Introduction
Regular physical exercise reduces cardiovascular morbidity.1,2 However, our clinical impression is that atrial fibrillation is quite common in otherwise healthy middle aged men engaged in long term vigorous endurance sports. We therefore compared the prevalence of atrial fibrillation in middle aged men doing intense endurance training and men from the general population.
Subjects, methods, and results
We chose top level veteran orienteers to represent subjects doing long term vigorous exercise. A high position in the veteran ranking list is an indicator of years of intense training. We enrolled the 60 top ranked orienteers in 1984 from the race classes age 35-39 years, 40-44 years, 45-49 years, and 55-59 years, a total of 300 runners. The 495 controls comprised all men aged 35-59 enrolled for an earlier study.2 At 20 years old these subjects had been completely healthy (fully fit for military service). Mean (SD) age at baseline was 47.5 (7.0) years in orienteers and 49.6 (5.3) years in controls. Controls had responded in 1985 to a questionnaire which included items on physical activity and occurrence of various diseases.2
In 1995 we sent a similar questionnaire to the orienteers and controls but which contained an additional question on cardiac arrhythmias: “Has a doctor ever told you that you have atrial fibrillation or atrial flutter.” Those who answered “yes” completed another detailed questionnaire on atrial fibrillation, and electrocardiograms and other data were obtained from their medical records to confirm the diagnosis. We excluded all subjects who reported known risk factors for atrial fibrillation.3
Ninety per cent (262) of the orienteers and 83% (373) of the controls responded to the questionnaire (figure). Compared with the general population orienteers had much lower mortality (1.7% (95% confidence interval 0.5 to 3.8%) v 8.5% (6.2% to 11.3%)), lower reported coronary heart disease since 1985 (2.7% (1.1 to 5.4%) v 7.5% (5.1% to 10.7%)), and fewer risk factors for atrial fibrillation (figure). However, in men without known risk factors, lone atrial fibrillation had been diagnosed in 12 of 228 (5.3% (2.8% to 9.0%)) orienteers and in 2 of 212 (0.9% (0.1% to 3.4%)) controls (P=0.012, two tailed Fisher’s exact test), the relative risk being 5.5 (1.3 to 24.4) in orienteers. The two controls with lone atrial fibrillation also took vigorous exercise. The age-specific prevalence of lone atrial fibrillation at the end of 1995 in orienteers was 4.2% (4/95) for those aged 46-54 years, 5.6% (4/72) for those aged 55-62 years, and 6.6% (4/61) for those aged 63-70 years. In subjects with risk factors atrial fibrillation had been diagnosed in 12% (4/34) of orienteers and 9% (15/161) of controls (P>0.05).
The first attack of lone atrial fibrillation in orienteers was at a mean age of 52 years (SD 10, range 34 to 68) after an average training history of 36 years. Three also had documented episodes of atrial flutter.
Comment
Vigorous long term exercise is associated with atrial fibrillation in healthy middle aged men despite protecting against coronary heart disease and premature death. In population studies the average prevalence of atrial fibrillation, persistent or paroxysmal, is 0.5% in subjects aged 45-54 years, about 1% at 55-64 years, and 4% at 65-74 years.4 The prevalences of lone atrial fibrillation in our sportsmen were higher.
The reasons for the increased risk of atrial arrhythmias in middle aged endurance athletes can only be speculated. Enhanced vagal tone, characteristic of endurance athletes, predisposes normal hearts to atrial fibrillation.5 Atrial enlargement and left ventricular hypertrophy, both features of the endurance athlete’s heart, may further increase the tendency to atrial fibrillation. We do not know whether stopping exercise would have prevented recurrence of atrial fibrillation. Most of the orienteers with commonly relapsing cases had responded adequately to antiarrhythmic drugs and continued competing.
Figure.
Flow chart of study. Other risk factors for atrial fibrillation were hypertension, myocardial or valve disease, diabetes, thyroid disorder, and severe obesity
Footnotes
Funding: Finnish Defence Forces.
Conflict of interest: None.
References
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