ABSTRACT
Background: Pentraxin 3 (PTX3) is an acute phase protein, which regulates the outcomes of inflammation. Currently, there are no myocarditis-typical biomarkers that allow a non-invasive diagnosis, and endomyocardial biopsy (EMB) is still the gold standard. Finally, risk stratification is often challenging in these patients. Aim(s): To investigate whether PTX3 could be expressed in cardiomyocytes and released during myocarditis, serving as a novel and independent diagnostic indicator of myocardial inflammation, and contributing to prognosis prediction. Method(s): Fifty-five patients with a diagnosis of acute or chronic active myocarditis proven by cardiac magnetic resonance (CMR) and/or endomyocardial biopsy (EMB), were included. First, we evaluated tissue PTX3 expression by immunohistochemistry (IHC). Then, we assessed circulating blood PTX3 by ELISA technique. Result(s): On cardiac tissue, PTX3 at IHC did not localize in the interstitium, and showed an inconstant expression in the vascular endothelium, but a marked staining by cardiomyocytes in all myocarditis patients. The only exception was represented by two patients with systemic COVID-19, with SARS-CoV-2 and PVB-19 intracardiac genomes, respectively, who showed a diffuse cardiac PTX3 expression. Remarkably, at semi-quantitative pixel analysis, viral aetiology showed higher levels of tissue expression, rather than the autoimmune one. Circulating PTX3 levels were significantly higher in myocarditis patients than controls, with pathologic values in 87% of myocarditis patients, and none among controls. Remarkably, plasma PTX3 proved to be more sensitive in myocarditis detection than CRP, ESR, troponin T, and NT-proBNP. As regards of prognosis, we observed that patients with heart failure (HF) presentation all had elevated PTX3 levels, as compared with chest pain or arrhythmia. Remarkably, patients with reduced LVEF (<50%) at admission who recovered during follow-up had higher baseline PTX3 levels, rather than those whose systolic function did not improve. Conclusion(s): Tissue PTX3 is mostly expressed by cardiomyocytes in patients with active myocarditis on EMB samples. In addition, plasma PTX3 is a sensitive diagnostic and prognostic marker in patients with inflammatory cardiomyopathy.