Blood clots in the heart are common in patients with COVID-19

Researchers continue to study the effects of COVID-19 on the heart, including myocarditis — a focused inflammation of the heart muscle. New research from Mayo Clinic suggests that myocarditis might not be responsible for cardiac injury in many cases of COVID-19.

A small but in-depth study conducted a postmortem evaluation of the heart tissue of 15 patients with COVID-19, including the first postmortem cardiac findings of three patients who had cleared the virus. These patients were compared to a control group of patients with influenza and a control group of patients who did not have a viral infection.

One-third of patients with COVID-19 ― both active and cleared cases ― showed at least some measure of myocarditis. However, the study did not find solid evidence of SARS-CoV-2, the virus that causes COVID-19, in the heart tissue of the patients studied.

But the research revealed something else of importance in the heart of each patient with COVID-19 in the study.

“The study shows that COVID-19, unlike other viruses, seems to impact the heart’s small blood vessels,” says Melanie Bois, M.D. (MED ’12, PATH ’16, CPTH ’17, CYPAT ’18), Division of Anatomic Pathology, Department of Laboratory Medicine and Pathology at Mayo Clinic in Rochester and first author of the study.

Chemical staining tests revealed blood clotting in the small blood vessels of the heart tissue. These fibrous blood clots may remain even after the virus is gone, which may suggest blood-thinning therapy as a treatment for patients with COVID-19, possibly even after the virus is cleared.

Underlying heart conditions that are known to be related to worse outcomes for patients with COVID-19 also were cited in the study. Of note, more than 26% of patients with COVID-19 who were studied were found to have cardiac amyloidosis ― a cohesive buildup of abnormal proteins that interferes with the heart’s ability to function. This is a much higher rate than the 3.7% occurrence of cardiac amyloidosis typically found at autopsy in patients at Mayo Clinic. It suggests that this underlying heart condition may carry a higher risk of death from COVID-19.

“This study highlights the importance of an autopsy in understanding how diseases affect the body, which helps us to explore new and potentially more effective treatments,” says Joseph Maleszewski, M.D. (CPTH ’10, MGP ’14), Division of Anatomic Pathology, Department of Laboratory Medicine and Pathology at Mayo Clinic in Rochester and senior author of the study.