What causes cardiac arrest in young, seemingly healthy athletes like Bronny James? Dr. Celine Gounder explains

Bronny James, the son of basketball legend LeBron James, suffered cardiac arrest during practice with his college team on Monday — raising questions about how it's possible for a seemingly healthy 18-year-old to lose heart function.

Dr. Celine Gounder, a CBS News medical contributor and editor-at-large for Public Health at KFF, said that several scenarios could have played out that resulted in James suffering from the life-threatening condition.

One possibility is hypertrophic cardiomyopathy, a thickening of the heart muscle that is often observed in elite athletes and sometimes in individuals with certain genetic predispositions, Gounder said. Another scenario is commotio cordis, in which a sudden blow to the chest disrupts the cardiac rhythm, leading to cardiac arrest. The third possibility is a genetic arrhythmia, an abnormal heart rhythm, she said. 

While cardiac arrest in athletes may not always make headlines, it occurs more often than many realize, Gounder said.

"It really hits the headlines when it's somebody famous, like Damar Hamlin, like Bronny James. But this is certainly something that happens," Gounder said.

A study by researchers at the University of Washington found that among NCAA athletes, those at highest risk for sudden cardiac deaths are Black, male college basketball players, although the reason for that is unknown, she said, adding, "that really needs to be studied more closely."

A family spokesperson confirmed Tuesday that James was in stable condition and had been moved out of the intensive care unit. Information hasn't been released about what caused him to suffer the condition, or what's next for him in the coming days. 

Gounder said that elite athletes typically undergo some kind of cardiac screening, such as an EKG and echocardiogram. If James received this kind of screening, it would have detected hypertrophic cardiomyopathy.

According to Gounder, the next steps in James' work-up might include an MRI of the heart, rhythmic monitoring and possibly genetic testing to explore other potential causes before returning to training and play. 

"You're talking about probably a couple of months at least of testing, follow-up, trying to assess does he have a recurrence before easing back into training and play," Gounder said.

James' incident has prompted speculation from anti-vaccine proponents, who have raised doubts about vaccine safety. Gounder said that is important to separate the incident from any association with COVID-19 vaccines.

"This has nothing to do with COVID-19 vaccines," she said. "Over 80% of the American population has now had a COVID vaccination if not more than one. That would be like saying, 'I need my tooth pulled out next week. That must be because I had a COVID vaccine, vaccination.'"

"These are unrelated events," she said. "But this is straight out of the anti-vax playbook to say, 'Well, just asking questions, you know, maybe. How do you know?' And I think the intent here is to sow confusion to make people wonder."