Sudden Cardiac Arrest on National TV: An Explainer and What it Means for Triathletes

Last night much of the American television viewing public was taking in Monday Night Football to see a big game with playoff implications. The Buffalo Bills were visiting the Cincinnati Bengals when, after a fairly routine play, 24-year-old safety Damar Hamlin unexpectedly collapsed to the ground. The game announcers initially thought that Hamlin had simply been injured on the play, but very quickly it became apparent that something far more serious was going on.

Hamlin, it turns out, was in cardiac arrest. Once the training staff realized what was happening began to administer cardiopulmonary resuscitation (CPR). He was resuscitated again upon arriving at the University of Cincinnati Medical Center’s intensive care unit, where he remains in critical condition.

At this point, I think that is helpful to dispel confusion about some common terms that are frequently thrown around the media in these situations. Doing so now will allow for a much clearer description of what happened to this player, and help unpack whether this incident should be a cause for concern for endurance athletes who are all too familiar with the specter of sudden cardiac death (SCD) in our own sports.

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Heart Attack vs. Cardiac Arrest

The first thing that needs to be made clear is the difference between a heart attack and cardiac arrest. A heart attack occurs when there is a blockage in one of the arteries that carries blood to the tissue of the heart. The heart muscle is exquisitely sensitive to dips in oxygen-rich blood flow, so if a coronary artery becomes obstructed, the cells that are being fed by that artery do not receive oxygen—they become injured and quickly die. In medical terminology this is called a myocardial infarction. In the spring of 2021, professional triathlete Tim O’Donnell experienced a heart attack while competing in a race. Fortunately, he did not suffer cardiac arrest.

Cardiac arrest, on the other hand, occurs when the heart ceases pumping blood forward to the brain and the rest of the body. There are many causes for cardiac arrest and one of the more common ones is a heart attack. However, while cardiac arrest is frequently caused by heart attacks, only a small percentage of heart attacks cause cardiac arrest. During cardiac arrest, the heart can come to a standstill in which case all electrical activity ceases. This is known as asystole, and is typically represented in popular culture or on TV as a “flat line” on a cardiac monitor. More commonly, the initial electrical rhythm in cardiac arrest is either ventricular tachycardia—in which the ventricles of the heart are being stimulated to beat so fast that they do not have an adequate amount of time to fill with blood and therefor the pumping action does not result in any blood flow—or, ventricular fibrillation, in which the electrical activity in the heart is chaotic and disorganized and the muscle just quivers and no pumping occurs at all.

Whatever the underlying rhythm, during cardiac arrest there is no blood flow to the brain and it is imperative that two things happen as quickly as possible: CPR must be initiated and if indicated, cardiac defibrillation must be done. CPR is the application of chest compressions to the victim and is how some forward blood flow can be re-established until such time as the heart’s normal electrical activity can be restarted. Cardiac defibrillation is the application of an electrical shock to the heart. In the setting of either ventricular tachycardia or ventricular fibrillation, this shock works to depolarize the entire heart muscle and resets the electrical system. That brief moment of pause is then hopefully when the heart’s normal pace making activity can kick in and a normal rhythm can resume. Defibrillation does not work for asystole, so all those times you see characters on television or movies attempting to shock a patient who has a flat line shown on a cardiac monitor, that is just not going to work!

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Understanding Commito Cordis

Returning to the case of Damar Hamlin, when he first collapsed on the field, the training and medical staff quickly recognized that he was in cardiac arrest and began administering CPR. Almost certainly an automatic external defibrillator was called for, applied and used to obtain the restoration of a normal rhythm and with that, there was a return of spontaneous circulation (ROSC).

When a victim of cardiac arrest has ROSC one of two things happen: After blood flow to the brain is restored, the patient may regain consciousness or they will not. The former situation is the best scenario, as it indicates that the brain was deprived of blood flow for a very brief period and the patient will be expected to recover quite well. But even in the latter case, when the patient does not immediately wake up, all is not lost. In those cases, patients are sedated and have their body temperature lowered by several degrees for twenty-four hours. This has been shown to protect the injured brain and allow for significant recovery in function. For a young athlete like Hamlin, who had CPR rendered quite quickly and ROSC soon after that, the likelihood of his having a full recovery remains quite high. The next few days will be very telling in this regard.

So why did this happen to this otherwise very well and for all appearances healthy athlete? I wrote earlier that cardiac arrest can come about for many different reasons. Heart attack is one such reason but is not likely in a 24-year-old with no known previous cardiac disease (though in October 1971, 28-year-old Detroit Lions player Chuck Hughes collapsed and died on the field during a game from cardiac arrest secondary to a heart attack, this is still exceedingly unusual). Rather the most likely cause for Hamlin’s cardiac arrest is a rare event called commotio cordis or cardiac concussion (CC).

CC has been recognized for many decades and is a known cause of cardiac arrest in young, healthy athletes that arises after seemingly innocuous blunt injury to the chest wall directly over the heart. The definite incidence of CC remains unknown but the most common sports in which it has been reported to occur include baseball, ice hockey, lacrosse, softball, and football. These are all sports in which players receive a blow to the chest (similar to what Hamlin received during the game) and then suddenly collapse in cardiac arrest.

Along with the nature and location of the injury, the timing of the injury is critical. Experiments have shown that the blow has to occur during a very brief 15-millisecond window of the electrical cycle of the heartbeat in order for electrical disruption to occur and ventricular fibrillation to be initiated as a result. In all known cases of CC, post-mortem examination has never revealed any structural causes for the dysrhythmia nor any coronary artery disease, though there is a theory that genetically inherited issues related to sodium channels of the heart cells might be implicated, this remains speculative.

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Are endurance athletes at risk?

As I mentioned earlier, SCD is a very real issue for endurance athletes, and Damar Hamlin’s incident rightly heightens awareness once again on the potential tragic consequences of training for and racing in our sport or any other where we put our hearts under stress. I have spoken on my podcast on more than one occasion about this subject as well, but the situation that Hamlin experienced last night needs to be clearly distinguished from those which triathletes and other endurance athletes face.

CC is a very specific and rare event that is specifically related to a blunt force trauma to the chest directly overlying the heart. Triathletes, on the other hand (as well as other endurance athletes who develop dysrhythmias or SCD) typically experience heart conditions related to structural problems from years of high-volume and high-intensity training or because of the development over time of atherosclerotic coronary artery disease that in many cases is silent.

There is unfortunately little in the way that can be done to screen athletes for these problems because as horrifying as SCD is, it remains a fortunately rare event and no screening has been shown to effectively and reliably identify those who are at risk. Instead, it remains the athletes’ responsibility especially as they age to be diligent about paying attention to their body and being attentive to any signs or symptoms that could be attributable to an underlying cause.

Palpitations, shortness of breath at lower than expected amounts of exertion or any kind of chest pain with exertion should be signals to an athlete to cease training and seek immediate medical evaluation before returning to training. While commotio cordis is simply not likely to be an issue for triathletes, SCD remains a very real—if thankfully rare—event. While the cause may be different, an outcome similar to what Damar Hamlin experienced is still a possibility, one that we would all like to avoid at all costs.

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Dr. Jeffrey Sankoff is a Denver, Colorado-based emergency room physician, who produces the TriDoc Podcast. Dr. Sankoff is also a triathlete himself and a USAT- and Ironman-certified coach.