Constantine Mavroudis1, Carl L. Backer2, and Robert H. Anderson3 1Peyton Manning Children’s Hospital, Indianapolis, IN, USA 2UK HealthCare Kentucky Children’s Hospital, Lexington, KY, USA 3Institute of Genetic Medicine, Newcastle University, Newcastle‐upon‐Tyne, UK Disparate lesions are grouped together under the heading of double‐outlet right ventricle (DORV) simply because both of the arterial trunks are supported in their greater part by the morphologically right ventricle. As such, the lesions themselves can be interpreted as representing a complex spectrum between, on the one hand, overriding of the aorta above the crest of the muscular ventricular septum and, on the other hand, transposition with overriding of the pulmonary trunk. Not all patients with this ventriculoarterial connection fall neatly into these spectrums, however. In some, the channel between the ventricles is uncommitted to the ventricular outflow tract. In others, the interventricular communication is located directly beneath both arterial roots. The group as an entirety remains controversial in terms of both its anatomic definition and its surgical management. Included within the overall banner are multiple phenotypes, with each phenotype including a rich spectrum of different anatomic and physiologic forms. The complexity is then further compounded by the frequent presence of associated cardiac malformations. A degree of simplicity has now been introduced by the recognition that DORV is one type of ventriculoarterial connection, in which both great vessels arise entirely or predominantly from the right ventricle [1–4]. It follows, therefore, that although DORV is usually associated with concordant atrioventricular connections, it can also be found in the setting of discordant [5], mixed, or functionally univentricular [6] atrioventricular connections. In this chapter, we focus on the forms of DORV with two functional ventricles. For a long period, controversy revolved around whether the definition of DORV should include the presence of aortic to mitral discontinuity. This issue may have arisen from the initial description of the Taussig–Bing heart [7, 8], which did indeed have bilateral and well‐developed subpulmonary and subaortic muscular coni. Definition of the lesion on the basis of presence of bilateral infundibulums, however, contravenes the basic rule of anatomic description propounded by Van Praagh and his colleagues as “the morphological method” [9]. This rule stated sensibly that one feature of the heart should not be defined on the basis of a second feature that is itself variable. It is also the case that, when pathologic specimens are examined with the ventriculoarterial connection of double outlet, the majority exhibit fibrous continuity between the leaflets of an atrioventricular and an arterial valve [10, 11]. A more recent controversy now concerns the name of the channel between the ventricles. When both arterial trunks arise in their entirety above the cavity of the right ventricle, it is an undeniable fact that the channel between the ventricles is the outflow tract for the left ventricle. The essence of surgical repair is the ability to channel this opening to one or other of the arterial roots. The surgeon achieves this goal by creating a tunnel within the cavity of the right ventricle. This is exactly the same process that takes place during normal cardiac development so as to commit the aortic root to the morphologically left ventricle (see Embryology). It is also the case that the area of space closed by the surgeon so as to tunnel one or other arterial root to the left ventricle is analogous to the area described as the “ventricular septal defect” in the setting of tetralogy of Fallot (Figure 24.1). The channel between the ventricles, in fact, is equivalent to the secondary interventricular communication as seen during normal cardiac development. This channel, when found in the setting of DORV, cannot itself be closed during surgical correction. For all of these reasons, it makes sense to describe the channel as the interventricular communication. Figure 24.1 The “name” of the channel between the ventricles. (A) is from a heart with tetralogy of Fallot. (B) is from a heart with double‐outlet right ventricle (DORV). Note that the “VSD” (ventricular septal defect) label in (B) is equivalent to the “outflow tract” in (A). The area for ventricular septation in (B) is the area equivalent to the VSD in (A). The “VSD” in the DORV heart cannot be closed as it is the interventricular communication necessary for there to be egress from the left ventricle. The channel between the ventricles in DORV is equivalent to the outflow tract of the left ventricle in tetralogy of Fallot. Peacock [12] and Rokitansky [13] illustrated examples of hearts in which both arterial trunks were supported above the cavity of the morphologically right ventricle in the mid‐nineteenth century. Intriguingly, one of the hearts described by Fallot was also noted to have both arterial trunks arising above the right ventricle. None of these authors, however, used the term “double‐outlet ventricle.” As far as we can establish, it was Braun and colleagues, in 1952, who first described a heart on the basis of double outlet [14]. They were providing a postmortem description of the heart from a 19‐year‐old male with anterior and right‐sided aorta, subaortic interventricular communication, and pulmonary stenosis. The first correct intraoperative recognition and surgical repair was at the Mayo Clinic in May 1957. This 18‐month‐old male died two hours postoperatively of low cardiac output, perhaps owing to inadequate myocardial protection and subaortic stenosis [15]. Witham shortly thereafter published a postmortem description of four cases of what he termed double‐outlet right ventricle [16]. Engle and associates emphasized the surgical importance of preoperative angiocardiography to distinguish DORV with subaortic defect and no pulmonary stenosis from simple ventricular septal defect (VSD), and suggested angiographic criteria to differentiate between the two diagnoses [17, 18]. Neufeld and colleagues published detailed clinicopathologic descriptions of two distinct subsets of patients with “origin of both great vessels from the right ventricle,” those with [19] and those without [20, 21] pulmonary stenosis. They described the similarities of the pathophysiology of DORV with pulmonary stenosis to that of tetralogy of Fallot, and underscored the importance, at that time, of distinguishing between the two diagnoses in planning for surgical repair [19]. In a paper on DORV without pulmonary stenosis, Neufeld and coworkers described the location and pathophysiology of the interventricular communication being committed