Damar Hamlin may have suffered a one-in-200million heart injury that shut off blood to his brain and triggered a cardiac arrest, doctors say.

The Buffalo Bills safety - a position described as the 'last line of defense' - collapsed during Monday night's game against the Cincinnati Bengals and was administered CPR on the field.

This morning, the Bills revealed Hamlin, 24, had suffered a cardiac arrest and that his heartbeat was restored on the field. He has been taken to hospital, where he remains in a critical condition.

Doctors believe the blow to the star's chest threw his heart's pumping mechanism out of rhythm, disrupting blood flow around his body and shutting off his brain.

But to make matters worse, experts speculate this may have happened during a very vulnerable moment in the heart’s electrical cycle, triggering a condition called 'commotio cordis'. 

This occurs when something makes contact with the chest wall precisely when the heart's lower chambers start to refill with blood. The impact then causes a rapid and disorganized contraction of the heart’s lower chambers, preventing the heart from getting blood to the rest of the body.

The window for this to happen is just 20 milliseconds, making commotio cordis incredibly rare. Just 30 people a year suffer the injury worldwide and only around 200 cases have been reported among Americans. It has previously been noted in young baseball or hockey players who receive a blow from a baseball or hockey puck to the center of their chests.

The critical question, doctors say, is how long Hamlin’s brain went without the oxygen carried to organs by blood flow. 

Brain tissue dies rapidly when deprived of oxygen, which could leave permanent injuries. But there is hope for Hamlin because he was given treatment so quickly. 

About nine in 10 people who have cardiac arrest outside the hospital die, but rapid CPR can improve those odds, doubling or even tripling a person's chance of survival if it is performed in the first few minutes of cardiac arrest.

Medics say that survival rates drop to three percent when resuscitation is delayed beyond three minutes. 

Damar Hamlin remains in a critical condition in hospital but his vitals are 'back to normal' after he suffered a cardiac arrest during the Buffalo Bills' game in Cincinnati last night. 

Dr Deepak Bhatt, a top cardiologist at Mount Sinai Heart in New York City, told DailyMail.com that Damar Hamlin had likely suffered commotio cordis.

'The first thought that occurred to me was that it was something called commotio cordis,' he said.

'It really refers to the classic situation of injury to the chest.

'This is usually in baseball when someone hits a line into the pitcher's chest and that sudden impact can trigger abnormal heart rhythms.

'The only way to come out of that is to deliver an electric shock and perform CPR.'

Asked why the player was able to stand up moments afterwards, he said: 'It could be the case that for a couple of seconds there was enough blood getting to the brain.

'When the heart stops beating we lose consciousness within a matter of seconds. Those may have been the few seconds before the brain stopped getting enough blood.'

Dr Bhatt said it would be 24 to 48 hours before doctors would be able to give an accurate prognosis.

'People may be out cold for that long, and the heart and brain function can take a good 24 to 48 hours to recover,' he said.

In the best-case scenario, he said that patients may be in the hospital for at least a week to ten days. In worse cases, it could be longer.

Asked whether the player could ever return to football, Dr Bhatt did not rule it out but said this was a 'much, much more complex question'.

'Assuming minimal damage to the player, [doctors] would want to do a lot of testing,’ he said.

Commotio cordis is when a sudden blunt impact to the chest causes sudden death without damage to the ribs, sternum or heart and without underlying cardiac problems. 

More than 224 cases have been reported to the US Commotio Cordis Registry since 1995, and the survival rate is 24 per cent.

Commotio Cordis is a primary arrhythmic event that occurs when the energy generated by a blow is confined to a small area of the heart -called the precordium - generally over the left ventricle. 

It profoundly alters the electrical stability of the myocardium, the muscular wall of the heart, which contracts and relaxes in the process of pumping blood.

This results in ventricular fibrillation, the most serious cardiac rhythm disturbance whereby the heart quivers instead of beats, disrupting the functioning of blood pumping.

