Morphology By definition, the unifying morphologic abnormality is complete obstruction of the outflow from the morphologically right ventricle in the presence of an intact ventricular septum The cavity of the RV is usually hypoplastic, but it can be grossly dilated when the tricuspid valve is incompetent or its leaflets are absent, giving the “wall-to-wall” heart.1 This latter lesion, therefore, can be considered a variant of pulmonary atresia with intact ventricular septum, indeed one of its most lethal forms It is certainly one of the most difficult to treat This form of the lesion is discussed in this chapter, even though the cavity of the RV is dilated, along with the tricuspid valvar orifice In this regard, there had been a vogue for considering the right ventricular cavity as either small or large.33 Recognition of the degree of cavitary hypoplasia produced by mural hypertrophy is now accepted as the best way of assessing the severity of the malformation,34,35 while accepting that some individuals have dilation of the RV, and that patients showing the latter features tend to have a very poor prognosis (Fig 43.2) The lesion is a global condition affecting the entirety of the RV.36–38 The extent of morphologic heterogeneity is illustrated by the frequency in which each anatomic feature occurs within the United Kingdom and Ireland population-based study (Table 43.1).39 FIG 43.2 Variation in size of the cavity of the right ventricle in the setting of pulmonary atresia with intact ventricular septum assessed relative to the size of the left ventricle in the same heart, and compared to similar measurements in normal hearts The majority of hearts have hypoplastic cavities, with the upper end of these overlapping the spectrum of normality Those with dilated cavities are outliers from the spectrum Table 43.1 Principal Morphologic Findings of a UK/Ireland Population-Based Study (1991–1995) Morphologic Feature Type of pulmonary atresia Type Membranous Muscular Partite state of the RV Tripartite Bipartite Unipartite Coronary arterial abnormalities RV-to-coronary fistulas Coronary arterial stenoses, interruption and ectasia Ebstein malformation Significant RV dilatation Size of tricuspid valve Median z-score: echocardiograma Median z-score: autopsyb Size of RV inlet Median z scorea N (%) 130/174 (74.7) 44/174 (25.3) 84/143 (58.7) 48/143 (33.6) 11/143 (7.7) 60/132 (45.5) 10/132 (7.6) 18/183 (9.8) 8/183 (4.4) −5.2 (range, −18.3 to 9.4) −1.6 (range, −2.9 to −0.4) −5.1 (range, −16.0 to 3.5) az-Scores calculated from echocardiographically derived normal values,7 rather than bpostmortem-derived normal values.77 In all, 15 abnormalities of the left ventricle were documented, including four with extreme septal hypertrophy with bulging into the left ventricular outflow RV, Right ventricle From Daubeney PE, Delany DJ, Anderson RH, et al Pulmonary atresia with intact ventricular septum: range of morphology in a population-based study J Am Coll Cardiol 2002;39:1670– 1679 Hypoplastic Ventricular Cavities In those with small ventricles, the cavitary hypoplasia is due to mural hypertrophy First, the thickened walls squeeze out the apical trabecular component of the ventricle Then, with ongoing hypertrophy, the outlet is obliterated Eventually, therefore, the inlet is the only effective cavity in those with the smallest RVs.36 If describing this spectrum in terms of “unipartite” and “bipartite” ventricles, it should be remembered that all three ventricular components are present in all cases The key to appropriate interpretation is recognition that the increasing muscular hypertrophy squeezes out the different parts of the RV cavity.40 In those with the least severely affected hearts, therefore, all three parts of the ventricular cavity are well formed, with minimal mural hypertrophy (Fig 43.3) FIG 43.3 Left, Heart with the parietal wall of the right ventricle removed; the pulmonary valve is imperforate, but all three parts of the ventricular