to the aorta, the pulmonary trunk, or being doubly committed [20]. This insight laid the foundation for a classification based on the relationship of the interventricular communications to the arterial roots [1], with this approach gaining widespread approval subsequent to several studies of autopsied hearts [3, 22–24]. While Pernkopf [25] had discussed the relationship of the overriding pulmonary trunk as long ago as 1926, it was Helen Taussig and Richard Bing who first provided a complete clinical, angiographic, and pathophysiologic discussion of this disorder in 1949 [7]. In the postmortem examination of their 5½‐year‐old patient, they described the origin of the aorta from the right ventricle, the slight leftward position of the pulmonary trunk over a subpulmonary defect, and a muscular ridge separating the pulmonary and aortic roots. They correctly suggested that streaming accounted for the higher oxygen saturation in the pulmonary arteries compared with that in both the right ventricle and the aorta. Later reports of similar cases classified Taussig–Bing hearts as a subset of transposition, simply because the physiology of the two disorders was so similar [26, 27]. Neufeld and associates recognized that Taussig–Bing hearts could also be considered as an anatomic subset of DORV, even though they were more similar physiologically to transposition of the great arteries (TGA) with VSD [20]. Lev and colleagues, nonetheless, had already deemphasized the significance of infundibular morphology, and more simply defined the Taussig–Bing heart as one form of DORV with a subpulmonary defect [1]. Daicoff and Kirklin [28] and Hightower and coworkers [29] performed the first successful surgical repairs of the Taussig–Bing malformation by tunneling the interventricular communication to the pulmonary root and performing an atrial switch (Mustard procedure). Patrick and McGoon [30] and Kawashima and coworkers [31] subsequently achieved direct repair by constructing an intraventricular tunnel from the defect to the aortic root, despite the adjacency of the defect to the pulmonary root. Understanding the normal development of the heart now provides the basis for appreciating that the channel between the ventricle is nothing more than an interventricular communication. We now know that, shortly after formation of the ventricular loop, the developing heart essentially exhibits a double inlet to the developing left ventricle, and a double outlet from the developing right ventricle. It follows that, in this setting, it is not possible to close the channel between the developing ventricles, which can be nominated as the primary interventricular communication (Figure 24.2A). With ongoing development, there is remodeling of this primary communication so as to provide the right ventricle with its inlet and the left ventricle with its outlet. The first stage of this remodeling involves expansion of the atrioventricular canal. At the conclusion of this stage, the right ventricle is furnished with an inlet guarded by the developing tricuspid valve, but both arterial trunks remain supported exclusively by the developing right ventricle (Figure 24.2B). The channel between the developing ventricles at this stage, therefore, can be considered to represent the secondary interventricular communication. The second stage of normal development involves providing the left ventricle with its outlet. This is achieved by the embryo creating a shelf in the roof of the right ventricle by fusing together, and muscularizing, the proximal parts of the ridges that divide the outflow tract itself into the pulmonary and aortic channels (Figure 24.3A). In essence, this is exactly the same procedure as undertaken by the surgeon when correcting DORV. The process turns the secondary interventricular communication into the outflow tract of the left ventricle. The space above the cavity of the right ventricle that is then closed by tissues derived from the embryonic atrioventricular cushions is the tertiary interventricular communication (Figure 24.3B). It is this space, should it remain open, that represents the simple perimembranous defect. Figure 24.2 Embryology of normal heart development. These are images from a developing mouse heart. They demonstrate how it is necessary to remodel the channel between the ventricles before it is possible to complete ventricular septation. (A) The initial arrangement of the atrioventricular septal defect and outflow tract. The atrioventricular septal defect opens exclusively to the left ventricle and the unseptated outflow tract arises exclusively from the right ventricle. The star shows the inner heart curvature, which is remodeled as the right ventricle acquires its inlet, as shown in (B). The arterial trunk at this intermediate stage remains supported by the developing right ventricle. The channel between the right and left ventricles is now the secondary interventricular foramen. This will become the outflow tract for the developing left ventricle (see Figure 24.3). Figure 24.3 Embryology of normal heart development. These are also images from developing mouse hearts. These demonstrate how the embryo (like the cardiac surgeon) builds a shelf in the roof of the right ventricle. This connects the aortic root to the left ventricle through the secondary interventricular foramen (A). The remaining space between the aortic root and the right ventricle is closed by formation of the membranous septum from the atrioventricular cushions (B). When the tertiary defect is closed during normal development, the developing aortic root is itself supported by a completely myocardial infundibulum. It is only with ongoing development, as the root is more completely integrated into the left ventricle, that the myocardium of the inner heart curvature involutes to produce aortic to mitral valvar continuity. If development proceeds normally, then the muscularized proximal ridges that produce the shelf in the roof of the right ventricle become converted into the free‐standing muscular subpulmonary infundibulum. Should the aortic root retain its location above the right ventricle, then the muscularized ridges persist as the muscular outlet septum. Should the ridges fail to muscularize, however, then the interventricular communication is able to open beneath both arterial roots. This is the essence of the doubly committed defect in the setting of double outlet. Should the outflow ridges fuse in straight rather than spiral fashion, however, the interventricular communication will be positioned beneath the pulmonary, rather than the aortic, root. It is this maldevelopment that produces the Taussig–Bing spectrum of lesions (Figure 24.4). On rarer occasions, the interventricular communication can retain