Myocarditis may be less common among COVID-19 patients than previously believed

Myocarditis could be much more rare among COVID-19 patients than researchers previously predicted, according to new findings published in Cardiovascular Pathology.

The authors reviewed data from 22 different studies, tracking findings related to the autopsied hearts of a total of 277 COVID-19 patients. The average patient age was 75 years old, and 97.6% had at least one comorbidity.

Signs of myocarditis were present in 7.2% of patients from the autopsy population, but researchers said this number is “likely a significant overstatement” related to how specialists thought during the early stages of the pandemic.

“A desire by pathologists to identify myocarditis might have played a role,” wrote co-authors Marc Halushka, MD, PhD, a professor of pathology at Johns Hopkins University School of Medicine in Baltimore, and Richard Vander Heide, MD, PhD, director of pathology research at LSU Health New Orleans School of Medicine. “The first COVID-19 autopsy series appeared in early April 2020. Prior to that, our understanding of cardiovascular pathology was based upon clinical and radiological findings. Those reports indicated frequent cases of myocarditis, even fulminant myocarditis. Thus, when postmortem examinations began to occur, there was a strong desire by pathologists to validate that clinical finding and declare any inflammation as myocarditis.”

The actual myocarditis rate, the authors estimated, is somewhere in the range of 1.4% to 7.2%. This is significantly lower than the rate of 60% reported by some researchers.

“What we have learned is that myocarditis is not nearly as frequent in COVID-19 as has been thought,” Halushka said in a prepared statement. “This finding should be useful for our clinical colleagues to reconsider how to interpret blood tests and heart radiology studies.”

“By bringing the data together from this large number of autopsy cases, we have better determined the spectrum of histologic findings,” Vander Heide added in the same statement. “Even a low myocarditis rate of 1.4% would predict hundreds of thousands of worldwide cases of myocarditis in severe COVID-19 due to the enormous numbers of infected individuals. Low rates of myocarditis do not indicate that individuals infected with SARS-CoV-2 are not having cardiovascular problems, but rather those complications are likely due to other stressors such as endothelial cell activation, cytokine storms, or electrolyte imbalances.”

The full analysis is available here.