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COVID-19 Myocarditis Might Be Much Less Common Than Previously Feared

Inconsistent data might mean that the risk of myocarditis with COVID-19 has been overstated. An autopsy study advises that the rate ranges from 1.4% to 7.2%, instead of much higher rates previously suggested for the feared side effect. Here is more information.

NEW ORLEANS – Earlier in the COVID-19 pandemic, myocarditis was one of the most feared side-effects of infection with the virus. Now, a new study suggests that the cardiovascular condition might be relatively rare with the virus.

Their findings published online in Cardiovascular Pathology points out that reports of the rate of COVID-19 myocarditis have varied widely, ranging from 60% among middle-aged and elderly recovered patients to 14% among recovered athletes.

"Although it is clear that COVID-19 impacts the heart and blood vessels, to date, it has been difficult to know how reproducible any changes are due to the relatively small sample size of most autopsy series," noted Richard Vander Heide, MD, PhD, Professor and Director of Pathology Research at LSU Health New Orleans School of Medicine Dr. Vander Heide.

For the study, researchers collected data from 277 autopsy cases to analyze cardiovascular pathological findings from patients who died from COVID-19 in nine countries. Data published in 22 papers reviewed by the authors, who determined that the rate of myocarditis in those patients ranged from 1.4% to 7.2%.

The report suggests that many SARS-CoV-2-related histopathologies are skewed and that an autopsy checklist can provide more accurate information.

Based on the literature review, the median age of the autopsy cohort was 75 and 97.6% had one or more comorbidities, according to the researchers, who add, “Initial review of the data indicate that myocarditis was present in 20 hearts (7.2%); however, closer examination of additional reported information revealed that most cases were likely not functionally significant and the true prevalence of myocarditis is likely much lower (<2%).”

They advise that at least one acute, potentially COVID-19-related cardiovascular histopathologic finding, such as macro or microvascular thrombi, inflammation, or intraluminal megakaryocytes, was reported in 47.8% of cases.

“Significant differences in reporting of histopathologic findings occurred between studies indicating strong biases in observations and the need for more consistency in reporting. In conclusion, across 277 cases, COVID-19-related cardiac histopathological findings, are common, while myocarditis is rare,” according to the report.

"What we have learned is that myocarditis is not nearly as frequent in COVID-19 as has been thought," added Richard Vander Heide, MD, PhD, Professor and Director of Pathology Research at LSU Health New Orleans School of Medicine. "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 stated. "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 authors also created a checklist for pathologists to use going forward when evaluating COVID-19 at autopsy to provide consistency in investigating and reporting findings.