its position opening to the inlet of the right ventricle. This change, or presence of a defect within the muscular ventricular septum, can produce a defect in noncommitted location. All variants of DORV, therefore, are now readily understood on the basis of remodeling of the embryonic interventricular communication [32–39]. Sakata and associates [40] and Lecompte and colleagues [41] argued that the classification and terminology of this complex group of patients, unified because of the same ventriculoarterial connection, are less important than a precise definition of the preoperative anatomic criteria that are useful in determining the best type of surgical repair. Accurate categorization of patients with DORV, nonetheless, is necessary to make valid inferences regarding the results of different surgical treatments [3, 24] for comparable anatomic subsets. Almost nine‐tenths of surgical patients with DORV have concordant atrioventricular connections [42]. Discordant connections are found in around one‐tenth, excluding those with isomeric atrial appendages [5, 42–44]. There is typically the usual atrial arrangement, although DORV is frequent in the setting of right isomerism [43, 45]. In the setting of discordant atrioventricular connections, of course, there is left‐hand ventricular topology, as in congenitally corrected transposition. This also produces additional complications, notably with an abnormal arrangement of the atrioventricular conduction axis. Left‐hand ventricular topology is also frequent in the setting of right isomerism with DORV. Figure 24.4 Computed tomography scan, three‐dimensional volume‐rendered anterior view of an 8‐day‐old infant with double‐outlet right ventricle, Taussig–Bing variant, and type A interrupted aortic arch. Note that the aorta and pulmonary artery both originate from the right ventricle. There are three basic patterns of the relationship of the great arteries to each other in DORV [23]. In most cases the great arteries are normally related to one another – the aortic trunk is situated posteriorly and to the right of the pulmonary trunk, and the two great arteries spiral around each other as they leave the base of the heart. In the second group the aorta is to the right of the pulmonary trunk, but these two vessels lie parallel to each other (they do not spiral). They are usually side by side, although there can be any degree of anteroposterior variation. The third major group is the least common and consists of parallel trunks with the aorta anterior and to the left of the pulmonary trunk. While it was once thought that the relationship of the interventricular communication to the arterial roots could be predicted with a reasonable degree of certainty from the relationship of the great arteries to each other [24], this has been disputed by Kirklin and coworkers [6]. This channel, which represents the only outflow tract for the left ventricle, is usually unrestrictive (diameter equal to or larger than the diameter of the aortic annulus) (Figure 24.5). The location of this channel has also become part of the method of categorizing DORV patients. In one‐tenth of cases [6], the defect is restrictive [28, 46–53]. Very rarely, there is no interventricular communication [46, 54–60]. When the ventricular septum is intact, mitral valvar and left ventricular hypoplasia usually coexist. A small atrial septal defect (ASD) serves as the only source of a left‐to‐right shunt. In one isolated case of DORV without an interventricular communication, the anterior leaflet of the mitral valve closed the defect. Blood shunted left to right through a small ASD, and a small opening in the anterior leaflet of the mitral valve, allowed blood to flow from the left atrium directly into the right ventricle. In up to one‐sixth of cases, the defects are multiple [6]. The actual anatomic location of the interventricular communication in DORV is fairly constant relative to the ventricular septum. Most of these defects lie nestled within the anterior and posterior limbs of the trabeculoseptomarginalis (TSM or septal band) (Figure 24.6) [24, 61]. When the defects extend inferiorly to open primarily to the inlet of the right ventricle, or are within the apical muscular septum [24], they are said to be noncommitted. This creates a major challenge to repair with an intraventricular tunnel, and can be associated with any relationship of the great arteries [24]. The defect in DORV is usually described in relational terms as subaortic, subpulmonary, doubly committed, or noncommitted (Figures 24.5 and 24.6) [1, 19, 24, 57]. This relationship to the great vessels has special surgical, rather than anatomic or embryologic, significance. These terms, however, do not imply that the defect moves around relative to the crest of the muscular ventricular septum. To the contrary, this important relationship of the defect to the great arteries depends more on the highly variable relationships of the great arteries to each other and on the orientation and size of the muscular outlet (infundibular or conal) septum [24]. In DORV the terms subaortic or subpulmonary can, but do not necessarily, demand that one of the borders of the defect is formed by an arterial valve (juxta‐arterial). This distinction between the location of the defect relative to the ventricular septum and its relationship to the great arteries is important to complete the understanding of this disorder. Figure 24.5 The relationship of the interventricular communication to the arterial roots in double‐outlet right ventricle. (A) Subaortic defect without pulmonary stenosis. (B) Subaortic defect with pulmonary stenosis. (C) Subpulmonary defect (Taussig–Bing malformation). (D) Doubly committed defect. (E) Noncommitted (remote) defect. (F) Intact interventricular septum. Source: Reproduced by permission from Walters HL III, Pacifico AD. In: Pediatric Cardiac Surgery, 3rd ed. Philadelphia, PA: Mosby; 2003, pp. 408–441. Figure 24.6 Diagrammatic representation of the location of the interventricular communication in hearts with an isolated perimembranous ventricular septal defect (VSD), tetralogy of Fallot, double‐outlet right ventricle (DORV) with subpulmonary defect, DORV with doubly committed defect, and DORV with subaortic defect. Note the location of the defect nestled within the limbs of the trabeculoseptomarginalis (TSM). APM, anterior tricuspid papillary muscle; IL, inferior (posterior) limb of TSM; IS, infundibular (conal) septum; MB, moderator band; PT, pulmonary trunk; SL, superior (anterior) limb of TSM; VIF, ventriculoinfundibular fold. Source: Reproduced by permission from Edwards WD. J Thorac Cardiovasc Surg. 1981;82:418–422. Subaortic defects (Figure 24.5) [60] are the most common type and occur in