Leo Lopez1, Kuberan Pushparajah2, and Tal Geva3 1 Stanford University School of Medicine, Stanford, CA; Lucile Packard Children’s Hospital Stanford, Palo Alto, CA, USA 2 King’s College London; Evelina London Children’s Hospital, London, UK 3 Boston Children’s Hospital; Harvard Medical School, Boston, MA, USA Double‐outlet ventricle exists when both great arteries are aligned with the right ventricle (RV: double‐outlet right ventricle, or DORV), with the left ventricle (LV: double‐outlet left ventricle, or DOLV), or with the infundibulum (double‐outlet infundibulum). It is one type of ventriculoarterial alignment within a classification system that describes the relationship of the semilunar valves and corresponding great arteries to the underlying ventricles (see Chapter 3). Other types of ventriculoarterial alignments include: (i) concordant relationship, wherein the aorta arises from the LV and the pulmonary artery arises from the RV (normally related great arteries or anatomically corrected malposition of the great arteries); (ii) discordant relationship, wherein the aorta arises from the RV and the pulmonary artery arises from the LV (transposition of the great arteries (TGA)); and (iii) common outlet (truncus arteriosus). Because the spectrum of ventriculoarterial alignments is in fact a continuum, any classification system must involve drawing sharp borders within transition zones between “discrete” groups. As a result, some anatomic variations may straddle distinct categories at these transition zones. Nevertheless, classification is indispensable in the study of congenital heart diseases, especially in terms of defining etiology, epidemiology, prevalence, natural history, and treatment outcome. Double‐outlet right ventricle occurs when both great arteries are completely or nearly completely aligned with the RV. Although this definition appears straightforward at first glance, the approach to making the diagnosis has been fraught with controversy [1–5]. Over the past several decades, the diagnostic debate over this so‐called “morphogenetic monster” [3] has focused primarily on whether the term DORV refers to a specific morphologic entity or to a broader group of defects with the same abnormal ventriculoarterial alignment. In addition, the extent that one of the semilunar valves overrides the ventricular septal plane has contributed significantly to the confusion over this definition. Some argue that the “50% rule” should be utilized, defining the origin of a great artery from a ventricle if more than half of the semilunar valve is related to that ventricle over a ventricular septal defect (VSD) [2,3]. Many others argue that the diagnosis should be reserved for cases where the great arteries are completely or nearly completely aligned with the RV (absent or minimal override) [6–9], an approach that minimizes overlap among the ventriculoarterial alignment categories. Assigning a percentage to the degree of override can be arbitrary and imprecise, especially given the complex 3D relationship between the ventricles and great arteries, the curved geometry of the ventricular septum, and the rotational and translational motion of the heart during the cardiac and respiratory cycles. In addition, the aortic valve overrides the ventricular septum in the normal heart, and the degree of override is more pronounced in the setting of tetralogy of Fallot (TOF). Hence, the “50% rule” may classify some patients with TOF or with a VSD and normally related great arteries as DORV, an approach that by itself contributes little to the clinical tasks of choosing appropriate intervention and predicting outcome. Regardless of the debates over definitions and classification systems, however, the primary task when caring for this heterogeneous group of patients is to obtain a precise morphologic and functional description of the heart in order to formulate a rational surgical approach [10–13]. In this chapter, DORV is defined as a distinct type of ventriculoarterial alignment in which both great arteries are completely or nearly completely aligned with the RV. In 1793, Abernathy provided one of the earliest descriptions of a heart where both great arteries originated from the RV [14]. However, during the nineteenth and early twentieth centuries, any abnormal relationship between the great arteries and ventricles was often considered as some form of TGA, and DORV was frequently classified as a subtype of TGA [15–17]. In 1949, Taussig and Bing described their famous heart