The concern is whether, during those long minutes before Mr. Hamlin’s heart rhythm returned, when his heart wasn’t pumping normally, a lack of blood damaged his brain, heart experts said. If a cardiac arrest patient doesn’t recover right away, doctors will often induce a coma to give the brain a chance to rest, said Dr. Mack. Sometimes doctors also cool the brain to slow its metabolism while it recovers, using cooling blankets — which have coils that circulate chilled water — and headgear.
“The more concerns there are about brain injury, the more aggressive doctors are about sedation and hypothermia,” added Dr. Mack to it. If Mr. Hamlin remains unconscious 72 to 96 hours after his cardiac arrest, “there is a real concern,” said Dr. Mack.
Other athletes, such as marathon runners, have collapsed and even died when their hearts stopped due to heart attacks or arrhythmias caused by underlying heart defects. Some examples, said Dr. Mack, are hypertrophic cardiomyopathy, where the heart walls are thickened, or long QT syndrome, which is a heart signaling disorder.
But while they can’t rule them out, heart experts doubt Mr. Hamlin has these conditions. Dr. Rajat Deo, an arrhythmia specialist at the Perelman School of Medicine at the University of Pennsylvania, said the NFL has extensively tested its athletes and is expected to find such problems.
Cardiac arrests differ from heart attacks, which are caused when an artery supplying the heart with blood becomes blocked, depriving the organ of blood. That can cause an arrhythmia or even sudden death.
“Could it be due to a blockage?” asked Dr. Brahmajee Nallamothu, a professor of internal medicine and cardiology at the University of Michigan. “I think so, but probably unlikely in a young guy.”
Ken Belson reporting contributed.