Background:
Viral infections are among the most common causes of acute myocarditis. However, conventional PCR diagnostics often underestimate the actual viral load and can only identify transcriptionally active or rare infections to a limited extent. Here, we applied a targeted metagenomic next-generation sequencing (NGS) approach to endomyocardial biopsies (EMB) from patients with acute myocarditis to comprehensively evaluate the viral etiology, its association with myocardial inflammation, and the clinical implications for treatment.
Methods:
Endomyocardial biopsies from 38 patients (mean age = 44±16 years; 57% female) with histologically confirmed acute myocarditis were analyzed. The nucleic acids were extracted and subjected to targeted metagenomic NGS. Patients with ≥10 specific virus reads were defined as virus-positive. For comparison, parallel PCR for most common cardiotropic viruses was performed. Immune cell infiltration was quantified by immunohistochemistry (CD3, CD45R0, CD11a, CD11b, perforin). Statistical analyses (Kruskal-Wallis test with Benjamini-Hochberg correction) were performed to compare virus-positive and virus-negative groups.
Results:
Targeted metagenomic NGS detected viral infections in 25 of 38 patients (66%) compared to 23 (60%) by conventional PCR. Overall, NGS identified 51 viral infections versus 36 with PCR, including slightly more viral DNA genomes (38 vs. 32) and markedly more viral RNA transcripts indicating active replication (13 vs. 4). The most frequent cardiotropic viruses were parvovirus B19 (n=18), human herpesvirus 6 (n=7), Epstein-Barr virus (n=6), and adenovirus (n=2). Unexpected viral agents such as human herpesvirus 7 (n=4) and adeno-associated virus (n=1) were also detected exclusively by NGS. NGS-positive patients showed significantly stronger myocardial inflammation, with higher densities of CD3+ and CD11a+ lymphocytes (p<0.05). Parvovirus B19-positive myocarditis demonstrated the most pronounced inflammatory activity.
Conclusions:
Targeted metagenomic NGS improves viral diagnostics in myocarditis compared to PCR by identifying additional infections, including transcriptionally active viruses. Virus-positive patients exhibit stronger lymphocytic inflammation, reflecting active virus-driven immune responses. These findings have direct therapeutic relevance: virus-negative cases may benefit from immunosuppression, whereas virus-positive patients are candidates for antiviral therapy. NGS-based molecular diagnostics should therefore be integral to the evaluation of acute myocarditis.
