Stroke in endurance athletes with atrial fibrillation

Atrial fibrillation is a common cardiac arrhythmia affecting >33 million individuals worldwide.1 The prevalence increases with age, with a higher age-adjusted prevalence in men than in women. Atrial fibrillation increases the risk of stroke and stroke severity, and approximately one of three ischaemic strokes is related to atrial fibrillation.2 While moderate physical activity prevents atrial fibrillation, prolonged endurance exercise seems to increase the risk of atrial fibrillation, at least in men.3 Despite a low prevalence of established atrial fibrillation risk factors, male non-elite endurance athletes aged ≥65 years have a prevalence of atrial fibrillation comparable to that of their less active peers in the same age group.4 Whether the high prevalence of atrial fibrillation related to exercise translates into an increased risk of stroke is unknown. The role of exercise for stroke prevention in individuals with atrial fibrillation is sparsely investigated,5 and we are not aware of any studies that have investigated the occurrence of stroke in athletes with atrial fibrillation. The aim of the current study was to assess the association between atrial fibrillation and stroke among non-elite endurance athletes. The main aim of the Birkebeiner Atrial Fibrillation Study was to study the association between prolonged endurance exercise and risk of atrial fibrillation. We have described the study population and the methods of this retrospective cohort study previously.6 During 2012, we invited all 3485 men and women who participated in the annual 54-km cross-country ski race Birkebeinerrennet in 1999, and were aged ≥40 years at that time, to participate in the study. The majority was non-elite endurance athletes practising regular endurance exercise.7 All participants signed an informed consent in accordance with the Declaration of Helsinki. The study was approved by the Regional Committee for Medical and Health Research Ethics. Atrial fibrillation, stroke and related conditions were self-reported by response to the questions ‘Do you have or have you ever had [disease]?’ and ‘Have you been diagnosed as suffering from [disease] by a physician?’ Self-reported atrial fibrillation was adjudicated by reviewing electrocardiograms and hospital records. We used Student’s t-test for means of continuous variables and Pearson’s chi-square test of independence for categorical variables for subgroup comparison. Adjudicated and self-reported atrial fibrillation were the main explanatory variables and self-reported stroke the main outcome. We calculated risk estimates by logistic regression analysis with adjustments for age, sex, level of education, body mass index (BMI), concomitant heart diseases, anti-hypertensive treatment, lipid-lowering treatment, diabetes mellitus, smoking and alcohol consumption. We present adjusted odds ratios (aORs) with 95% confidence intervals (CIs) for self-reported and adjudicated atrial fibrillation, for the whole study population and for subgroups aged <65 and ≥65 years. Individuals aged >85 years were excluded in order to reduce the heterogeneity of the study population and minimize recall bias. We used SPSS version 25.0 (IBM, Armonk, New York, USA) for all statistical analyses. In total, 2653 of the invited athletes (76.1 %) participated and 2626 individuals were eligible for the current analysis, after exclusion of 27 individuals aged >85 years. The prevalence of self-reported atrial fibrillation was 12.3% (n = 322). The prevalence of self-reported stroke was 4.2% (n = 111); 6.8% in athletes with atrial fibrillation and 3.9% in athletes without atrial fibrillation (p < 0.05). Characteristics of the study participants by self-reported atrial fibrillation are shown in Table 1. Individuals with atrial fibrillation were older, taller, had a higher BMI, a higher prevalence of cardiovascular risk factors and a longer history of endurance sport practice. After multivariate adjustment, the aOR for stroke in athletes with self-reported atrial fibrillation was 1.85 (95% CI 0.99–3.46, p = 0.06) compared with athletes without atrial fibrillation. Both self-reported (aOR 2.16, 95% CI 1.07–4.38, p < 0.05) and adjudicated atrial fibrillation (aOR 2.38, 95% CI 1.05–5.40, p < 0.05) were associated with higher prevalence of stroke in athletes aged ≥65, but not in in athletes <65 years (Supplementary Material online). Characteristics of non-elite endurance athletes with and without self-reported atrial fibrillation, N = 2626. Current or previous. Estimated based on age, sex and self-reported coronary heart disease, current or previous hypertension, stroke and diabetes mellitus. Bouts of endurance exercise of ≥30 min ≥3 times per week with the goal to improve or maintain physical capacity. Characteristics of non-elite endurance athletes with and without self-reported atrial fibrillation, N = 2626. Current or previous. Estimated based on age, sex and self-reported coronary heart disease, current or previous hypertension, stroke and diabetes mellitus. Bouts of endurance exercise of ≥30 min ≥3 times per week with the goal to improve or maintain physical capacity. Despite a high prevalence of atrial fibrillation among endurance athletes, atrial fibrillation is sparsely studied in this group and more knowledge is needed regarding its treatment and consequences.3 To our knowledge, our study is the first to report on the association between atrial fibrillation and stroke occurrence in athletes. Sanchis-Gomar et al. have suggested that paroxysmal atrial fibrillation in young and middle-aged athletes is a unique clinical entity caused by exercise-induced cardiac remodeling.8 The individuals with atrial fibrillation in our study share many characteristics with younger athletes with atrial fibrillation: They are men exposed to prolonged endurance exercise, atrial fibrillation is most often paroxysmal and the majority has a BMI < 25 kg/m2 and absence of diabetes, hypertension and concomitant heart diseases. On the other hand, our study demonstrates that these conditions do exist among athletes, indicating that middle-aged and older athletes represent a more heterogeneous group requiring individualized clinical management. Guidelines advocate the use of the CHA2DS2VASc-score and recommend that atrial fibrillation patients who are aged ≥65 years and have at least one additional risk factor for stroke should be treated with oral anticoagulation therapy (OAC).9 In the Birkebeiner Atrial Fibrillation study only two out of three athletes with atrial fibrillation and an estimated CHA2DS2VASc-score of ≥2 received OAC.7 While OAC is rarely indicated in young athletes, the current study supports that athletes aged ≥65 years should receive OAC to prevent stroke, in line with current guidelines. The main limitation of this study is the cross-sectional design, without information about the temporal relationship between atrial fibrillation and stroke events. Paroxysmal atrial fibrillation often remains undetected, and individuals who have suffered from a stroke are more likely to have atrial fibrillation diagnosed.10 This might have caused an overestimation of the association between atrial fibrillation and stroke in our study. Stroke was self-reported, the study did not differentiate between intracranial haemorrhage and ischaemic stroke, and no information on the use of previous antithrombotic medication was available. Finally, few female athletes participated. In conclusion, the current study supports that atrial fibrillation might be associated with stroke in endurance athletes aged ≥65 years. The risk of stroke in athletes with atrial fibrillation should be investigated further in prospective studies. Meanwhile, we suggest that endurance athletes aged ≥65 years with atrial fibrillation should be treated with OAC in line with existing guidelines to prevent stroke. Preliminary results were presented (poster presentation) at the ESC congress in 2015. Prevalences of atrial fibrillation and stroke have been presented in the previous paper: Myrstad M, Aaronaes M, Graff-Iversen S, et al. Physical activity, symptoms, medication and subjective health among veteran endurance athletes with atrial fibrillation. Clin Res Cardiol 2016; 105: 154-161.