Doctors confirm Damar Hamlin experienced commotio cordis—but what is it?

Buffalo Bills safety Damar Hamlin, 24, has been cleared to resume playing football after experiencing cardiac arrest during a January 2 game against the Cincinnati Bengals. Hamlin collapsed shortly after making a tackle. He was administered CPR on the field, which restored his heartbeat.

Hamlin was hospitalized in "critical condition" for several days following the event. But after three days, the Buffalo Bills relayed a positive update from Hamlin's medical team that his condition had already dramatically improved. When the heart stops beating, the brain is deprived of oxygen-rich blood. Hamlin's brain function, however, remains fully intact.

Hamlin's healthcare team later confirmed that he experienced commotio cordis—a condition that occurs when a blunt force to the chest results in a dangerous abnormal heart rhythm that triggers cardiac arrest.

But tackles and hard hits in football are common—and commotio cordis is not. In fact, it’s rare. Fewer than 30 cases of commotio cordis are reported in the United States each year. So, how could this have happened to Hamlin?

It’s a “perfect storm”

Commotio cordis, which is Latin for “agitation of the heart,” results from a perfect storm of events: a force of impact that occurs at a specific location (left side of chest) at a precise time (a specific moment between one heartbeat and the next when the heart is recharging).

As a result, even without a structural abnormality or underlying condition, the blow Hamlin sustained may have triggered ventricular fibrillation (VFib)—the most serious type of abnormal heart rhythm.

VFib occurs when the heart’s lower chambers start to quiver rather than beat normally, which stops blood flow. This could trigger cardiac arrest.

Commotio cordis is usually associated with sports that involve smaller, hard balls, like baseballs, lacrosse balls, or hockey pucks. Children and teens younger than 16 that participate in the sports involved are at higher risk as they have thinner chest walls.

But the condition can occur in other sports, including football or karate, or daily activities in which there is a blow from an elbow, fist, helmet, or other object.

The use of chest wall protectors hasn’t effectively reduced rates of commotio cordis. In fact, 37 percent of cases have occurred among those wearing this protective layer. Researchers point out, however, that increasing training and awareness about the condition, particularly among coaches and staff, can help improve outcomes.

How dangerous is it?

Cardiac arrest is a life-threatening emergency. Immediately administering CPR to those affected is critical to ensure that oxygen-rich blood continues to flow to their brain and other vital organs until more-advanced emergency care can be provided. This is one reason why automatic external defibrillators (AEDs) are becoming increasingly commonplace in public spaces.

Cardiac arrest is often fatal, particularly if resuscitation is delayed. Timely treatment is essential to recovery. Due to the lack of blood flow, those that do survive may be at risk for brain injury or other issues with brain function. The longer a person has limited oxygen or blood flow to the brain, the greater the risk for these consequences.

Following cardiac arrest, survivors will likely be admitted to the hospital to determine what caused their heart to stop beating. For those with an underlying heart disease or arrhythmia, treatment will include restoring the heart’s normal rhythms and preventing future events.