Too early to say what caused Hamlin's cardiac arrest - medical experts

After making a routine tackle in the first quarter, he rose to his feet, then collapsed on his back as his body went limp. Hamlin received CPR on the field as players from both teams and millions of television viewers watched in horror.

The Bills on Wednesday said Hamlin had shown "signs of improvement" but remained in critical condition at University of Cincinnati Medical Center.

With scarce information to go on, devoted fans scoured television news and online forums for any clue as to what may have prompted this unprecedented incident in the United States' most popular pro sport.

Medical professionals not directly involved in the case have floated possible causes for what caused Hamlin's heart to stop, including commotio cordis, a very rare occurrence in which blunt force trauma to the chest can cause an arrhythmia.

But the NFL's chief medical officer, Allen Sills, told reporters on Wednesday that there was "still a lot of investigation that needs to happen" to understand Hamlin's case.

"Many people have discussed this condition commotio cordis, and it certainly is possible," Sills said. "But I think what's more important is, regardless of the cause, the key of any type of sudden cardiac event is the rapid response of trained personnel."

He added that the incident showed a need for "every sport, at every level" to prepare for sudden cardiac events.

RECKLESS SPECULATION

Meagan Wasfy, a sports cardiologist at Massachusetts General Hospital, told Reuters that speculating about what caused the cardiac arrest was not helpful and "could have more negative consequences than positive ones."

Wasfy was one of seven members of the American College of Cardiology who put out a statement on Wednesday warning medical professionals and others against making armchair diagnoses.

"Reckless speculation on social media is a source of disinformation and could lead to other unintended negative consequences," the physicians said. "We would encourage all to avoid this practice and allow the medical evaluation to proceed by those in charge."

Wasfy said quickly treating someone experiencing cardiac arrest was "absolutely crucial."

"We know that the time between the sudden cardiac arrest and initiation of CPR and defibrillation is what helps determine the outcomes, first of all whether the life is saved or not in the moment and then how the individual does after," she said.

It is far too soon to say when or whether Hamlin, in his second year in the league, would play again, though he is not the first athlete to suffer cardiac arrest during a game.

National Hockey League defenseman Chris Pronger, who collected two Olympic gold medals for Canada, collapsed and suffered a cardiac arrest when a slap shot hit him in the chest at the 1998 Stanley Cup playoffs.

He was able to continue his career, playing for more than a decade after recovering from the incident. On Tuesday, he tweeted his well wishes for Hamlin.

Former Bolton Wanderers midfielder Fabrice Muamba was retired at 24 after collapsing on the pitch in an FA Cup match in 2012 and being technically "dead" for 78 minutes.

He was saved in part by the intervention of an off-duty heart specialist in the crowd who used a defibrillator to revive Muamba's heart, leading to a campaign to have more of the emergency devices at sports clubs and public places.

Christian Eriksen returned to the Premier League in January last year after his cardiac arrest on the pitch at the European Championship in 2021.

The Denmark international has been fitted with a heart-starting device known as an Implantable Cardioverter Defibrillator (ICD).