Andersons pediatric cardiology 1811

FIG 69.13 Effects of the fistulous communications between the cavity of the right ventricle and the coronary arteries, which are a feature of patients with the functionally univentricular variant of pulmonary atresia and intact ventricular septum Left, Mural hypertrophy has squeezed out the apical and outlet ventricular components A fistulous communication has produced ectasia of the anterior interventricular coronary artery (right) Atrioventricular Valvar Atresia The variations in morphology encountered in the setting of pulmonary atresia with an intact ventricular septum served to demonstrate how hearts with comparable segmental connections can be functionally univentricular or functionally biventricular depending on the size of the ventricular cavity and the morphology of the ventricular outflow tract Hearts having atrioventricular valvar atresia, in contrast, will always be functionally univentricular The functionally univentricular arrangement can be found in the setting of either univentricular or biventricular atrioventricular connections This anatomic heterogeneity is further complicated by the possibilities regarding ventricular topology and ventriculoarterial connections The space available here precludes the possibility of illustrating all the potential combinations It was patients with atrioventricular valvar atresia, specifically tricuspid atresia, that were the first individuals to be converted to the Fontan circulation At that early stage, it was believed that pulsatile flow would be an advantage in the pulmonary circuit, so valves were placed at the venoatrial junctions Attempts were made to include the right ventricle in the circulation It is now accepted that the best surgical results are obtained by excluding the right ventricle, or a second hypoplastic ventricle, from the pulmonary circuit At the time of the initial experiences, it was generally believed that atrioventricular valvar atresia was produced by an imperforate atrioventricular valve Such an anatomic variant can be found (Fig 69.14, left) but is rare When present, it is usually in the setting of pulmonary atresia with intact ventricular septum or an imperforate Ebstein malformation The substrate for the commonest variant of tricuspid atresia, however, is absence of the right atrioventricular connection (Fig 69.14, right) Mitral atresia can also be produced by an imperforate atrioventricular valve (Fig 69.15A) or by absence of the left atrioventricular connection (Fig 69.15B) Problems are sometimes encountered in describing the arrangement as “mitral” or “tricuspid” atresia In the hearts shown in Fig 69.15, the right atrium is connected to the morphologically right ventricle; this ventricle is dominant in the heart shown, with absence of the left atrioventricular connection The left atrioventricular connection can also be absent when the right atrium is connected to a dominant left ventricle In the latter situation, the incomplete right ventricle is usually carried on the anterior and left-sided shoulder of the dominant left ventricle In such circumstances, had the left atrioventricular connection been formed, it would likely have been guarded by a tricuspid valve A case can be made, therefore, for describing the entity as “tricuspid atresia,” despite the fact that the left atrium is blind-ending in this setting, as it is in typical mitral atresia produced by absence of the left atrioventricular connection (see Fig 69.15B) Irrespective of the nature of the valve that might have been present, it is the arrangement of the pulmonary venous connections and the atrial septum that largely determines the clinical presentation For these reasons we prefer to distinguish the variants by describing absence of the left atrioventricular connection and specifying the ventricular morphology, thus removing any potential ambiguity When the valvar atresia is the consequence of absence of the left- or right-sided atrioventricular connection, the muscular floor of the atrial chamber is blind-ending It is separated from the ventricular mass by the fibroadipose tissue of the atrioventricular groove (see Fig 69.14, right) It used to be thought that the dimple seen in the floor of the blind-ending atrium (see Figs 69.4 and 69.16) represented the atretic atrioventricular valve As shown in Fig 69.4, in classic tricuspid atresia the dimple overlies the atrioventricular component of the membranous septum Perforating the floor at the site of the dimple produces a communication with the dominant left ventricle and not the incomplete right ventricle In the usual form of tricuspid atresia, the right ventricle is incomplete because it lacks its inlet component Clinical presentation in all forms of atrioventricular valvar atresia is influenced significantly by the ventriculoarterial connections and the size of the ventricular septal defect, which is almost always part of the lesion In tricuspid atresia, the ventriculoarterial connections are usually concordant The incomplete right ventricle has a long infundibulum supporting the pulmonary trunk, which spirals around the aorta as it extends into the mediastinum In a minority of cases, the ventriculoarterial connections are discordant The arterial trunks are usually parallel as they move away from the ventricular mass Parallel arterial trunks can rarely be found when the ventriculoarterial connections are concordant, with this combination sometimes being described as anatomically corrected malposition It is better to consider the arrangement in terms of concordant ventriculoarterial connections with parallel arterial trunks It is also possible to find a double outlet from either the dominant left ventricle or the incomplete left ventricle Rare cases have been described with a common arterial trunk Pulmonary atresia is also a possibility When the ventricular septal defect is restrictive and the ventriculoarterial connections are discordant, it is also usual to find either aortic coarctation, or interruption of the aortic arch These features are also to be anticipated when