with “transposition of the aorta and levoposition of the pulmonary artery” [18], noted over a decade later to be a case of DORV with a subpulmonary VSD, bilateral conus (infundibulum), and side‐by‐side great arteries [1,19]. The specific term “double‐outlet right ventricle” was first introduced by Witham in 1957 [20]. Witham, however, still described DORV as a “partial transposition complex,” and it was not until 1961 when McGoon utilized the term DORV on its own [9]. The role of the subarterial conus or infundibulum (outflow tract) in TGA and DORV has long been a focus of attention [1,5,18,21–23]. Van Praagh et al. highlighted the importance of abnormal conal development in the morphogenesis of abnormal great artery relationships [24]. They argued that DORV and TOF are separate entities with mutually exclusive diagnostic criteria, an important distinction when classifying congenital heart disease and reporting outcomes [5]. Although earlier reports by Hallermann et al. [21] and by Baron [22] suggested that the presence of both subaortic and subpulmonary conus defined DORV, Van Praagh et al. recognized that not all cases of DORV had bilateral conus and emphasized that the diagnosis is based not on the conal morphology but on the ventriculoarterial alignment. In 1972, Lev et al. proposed a classification system for DORV based on the anatomic position of the VSD relative to the great arteries, a system that is still widely used today [25]. In 1973, Kirklin et al. used the percentage by which a semilunar valve is related to each ventricle over a VSD to determine the ventriculoarterial alignment in cases of anatomically corrected malposition of the great arteries with a VSD [26]. Anderson et al. subsequently proposed the “50% rule” in an effort to synthesize a nomenclature for the various ventriculoarterial connections [2,3,27]. In 2000, the Congenital Heart Surgery Nomenclature and Database Committee of the Society of Thoracic Surgeons defined DORV as “a type of ventriculo‐arterial connection in which both great vessels arise either entirely or predominantly from the RV,” a deliberately broad definition allowing for individual interpretation of how a great artery arises “predominantly” from the RV [28]. Double‐outlet right ventricle is an uncommon congenital heart disease with an estimated incidence of 12.7 per 100,000 live births, based on an analysis of 16 published articles spanning many decades [29]. However, the reported incidence per 100,000 live births has varied widely in individual reports: 3.2 in the New England Regional Infant Cardiac Program (1968–1974) [30]; 5.6 in the Baltimore‐Washington Infant Study (1981–1982) [31]; 14.5 in the Alberta Heritage Pediatric Cardiology Program (1981–1984) [32]; and 22 in the Metropolitan Atlanta Congenital Defects Program (1995–1997) [33]. Among all the congenital heart lesions in the Baltimore‐Washington Infant Study, DORV ranks twelfth in frequency, representing 2% of all the cases [34]. Among all the cardiac diagnoses made at Children’s Hospital Boston from 1988 to 2002, DORV ranks sixteenth in frequency [35]. These differences may in part be due to how DORV is defined in each study. The etiology of DORV is not known and most cases are sporadic. A small number of familial cases have been reported [36]. A recent study of published case reports, epidemiologic analyses, and animal studies of DORV revealed distinct pathogenetic mechanisms associated with DORV [37]. Chromosomal abnormalities were present in up to 41% of the cases, mostly trisomies 13 and 18, and a significant percentage of these patients had hypoplasia of left heart structures in association with DORV. Population‐based studies, including the Baltimore‐Washington Infant Study, revealed a lower prevalence of associated chromosomal abnormalities (12%) [34,38,39]. Although frequently associated with other conotruncal anomalies, chromosome 22q11 deletion occurs rarely with DORV [37,40]. Examples of mutations that have been described in association with the DORV phenotype in humans and animals include genes related to the neural crest (NF‐1, Pax‐3, RXRα) [41–44], genes controlling laterality (CFC1, Pitx2) [45, 46], genes controlling transcriptional factors (GATA4, Nkx2.5, ZFPM2/FOG2) [47–51], genes controlling cell proliferation and transformation from endothelial to mesenchymal cells (TGF‐β2) [52], genes controlling cell‐to‐cell communication (Cx40) [53], and genes controlling outflow tract myocardialization (ECE‐1, ECE‐2) [54] and polarization (Vangl2 