The collapse of Buffalo safety Damar Hamlin during Monday night's NFL game between the Bills and Cincinnati Bengals with millions watching at home is bringing cardiac arrest, even among young professional athletes, into a larger focus.
Hamlin, 24, "suffered a cardiac arrest following a hit" in the on-field episode, the Bills said in a tweet. "His heartbeat was restored on the field and he was transferred to the UC Medical Center for further testing and treatment.
He is currently sedated and listed in critical condition," the team added.
ABC News' Chief Medical Correspondent Dr. Jennifer Ashton said Tuesday on "Good Morning America" that what the public knows otherwise about Hamlin's condition comes only from the CPR treatment he was seen receiving on the field.
"There's a lot we don't know. We don’t know what caused his heart to stop on the field," Ashton said. "We know his heart did stop because CPR was performed and that’s only done in the setting of a cardiac arrest when there is no pulse or heartbeat."
Hamlin's young age puts him in the category of "rare" when it comes to experiencing cardiac arrest, according to the National Institutes of Health. But Ashton said his youth is likely to help when it comes to his recovery.
"He’s a 24-year-old, very healthy, elite professional athlete, so that’s obviously in his favor," Ashton said.
Here is more information on cardiac arrest in light of Hamlin's on-field collapse.
What is cardiac arrest?
Cardiac arrest refers to when the heart unexpectedly stops beating, causing the heart to stop pumping blood to the rest of the body and to vital organs such as the brain and lungs, according to the American Heart Association.
Between 70% to 90% of people who experience cardiac arrest die before reaching the hospital, according to the Centers for Disease Control and Prevention.
The NIH reports that as many as 450,000 deaths each year in the U.S. are caused by cardiac arrest.
What causes cardiac arrest?
The term cardiac arrest, as defined by the American Heart Association, indicates there is an electrical malfunction that affects the heart, causing arrhythmia or an irregular heartbeat.
Other causes for cardiac arrest may include vascular or blood vessel injury, a traumatic event such as a blow to the head or a sudden brain injury or neurological injury, scarring of heart tissue, thickened heart muscle, certain heart medications, electrical abnormalities and blood vessel abnormalities.
In rare cases, a direct hit to the chest can also lead to a cardiac arrest.
Who is at risk for cardiac arrest?
Most cardiac arrests occur in men, and the risk for both men and women increases with age, according to the NIH. The condition is considered "rare" in people younger than age 30.
According to the CDC, approximately 2,000 people under 25 die from sudden cardiac arrest each year – many without previously known heart issues.
The risk of cardiac arrest is nearly four times higher in student athletes, Dr. Jonathan Drezner, head of the UW Medical Center for Sports Cardiology in Seattle, told "GMA" last year, citing published research.
Overall, individuals with preexisting heart conditions, such as coronary heart disease or heart valve disease, or those born with heart issues, such as a congenital heart defect, may be at risk for cardiac arrest, according to the NIH.
What are the signs of cardiac arrest?
The NIH notes that someone may be in cardiac arrest if they pass out or collapse and lose consciousness, similar to what happened to Hamlin midfield.
Other symptoms of cardiac arrest include someone gasping for air, someone who stops breathing or someone who does not have a pulse.
What is the treatment for cardiac arrest?
Cardiac arrest is considered an emergency and those who experience cardiac arrest need medical attention immediately. Dial 911 if you suspect someone near you is in cardiac arrest.
Two immediate treatments for someone in cardiac arrest include cardiopulmonary resuscitation, or CPR, and rapid defibrillation.
Using an automated external defibrillator, or AED, can assist with resuscitation, although Ashton noted on "GMA" that not every cardiac arrest event can benefit as someone needs to have a "shockable rhythm."
Ashton noted that intubation is also normal when it comes to cardiac arrest treatment.
"When there's any question of brain injury, and certainly after a cardiac arrest, you want to make sure that those vital signs and ... anyone's ability to keep their blood oxygenated is protected," she said. "And the best way to do that is with intubation and sedation."
"I think that's the take home [message] here. Learn CPR," Ashton said. "If you see a defibrillator there, it will talk you through the entire process."