Physical activity and incidence of atrial fibrillation: A systematic review and meta-analysis
Introduction
Physical activity is associated with reduced risk of coronary heart disease [1] and modulates key cardiovascular risk factors including blood pressure, body mass index, lipids and fibrinogen levels [2], [3]. As a result, regular physical activity is recommended for the general population by the United States Government [4], Department of Health in the United Kingdom [5] and World Health Organization [6]. However, several studies have reported increased risk of atrial fibrillation (AF) among athletes [7], [8], [9] and participants with increased level of physical activity [10], [11] compared to controls.
The mechanism for increased AF with physical activity is not fully understood but the potential mechanisms include increased parasympathetic tone, left atrial enlargement, left ventricular hypertrophy and left ventricular dilatation [12]. Regular exercise alters the sympathetic and parasympathetic stimulations to the heart and results in reduced sympathetic activity at rest [13]. The resultant increase in vagal tone is known to shorten the atrial refractory period, which can induce AF as long as the increased vagal tone is maintained [14]. This is also supported by an animal study that revealed that administration of intravenous cholinergic drugs is associated with auricular fibrillation in dogs [15]. In addition, dynamic exercise can trigger increase in dimension of the heart cavity and static exercise promotes hypertrophy [16]. It has further been suggested that interstitial fibrosis may play a role in the pathogenesis of AF with chronic sports practice [17].
Previous systematic reviews have shown the inconsistent findings between physical activity and the risk of AF [18], [19], [20]. The review of four studies by Ofman et al. [18] reported no association between AF and regular physical activity, but a more recent review by Nielsen et al. [19] including ten studies concluded that long-term vigorous physical training is associated with increased risk of AF. A third review highlighted that the overall quality of the evidence indicating increases in risk of AF is low and that risk appears to be overestimated substantially [20].
Since these reviews several new studies have been published. Drca et al. recently evaluated the risk of AF with different levels of physical activity using the Swedish National Inpatient Register and found that leisure-time exercise at younger age is associated with increased risk of AF [21]. Knuiman et al. examined the risk factors for AF using the Busselton Health Study and found that some vigorous exercise each week is associated with non-significant trend towards reduced risk of AF [22]. Thelle et al. used the Norwegian Prescription Database and found that increasing levels of self-reported physical activity in men is associated with flecainide treatment, which was used as surrogate marker for lone AF [23].
In view of the new studies and divergent findings of previous systematic reviews, we aimed to conduct a more comprehensive systematic review and meta-analysis of the risk of AF with physical activity.
Section snippets
Eligibility criteria
We selected studies that evaluated the link between the history of physical activity and the subsequent risk of AF. For physical activity there was no strict definition and we also included studies that evaluated outcomes in athletes. In addition, studies had to have a comparator group with less physical activity which would allow risk estimates to be calculated. Studies had to monitor or follow up participants for AF or a surrogate marker of AF (e.g. flecainide use). There was no restriction
Results
A total of 19 studies were included in this review which included 2 post-hoc analyses of randomized controlled trials [10], [12], 10 cohort studies [8], [11], [16], [17], [21], [22], [23], [26], [27], [28] and 7 case–control studies [7], [9], [29], [30], [31], [32], [33] with 511,503 participants. The process of study selection is shown in Fig. 1.
Discussion
Our results suggest that there is no significant increase in AF with either moderate or rigorous physical activity. In terms of athletes and sports, there was a non-significant trend towards increased risk of AF but all the included studies were at high risk of bias. While there are studies supporting a possible association between AF and physical activity, in general many are case–control in design and are of poor methodological quality. Thus the current evidence suggests that there is no
Conflict of interest disclosures
The authors have no conflicts of interest to declare.
Acknowledgments
SGA is an Academic Clinical Lecturer in Cardiology and is funded by the National Institute of Health Research.
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This author takes responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation.