What to Know About Damar Hamlin’s Heart Event, Commotio Cordis

6 minute read

Nobody watching the Jan. 2, 2023 National Football League game between the Buffalo Bills and Cincinnati Bengals will forget the searing sight of Bills safety Damar Hamlin collapsing to the turf after an otherwise unremarkable tackle late in the game’s first quarter led to his cardiac arrest. Emergency CPR and the use of a defibrillator saved his life, but the now 25-year-old spent a week in intensive care at the University of Cincinnati Medical Center (UCMC), where he was rushed straight from the field, as doctors fought to restore him to health and determine the cause of his near-death experience. He was later transferred to a Buffalo-area hospital where he spent several days before being released, having made a full recovery.

On Apr. 18, at a press conference at the Bills’ training facility in Orchard Park, N.Y., Hamlin announced that after months of consultation with team physicians and three outside cardiac specialists, he had been cleared to return to play next season. “My heart is still in the game,” he said. “I just want to show people that fear is a choice, that you can keep going in something without having the answers and without knowing what’s at the end of the tunnel.”

Added Bills coach Sean McDermott, “We’re super excited for Damar. He’s moving forward one step at a time here. He’s been cleared from a physical standpoint, and we’ll provide all the mental help we can from a mind, body and spirit standpoint.”

One mystery that was at last resolved at the press conference was the cause of Hamlin’s sudden heart stoppage: an exceedingly rare event known as commotio cordis.

What is commotio cordis?

Commotio cordis involves a sudden blow to the chest at a precise moment in the heart’s rhythm when the cardiac muscle has completed a contraction and its electrical signals are undergoing what cardiologists call repolarization.

Think of the electrical system in the heart as going down a sliding board, explains Dr. Lawrence Phillips, medical director of outpatient cardiology at NYU Langone Health. “Each muscle cell is electrically charged, then that charge gets released and it has to reset. That’s repolarization.”

Anyone can suffer a case of commotio cordis, regardless of heart health. And doing so requires colossally bad luck: repolarization takes place in just 40 milliseconds or so. Still, there are 30 or so commotio cordis cases in the U.S. each year, often in boys and young men playing sports in which a hard object like a baseball or lacrosse ball strikes the chest.

How could an elite athlete have this heart incident?

Commotio cordis occurs in people with no underlying cardiac conditions. Hamlin had no known cardiac risk factors—any of which would have turned up in the extensive cardiac screening NFL players go through.

That scrutiny begins at the NFL’s scouting combine, an annual event at which potential draftees are put through their athletic paces and undergo medical tests leading up to draft day. “Professional athletes in the U.S. are probably among the most-screened from a cardiac perspective of anybody in the world,” says Dr. William Roberts, past president of the American College of Sports Medicine and director of family medicine and community health at the University of Minnesota. “Teams don’t want to draft somebody who’s at high risk. So at the combine, people get funneled through and have a pretty intensive cardiac workup and that includes EKGs, stress testing, echocardiogram, and in some circumstances, they may do more advanced imaging like a CT scan or arteriograms.”

Cardiac care does not stop there. The latest collective bargaining agreement between the NFL Players Association and the team owners, ratified in 2020 and in force until 2030, includes heart screening as a mandatory part of each player’s annual preseason physical. An appendix of the agreement goes further, specifying that, when warranted, further tests shall be performed, including stress testing and echocardiograms. None of these tests would detect commotio cordis, since it is not caused by an underlying condition..

All of that always made commotio cordis the likeliest cause of Hamlin’s heart stoppage, especially since footage of the tackle that led to his collapse appeared to show the shoulder pad of Bengals receiver Tee Higgins striking Hamlin in the chest. That collision was routine; the result wasn’t.

How rare is this in professional sports?

Hamlin was actually relatively old to suffer a case of commotio cordis. The mean age for incidents is 15, with very few cases occurring for the first time past age 20, according to the American Heart Association (AHA). This is thought to be due to a stiffening and thickening of the chest wall as children mature into adults, which helps protect against commotio cordis.

Another reason we don’t see a lot of commotio cordis episodes in professional football is the uniform. The shoulder pads Hamlin was wearing as a standard part of his equipment ought to have provided additional protection to the sternum and overall chest area. Still, the violence of the hit—also a standard part of an NFL game—was apparently enough to overcome that protection. “Interventions such as protective padding are important for decreasing the risk, but does not reduce the risk to zero,” says Phillips.

“It’s indeed an unusual incident,” says Dr. Manesh Patel, chief of the division of cardiology at Duke University school of medicine. “But it does look like the tackle was responsible. If you have enough people playing football, this kind of thing could happen.”

If Hamlin was particularly unfortunate to have suffered commotio cordis despite all of the protection to his heart, he was very fortunate to have suffered it where he did—in the midst of highly skilled trainers and team doctors, adept at providing CPR and equipped with electrical defibrillators able to shock a stopped heart back into rhythm.

“Hopefully, this is going to raise awareness on making sure people know how to do CPR and how to use a defibrillator,” says Patel. “Because it’s certainly very sad that [cardiac arrest] happens all the time in our shopping malls and our airports and our streets.” In those cases, trained bystanders with the right equipment are rarely available. Only about one in 10 people survive a cardiac arrest that occurs outside of a hospital, according to the AHA.

Hamlin’s decision to return to the field may seem risky, but that is not necessarily the case. Having one incident of commotio cordis does not necessarily predispose a person to suffering another, since the incident is not caused by underlying structural abnormalities in the heart. “Commotio cordis is a rare event and is related to trauma to the chest at a very specific moment in the heart’s cycle,” says Phillips. “A person should not be at an increased risk of it occurring again.”

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Write to Jeffrey Kluger at jeffrey.kluger@time.com