cavity are well formed The tricuspid valve is similarly well formed Right, The pulmonary valve is represented by an imperforate shelf interposed between the infundibular cavity and the cavity of the pulmonary trunk In these hearts with minimal mural hypertrophy, the outlet component is patent to the undersurface of the imperforate pulmonary valve, which separates the right ventricular cavity from that of the pulmonary trunk (see Fig 43.3, right) With increasing hypertrophy of the walls and obliteration of the apical component of the ventricle, the cavity is effectively formed by the inlet and outlet components In this situation, the infundibulum still extends to the undersurface of the imperforate valve, but through a very narrow channel The inlet component also becomes hypoplastic, with the tricuspid valve tethered by short cords to the margins of the obliterated apical component All three initial parts of the morphologically right ventricle remain identifiable in the hearts with effectively bipartite ventricular cavities This remains the case when mural hypertrophy has also squeezed out the outlet of the ventricle (Fig 43.4) Individuals having hearts with the cavity effectively represented by only the grossly hypoplastic ventricular inlet (Fig 43.5) represent the most severely incapacitated patients with pulmonary atresia and intact ventricular septum FIG 43.4 Computed tomographic angiogram in a neonate with unipartite pulmonary atresia based on echocardiographic data The “squeezed-out” apical and outlet segments are seen as “tongues” of contrast extending toward the apex and imperforate pulmonary valve, respectively Inset, Branch pulmonary arteries and ductus from above The data were acquired to show morphology of the ductus arteriosus to assess the feasibility of stenting FIG 43.5 Left, The increasing mural hypertrophy has squeezed out the apical and outlet ventricular components, leaving the ventricular cavity represented only by the inlet In this setting (right), the base of the pulmonary trunk is represented by the triradiating remnants of the valvar sinuses, with no remaining evidence of the valvar leaflets When the outlet component is also obliterated, it is not possible to trace a patent infundibulum to the ventriculoarterial junction, although evidence of the channel initially present can be seen within the ventricle (see Fig 43.5, left) When examined from the arterial aspect, it can be seen that the pulmonary trunk retains its origin from the RV (see Fig 43.5, right) so that the ventriculoarterial connections remain effectively concordant The blind-ending pulmonary trunk originates above the triradiating sinuses, with the central dimple indicating that they did, initially, support valvar leaflets The tricuspid valve is grossly hypoplastic in the hearts in which the cavity of the RV is represented essentially by only the inlet component, but the leaflets themselves are usually minimally malformed Because of this, the hypertrophied myocardium is able to generate suprasystemic ventricular pressures Hearts of this type are typically associated with abnormalities of the coronary arteries In the most severe cases, the proximal portions of both coronary arteries can be obliterated, with the entirety of the coronary arterial tree fed through fistulous communications from the RV.41 In less severe instances, interruptions are still found in the origin or course of either the right or the left coronary arteries (Fig 43.6) FIG 43.6 Left, Magnification of the base of the heart in a patient having an effectively unipartite ventricular cavity The right coronary artery (RCA) is atretic at its origin from the aorta The territory of the anterior interventricular artery is fed primarily from the right ventricle by two prominent and ectatic fistulous communications The pulmonary trunk is also grossly hypoplastic Right, A second heart with a fistulous communication again feeding the anterior interventricular artery, which is ectatic A significant portion of the coronary arterial supply in such instances will again be provided by fistulous communications from the RV, underscoring the so-called right ventricular–dependent coronary arterial circulation, which creates major problems in treatment.2 Therefore fistulous communications are the key to diagnosis of the state of the coronary arterial tree It is rare to find such communications except when there is gross mural hypertrophy and a poorly formed cavity This makes recognition of obliteration of the infundibulum an important diagnostic feature when seeking to determine the best options for treatment