The suspected link between the SARS-CoV-2 virus — the cause of the COVID-19 pandemic — and myocarditis, an inflammation of the heart muscle (myocardium), made news this past August when a German research study claimed that 60 out of 100 patients who had recovered from the coronavirus showed signs of the dangerous heart condition via MRI. Shortly after that announcement, stories arose about several athletes with possible COVID-19-related myocarditis — including major league pitcher Eduardo Rodriguez, who was sidelined for the entire 2020 season — that appeared to support the connection.

However, following a recent review of clinical findings from 277 hearts autopsied from people in nine countries who died from COVID-19, researchers at Johns Hopkins Medicine and the Louisiana State University suggest otherwise, saying their evaluation provides evidence that myocarditis related to the viral disease may actually be a rare occurrence.

The study was published online Oct. 29, 2020, in the journal Cardiovascular Pathology.

The data from the autopsied hearts were published in 22 papers. After careful review, the researchers determined that the rate of myocarditis found in these patients is between 1.4% and 7.2%. Earlier studies, using imaging of hearts rather than a physical examination of the organs following death, reported rates ranging between 14% and 60%.

“What we have learned is that myocarditis is not nearly as frequent in COVID-19 as has been thought,” says Marc Halushka, M.D., Ph.D., professor of pathology at the Johns Hopkins University School of Medicine and one of two study authors. “This finding should be useful for our clinical colleagues when considering how to best interpret blood tests and heart radiology studies.”

“By bringing the data together from this large number of autopsy cases, we have better defined the spectrum of histologic findings that can be seen in the hearts of people with COVID-19,” adds co-author Richard Vander Heide, M.D., Ph.D., M.B.A., professor of pathology at the LSU Health New Orleans School of Medicine.

The researchers say that even a low myocarditis rate of 1.4% would predict hundreds of thousands of worldwide cases of myocarditis following severe COVID-19. Low rates of myocarditis, they add, do not indicate that individuals infected with SARS-CoV-2 are not having cardiovascular problems, but rather those complications are likely due to other factors such as immune responses or electrolyte imbalances.

Based on the results of their study, the researchers have created a checklist for pathologists to use when evaluating COVID-19 at autopsy to provide consistency in investigating and reporting cardiovascular pathologic findings.

“This study demonstrates the importance of the autopsy in helping us determine what is occurring in the hearts of individuals passing away due to COVID-19,” says Halushka.