approximately half of surgical patients [4, 62]. They are located beneath the aortic valve and are separated from the valve by a variable distance, depending on the presence and length of the subaortic infundibulum. When there is aortic to mitral fibrous continuity, the left leaflet of the aortic valve, or the base of the anterior leaflet of the mitral valve, forms the posterosuperior margin of the defect (juxta‐aortic) [6]. Typical subaortic defects in hearts with a right‐sided aorta are located in the superior interventricular septum, posterior to the outlet septum (Figure 24.7) [19, 24]. The defects are usually perimembranous; they reach the annulus of the tricuspid valve at its anteroseptal commissure, and there is mitral to tricuspid continuity at the posteroinferior rim of the defect. Occasionally the posterior margin of the defect is separated from the base of the tricuspid valve by a rim of muscular tissue. This represents fusion of the ventriculoinfundibular fold and the posterior limb of the TSM (Figure 24.8) [11, 24, 63]. The defect can extend inferiorly from the perimembranous region to lie partly beneath the base of the septal leaflet of the tricuspid valve [63]. Figure 24.7 Double‐outlet right ventricle with subaortic defect. (A) A coronal section of the right ventricle through the aortic and pulmonary valves shows the side‐by‐side relationship of the great vessels. The defect is related to the aortic valve, but is separated from it by the subaortic infundibulum. (B) A sagittal section across the defect demonstrates its subaortic commitment. The defect serves as the only outlet for the left ventricle. The subaortic infundibulum is interposed between the aortic valve and the anterior leaflet of the mitral valve. AC, subaortic infundibulum; Ao, aorta; CS, outlet, conal, or infundibular septum; LA, left atrium; LV, left ventricle; MV, mitral valve; PT, pulmonary trunk; RV, right ventricular free wall; TV, tricuspid valve; VS, interventricular septum. Source: Reproduced by permission from Neufeld HN et al. Circulation. 1961;23:603–612. When DORV is associated with left‐sided aorta [64–68], the defect is usually subaortic. Although still nestled within the limbs of the TSM, the defect lies more anteriorly and superiorly within the muscular interventricular septum than it does when the aorta is on the right side (Figure 24.9) [57]. This is similar to the position of the defect in the Taussig–Bing heart. Typically the superior border of the defect is the aortic valve (juxta‐aortic), and the anterior and posterior limbs of the TSM form its inferior and posterior borders, respectively. The defect can extend to the annulus of the tricuspid valve posteriorly and be perimembranous. Rarely in this setting, the defect can be subpulmonary [69], noncommitted [70], or doubly committed [71]. Doubly committed defects (Figure 24.5D) [60] occur in approximately one‐tenth of surgical series of DORV [4, 62]. The defect still lies within the divisions of the TSM superiorly and immediately beneath the leaflets of the aortic and pulmonary valves (juxta‐arterial). The pulmonary and aortic valves generally are contiguous because the outlet septum is deficient or absent. The leaflets of the arterial valves form the superior border of this typically large defect. The TSM, with its anterior and posterior divisions, makes up its anterior, inferior, and posterior borders. There can be bilaterally deficient infundibulums combined with an absent or deficient outlet septum [6, 72], or a common infundibulum may exist beneath the two arterial valves [6]. As both great arteries contribute to the superior border of the defect and override the interventricular septum to varying degrees, it is often difficult to determine from which ventricle the great arteries predominantly arise. For this reason Brandt and his colleagues called this variant of DORV double‐outlet both ventricles [72]. Subpulmonary defects (Figure 24.5C) [60] are present in approximately one‐third of patients in surgical series of DORV (Taussig–Bing malformation) [4, 62]. These defects are usually unrestrictive. They lie anteriorly and superiorly beneath the pulmonary valve, and are again cradled within the limbs of the TSM (Figure 24.10) [73]. This position is similar to that described for DORV with left‐sided aorta (Figure 24.9) [57, 63]. In the presence of a subpulmonary infundibulum the defect is separated from the pulmonary valve by a variable distance, and the inner heart curvature forms the superior boundary of the defect. If there is pulmonary to mitral continuity, the pulmonary valve will override the crest of the muscular septum to a variable extent and will form its superior border (juxtapulmonary). The outlet or infundibular (conal) septum is sagittally oriented and extends from the ventricular septum to the anterior wall of the right ventricle. So oriented, the outlet septum does not constitute part of the muscular ventricular septum, but separates the defect and subpulmonary region from the subaortic region. This commits the defect to the pulmonary trunk [74]. Hypertrophy of the outlet septum can cause varying degrees of subaortic obstruction [74, 75]. This may account for the relatively common occurrence of coarctation of the aorta, found in up to four‐fifths of patients with Taussig–Bing malformation [74, 76]. Noncommitted [1] (remote [56]) defects (Figure 24.5E) [60] occur in up to one‐fifth of patients in surgical series [4, 62, 77]. Lacour‐Gayet and associates have noted that the superior edge of these defects is located at least the distance of one aortic valve diameter from either arterial valve, both great vessels arise “200%” from the right ventricle, and infundibulums exist beneath both arterial valves [78–80]. These noncommitted defects are not nestled within the limbs of the TSM, but rather are located to open to the right ventricular inlet and/or within the muscular ventricular septum (Figure 24.11) [1, 79, 81–86]. A restrictive defect and subaortic infundibulum can frequently cause subaortic obstruction. Figure 24.8 Comparison of two hearts with double‐outlet right ventricle and subaortic defect. (A) The posterior limb of the trabeculoseptomarginalis fuses with the ventriculoinfundibular fold to produce the muscular posterior margin of the defect that protects the conduction tissue. (B) In this specimen, there is no fusion of the posterior limb of the trabeculoseptomarginalis and ventriculoinfundibular fold. The defect reaches the annulus of the tricuspid valve at its anteroseptal commissure where there is aortic–mitral–tricuspid valve continuity. The conduction tissue is vulnerable along the posteroinferior free margin of the defect. OS, outlet (infundibular, conal) septum; PT, pulmonary trunk; TSM, trabeculoseptomarginalis; VSD, ventricular septal defect. Source: Reproduced by permission from Anderson RH et al. Am J Cardiol. 