Buffalo Bills defensive back Damar Hamlin collapsed last night after making a tackle during the Monday night football game. He is said to have suffered a cardiac arrest and is hospitalized in critical condition. All I have to go on are the press reports and the video of the event. Look at it below and pause it at the 10 second mark. Observe where #85’s shoulder is in relation Hamlin’s chest. It’s directly over his heart .

I have no information about this event save what was reported in the media. But a cardiac arrest after a blow to the chest strongly suggests a condition known as commotio cordis. This event is an often lethal disruption of heart rhythm that occurs as a result of a blow to the area directly over the heart (the precordial region) at a critical time during the cycle of a heart beat, producing what is termed an R-on-T phenomenon that leads to the condition. It is a form of ventricular fibrillation  not mechanical damage to the heart muscle.

If the blow to the chest occurs at the exact point in the heart’s electrical cycle when it is vulnerable ventricular fibrillation may occur. See electrocardiogram below

This event is very rare; it is most common in young teens. The average age is 15. This is a potentially lethal event. CPR and prompt electrical shock to abort the ventricular fibrillation within 3 minutes of the event is needed to successfully resuscitate the patient. I don’t know if a defibrillator is part of the medical gear kept on the sidelines during an NFL game. Given the extreme rarity of commotio cordis in adult athletes, I suspect a defibrillator was not present at yesterday’s game.

The illustrations above are from the Wikipedia article on this subject.