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.