Cardiotoxic: Too Much Marathon, Triathlon, Heavy Cycling Type of Exercise Might Be Bad for Heart

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Research finds that long, intense exercise can lead to heart abnormalities. Dr. Nesochi Igbokwe from the New York University Langone Medical Center joins CBSN to discuss.

Sports cardiologist André La Gerche, MD, PhD in late February 2016 published a review in the Canadian Journal of Cardiology that questions the effect of intense exercise on heart structure and function. Part of the research considered the presence of arrhythmias — a heartbeat that is irregular, too fast or too slow. Research also considered what might be related to the cause of arrhythmias. The study review also considered the ventricles (heart chambers that pump to the body or lungs) and atria (heart chambers that pump blood to the ventricles).

A review of studies found some of the following concerns affecting endurance athletes compared to non-athletes, including fibrillation and flutter (ineffective heart contractions), tachycardia (rapid heart rate), and bradycardia (slow heart rate), tachyarrhythmias (fast irregular beats), bradyarrhythmias (slow irregular beats), and hypertrophic myopathy (abnormal heart enlargement).

In a study published in the European Heart Journal in 2007, researchers studied 134 former Swiss professional cyclists that were compared to 62 golfers. Ventricular tachycardias tended to occur more often in the cyclists. Paroxysmal (sudden, recurrent attacks) or persistent atrial fibrillation or flutter was also reported more frequently in the cyclists. Sinus Node Disease defined as bradycardia (heart rate less than 40 beats per minute), atrial flutter (six percent among cyclists/non-existent among golfers), pacemaker for bradyarrhythmias (three percent among cyclists/non-existent among golfers), and/or maximal RR interval (time between heartbeats) of greater than 2.5 seconds (six percent among cyclists/non-existent among golfers) was more common in the cyclists.

In a study published in Heart researchers studied 638 patients who underwent ablation for atrial flutter. Sixty-one patients fitted the criteria of ‘lone atrial flutter’ which is atrial flutter without any other underlying cardiac or other disease. Regular athletes who trained greater than three hours per week had lone atrial flutter significantly higher than people in the general population that were observed with lone flutter (50 percent vs 17 percent). The proportion of athletes engaged in long-term endurance sports (participation in cycling, running or swimming for greater than three hours per week) were also found to have significantly higher lone flutter than in the general population (31 percent vs 8 percent). Those flutter patients performing endurance sports also had a larger left atrium than non-sportsmen.

In a study published in European Heart Journal, researchers studied 46 high-level endurance athletes (mean age 31 years) with ventricular arrhythmias. Eighty percent of the athletes were cyclists. Hypertrophic cardiomyopathy or coronary abnormalities were present in less than 5 percent. Right ventricular (RV) arrhythmogenic involvement (based on a combination of multiple criteria) was present in 59 percent of the athletes, and suggestive in another 30 percent. Eighteen athletes developed a major arrhythmic event. Sudden death occurred in nine of the athletes, and all were cyclists. The researchers concluded that endurance sports seems to be related to the development and/or progression of the underlying arrhythmogenic cause.

Other studies were also reviewed, and La Gerche communicated the following emerging controversies related to endurance training and heart health:

Is there a non-linear dose-response relationship with exercise? We know that the correct dose of a drug can be therapeutic, but too much of a drug can be harmful. Is it the same for exercise?

Elite athletes tend to live longer, but is this the effect of exercise or other factors such as the absence of smoking and alcohol consumption?

Is endurance exercise in athletes associated with arrhythmias?

What are the potential mechanisms that predispose athletes to arrhythmias?

Is chronic cardiac remodelling a consequence of repeated bouts of injury?

Why is there disproportionate right ventricular (RV) injury following an acute bout of intense exercise and are there any long-term consequences?

Is the risk of ischemic heart disease increased with intense exercise?


La Gerche A. The Potential Cardiotoxic Effects of Exercise. Can J Cardiol. 2016 Feb 16. pii: S0828-282X(15)01594-9. doi: 10.1016/j.cjca.2015.11.010. [Epub ahead of print]

Baldesberger S1, Bauersfeld U, Candinas R, Seifert B, Zuber M, Ritter M, Jenni R, Oechslin E, Luthi P, Scharf C, Marti B, Attenhofer Jost CH. Sinus node disease and arrhythmias in the long-term follow-up of former professional cyclists. Eur Heart J. 2008 Jan;29(1):71-8. Epub 2007 Dec 7.

Claessen G1, Colyn E, La Gerche A, Koopman P, Alzand B, Garweg C, Willems R, Nuyens D, Heidbuchel H. Long-term endurance sport is a risk factor for development of lone atrial flutter. Heart. 2011 Jun;97(11):918-22. doi: 10.1136/hrt.2010.216150. Epub 2011 Mar 12.

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