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Further observations on the morphology of atrioventricular septal defects
Insights
Atrioventricular septal defects are a distinct group of congenital heart conditions. Morphological analysis confirms their unique characteristics, differentiating them from other septal defects and normal heart structures.
Area of Science:
- Cardiovascular Pathology
- Congenital Heart Disease
- Morphological Analysis
Background:
- Morphological aspects of atrioventricular septal defects (AVSDs), also known as endocardial cushion defects or atrioventricular canal malformations, remain controversial.
- Uncertainty exists regarding the precise classification of certain lesions, such as isolated mitral valve clefts or perimembranous inlet ventricular septal defects, within the AVSD category.
- The distinct morphology of the left atrioventricular valve in AVSDs compared to a typical mitral valve is not universally accepted.
Purpose of the Study:
- To clarify controversial morphologic aspects of atrioventricular septal defects.
- To determine if specific lesions, like isolated mitral valve clefts or perimembranous inlet ventricular septal defects, should be classified as AVSDs.
- To investigate the morphological characteristics of the left atrioventricular valve in AVSDs.
Main Methods:
- Mensuration and observation of cardiac specimens.
- Measurement of the junctional circumference of left atrioventricular valve leaflets and ventricular dimensions.
- Analysis of 130 AVSDs (95 common orifice, 35 separate orifices), 50 perimembranous VSDs, 7 isolated mitral valve clefts, and 10 normal hearts from the Children's Hospital of Pittsburgh cardiopathological collection.
Main Results:
- Atrioventricular septal defects form a discrete morphological group, distinct from all other specimens with normal atrioventricular septation.
- Measurements conclusively showed that AVSDs are directly comparable regardless of the specific atrioventricular valve morphology.
- The left atrioventricular valve in AVSDs is fundamentally a three-leaflet valve, differing from the normal mitral valve in leaflet structure, chordal support, and papillary muscle arrangement, though it resides in the left ventricle and guards the left atrioventricular junction.
Conclusions:
- Atrioventricular septal defects represent a distinct morphological entity.
- The left atrioventricular valve in AVSDs exhibits unique features differentiating it from a normal mitral valve.
- This study provides conclusive evidence supporting the discrete classification of AVSDs based on comprehensive morphologic and mensural analysis.
Abstract:
Certain morphologic aspects of atrioventricular septal defects ("endocardial cushion defects," "atrioventricular canal malformations") remain controversial. It is still not clear which precise lesions should not be placed in this category. For example, is an "isolated" cleft of the mitral valve or a perimembranous inlet ventricular septal defect to be so described? It is also not fully accepted that the left atrioventricular valve in these lesions bears little resemblance to a morphologically mitral valve. We have investigated these problems by both observation and mensuration. We determined the junctional circumference of the left atrioventricular valve leaflets and the ventricular dimensions in 130 atrioventricular septal defects (95 with common valve orifice and 35 with separate right and left atrioventricular orifices); in 50 hearts with perimembranous ventricular septal defects (20 extending into the inlet septum and 30 with outlet or trabecular extensions); in seven hearts with isolated cleft of the mitral valve, and in 10 normal hearts. All specimens came from the cardiopathological collection of Children's Hospital of Pittsburgh. The measurements showed conclusively that the atrioventricular septal defects were all directly comparable irrespective of the detailed morphology of the atrioventricular valve or valves. The group of atrioventricular septal defects was totally discrete as compared with all the other specimens that had normal atrioventricular septation. The left atrioventricular valve in atrioventricular septal defects is basically a three-leaflet valve which differs from the normal mitral valve in terms of its leaflet, its chordal support, and the arrangement of its papillary muscle. Its only similarity with the normal mitral valve is that it resides in the morphologically left ventricle and guards the left atrioventricular junction.