Marathon Runners at Low Risk of Cardiac Arrest
Credit: Sergey Khakimullin | Dreamstime

Running marathon races may notincrease the risk of cardiac arrest as previously thought, a new study suggests.

Researchers found the risk of cardiac arrest, which is when the heart suddenly stops beating, among long-distance runners was lower than or equal to the risk in athletes who participated in other sports.

Cardiac arrest is caused by an "electrical problem" in the heart. It follows from the heart developing an irregular rhythm that disrupts its pumping action, and stops blood flow to the rest of the body.

"This study shows that long-distance running is a safe and well-tolerated sport," said lead author Dr. Aaron Baggish, a cardiologist at Massachusetts General Hospital.

"However, even though it's a safe sport, it's not completely protective against heart disease," Baggish said.

The paper was published yesterday (Jan. 11) in the New England Journal of Medicine.

Running long-distance races isn't necessarily bad for you

Nearly 2 million people participated in marathon and half-marathon races in the U.S. in 2010, according to Running USA.

As more people participate in marathons, reports of runners collapsing and sometimes dying on race courses have also increased, causing concern about the safety of long-distance running.

"There's been an increase in cardiac arrest because more people are running marathons," Baggish said. "So it's not becoming more risky to do these runs. It actually helps people more than it hurts."

Out of nearly 11 million runners who participated in marathon races over a 10-year period, researchers identified 59 cases of cardiac arrest — 40 in marathons and 19 in half-marathons.

That means that cardiac arrest occurred in 1 out of 184,000 participants. Sudden death occurred in 1 out of 259,000 participants, the researchers also found.

These rates were relatively low compared with those of people doing other sports, including college athletics, triathlons and recreational jogging.

Heart disease goes unnoticed in some athletes

The researchers had detailed medical information for some of the affected runners, and found that hypertrophic cardiomyopathy — the abnormal thickening of heart muscle — was one of the main causes of cardiac arrest.

Hypertrophic cardiomyopathy is also a common cause of sudden cardiac death in young athletes.

"Heart disease can be silent," said Dr. Byron Lee, a cardiologist at the University of California, San Francisco, who was not involved with the work.

"People with hypertrophic cardiomyopathy can perform high levels of exercise, and may not even realize they have it," he said.

In the study, runners who had the condition were between29 and 42 years of age. Researchers found that while these younger runners tended to have hypertrophic cardiomyopathy, older runners were more likely to have coronary heart disease.

 More than 85 percent of cardiac arrests occurred in men. Moreover, the risk among male marathon runners increased over time, suggesting that long-distance running may be attracting more men who are at risk of having coronary artery disease, which is the buildup of plaque in the major arteries of the heart. 

"It's true that when you exercise, the risk for heart attacks and dangerous heart rhythms can go up slightly, Lee said.  "But exercise in itself is overall a good thing."

Leerecommended getting checked by a doctor, especially if you're older, before starting a new exercise regimen.

CPR could be key to survival

Of the 59 cardiac arrests, 41 people, or 70 percent, died, which authors noted was better than the roughly 95 percent of people who usually die from cardiac arrest.

Results also showed that survival was mainly due to bystanders and on-site medical services who were able to respond quickly and perform CPR.

"The most important factor that determined whether someone lived or died was a bystander performing CPR," Baggish said.

Pass it on: Running long-distance races is less likely to increase risk of cardiac arrest than some other sports.

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