in the Lp mutant mouse) [55,56]. The large number and heterogeneity of genetic defects associated with DORV suggest that multiple developmental abnormalities may result in this phenotype. In addition, DORV has been produced in several experimental models, including surgical ligature of the chick embryonic conus to prevent its incorporation onto the LV after conal division [57], and surgical ablation of “cardiac” neural crest cells in the chick embryo [58]. Finally, several maternal risk factors have been associated with the development of DORV, including nongestational diabetes [59], assisted reproductive technology [60], exposure to solvents [36], and prenatal use of codeine [61], retinoic acid [62], and theophylline [63]. Knowledge of the normal development of the ventricular outflow tracts helps to elucidate some of the factors involved in the morphogenesis of DORV. A comprehensive review of cardiac embryology is beyond the scope of this chapter and can be found elsewhere [64–71]. At the conclusion of cardiac looping, the conotruncus relates exclusively to the developing RV. Shortly thereafter, pairs of internal ridges or cushions develop along the proximal and distal outflow tracts in a spiraling orientation. This is followed by migration of mesenchymal cells from the pharyngeal pouches into the distal outflow tract walls, contributing to their transformation from myocardial tissue to arterial tissue. At approximately the same time, there is also migration of cells derived from the neural crest into the developing cushions located in the distal segment of the conus and in the truncus arteriosus. The cushions with their neural crest‐derived cells begin to fuse distally within the truncus arteriosus, separating the future proximal aorta from the future pulmonary artery. The arterial valve leaflets and sinuses also evolve from the developing cushions at the base of the truncus arteriosus. The proximal (conal) cushions now begin to fuse, separating the subpulmonary outflow tract from the subaortic outflow tract, both of which are still committed to the developing RV. At around the same time, the endocardial cushion and muscular ventricular septum develop within the primordial ventricle. The fused proximal cushions eventually merge with the muscular ventricular septum, committing the pulmonary valve and artery to the RV, and the aortic valve and aorta to the LV. The subaortic outflow tract or conus is still present at this time, and its regression with consequent fibrous continuity between the mitral and aortic valves does not occur until approximately 12 weeks of gestation. Although the exact mechanisms of morphogenesis in humans is unknown at this time, studies suggest that DORV can result from abnormalities in genetic and environmental signals for differentiation, proliferation, and migration of cardiogenic cells in the primary and secondary heart fields as well as neural crest‐derived cells. As discussed previously, the marked heterogeneity that characterizes DORV morphology strongly suggests that several developmental mechanisms are involved. Developmental arrest at the embryonic stage when the conotruncus relates exclusively to the RV, disruption in the development of the proximal cushions, and abnormal ventricular development (such as hypoplasia and malposition) with or without abnormal conus are some of the proposed mechanisms. Given the morphologic and physiologic diversity of DORV, the following anatomic features are crucial in understanding each case and determining the optimal interventional approach: Description of the VSD location, especially in terms of its spatial relationship to the great arteries, has long been recognized as a clinically useful classification system for DORV [8,25,72–74]. When present, the VSD may fall into one of four geographic categories [5,12,13,73,75–79]: subaortic, subpulmonary, doubly committed, or noncommitted (remote) VSD. It is important to recognize that the VSD in most cases of DORV is located between the anterosuperior and posteroinferior limbs of the septal band and is considered a malalignment defect. The only exceptions are cases with noncommitted (remote) VSD that are either inlet or muscular defects. The spatial relationship of the VSD to the semilunar valves is dictated by the presence, size, and position of the subarterial conus and by deficiency of the adjacent septal segments such as the conal septum and AV canal septum. The size of the VSD, the distance from the VSD to the semilunar valves, and