Role of Endomyocardial Biopsy and Aetiology-based Treatment in Pediatric Patients with Inflammatory Heart Disease in Arrhythmic and Non-arrhythmic Clinical Presentations: an Integrated Approach for the Optimal Diagnostic and Therapeutic Management (MYOPED)

Myocarditis is a complex inflammatory disease, usually occurring secondary to viral infections, autoimmune processes or toxic agents. Clinical presentations are multiple, including chest-pain, heart failure and a broad spectrum of arrhythmias. In turn, outcome is largely unpredictable, ranging from mild self-limiting disease, to chronic stage and progressive evolution towards dilated cardiomyopathy, to rapid adverse outcome in fulminant forms. Subsequently, myocarditis is often underdiagnosed and undertreated, and optimal diagnostic and therapeutic strategies are still to be defined. This study, both retrospective and prospective, originally single-center and subsequently upgraded to multicenter, aims at answering multiple questions about myocarditis, with special attention to its arrhythmic manifestations.

Optimal diagnostic workflow is still to be defined. In fact, although endomyocardial biopsy (EMB) is still the diagnostic gold standard, especially for aetiology identification, it is an invasive technique. Furthermore, it may lack sensitivity because of sampling errors. By converse, modern imaging techniques - cardiac magnetic resonance (CMR) in particular - have been proposed as alternative or complementary diagnostic tool in inflammatory heart disease. Other noninvasive diagnostic techniques, like delayed-enhanced CT (DECT) scan or position emission tomography (PET) scan, are under investigation.

Biomarkers to identify myocarditis aetiology, predisposition, prognosis and response to treatment are still to be defined.

Arrhythmic myocarditis is largely underdiagnosed and uninvestigated. Importantly, myocarditis presenting with arrhythmias requires specific diagnostic, prognostic and therapeutic considerations. At the group leader hospital, which is an international referral center for ventricular arrhythmias management and ablation, a relevant number of patients with unexplained arrhythmias had myocarditis as underlying aetiology. The experience of a dedicated third-level center is going to be shared with other centers, to considerably improve knowledge and management of arrhythmic myocarditis.

The role of CMR, as well as alternative noninvasive imaging techniques, in defining myocarditis healing is a relevant issue. In particular, optimal timing for follow-up diagnostic reassessment is still to be defined, in patients with myocarditis at different inflammatory stages, either with or without aetiology-dependent treatment.

Uniformly-designed studies are lacking, to compare myocarditis among different patient subgroups, differing by variables like: clinical presentations, myocarditis stage, associated cardiac or extra-cardiac diseases, aetiology-based treatment, associated arrhythmic manifestations, diagnostic workup, and devices or ablation treatment.

This study, previously designed as a single-center experience, is multicenter, observational and both retrospective and prospective.

Retrospective phase includes all clinical data occurring before the index event (hospitalization or clinically suspected myocarditis) and myocarditis diagnosis. Prospective phase includes all data following index event and myocarditis diagnosis.

This study has multiple aims.

To compare EMB with noninvasive diagnostic techniques (CMR, DECT, PET scan, either alone or in association).

To assess the role of blood biomarkers for identification of aetiology, predisposition, prognosis, response to treatment, inflammatory activity, clinical presentation.

To describe myocarditis presenting with arrhythmias, with special focus on ventricular arrhythmias at different myocarditis stages and in different clinical contexts. To validate and generalize the leader hospital model for optimal diagnostic and therapeutical management of arrhythmias in myocarditis patients (given the role of the leader hospital as an international referral center for arrhythmias ablation and management).

To evaluate the timing needed for myocarditis healing in different patients subgroups, as assessed by noninvasive imaging techniques (CMR, DECT, PET scan), either alone or in association.

To compare patients subgroups of myocarditis, in terms of epidemiology, aetiology, prognosis, and diagnostic-therapeutical strategies. Among the others, the main study subgroups will be:

A. Arrhythmic vs. non-arrhythmic myocarditis. B. Arrhythmic myocarditis subgroups. C. Non-arrhythmic myocarditis subgroups (i.e.: fulminant, acute coronary syndrome-like, pericarditis-like, heart failure, non-ischaemic dilated/hypokinetic cardiomyopathies of unknown aetiology...).

D. Infectious vs. autoimmune vs. toxic myocarditis. E. Myocarditis treated by aetiology-based treatment vs. isolated cardiac medical treatment.

