Expert Review: Arrhythmia

Risk of arrhythmias in 52 755 long-distance cross-country skiers: a cohort study

Background and objectives:
It has been hypothesised that athlete’s heart, secondary to long term endurance sport practice, may increase the incidence of arrhythmias, particularly atrial fibrillation (AF), atrial flutter, sinus node dysfunction, and eventually right ventricular tachycardia. Several mechanisms have been proposed to explain the increased incidence of arrhythmias in athletes1. It is well accepted that arrhythmias depend on triggers, substrates and modulators, and these factors may be present in relation to physical activity. The increased vagal tone induced by endurance sport practice may indeed facilitate the appearance of these rhythm disturbances. In addition, long term endurance sport practice may induce structural changes in the atrium (enlargement, fibrosis) that may create a favourable substrate for the disease. An in depth review of the literature that suggests interesting connections between overtraining and chronic systemic inflammation that may be a contributory effect for AF in athletes2. In fact, there is a relationship between AF and C reactive protein2. However, the real risk of arrhythmias and their clinical consequences in terms of hospitalisation and death have not been stablished.
The hypothesis held in the present study defended that both the number of races completed (exercise dosage) and finishing time (exercise intensity) associate with arrhythmia. Therefore, the aims of the study were to assess the presence of:
a) Any arrhythmia, as the primary outcome (including all of the diagnoses below)
b) Specific arrhythmias, as secondary endpoints, as follows:
– Bradyarrhythmias
– AF or atrial flutter
– Other supraventricular tachycardias
– Ventricular tachycardia/ventricular fibrillation/cardiac arrest

Methods
The study included all the participants who completed a 90 kilometre-skiing race (the Vasaloppet event) during the period 1989-1998. Duration and intensity of exposure to physical exercise were measured by the number of finished races and finishing time.
Participants were followed from the last participation in the race during the period from 1989–1998 (the baseline date) to the date of first diagnosis of the outcome of interest, death, date of emigration, or the end of the follow-up (31st December 2005).

Results
This cohort study included 52755 cross-country skiers followed for a medium period of 9.7 years. The average age of athletes at study entry was 38 years, while the average age of the first arrhythmia was 57 years. Of all the athletes studied, there were 919 inpatient visits for any arrhythmia during the mean follow up.
The overall incidence of arrhythmia was 1.9%. Although low, this incidence more than doubled the rate one would expect in an age-matched group. The most common diagnosis was AF (n=681), followed by bradyarrhythmia (n=119), including 34 athletes with complete AV block. Typical supraventricular tachycardia occurred in 105 athletes, and premature ventricular contractions/ventricular tachycardia in 90.
Athletes who completed the highest number of races had the highest risk of arrhythmia (HR1.30; 95% CI1.08–1.58; for ≥5 vs.1 completed races). Arrhythmia risk increased on a continuum by races completed, up to a 30% higher for five-time finishers. The increase was linear, with a 10% increase per race completed.
Those who had the fastest finishing times also had the higher risk of arrhythmia (HR1.30; 95%; CI 1.04–1.62; for 100–160% vs. >240% of winning time). On the contrary, the “strollers”, or those who finished in more than double the fastest finishing time, had the lowest risk of arrhythmia. No associations of number of completed races or finishing time with other supraventricular arrhythmias or dangerous arrhythmias such as ventricular tachycardia/ventricular fibrillation/cardiac arrest were observed.

Conclusion
Among male participants of a 90 km cross-country skiing event, a faster finishing time and a high number of completed races were associated with higher risk of arrhythmias. While a strong association between the duration/intensity of physical exercise and the development of AF and bradyarrhythmias existed, No association with supraventricular tachycardia or ventricular tachycardia/ventricular fibrillation/cardiac arrest was found.

Clinical Impact:
Intense endurance sport practice carries a higher arrhythmic risk. However, while more frequent episodes of AF and bradyarrhythmias were shown, no malignant rhythm disturbances developed in this cohort. Therefore, the general recommendation of reducing sport practice in this population should be balanced with the symptomatic burden of the arrhythmia and the individual’s own desire. Further research to assess the implications of cardiac remodeling and inflammation is warranted.

Corresponding author from original paper
Kasper Andersen, MD, 1Department of Medical Sciences, Uppsala University Hospital, Entrance 40, 5th floor, SE-751 85 Uppsala, Sweden;
Tel: +46 186110000, Fax: +46 18509297,
Email: kasper.andersen@medsci.uu.se

Citation: Andersen K, Farahmand B, Ahlbom A, Held C, Ljunghall S, Michaëlsson K, Sundström J. Risk of arrhythmias in 52 755 long-distance cross-country skiers: a cohort study. Eur Heart J. 2013; 34(47):3624-31

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