the presence of AV valve attachments along the VSD margins to the conal septum or within the defect are important variables when planning surgical repair. Occasionally, there are multiple VSDs [12], and rarely, the ventricular septum is intact [73,80,81]. It worth noting that in contrast to hearts with concordant or discordant ventriculoarterial alignments where the conal septum usually represents the superior border of a conoventricular septal defect, in hearts with DORV the conal septum is a purely RV structure that does not contribute to the VSD margins. Thus, biventricular repair of DORV involves a baffle from the VSD to the closest semilunar root as opposed to simple patch closure of a VSD. The course of the conduction system relative to the VSD is an important consideration for biventricular repair of DORV, especially when enlargement of the defect is required to ensure an unobstructed pathway from the LV to the aortic valve. Subaortic VSD (42 –57% of cases): The defect is cradled between the limbs of the septal band below the aortic valve. The posteroinferior margin may be in fibrous continuity with the tricuspid valve (confluent with the membranous septum), or it may consist of muscular extension of the posterior limb of the septal band [27,82]. This type of defect is termed malalignment VSD or conoventricular septal defect because the conal septum is misaligned with the underlying muscular septum. In DORV with D‐malposition of the great arteries (aorta to the right of the pulmonary artery), the conal septum is rotated out of the plane of the ventricular septum and attaches to the anterosuperior limb of the septal band (Figure 26.1) [82]. Pulmonary outflow tract obstruction is often present, and its severity is determined by the degree of anterior and leftward deviation of the conal septum and by associated pulmonary valve stenosis (Figure 26.2, Video 26.1). In DORV with L‐malposition of the great arteries (aorta to the left of the pulmonary artery), the subaortic VSD is situated more anteriorly and superiorly within the limbs of the septal band [83]. Figure 26.1 Double‐outlet right ventricle with a subaortic ventricular septal defect (VSD) where the conal septum (CS) is attached to the anterosuperior limb of the septal band (SB). (a) Diagram. (b) Pathology specimen. (c) Modified subxiphoid short‐axis view. (d) 3D echocardiographic view from the right ventricular aspect demonstrating the same anatomy. The septal band is marked with a dashed line. Ao, aorta; LV, left ventricle; PA, pulmonary artery; RV, right ventricle; TV, tricuspid valve. Figure 26.2 Double‐outlet right ventricle with a subaortic ventricular septal defect (VSD) and pulmonary stenosis (TOF type) secondary to a significant anterior attachment of the conal septum (CS) to the anterosuperior limb of the septal band (SB). (a) Diagram. (b) Pathology specimen. (c) Modified subxiphoid long‐axis view (right axial oblique view) where the star represents the conal septum. Ao, aorta; PA, pulmonary artery; RA, right atrium; RV, right ventricle; TV, tricuspid valve. Subpulmonary VSD (24–37% of cases): The defect is also cradled between the limbs of septal band. However, the conal septum is rotated out of the plane of the ventricular septum and attaches to the more posteriorly located ventriculoinfundibular fold rather than to the anterosuperior limb of the septal band (Figure 26.3, Video 26.2 and 26.3) [82]. As a result, the conal septum shields the aortic valve from the defect with only a short distance from the defect to the pulmonary valve. In 60% of cases, the posteroinferior margin of the defect is in fibrous continuity with the AV valves (confluent with the membranous septum); a muscular inferior border occurs in the other 40% [75]. The subaortic conus is usually well developed, and the aortic valve is rightward relative to the pulmonary valve with either a side‐by‐side or slightly anterior position. The subpulmonary conus varies in size. In some cases, the subpulmonary conus is incomplete, allowing fibrous continuity between the pulmonary and tricuspid and/or mitral valves. The distinction between DORV and TGA in this scenario is dictated by the alignment between the pulmonary valve and the underlying ventricles: DORV is present when the pulmonary valve relates nearly exclusively to the RV, and TGA is present when the pulmonary valve relates nearly exclusively to the LV. Categorization of intermediate cases is challenging and one can describe such cases as having biventricular origin