Assessing the criteria for definition of perimembranous ventricular septal defects in light of the search for consensus

Abstract

Background Discussions continue as to whether ventricular septal defects are best categorized according to their right ventricular geography or their borders. This is especially true when considering the perimembranous defect. Our aim, therefore, was to establish the phenotypic feature of the perimembranous defect, and to establish the ease of distinguishing its geographical variants. Methods and results We assessed unrepaired isolated perimembranous ventricular defects from six historic archives, subcategorizing them using the ICD-11 coding system. We identified 365 defects, of which 94 (26%) were deemed to open centrally, 168 (46%) to open to the outlet, and 84 (23%) to the inlet of the right ventricle, with 19 (5%) being confluent. In all hearts, the unifying phenotypic feature was fibrous continuity between the leaflets of the mitral and tricuspid valves. This was often directly between the valves, but in all instances incorporated continuity through the atrioventricular portion of the membranous septum. In contrast, we observed fibrous continuity between the leaflets of the tricuspid and aortic valves in only 298 (82%) of the specimens. When found, discontinuity most commonly was seen in the outlet and central defects. There were no discrepancies between evaluators in distinguishing the borders, but there was occasional disagreement in determining the right ventricular geography of the defect. Conclusions The unifying feature of perimembranous defects, rather than being aortic-to-tricuspid valvar fibrous continuity, is fibrous continuity between the leaflets of the atrioventricular valves. While right ventricular geography is important in classification, it is the borders which are more objectively defined.

A reassessment of the anatomical features of multiple ventricular septal defects

“…These processes, in themselves, show that an outlet defect could not open into the apical part of the right ventricle. It is also clear from the anatomical arrangement that the infundibular part of the right ventricle is found cranial to the limbs of the septomarginal trabeculation, or septal band 16 …”

“…Its phenotypic feature is fibrous continuity between the leaflets of the mitral and tricuspid valves (Figure 4B). 16 The defect incorporates within its borders the atrioventricular component of the membranous septum. It often additionally has a flap in its posteroinferior border formed by the interventricular part of the membranous septum.…”

“…This, of course, is the phenotypic feature of the perimembranous defect. 16 In a small number of the mice with perturbation of the Furin enzyme, furthermore, there was evidence that the proximal outflow cushions had fused so as to separate the aortic and pulmonary roots, but had failed to muscularize. This had left an interventricular communication between the outflow tracts that was bordered cranially by the fused proximal outflow cushions.…”

A Reassessment of the anatomical features of multiple ventricular septal defects

“…This, of course, is the phenotypic feature of the perimembranous defect. 16 In a small number of the mice with perturbation of the Furin enzyme, furthermore, there was evidence that the proximal outflow cushions had fused so as to separate the aortic and pulmonary roots, but had failed to muscularise. This had left an interventricular communication between the outflow tracts that was bordered cranially by the fused proximal outflow cushions.…”

“…15 Its phenotypic feature is fibrous continuity between the leaflets of the mitral and tricuspid valves (Figure 4B). 16 The defect incorporates within its borders the atrioventricular component of the membranous septum. It often additionally has a flap in its postero-inferior border formed by the interventricular part of the membranous septum.…”