Introduction
Double-outlet ventricle is no more than an abnormal ventriculoarterial connection. Therefore the feature may occur with each atrial arrangement, any atrioventricular connection, and all possible variations of ventricular morphology. The morphologic arrangement can then be further complicated by associated defects, some common and others rare. The clinical picture is as inconstant as the anatomic permutations and associations suggest. This chapter reviews the various combinations in which the outflow tracts arise from the same ventricle but in the setting of concordant atrioventricular connections. When both arterial trunks are found in the setting of discordant or mixed atrioventricular connections, the abnormal arrangements at either the atrioventricular or venoatrial junctions dominate the picture. Double-outlet ventricle can also be found in the setting of the functionally univentricular heart.
Historical Considerations
Abernethy of St. Bartholomew’s Hospital in London described the first known example of double-outlet right ventricle: “Both ventricles, the left by means of an opening in the upper part of the septum ventriculorum, projected their blood into the aorta.” The term double-outlet right ventricle , however, did not appear until 1957, although Fallot described the origin of the aorta as arising exclusively from the right ventricle when he was assessing the pathologic findings in hearts obtained from patients presenting with la maladie bleue. Prior to 1957, hearts with both arterial trunks arising from the right ventricle were usually considered to represent partial transposition. This was because only the aorta was deemed to be placed across the ventricular septum. Transposition was considered complete when both arterial roots were placed across the septum to rise from morphologically inappropriate ventricles. It is now generally accepted that the discordant ventriculoarterial connections are the essence of transposition (see Chapter 37 ). Transposition, therefore, is now considered to be mutually exclusive from double-outlet right ventricle. The relationship between double-outlet right ventricle and tetralogy of Fallot has also been contentious. This is perhaps surprising since, as already indicated, the aorta was observed to arise exclusively from the right ventricle in one of the original hearts examined by Fallot himself. In many examples with the phenotypic morphology of tetralogy (see Chapter 35 ), the greater part of the overriding aortic root, when considered relative to its short axis, is supported predominantly by right ventricular structures. Patients having such hearts are included in this chapter. The arguments regarding the relationship between tetralogy and double-outlet ventricles had centered on whether it was necessary to find bilaterally complete muscular infundibula to diagnose double-outlet right ventricle. As emphasized in Chapter 1 , structures should be defined in their own right and not on the basis of another feature, which is variable. Application of this principle, known as the morphologic method, means that it is inappropriate to define double-outlet ventricle, a specific form of ventriculoarterial connection, on the basis of infundibular morphology. The latter is but one of the many complicating features seen when both arterial trunks arise in larger part from the same ventricle. Our recent investigation of a large series of hearts having both arterial trunks exclusively supported by the right ventricle revealed that two-thirds lacked bilaterally complete infundibula. Double-outlet from the right ventricle, however, accounts for only part of the overall group of hearts to be described in this chapter. The other group, namely involving a double-outlet from the morphologically left ventricle, is very much rarer. At one point this finding was considered an embryologic impossibility. However, description of a heart with both arterial trunks arising from the left ventricle in the setting of an intact ventricular septum proved its existence beyond doubt. However, cases still tend to be described in isolation rather than in large series either from the pathologic or clinical viewpoint.
Epidemiology
Double-outlet right ventricle forms a rare spectrum of congenital cardiac anomalies that represents approximately 1% of all cardiac defects. Its reported prevalence varies widely and ranges between 3 and 24 in 100,000 live births. Variability in the reported prevalence exists due to controversies in the definition of double-outlet right ventricle and the resulting inconsistent classification. Despite the rare occurrence of the malformation, its clinical implications are significant, as its morphologic spectrum demands complex decision making in both medical and surgical therapy. Among the subtypes proposed by Lev et al., subaortic interventricular communications are most common, followed by subpulmonary, noncommitted, and doubly committed communications ( Table 39.1 ). Even rarer is the malformation where the arterial trunks are supported to a greater degree by the left ventricle, so-called double-outlet left ventricle. Double-outlet left ventricle is estimated to occur in fewer than 1 in 100,000 live births; however, exact data are lacking. Genetic anomalies associated with double-outlet ventricles have been identified in approximately 40% of patients. Trisomy 13 and 18, as well as 22q11.2 deletion syndrome, have been the most common chromosomal abnormalities.
