthogonal leads, a P wave duration >155 ms could successfully detect patients with atrial fibrillation (sensitivity = 80% and specificity = 93%). They therefore concluded that the signal-averaged P-wave duration is capable of detecting atrial conduction delay noninvasively and may therefore be a useful prognostic marker for atrial fibrillation.
Dixen et al. The researchers performed an observational trial in 131 patients who had previously displayed atrial fibrillation but who had since successfully achieved a return to cardiac rhythm. The researchers found that a prolonged signal-averaged P wave duration was associated with an increased risk of development of permanent atrial fibrillation. However, age, gender, dilated left atrium, duration of atrial fibrillation history, and duration of the most recent episode of atrial fibrillation were not found to be risk factors.
Gonna et al. The researchers assessed whether differences in P wave duration on the surface electrocardiogram (ECG) could predict the recurrence of atrial fibrillation after 1 month following successful electrical cardioversion. The researchers reported that 62% of patients experienced a recurrence of atrial fibrillation. They found that those with recurrent atrial fibrillation displayed significantly greater P wave duration.
Opolski et al. The researchers assessed whether signal-averaged P-wave duration as assessed by electrocardiography (ECG) could predict the recurrence of atrial fibrillation in 35 patients who experienced successful electrical cardioversion for chronic atrial fibrillation over a 6-month follow-up period. The researchers found that recurrence of atrial fibrillation occurred 31% of the subjects. The researchers reported that the signal-averaged filtered P-wave was significantly longer in the group who displayed atrial fibrillation recurrence than in the group who displayed no relapse (145 ± 11.8 vs. 130 ± 10.8ms). The researchers therefore concluded that signal-averaged P-wave duration as assessed by ECG be useful for identifying patients at risk of recurrence of atrial fibrillation following successful cardioversion.
Aytemir et al. The researchers performed a prospective trial in order to assess whether P wave signal-averaged electrocardiography (ECG) can predict the recurrence of atrial fibrillation following cardioversion to correct this problem. They therefore measured the P wave signal-averaged ECG in 73 patients following successful cardioversion and before performing a 6-month period of follow-up for recurrence of atrial fibrillation. The researchers observed that recurrence of atrial fibrillation occurred in 42.5% of the patients. The researchers observed that the filtered P-wave duration measured prior to follow-up was longer in patients in whom atrial fibrillation recurred than in patients in whom atrial fibrillation did not recur. They therefore concluded that a P wave signal-averaged ECG could help identify patients at risk for recurrence of atrial fibrillation after cardioversion.
Steinberg et al. The researchers performed a prospective trial in order to assess whether P wave signal-averaged electrocardiography (ECG) can predict the risk of atrial fibrillation occurring following cardiac surgery in 130 patients. The researchers reported that 25% of the patients developed atrial fibrillation 2.6 ± 2.0 days after surgery. The researchers found that P-wave duration on the signal-averaged ECG was significantly longer in the patients who developed atrial fibrillation than  in those who did not (average of 155 ± 18ms vs. 139 ± 17ms). The researchers found that the likelihood of developing atrial fibrillation post-cardiac surgery was increased by 3.9 times if the P-wave duration on the signal-averaged ECG was prolonged.
Klein et al. The researchers performed a prospective trial in order to assess whether P wave signal-averaged electrocardiography (ECG) can predict the risk of atrial fibrillation occurring following coronary artery bypass surgery in 45 patients. The researchers reported that 36% of the patients developed atrial fibrillation post-surgery. The researchers found that P-wave duration on the signal-averaged ECG was significantly longer in the patients who developed atrial fibrillation than  in those who did not (average of 163 ±19ms vs. 144 ± 16ms). The researchers concluded that signal-averaged P wave duration on an ECG provides a good pre-surgery predictor of post-operative atrial fibrillation in patients undergoing coronary artery bypass surgery.
Caldwell et al. The researchers investigated the association of prolonged P-wave duration on standard 12 lead ECG with the recurrence of atrial fibrillation post-pulmonary vein isolation for paroxysmal atrial fibrillation. The researchers identified a cohort of 100 patients with a mean age of 58 ± 11 years who had undergone pulmonary vein isolation for paroxysmal atrial fibrillation. The researchers reported that 35% of the subjects had prolonged P-wave duration and this factor was associated with a greater recurrence rate of atrial fibrillation in comparison with those subjects who did not display prolonged P-wave duration (63 vs. 38 %).
Altunkeser et al. The researchers investigated the electrocardiography parameters associated with the risk of developing atrial fibrillation in 82 patients with structural heart disease (45 with and 37 without a history of atrial fibrillation). The patients who had a history of atrial fibrillation had received either pharmaceutical or electrical cardioversion. The researchers found that a 12-lead electrocardiography (ECG) measure of maximum P wave duration was an independent predictors of chronic atrial fibrillation in patients with structural heart disease.

