Double outlet right ventricle
Double outlet right ventricle (DORV) refers to a complex diagnostic
entity that commonly occurs as part of a range of heterogeneous cardiac
defects. Although early reports date back to the 18th century, the first
detailed descriptions of the clinical appearance of a large range of
anatomical variations were written later66. In 1949,
Taussig and Bing reported on a case of a transposed aorta and pulmonary
trunk that both originated from the right ventricle67.
Subsequently, this anomaly and accompanying defects have been further
characterized with the spatial relationship of the VSD to the semilunar
valves of the great arteries and the presence and extension of the
outflow tract obstruction, building the morphological basis for the most
widely used clinical classification68-72.
Embryologically, DORV is supposed to represent a relatively primitive
cardiac condition with failed conotruncal rotation and a leftward shift
of either the aortic or pulmonary conus. The precise mechanisms by which
specific genetic lesions or teratogenic exposures result in
maldevelopment from normal anatomy to DORV phenotypes remain unknown and
may underscore etiologic heterogeneity. Although DORV constitutes a
conotruncal anomaly estimated to occur in 0.03-0.07 of 1,000 live
births, this spectrum of anomalies is committed to the RV, and its
physiology and will be discussed below. Notably, the frequency of double
outlet left ventricle (DOLV) seems to be significantly lower than that
of DORV. As a conotruncal anomaly, it is described to have similar
anatomic features to those observed in DORV; these include features of a
variety of entities ranging from a simple large VSD to TOF and complete
TGA.
According to the consensus definition made by the Congenital Heart
Surgery Nomenclature and Database Project, four major anatomic types
have been proposed that merely rely on the relationship of the ascending
aorta to the pulmonary artery (PA) at the level of the semilunar
valves71. These types include (1) right lateral aorta
to the PA as the most common condition in DORV (side-by-side
relationship); (2) right anterior aorta (d-transposition type); (3)
right posterior aorta (ToF type); and (4) left anterior aorta
(l-transposition type). With respect to the location of the VSD
(subaortic as the most frequent type followed by subpulmonary, doubly
committed or noncommitted) and given that there is AV concordance, up to
16 variations of DORV may be found. Even more variants of DORV are
possible in case of situs ambiguous and/or an intact interventricular
septum. However, from a surgical perspective, based on the clinical
presentation, a functional classification scheme has been introduced
that considers four general types of DORV – VSD-type (DORV with
normally arranged vessels and a subaortic or doubly committed VSD);Fallot-type (DORV with a subaortic or doubly committed VSD and
RVOTO); TGA-type (Taussig-Bing, DORV with a subpulmonary VSD but
usually no RVOTO); and noncommitted VSD-type (DORV with a remote
VSD and possible RVOTO). Recently, a fifth type referred to asAVSD-type (DORV with AVSD/heterotaxy) has been
proposed73. In a recent series by Gottschalk et al.,
the accuracy of prenatal diagnosis taking into account all the anatomic
details of DORV was 92 %, which was in line with previous
studies74-76. In their study, all fetuses had
additional cardiac anomalies, including severe RVOTO and LVOTO, HLV,
partial or total anomalous pulmonary venous connection or coronary
anomalies, which, when present, may commonly lead to an abnormal 4CV
view, as exemplified in figure 5. The frequency of extracardiac
anomalies ranges between 19 and 73 %, and additional chromosomal
defects are found in 12 to 45 % of cases in current
literature70,74-78.
A number of case series have stated that ascertaining an antenatal
diagnosis of DORV continues to be difficult given the pronounced
anatomic variability as this cardiac defect may share morphological
similarities with either tetralogy of Fallot (ToF) or transposition of
the great arteries, as stated below74,78. Moreover,
during grayscale US, the four-chamber view is usually normal, and, on
the other hand, the exact position of the accompanying VSD defining the
subtypes of DORV may be hard to characterize. Detailed anatomic
evaluation tends to be more accurate in fetuses with biventricular
anatomy than in those with single-ventricle hearts 74.
The challenge of antenatal evaluation is to elaborate the exact course,
size and relation of both great arteries and to distinguish a genuine
double outlet situation from classical ToF and or TGA. Due to the
malposition of the great arteries, only a single vessel (typically the
aorta) may be noticed when imaging the 3VT view, while angling the US
probe can allow visualization of the parallel arrangement of both outlet
vessels (even when the aorta is right posterior to the PA). In this
regard, Zidere et al. reported on the enhancement of visualization of
cardiac anatomy using 3D reconstruction that led to the accurate
categorization of the morphological type and prediction of surgical
repair79. As illustrated in figure 6 a-d, a
standardized reconstruction of both axial and sagittal views of fetal
hearts with DORV enables a more detailed assessment of the malpositioned
vessels and gives valid inferences regarding the most likely anatomic
subset of the disease.
Although the majority of cases of misdiagnosed DORV were shown to have a
final diagnosis within the same spectrum of disease, the morphologic
subtype, irrespective of pre- or postnatal diagnosis, is a major
determinant of the outcome74,80. Notably, only a few
studies correlated their antenatal diagnostic accuracy with the
prediction of the expected postnatal surgical approach, namely, the need
for uni- or biventricular repair. According to Lacour-Gayet et al.,
intracardiac repair of DORV, in the case of two viable ventricles, can
currently be achieved in nearly all anatomical subtypes including
DORV-nc-VSD and DORV-AVSD-heterotaxy73. Nevertheless,
DORV, even without heterotaxy, is associated with complex postnatal care
and a high risk of early demise.