| All | Brown et al. | Bradley et al. | Li et al. | Villemain et al. | |
|---|---|---|---|---|---|
| N (%) | N (%) | N (%) | N (%) | N (%) | |
| Number of patients | 1272 (100.0) | 124 (100.0) | 393 (100.0) | 380 (100.0) | 433 (100.0) |
| Subaortic | 432 (48.2) a | 57 (46.0) | 156 (46.6) | 219 (57.6) | 271 (62.6) |
| Subpulmonary | 331 (26.0) | 39 (31.5) | 76 (22.7) | 77 (20.3) | 139 (32.1) |
| Doubly committed | 38 (4.2) a | 6 (4.8) | 15 (4.5) | 17 (4.5) | – b |
| Noncommitted | 200 (15.7) | 22 (17.7) | 88 (26.3) | 67 (17.6) | 23 (5.3) |
| Pulmonary obstruction | 672 (52.8) | 65 (52.4) | 257 (65.4) | 166 (43.7) | 184 (42.5) |
| Era | 1980–2000 | 1980–2000 | 2005–2012 | 1992–2013 |
a Excluding patients from Villemain et al.
b In this study, the authors did not differentiate between interventricular communications that were subaortic or doubly committed, but referred to them as subaortic only. Therefore, the number given for subaortic interventricular communications combines interventricular communications that authors of other papers have separated into subaortic and doubly committed interventricular communications.
Morphology and Classification
Since double-outlet ventricle is only one variety of ventriculoarterial connection, it follows that multiple phenotypes are appropriately described within this grouping. It helps, therefore, to consider first the categorization of the various malformations and only then proceeding to provide details of specific morphology. We concentrate in this regard on the more common and more important lesions to be found within the groups.
Categorization
Analysis, be it in the clinical or pathologic situation, follows the sequential segmental approach (see Chapter 1 ). The first step is to ascertain the atrial arrangement and venous connections. The atrioventricular connections must then be established with certainty. At the ventricular level, note must be taken of the interrelationships of the arterial trunks, the specific infundibular morphology, and the nature and severity of any obstructive problems in the subaortic and subpulmonary outflow tracts. The size, site, and morphology of the interventricular communication, however, are the most important features. This channel provides the outflow tract for the other ventricle when both arterial trunks arise from the same ventricle ( Fig. 39.1 ).
The relationship of the interventricular communication with the subarterial ventricular outlets has provided the basis for most categorizations. In these previous categorizations, however, the channel has usually been described as a ventricular septal defect . The borders of the channel between the ventricles that exists in the setting of double-outlet right ventricle, however, are markedly different from those that are found when the ventriculoarterial connections are concordant or discordant. In tetralogy of Fallot, for example, the cranial border of the channel between the ventricles, which is the area usually described as the ventricular septal defect, is the outlet septum. When both arterial trunks arise from the right ventricle or when one arterial trunk is overriding with the other arising from the right ventricle, the outlet septum of necessity will itself be a right ventricular structure. Contrariwise, should both arterial trunks arise from the left ventricle, the outlet septum will be a left ventricular structure. It follows that when both arterial trunks arise predominantly from the right ventricle, the outlet septum will form the cranial border of the area of surgical ventricular septation. The cranial margin of the channel between the ventricles, in contrast, is the inner heart curvature, also known as the ventriculoinfundibular fold. This is the area of putative ventricular septation, representing the locus around which the surgeon will place a patch to tunnel the channel into the aortic root; it is described as the ventricular septal defect in the setting of tetralogy of Fallot ( Fig. 39.2 ).
In light of the earlier discussions, it is questionable whether the channel found between the ventricles when both arterial trunks arise from the right ventricle can justifiably be called a ventricular septal defect. The channel can never be closed surgically, unless an alternative channel is constructed to provide the outlet from the ventricle not directly supporting an arterial trunk. Throughout this chapter, we describe the channel as the interventricular communication rather than a ventricular septal defect, although we recognize that most will continue to describe it in the latter fashion. More importantly, because of the marked phenotypic variability coupled with the additional variation within recognized phenotypes, the categorization of each case should be individualized. In comparable fashion, the medical and surgical management must be tailored to cater for the particular problems of the individual patient. Certain anatomic combinations, nonetheless, do occur with sufficient frequency to merit specific discussion.