Based on the above studies, it seems that a signal-averaged electrocardiogram (ECG) can be used in order to predict the risk of atrial fibrillation in individuals with a structural heart disease, with a prior history of atrial fibrillation, in patients undergoing either cardiac surgery or coronary artery bypass surgery, and in patients who have received successful cardioversion or post-pulmonary vein isolation for atrial fibrillation.

What are the risk factors for atrial fibrillation?

A wide range of lifestyle risk factors for atrial fibrillation have previously been proposed. The following table sets out the risk factors for atrial fibrillation in various populations:

Study Approach Finding
Wang et al. The researchers investigated the association between body mass index (BMI) and the risk of developing atrial fibrillation in a prospective, community-based observational US-based cohort of 5,282 male and female subjects with a mean age of 57 ± 13 years over a mean follow-up period of 13.7 years. The researchers reported that the incidence rate for atrial fibrillation increased with increasing BMI. They reported that males with a BMI of <25, 25 – 30 and >30 displayed an incidence of atrial fibrillation of 9.7, 10.7, and 14.3 per 1,000 person-years while females displayed an incidence of 5.1, 8.6, and 9.9 per 1000 person-years. They calculated in an adjusted model that each unit of increase in BMI led to a 4% increase in the risk of developing atrial fibrillation.
Frost et al. The researchers investigated the association between body mass index (BMI) and the risk of developing atrial fibrillation or flutter in a population-based prospective cohort study of 47,589 male and female subjects with a mean age of 56 years and with no preexisting cardiovascular or endocrine disease over a mean follow-up period of 5.7 years. The researchers reported that in comparison with normal weight the relative risk for atrial fibrillation or flutter in overweight individuals was 1.75 times in males and 1.39 times in females. In comparison with normal weight, the relative risk for atrial fibrillation or flutter in obese individuals was 2.35 times in males and 1.99 times in females.
Dublin et al. The researchers investigated the association between body mass index (BMI) and the risk of developing atrial fibrillation in a case-control study of 425 subjects with new-onset atrial fibrillation and 707 controls. The researchers reported that the overall risk of atrial fibrillation was 3% higher per unit of BMI, while for sustained, intermittent and transitory atrial fibrillation, the risk was 7%, 4% and 1% higher per unit of BMI. The researchers reported that in comparison with normal weight the relative risk for atrial fibrillation in overweight individuals was 0.97 times. In comparison with normal weight, the relative risk for atrial fibrillation in obese individuals (BMI = 30 – 35) was 1.18 times, in very obese individuals (BMI = 35 – 40) was 1.34 times, and in morbidly obese individuals (BMI = >40) was 2.31 times.
Wanahita et al. The reviewers carried out a meta-analysis to assess whether obesity increases the risk of developing atrial fibrillation. They included population-based cohort or post-cardiac surgery cohort studies in order to investigate the incidence of atrial fibrillation in relation to the body mass index (BMI) categories. The reviewers identified 16 studies involving 123,249 subjects, including 5 population-based cohort studies and 11 post-cardiac surgery studies. The reviewers reported that based on the data from population-based cohort studies, obese individuals have a 49% increased risk of developing atrial fibrillation compared to non-obese individuals and this risk increases with increasing BMI. However, the reviewers reported that  based on the post-cardiac surgery studies, obese individuals do not display any increased risk of developing atrial fibrillation compared to non-obese individuals, suggesting that other factors may be more important.
Watanabe et al. The investigated the association between the metabolic syndrome and the risk of developing atrial fibrillation in prospective, community-based, observational cohort study of 28,449 subjects without atrial fibrillation undergoing an annual health check-up program in Japan. At baseline, the metabolic syndrome was present in 13 – 16% of subjects, depending on the definitions used. The researchers followed-up with the subjects over a mean period of 4.5 years, during which 0.93% developed atrial fibrillation. The researchers found that obesity displayed a relative risk of 1.64 times, high blood pressure displayed a relative risk of 1.69 times, hypercholesterolemia (low high-density lipoprotein cholesterol) displayed a relative risk of 1.52 times, and impaired fasting glucose displayed a relative risk of 1.35 – 1.44 times (depending on the definition used). The researchers reported that depending on the overall definition used, the risk of atrial fibrillation was significantly in untreated subjects with the metabolic syndrome (relative risk of 1.78 times).
