OSLO, NORWAY. In 1998 Finnish researchers reported that middle-aged, elite orienteers had a 5 times higher incidence of lone atrial fibrillation (LAF) than did the general population. Now Norwegian sports medicine experts report that the prevalence of LAF in elite cross-country skiers is about 13% as compared to about 0.5% in the general population. The Norwegian study began in 1976 when 122 healthy, long-term trained cross-country skiers from 3 different age groups (26-33 years, 43-50 years, 58-64 years) were enrolled in the study. None of the participants had hypertension or heart disease at enrolment. Follow-ups were carried out in 1981 (117 participants) and in 2004-2006 (78 participants) and consisted of an ECG during rest and exercise and a maximal exercise test. Electrocardiography was added for the 2004-2006 examination.

The average age at which a first afib episode was observed was 53 years in the youngest age group at enrolment, 67 years in the middle age group, and 76 years in the oldest group with an average for all age groups of 62 years. At the most recent follow-up, 13 of the 78 skiers still participating in the study had experienced afib and the current prevalence was 12.8%. The Norwegian researchers observed that skiers with LAF had a lower resting heart rate (bradycardia) and a longer PQ interval (interval from beginning of p-wave [atrial contraction] to beginning of QRS interval [ventricular contraction]) than did skiers who did not develop LAF. The echocardiographic investigation in 2004-2006 also noted that "LAF skiers" had a larger left atrial diameter and area than did those skiers maintaining normal sinus rhythm.

The researchers did not find any correlation between years of practicing cross-country skiing and the risk of AF; however, they did notice that a long PQ interval is associated with an increased risk of developing AF later in life. They recommend that endurance athletes who develop LAF should stop or significantly reduce their training until they regain NSR.

Grimsmo, J, et al. High prevalence of atrial fibrillation in long-term endurance cross-country skiers. European Journal of Cardiovascular Prevention and Rehabilitation, Vol. 17, No. 1, 2010, pp. 100-05

Editor's comment: These recent findings add to an impressive collection of evidence that endurance exercise and sports increase the risk of developing LAF. See Session 64 for further details. Although the Norwegian researchers stopped short of suggesting when to cut back on endurance exercise (lasting longer than 45 minutes), their data would indicate that a resting heart rate below 50 bpm and a PQ interval above 0.20 seconds might serve as early warnings signs to start taking it easy.