of the pulmonary artery. Figure 26.3 Double‐outlet right ventricle with a subpulmonary ventricular septal defect (VSD) where the conal septum (CS) is attached to the right ventriculo.infundibular fold. (a) Diagram. (b) Pathology specimen. (c) Subxiphoid long‐axis view. (d) 3D transthoracic subxiphoid echocardiographic view of from the right ventricular aspect demonstrating the same anatomy. Ao, aorta; LV, left ventricle; PA, pulmonary artery; RV, right ventricle; SB, septal band; TV, tricuspid valve. Although many consider DORV with a subpulmonary VSD synonymous with the Taussig–Bing anomaly, it worth noting that the original heart described by Taussig and Bing was a distinct anatomic entity in that it had DORV with a subpulmonary VSD, bilateral conus, and side‐by‐side great arteries [18]. In patients with this anatomy, hypertrophy and rightward deviation of the conal septum as well as hypertrophy of the subaortic conal free wall can result in varying degrees of subaortic stenosis, which in turn is associated with coarctation of the aorta or aortic arch interruption. In addition, the mitral valve may straddle the VSD with attachments to the subpulmonary conus in approximately 20% of cases. Doubly committed VSD (3–12% of cases): As a result of absent or markedly deficient conal septum, the VSD is in close proximity or even contiguous with both semilunar valves (Figure 26.4, Video 26.4). The VSD is located superiorly and is often large. The semilunar valves represent the anterosuperior margin of the defect and the aortic valve and pulmonary valve are in fibrous continuity. Because the VSD is cradled between the limbs of the septal band, this part of the septal band along with the right ventriculoinfundibular fold form the entire posteroinferior margin of the defect; occasionally, however, the defect extends into the fibrous area of the membranous septum. Infrequently, these defects are sometimes associated with pulmonary or aortic outflow tract obstruction (Figure 26.4) [84]. There is also a rare form of DORV with doubly committed VSD in which the conal septum is perpendicular to the large VSD with the aorta and pulmonary artery in an anteroposterior relationship. Thus, both great arteries straddle the VSD. Figure 26.4 Double‐outlet right ventricle with a doubly committed ventricular septal defect (VSD) and absent conal septum. (a) Diagram. (b) Pathology specimen. (c) Subxiphoid long‐axis view showing pulmonary stenosis. Ao, aorta; LV, left ventricle; PA, pulmonary artery; RV, right ventricle; SB, septal band; TV, tricuspid valve. Noncommitted (remote) VSD (9–19% of cases): The defect is not cradled between the limbs of the septal band and is thereby considered noncommitted or remote because of the distance from the semilunar valves (Figure 26.5, Video 26.5). The defect can be located in the AV canal (inlet) septum, along the posterior aspect of the membranous septum, or within the muscular septum. It is important to recognize that some subaortic and subpulmonary VSDs cradled between the limbs of the septal band may appear remote because of elongated subarterial conus [82]. Figure 26.5 Double‐outlet right ventricle with a remote ventricular septal defect (VSD). (a) Diagram. (b) Pathology specimen. (c) Modified subxiphoid short‐axis view showing the relationship of the great arteries to the VSD. (d) 3D transthoracic echocardiographic image from the right ventricular aspect illustrating the position of the VSD in relation to the great arteries. Ao, aorta; CS, conal septum; LV, left ventricle; PA, pulmonary artery; RV, right ventricle; SB, septal band; TV, tricuspid valve. Conal morphology is important in the comprehensive description of DORV cases, but it is important to note that it is not a determining factor in the definition of DORV [10,85]. Many configurations of conal morphology occur in DORV cases (Figure 26.6), including bilateral conus, subpulmonary conus with absent subaortic conus, subaortic conus with absent subpulmonary conus, or bilaterally absent conus. Van Praagh et al. [5,24] as well as Kirklin [78] have suggested that conal morphology is the primary determinant of the various patterns of great artery relationships seen in DORV. Moreover, subarterial conus tends to move a great artery anteriorly and more distant from the AV valves. This view, however, has not been endorsed unanimously [10,86]. Other classification schemes of conal anatomy have been proposed as well [87]. Figure 26.6 Diagrams depicting the four types of conal morphology: (a) bilateral conus, (b) absent subaortic conus, (c) absent subpulmonary conus, and (d) bilaterally absent conus. Ao, aorta; CS, conal septum; MV, mitral valve; PA, pulmonary artery; TV, tricuspid valve. An important aspect of the description of conal morphology is the distance from the VSD to each semilunar valve. This is particularly relevant in the setting of bilateral conus where surgical repair involves a baffle from the LV through the VSD to the nearest semilunar valve (Figure 26.7, Video 26.6). This distance has been shown to be predictive of adverse postoperative events such as residual LV outflow tract obstruction and death [88]. In patients with DORV and subaortic VSD, as the size of the subaortic conus increases, the distance from the tricuspid valve to the aortic valve increases and the distance from the tricuspid valve to the pulmonary valve decreases. Because the pathway from the LV to the aortic valve usually passes between the tricuspid and pulmonary valves, this distance is important in determining the feasibility of intraventricular baffling (Figure 26.8) [10,11,89]. Another important consideration in planning surgical repair is the morphology of the conal septum within the RV. The conal septum may be prominent with significant AV valve attachments, potentially hindering the course of an intraventricular baffle from the VSD to the closest semilunar valve. These attachments may also be problematic in cases where the semilunar valve adjacent to the VSD is hypoplastic and/or stenotic, and biventricular repair would require baffling from the VSD to the distant semilunar valve and resection of the conal septum. The conal septum may also deviate into one or the other subarterial outflow tract, resulting in subaortic or subpulmonary stenosis. In DORV with pulmonary outflow tract obstruction, this deviation may or may not be associated with subpulmonary conal hypoplasia (see Figure 26.2). Often there is also pulmonary valve involvement with hypoplasia of the pulmonary annulus and pulmonary artery as seen in TOF. In DORV with a subpulmonary VSD, the conal septum occasionally deviates into the subaortic region resulting in subaortic stenosis, coarctation, or aortic arch interruption (Figure 26.9). Figure 26.7 Double‐outlet right ventricle with bilateral conus (represented by the stars). (a) Pathology specimen. (b) Subxiphoid 3D transthoracic echocardiogram. Ao, aorta; CS, conal septum; PA, pulmonary artery; VSD, ventricular septal defect; RV, right ventricle. Figure 26.8 Diagram demonstrating how the distance from the tricuspid valve (TV) to the pulmonary valve (PV) can affect the potential baffle pathway from the left ventricle to the aorta. AoV, aortic valve; VSD, ventricular septal defect. Figure 26.9 Double‐outlet right ventricle with a subpulmonary ventricular septal defect, narrow subaortic region, and coarctation of the aorta. (a) Subxiphoid long‐axis view (the star represents the conal septum). (b) Suprasternal view. Ao, aorta; DAo, descending aorta; LCCA, left common carotid artery; LV, left ventricle; PA, pulmonary artery; PDA, patent ductus arteriosus; RV, right ventricle. The spatial relationships between the semilunar valves and their corresponding proximal great arteries vary markedly. Common examples include side‐by‐side great arteries with either D‐ or L‐malposition of the aortic valve relative to the pulmonary valve, posterior and rightward aortic valve relative to the pulmonary valve (as in normally related great arteries), anterior and rightward aortic valve (D‐malposition), aortic valve directly anterior to the pulmonary valve (A‐malposition), posterior and leftward aortic valve (as in situs inversus totalis), or anterior and leftward aortic valve (L‐malposition). The spatial orientation of the great arteries relative to each other can be crossed (as in normally related great arteries) or parallel. In the most common variant of DORV with subaortic VSD, the aorta is often rightward and either slightly posterior or side by side relative to the main pulmonary artery although the great arteries are often normally related to each other, similar to TOF. In DORV with subpulmonary VSD, the great arteries are generally side by side and parallel in their relationship, but the aorta can also be anterior and rightward relative to the pulmonary artery at the base of the heart (similar to typical D‐loop TGA). Notably, the spatial relationship of the great arteries does not always predict the VSD location [78] or the conal morphology [10]. Outflow