By Linda Carroll

(Reuters Health) – Former players from the National Football League may face an increased risk of a type of irregular heartbeat that could lead to stroke, a new study suggests.

Researchers found that retired NFL players were nearly six times as likely to develop atrial fibrillation as men of the same age in the general population, according to results published in the Journal of the American Heart Association.

“We have to be aware that athletes who participate in these kinds of sports, particularly retired NFL players, do have an increased risk of atrial fibrillation compared to the general population,” said Dr. Dermot Phelan, director of the Sports Cardiology Center at the Cleveland Clinic in Ohio and the study’s senior author. “Athletes need to make sure they continue to go for annual physicals where this can be checked out.”

Atrial fibrillation occurs when the electrical impulses that spark each heartbeat fire erratically. That causes the atria, the top chambers of the heart, to almost quiver rather than pumping blood out, which can result in blood pooling and clotting. If a clot in an atrium travels to a blood vessel that leads to the brain, there can be a stroke.

The American Heart Association estimates that more than 2.7 million people in the U.S. experience atrial fibrillation – sometimes known as AFib – making it the most common irregular heart rhythm.

Studies have linked long-term participation in endurance sports such as marathon running with an increased risk of atrial fibrillation. Phelan and his colleagues suspected that a similar connection might be found in sports that require muscle strength.

To test the hypothesis, the researchers compared 460 retired pro football players to 925 men from the Dallas Heart Study, who served as the control group. Both groups of men were middle aged and about half in each group were African American.

In both groups, information on participants’ history of high blood pressure, high cholesterol, diabetes, coronary artery disease, stroke and heart failure came from self-reports and were not measured.

Overall, the retired NFL players had fewer cardiovascular risk factors, such as type-2 diabetes and high blood pressure. Most of the former players also had lower resting heart rates compared to the men from the DHS.

But 23 of the retired players, or 5%, had atrial fibrillation, as compared with five men in the control group, or 0.5%. Accounting for other AFib risk factors like heart failure, coronary artery disease, hypertension and diabetes, the researchers calculated the retired NFL players had 5.7 times the risk of developing atrial fibrillation compared to the control group.

Fifteen of the 23 NFL players with atrial fibrillation had not previously been diagnosed and had no symptoms. No new cases of atrial fibrillation were found in the control group.

“It’s known that endurance athletes – the elite ones who are middle aged and have done it for many years – are at increased risk,” Phelan said. “This is the first time this has been looked at in strength-type sports.”

It’s not clear why strength sports might lead to irregular heart rhythms, Phelan said.

The new study is a “good initial observation, but we will have to have more objective evidence of (other health conditions) and risk factors plus long-term monitoring of atrial fibrillation for there to be a clear correlation,” said Dr. Johanna Contreras, an assistant professor of medicine at the Icahn School of Medicine at Mount Sinai and director of heart failure at Mount Sinai St Luke’s in New York City.

One issue with the study is that “there are many other factors that can increase the incidence of atrial fibrillation, like age, smoking, alcohol use, steroid use, poor sleeping hygiene, and sleep apnea,” Contreras said. “There was also no objective verification of diabetes, hypercholesterolemia and hypertension, which are associated with an increased incidence of atrial fibrillation.”

SOURCE: Journal of the American Heart Association, online July 24, 2019.