Workup and management of rhythm disorders in myocarditis and inflammatory cardiomyopathy: a clinical consensus statement of the European Heart Rhythm Association and the Heart Failure Association of the ESC, the ESC Working Group on Myocardial & Pericardial Diseases, the European Association of Preventive Cardiology of the ESC, the Heart Rhythm Society, the Asian Pacific Heart Rhythm Society, and the Latin American Heart Rhythm Society

Figure 1. Phases of arrhythmic myocarditis. Phases (or stages) or arrhythmic myocarditis are shown. VA, ventricular arrhythmias.

Figure 2. EMB-defined stages and histotypes of arrhythmic myocarditis. EMB-defined stages and histotypes of arrhythmic myocarditis. (A) Lymphocytic myocarditis, hot phase (acute): inflammatory infiltrates, oedema, non-ischaemic necrosis (A1, HE), CD3+ T lymphocytes > 7/mm2 and >15/high power field (mild myocarditis according to 2025 Seaport criteria) (A2, IHC). (B) Lymphocytic myocarditis, hot-to-cold phase (chronically active): inflammatory infiltrates, replacement fibrosis (B1, HE), >2 clusters of CD3+ T lymphocytes (moderate myocarditis according to 2025 Seaport criteria) (B2, IHC). (C) Special histotypes with strong arrhythmic associations, namely: giant cell myocarditis (C1, HE) and cardiac sarcoidosis with noncaseating granulomas (C2, HE). EMB, endomyocardial biopsy; HE, haematoxylin eosin; IHC, immunohistochemistry.

Figure 3. Diagnostic workup for arrhythmic myocarditis. Diagnostic workup for arrhythmic myocarditis is shown, along with comparison between gold standard techniques (CMR and EMB). CMR and EMB provide complementary information; neither modality alone is sufficient to fully characterize arrhythmic myocarditis. CAD, coronary artery disease; CMR, cardiac magnetic resonance; CT, computed tomography; EAVM, electroanatomic voltage map; EMB, endomyocardial biopsy; FDG-PET, 18F-fluorodeoxyglucose positron emission tomography; ICD, implantable cardioverter defibrillator; LGE, late gadolinium enhancement; VA, ventricular arrhythmias.

Figure 4. Imaging findings in arrhythmic myocarditis. Imaging findings are shown for patients with arrhythmic myocarditis. (A–C). CMR showing nonischaemic LGE in a patient with: (A) autoimmune myocarditis (inferolateral distribution, arrow); (B) FLNC gene variant (septal distribution, arrow); (C) DSP gene variant (ring-like distribution, arrows). (D) CT scan showing nonischaemic late iodine enhancement (lateral apical distribution, arrow) in a patient with acute myocarditis and normal coronary arteries. (E) FDG-PET scan consistent with hot-phase cardiomyopathy in a patient with LMNA gene variant (septal distribution, arrow). (F) Endocardial bipolar EAVM (left anterior oblique view; cut-off values 0.5 mV for dense scar—red; 1.5 mV for normal voltage—purple) showing low-voltage areas (dominant inferolateral distribution, arrow) in a patient with chronic myocarditis (cold phase). CMR, cardiac magnetic resonance; DSP, desmoplakin gene; EAVM, electroanatomic voltage mapping; FDG-PET, 18F-fluorodeoxyglucose positron emission tomography; FLNC, filamin C gene; LGE, late gadolinium enhancement; LMNA, lamin A/C gene.

Figure 5. EAVM-guided EMB. Usefulness of EAVM in guiding EMB in a patient with cardiac sarcoidosis and patchy distribution of substrate abnormalities. Low-voltage areas (endocardial bipolar map, left anterior oblique view; cut-off values 0.5 mV for dense scar—red; 1.5 mV for normal voltage—purple) reveal inflammation and noncaseating granulomas, whereas normal voltage points to healthy tissue. Permissions for Figure obtained by Tschöpe et al. 2021.2 EAVM, electroanatomic voltage mapping; EMB, endomyocardial biopsy.