1983;52:555–559. Figure 24.9 Double‐outlet right ventricle with left‐sided aorta and subaortic defect. Coronal section of the right ventricle through the aortic and pulmonary valves. The aorta is to the left and slightly anterior to the pulmonary valve. The defect lies anteriorly and superiorly just beneath the aortic valve. This is similar to the position of the defect in the Taussig–Bing malformation. Ao, aorta; PT, pulmonary trunk; RV, right ventricle; VSD, ventricular septal defect. Source: Reproduced by permission from Sridaromont S et al. Mayo Clin Proc. 1978;53:555–577. All of the variations of right ventricular outflow tract obstruction (RVOTO) that are present in hearts with tetralogy of Fallot can be present in hearts with DORV. RVOTO is most common in hearts with subaortic or doubly committed defects. It is extremely uncommon in patients with the Taussig–Bing malformation [74, 87–93] and in those with noncommitted defects [1]. While RVOTO is most often infundibular, it can also be purely valvar, with or without a small pulmonary valve annulus and hypoplasia of the central pulmonary arteries. RVOTO rarely can be caused by a diaphragm of muscle inserting between the inflow and outflow portions of the right ventricle. This produces a double‐chambered right ventricle [50, 94–97]. Other mechanisms of RVOTO occur uncommonly: (i) straddling atrioventricular valve [98]; (ii) accessory tissue tags; and (iii) aneurysms of the membranous interventricular septum [99]. DORV can occur rarely in association with pulmonary atresia. Figure 24.10 Coronal section of the right ventricle through the aortic and pulmonary valves in a heart with double‐outlet right ventricle and subpulmonary defect (Taussig–Bing malformation). The defect is closely related to the pulmonary valve and is separated from the aortic valve by the outlet (infundibular, conal) septum. The defect extends to the tricuspid valve annulus posteriorly and, as such, is a perimembranous lesion. Note the sagittal orientation of the outlet (conal, infundibular) septum. TSM, trabeculoseptomarginalis; VSD, ventricular septal defect. Source: Reproduced by permission from Stellin G et al. J Thorac Cardiovasc Surg. 1987;93:560–569. Subaortic stenosis is an uncommon, but clinically important, feature of DORV [56]. It occurs most often in those patients with subpulmonary defects (35% of the Taussig–Bing hearts in Sondheimer’s series) [42]. It is especially common in Taussig–Bing hearts with aortic arch obstruction [100]. In this setting the subaortic stenosis is usually owing to a hypoplastic left ventricular outflow tract (LVOT). Subaortic stenosis can also be caused by atrioventricular valve tissue, by accessory tissue tags, or by hypertrophied muscle bundles [75, 101, 102]. Aortic valvar stenosis [23, 56] or atresia [103] can also be present. In DORV with concordant atrioventricular connections, the atrioventricular node lies in the usual position in the muscular portion of the atrioventricular septum. The bundle of His penetrates the central fibrous body and lies along the posteroinferior margin of the defect in lesions that are juxtatricuspid (perimembranous), whether the defect is subaortic, doubly committed, or subpulmonary. When muscle is interposed between the defect and the tricuspid valve, this muscle protects the bundle, which no longer runs along the posteroinferior free margin of the defect (Figure 24.8) [24]. In the normal heart there are three aortic cusps. One is oriented posteriorly and is called the noncoronary sinus. The sinuses giving rise to the coronary arteries are adjacent to the pulmonary trunk, irrespective of the relationships between the arterial roots. In most cases of DORV, the aortic root, and hence the sinuses giving rise to the coronary arteries, are rotated clockwise [104] as the observer looks from below. Hence, the left coronary artery arises more posteriorly and the right coronary artery arises more anteriorly. With a right‐sided and anterior aorta, the coronary arterial pattern is similar to that seen in TGA. The right coronary artery arises from the right‐facing sinus (sinus #2), and the left coronary artery arises from the left‐facing sinus (sinus #1) [104, 105]. As in transposition, nonetheless, variations are frequent, but usually when the defect is subpulmonary. Almost any anomaly of the atrioventricular valves can complicate DORV. When severe, they create formidable obstacles to the performance of an anatomic repair. Examples of such anomalies include atrioventricular valve stenosis and atresia [23, 55, 56, 106, 107], straddling [23, 108–114], and atrioventricular septal defect with common atrioventricular junction [115–118]. Coarctation of the aorta and other forms of left ventricular outflow tract obstruction (LVOTO) are more common in hearts with the Taussig–Bing malformation [20, 41, 100, 119, 120]. Various other cardiac abnormalities can occur, including patency of the arterial duct, ventricular hypoplasia (especially associated with atrioventricular valve abnormalities), unroofed coronary sinus syndrome, abnormalities of systemic venous return, juxtaposed atrial appendages, isomerism, mirror‐imaged atrial arrangement, right‐sided heart, and ASD. As described earlier in the section on morphology, DORV has most often been classified anatomically in the literature according to the pure relational anatomy of the defect to the arterial roots: subaortic, doubly committed, subpulmonary, and noncommitted (remote). The Society of Thoracic Surgeons (STS) Congenital Heart Surgery Nomenclature and Database Project Committee, the European Association of Cardiothoracic Surgery (EACTS), and the Association of European Pediatric Cardiologists (AEPC) have adopted a more practical and functional classification of DORV. While this nomenclature system groups these four classical anatomic subtypes into categories that convey a broad sense of the relational anatomy of the interventricular communication, it also categorizes them according to their clinical presentation and the general approach to their surgical repair [121]. These categories are: Figure 24.11 Double‐outlet right ventricle with noncommitted defect. (A) Right ventricular view at the outflow tract of the pulmonary trunk. (B) Right ventricular view at the outflow tract of the aorta. A, aorta; P, pulmonary trunk; PB1, first parietal band; PB2, second parietal band; SB, septal band (trabeculoseptomarginalis); VSD, ventricular septal defect. Source: Reproduced by permission from Lev M et al. J Thorac Cardiovasc Surg. 1972;64:271–281. A fifth group, DORV + atrioventricular septal defect (AVSD; AV canal), has