Myocarditis and COVID-19 related issues

The recent COVID-19 (Coronavirus Disease 2019) pandemic by SARS-CoV2 infection has caused millions of deaths and hospitalizations across the globe. In the early pandemic phases, the infection had been initially considered a primary pulmonary disease. However, increasing evidence has demonstrated a wide range of possible cardiac involvement. Most of systemic and cardiac damage is likely sustained by a complex interplay between inflammatory, immune-related and thrombotic mechanisms. Biventricular failure and myocardial damage with elevation of cardiac biomarkers have been reported in COVID-19 patients, although histological demonstration of acute myocarditis has been rarely documented. Indeed while cardiac magnetic resonance findings include different patterns of myocardial involvement in terms of late gadolinium enhancement, histological data from necropsy and endomyocardial biopsy showed peculiar inflammatory patterns, mostly composed by macrophages. On the other hand COVID-19 vaccines based on mRN technology have been also associated with increased risk of myocarditis. COVID-19 and mRNA vaccine-related myocarditis present different clinical and imaging presentations and recent data suggest the presence of distinctive immunological mechanisms involved.


INTRODUCTION
During the early phases of COVID-19 pandemic, pulmonary involvement was deemed to be the predominant systemic involvement in SARS-CoV-2 infection.Over the course of the pandemic, cardiovascular involvement has emerged as an important negative prognostic factor 1,2 .Increases in troponin, natriuretic peptide and D-dimer levels have been independently associated with increased mortality in COVID-19 patient [1][2][3] .However, these initial studies were limited by the heterogeneity of the cohorts and by the restricted availability of invasive and advanced evaluation (such as coronary angiography and cardiac magnetic resonance, CMR).Most of these studies focused on moderate and severe COVID-19 patients, often presenting elevated cardiovascular risk profiles and ongoing acute respiratory distress (ARDS) syndrome.These elements reduced the specificity of circulating biomarkers in the definition of cardiovascular involvement in COVID-19 infection.
In this review we will discuss the clinical, imaging and immunological aspects of COVID-19 and mRNA vaccine related myocarditis.
Cytokine storm syndrome has emerged as a hallmark feature of moderate and severe COVID-19 infections, leading to multiorgan failure and worse outcome 18,21,22 .Accordingly, multisystemic inflammatory syndrome in children (MIS-C) represents a serious complication of SARS-CoV-2 infection in the paediatric population 23 .
Left ventricular dysfunction, haemodynamic instability, troponin release, pericardial effusion and coronary aneurysms have been reported in MIS-C 24 .Of note these aneurysms may completely regress after treatment with steroids 25 .Rare reports of coronary aneurysms possibly related to concomitant or recent SARS-CoV2 infection have been described also in adults 26 .
Taken together, these data suggest that most of COVID-19 related damage could be mediated by direct and indirect effects of marked dysregulated immune response rather than direct viral damage.Evidence of direct myocardial damage by SARS-CoV2 is limited to some cases demonstrating viral localization in interstitial cells and positive genome analysis in endomyocardial biopsies (EMBs) 27,28 .
Beta-coronaviruses, including SARS-CoV-2, use ACE-2 as cell entry by its receptorbinding domain (RBD) 15 and this element could explain its preferential vascular tropism.Bradley et al. described the presence of myocardial fibrosis in 14 patients undergoing autopsies after severe COVID-19 infection with evidence of lymphocytic infiltrates in only one case 29 .Notably, immunohistochemistry did not detect SARS-CoV-2 in any tissue sample.Other authors reported the presence of extensive inflammatory and thrombotic processes in 12 COVID-19 lung autopsies, but they detected right ventricular (RV) lymphocytic myocarditis in only one case 30 .
Similarly, Lax et al. described one case of lymphocytic infiltrates in 48 cardiac autopsies with evidence of fibrosis in 10 patients 31 .Another group reported only one case of lymphocytic myocarditis in 23 COVID cardiac autopsies 32 presenting viral particles in interstitial and perivascular cells.Moreover, small vessel vasculitis was found in some tissue samples.The presence of SARS-CoV-2 viral genome was detected by quantitative polymerase chain reaction in 5/104 subjects undergoing EMBs in the early pandemic phase 28 .Infiltrates of lymphocytes, macrophages and memory T cells were detected, but the Dallas criteria for active myocarditis were reached in only one case.Tanacli et al. reported the presence of fibrosis and macrophage infiltration in 5/10 subjects undergoing EMB 5 .Lymphocytic infiltrates were found in 5/5 COVID-19 patients undergoing EMB due to the presence of increased cardiac biomarkers by Weckbach et al. 33 .Notably, CMR was able to detect active myocarditis in only 39% of subjects.Moreover, the same group described the presence of predominant T-lymphocytes and macrophages infiltrates and prominent complement and mitogen activated protein kinase (MAPK) pathways activation in COVID-19 EMBs 34 (Table 1).

