Andersons pediatric cardiology 924

of the septoparietal trabeculations Right, Dissection of a normal heart revealing that the greater part of the supraventricular crest is the ventriculoinfundibular fold, or inner heart curvature, that supports the freestanding subpulmonary infundibulum A small part of the area between the limbs of the septomarginal trabeculation can be resected to gain entrance to the left ventricle, but there are no anatomic landmarks delineating this from the inner heart curvature In tetralogy, these components of the normal supraventricular crest are separated This permits the muscular outlet septum to be recognized in its own right, still supporting a freestanding subpulmonary infundibular sleeve but one that is also narrowed (Fig 35.3) FIG 35.3 The adjacent parts of the subaortic and subpulmonary outlets have been removed from a heart with tetralogy of Fallot The section shows how the narrowed subpulmonary infundibulum is made up of the outlet septum (star) and the freestanding infundibular sleeve (arrow) Note the tissue plane (dots) between the infundibulum and the aortic root Because of the abnormal position of the outlet septum, which is exclusively a right ventricular structure, the channel between the ventricles opens on the right side between the limbs of the septomarginal trabeculation, with the right ventricular component of the overriding aortic root supported by the ventriculoinfundibular fold (see Fig 35.1) The three anatomic features of the tetralogy therefore depend on the abnormal location of the outlet septum.4 This particular phenotypic combination cannot be produced in the absence of abnormal positioning and hypertrophy of the septoparietal trabeculations The outlet septum, for example, can be markedly deviated in the anterocephalad direction without subpulmonary stenosis, as in the so-called Eisenmenger complex (Fig 35.4) FIG 35.4 Heart that has been sectioned in the same plane as that shown in the right panel of Fig 35.1 There is anterocephalad deviation of the insertion of the muscular outlet septum, but in this instance without producing muscular subpulmomary (sub-pulm.) obstruction This is the Eisenmenger ventricular septal defect, or the perimembranous outlet defect It is not an example of tetralogy of Fallot The separation of the outlet septum, ventriculoinfundibular fold, and septomarginal trabeculation is the essence of tetralogy Despite each of these features now being recognizable anatomically in its own right, there have been significant confusion and controversy in the description of the abnormal outflow tracts This is because each of these three structures, at various times and in various places, had been nominated as a component of the so-called crista Consequently, when alleged parts of the crista were described in the setting of tetralogy, it was difficult to be sure which of the different structures was being described Because of these problems, we suggested quite some time ago7 that the term “crista,” or its translation as supraventricular crest, be reserved for description of the muscular structure separating the attachments of the leaflets of the tricuspid and pulmonary valves in the normal right ventricular outflow tract (Fig 35.2, left; Fig 35.5, left)