also more recently been added to encompass DORV associated with complete AVSD. This especially complex subset of DORV patients is frequently associated with isomeric atrial appendages. These patients have frequent major associated cardiac lesions, including some degree of RVOTO, total anomalous pulmonary venous connection (TAPVC), and partial anomalous systemic venous return (left superior caval vein), along with right isomerism and asplenia. DORV with intact ventricular septum, though very rare, has always been included in this classification for the sake of completeness. Patients with DORV tend to present early in life at a mean age of 2 months (range 1 day–4 years) [42]. Without other major cardiac anomalies, the clinical presentation of patients with DORV depends on the relationship of the defect to the great arteries and the presence or absence of pulmonary stenosis. These basic patterns of presentation for patients with DORV can be profoundly altered by the effect of major associated cardiac lesions [123]. Patients with unrestricted subaortic doubly committed or noncommitted defects without pulmonary stenosis have unrestricted pulmonary blood flow and present with congestive heart failure. This presentation is indistinguishable from patients with an isolated and large defect. Although these patients are usually mildly desaturated, they are not clinically cyanotic because the high pulmonary blood flow results in well‐saturated right ventricular blood owing to mixing with left ventricular blood through the defect. There is also some preferential streaming of well‐saturated left ventricular blood into the aorta if the defect is subaortic or doubly committed. Congestive heart failure can also be caused by LVOTO and an obstructive left atrioventricular valve that produces pulmonary venous obstruction. Cyanosis can be produced in patients with DORV either by restriction to pulmonary blood flow, streaming, or a combination of both. In the Taussig–Bing malformation, highly saturated left ventricular blood is preferentially directed into the pulmonary artery by the sagittally oriented infundibular (conal) septum. Since relatively desaturated right ventricular blood tends to flow into the aorta, these Taussig–Bing patients mimic patients with TGA and VSD physiologically and present early in infancy with cyanosis and congestive heart failure. In the presence of significant pulmonary stenosis with any type of defect, cyanosis can become severe owing to reduced pulmonary blood flow. These infants are similar to patients with tetralogy of Fallot in their presentation. There are no physical findings or electrocardiogram (ECG) criteria [124] that distinguish DORV from other congenital cardiac malformations with similar clinical presentations. The usual ECG findings are right axis deviation and right ventricular or biventricular hypertrophy. The chest radiograph findings are varied and nonspecific. They depend primarily on the amount of pulmonary blood flow and the presence of associated major cardiac anomalies. In any type of DORV with an unrestrictive defect and without pulmonary stenosis, the chest radiograph will show evidence of pulmonary overcirculation. Conversely, patients with significant pulmonary stenosis will have relatively clear or oligopenic lung fields. Patients with L‐malposition of the aorta can demonstrate a vertical left upper mediastinal aortic shadow on the posterolateral chest radiograph, although this is not a specific finding for DORV. Echocardiography is the basis of the diagnosis of DORV and, because of the subtleties and complexity of the diagnosis, it is often useful for the study to be performed in cooperation with the surgeon. Two‐dimensional studies accurately define the diameter, location, number, and commitment of the defect(s), the origin of both great arteries and their relationship to each other, semilunar‐atrioventricular valve continuity or discontinuity, and absence of the normal LVOT. Echocardiography also allows the accurate identification of (i) right and left ventricular volumes; (ii) pulmonary stenosis; (iii) LVOTO; (iv) atrioventricular valve abnormalities such as straddling and/or overriding; (v) abnormal insertions of the tensor apparatus; (vi) the distance between the tricuspid and the pulmonary valve annuli; (vii) abnormalities of systemic and pulmonary venous return; (viii) coronary artery abnormalities; and (ix) the presence of complete atrioventricular canal defects [125–128]. Cineangiography with cardiac catheterization (Figure 24.12) [10, 57] is not routinely performed unless there are anatomic features that are not adequately elucidated by the echocardiogram. If performed, these studies should be carefully examined for at least eight findings: (i) the size and relationship of the defect to the great arteries; (ii) the presence or absence of multiple defects; (iii) the relationship of the great arteries to each other; (iv) the presence or absence of pulmonary stenosis and the level(s) at which it occurs; (v) the coronary artery anatomy; (vi) the presence and level(s) of LVOTO; (vii) the relationship of the atria to the ventricles (concordant or discordant); and (viii) other associated cardiac anomalies. Because of the accuracy of two‐dimensional echocardiography in defining most of these features, cardiac catheterization is usually not essential for diagnosis and preoperative planning. Rather, it is reserved to define associated cardiac anomalies that are not clearly identified by the echocardiogram (coronary artery anomalies, peripheral pulmonary artery stenoses, etc.), to provide an integrated image of the pulmonary arterial tree, and to identify irreversible pulmonary vascular disease. If cardiac catheterization is not performed in a given case, there should be no suspicion of pulmonary vascular disease or peripheral pulmonary artery stenoses, and the coronary anatomy should be clearly defined by the two‐dimensional echocardiogram. Cardiac catheterization of a patient with DORV, unrestrictive defect, and no pulmonary or subaortic stenosis will demonstrate equal pressures in both ventricles and both great arteries. Pulmonary blood flow will be high in the presence of normal pulmonary vascular resistance, and both left atrial and left ventricular blood will be highly saturated. Saturations in the right ventricle will be lower owing to the admixture of left ventricular blood with the desaturated systemic venous return. Saturations in the great arteries will depend on the position of the defect relative to each individual great artery and the streaming produced thereby. Patients with subaortic and doubly committed defects will tend to have higher aortic saturations than patients with subpulmonary defects. Patients with