Clinical presentation and imaging findings
Left and right ventricular dysfunction are relatively common in severe COVID-19 and have been associated with worse outcomes in literature [35][36][37][38] 2) 25,39 .Electrocardiographic signs of RV strain, presence of left bundle branch block, QRS fragmentation, repolarization abnormalities and supraventricular arrhythmias have been associated with a worse prognosis in COVID-19 patients [40][41][42][43] .Advanced atrioventricular block and ventricular arrhythmias are relatively uncommon and limited to most severe cases 26 .
Echocardiography can demonstrate the presence of right and left ventricular dysfunction, reduced biventricular strain and pericardial effusion 26,[35][36][37][38][39] .CMR studies performed in patients hospitalized for COVID-19 demonstrated the presence of ischaemic LGE patterns in 6-22% of patients, even in patients without significant lesions at coronary angiography 4,44 .Coronary vasculitis and biventricular dysfunction have been described in paediatric patients with COVID-19 related MIS-c 23,24 .Presence of multisystemic inflammatory syndrome has been reported also in the adult population (MIS-A) 26 .
Presence of oedema and non-ischaemic LGE patterns compatible with myocarditis have been reported in a significant proportion of patients after SARS-CoV-2 infection 4,5,44,45 .Although the authors could not exclude the presence of concomitant inherited or acquired cardiac diseases in all cases, the relatively high prevalence of these alterations and the frequent association with CMR signs of oedema (in terms of positive T2-weighted or T2 mapping sequences) suggest a pathogenetic role of SARS-Cov-2 infection.Ammirati etal.reportedhigh rates of biventricular dysfunction in patients with COVID-19 related myocarditis with frequent need of vasoactive drugs and/or mechanical support 39 .A case of severe COVID-19 patient with complex cardiovascular involvement is described in Figure 3. Cardiac screening performed on athletes recovering from SARS-CoV-2 infection revealed the presence of cardiac abnormalities in 0.7−2.3% of subjects by use of CMR in terms of pathological T2-derived sequences, presence of increased native T1 mapping and non-ischaemic LGE 46,47 .Patients with cardiopulmonary symptoms and abnormal ECG, stress testing or echocardiographic findings more likely presented pathological findings at CMR.

Histology and proposed mechanisms
Cardiac autopsies in COVID-19 patients demonstrated the presence of fibrosis and macrophage infiltration in tissue samples with low prevalence of active lymphocytic myocarditis following Dallas criteria [29][30][31][32]48 . Smal vessel vasculitis has been detected in a cardiac autoptic COVID-19 cohort 32 .
EMBs demonstrated the presence of SARS-CoV-2 viral genome in only a minority of cases 27,28,39 .Macrophages, neutrophils and T lymphocytes were the main cellular lines found in tissue samples and many cases did not reach the classical Dallas criteria for the histological diagnosis of acute myocarditis 33,34,39 .The low prevalence of pathological infiltrates could be potentially explained by sample biases related to EMB technique, especially when performed only in the RV 49 .However, these findings were concordant across multiple studies, suggesting the presence of peculiar pathological features in COVID-19 related myocarditis.These elements, together with the evidence of MAPK and complement pathways activation, further support the hypothesis of a predominant immune response activation in patients with COVID-19 cardiac involvement.

Management and outcome
Treatment of hospitalized patients with SARS-CoV-2 infection is based on corticosteroids, heparin and remdesivir [50][51][52] .The important role of cytokines in the pathogenesis of COVID-19 related systemic damage led many groups to use specific immunosuppressive drugs in the management of these patients.Use of interleukin-6 (IL-6) inhibitors has been associated with mixed results in literature 53 although a recent meta-analysis reported improved outcomes in COVID-19 patients receiving IL-6 inhibitors in combination with steroid therapy 54 .Interestingly, the use of baricitinib (a janus kinase inhibitor) in combination with remdesivir has been associated with improved outcomes compared to remdesivir alone in a randomized controlled trial 55 .Steroid therapy is recommended in case of COVID-19 related myocarditis with heart failure, MIS-A or haemodynamic instability 56 .Ammirati etal.reported the use of remdesivir, IL-6 inhibitors and intravenous immunoglobulins in a large cohort of patients with COVID-19 related myocarditis 39 .Anecdotal use of immunoadsorption in severe cardiac and pulmonary COVID-19 infection has been also described 57 .