Chamberlain et al. The researchers assessed the risk of incident atrial fibrillation in relation to the existence of metabolic syndrome and its 5 components at baseline in 15,094 subjects included in the Atherosclerosis Risk in Communities study over a mean follow-up period of 15.4 years. The researchers reported that there were 1,238 cases of incident atrial fibrillation. The researchers found that the relative risk of developing incident atrial fibrillation was higher in individuals with metabolic syndrome at baseline than those without. They found that there was no effect of ethnicity on this risk modification. They reported that the relative risks of each of the 5 components of metabolic syndrome (high blood pressure, large waist circumference), low high-density lipoprotein cholesterol, impaired fasting glucose, and high levels of triglycerides) were 1.95, 1.40, 1.20, 1.16 and 0.95 times, respectively. They found that additional metabolic syndrome components led to an additive effect on the relative risk and those with all 5 components displayed a 4.4 times greater risk of developing incident atrial fibrillation than those with none.
Mitchell et al. The researchers wanted to investigate the association between pulse pressure and risk of developing atrial fibrillation. Pulse pressure is simply the difference between systolic and diastolic blood pressure measurements, is a reflection of aortic stiffness and increases cardiac load. The researchers therefore performed a prospective, community-based US observational cohort study with 5,331 subjects who were free from atrial fibrillation at baseline. The researchers followed up the subjects over an average of 12 years. The researchers reported that 13.1% of the subjects developed atrial fibrillation during follow-up. They reported that high pulse pressure was associated with a 1.26 times greater risk for atrial fibrillation for each 20mmHg increment of pressure. The researchers also found that systolic blood pressure was associated with a 1.14 times greater risk for atrial fibrillation for each 20mmHg increment of pressure.
Conen et al. The researchers wanted to investigate the association between systolic and diastolic blood pressure and risk of developing atrial fibrillation in 34,221 initially healthy, middle-aged women over 12.4 years of follow-up. The researchers reported that the long-term risk of developing atrial fibrillation was significantly increased with increasing systolic and diastolic blood pressure. Specifically, the researchers found that relative to <120, the for systolic blood pressure categories of 120 – 129, 130 – 139, 140 – 159 and >160mmHg, the relative risks of developing atrial fibrillation were 1.00, 1.28, 1.56 and 2.74 times, respectively. Relative to <65, the for systolic blood pressure categories of 65 – 74, 75 – 84, 85 – 89, 90 – 94, and >95mmHg were 1.17, 1.18, 1.53, 1.35 and 2.15 times, respectively.
Fox et al. The researchers wanted to explore the extent to which mitral annular calcification is associated with atrial fibrillation in 1,126 participants of the original cohort of the Framingham Heart Study who were free from atrial fibrillation at baseline, over 16 years of follow-up. The researchers found that the incidence of atrial fibrillation was 362 per 10,000 person-years in subjects with mitral annular calcification compared with 185 per 10,000 person-years in those without. The relative risk of developing atrial fibrillation for subjects with mitral annular calcification was 1.6 times.
Porthan et al. The researchers investigated the association between obstructive sleep apnea and lone atrial fibrillation using a case-control study. The researchers therefore recruited 59 subjects with lone atrial fibrillation and a mean age of 59 years as well as 56 gender- age- and cardiovascular morbidity-matched community control subjects. The researchers performed an overnight sleep study to assess the extent of obstructive sleep apnea. The researchers reported that the prevalence of obstructive sleep apnea in the group with lone atrial fibrillation was 32% and the prevalence in the control group was 29%, which was not significantly different.
Kanagala et al. The researchers prospectively investigated the association between untreated obstructive sleep apnea following cardioversion and the risk of recurrent atrial fibrillation. They followed-up 43 patients with obstructive sleep apnea (27 who were not being treated and 16 who were being treated) as well as in 79 randomly selected post-cardioversion patients without obstructive sleep apnea over a 12-month period. The researchers found that 1-year recurrence of atrial fibrillation was higher in the untreated obstructive sleep apnea group than in the treated or control groups (82% vs. 42% vs. 53%).
Gami et al. The researchers performed a prospective case-control study to assess the association between obstructive sleep apnea and  atrial fibrillation. The case group comprised 151 consecutive patients undergoing electro-cardioversion for atrial fibrillation and the control group comprised 312 consecutive patients without any history of atrial fibrillation. The researchers reported that the proportion of patients with obstructive sleep apnea was significantly higher in the case group (who had a history of atrial fibrillation) than in the control group (49% vs. 32%).