subpulmonary defects will tend to have pulmonary saturations equal to or higher than the systemic saturation [129]. Figure 24.12 (A) Lateral view of right ventricular injection in a patient with double‐outlet right ventricle (DORV) and subpulmonary defect (Taussig–Bing malformation). The aorta is directly anterior to the right pulmonary artery. The aortic conus (anterior to aorta), infundibular (conal) septum (between the two great arteries), and the pulmonary conus (posterior to the pulmonary trunk) are well demonstrated. (B) Lateral view of a left ventricular injection in a patient with DORV and subpulmonary defect (Taussig–Bing malformation). The defect is located beneath the pulmonary artery (VSD). Ao, aorta; LV, left ventricle; MV, mitral valve; PT, pulmonary trunk; RV, right ventricle; VSD, ventricular septal defect. Source: Reproduced by permission from Sridaromont S et al. Mayo Clin Proc. 1978;53:555–577. Magnetic resonance imaging can be useful in documenting the adequacy of the ventricular volumes for biventricular repair and in elucidating coexisting cardiac anatomy, such as abnormalities of systemic or pulmonary venous connections and other abnormalities, in some complex cases. Computed tomographic imaging is also useful, particularly in defining the extracardiac features and spatial relationships of the great arteries and coronary arteries (Figure 24.4). The introduction of three‐dimensional (3D) printing to demonstrate complex intracardiac structures, ventricular to great vessel relationships, and ventricular volume measurements has been used in specialized centers to diagnose complex DORV anatomy and planning for operative repair. Physical 3D print models allow for rapid and explicit perception of the complex DORV anatomy and can augment and complement the classic diagnostic imaging techniques [130, 131]. In addition, 3D print models can also be used to rehearse the intended procedure before the actual surgery, providing insight and denotative predictive surgical outcome. The authors conclude that 3D print models are an invaluable resource for hands‐on surgical training of congenital heart surgeons. The natural history of DORV with a subaortic, doubly committed, or noncommitted defect without pulmonary stenosis is similar to that of a large, isolated VSD, except that spontaneous closure of the defect in DORV, a fatal event, is extremely rare [132]. The pulmonary vasculature of patients with DORV, pulmonary stenosis, and a subaortic, doubly committed, or noncommitted defect is relatively protected against the development of pulmonary vascular disease. The natural history of these patients is similar to that of patients with tetralogy of Fallot. The natural history of patients with DORV and subpulmonary defects is similar to that of patients with TGA and VSD, except for the tendency of the Taussig–Bing patients to develop pulmonary vascular disease earlier in life [6]. The natural history of any of these subsets of patients with DORV can be dramatically altered by major associated cardiac lesions such as LVOTO and atrioventricular valve abnormalities with or without ventricular hypoplasia. The goal of the surgical treatment of DORV is complete anatomic repair. This is defined as connection of the left ventricle to the aorta and the right ventricle to the pulmonary artery, and closure of the defect. In general, the timing of surgical intervention depends on the symptomatic state of the patient and the anatomy of and other cardiac anomalies associated with the DORV itself. The anatomy determines the ultimate, corrective surgical approach, which, in turn, influences the optimal age for definitive repair. The clinical state of the patient before the age at which definitive repair is planned will determine the need for initial palliative procedures. In general, a complete repair is undertaken at an early an age as possible. In a review of 238 patients with DORV who underwent biventricular repair, primary repair was possible in 88% of patients with a subpulmonary defect, 79% of patients with a subaortic defect, and 66% of patients with a doubly committed defect. In contrast, only 37% of patients with a noncommitted defect underwent primary repair. The mean age at primary biventricular repair was 2.6 months. The mean age of patients undergoing a staged approach was 29.8 months [133, 134]. Anatomic repair of DORV can be contraindicated by the presence of ventricular hypoplasia, serious abnormalities of either atrioventricular valve, the presence of very remote and/or multiple defects, and the presence of irreversible pulmonary vascular disease. An atrioventricular valve with a diameter more than two standard deviations smaller than the mean normal value for the patient’s body surface area is usually attended by surgically important ventricular hypoplasia. In this situation successful anatomic repair is seldom possible. Severe straddling and/or overriding of either atrioventricular valve can render anatomic repair impossible. The presence of a single defect far removed from either of the semilunar valves and the presence of multiple defects can render anatomic repair more difficult or ill‐advised, depending on the anatomic situation. The presence of a borderline‐size right ventricular volume is a limiting factor for biventricular repair, because the construction of the intracardiac right ventricular tunnel will reduce the right ventricular volume even more. This issue has been explored by a number of authors with mixed results for biventricular repair. In a comprehensive review from Toronto of 276 patients with DORV, biventricular repair was achieved in 194 patients, and Fontan operation in 82 patients [135]. In particular, attempts at biventricular repair in patients with DORV, noncommitted defect, and ASD have a very high early mortality [136, 137]. The anatomy is assessed through the tricuspid valve and a repair is planned. The repair is performed through the tricuspid valve and/or a vertical right ventriculotomy incision. Sometimes, when the repair is carried out entirely through the tricuspid valve, exposure of the most superior portion of the interventricular defect is enhanced by performing a radial incision along the base of the septal and anterior leaflets of the tricuspid valve and/or by exerting gentle, external, inferior pressure at the aorto‐ventricular junction. This variant represents approximately 25% of all DORV and in 20% the defects can be restrictive [80, 138]. These patients should undergo complete repair in early infancy [139], because the onset of pulmonary vascular disease is at least as rapid as it is in untreated patients with large, isolated VSDs. It has also been shown that young age, per se, is not a risk factor for hospital death [4, 140, 