Increased levels of exercise raise the risk of atrial fibrillation in active men, in both serious athletes and leisure-time exercisers, two Scandinavian studies show.
Atrial fibrillation isn't good, but that doesn't mean exercise is bad. Investigators from both studies, speaking at a press briefing at the annual congress of the European Society of Cardiology, emphasized that the general health benefits from physical exercise outweigh the risk of this heart rhythm disorder.
Courtesy Wikimedia Commons/Steven Hale/Creative Commons
Skiers in the Swedish endurance race Vasaloppet.
In that study, Dr. Knut Gjesdal and associates at Oslo (Norway) University Hospital merged data on 428,519 patients from three population-based Norwegian surveys conducted from 1974 through 2003. During follow-up, from 2004-2009, 1,183 men and 609 women had a first-time prescription for flecainide, which the study used as a surrogate marker for atrial fibrillation in otherwise healthy adults. Flecainide is prescribed to prevent atrial fibrillation recurrence and is well tolerated by normal hearts, but it is not given to people with heart disease other than atrial fibrillation because it causes serious complications under those conditions.
Patient exercise levels were classified in four ways: 1) sedentary; 2) moderate (walking, cycling, or other exercise at least 4 hours per week); 3) intermediate (at least 4 hours per week of participation in recreational sports or heavy gardening), or 4) intensive (participating in hard training or sports competitions regularly or several times per week).
For men, intensive exercisers had nearly three times the risk for atrial fibrillation as sedentary men. The risk for atrial fibrillation was 40% higher in intermediate exercisers and 20% higher in moderate exercisers compared with sedentary men.
The number of women in the study was too small (especially at the higher levels of exercise) to draw conclusions about atrial fibrillation risk.
Because flecainide doesn't affect physical performance and thus is preferred by athletes with atrial fibrillation, the investigators tried to avoid a bias from athletes in a separate analysis using sotalol prescriptions as the marker for atrial fibrillation. This beta-blocker drug reduces endurance but is used to treat nonpermanent atrial fibrillation even in patients with coronary heart disease. Again, the same association was seen: the more leisure-time activity at the time of the survey, the higher the chance of future sotalol use.
A separate study focused just on athletes, specifically cross-country skiers. Every year in Sweden, elite and recreational athletes participate in a 90-kilometer, endurance cross-country skiing event called "Vasaloppet."
Dr. Kasper Anderson and associates at Uppsala (Sweden) University looked at arrhythmia rates in all Swedish participants of the race from 1989 to 1998, a total of 47,477 people. They stratified risk based on elite or recreational training level (defined by the participant's finishing time in the race) and by duration of athletic training (defined by the number of races completed by the participant).
Participants who had completed at least seven races had a 29% higher risk for arrhythmia, compared with those who had completed a single race, after adjusting for the effects of age, socioeconomic status, and education. Participants who finished the race at 100%-160% of the winner's time (the elite athletes) had a 37% higher risk for arrhythmias, compared with recreational skiiers whose finishing times were more than 241% of the winner's time.
Atrial fibrillation and bradyarrhythmias drove most of these associations. No significant increase in ventricular arrhythmias was seen with higher exercise levels.
"Even though physical activity is generally healthy, athletes committed to endurance sports at elite levels have highier risk of suffering from a heart rhythm disorder," Dr. Anderson said.
---Sherry Boschert (@SherryBoschert on Twitter)