Remodeling of the embryonic interventricular communication in regard to the description and classification of ventricular septal defects
Ventricular septal defects are the commonest congenital cardiac malformations. It is axiomatic that appropriate knowledge of the steps involved in formation and completion of ventricular septation should provide clues as to the morphology of the different types of such defects. Currently, however, consensus is lacking regarding the components of the developing ventricular septum, and how best to describe the different phenotypes seen in postnatal life. In this review, therefore, we have re‐assessed the previous investigations devoted to closure of the embryonic interventricular communication. We discuss how the studies of Odgers, in the early part of the 20th century, correctly identified the steps involved in the remodelling of the embryonic interventricular foramen subsequent to the stage at which the outflow tract arises entirely above the cavity of the developing right ventricle. There has, however, already been remodelling of the foramen from the stage at which the atrioventricular canal is supported exclusively by the developing left ventricle. We show how these temporal changes in morphology can provide explanations for the different ventricular septal defects seen in the setting of congenital cardiac diseases. Thus, muscular defects represent inappropriate coalescence of the cardiomyocytes forming the muscular ventricular septum. The channels that are perimembranous are due to failure of closure of the persisting embryonic interventricular foramen. Those that are doubly committed and juxta‐arterial reflect failure of formation of the free‐standing subpulmonary muscular infundibular sleeve. The findings also point to the importance of appropriate alignment, during development, between the developing atrial and ventricular septums, and between the apical component of the ventricular septum and the ventricular outlet components.
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Publisher URL: https://onlinelibrary.wiley.com/doi/abs/10.1002/ar.24020