Viral Myocarditis-From Pathophysiology to Treatment

Abstract

The diagnosis of acute and chronic myocarditis remains a challenge for clinicians. Characterization of this disease has been hampered by its diverse etiologies and heterogeneous clinical presentations. Most cases of myocarditis are caused by infectious agents. Despite successful research in the last few years, the pathophysiology of viral myocarditis and its sequelae leading to severe heart failure with a poor prognosis is not fully understood and represents a significant public health issue globally. Most likely, at a certain point, besides viral persistence, several etiological types merge into a common pathogenic autoimmune process leading to chronic inflammation and tissue remodeling, ultimately resulting in the clinical phenotype of dilated cardiomyopathy. Understanding the underlying molecular mechanisms is necessary to assess the prognosis of patients and is fundamental to appropriate specific and personalized therapeutic strategies. To reach this clinical prerequisite, there is the need for advanced diagnostic tools, including an endomyocardial biopsy and guidelines to optimize the management of this disease. The severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) has currently led to the worst pandemic in a century and has awakened a special sensitivity throughout the world to viral infections. This work aims to summarize the pathophysiology of viral myocarditis, advanced diagnostic methods and the current state of treatment options.

Keywords: autoimmunity; dilated cardiomyopathy; endomyocardial biopsy; pathophysiology; therapeutic approach; viral myocarditis.

Figure 1

Phases of viral-mediated myocarditis. Cardiotropic viruses enter the myocardium via different host-cellular routes. Coxsackievirus B3 (CVB3) and adenovirus (ADV) directly target cardiomyocytes via the transmembrane coxsackievirus and adenovirus receptor (CAR). The decay-accelerating factor (DAF) serves as an additional CVB3 receptor, whereas integrins (αvβ3 and αvβ5) act as co-receptors for ADV internalization. Human herpesvirus 6 (HHV6) primarily targets CD4⁺ t lymphocytes and endothelial cells using CD46 as a cellular receptor. Epstein–Barr virus (EBV) enters cardiac tissue by infection of resting human b lymphocytes and subsequent infiltration into adjacent tissue. Parvovirus B19 (B19V) infects endothelial cells using erythrocyte P antigen (P-Ag) and integrin αvβ1 as a co-receptor. For SARS-CoV-2, several cardiac targets, such as cardiomyocytes, endothelial cells and circulating macrophages, are suggested. Its cellular entry depends on the expression of angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine subtype 2 (TMPRSS2) on the host-cell surface. Internalization of viral particles triggers a broad spectrum of host-cell responses and the activation of the innate immune system. Direct cardiomyocytolysis or apoptosis is induced by active viral replication and its transcription products (CVB3 and ADV). Indirectly, cardiomyocyte impairment can arise as a consequence of vascular endothelial dysfunction (B19V, HHV6). In addition, myocarditis is suggested to be induced by infected immune cells carrying viral genomes into the myocardium (HHV6, EBV). As a result of cardiac damage, inflammatory cytokines, as well as damage-associated molecular patterns (DAMPs), are released, triggering the infiltration of mononuclear cells, such as lymphocytes and monocytes, which differentiate into M1 or M2 macrophages depending on the inflammatory milieu. The further release of proinflammatory chemo and cytokines leads to the activation of heart-resident myofibroblasts and an increased generation of fibrous tissue. In the case of viral persistence, viral myocarditis can contribute to the chronic deterioration of cardiac function and the clinical presentation of dilated cardiomyopathy (DCM).

Figure 2

Gel electrophoresis blots (A–D) and real-time PCR amplification (E) of viral PCR amplicons of (A) three CVB3 positive samples (lanes 1 and 2 = ntc; lanes 3 and 4 = pc; lane 5 = negative patient sample; lanes 6–8 = CVB3 positive patient samples), (B) three EBV positive samples (lane 1 = pc; lane 2 = ntc; lanes 3–5 = EBV positive patient samples), (C) three HHV6 positive samples (lanes 1–3 = HHV6 positive patient samples; lane 4 negative patient sample; lane 5 = ntc; lanes 6 and 7 = pc), (D) three B19V positive patient samples (lanes 1 and 2 = ntc; lanes 3 and 4 = pc; lane 5 = negative patient sample; lanes 6–8 = B19V positive patient samples) and (E) one SARS-CoV-2 positive sample (1 = pc E-gene; 2 = pc Orf-gene; 3 = patient sample positive for SARS-CoV-2 E-gene; 4 = patient sample positive for SARS-CoV-2 Orf-gene; 5 = ntc E-gene; 6 = ntc Orf-gene). Abbreviations: ntc = no template control, pc = positive control.