Figure 6. ECG-guided treatment in arrhythmic myocarditis. ECG features of sustained monomorphic VTs are shown in two patients with myocarditis. (A) Right bundle branch block, superior right axis (negative in lead DI) morphology suggests inferolateral LV VT exit, as commonly observed in the cold phase of myocarditis; variability in cycle length suggests hot-to-cold transition phase in a patient with acute presentation (VT) but evolving inflammatory process: immunomodulatory treatment is suggested to target VT before considering ablation (‘cool down, then ablate’ strategy). (B) Regular VT with qR in V1 and RS V4-V6 and inferior axis, suggesting cold-phase and septal origin in a patient with history of cardiac sarcoidosis: immunomodulatory therapy may not help, and referral to an experienced centre for VT ablation is advised. In all cases, ECG provides only partial information. Treatment strategies are driven by the clinical context and gold standard diagnostic techniques for myocarditis (cardiac magnetic resonance, endomyocardial biopsy), LV, left ventricular; VT, ventricular tachycardia.

Figure 7. Cardiac devices in arrhythmic myocarditis. Algorithms to guide the choice of cardiac devices in arrhythmic myocarditis are shown, for high-degree AV block (panel A) and VA (panel B) scenarios. Where relevant, myocarditis phases (hot/hot-to-cold/cold) are shown. AV, atrioventricular; CMR, cardiac magnetic resonance; CRT, cardiac resynchronization therapy; CSP, conduction system pacing; DSP, desmoplakin gene; EMB, endomyocardial biopsy; FLNC, filamin C gene; GCM, giant cell myocarditis; ICD, implantable cardioverter defibrillator (EV−, extravascular; S−, subcutaneous; TV−, transvenous); LBBB, left bundle branch block; LGE, late gadolinium enhancement; LMNA, lamin A/C gene; LVEF, left ventricular ejection fraction; NSVT, nonsustained ventricular tachycardia; PM, pacemaker; PVS, programmed ventricular stimulation; VA, ventricular arrhythmias; VT, ventricular tachycardia; WCD, wearable cardioverter defibrillator.

Figure 8. Treatment of arrhythmic myocarditis. Treatment principles are shown for arrhythmic myocarditis, ranging from rhythm stabilization to cardiologic and aetiology-/phase-specific treatment. AADs, antiarrhythmic drugs; ACLS, advanced cardiovascular life support; BB, betablockers; CSD, cardia sympathetic denervation; ECV, electrical cardioversion; HF, heart failure; HTx, heart transplant; ICD, implantable cardioverter defibrillator; IST, immunosuppressive therapy; iv, intravenous; LVAD, left ventricular assist device; LVEF, left ventricular ejection fraction; MCS, mechanical circulatory support; OMT, optimal medical therapy (guideline-directed); PLSGB, percutaneous left stellate ganglion blockade; TEA, thoracic epidural anaesthesia; VA, ventricular arrhythmias; VA-ECMO, venoarterial extracorporeal membrane oxygenator.

Figure 9. Findings during VT ablation in cold-phase myocarditis. Findings of VT ablation are shown for patients with myocarditis. A-C. EAVM in a patient with a history of myocarditis and extensive inferolateral LV scar. Dense scar (red) and borderzone (rainbow) are compared as recorded by endocardial bipolar (A), endocardial unipolar (B) and epicardial bipolar map (C). (D) Late potentials (arrow) in a patient with chronic myocarditis (cold phase) and inferolateral scar. (E) Ablation lesions (arrows) at both sides of interventricular septum in a patient with giant cell myocarditis and multiple septal VTs refractory to triple immunosuppression. EAVM, electroanatomic voltage mapping; VT, ventricular tachycardia.

Figure 10. CMR (A) demonstrating septal and right ventricular late gadolinium enhancement (LGE); FDG-PET (B) showing extensive myocardial inflammation (arrows) and mediastinal/hilar lymph node uptake, consistent with cardiac sarcoidosis presenting with high-degree AV block (C).

Figure 11. CMR (A) revealing extensive lateral wall LGE and myocardial oedema on T2-weighted imaging; acute inflammation identified as the underlying substrate for polymorphic non-sustained ventricular tachycardia (B).

Figure 12. Monomorphic VT documented on 12-lead ECG (A). CMR without oedema but with subepicardial LGE (B), indicating a chronic scar-related re-entrant substrate. High-density epicardial voltage mapping of the lateral left ventricle (C) showing extensive low-voltage areas (<1.5 mV); Genetic testing was planned.