Long-term high-intensity physical training can be harmful for the heart

2013, June 4, 2013

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Study at the Montreal Heart Institute

Long-term high-intensity physical training can be harmful for the heart

Montréal, 4 June, 2013 – A study from the Montreal Heart Institute (MHI) that was published in the Journal of the American College of Cardiology confirms that high-intensity endurance exercise practised over the long-term can be harmful to the heart for certain athletes, making them more at risk of suffering from atrial fibrillation (AF). This Canadian study is the first to precisely identify the mechanisms that lead to this form of heart arrhythmia, which is the most common type found in the Canadian population. Patients with AF can experience a variety of symptoms and problems, of which the most serious and worrisome is stroke from a blood clot that dislodges from the fibrillating atrium and goes to the brain.

Directed by Dr. Stanley Nattel, cardiologist and MHI researcher, in collaboration with Drs Eduard Guasch and Begonia Benito, MHI research fellows, this study entitled “Atrial Fibrillation Promotion by Endurance Exercise” involved laboratory tests using an animal model to simulate intense human exercise. The researchers had rodents run on a treadmill for 1 hour per day over a period of 8 to 16 weeks, which is the equivalent of 5 to 10 years of high-intensity exercise in a human being.

The results were conclusive: practising high-intensity exercise can cause certain subjects to become susceptible to AF. The mechanisms underlying AF were related to the adaptations the heart makes to repeated high-intensity training for prolonged periods, including changes in heart control by the autonomic nervous system, microscopic scarring and heart-chamber enlargement. The underlying molecular mechanisms were analyzed, and included changes in regulatory proteins (called “RGS proteins”) that control autonomic activity and could become a therapeutic target.

Dr. Stanley Nattel believes that even though subsequent human studies must confirm the mechanisms described in these results and determine the impact of other types of highintensity training, these results nevertheless open avenues to better understand, prevent and manage AF in athletes.

Before this study, researchers had only demonstrated that practising an endurance sport such as marathon running, cross-country skiing or cycling increases the risk of AF. The mechanisms of this arrhythmia had not yet been explained. These new findings represent an important advance in this field, because understanding the mechanisms is a key step in improving clinical management options.

About atrial fibrillation

It is estimated that 1 out of 4 people will suffer from atrial fibrillation in their lifetimes. In Canada, nearly 250,000 people have this form of arrhythmia at any given time. Its main symptoms are palpitations, dizziness and shortness of breath. The condition causes the heart to beat very quickly in an irregular and unpredictable way, which can weaken it and promote the formation of blood clots that can lead to stroke or an arterial embolism. Over a decade ago, atrial fibrillation was only treated with medication; however, thermal radiofrequency ablation has been conducted on patients since 1997, and cryoablation has been used since 2011 on patients who do not respond to conventional pharmacotherapy.

About the Montreal Heart Institute:

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For more information or to schedule an interview with Dr. Stanley Nattel:

Livia Dayan Edelman
Phone: 514-315-1974

Marie-Josée Nantel
Communications Officer
Montreal Heart Institute
Phone: 514 376-3330, extension 2641