tract obstruction occurs in up to 70% of DORV cases [12,13,75,78,90]. This usually requires some modification to surgical management. The most common variant involves pulmonary outflow tract obstruction at the subvalvar and/or valvar level, often seen in DORV with a subaortic VSD (see Figure 26.2). Subpulmonary stenosis results from similar anatomic abnormalities seen in TOF: leftward, anterior, and superior deviation of the conal septum relative to the muscular septum, and hypertrophy of the conal free wall. In these cases, the subpulmonary conus is hypoplastic, usually with significant obstruction. In the most severe cases, there is pulmonary atresia. Although the term DORV with pulmonary atresia can be problematic, the pulmonary trunk in most cases is clearly anchored to the RV such that the absence of luminal continuity does not preclude determination of spatial alignment between the RV and the pulmonary trunk (Figure 26.10, Video 26.7). If the pulmonary artery segment is difficult to identify, the anatomy can be labeled as right ventricular origin of the aorta with pulmonary atresia. Subaortic stenosis and/or aortic arch obstruction (coarctation or aortic arch interruption) can occur in up to 50% of DORV cases with a subpulmonary VSD (Figure 26.9) [87,91,92]. In these cases, subaortic stenosis usually results from muscular narrowing produced by the conal septum (which is deviated to the right), a hypertrophied right ventriculoinfundibular fold, and the RV conal anterior free wall. Figure 26.10 Double‐outlet right ventricle with membranous pulmonary atresia from a severely deviated conal septum shown in an apical view. Note the large ventricular septal defect. Ao, aorta; LV, left ventricle; PA, pulmonary artery; RV, right ventricle. Atrioventricular valve anomalies, including a common AV valve in the setting of an AV canal defect, occur in up to 35% of DORV cases (Figure 26.11, Video 26.8) [75,90]. Anomalies of the mitral valve in DORV can pose a challenge for surgical repair [13,77,93]. In particular, a straddling mitral valve, which can occur in up to 20% of DORV cases with a subpulmonary VSD (Figure 26.12, Video 26.9) [75,92,94], may complicate a biventricular repair by causing subaortic obstruction or significant mitral regurgitation [95,96]. However, recent advances in surgical technique have allowed biventricular reconstruction in patients with straddling mitral valve as long as the size and function of the LV are adequate to support cardiac output [97,98]. Parachute mitral valve, annuloleaflet ring, mitral valve hypoplasia, and typical forms of mitral stenosis can also influence the surgical approach and may affect long‐term prognosis. DORV with mitral atresia is a rare association that requires single ventricle palliation. A straddling tricuspid valve can also occur in DORV with an inlet or AV canal‐type VSD. Rarely, the AV valves are situated in a crisscross orientation, resulting in a complex relationship between the VSD and the great arteries (Figure 26.13, Video 26.10). AV valve abnormalities in DORV can also be seen in the setting of ventricular inversion {S,L,L} (Figure 26.14, Video 26.11) Figure 26.11 Double‐outlet right ventricle in the setting of a complete atrioventricular (AV) canal defect with a common AV valve as seen on 3D TEE. The image is cropped and viewed from the ventricular apex to the base of the heart. The position of the interventricular septum is marked by the dashed line. Both great arteries are clearly arising from the right ventricle (RV). Ao, aorta; LV, left ventricle; PA, pulmonary artery. Figure 26.12 Double‐outlet right ventricle with a subpulmonary ventricular septal defect and straddling mitral valve (MV). (a) Pathology specimen showing the attachment of the MV to the right ventricle (RV, asterisk); the aorta is located behind the conal septum (CS). (b) Subxiphoid short‐axis view. (c) 3D transthoracic echocardiogram. Ao, aorta; LV, left ventricle; PA, pulmonary artery. Figure 26.13 Double‐outlet right ventricle with crisscross atrioventricular valve orientation and superior–inferior ventricles in subxiphoid long‐axis views showing (a) the right–left relationship of the right atrium (RA) to the superior right ventricle (RV), and (b) the posteroanterior relationship of the left atrium (LA) to the inferior left ventricle (LV). VSD, ventricular septal defect. Figure 26.14 Double‐outlet right ventricle in the setting of an L‐looped heart ({S,L,L}) as demonstrated on a 3D TTE image. The image is cropped and