Normally we think of the hearts of athletes as healthier than those of us who are more sedentary, but this is not always the case, as a recent study shows.

Older elite athletes seem to be prone to myocardial fibrosis and ventricular tachycardia.

Ventricular tachycardia, an abnormally fast rhythm of the lower chambers of the heart, can be dangerous. It can lead to cardiac arrest and death and has also been associated with myocardial fibrosis, a thickening or scarring of the heart muscle.

Over 47 percent of the athletes showed signs of fibrosis in the left ventricle of the heart.

A team led by researchers at the University of Leeds in the United Kingdom recently found an association between myocardial fibrosis and ventricular tachycardia in a group of male endurance athletes who were 50 years old or older.

The small study, named VENTOUX after a difficult uphill segment of the Tour de France bicycle race, involved white European cyclists or triathletes who had no symptoms of heart disease. Participants reported they had been training 10 or more hours a week for at least 15 years.

Participants underwent cardiovascular magnetic resonance imaging to see if they had fibrosis. They also had an electrocardiogram loop recorder implanted under the skin of their chest to record their heartbeat during the follow up period.

A control group of male non-athletes matched in age underwent the same imaging tests.

Over 47 percent of the athletes showed signs of fibrosis in the left ventricle of the heart after about two years of follow up. About three percent had sustained tachycardia in the ventricles of the heart, and almost 20 percent had tachycardia that came in short bursts. Those who developed potentially dangerous tachycardia were instructed to get an independent second opinion.

The strength of the association between fibrosis and ventricular tachycardia surprised the researchers. “Similar findings have been reported in patients with heart muscle disease; however, we were not expecting to find this in healthy performance athletes,” Peter Swoboda, senior author on the study and an associate professor of cardiology at the University of Leeds, said in a statement.

“Our main aim was to help endurance athletes continue to participate safely in sports, particularly as they get older,” added Swoboda.

People who experience chest pains, heart palpitations or dizziness while exercising or playing sports should seek help immediately. Everyone involved in sports should know CPR and how to use an automated external defibrillator.

Athletes in the study had been training 10 or more hours a week for at least 15 years.

More studies are needed to determine if fibrosis is the result of tachycardia or caused by another underlying condition and to expand the results to include other study populations, including women.

The study and a related editorial are published in Circulation: Cardiovascular Imaging.