F. Myocarditis at different disease stages: acute, hyperacute, fulminant, chronic active, post-inflammatory, or active vs. previous vs. non-myocarditis.

G. Myocarditis presenting as organ-specific diseases vs. in the context of a genetic disorder or systemic disease.

H. Myocarditis vs. peri-myocarditis/myo-pericarditis. I. Other analyses.

Any adult patient with clinically suspected myocarditis, of any clinical presentation and any degree of severity, will be considered as suitable for study enrollment.

Patients will undergo diagnostic and therapeutical strategies considered as clinically indicated in a patient-tailored manner, as suggested by international guidelines recommendations and best local clinical practice. Patients will be free of either accepting or refusing any diagnostic or therapeutical proposal. Whenever accepted, data will be simply collected and analyzed.

Based on clinical presentation, patients will be divided into two groups, arrhythmic (group A) and non-arrhythmic (group NA, including any other clinical presentation).

Independently of A/NA groups, all patients will undergo optimal diagnostic and therapeutic strategies, as summarized in panel A. In parallel, special diagnostic and therapeutical strategies will be performed in patients with arrhythmic presentation or evidence of arrhythmias, as shown in panel B. Proposed flowcharts (Panels A and B) represent only an approximate algorithm. Exceptions can be made in single cases, based on clinical indications.

Panel A - Diagnostic and therapeutical workup in all patients. Independently of groups (A/NA), all patients will undergo optimal diagnostic and therapeutical workup, guided by updated scientific evidence merged with the clinical experience of the center.

Baseline diagnostic workup will include: complete blood exams, 12-leads ECG, continuous telemetric monitoring, transthoracic doppler echocardiogram, coronary artery imaging (coronary angiography or CT scan). Any other clinically relevant diagnostic test will be collected.

In life-threatening presentations (cardiogenic shock or malignant arrhythmias), support treatment by optimal medical therapy, inotropic or mechanical circulatory support, and acute-phase arrhythmia management (including cardioversion, defibrillation, or temporary pacing) will be performed, as indicated, before completing diagnostic workup.

Final diagnosis of myocarditis will include, whenever applicable:

A. For stable patients: 1) a second-level imaging technique (CMR as first choice; and/or DECT, PET, or multiple/fusion imaging techniques, based on clinical indications); followed by: 2) EMB, whenever clinically indicated. Blood exams for aetiology screening will be personalized upon clinical indications.

B. For unstable patients: EMB only, as recommended. Blood exams for aetiology screening will be personalized upon clinical indications.

Diagnostic criteria for myocarditis, as assessed by any diagnostic technique, will be defined based on international scientific evidence and will be constantly updated. Similar considerations apply to myocarditis staging and aetiology definition. Whenever not available at local institutions, diagnostic exams can be performed and analyzed at external centers.

All patients with myocarditis (or any alternative final diagnosis), will undergo standard cardiological optimal medical treatment (COMT), as indicated. By converse, aetiology-dependent treatment will be performed only in patients with a final diagnosis of any active (acute, fulminant, chronic active) myocarditis of defined aetiology (EMB-proved). Multidisciplinary assessment, including infective disease specialists (in viral/infective myocarditis), immunologists (in non-infective/autoimmune myocarditis) or any other specialist as needed, will be used to identify indications to treatment, drug choice (either approved or with a justified unapproved indication), treatment duration and safety profile, aiming at the best patients\&#39; interest. Toxic myocarditis will be treated accordingly, by evaluating the opportunity of withdrawing pathogenic noxa.

This protocol will not interfere with local best clinical practice. Patients with non-active myocarditis (previous or healed) or with non-myocarditis, will undergo \&#34;standard FU\&#34;; (see below). Patients with active myocarditis will undergo \&#34;intensive FU\&#34;; (see below).

Independently of FU modalities, diagnostic reassessment will be considered in the presence of at least one of the following instability criteria: a) new unexplained cardiac symptoms (dyspnoea, chest pain, syncope, palpitation); b) new unexplained increase in troponin or natriuretic peptides; c) new imaging abnormal signs; d) new unexplained clinically relevant arrhythmias. Diagnostic reassessment will include second-level imaging and/or EMB, as shown above. Subsequent therapeutical workup will be in line with the above explanations. In stable patients or undergone myocarditis healing, exercise stress test will be obtained, whenever possible.

Panel B - Diagnostic and therapeutical workup of patients with arrhythmias In parallel with (and independently of) Panel A content, patients with arrhythmias (group A) will undergo specific diagnostic and therapeutical management for arrhythmias, as a result of the integration between international guidelines recommendations and the experience of an international referral center for arrhythmia management and ablation.