Ng et al. The reviewers investigated the association between of obstructive sleep apnea and the recurrence of atrial fibrillation after catheter-based pulmonary vein isolation through a meta-analysis. The reviewers identified 6 studies with a total of 3,995 patients. The reviewers reported that patients with obstructive sleep apnea displayed a 25% greater risk of recurrence of atrial fibrillation after catheter-based pulmonary vein isolation than patients without. The reviewers found that obstructive sleep apnea diagnosed using polysomnography is a strong predictor of atrial fibrillation recurrence.
Gami et al. The researchers explored whether obesity and obstructive sleep apnea can independently predict the incidence of atrial fibrillation and flutter. They therefore performed a retrospective cohort study in 3,542 subjects without no history of atrial fibrillation who undertook a diagnostic polysomnogram to assess whether they had obstructive sleep apnea. The researchers followed up the subjects over a mean follow-up  period of 4.7 years to assess the incidence of atrial fibrillation. The researchers found that in subjects aged <65 years, age, male gender, coronary artery disease, the decrease in nocturnal oxygen saturation (as a proxy for obstructive sleep apnea) and BMI (as a proxy for obesity) were all independent predictors for atrial fibrillation. However, in subjects aged >65 years, only heart failure predicted atrial fibrillation.
Djoussé et al. The researchers wanted to assess the contribution of long-term alcohol consumption on the risk of developing atrial fibrillation among participants in the Framingham Study by means of a case-control design including 1,055 cases of atrial fibrillation over a follow-up period of 50 years. The researchers found that compared to no drinks per day, for alcohol consumption in the proportions 0.1 – 12, 12.1 – 24, 24.1 – 36 and >36g per day, the relative risk of developing atrial fibrillation was 0.97, 1.06, 1.12 and 1.34, respectively. The researchers concluded that there is only a significantly increased risk of developing atrial fibrillation among subjects consuming >36 g/day (which is 4.5 units per day, as 1 unit = 7.9g or 10ml of ethanol).
Mukamal et al. The researchers wanted to assess the contribution of long-term alcohol consumption on the risk of developing atrial fibrillation using a prospective cohort study including 16,415 males and females from the Copenhagen City Heart Study. The researchers found that alcohol consumption throughout the moderate range was not associated with risk of atrial fibrillation. However, consuming 35 or more drinks per week led to a 1.45 times greater risk of developing atrial fibrillation in males.
Frost and Vestergaard. The researchers wanted to assess the contribution of long-term alcohol consumption on the risk of developing atrial fibrillation or flutter using a prospective cohort study including 47,949 subjects with a mean age of 56 years in the Danish Diet, Cancer, and Health Study. The researchers noted that the average consumption of alcohol per day was 28.2 ± 25g in men and 13.9 ± 15g in women. The researchers reported that in comparison with the lowest quintile of alcohol consumption in males, the relative risks of developing trial fibrillation in quintiles 2, 3, 4, and 5 were 1.04, 1.44, 1.25, and 1.46 times, respectively. For females, the relative risks were 1.09, 1.27, 1.23, and 1.14 times, respectively. The researchers found that the frequency and source of alcohol did not have any effect on these associations.
Eaker et al. The researchers wanted to investigate whether type A behavior, expressions of anger, and/or hostility would affect the risk of developing atrial fibrillation. The researchers therefore prospectively followed 3,873 subjects aged 18 – 77 years in the Framingham Offspring Study for a 10-year period. The researchers found that individuals displaying the personality features of trait-anger, symptoms of anger and hostility were 1.1, 1.2 and 1.3 times more likely to develop atrial fibrillation than individuals who did not display any of these traits.
Mattioli et al. The researchers assessed the effects of personality factors, socio-economic factors and acute life stress on the risk of developing acute lone atrial fibrillation using a case-control study. The researchers recruited a group of 116 patients with lone atrial fibrillation and measured their psychological stress and personality type, socio-economic status as well as other known covariates (alcohol consumption, smoking and body mass index). For a control group, the researchers sourced an age- and sex-matched group of individuals. The researchers found that type A behaviour pattern was found in 20% of the patients with atrial fibrillation but only in 9% of controls. The researchers found that the acute life stress score among patients with atrial fibrillation was 56 ± 33 but in controls it was 34 ± 27 points. The researchers observed that a high body mass index was also associated with a 1.5 times greater risk of atrial fibrillation.

