Low Incidence of A-fib Seen in Elite Athletes, Including Runners and Triathletes

The incidence of atrial fibrillation in relatively young athletes in Spain is extremely low, with just 0.3% of elite-level athletes identified as having the arrhythmia. Among 6,813 individuals, of whom nearly 30% participated in endurance events such as long-distance running and triathlons, atrial fibrillation was identified in 20 men and one woman, according to a new study published October 31, 2018, in JAMA Cardiology.

Eighteen of these athletes had paroxysmal atrial fibrillation, and three had persistent or longstanding atrial fibrillation. Atrial fibrillation was detected in five basketball players, one trail runner, two soccer players, five middle- and long-distance runners, and two triathletes, among others. Only one athlete was symptomatic.

The researchers, led by Araceli Boraita, MD, PhD (Spanish Sports Health Protection Agency, Madrid, Spain), say the incidence of atrial fibrillation in young athletes is low and in line with previous studies. Those who did develop the arrhythmia tended to be older (mean, 38 years vs 22 years) and to have spent more time participating in sport at the elite level (mean, 21 vs 8 years of competition).

Senior researcher Alejandro Lucia, MD, PhD (European University of Madrid, Spain), noted that they also identified changes in the heart that might serve as a trigger for future arrhythmias. With exercise, there is increased arterial pressure, along with atrial wall stretching, and long-term exposure could lead to “microtrauma, inflammation, and fibrosis, which are arrhythmogenic,” according to the researchers. 

To TCTMD, Lucia said they found that an enlargement of the anteroposterior diameter of the left atrium relative to the longitudinal diameter—in essence, the left atrium becomes more spherical, like a tennis ball rather than a rugby or American football—was associated with an increased risk of atrial fibrillation.

“The atria becomes a little bit too round-shaped,” said Lucia. “We can’t predict whether atrial fibrillation is going to happen for sure, but the good news is that if it happens, it can be very well managed,” he added. Increased left atrium size in athletes is usually considered a nonpathologic cardiac adaptation to exercise, but follow-up of left atrium dimensions with echocardiography might be useful to track changes in the dimensions over time, say the researchers.

On the whole, the low rate of atrial fibrillation is reassuring, particularly given some recent concerns about the risks of “too much” exercise, said Lucia. Those risks, however, are unlikely to manifest in such young competitive athletes but rather in older, master’s athletes with a lifetime of high-volume/high-intensity exercise behind them, he noted.

No Surprises Here

The overall low incidence of atrial fibrillation in the Spanish athletes is absolutely unsurprising given their age, according to Paul Thompson, MD (Hartford Hospital, CT). Nonetheless, there does remain a concern about the risk of atrial fibrillation among older endurance athletes who have participated in elite-level athletics for many years, he said.

One of the biggest and most commonly cited papers to date is a study of the risk of arrhythmias in more than 52,000 elite Nordic skiers (mean age 38.5 years) who participated in the Vasaloppet, a 90-km cross-country skiing event. In that study, researchers observed an increased risk of arrhythmias, driven mainly by atrial fibrillation, among skiers who completed the most races and who had faster finishing times, leading researchers to conclude that a higher training level was associated with an increased risk of arrhythmias.  

“The question is not whether atrial fibrillation is a problem in young athletes—I don’t think it is—but whether atrial fibrillation is a problem in older athletes,” Thompson told TCTMD. “We do think it’s a problem in these older athletes. Why? Probably because when you train you increase the left atrium. All four chambers of the heart—the right and left ventricles, the right and left atria—get bigger. With bigger left atria, you’re more likely to go into atrial fibrillation.”

David Peritz, MD (University of Utah, Salt Lake City), was also unsurprised by the low rate of atrial fibrillation in the Spanish athletes given their age. Like Thompson, he cited a potential increased risk as these young adults transition into adulthood and continue playing sports. For example, high-level master’s athletes with a history of high-volume training—those over 35 years old who have trained for at least 10 hours per week for 10 years—are at roughly a tenfold increased risk of atrial fibrillation compared with healthy controls, Peritz said, noting, “But again, we only see this in older people, those over the age of 35, and we really only see it in men, not women.”

At the European Society of Cardiology Congress in Munich, Germany, this year, Peritz presented data showing that highly trained master’s endurance athletes (mean age 48 years) had significantly more left atrial fibrosis compared with healthy controls.

“Young people are healthy enough that they are probably not getting atrial fibrillation,” Peritz told TCTMD. Whether high-level physical activity is “laying down fibrosis or stretch or increased strain from high stroke volumes and increased afterload, we don’t know,” he added. “I think there’s definitely some microscopic damage being done with training and whether this can go away with detraining, or whether this is actually causing atrial fibrillation, we can’t clearly connect the dots just yet. The picture is starting to unfold slowly.”

To TCTMD, Jonathan Kim, MD (Emory University School of Medicine, Atlanta, GA), also noted the previously reported strong association between long-term strenuous endurance exercise and atrial fibrillation, highlighting the study of the elite Vasaloppet cross-country skiers as some of the best evidence to date. While the arrhythmia is less likely to occur in young athletes, it can manifest earlier in older master endurance athletes compared to the general population, he pointed out.

However, Kim cautioned that the association does not imply causality and specific mechanisms underlying the heightened risk remain only hypothesized at this point. While pathologic left atrial remodeling is one of those proposed mechanisms, Kim said he is careful in implicating just endurance exercise as the cause of the arrhythmia as there may be other factors contributing to atrial fibrillation in these older athletes.  

Regular Folks Needn’t Worry Too Much

Thompson said research into the long-term risk of endurance sport is only coming into view now. The jogging boom took off in the 1960s, so researchers have not had an opportunity to study athletes, specifically endurance athletes, who have exercised for 30, 40, or even 50 years, he said.

To TCTMD, Thompson stressed that the issue is complex, noting that as individuals get more exercise, the risk of atrial fibrillation decreases. Higher levels of cardiorespiratory fitness have also been shown to reduce the recurrence of atrial fibrillation in obese patients with the arrhythmia. However, as individuals approach the extreme levels of exercise training, at least in older athletes, the risk of atrial fibrillation goes in the other direction. He added, though, that too much exercise is not the concern for most individuals, nor is it a concern for most patients. Unless they are a lifelong athlete, they are not going to be at risk of developing atrial fibrillation from exercise, stressed Thompson.

Peritz provided further reassurances.

“The people who are at high risk are people who are doing three Ironman [triathlons] a year and the people who are finishing in the top 10,” he said. “The faster you are and the more you train, there certainly is a dose response [to the risk of developing atrial fibrillation]. For you and me, or the weekend-warrior people doing one marathon or a few half-marathons a year, you’re fine.”

Lucia agrees. He added that telling someone to stop exercising is simply not in the cards for the vast majority of athletes. Instead, even if an older athlete develops atrial fibrillation, there are ways to manage the condition while also continuing to participate in sport. As an ongoing cyclist and former marathon runner, Lucia said that benefits of exercise far outweigh the risks.