To oversimplify, 4 groups of patients will be considered.

Group 1: major ventricular arrhythmias, including haemodynamically unstable VT (hu-VT) and ventricular fibrillation (VF).

After electrical stabilization and support treatment (panel A), indication to secondary prevention ICD implant will be multiparametric and patient-tailored. In patients with active myocarditis, subcutaneous ICD (S-ICD) or wearable CD (WCD) will be considered. Antiarrhythmic drugs will be considered in all Group 1 patients. In addition, all Group 1 patients will undergo COMT and aetiology-dependent treatment whenever applicable (panel A). Ablation of ventricular arrhythmias will be considered in patients with severe arrhythmic presentation, or symptomatic, or refractory to optimal medical treatment. Electrophysiological study (EPS) may be used in selected cases. A cardiac resynchronization therapy with defibrillator function (CRT-D) will replace ICD whenever indicated.

Group 2: other ventricular arrhythmias, including high-burden (hb) premature ventricular complexes (PVC); nonsustained VT (NSVT); haemodynamically stable VT (hs-VT).

Whenever clinically indicated, Group 2 patients will undergo invasive EPS (or in alternative noninvasive programmed ventricular stimulation in ICD carriers) to stratify arrhythmic risk. Patients with positive EPS will undergo ICD (or S-ICD/WCD) as in Group 1. Patients with negative EPS, as well as Group 2 cases not undergoing EPS, will undergo watchful waiting strategy (always with an intensive FU) with or without loop recorder implant: in these cases, ICD (or S-ICD/WCD) will be implanted only following documentation of relevant VA in FU. In addition, all Group 2 patients will undergo antiarrhythmic treatment, COMT and aetiology-dependent treatment whenever applicable (panel A). In symptomatic or drug-refractory cases, ablation of ventricular arrhythmias will be considered. A CRT-D will replace ICD whenever indicated.

Group 3: bradyarrhythmias, including advanced (2nd type II or 3rd degree) atrioventricular block (AVB); critical sinus pauses from sinus node disease (SND).

After electrical stabilization and support treatment (panel A), including the use of temporary pacemaker as a bridge-to-decision, patients will undergo watchful waiting strategy or definitive device implant. Instead of a pacemaker (PM), ICD will be considered in the presence of high-risk criteria for ventricular tachyarrhythmias, including: a) overlap with Group 1 presentation; b) overlap with Group 2 presentation, especially in the presence of positive EPS; c) other indications for primary prevention ICD implant (severe systolic dysfunction); d) signs of increased tachyarrhythmic risk (scar signs); e) patients with special aetiologies leading to an increased tachyarrhythmic risk (i.e: cardiac sarcoid, giant cell myocarditis, Chagas disease, overlapping genetic syndromes). In addition, all Group 3 patients will undergo COMT and aetiology-dependent treatment whenever applicable (panel A). A CRT-D or a CRT-P will replace ICD or PM, respectively, whenever indicated.

Group 4: supraventricular arrhythmias, including atrial fibrillation (AF); atrial flutter (AFlu); atrial tachycardia (AT).

Following acute-phase rate control (RaC), stable rhythm control (RyC) strategy will be considered as the therapeutical target, together with appropriate anticoagulation, as needed. Normal sinus rhythm will be obtained through either electrical or pharmacological cardioversion. In patients with unsuccessful attempts of sinus rhythm conversion, optimal treatment of active myocarditis will be considered as a primary target. Following myocarditis healing, in the presence of persistent arrhythmias, patients will be considered for RyC via electrical or pharmacological cardioversion. Transcatheter ablation will be an option for patients with drug-symptomatic, recurrent or refractory arrhythmias. Permanent RaC strategy will be considered only in non responders. Widespread use of implantable loop recorders will apply, as clinically indicated. In addition, all Group 4 patients will undergo COMT and aetiology-dependent treatment whenever applicable (panel A).