Based on these studies, it seems that the main lifestyle risk factors for atrial fibrillation are obesity, metabolic syndrome, high pulse pressure, high blood pressure and hypertension, atherosclerosis, sleep apnea, long-term alcohol consumption, stress, and certain personality traits (type A behaviour, anger and hostility).

Is endurance exercise a risk factor for atrial fibrillation?

It is widely assumed that long-term endurance exercise is a risk factor for atrial fibrillation. The following studies have assessed whether this is the case:

Study Approach Finding
Karjalainen et al. The researchers performed a case-control study in which they compared the prevalence of atrial fibrillation in middle-aged males regularly performing endurance training and males from the general population. They therefore recruited 300 subjects, being the 60 top ranked orienteers in 1984 from each of the 35 – 39 years, 40 – 44 years, 45 – 49 years, and 55 – 59 years classifications in addition to 495 controls aged 35 – 59 years. The researchers found that in comparison with the general population, the orienteers had a lower mortality (1.7%  vs. 8.5%), lower coronary heart disease incidence (2.7% vs. 7.5%), and fewer known risk factors for atrial fibrillation. However, atrial fibrillation was diagnosed in 5.3% orienteers but only in 0.9% control subjects, which is a relative risk of 5.5 times. The researchers therefore concluded that long term endurance exercise is associated with an increased risk of atrial fibrillation in healthy middle-aged males despite protecting against both coronary heart disease and premature death.
Elosua et al. The researchers performed an age-matched case-control study in order to assess the association between sports practice and the prevalence of atrial fibrillation in 51 consecutive patients who attended an outpatient clinic compared with 109 control subjects from the general population. The researchers found that the proportion of patients with atrial fibrillation who reported current sport practice was higher than the proportion of control subjects who reported current sports practice (31 vs. 14%) and sports practice was associated with a 3.13 times greater risk of atrial fibrillation.
Mont et al. The researchers performed an age-matched case-control study in order to assess the association between chronic sport practice and the prevalence of atrial fibrillation. They therefore reviewed the records of 70 patients with cardiac arrhythmia outpatient clinic and compared the incidence of sports practice with that in the general population. The researchers found that the incidence of sports participation was greater in cardiac arrhythmia patients than in the general population (63% vs. 15%).
Heidbüchel et al. The researchers assessed the effect of endurance sports activity pre- and post-intervention on the incidence of atrial fibrillation in 137 patients (83% men). The intervention involved ablation for isthmus-dependent atrial flutter and the researchers followed-up the patients over a mean period of 2.5 years. The researchers reported that performing endurance sports pre-intervention was a significant risk factor for atrial fibrillation with a relative risk of 1.81 times. The researchers also observed a non-significant trend for performing endurance sports post-intervention to be a risk factor for atrial fibrillation with a relative risk of 1.68 times. The researchers calculated that each hour per week of additional endurance exercise performed pre- and post-ablation led to a 10% and 11% increased risk for developing atrial fibrillation.
Molina et al. The researchers set out to calculate the incidence of lone atrial fibrillation in a case-control study performed in a group of 252 male marathon runners and a population-based sample of 305 sedentary men. The researchers reported that the annual incidence rate of lone atrial fibrillation among marathon runners and sedentary men were 0.43 per 100 and 0.11 per 100, respectively. Therefore, marathon running was associated with an 8.8 times greater risk of lone atrial fibrillation than being sedentary.
Aizer et al. The researchers performed a prospective cohort study in order to assess the relationship between vigorous exercise the risk of developing atrial fibrillation among 16,921 apparently healthy men in the Physicians’ Health Study over a 12-year follow-up period in which 1,661 men reported developing atrial fibrillation. The researchers found that there was a complex association between exercise and the risk of developing atrial fibrillation. The researchers reported that a higher frequency of exercise participation at 3 years was associated with a slightly greater risk of developing atrial fibrillation (mainly in those who exercised 5 − 7 times weekly, who had a 20% greater risk than the non-exercisers). However, the researchers did not find a significant relationship between exercise habits and the risk of developing atrial fibrillation at 9 years. Additionally, the researchers found that the increase in risk reduced with increasing age and in males aged >50 years, there was no significant association between exercise habits and the risk of developing atrial fibrillation. Finally, the researchers found that jogging was the form of exercise that was most strongly associated with the development of atrial fibrillation. Jogging 5+ days per week leads to a 53% increased risk of developing atrial fibrillation compared to non-exercisers. Indeed, the researchers found that after excluding jogging from the analysis, there was no relationship between exercise and the risk of developing atrial fibrillation, suggesting that it may be jogging and not exercise per se that is the risk factor.
Myrstad et al. The researchers performed a cross-sectional study in order to investigate whether long-term endurance sport practice is a risk factor for atrial fibrillation. They therefore carried out a case-control study in 509 males aged 65 – 90 years who were due to take part in a long-distance cross-country ski race and in 1,768 male control subjects aged 65 – 87 years from the general population. The researchers found that a history of endurance sport practice led to a small but significant increase in the risk for atrial fibrillation. However, they also reported a non-significant trend for a reduction in the risk for atrial fibrillation in individuals who reported light and moderate leisure-time physical activity in the last 12 months.
