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Bigger Hearts OK for Elite Athletes?

New research shows that in world-class athletes, an enlarged heart may not raise the risk of heartbeat problems.

Specifically, researchers looked at the heart's upper left chamber (the left atrium) in more than 1,700 competitive athletes.

They found that relatively few athletes had left atrial enlargement and that the condition didn't raise the odds of having an irregular or abnormally fast heartbeat called atrial fibrillation.

But most of us are nowhere near that level of athletic achievement. It's always wise to get any heart concerns checked out by a doctor and to follow medical advice about heart care.

The study appears in the Journal of the American College of Cardiology. The researchers included Antonio Pelliccia, MD, of the National Institute of Sports Medicine with the Italian National Olympic Committee.

Supersized Hearts

Theheart of athletes undergoes changes during training. In well-conditioned athletes these common structural and electrical changes are known as the athletic heart syndrome.

In atrial fibrillation blood isn't completely pumped out of the upper chambers of the heart. Blood that doesn't circulate pools in the chamber and can clot. If the clot travels, leaving the heart, it can block arteries in the brain, causing a stroke.

The stats on the study's athletes:

— Men: 71 percent

— Average age: 24

— Average time in vigorous training: 6 years

— Players in the Olympics or world championships: 390

The other athletes in the study had participated in national and regional competitions. All were screened between 1992 and 1995. The findings:

— Most didn't have enlarged hearts or heartbeat problems.

— 24 percent (347 athletes) had a heart with an enlarged left atrium.

— Less than 1 percent of the entire group had irregular or abnormally fast heartbeats.

— Those with an enlarged left atrium weren't more likely to have irregular or abnormally fast heartbeats.

In 2003, the researchers checked in with the athletes who had had enlarged left atria and no other heart problems. The "vast majority" was still training and competing as hard as ever, and "virtually all" were healthy and had no heart problems, write the researchers.

Read WebMD's "Ending Training May Protect Athletes' Hearts"

How Big Is Big?

An enlarged left atrium was 40 millimeters or bigger. Only 2 percent of the athletes had a left atrium that was 45 millimeters or bigger. The upper range was 46 millimeters in women and 50 millimeters in men.

That might be the "outer limit" of exercise's effect on heart size, and enlargements beyond that might stem from health problems, write the researchers.

Chalk It Up to Training?

The heart's left atrium probably got bigger in response to intense athletic conditioning, note the researchers.

"Left atrial remodeling in competitive athletes may be regarded as a physiological adaptation to exercise conditioning, largely without adverse clinical consequences," they write.

Read WebMD's "Enlarged Hearts More Common in Blacks"

Other Heart Chambers Enlarged

WebMD contacted professor Edward Coyle, PhD, about the study.

Coyle directs the Human Performance Laboratory at the University of Texas at Austin. He studies the physiological factors that limit human exercise performance. His subjects have included seven-time Tour de France winner and cancer survivor Lance Armstrong.

In an email, Coyle tells WebMD that the study showed that endurance athletes have larger left atria, as well as the thicker chamber below it (the left ventricle).

"Although this is well known for the ventricles, [which] perform most of the [heart's] work in pumping, it is clear this is the case for the atria," writes Coyle.

"It would be surprising if both chambers were not enlarged, as they work in tandem, and the volume and size of one should generally match the other," he continues. "More importantly, this study documented that enlargement of the atrial chamber is a healthy adaptation and it is not associated with increased irregular heartbeats or disruption of heart rhythm."

Coyle writes that he has not attempted to measure the size of the left atria but has seen "a healthy enlargement" of the left ventricle in endurance athletes. "This has been well documented by other investigators," writes Coyle.

Read WebMD's "Exercise for a Healthy Heart"

More Study of Athletes

In a news release from the American College of Cardiology, heart expert Norbert van Hemel, MD, PhD, calls for more study of aging athletes.

"One must question whether this 'adaptation' is sound, and whether it might become the source of physical problems in the years after the intensive sport training is stopped," says Hemel. He is the Pasman Chair of Cardiac Stimulation at Utrecht University in the Netherlands.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Pelliccia, A. Journal of the American College of Cardiology, Aug. 16, 2005; vol 46: pp 690-696. WebMD Medical News: "Enlarged Hearts More Common in Blacks." Edward Coyle, PhD, professor, kinesiology, director, Human Performance Laboratory, University of Texas, Austin. News release, American College of Cardiology. American Heart Association.