Bronny James, LeBron James's 18-year-old son, suffered cardiac arrest. Here's what you need to know about the condition.

LeBron James’s son Bronny James was working out Monday when he suddenly suffered cardiac arrest. The University of Southern California basketball player, 18, was taken to the hospital immediately and is now in stable condition and no longer in the ICU, per a statement from the James family.

Bronny James is one of more than 350,000 people who will experience cardiac arrest this year outside of a hospital, according to data from the American Heart Association. Nearly 90% of the episodes are fatal. But what does it mean to experience cardiac arrest, and why does it happen — especially in young people? Here’s what we know.

What is cardiac arrest? Is a heart attack the same thing?

According to cardiologist Dr. Siyab Panhwar, “cardiac arrest refers to when the heart suddenly stops beating and comes to a standstill. This is often accompanied by loss of breathing and loss of consciousness as well as the brain no longer gets oxygen.”

Though the terms “heart attack” and “cardiac arrest” may often be used interchangeably, they are not the same thing from a medical perspective.

“Cardiac arrest refers to sudden standstill of the heart and can be caused by many things,” Panhwar notes. “A heart attack refers to when there is a sudden blockage that develops in the arteries of the heart (coronary arteries) that causes an acute lack of blood flow to the heart muscle, resulting in symptoms such as severe chest pain, shortness of breath, dizziness and so on. The heart can continue beating. If the heart attack is severe enough, it can lead to cardiac arrest.”

What causes cardiac arrest?

There are many potential causes of cardiac arrest. According to the Mayo Clinic, the most common cause is irregular heart rhythm called ventricular fibrillation, which means “rapid, erratic heart signals cause the lower heart chambers to quiver uselessly instead of pumping blood.”

Different heart conditions, such as coronary artery disease, cardiomyopathy (enlarged heart), heart valve disease, long QT syndrome and Brugada syndrome, and heart problems that present at birth, such as a congenital heart defect, can all lead to cardiac arrest later in life.

Panhwar adds that chronic medical conditions, such as obesity, diabetes and chronic kidney disease can increase a person’s risk as well, as can the use of drugs and alcohol.

Why does cardiac arrest occur in seemingly healthy young people?

“While it is always alarming when it happens, sudden cardiac arrest in young people is not that uncommon,” Panhwar says, noting that generally the rates of sudden cardiac arrest range from 1 in 100,000 people to 5 in 100,000 people in young people.

The most common causes in young athletes include:

• Structural abnormalities in the heart such as hypertrophic cardiomyopathy, an inherited condition.

• Arrhythmogenic right ventricular cardiomyopathy.

• Heart valve disease.

• Anomalous coronary arteries.

In young athletes, Panhwar notes that a common cause of cardiac arrest is hypertrophic cardiomyopathy (abnormally thickened heart muscle), in which intense physical activity can cause cardiac arrest.

One other thing that can potentially cause cardiac arrest is myocarditis, but according to Panhwar, myocarditis has to be acute and severe enough to trigger cardiac arrest. Most people will usually have at least a few days of symptoms of chest pain or shortness of breath. The trigger for myocarditis — which, most of the time, is a viral infection — has to happen within a few days of the arrest as well.

Dr. Matthew Wheeler, a heart failure cardiologist at Stanford Health Care, notes that even for people with one of these preexisting conditions, there’s a “low to extremely low” risk of experiencing cardiac arrest on a day-to-day basis. It can be triggered by a number of things, but it can also come “out of the blue,” without an obvious trigger.

“Very high-intensity activities, particularly burst-type activity where you’re stopping and starting again at full speed, can be a trigger,” he explains. “There is some evidence that young males doing high-intensity burst-type activities have a slightly higher risk than the general population, and if you have one of these preexisting conditions, then the risk of cardiac arrest can be much higher.”

How does COVID and the COVID vaccine come into play here?

First, it’s important to note that there is no evidence linking either COVID-19 or the COVID vaccine to what happened to Bronny James. It is still too early to know what caused the teenager’s health emergency.

So why are people talking about it? It’s likely because there has already been a lot of chatter about the connection between heart issues and COVID.

Dr. Susan Cheng, director of the Institute for Research on Healthy Aging in the Department of Cardiology at the Smidt Heart Institute, previously spoke to Today about how there has been a 30% increase in heart attack deaths among people between the ages of 25 and 44.

“There are a lot of things that COVID can do to the cardiovascular system,” she explained in her interview with Today. “It appears to be able to increase the stickiness of the blood and increase ... the likelihood of blood clot formation. It seems to stir up inflammation in the blood vessels. It seems to also cause in some people an overwhelming stress — whether it’s related directly to the infection or situations around the infection — that can also cause a spike in blood pressure.”

One possible explanation is that COVID is linked to myocarditis. Studies have confirmed that the overall myocarditis risk is higher after a COVID infection and that people recover from myocarditis better than from infection, and according to the Centers for Disease Control and Prevention (CDC), “the known risks of COVID-19 illness and its related, possibly severe complications, such as long-term health problems, hospitalization, and even death, far outweigh the potential risks of having a rare adverse reaction to vaccination, including the possible risk of myocarditis or pericarditis.”

The CDC also notes that cases of myocarditis and pericarditis have occurred most frequently in adolescent and young adult males within seven days after receiving the second dose of an mRNA COVID-19 vaccine. Cases have also been observed after dose one and booster doses.

“There is a lot of misinformation that myocarditis from a COVID vaccine that was administered months or even years prior can cause sudden cardiac arrest — there is absolutely no evidence or scientific reason for this to be true,” Panhwar explains.

He adds, "We have seen from two and a half years of research now that COVID vaccine myocarditis, while it can happen, is overall less likely than myocarditis from COVID infection. Additionally, vaccine myocarditis is generally much, MUCH milder, short lived, and treated easily, compared with myocarditis from COVID infection which can lead to severe heart damage and death, among other complications."