Grimsmo et al. The researchers wanted to determine the prevalence of lone atrial fibrillation in long-term endurance cross-country skiers. They therefore recruited 149 healthy, long-term trained cross-country skiers and followed-up over a 28 – 30-year period. The researchers reported that there was a high prevalence of lone atrial fibrillation (12.8%) in this population.
Hoogsteen et al. The researchers assessed the course of lone, paroxysmal atrial fibrillation in 30 well-trained, male endurance athletes aged 48.1 ± 7.8 years using a specially designed questionnaire. The researchers found that after 9-year follow-up, 10% of the athletes had died, paroxysmal atrial fibrillation continued in 50% of the athletes, permanent atrial fibrillation had emerged in 17% of the athletes and 23% displayed no atrial fibrillation.
Mont et al. The researchers wanted to identify the risk factors for developing lone atrial fibrillation by means of a case-control study. They therefore recruited a series of 107 consecutive patients aged <65 years, who were seen in the emergency room for an episode of lone atrial fibrillation of <48 hours duration. The researchers also recruited a group of 107 healthy age- and sex-matched volunteers to act as controls. The subjects received a validated questionnaire designed to estimate the accumulated hours of lifetime leisure and occupational physical activities performed, assessed as either moderate or heavy. The subjects were 48 ± 11 years old. The researchers reported that subjects with atrial fibrillation performed more hours of both moderate and heavy physical activity.
Mozaffarian et al. The researchers performed a prospective trial in order to investigate the associations between leisure-time activity, exercise intensity and walking habits, and the incidence of atrial fibrillation in  5,446 adults aged >65 years in the Cardiovascular Health Study. The researchers reported that the incidence of atrial fibrillation was 22.4 per 1,000 person-years. The researchers reported that leisure-time activity was associated with a lower incidence of atrial fibrillation. Moreover, they found that a progressively greater amount of leisure-time activity was associated with a progressively lower incidence of atrial fibrillation, with the third quintile displaying a 25% lower risk and the fifth quintile displaying a 36% lower risk than the first quintile. On the other hand, the researchers found that exercise intensity displayed a U-shaped relationship with the incidence of atrial fibrillation. The risk was significantly lower with moderate-intensity exercise (by 28%) but not with high-intensity exercise. Specifically in respect of walking, the researchers found that increased walking distance and pace were both associated with a progressively lower incidence of atrial fibrillation. In a combined analysis of both distance and pace, the second quartile displayed a 25% lower risk and the fourth quartile displayed a 44% lower risk than the first quartile. Thus, while it appears that higher intensities of endurance exercise may be associated with an increased risk of atrial fibrillation, low-intensity exercise, such as walking, is strongly associated with a reduced risk.
Brugger et al. The researchers assessed the association between running mileage and the incidence of risk factors for atrial fibrillation in 95 amateur male runners >30 years old. The subjects were assigned to 1 of 3 groups according to their lifetime training hours: low (<1,500 hours), intermediate (1,500 – 4,500 hours) and high (>4,500 hours). The researchers reported that no significant differences were found between the groups in respects of age, blood pressure, and diastolic function. They reported that left atrial maximal volume and conduit volume index increased significantly from the low to the high group. They reported that there was only a single instance of atrial fibrillation recorded in the whole population. They reported that pump strain and conduit strain were not associated with life-time training volume. The researchers concluded that the left atrial anatomical and electrical remodeling that occurs with increased training volumes does not have a negative impact on atrial mechanical function. The researchers concluded that they found no evidence to suggest any link between these factors and an increased risk of atrial fibrillation.
Wilhelm et al. The researchers assessed the impact of lifetime training hours on risk factors for atrial fibrillation (including signal-averaged P-wave duration) in 60 non-elite male endurance athletes aged 42 ± 7 years taking part in the 2010 Grand Prix of Bern, a 10-mile running race. The subjects were assigned to 1 of 3 groups according to their lifetime training hours: low (<1,500 hours), intermediate (1,500 – 4,500 hours) and high (>4,500 hours). The researchers reported that signal-averaged P-wave duration and left atrial volume increased significantly from the low to the high group. The researchers therefore concluded that in endurance athletes, lifetime training hours are associated with longer signal-averaged P-wave duration and an increase in left atrial volume, which may increase the risk of atrial fibrillation.
Giacomantonio et al. The reviewers performed a systematic to assess the effect of physical activity on atrial fibrillation. The reviewers identified 6 relevant long-term studies of exercise. The reviewers reported that the findings of 2 studies indicate that the incidence of atrial fibrillation is not associated with physical activity in the general population. However, they reported that the findings of 7 studies indicate that long-term vigorous endurance exercise may be associated with increased incidence of atrial fibrillation.
Abdulla et al. The reviewers performed a systematic review and meta-analysis in order to ascertain whether the risk of atrial fibrillation is greater in athletes compared with non-athletes. The reviewers identified 6 case-control studies that were eligible for meta-analysis, including 655 athletes and 895 controls with an average age of 51 ± 9 years. The reviewers found that the overall risk of atrial fibrillation was significantly higher in athletes than in controls. The reviewers reported that the relative risk of atrial fibrillation was 5.29 times greater in athletes than in control subjects.