141]. An intraventricular tunnel repair, connecting the left ventricle to the aorta, is preferred for patients with DORV, interventricular defect type (Figure 24.13) [60]. Rarely, in patients with refractory congestive heart failure who are thought not to be immediate candidates for complete repair, pulmonary artery banding is required. This procedure is not recommended routinely; total correction should be performed in early infancy, as soon as it is felt that the patient is a suitable candidate. The size of the defect, as well as its location relative to the aorta, is noted. If the defect appears to be restrictive (diameter less than that of the aortic valve), it is enlarged by making an incision anterosuperiorly or by resecting a wedge of the interventricular septum in this area (Figure 24.13A) [53, 60]. Care is taken not to injure the mitral valve or its tensor apparatus and to avoid injury to the anterior ventricular wall with its left anterior descending coronary artery and septal perforator [142]. Obstructive right ventricular muscle bundles are resected. Often a portion of the infundibular septum must be resected in order to construct a straight tunnel between the defect and the aorta. It is usually possible to construct a tunnel from the left ventricle to the aorta without obstructing the pulmonary outflow tract, if the minimal distance between the tricuspid valve annulus and the pulmonary valve annulus is equal to or greater than the diameter of the aortic valve annulus. Preoperatively, this distance can generally be estimated accurately with the subxiphoid view of the two‐dimensional echocardiogram [40, 41]. Figure 24.13 Intraventricular tunnel repair of double‐outlet right ventricle with subaortic or doubly committed defect without pulmonary stenosis. (A) If the defect is restrictive, it is enlarged by resection of the interventricular septum in the shaded area. Stippling indicates the portion of the infundibular septum that may require resection to prevent subaortic stenosis. (B) The creation of a tunnel connecting the ventricular septal defect to the aorta (see text for details). (C) The completed tunneling of the defect to the aortic valve, creating an unobstructed pathway for left ventricular blood to exit the heart. We create the intracardiac tunnel with an appropriately trimmed flat polytetrafluoroethylene (PTFE) patch secured with running or interrupted sutures. Alternatively, the tunnel can be constructed with a tailored Dacron or PTFE tube graft that takes advantage of the inherent graft curvature to create a naturally shaped and unobstructed intraventricular tunnel (Figure 24.13B,C) [60]. The long axis of the patch is oriented perpendicular to a line drawn through the center of the defect and the center of the aortic orifice. The determination of the actual length of the patch long axis depends on the degree of dextroposition of the aorta. When the entire aorta is dextroposed into the right ventricular cavity, the patch length should be two‐thirds of the circumference of the aorta. One‐third of the circumference of the intraventricular tunnel so created will be composed of autologous tissue and will, therefore, retain the capacity for growth. The width of the patch should extend from the inferior edge of the defect to the superior margin of the aortic annulus. The suture line is carried well away from the edge of the defect along its posteroinferior margin in order to avoid damage to the conduction tissue. Posteriorly, the patch is secured to the base of the septal leaflet of the tricuspid valve. If there is a ledge of muscle separating the posterior edge of the defect from the tricuspid annulus, the defect sutures can be placed on the right ventricular side of the free edge of this muscle bundle; the conduction tissue does not run in this muscle along the edge of the defect. That notwithstanding, we generally choose to suture the patch to the base of the septal leaflet of the tricuspid valve and to avoid the posteroinferior margin of the defect entirely. Sometimes the dimensions of the right ventricular outflow tract (RVOT) must be augmented with an outflow patch because of the production of RVOTO by the intraventricular tunnel. Complications are infrequent after the intraventricular tunnel repair of DORV, interventricular defect type. Complete heart block is uncommon, and the functional status of at least 87% of the survivors is New York Heart Association class I [4]. Over 90% of patients who require only intraventricular tunnel repair for subaortic or doubly committed defects are free of reoperation at follow‐up. Indications for reoperation should be rare, but can include tunnel dehiscence, tunnel obstruction, residual defect, and discrete, localized subaortic stenosis unrelated to the tunnel itself [4, 143]. In the current era, the risk of death is low early after repair of DORV, interventricular defect type [4, 77]. The actuarial 15‐year survival, including hospital death, is 96%. In an earlier era, younger age was a risk factor for death after repair. At the present time, the effect of younger age has been neutralized; however, older age has been shown to be a significant risk factor, possibly owing to the presence of increasing pulmonary vascular disease with age [4].
CHAPTER 24
Double‐Outlet Right Ventricle
Controversies
History
Embryology
Morphology
Atrioventricular and Ventriculoarterial Connections
Atrial and Ventricular Arrangement
Great Arterial Relationships
Characteristics of the Interventricular Communication
Location of the Defect
Relationship of the Defect to the Great Arteries
Subaortic Defects
Double‐Outlet Right Ventricle with Left‐Sided Aorta
Doubly Committed Defect
Subpulmonary Defect (Taussig–Bing)
Noncommitted (Remote) Defects
Right Ventricular Outflow Tract Obstruction
Subaortic Stenosis
Conduction System
Coronary Arterial Anatomy
Associated Cardiac Abnormalities
Classification
Pathophysiology
Congestive Heart Failure
Cyanosis
Diagnosis
Physical Examination, Electrocardiogram, and Chest Radiograph
Echocardiogram
Cardiac Catheterization and Cineangiography
Magnetic Resonance Imaging/Computed Tomographic Imaging
Three‐Dimensional Imaging
Natural History
Treatment
Impediments to Complete Anatomic Repair
General Aspects of Surgical Repair
Double‐Outlet Right Ventricle, Interventricular Defect Type (Subaortic or Doubly Committed Defects without Pulmonary Stenosis)
Timing of Surgical Repair
Technique of Intraventricular Tunnel Repair
Complications after Intraventricular Tunnel Repair
Results after Intraventricular Tunnel Repair
Double‐Outlet Right Ventricle, Tetralogy of Fallot Type (Subaortic or Doubly Committed Defect with Pulmonary Stenosis)
Timing of Surgical Repair
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