Clinical presentation and imaging findings
Chest pain is the most typical symptom, sometimes associated with fever and flu-like symptoms 62 .Heart failure and cardiogenic shock are uncommon (less than 10% of cases) 12 .Ammirati etal.reported the presence of ST segment elevation in 60% of cases and non-sustained ventricular tachycardia in 11% of subjects 62 .Most of the patients presented preserved biventricular function with pericardial effusion in 16% of them.CMR demonstrated the presence of oedema on T2-weighted images and T2 mapping sequences 14,62,64 .Signs of oedema, late gadolinium enhancement and increased T1 mapping values were mostly observed in inferolateral and anterolateral segments 14,62,64 .

Histology and proposed mechanisms
EMBs performed in patients with clinically suspected vaccine-related myocarditis demonstrated the presence of B and T lymphocytes, plasma cells, macrophages and degranulated eosinophils [65][66][67] .Notably, EMBs revealed the presence of chronic healed myocarditis and sarcoidosis in patients with clinically suspected COVID-19 vaccine related myocarditis 66 .
The mechanisms leading to myocarditis following mRNA vaccine administration remain largely unclarified.An exaggerated immune response to vaccine has been claimed but not conclusively demonstrated 65 .Interestingly, a recent work by Yonker and colleagues 68 demonstrated that patients with myocarditis following mRNA vaccine administration present high levels of unbound circulating spike protein compared to vaccinated controls without myopcarditis.Extensive immunophenotype characterization also demonstrated the presence of increased effector memory T cells and PD-1-expressing bulk CD4+ T cells in patients with myocarditis, suggesting a potential exhaustion in these cellular lines.Moreover, the author reported increased levels of IL-8, IL-6, tumor necrosis factor-α, IL-10, interferon-γ , and IL-1 β and lower IL-4 levels in subjects with myocarditis compared to controls (Figure 4).
Compared to COVID-19 myocarditis, vaccine-related myocarditis present a milder clinical course with frequent infarct-like presentation (Table 2).CMR usually demonstrates preserved biventricular function, while COVID-19 myocarditis can be frequently associated with RV or LV impairment.Oedema and non-ischaemic LGE has been usually detected in the inferolateral segments, similarly to classical viral myocarditis.CMR signs of ischaemic scars have not been described in these patients, differently from COVID-19 myocarditis.Tissue samples obtained from EMB demonstrated florid lymphocytic, macrophage and eosinophilic infiltrates, while COVID-19 EMBs usually present scarce macrophage infiltration and rare cases of lymphocytic myocarditis (Table 2).

Management and outcome
From a clinical point of view, most of these patients present a benign course with low rates of fulminant myocarditis or sustained ventricular arrhythmias [10][11][12][13]62 . Ammrati et al. reported persistence of oedema in only 20% of subjects and significant LGE reduction at 3-months CMR follow-up, in line with imaging findings of classical myocarditis 62 .A case of acute myocarditis following mRNA vaccination is illustrated in Figure 5.
Rare cases of fulminant myocarditis with haemodynamic instability should be treated with inotropes and mechanical support 24,66 .The use of corticosteroids, colchicine and nonsteroidal anti-inflammatory drugs has been described in literature 62,69 , but comparative efficacy data are still lacking.
It has been debated whether patients with a previous non-COVID-19-related myocarditis could present a higher risk of myocarditis recurrence following COVID-19 vaccination.Pieroni et al. reported no cases of COVID-19 vaccine related myocarditis in a cohort of patients with a history of a previous acute myocarditis undergoing mRNA COVID-19 vaccination 70 .These preliminary data suggest that a clinical history of previous acute myocarditis does not portend per se an increased risk for myocarditis following mRNA-based vaccination.

CONCLUSIONS
Myocardial damage in COVID-19 can be extremely heterogeneous and only in a subset of cases can be properly classified as myocarditis.While CMR can frequently show signs of acute and chronic myocarditis in patients with COVID-19, in these subjects histologic findings usually differ from those obderved in classical myocarditis, while a direct SARS-CoV-2 myocaridal damage is still debated.
COVID-19 vaccines based on mRNA technology have been associated with an increased risk of myocarditis, especially in young males.In these patients CMR findings are comparable to those observed in classical myocarditis, while histology demonstrated the presence of lymphocytic and eosinophilic infiltrates.Most patients present mild forms with a favourable outcome also in terms of residual scar at follow-up CMR, with a possible beneficial effect of steroids and immunomodulatory drugs being reported.

