A small but growing body of evidence shows that COVID-19 can damage the heart, sometimes fatally, even in a previously healthy young athlete.
This frightening fact is shrouded in so many unknowns that even expert medical groups can offer only limited guidance. That's why collegiate athletic conferences, professional sports leagues, and high school teams are debating what to do. The Big Ten Conference's debate ended with a decision to err on the side of caution.
"We just believed, collectively, there's too much uncertainty," Big Ten commissioner Kevin Warren said Tuesday in explaining why the conference decided to suspend all fall sports competition.
Here are some of the questions medical and sports authorities are grappling with.
What is myocarditis? Myocarditis is inflammation of the heart muscle, or myocardium, usually triggered by infection with a virus, including germs that cause the common cold. The inflammation is generally mild and goes away with rest. But it can also cause temporary or permanent heart problems, notably abnormal rhythms, progressive heart failure, even sudden cardiac death.
How does the coronavirus damage the heart? The exact mechanisms are unclear, but studies suggest an immune system overreaction or an autoimmune response (a self-destructive attack on healthy tissue), or both.
It is also possible that the virus directly invades heart cells in the same way it invades the lungs, by binding to a protein called ACE2 on the surface of cells. This direct attack was seen in patients with MERS, a previous disease caused by a new coronavirus, but so far the evidence on COVID-19 is scant.
Are athletes at risk of COVID-19-related heart damage? They clearly are, but no one knows the level of risk.
In hospitalized COVID-19 patients, myocarditis is relatively common -- affecting 7% to 23% of intensive care patients, studies suggest -- and dramatically increases the risk of death.
A disturbing finding is that heart inflammation can persist after recovery from coronavirus infection. A study conducted in Germany and published in July in JAMA Cardiology evaluated 100 recovered patients; 60% had evidence of ongoing myocarditis.