Sudden Cardiac Death and the Endurance Athlete

By Patrick McCrann
Patrick is head coach and founder of Endurance Nation.

With the recent passing of our friend Chris Gleason, many here at Endurance Nation have been wondering whether we should be doing more to ensure that our participation in our beloved hobby is a safe, smart idea. To that end, a few of the MD’s in the haus have offered up a summary of the risks and recommendations specifically for endurance athletes.

Risks

According to a literature review, the heart responds in a variety of ways to exercise.

1. Short Term Response

a. “Exercise induced cardiac fatigue” which is a decrease in pumping and resting functions of the heart associated with ultra-endurance events

i. Decrease in pumping function is variable and seems to be associated with duration of event and training status.

ii. Not all studies report a decrease in pumping function.

iii. Decreased resting function is more consistent and repeatable.

iv. Exercise induced cardiac fatigue seems to be more prevalent in the right ventricle (lower chamber) and may lead to remolding (changes within the heart muscle) in some athletes that might predispose them to the development of ventricular arrhythmias.

v. The decrease in pumping and resting function appear to be transient and resolve within 48 hours but may persist up to 1-4 weeks.

b. Elevations in troponin (c-Tn)

i. Overall rate of c-TnT elevation in endurance events is 47%. However, single blood draws post event may underestimate the overall number of post event elevations in c-TnT.

ii. Most studies have shown no correlation between elevations in c-TnT with altered function in the left ventricle but many have linked c-TnT elevation with dysfunction of the right ventricle.

iii. The cause of c-TnT elevation is also unknown but leakage of unbound protein across the cell membranes is suspected. Myocardial damage (ischechemic injury) and death of the heart muscle cells is the other possibility.

iv. Bottom line it is unknown if the elevation results from reversible or irreversible damage to the heart muscle cells

2. Long Term Effects

a. Change to heart structure and function (these changes are expected and are not considered to raise health concerns)

i. Eccentric hypertrophy is an adaptive response to endurance training

1. This is dilation of the cardiac chamber to improve stroke volume or the amount of blood the heart pumps every time it beats.

2. Finding is well documented and balanced between the right and left ventricles.

ii. Changes result in an increased maximal stroke volume with exercise which raises cardiac output during exercise

b. Other changes

i. Studies overall show that endurance exercise decreases cardiovascular risk. However, a 1995 study hints that a high dose of physical activity (>4000 kcal/week) may lead to a small increase in risk.

ii. Greater incidence of atrial fibrillation/atrial flutter in endurance athletes.

iii. Two studies have shown an increase in asymptomatic ventricular arrhythmias in endurance athletes and another has shown 25% of those with ventricular arrhythmia’s have inducible non-sustained ventricular tachycardia. The studies differ on the impact of decreasing training volume of stopping training on the development of the arrhythmia.

iv. Studies have also suggested that there may be a link between the right ventricular changes mentioned above and the development of ventricular arrhythmias that is termed “Exercise Induced Right Ventricular Cardiomyopathy”. This process is not seen in all study participants and I stress that this is not a proven entity.

v. Some endurance athletes have fibrosis (scarring) of their heart muscle noted on MRI that is not consistent with coronary artery disease. This fibrosis can lead to the development of ventricular arrhythmia’s but no link or risk information is available on athletes with scarring of there heart.

In Summary

a. Overall endurance training leads to healthy changes to the heart that promotes long life with a decreased risk of death from all causes.

b. There is a slight increase in the risk of death during and for ~ 24 hours following an endurance event. That risk is about 1:50,000 at the highest but may actually be lower.

c. For a small subset of endurance athletes there may be an increased risk for the development of ventricular arrhythmias that may increase the risk of sudden death whether engaged in activity or not. At this time, there is no screening method known to identify the population at risk for arrhythmia development, though evaluation with a Holter and/or contrast MRI may identify athletes with a potential increased risk.

d. Bottom-line the risk seems to be very small that exercise induces changes to the heart could lead to sudden death. This does not take into account the presence of coronary artery disease, or a congenital/genetic cardiac disease that might predispose to sudden death with physical exertion.

Recommendations

1. If you feel like you want to get your heart checked out, do it. But don’t forget that heart disease is not something that happens due to a single cause. It is typically a combination of different risk factors that interact with your individual genetic makeup to create and build atherosclerotic placques in your body’s arteries. These things take years to build to significant levels which is why older people have more heart disease, but why youth does not make you immune. Because it is so uncommon in people under 40 (without family history of heart attacks in 40ish family members), don’t be surprised if you get a history, physical, EKG, and a clean bill of health. For people over 40 with few, if any, risk factors, your check up may not be much different. Of course, if you have any symptoms like chest pain, shortness of breath, progressive fatigue, etc., your risk is higher and your workup will likely be more extensive. But if you are having symptoms, you are stupid if you are ironman training without medical clearance. Assuming Chris was never evaluated for heart disease, chances are that if he truly had few, or no, risk factors, he would have received a routine workup that probably would have been negative. So would him walking into his doctor’s office 3 months ago saved his life? No one will ever know, but it probably wouldn’t have. Then we would all be sitting here having the conversation about what the point of having heart check-ups was if they didn’t prevent sudden cardiac death.

2. Being physically fit, whatever that means to you, is always healthier for your heart than a sedentary lifestyle.

3. It makes no sense whatsoever that it’s OK for your heart to race for 10-16 hours, but not OK to sprint the last 200 yards to the finish.

4. While it may often be true that many people die near the end of different types of races, my understanding is that the majority of people who die in triathlon do so during the swim……of heart-related causes.

5. Everyone needs to assess their own perceived risk of participating in triathlon and weigh their own personal consequences in determining if they want to participate. I certainly do respect the person that quits to eliminate the risk of leaving behind a spouse and kids for what they consider a hobby. But don’t forget that this is extremely rare. Trying to explain statistics to Chris’ wife will mean nothing because as far as they are concerned it was 100% in him. But the statistics are real. Whether it’s 1 in 50,000 or 1 in 200,000, it’s still extremely rare. And while I don’t know her, I would bet that she would encourage people to get checked, to be careful, but not to stop racing because of Chris. I never knew the guy, but reading all the stuff from people who did, I would doubt that he would discourage anyone from doing it either.

Folks, at the end of it all, the one thing we can say with certainty is this.

If you have concerns or experience any unexplained chest or upper body ( back, arm, jaw or stomach) pain, palpitation, unusually high heart rate, or feel faint or light headed during or after exercise stop the activity and please consult with your physician and/or cardiologist for further guidance as soon as possible.

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About swimbikerun1
Devoted Father, Husband and Employee.Endurance sports fanatic (running,cycling,swimming).Triathlon athlete and coach.If only days had more than 24 hours.

2 Responses to Sudden Cardiac Death and the Endurance Athlete

  1. bgddyjim says:

    An anomaly showed up on an EKG at my 40 year check up, doc brought me in for an ultra sound a couple of weeks later (never did stop running either) and it turned out to be nothing… Either way, I run a little bit easier after having been checked out. I also called him to make sure I was cool to start in with the triathlon training just to make sure.

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