viewed from the ventricular apex to the base of the heart and shows the aorta (Ao) to the left of the pulmonary artery (PA). LV, left ventricle; RV, right ventricle; TV, tricuspid valve. Other associated lesions include aortopulmonary window [99], atrial septal defects, persistent left superior vena cava, and leftward juxtaposition of the atrial appendages, which occurs most frequently when the ascending aorta and pulmonary trunk are located along the extreme rightward aspect of the heart (Figure 26.15, Video 26.12) [100]. DORV is common in patients with heterotaxy syndrome (usually of the right isomerism or asplenia type), often with associated systemic and pulmonary venous anomalies, common AV canal defects, and/or LV hypoplasia [101–103]. Some heterotaxy cases cannot support a biventricular circulation and therefore undergo single ventricle palliation. A distinct constellation of cardiac anomalies involves a DORV with hypoplasia of the tricuspid valve and RV sinus, superior–inferior ventricles with crisscross AV valves, and subvalvar and valvar pulmonary stenosis [5,104]. Figure 26.15 Double‐outlet right ventricle with leftward juxtaposition of the atrial appendages. (a) Subxiphoid long‐axis view. (b) Apical view. LA, left atrium; LV, left ventricle; RA, right atrium; RAA, right atrial appendage; RV, right ventricle. Coronary artery abnormalities occur in up to 30% of DORV cases (Figure 26.16) [3], with an increased frequency in those with a subpulmonary or a remote VSD [12,105–107]. Side‐by‐side great arteries is another risk factor for an abnormal coronary arterial pattern [108]. Coronary artery anatomy can be an important determinant of surgical management. For example, in DORV with a subpulmonary VSD requiring an arterial switch operation, an intramural coronary artery can increase the complexity of the operation. In DORV with a subaortic VSD and pulmonary stenosis, a coronary artery crossing the RV outflow tract can influence surgical management of the pulmonary stenosis (Figure 26.17, Video 26.13). Figure 26.16 Diagram of the coronary artery variants seen with double‐outlet right ventricle. Ao, aorta; CC, conal coronary artery; Cx, circumflex coronary artery; LAD, left anterior descending coronary artery; RCA, right coronary artery. Figure 26.17 Double‐outlet right ventricle with a subaortic ventricular septal defect and pulmonary stenosis (TOF type) where the right coronary artery conal branch (star) crosses anterior to the pulmonary outflow tract and supplies the anterior descending coronary artery in a parasternal short‐axis view. AoV, aortic valve; PV, pulmonary valve. The variable clinical presentation and course of DORV in patients reflects the anatomic and hemodynamic heterogeneity of this group [28]. The pathophysiology is determined primarily by VSD size, VSD relationship to the great arteries and the consequent effects of blood flow streaming, presence of outflow tract obstruction, pulmonary vascular resistance, and associated cardiovascular anomalies. The most common pathophysiologic variants include: The diagnosis of DORV is usually established by transthoracic echocardiography (TTE), which is the primary diagnostic tool used to determine the anatomic and physiologic features necessary for management decisions. In the majority of patients, a comprehensive evaluation with 2D, 3D, and Doppler echocardiography provides the relevant information for planning treatment. Preoperative cardiac catheterization is seldom used in infants with DORV except when a transcatheter intervention is expected (e.g., balloon atrial septostomy). In selected cases with complex anatomy and uncertainty regarding complex venous or arterial anatomy or when a single versus biventricular approach is contemplated, cardiac magnetic resonance (CMR) imaging or computed tomography (CT) may be used as an adjunct to TTE. Advanced techniques such as 3D printing and virtual reality imaging can be helpful to assess for adequate pathways from the LV to a great artery. Intraoperative transesophageal echocardiography (TEE) is often preformed at the conclusion of cardiopulmonary bypass to evaluate the repair.
CHAPTER 26
Double‐Outlet Ventricle
Introduction
Double‐outlet right ventricle
Definition
Historical perspective
Incidence
Etiology
Morphology and classification
Developmental considerations
Anatomy
VSD location and size
Conal (infundibular) morphology
Great artery relationship
Associated lesions
Pathophysiology
Imaging
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