Based on these studies, the relationship between exercise and the risk of developing atrial fibrillation appears complex. There is some evidence to suggest that the mode of exercise (e.g. running or cycling), the intensity and the volume may all be important modifying factors for the association. It may be the case that running, high-intensity exercise, and large amounts of exercise are associated with an increased risk of developing atrial fibrillation. However, partaking in low-intensity physical activity, such as walking, may not be well-correlated.

What effect does exercise training have on atrial fibrillation?

Although there are concerns about the associations seen between high-level endurance training and the incidence of atrial fibrillation, a small number of studies have been performed to assess the effects of exercise on atrial fibrillation, as shown in the table below:

Study Approach Finding
Reed The reviewers performed a systematic review in order to assess the effects of short-term chronic exercise in patients with permanent atrial fibrillation. They identified 3 randomized controlled trials with a total of 118 subjects and 3 observational studies with a total of 93 subjects. The reviewers reported that short-term chronic exercise in adults with permanent atrial fibrillation led to significant improvements in rate control, functional capacity, muscular strength and power, activities of daily living, and quality of life. However, they reported that the studies reported conflicting results in respect of the ability of exercise to improve aerobic capacity in adults with permanent atrial fibrillation. Interestingly, they noted that there was no difference in effects dependent upon exercise intensity, as low, moderate, or vigorous intensity all led to improvements in the affected parameters.
Giacomantonio et al. The reviewers performed a systematic to assess the health benefits of physical activity in patients with atrial fibrillation. The reviewers reported that moderate-intensity physical activity led to improvements in exercise capacity, quality of life, and the ability to carry out activities of daily living in patients with atrial fibrillation. Additionally, they reported that 6 studies suggested that physical activity may improve the management and treatment of atrial fibrillation. Finally, they suggested that physical activity may reduce the incidence of atrial fibrillation in at-risk populations.
Osbak et al. The researchers performed a randomized clinical trial to assess the effects of 12 weeks of exercise training in 49 patients with permanent atrial fibrillation. The researchers investigated the effects on the exercise training on muscular strength, body composition, maximal exercise capacity and walking ability (as measured by the 6-Minute Walk Test), as well as health-related quality of life (using both Minnesota Living with Heart Failure Questionnaire and the Short-Form-36). The researchers randomly allocated the subjects to either an exercise training group or to a non-training control group. The exercise training comprised aerobic training for 1 hour per session, 3 times per week at 70% of maximal exercise capacity. The researchers reported that the exercise group displayed significant increases in muscular strength, body fat percentage, exercise capacity, walking ability and health-related quality of life as measured by the  Minnesota Living with Heart Failure Questionnaire and by 3 out of 8 subscales on the Short-Form-36 (physical functioning, general health perceptions and vitality). The researchers observed that no adverse effects of exercise occurred.
Hegbom et al. The researchers performed a randomized 2-month study to assess the effects of short-term exercise training in 30 patients aged 65 ± 7 years with permanent atrial fibrillation. In particular, the researchers wanted to explore the effects of an exercise training program on exercise capacity (using work done at Borg scale 17 on a cycle ergometer test), quality of life (using the Short-Form-36 questionnaire), and atrioventricular conduction (using a 15-minute resting high-frequency spectral electrocardiogram analysis). The researchers randomly allocated the subjects to either an exercise training group or a non-training group. The exercise training group performed 24 training sessions including both aerobic exercise and resistance-training. The researchers reported that in the exercise group, work at Borg scale 17 increased by 41 ± 36%, measures of atrioventricular conduction improved, and 4 of the 8 subscales and 1 of the 2 summary scales of the Short-Form-36 quality of life questionnaire improved.
Vanhees et al. The researchers performed a trial comparing the effects of exercise training in 53 cardiac patients with and without chronic atrial fibrillation. The researchers took measurements of maximal aerobic capacity while the patients performed a maximal cycle ergometer exercise test to exhaustion before and after a 3-month exercise training intervention. The researchers also measured resting heart rate. Both groups performed walking exercise 3 times a week for the 3-months period. The researchers found that pre-intervention, VO2-max was significantly lower in the patients with chronic atrial fibrillation compared to the patients without chronic atrial fibrillation. The researchers also found that the exercise intervention lead to significant improvements in VO2-max in both groups (31% in the chronic atrial fibrillation group and 25% in the control group) but there was no significant difference between the improvement in VO2-max between groups. Similar findings were observed for resting heart rate.
Mertens and Kavanagh The researchers investigated the effects of 1 year of exercise training in 20 patients (13 men and 7 women) with chronic atrial fibrillation. The exercise training involved walking at a pace based on 60 – 80% of peak oxygen intake (VO2-max) as well as by reference to a perceived exertion of 12 – 14 on the original Borg scale of rating perceived exertion (RPE). The researchers reported that there was a significant effect of the exercise training intervention on VO2-max, which increased by an average of 15% from 14.8 ± 3.6 to 17.0 ± 3.6 mL/kg/min, on ventilatory threshold, which increased by an average of 14%, from 11.2 ± 2.2 to 12.8 ± 2.6 mL/kg/min, peak power output, which increased by an average of 21%, from 92.5 ± 29.3 to 112 ± 3.7W. This demonstrates that walking at a moderate-to-fast pace can elicit improvements in aerobic capacity in individuals with chronic atrial fibrillation.
Pippa et al. The researchers performed a randomized controlled trial to test a 16-week qi gong physical training program in 43 patients with chronic atrial fibrillation. The researchers assessed the effects of the intervention on functional capacity as assessed using the 6-Minute Walk Test. The subjects were randomly assigned either to the intervention protocol or to a waiting-list control group. The researchers found that the trained group improved 6-Minute Walk Test by 114m (27%) post-intervention. They noted that a 57m improvement (14%) was maintained after a 16-week follow-up. This demonstrates that qi gong physical training can elicit improvements in functional walking capacity in individuals with chronic atrial fibrillation.

Based on these studies and reviews, it appears that exercise can in fact lead to significant improvements in rate control, functional capacity, muscular strength and power, activities of daily living, and quality of life in individuals with atrial fibrillation.

