Abstract Fri033: Tissue transcriptomics of endomyocardial biopsies in human myocarditis reveals widespread molecular perturbations independent of leukocyte-rich foci

Introduction: Myocarditis is an inflammatory disease of the cardiac muscle, with a mortality rate of over 400,000 annually. Myocarditis has traditionally been viewed as a focal disease, characterized by localized immune infiltrates and necrosis. The gold-standard for diagnosing the disease is endomyocardial biopsy (EMBx). However, EMBx fails to detect myocarditis in >50% of cases, when focal immune cell infiltrates are missed. Hypothesis: We propose that myocarditis is not a focal disease, but rather a diffuse disease of the entire cardiac muscle. Aim: To assess whether myocarditis exhibits widespread transcriptional dysregulation independent of immune cell localization using spatial transcriptomics. Methods: We performed spatial transcriptomics (10X Visium-FFPE) on EMBx from patients with myocarditis of various etiologies ( n = 10), HFpEF, (Controls, n = 12) and borderline myocarditis ( n = 15). Differential gene expression analysis was computed using multiple algorithms to determine the top common differentially expressed genes (DEGs) among experimental groups. Ingenuity Pathway Analysis (IPA) was subsequently performed to assess the biological significance of these findings. Results: We identified 16,802 barcoded spots from all EMBx samples, whereby UMAP projections showed myocarditis tissue as transcriptionally distinct to controls. Differential expression analysis revealed known and novel myocarditis-associated genes. Samples from borderline myocarditis exhibited an intermediate transcriptional state. Leukocyte-rich regions were removed, and spots were subsequently enriched for cardiomyocytes. DEGs confirmed widespread transcriptional dysregulation independent of immune cells, congruent with IPA showing the dysregulation of unexpected biological pathways. Conclusions: This seminal spatial transcriptomics study of human myocarditis demonstrates that myocarditis is a diffuse pathological state independent of immune cell foci, with dysregulation of novel pathways not currently described. These findings provide a renewed perspective into the biology of myocarditis and provide a framework for developing novel diagnostics, which could surpass traditional histology-based criteria.