Table 1.

Important definitions required for accurate diagnosis of myocarditis.

Definite Diagnosis of Myocarditis Based on Endomyocardial Biopsy
Myocarditis	EMB-proven myocarditis confirmed by histological and immunohistochemical criteria and presence of abnormal inflammatory infiltrate: - typically ≥14 leucocytes/mm2 including up to 4 monocytes/mm2, with the presence of CD3-positive T lymphocytes ≥ 7 cells/mm2; - specific cells, i.e., eosinophils, giant-cell, sarcoid granulomas; Additional analyses (i.e., molecular) necessary for etiology assessment; ±serum positive AHA
Infective myocarditis	EMB-proven myocarditis confirmed by histological and immunohistochemical criteria; Specific infective agent detected in EMB; - i.e., EMB viral PCR positive, borrelia (Lyme disease) positive; ±serum AHA positive
Myocarditis temporarily associated with infective agent	Possible or proven systemic infection (i.e., positive nasal swab for virus); EMB for infective cause negative
Immune-mediated myocarditis	EMB-proven myocarditis confirmed by histological and immunohistochemical criteria; ±systemic immune-mediated diseases (lupus erythematosus, GPA); EMB for infective cause typically negative; ±serum positive AHA
Autoimmune myocarditis	Organ-specific autoimmune myocarditis, exclusion of other known inflammatory causes; EMB-proven myocarditis confirmed by histological and immunohistochemical criteria; EMB for infective cause typically negative; ±serum positive AHA
Clinically suspected myocarditis	Suspicion of myocarditis based on clinical presentation and non-invasive tests (according to ESC criteria [3,5]); Without EMB confirmation
Inflammatory cardiomyopathy	Biopsy-proven myocarditis with systolic and/or diastolic cardiac dysfunction

AHA: anti-heart autoantibodies; CD: cluster of differentiation; EMB: endomyocardial biopsy; ESC: European Society of Cardiology; GPA: granulomatosis with polyangiitis; PCR: polymerase chain reaction; ±: with or without.