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Developmental aspects of atrioventricular septal defects
1Department of Anatomy and Embryology, University of Leiden, The Netherlands.
Insights
Deficiency in the inlet ventricular septum causes abnormal left valve morphology in human embryos with atrioventricular septal defects. This defect impacts leaflet formation and attachment, affecting heart development.
Area of Science:
- Embryology
- Cardiovascular Science
- Developmental Biology
Background:
- Atrioventricular septal defects (AVSDs) are congenital heart abnormalities.
- Understanding the morphological basis of AVSDs is crucial for diagnosis and treatment.
Purpose of the Study:
- To investigate the morphological characteristics of human embryos with atrioventricular septal defects.
- To compare malformed embryos with normal autopsy specimens, focusing on septal leaflet attachments.
Main Methods:
- Morphological analysis of three human embryos with AVSDs.
- Comparison with 67 autopsy specimens of normal hearts.
- Detailed examination of septal attachments of bridging leaflets.
Main Results:
- Malformed embryos exhibited inlet ventricular septal deficiency.
- Bridging leaflets were predominantly muscular with distinct superior and inferior components.
- Myocardial development anomalies prevented normal mitral valve formation.
Conclusions:
- Inlet septal deficiency is the primary cause of abnormal left valve morphology in AVSDs.
- Endocardial cushion tissue likely serves to integrate myocardial structures, influencing leaflet attachment variability.
Abstract:
Three human embryos with an atrioventricular septal defect were studied. Their morphology was compared with that of 67 autopsy specimens, in which particular attention was paid to the septal attachments of the bridging leaflets. The malformed embryos showed deficiency of the inlet component of the ventricular septum. They had distinct superior and inferior bridging leaflets, which were nearly completely muscular. Myocardial undermining had taken place at two independent sites but had not been able to lead to the formation of a valve of mitral morphology. Normal delamination of myocardium to form the leaflets could not continue directly below the aortic root because the rim of the inlet septum had a more apical position. From this, we conclude that the deficiency of the inlet septum is the cause of the typical morphology of the left valve in these hearts. The role of endocardial cushion tissue is probably restricted to glueing together myocardial structures, thus determining the variable septal attachment of the bridging leaflets in atrioventricular septal defect.