BARCELONA. SPAIN. Several studies have concluded that long-term participation in vigorous, sustained exercise (sports) increases the risk of developing lone atrial fibrillation (LAF). A group of Spanish researchers now confirm this connection. Their study included 183 male marathon runners (between the ages of 20 and 60 years) who had participated in the 1990 Barcelona marathon and joined the study between 1990 and 1992. The annual incidence of LAF in this group was compared to the incidence in a group of 290 largely sedentary men recruited from a general population study conducted in 1994-96.

The two groups were followed for 12 years and 6 years respectively. At the end of the follow-up period, 9 of the marathon runners and 2 of the control subjects had developed LAF. This corresponds to an annual incidence of 0.43% among the athletes as compared to 0.11% among the sedentary men.

The researchers conclude that the overall incidence of LAF among marathon runners is still relatively low at less than 0.5%/year, but distinctively higher than the incidence associated with a more sedentary lifestyle. The only statistically significant difference between athletes who developed afib and those who did not was a larger inferosuperior left atrial diameter in the afibbers. However, as the measurement of atrial dimensions was done after the diagnosis of LAF, it is not clear whether the enlargement helped precipitate the atrial fibrillation, or the atrial fibrillation caused the enlargement.

Molina, L, et al. Long-term endurance sport practice increases the incidence of lone atrial fibrillation in men: a follow-up study. Europace, Vol. 10, 2008, pp. 618-23

Editor's comment: There would seem to be little doubt now that long-term, vigorous endurance exercise is a risk factor for the development of LAF. Whether a risk increase of 0.3%/year over that of sedentary men is acceptable is clearly a decision to be made by each athlete. Unfortunately, it is unlikely that endurance athletes worry about developing LAF until it is too late. It is interesting that the Spanish researchers use the following definition for LAF: "Lone atrial fibrillation is characterized by the presence of atrial fibrillation in the absence of structural heart disease or other identifiable causes of arrhythmia such as hypertension, hyperthyroidism, or alcohol use." This definition is actually more akin to the definition of idiopathic atrial fibrillation, i.e. afib with no known cause, but close to the definition we generally use.