Thông tin tài liệu
FIG 35.5 Building blocks of the outflow tract of the normal right ventricle (A) compared with the arrangement found in tetralogy of Fallot (B) Although a segment is shown in yellow in the normal heart between the ventriculoinfundibular fold and the limbs of the septomarginal trabeculation, this portion cannot be distinguished without resorting to dissection (see Fig 35.2) The stars show the location of the septoparietal trabeculations, with the yellow bracket showing the squeeze producing the phenotypic feature of tetralogy Sub-pulm., Subpulmomary In situations where the muscular structures are separated one from the other, as is the case in tetralogy, and there is also a double-outlet right ventricle,8 it is best to account for each structure in its own right using descriptive and mutually exclusive terms (Fig 35.5, right) Thus the outlet septum is any muscular or fibrous structure that interposes between the subpulmonary and subaortic outflow tracts It has septal and parietal insertions and supports distally the sleeve of freestanding subpulmonary infundibular musculature The ventriculoinfundibular fold, being part of the muscular inner heart curvature, is a muscular structure that separates the leaflets of an arterial from an atrioventricular valve The septomarginal trabeculation, or septal band, is the extensive muscular strap that reinforces the septal surface of the morphologically right ventricle It has a body, together with anterocephalad and posterocaudal limbs The channel between the ventricles opens to the right side between its limbs not only in tetralogy but also in other lesions such as double-outlet right ventricle and common arterial trunk The septoparietal trabeculations arise from its anterior margin They are integral components of the normal heart but are hypertrophied as part of tetralogy (see Fig 35.5) Variability in the Interventricular Communication The channel between the ventricles is directly beneath the overriding aortic valvar orifice and hence is geographically an outlet defect Its cranial border is the outlet septum, which is malaligned relative to the rest of the muscular septum The outlet septum is usually muscular (see Fig 35.1, right), but it can be fibrous and virtually absent in the doubly committed and juxta-arterial variant (Fig 35.6) FIG 35.6 Heart from patient with tetralogy of Fallot in which the ventricular septal defect is roofed by a fibrous outlet septum, which provides continuity between the leaflets of the arterial valves, making it doubly committed and juxta-arterial The defect also extends to an area of fibrous continuity between the aortic and tricuspid valves, with the ventriculoinfundibular fold stopping short of the posterocaudal limb of the septomarginal trabeculation (yellow bars) This makes the defect perimembranous and indicates that the conduction axis is at potential risk in its posteroinferior margin (yellow dotted line) Note the remnant of the interventricular membranous septum, which forms the so-called membranous flap As we have emphasized, the essence of tetralogy is anterocephalad deviation of the septal insertion of the outlet septum, whether muscular or fibrous (compare Figs 35.1 and 35.6) The crest of the muscular ventricular septum, reinforced by the limbs of the septomarginal trabeculation, forms the floor of the defect The roof is formed by the attachments of the leaflets of the overriding aortic valve to the ventriculoinfundibular fold The overriding nature of the aortic orifice, however, creates problems in defining specifically the area to be considered as the “ventricular septal defect.” Three potential areas can appropriately be described as the interventricular communication (Fig 35.7) FIG 35.7 Three areas within the cone of space subtended from the crest of the ventricular septum to the attachments of the overriding aortic valve, which could be defined as the ventricular septal defect The red disc is the outlet from the left ventricle The yellow disc is the geometric
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