Figure 2 .
Figure 2. Cardiovascular manifestations of SARS-CoV2 infection.SARS-CoV-2 mainly causes macrophage and lymphocytic myocarditis, while its direct pathogenetic role is still debated.Due to its peculiar vascular tropism, many cases of arterial and venous thrombosis and coronary vasculitis have been described in literature.These pathogenetic mechanisms can lead to biventricular dysfunction, brady and tachyarrhythmias and myocardial infarction (even with non-obstructive coronary arteries).Pericarditis is another possible complication of COVID-19 infection.Key: COVID-19, coronavirus disease 2019; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 3 .
Figure 3.A case of COVID-19-related cardiovascular damage.A 65-year-old male presenting with severe left ventricular dysfunction and non-sustained ventricular tachycardia shortly after hospitalization due to COVID-19 pneumonia.(a) ECG at presentation showed the presence of sinus rhythm with normal atrioventricular conduction, left anterior hemiblock, QRS fragmentation in V1-V2 leads and negative lateral T waves; polymorphic ventricular beats were present.(b-c) Coronary angiography showed diffuse aneurysmatic lesions in the absence of critical stenosis in the circumflex (b) and right (c) coronary artery.(d) CMR demonstrated the presence of myocardial oedema in the LV inferolateral walls on T2-weighted images (short-tau inversion recovery, STIR) with mild pericardial effusion.(e-f) Late sequences after contrast administration showed the presence of extensive ischaemic LGE in the mid LV lateral wall and midwall LGE in the apical anterolateral wall.LGE was detected also in the anterior RV wall.(g) T2 mapping confirmed the presence of inflammation in the lateral LV wall.h and i: Image analysis of Native and post-contrast T1 mapping (ShMOLLI at 1.5 T) showed increased T1 and ECV values matching LGE sequences in the inferior and lateral wall.Key: COVID-19, coronavirus disease 2019; CMR, cardiac magnetic resonance; LV, left ventricle; STIR, short-tau inversion recovery; LGE, late gadolinium enhancement; RV, right ventricle; ECV, extracellular volume.

Figure 4 .
Figure 4. Proposed mechanisms of COVID-19 mRNA vaccine-related myocarditis.COVID-19 vaccines based on mRNA technology enter cells by endocytosis and release their mRNA (coding for COVID-19 spike protein) content in the cytoplasm.The mRNA is therefore transcripted in the endoplasmic reticulum into numerous spike proteins.These molecules are then exposed in the outer cellular membrane and presented to B and T-lymphocytes, dendritic cells, dedicated macrophages and other antigen presenting cells.The antigen exposure and recognition lead to marked immune cells activation and expansion with consequent immunoglobulin and cytokine production.It has been proposed that persistent free circulating spike proteins could determine an excessive and dysregulated adaptive immune response.These immune pathways could therefore play a role in determining myocarditis with extensive lymphocytes, macrophages and eosinophilic infiltrates.Key: COVID-19, coronavirus disease 2019; mRNA, messenger ribonucleic acid.

Figure 5 .
Figure 5.A case of CIVID-19 mRNA vaccine-related acute myocarditis.A 23-year-old male presenting with chest pain and elevation of markers of cardiac damage 3 days after the administration of a second dose of mRNA vaccine.(a) STIR sequences showed presence of subepicardial oedema in the mid-apical wall.(b) late sequences after contrast demonstrated corresponding LGE in the same segments.(c) T2 mapping sequences confirmed the presence of inflammation in the lateral wall.(d) presence of increased T1 mapping values in the corresponding segments on native T1 mapping sequences.Key: mRNA, messenger ribonucleic acid; STIR, short-tau inversion recovery; LGE, late gadolinium enhancement.
26Ammirati et al. reported high rates (39%) of fulminant presentation in a cohort of COVID-19 myocarditis39.Presence of concomitant pneumonia has been associated with worse prognosis in patients with COVID-19 myocarditis39.Ventricular arrhythmia, high-grade atrioventricular block, pericardial effusion and cardiac tamponade can complicate the clinical course26.Notably, Barhoum et al. reported lower left ventricular ejection fraction, increased use of mechanical circulatory support and higher intensive care unit complications in COVID-19 myocarditis without multisystem inflammatory syndrome (MIS-) compared to MIS+ subjects (Figure