BARCELONA, SPAIN. The team of Lluis Mont, Roberto Elosua and Josep Brugada of the University of Barcelona are tirelessly trying to get their message across – "extreme endurance sports practice is a potent risk factor for lone atrial fibrillation (LAF)". "Extreme" is usually defined as any sports activity (marathon running, cycling, swimming, jogging) that achieves a significantly elevated heart rate, lasts more than 45 minutes a session, and is performed regularly. It is estimated that 2 to 10% of the population now suffers from LAF and that about 30% of patients showing up in doctors' offices with paroxysmal AF are diagnosed with LAF. LAF is commonly associated with atrial flutter. The Spanish researchers quote the following studies to support their point:

• In 1998 Karjalainen and colleagues in Finland reported that the incidence of LAF (after 10 years of follow-up) was 5.3% in a group of elite orienteers versus 0.9% in the control group.
• Mont and colleagues at the University of Barcelona found that men engaging in vigorous, long-term sport practice were 5 times more likely to be diagnosed with LAF than were those in the general population. They also noted that there seemed to be a threshold of about 1500 lifetime hours of endurance sports after which the risk of LAF increased dramatically.
• The Barcelona team also studied a group of individuals who ran the Barcelona Marathon in 1990 and compared the incidence of LAF in this group with that in a group of more sedentary individuals. They found that the sportsmen were 4 times more likely to develop LAF over the 10-year follow-up period than were the more sedentary ones.
• A Swiss research team investigated 64 former Swiss professional cyclists who completed the Tour de Suisse at least once during the years 1955 to 1975. The cyclists (average age of 66 years) were compared with a group of age, weight, and hypertension presence matched golfers. The cyclists had a considerably lower heart rate and an incidence of LAF and atrial flutter of 10% as compared to 0% among the golfers.
• Heidbuchel et al. at the University of Leuven in Belgium observed that endurance athletes have a significantly higher risk of developing LAF after a common flutter ablation.

Mont et al. make a few other salient comments in their study:

• Physical activity may increase atrial and ventricular ectopy and there is evidence that this increased ectopy in elite athletes may be reversed by detraining.
• Elite athletes have increased vagal tone, which has been found to shorten the atrial refractory period, creating the conditions for re-entry.
• There is evidence that excessive endurance exercise and overtraining can lead to chronic system inflammation and there is a relationship between LAF and elevated CRP level (an inflammatory marker).
• There is some evidence that endurance athletes have larger left atria and significant evidence of fibrosis.

The Mont team makes the following critical comments:

The typical clinical profile of sport-related AF or atrial flutter is a middle-aged man (in his forties or fifties) who has been involved in regular endurance sport practice since his youth (soccer, cycling, jogging, and swimming), and is still active. This physical activity is his favourite leisure time activity and he is psychologically very dependent on it. The AF is usually paroxysmal with crisis, initially very occasional and self limited, and progressively increasing in duration. Characteristically, AF episodes occur at night or after meals. As many as 70% of patients may suffer predominantly vagal AF. They almost never occur during exercise. This makes the patient reluctant to accept a relationship between the arrhythmia and sport practice, particularly since his physical condition is usually very good. The crises typically become more frequent and prolonged over the years and AF becomes persistent. Progression to permanent AF has been described by Hoogsteen et al. in 17% of individuals in an observational series.

They conclude that, particularly in relatively recent LAF, limiting training may go a long way toward eliminating, or at least reducing, the severity of LAF in athletes. However, they point out, "these patients are very dependent on physical activity and it is difficult for them to follow this advice."

Mont, L, et al. Endurance sport practice as a risk factor for atrial fibrillation and atrial flutter. Europace, Vol. 11, 2009, pp. 11-17

Editor's comment: This latest article by Mont and colleagues add to the already substantial evidence that, while moderate exercise does the cardiovascular system a world of good, excessive endurance exercise, not only becomes an addiction, but also substantially increases the risk of developing lone AF. Fortunately, it would appear that it is possible to lessen the severity of the exercise-induced LAF by replacing the excessive training with some less intensive physical activity such as walking.