Double-Inlet Ventricle The combinations described earlier for atrioventricular valvar atresia are also to be found in patients having a double-inlet ventricle, the difference being that all such patients will have univentricular atrioventricular connections A double inlet is found when both atrioventricular junctions, in their greater part, are supported by the same ventricle In the majority of cases, the ventricle will be morphologically left The incomplete right ventricle forms the second chamber within the ventricular mass (Fig 69.17) As already discussed, for many years it was thought that the second chamber was no more than an infundibular outlet chamber The septum separating the small chamber from the dominant ventricle, however, carries the atrioventricular conduction axis and is nourished by delimiting coronary arteries It separates the apical component of the dominant ventricle from an apical part of the second chamber This is the apical ventricular septum, meaning that the hole between its crest and the muscular outlet septum is a ventricular septal defect (see Fig 69.17) The incomplete right ventricle is always carried on the anterosuperior shoulder of the dominant left ventricle It is most usually left-sided but can be right-sided or directly anterior In most instances, it supports the aorta, with the pulmonary trunk arising from the dominant left ventricle; in other words, there are discordant ventriculoarterial connections, or transposition In this setting, the outlet component of the ventricle is short In a minority of cases, the ventriculoarterial connections can be concordant When this is associated with spiraling of the pulmonary trunk relative to the aorta, the arrangement is known as the Holmes heart The incomplete right ventricle is virtually indistinguishable from the comparable chamber as seen in classical tricuspid atresia (see Fig 69.2) In even rarer circumstances, the arterial trunks can be parallel when the ventriculoarterial connections are concordant This is the arrangement known as an anatomically corrected malposition; it has also been described as isolated ventricular discordance As stated earlier, in considering the arrangement found with atrioventricular valvar atresia, it is better simply to describe the situation as concordant ventriculoarterial connections with parallel arterial trunks In other situations, both arterial trunks can arise either from the dominant or the incomplete ventricle Pulmonary atresia can also be found As with tricuspid atresia, narrowing of the ventricular septal defect is associated with coarctation or interruption of the aortic arch when the ventriculoarterial connections are discordant Such narrowing of the ventricular septal defect would obviously produce subpulmonary obstruction should the ventriculoarterial connections be concordant FIG 69.17 Characteristic features of double-inlet left ventricle Left, Replicating the four-chamber section, both atrioventricular (AV) junctions are committed to the dominant left ventricle Right, Incomplete right ventricle, which lacks its inlet component A double inlet can also be found when both atrioventricular connections are supported by the dominant right ventricle The left ventricle is incomplete The incomplete left ventricle is always found posteroinferiorly, or “in the hip pocket,” relative to the dominant ventricle Most usually it is located in a leftsided position, but it can rarely be right-sided The atrioventricular junctions in the setting of double-inlet right ventricle are usually guarded by a common atrioventricular valve, as indeed can also be the case with double-inlet left ventricle The connection of the junctions to the same ventricle is the essence of a double inlet, and not the nature of the valves guarding them Less frequently, a double-inlet right ventricle can be found with separate right and left atrioventricular valves (Fig 69.18) In the setting of double-inlet right ventricle, both arterial trunks also usually arise from the dominant ventricle, although it is possible to find concordant ventriculoarterial connections The combination with a common atrioventricular valve is particularly frequent in the setting of right isomerism A double-inlet ventricle can rarely be found when there is a solitary chamber within the ventricular mass (see Fig 69.1) In such settings, the ventricle has particularly coarse apical trabeculations It may be difficult, in the clinical setting, to make the distinction from double-inlet right ventricle In the latter setting, the incomplete left ventricle is often no more than a slit in the posteroinferior ventricular wall The solitary ventricle can also be confused with a huge ventricular septal defect An apical ridge, however, will separate the apical components, with the right ventricular apex having coarse trabeculations and the left ventricular apex having fine trabeculations Such patients with huge ventricular septal defects should be amenable to biventricular surgical repair Crossing of the tension apparatus of the atrioventricular valves coupled with the coarse apical trabeculations is usually sufficient to rule out the options for biventricular repair when the ventricle is of solitary and indeterminate morphology (see Fig 69.1) The conduction axis is also frequently bizarre in the setting of the solitary ventricle, particularly when associated with right isomerism FIG 69.18 Two hearts with double-inlet right ventricle (RV) sectioned in the four-chamber plane As can be seen, both atria connect to the dominant RV irrespective of whether the atrioventricular junctions are guarded by two separate atrioventricular valves (A) or a common