First paediatric cohort for the evaluation of inflammation in endomyocardial biopsies derived from congenital heart surgery.

Background: Endomyocardial biopsies (EMB) are the gold standard for the diagnosis of myocarditis in children and adults. The existing WHO/ISFC criteria for lymphocytic cell infiltrates by are based on the myocardium of adults. The aim of this study was to present a paediatric control cohort for the evaluation of inflammation in EMB of children.
Methods: In this study endomyocardial tissue from 62 children under 4 years of age was investigated, being collected during a planned open heart surgery with routine resection from ventricular site. Patients had no history of infection or myocardial inflammation. The heart tissue was formalin fixed and embedded in paraffin. Four μm thick tissue sections were stained with haematoxylin and eosin, Masson's trichrome, and Giemsa. Immunohistochemical stainings included quantitative evaluation of CD3 ⁺ T cells, CD20 ⁺  B cells, CD68 ⁺  macrophages and MHCII expression.
Results: The myocardium was obtained in 96.8% (n = 60) of the cases from the right and in 3.2% (n = 2) from the left ventricle. The median age (interquartile range) at biopsy was 0.5 years (0.3-0.9), 66.1% male. Within this cohort, a median of 2.5/mm ² (1.0-4.0) CD3 ⁺ T cells, 0.5/mm ² (0.0-0.6) CD20 ⁺  B cells and 4.0/mm ² (2.5-6.0) CD68 ⁺  macrophages were detected. The MHC II grade was 0 in 71.0% (n = 44) and 1 in 29.0% (n = 18).
Conclusion: This is the first paediatric control cohort being relevant for the correct interpretation of inflammatory heart diseases in EMB. The lymphocytic cell numbers in children needing congenital heart surgery without myocardial inflammation are below the existing values in adults.
(Copyright © 2019 Elsevier B.V. All rights reserved.)