Evidence-based recommendations for exercise

The following reviews and guidelines have provided practical recommendations for the prevention and treatment of atrial fibrillation:

Study Recommendations
Menezes et al. The reviewers provided a discussion of the risk factors for atrial fibrillation and commented on non-pharmacological strategies for reducing the risks and thereby preventing the disease. The reviewers note that metabolic syndrome, obesity, dyslipidaemia (specifically low HDL-C), hypertension, obstructive sleep apnoea and alcohol consumption are all risk factors. Therefore, strategies for addressing these conditions should be considered to reduce the risk of atrial fibrillation in all populations and particularly in at-risk populations. Exercise and physical activity are clearly strategies that are effective in most of these conditions. However, the reviewers also note that extreme levels of intense exercise are associated with an increased risk of atrial fibrillation. The reviewers therefore recommend limiting exercise prescription of vigorous aerobic training to <40 minutes per day for at-risk populations, as tolerated.
Heidbuchel et al. The reviewers provide important guidance for exercise in individuals with atrial fibrillation. They note that atrial fibrillation appears to be more prevalent in endurance sports athletes and enthusiasts in comparison with the general population. They suggest that it is likely that endurance sports participation may accelerates the development of atrial fibrillation from other underlying causes.  These reviewers recommend that where an external cause has clearly given rise to the incidence of atrial fibrillation (e.g. hyperthyroidism, illegal drug use or myocarditis), then sports participation should be temporarily suspended. They suggest that such participation can be resumed after achieving a stable cardiac rhythm for >2 months. The reviewers explain that where there is no cause, the ability to continue to participate in sports will depend upon the experience of the individual during exercise, as many individuals display dizziness and sudden onset of fatigue. Such circumstances therefore require the supervision and ongoing monitoring of a physician and possibly pharmacological interventions as deemed appropriate.

These guidelines note that since metabolic syndrome, obesity, dyslipidaemia, hypertension, and obstructive sleep apnoea are all key risk factors for atrial fibrillation, a prevention protocol for atrial fibrillation should include exercise training. However, since large amounts of vigorous endurance exercise have been associated with an increased risk of atrial fibrillation, they recommend that at-risk populations should limit participation in vigorous aerobic exercise to <40 minutes per day. Using exercise in the treatment of atrial fibrillation appears to be suitable only in certain circumstances, and only as advised by a physician.

Conclusions

Based on the above studies and analysis, the following conclusions can be drawn about atrial fibrillation:

Area Conclusions
Prevalence of atrial fibrillation The prevalence of atrial fibrillation ranges widely from around 0.65% – 17.8% and increases quickly with advancing age, although gender and ethnicity may also play a role. Other differences between studies are likely to reflect the measurement methods and the definitions of atrial fibrillation used.
Incidence of atrial fibrillation The incidence of atrial fibrillation ranges widely from around 1.1 – 42.7 per 1,000 person-years and increases quickly with advancing age. Other differences between studies are likely to reflect the measurement methods and the definitions of atrial fibrillation used.
Prognostic indicators for atrial fibrillation A signal-averaged electrocardiogram (ECG) can be used in order to predict the risk of atrial fibrillation in individuals with a structural heart disease, with a prior history of atrial fibrillation, in patients undergoing either cardiac surgery or coronary artery bypass surgery, and in patients who have received successful cardioversion or post-pulmonary vein isolation for atrial fibrillation.
Risk factors for atrial fibrillation The main lifestyle risk factors for atrial fibrillation are obesity, metabolic syndrome, high pulse pressure, high blood pressure and hypertension, atherosclerosis, sleep apnea, long-term alcohol consumption, stress, and certain personality traits (type A behaviour, anger and hostility).
Association between endurance exercise and atrial fibrillation The relationship between exercise and the risk of developing atrial fibrillation appears complex. There is some evidence to suggest that the mode of exercise (e.g. running or cycling), the intensity and the volume may all be important modifying factors for the association. It may be the case that running, high-intensity exercise, and large amounts of exercise are associated with an increased risk of developing atrial fibrillation. However, partaking in low-intensity physical activity, such as walking, may not be well-correlated.
Benefits of exercise for individuals with atrial fibrillation Exercise can in fact lead to significant improvements in rate control, functional capacity, muscular strength and power, activities of daily living, and quality of life in individuals with atrial fibrillation.
Preventing atrial fibrillation Since metabolic syndrome, obesity, dyslipidaemia, hypertension, and obstructive sleep apnoea are all key risk factors for atrial fibrillation, a prevention protocol for atrial fibrillation should include exercise training. However, since large amounts of vigorous endurance exercise have been associated with an increased risk of atrial fibrillation, at-risk populations should limit participation in vigorous aerobic exercise to <40 minutes per day.
Treating atrial fibrillation Using exercise in the treatment of atrial fibrillation appears to be suitable only in certain circumstances, and only as advised by a physician.

In summary, atrial fibrillation is a relatively uncommon disorder (albeit the most common form of cardiac arrhythmia) for which the main lifestyle risk factors are obesity, metabolic syndrome, high pulse pressure, high blood pressure and hypertension, atherosclerosis, sleep apnea, long-term alcohol consumption, stress, and certain personality traits (type A behaviour, anger and hostility. Large amounts of life-time endurance exercise are also predictive of an increased risk although lower intensities and amounts do not appear to have the same association and exercise itself can reduce the other risk factors substantially.


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