Aims in detail. Aim 1 Comparison between EMB and second level imaging findings (N=1000)

Primary:

Diagnostic concordance

Secondary:

Inflammatory activity (presence; type; quantification) Fibrosis (presence; type; quantification) Coronary microvascular disease Comparison between EMB sampling site and abnormal substrate localization at imaging (including substrate-guided EMB or alternative biopsy techniques) Role of EMB guided by electroanatomical map Diagnostic performance of DECT and/or PET, especially when CMR is contraindicated Comparison between CMR/DECT findings and PET scan (including fusion imaging) or advanced imaging techniques including strain analysis at echocardiogram Comparison between substrate abnormalities localizations (as assessed by second level imaging techniques) and arrhythmias (type, characteristics and origin site) Comparison among different diagnostic techniques (EMB, CMR/DECT, PET) in terms of safety and diagnostic accuracy Evaluation of differential diagnosis with other cardias diseases, and particularly with arrhythmogenic cardiomyopathy of any localization (left, right, biventricular, to identify updated diagnostic criteria) Comparison between information provided by all the techniques above, and data from electroanatomical mapping (EAM) Other analyses

Aim 2 Evaluation of blood exams and biomarkers (N=1000)

Primary:

Identification of diagnostic biomarkers Identification of aetiology biomarkers

Secondary:

Cardiac and inflammatory biomarkers evaluation in different myocarditis subtypes Identification of biomarkers of inflammatory stage (acute vs. chronic; active vs. previous) Comparison between local and systemic/peripheral inflammation Correlations with EMB and second-level imaging (CMR, DECT, PET...) findings Identification of genetic factors with any role in predisposition, prognosis, response to treatment, or any other correlation, either in the presence or in the absence of underlying cardiomyopathy or autoimmune/inflammatory disease Identification of prognostic biomarkers Identification of biomarkers associated with treatment response Evaluation of any tissue/organ damage or associated comorbidities Study of cardiac autoantibodies Study of any cell, tissue, genetic or circulating biomarker Correlations with clinical presentations Other analyses

Aim 3 Validation of optimal management of arrhythmic myocarditis (N=1000)

Primary:

Evaluation of effects on major endpoints

Secondary:

Evaluation of effects on minor endpoints Role of electrophysiological study in risk stratification Role of loop recorders in arrhythmia monitoring Role of transcatheter ablation (any technique) on arrhythmic outcomes Identification of optimal timing for any electrophysiological/device procedure Role of pharmacological antiarrhythmic treatment Role of aetiology-specific treatment on arrhythmic outcomes Identification of criteria for device implants (PM, ICD, S-ICD, CRT-D...) in myocarditis patients Validation of therapeutic strategies and their optimal timing in patients with supraventricular arrhythmias, bradyarrhythmias, or ventricular arrhythmias Correlation between arrhythmia type/features with any other diagnostic exam performed at baseline or during FU (mainly EMB, CMR/DECT/PET, echocardiogram, stress tests, blood exams, genetic/blood/tissue/cell biomarkers) Indications and timing for device (ICD, CRT-D) implant in primary prevention, based on multiparametric risk assessment, and in relation to different general and aetiology-dependent treatments Other analyses

Aim 4 Evaluation of healing timing in myocarditis (N=500) Primary Any degree of recovery by 3, 6, 9, 12 and 12 months Secondary Comparison of healing times in treated vs. untreated patients Correlations between healing times and clinical presentation types Correlations between healing times and any biomarker Correlations between healing times and any outcomes Validation of exercise stress test role after myocarditis healing Evaluation of PET scan or other diagnostic techniques as alternatives to CMR in special populations Other analyses

Aim 5 Subgroup analyses (N=500, hugely variable in each subanalysis) A vs. NA groups; A myocarditis subgroups; NA myocarditis subgroups (including fulminant); Infective vs. autoimmune vs. toxic forms; Treated by aetiology-driven therapy vs. standard cardiological treatment; Different myocarditis stages and differential diagnoses; Isolated vs. in the context o a systemic disease or genetic disease; Myocarditis vs. perimyocarditis/ myopericarditis Primary Differences in major outcomes Secondary Differences in minor outcomes Differences in any biomarker Differences in any diagnostic exam Differences in aetiology Differences in predisposition Differences in inflammatory activity Differences in pericardial involvement Differences in systemic involvement Differences in arrhythmias types and features Differences in clinical presentation Differences in treatment response, including novel treatments Validation of local aetiology/pathophysiology-dependent treatments Validation of biomarkers and imaging techniques in monitoring response to treatment Identification of optimal follow-up timeline Other analyses

Eligibility Criteria:
Inclusion Criteria:

* Written informed consent.
* Age \&lt; 18 years.
* Clinically suspected myocarditis.
* Enrollment performed by one of the participating Centers.

Exclusion Criteria:

* Absence of written informed consent.
* Age \&gt; 18 years (adults)