Figure 3

Representative immunohistological images. (A) Active myocarditis with B19V replicative activity. Massively increased CD3 positive t lymphocytes are stained in red/brown. Scale bar = 20 µm. (B) Inflammatory cardiomyopathy with positive detection of enterovirus genomes. Increased CD45R0⁺ T-memory cells are stained in brown. Scale bar = 50 µm. (C) EMB with positive detection of SARS-CoV-2 RNA. Increased cytotoxic perforin⁺ cells are stained in red/brown. Scale bar = 50 µm. (D) Staining of increased CD3⁺ t lymphocytes as a suspected consequence of COVID-19 vaccination. Scale bar = 50 µm.

Figure 4

Mortality rate among patients positive for enterovirus (EV) infection: unadjusted survival according to virus analysis at follow-up. Spontaneous or interferon (IFN)-β-drug-induced enterovirus clearance was associated with a significantly reduced mortality rate in comparison to patients who had enterovirus persistence (p = 0.0005 by the log-rank test) [44].

Figure 5

(A) Parvovirus B19 (B19V) genome detection and detection of viral transcription activity in EMBs of patients with unexplained heart failure (n = 576). (B) The group composition of EMBs with detectable active viral transcription (VP1/2-RNA-, NS1-RNA and VP1/2 and NS1-RNA positive samples) was shown in detail. Numbers represent the amount of EMBs. (C) The number of viral transcripts of NS1 compared to VP1/2. (D) Viral DNA loads in EMBs with active or latent infection. (E) Viral DNA load compared between EMBs with detectable VP1/2-RNA, NS1-RNA or NS1- and VP1/2-RNA expression (ANOVA p = 0.0427). Numbers above the bars represent p-values. Modified from [46].

Figure 5

(A) Parvovirus B19 (B19V) genome detection and detection of viral transcription activity in EMBs of patients with unexplained heart failure (n = 576). (B) The group composition of EMBs with detectable active viral transcription (VP1/2-RNA-, NS1-RNA and VP1/2 and NS1-RNA positive samples) was shown in detail. Numbers represent the amount of EMBs. (C) The number of viral transcripts of NS1 compared to VP1/2. (D) Viral DNA loads in EMBs with active or latent infection. (E) Viral DNA load compared between EMBs with detectable VP1/2-RNA, NS1-RNA or NS1- and VP1/2-RNA expression (ANOVA p = 0.0427). Numbers above the bars represent p-values. Modified from [46].

Figure 6

Kaplan–Meier plots. Natural all-cause mortality on long-term follow-up of B19V-positive patients with inflammatory cardiomyopathy in dependence of B19V transcriptional activity. The mortality rate was significantly higher in patients with transcriptional activity (n = 52) compared to those without transcriptional activity (n = 47) (p = 0.04 by the log-rank test).

Figure 7

(A) Transcriptionally active cardiotropic B19V infection patients treated antivirally with the nucleoside analog telbivudine (LTD). Bar height indicates the mean value ± SD expression rate of viral transcripts/µg RNA in non-responders’ (n = 3) and responders’ group (n = 14) pre (baseline) and post (follow-up) LTD-treatment. Whereas responders significantly reduce viral replication intermediates upon treatment, non-responders show a non-significant increase of viral RNA. (B) LVEF of non-responders and responders pre and post-treatment with LTD. Bar height indicates LVEF (%) in non-responders’ and responders’ groups pre and post LTD-treatment. LVEF improvement was significantly improved in patients who reduced or lost the replicative viral intermediates (positive B19V RNA). LVEF is given as mean value and error bars represent SD [19].

Figure 8

Example of a chromosomally integrated human herpesvirus 6B (ciHHV6B)-positive female patient with persisting high cardiac and systemic virus loads and cardiac involvement treated with antiviral gancyclovir. HHV6 RNA levels are shown as viral copy numbers per 1 µg of RNA. A symptomatic increase of mRNA (S) was noted between days 13 and 21 when i.v. ganciclovir was changed to oral administration. During short symptomatic phases (S) at days 41 and 75, again mild increases of mRNA were detected [13].