Is Running Breaking My Heart?

Many of us have heard about deaths in marathons and other endurance events. Although there are a number of possible causes surrounding fatality in long distance running, as I have written about this previously, the major culprit seems to be strongly related to the heart. A study recently proposed a name – Phidippides cardiomyopathy – to describe the cause of sudden death in endurance sports, as Phidippides‘ death was the first report of a long-distance runner.

Phidippides cardiomyopathy is an umbrella term for multiple cardiac abnormalities that together lead to fatality in prolonged physical exertion. The pathogenesis of it is illustrated by the follow diagram:

Phidippides Cardiomyophathy (from http://onlinelibrary.wiley.com)

The real surprise I find in this study is that sudden deaths in marathon running we hear about may not be sudden at all. In fact, they are caused by a series of related conditions that may be part of any training regimen. Below I outlined some interesting findings that are relevant to the development of Phidippides cardiomyopathy:

• Despite different training regimens and fitness levels, in all cases the heart faces increased pressure and volume overload and responds by increasing left ventricular chamber size, thickness, and mass.
• Running a marathon initiates multiple events within one’s body for cardiac injury, including increased release of catecholamines and resultant coronary vasoconstriction, increased heart rate leading to decreased diastolic filling time of the coronary arteries, increased demand for oxygen, changes in free fatty acid metabolism, lactic acidosis, and metabolic derangements.
• During the event, in susceptible individuals the heart is unable to keep up with the demands of marathon running and increasing right heart preload and afterload, and begins to dilate and stretch in response to these hemodynamic changes.
• With this repetitive stretch of the chambers and restoration of the chamber geometry, we believe there are individuals prone to developing chronic structural changes, including chamber dilation and myocardial fibrosis, as a response to the repetitive volume overload and dynamic strain of the heart.

In essence, endurance sports require a sustained cardiac demand, which results in scarring and stratifying (thickening) in the heart to cause cardiac arrhythmia or, in extreme cases, cardiac arrest. This isn’t entirely breaking news to the medical community. But to the less informed general public, it is worth noting that marathon runners don’t just drop to their death for no reason – albeit the complex nature and the exact cause of death aren’t always apparent.

However, despite all the negativity we might garner towards possible health threats encompassing endurance sports, the benefits still outshine the risks by a long shot. As I have pointed out in my previous article (and cited again by this study), the risk of dying suddenly while participating in a marathon is 0.8 per 100,000, or 1 per 125,000. To put that in perspective, the odds of being struck by lightning in your lifetime (est. 80 years) are 1 per 10,000; and the odds of fatality in auto accidents are 1 per 9083. That is to say, although marathon running could kill you – like everything else you do has the potential – it isn’t a particularly high-risk activity that you should avoid altogether.

Author Bio: Kevin Lu is an engineer, currently working in the field of orthopedic devices. He received his B.S. and M.S. in biomedical engineering from New Jersey Institute of Technology. Science, technology, and running are Kevin’s passions. In his spare time, Kevin trains for and participates in races of various distances. In addition to Beyond Distance, Kevin also writes for iRunnerBlog as a contributing tech columnist. Find out more about Kevin here and follow him on Twitter.

Related posts:

1. The Death March Known as Marathon: A Myth Debunked