Sometimes triggered by a heart attack, ventricular fibrillation causes blood pressure to drop, cutting off blood supply to the vital organs such as the brain.  

Commotio cordis events have most happened in sports, and so the phenomenon has become more well known to the sports communities and physicians. 

Commotio cordis primarily affects young men, with the mean age of 15 years. 

It is thought that the stiffening of the chest wall contributes to the decrease in incidence in older individuals, and possibly because not many older people play ball related sports.   

‘This would include some sort of a stress test on a treadmill, with exercise under monitoring circumstances to make sure the same thing does not happen again.

‘It would not be unexpected to also do a stress test pushing them to the limits and just making sure nothing bad happens.’

Other doctors also suggested that the player had suffered from commotio cordis, including Dr Bernard Ashby, a vascular cardiologist in Florida, and Dr Chris Haddock, a primary care physician in Georgia.

But doctors cannot yet rule out an undetected heart condition. The collision may also have caused a bulge in a blood vessel — known as an aneurysm — to burst.

Young males, aged between four and 18 years, are more vulnerable to commotio cordis because their chest walls are more flexible and offer less protection to the heart, doctors say.

This risk drops, however, as people get older as the chest wall hardens and adults take part in sports less often.

Commotio cordis may not cause direct damage to the heart because its tissue has not been torn.

But the disruption in blood supply to organs such as the brain can lead to lasting damage because they have been deprived of oxygen.

Medics treating Hamlin are yet to give a formal diagnosis of his condition. 

Hamlin's collapse has echoes of the injury suffered by Danish soccer player Christian Eriksen at the Euro 2020 competition.

The player suddenly collapsed on the pitch when he went to kick the football and was rushed to hospital, where doctors diagnosed him with a cardiac arrest.

This is when the heart stops beating altogether due to problem with the organ's electrical signals, which prevents blood from pumping around the body.

It is still unclear exactly what happened to Eriksen, but the player was fitted with an Implantable Cardioverter Defibrillator (ICD) device — which can reset the heart after a cardiac arrest.

He eventually had to leave his team Inter Milan, but was able to return to the pitch eight months after the injury — playing first for Brentford and then Manchester United.

Medics emphasized to DailyMail.com that commotio cordis is an extremely rare condition.

Dr Larry Phillips, a cardiologist at NYU Langone, told DailyMail.com 'there is no good registry that keeps track of all the cases,' which makes it difficult to work out exactly how many people are affected.

Dr Ashby, an Associate Professor at Florida International University, said on Twitter: 'The video of Damar Hamlin from a cardiologist's perspective resembled commotio cordis — a phenomenon that occurs when a sudden blunt impact to the chest causes cardiac arrest.

'Timely defibrillation is life saving and prevents anoxic brain injury. I pray an AED was near.'

Dr Haddock, who runs a family practice in Ringgold, Georgia, added: 'As a physician I believe Damar Hamlin was likely suffering from commotio cordis where a blow to the chest at a precise moment in the electrical cycle stops the heart.'

He also said: 'Those trying to tie this to vaccine status to project their unscientific beliefs are terrible, horrible people.'

Dr Anthony Cordillo, an emergency medicine expert in Los Angeles, California, suggested to ABC7 that the player had suffered a ventricular arrhythmia.

He told the broadcaster: 'This is a phenomenon that as the heart is going between its beats, as that heart is depolarizing and then repolarizing, if you have traumatic trauma to the chest at a very specific moment as that heart is repolarizing itself, then you can go into a lethal ventricular arrhythmia. 

'And that looks like what happened because he was able to stand up and at that point his heart started what we call fibrillating, that's that cardiac arrest where he collapsed back down. 

'And they would have recognized at that point the odd pulse.'

He ruled out an injury where the aorta — a major blood vessel — was severed, because people suffering that type of injury do not get back up.

Other doctors have suggested that the violent contact may have caused a bulge in a blood vessel — medically termed an aneurysm — to burst.

It may have combined with a previously undetected heart defect to trigger a life-threatening event, among other possibilities, they added.