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is seen in the structure of the subpulmonary outflow tract, with the muscular outlet septum, or its fibrous remnant, when present, being displaced anteriorly and cephalad relative to the limbs of the septomarginal trabeculation (Fig 36.2) FIG 36.2 Varying intracardiac morphology to be found in the setting of tetralogy of Fallot with pulmonary atresia (A–B) In these hearts the muscular outlet septum is attached to the cranial limb of the septomarginal trabeculation (yellow bars) The pulmonary valve is imperforate in (A), whereas the atresia is muscular in (B) (C) Heart with an atretic pulmonary trunk but no evidence of formation of the subpulmonary infundibulum The ventricular septal defect (star) is perimembranous in (A), has a muscular posteroinferior rim in (B), and is doubly committed and juxta-arterial in (C) In a small number of cases, the atresia is found at the mouth of the muscular infundibulum, and the pulmonary valve itself may be patent Alternatively, there can be an imperforate pulmonary valve (see Fig 36.2A) In the most common pattern, the muscular outlet septum fuses directly with the parietal musculature of the right ventricle, thus obliterating the ventriculopulmonary junction (see Fig 36.2B) There is a muscular wall between the cavities of the right ventricle and the pulmonary trunk Occasionally the subpulmonary outflow tract is completely absent, so that the leaflets of the aortic valve are attached directly to the parietal ventricular wall (see Fig 36.2C) This arrangement is reminiscent of common arterial trunk In the example shown in Fig 36.2, however, the atretic pulmonary trunk takes its origin from the right ventricular musculature, confirming that the patent arterial trunk is an aorta Should the intrapericardial pulmonary arteries also be absent, it would be impossible to be sure whether the patent trunk had, initially, been an aorta and not a common structure Thus the arrangement with absence of the pulmonary trunk is best described as a solitary arterial trunk, although that clinical presentation is the same as for TOF/PA In other cases, a fibrous remnant of the outlet septum interposes between the leaflets of the aortic valve and an imperforate pulmonary valve This arrangement represents TOF/PA in the setting of a doubly committed and juxtaarterial ventricular septal defect, as does the arrangement with complete absence of the subpulmonary infundibulum (see Fig 36.2C) The ventricular septal defect, roofed by the overriding aorta, usually has a fibrous posteroinferior border made up of continuity between the leaflets of the aortic and tricuspid valves and often reinforced by a membranous flap This arrangement makes the defect perimembranous (see Fig 36.2A) Cases can also be found, as in tetralogy with pulmonary stenosis, when the posteroinferior limb of the septomarginal trabeculation fuses with the ventriculoinfundibular fold In this setting, the defect has exclusively muscular borders when viewed from its right side (see Fig 36.2B) This muscular rim, when present, serves to protect the ventricular conduction tissues, separating them from the crest of the septum As discussed earlier, the defect can also extend to become doubly committed and juxta-arterial Such doubly committed defects can themselves extend to become perimembranous, but more usually they have a muscular posteroinferior rim (see Fig 36.2C) Rarely the ventricular septal defect may be restrictive due to tissue tags derived from the leaflets of the tricuspid valve In this setting, the overall anatomy of the heart is more like PA with intact ventricular septum, usually with a thick-walled right ventricle and a reduced cavity The precise connection of the leaflets of the aortic valve, as in tetralogy with pulmonary stenosis, can vary markedly In most instances, the leaflets of the aortic valve are connected largely within the left ventricle Hearts can also be found with predominant or even total commitment of the aorta to the right ventricle This last combination produces TOF/PA, but with the ventriculoarterial connection of double-outlet ventricle Intrapericardial (Native) Pulmonary Arteries When the pulmonary valve is imperforate, the pulmonary trunk is patent to the level of the ventriculopulmonary junction (see Fig 36.2A) Even in this setting, the trunk itself may supply only one pulmonary artery, the other either having no connection with the pulmonary trunk or being completely absent In many other cases, the pulmonary trunk itself is atretic In extreme cases, it is recognizable only as a fibrous strand between the ventricular outflow tract and the pulmonary arterial confluence (see Fig 36.2C) or one of the pulmonary arteries When the right and left pulmonary arteries are present, they are usually confluent The confluence itself, usually tethered by either a patent or atretic pulmonary trunk to the ventricular mass, has the characteristic angiographic appearance of a flying seagull It can vary markedly in size, usually depending on its source of arterial supply The right and left pulmonary arteries can be nonconfluent, but one of them usually retains its connection to the remnant of the pulmonary trunk Nonconfluent pulmonary arteries can rarely be found in the absence the pulmonary trunk Each can either be supplied by one of the bilateral arterial ducts or one lung can be supplied by systemic-to-pulmonary collateral arteries with the other fed by a duct through the persisting extrapericardial pulmonary artery In the most severe examples, the entire intrapericardial arterial tree can be lacking, with supply to the lungs exclusively through systemic-to-pulmonary collateral arteries Pulmonary Arterial Supply The final common pathway of pulmonary blood supply is the capillaries associated with the air sacs of the lungs These capillaries are connected to an intrapulmonary plexus of arteries, which ramifies within the bronchopulmonary segments Different parts of the plexus can be supplied with blood from different systemic sources If all intrapulmonary arteries are connected to unobstructed and confluent intrapericardial pulmonary arteries, the confluence typically supplies all of both lungs, and the pulmonary arterial supply is said to be unifocal When different parts of one lung are supplied from more than one source, the supply is said to be multifocal.2,3 Unifocal Pulmonary Blood Supply It is usually the persistently patent arterial duct that provides unifocal pulmonary arterial supply (Fig 36.3) It is exceedingly rare for confluent pulmonary arteries feeding all of both lungs to be supplied by a solitary systemic-to-pulmonary collateral artery In rare cases, however, the confluent pulmonary arteries can be fed in unifocal fashion through an aortopulmonary window or via a fistula from the coronary arteries The pulmonary arteries can also, rarely, be fed unifocally through a persistent artery of the fifth pharyngeal arch, such as an anomalous
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