Post-COVID versus non-COVID Myocarditis: Comparison of Morphological Activity, Toll-Like Receptor Expression and Response to the Immunosuppressive Therapy

Background. A direct clinical and morphological comparison of non-COVID myocarditis than was diagnosed before the SARS-CoV-2 pandemic and post-COVID myocarditis has not been performed so far. Purpose: to compare morphological activity, toll-like receptors expression and response to the immunosuppressive therapy in patients with non-COVID and post-COVID myocarditis. Metodhs. Seventy-seven patients (52 male and 25 female, 48.7±11.7 y.o.) with biopsy proven myocarditis, NYHA class 2 or more heart failure, ejection fraction (EF) <45% were included. A history of myocardial infarction, verified cardiomyopathies, systemic autoimmune diseases, viral DNA in the myocardium, except parvovirus B19, were exclusion criteria. The right ventricular endomyocardial biopsy with hematoxylin and eosin, Van Gieson stains, PCR for virus (herpes viruses, parvovirus B19, adeno-, enteroviruses and SARS-CoV-2), immunohistochemical study for CD3, CD45, CD68, CD20, nucleocapsid / spike proteins of SARS-CoV-2 and in addition toll-like receptors (TLR) type 4 and 9 expression (in 38 patients) were performed. The steroids (methylprednisolone 24-40 mg per day), azathioprine, mycophenolate mofetil were prescribed. The mean follow-up was 16 [6; 30] month. Results. In 45 patients, myocarditis was diagnosed before the SARS-CoV-2 pandemic (giant-cell in one case and lymphocytic in the others). Other 32 patients had post-COVID myocarditis positive for RNA or/and proteins of SARS-CoV-2 (giant-cell in one case, eosinophilic in three cases and lymphocytic in the others). There were no differences in age, NYHA class, CRP and anti-heart antibodies level, echocardiographic parameters (mean EF 30.2±7.8 vs 28.7±6.7%), parvovirus B19 positivity (22 vs 34%), doses of methylprednisolone (24-40 mg/day) and death / transplantation rate (11.1 vs 9.4%). Differences between non-COVID vs post-COVID myocarditis focused on higher CD3, CD 45*, TLR 4 (4+ vs 6+), TLR 9 (0 vs 2+) expression and better response to therapy [10% or more increase in EF in 53 vs 86%* of patients, mean EF (43.9±12.3 vs 49.8±7.6%*) by the end of follow-up], *p<0.05. Conclusion. Post-COVID myocarditis is characterised by different morphological types, higher morphological activity, tendency to higher TLR expression and the best response to the immunosupressive therapy in comparison with non-COVID myocarditis.