Isolated Ventricular Septal Defect: Development Basis for Various Types and Presentation of Classification

Abstract

A morphologic study was made of 101 specimens of heart containing 112 ventricular septal defects (VSD). Morphogenesis of defects was related to development of the ventricular septum. A classification of VSD based on morphogenesis resulted. VSD's may develop in one of the following components of the ventricular septum: (1) the crista supraventricularis, termed infundibular VSD; (2) pars atrioventriculare of septum membranaceum, termed atrioventricular septal defect or left ventricular-right atrial communication; (3) pars interventriculare of septum membranaceum, termed VSD of septum membranaceum; (4) smooth posterior septum, termed smooth VSD and (5) trabeculated posterior septum, termed trabeculated VSD. Among the 33 examples of infundibular VSD, there were five subtypes. In Type I, the defect lies at the inferior margin of the crista supraventricularis. Type II is a mid-cristal defect. A Type III defect lies in front of the crista. Type IV represents complete absence of the crista; and Type V defects lies at the junction between the crista and the posterior septum. Among the 17 examples of primary VSD's of pars interventriculare of septum membranaceum, there were three subtypes. In Type I the margins of the defect are barren of chordal insertions. In Type II, chordae of the septal leaflet of the tricuspid valve are inserted into the margins of the defect. In Type III, the defect is closed by dense chordae which insert into its margins. There were five subtypes among the 56 examples of smooth VSD's. Type I is a defect of the smooth septum along its junction with the anterior septum and also involves septum membranaceum. Type II denotes complete absence of the smooth septum. Type III is a defect at the junction between the smooth and trabeculated septa. Type IV is a perforationlike defect in the posterior smooth septum proper. Type V is a defect in the smooth septum along its junction with the anterior septum without involvement of the membranous septum. In four specimens, the trabeculated type of VSD was present. Two examples of a defect in pars atrioventriculare of the membranous septum were present.