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.