Double-inlet left ventricle
Double-inlet left ventricle (DILV) is a rare cardiac anomaly in which both the tricuspid and mitral valves enter the LV (double-inlet univentricular connection). This lesion is estimated to occur in approximately 0.05 to 0.1 per 1,000 live births68. In a recent retrospective report on 155 patients with a prenatal diagnosis of functionally univentricular hearts, the frequency of DILV in a subgroup of fetuses with dominant LV was 46.1%69. The term DILV was introduced by de la Cruz and Miller in 1968, but the earliest description is attributed to Andrew F. Holmes, who reported on a 21-year-old young man who died from severe cardiac distress70,71. His pathological findings of a cor triloculare biatriatum were reinspected and republished by M. Abbott in 190172,73.
According to its definition, a double-inlet ventricle exists when the greater part of both atrioventricular (AV) junctions is supported by a single ventricular chamber. Embryologically, a defect in the left-to-right expansion of the atrioventricular canal results in the connection of both atria to the primitive ventricle. Notably, solitary ventricles in which a second ventricular chamber is not distinguishable are exceedingly rare; more commonly, a rudimentary incomplete chamber adjacent to the dominant ventricle is found74. The commitment of both AV valves to the same ventricular chamber limits the characterization and localization of the AV valves as mitral or tricuspid valves75. In the vast majority of cases, there is ventriculoarterial discordance with a left anteriorly located ascending aorta from the RV and pulmonary trunk arising right posteriorly from the dominant LV (74%)76. Concordant ventriculoarterial connections with the aorta arising off the dominant morphologic left ventricle, whereas cases in which the pulmonary artery arises off the anterior hypoplastic right outlet chamber are considerably rare (15%; referred to as Holmes’ heart)77. According to van Praagh et al., the exact characterization of the morphology of the ventricular myocardium constitutes the most important aspect for proper identification of the underlying anatomic variant73. Semilunar valve stenosis or atresia (40%) and aortic arch abnormalities, such as coarctation and interrupted arch (12%) and AV valve abnormalities (39%)76,78, may be associated with a single LV.
Grayscale echocardiography usually shows an abnormal 4CV view with both atria being connected to a dominant left ventricle. The small underdeveloped right ventricle is occasionally seen in this cutting plane. A detailed assessment reveals smooth ventricular myocardium with fine mesh-like trabeculations corresponding to left ventricular morphology. As aforementioned, in most cases, the rudimentary outlet chamber is situated left anteriorly, and more cranial diagnostic planes are needed for proper visualization. In figure 5a, an enlarged LV and a smaller right-sided chamber with a rather coarse apical trabecular component are shown. The cardiac axis is normal (28.7°). The RV communicates with the dominant LV via a nonstenotic VSD (which is the embryologic remnant of the bulboventricular foramen), as displayed in the 4CV/5CV views. Both outlet vessels are normally arranged without hemodynamically significant flow obstruction, which is in line with the findings of a recent study on the relationship of the inflow and outflow tracts, which demonstrated no pulmonary stenosis in relation to the aorta in 72% of cases of DILV79. However, the 3VT view in the present case shows a slightly smaller main pulmonary artery. Figure 5b shows the more common anatomical arrangement of DILV with an apparent ventriculoarterial discordance. In contrast to panel a, the RV is barely seen, and the LV is the dominant chamber (fine trabeculation). The ascending aorta is anteriorly displaced and arises from the rudimentary RV (displayed in the LVOT and aortic arch views); the pulmonary artery shows severe stenosis. In fact, DILV is well toleratedin utero without important fetal consequences. The clinical presentation and postnatal management are mainly driven by the presence of associated lesions and the arrangement of great arteries. It generally involves staging toward the ultimate goal of Fontan palliation80.