Double-Outlet Right Ventricle
The more common variants, in approximate order of frequency, are as follows:
- ▪
Those with the interventricular communication in subaortic position, with the aorta spiraling from right to left relative to the pulmonary trunk but in combination with pulmonary stenosis. This is the Fallot variant.
- ▪
Those with the interventricular communication in subpulmonary position, with the aorta to the right of the pulmonary trunk and parallel to, it. This is the Taussig-Bing variant.
- ▪
Those with the interventricular communication in subaortic position, with the aorta spiraling from right to left relative to the pulmonary trunk but in the absence of pulmonary stenosis.
Less common variants are the following:
- ▪
Those with the interventricular communication uncommitted, or noncommitted, to either subarterial outlet and with the aorta to the right of the pulmonary trunk, with either spiraling or parallel arterial trunks.
- ▪
Those with the interventricular communication in doubly committed position, with the aorta to the right of the pulmonary trunk and spiraling arterial trunks.
- ▪
Those with the interventricular communication in subaortic position but with the aorta to the left of the pulmonary trunk with parallel arterial trunks.
- ▪
Those with the usual atrial arrangement and discordant atrioventricular connections, usually with the aorta parallel to and to the left of the pulmonary trunk. Because of the significance of the discordant atrioventricular connections, this variant is discussed in Chapter 38 .
- ▪
Those with mirror–imaged atrial arrangement and any of the above variations.
- ▪
Those with isomeric atrial appendages and, hence, mixed and biventricular atrioventricular connections. These variants are discussed in Chapter 26 .
Specific Anatomy of the More Common Variants
Subaortic Interventricular Communication, Aorta to the Right of the Pulmonary Trunk, Spiraling Arterial Trunks, and Pulmonary Stenosis
There is usually a complete muscular infundibulum supporting each arterial valve ( Fig. 39.3A ), although fibrous continuity between the aortic and atrioventricular valves is found in many cases (see Fig. 39.3B ). The subpulmonary outflow tract is narrowed, typically with hypoplasia of the infundibulum. Often the valve is additionally involved. The obstructive lesions are similar to those seen in tetralogy of Fallot. The interventricular communication, cradled within the limbs of the septomarginal trabeculation, is perimembranous in most cases (see Fig. 39.3 ), but can have a muscular posteroinferior rim.
The specific morphology of the interventricular communication has major surgical significance. When there is a muscular posteroinferior rim, the atrioventricular conduction axis is not directly related to the margins of the defect and is less vulnerable at operation. In many cases the aortic valve retains part of its connection within the left ventricle. As long as most of the aorta is supported by the right ventricle, it is appropriate to diagnose the ventriculoarterial connection as being double-outlet, remembering that commitment is assessed on the basis of the short axis of the overriding arterial root ( Fig. 39.4 ). Important associated lesions may include a restrictive interventricular communication, which in essence represents obstruction of the left ventricular outlet. Mitral stenosis can also be found.
Subpulmonary Interventricular Communication
These hearts are usually described as the Taussig-Bing malformation. In the initial heart thus described, both arterial valves were supported by complete muscular infundibula. The term is now used to describe the spectrum of overriding of the pulmonary trunk in the setting of parallel arterial trunks, with the ends of the spectrum being either double-outlet right ventricle ( Fig. 39.5 ) or discordant ventriculoarterial connections (see Chapter 37 ). The interventricular communication, again opening to the right ventricle between the limbs of the septomarginal trabeculation, does so beneath the pulmonary trunk, with the muscular outlet septum attached to the ventriculoinfundibular fold. A muscular posteroinferior rim, formed by union of trabeculation and fold, often separates the rim of the defect itself from the membranous septum (see Fig. 39.5A ). As explained earlier, when present, the rim protects the atrioventricular conduction axis. In most cases, nonetheless, the defect extends posteriorly, becoming perimembranous (see Fig. 39.5B ).
Subaortic Interventricular Communication and No Pulmonary Stenosis
This malformation is similar to the lesion having a subaortic defect and pulmonary stenosis (compare Figs. 39.3 and 39.6 ). There can be bilateral infundibula (see Fig. 39.6A ) or fibrous continuity between the leaflets of the aortic and mitral valves (see Fig. 39.6B ). When bilateral infundibula are found, the arterial valves are usually side by side. In the setting of fibrous continuity between the leaflets of the aortic and mitral valves, the aortic valve is typically posterior and to the right of the pulmonary valve. The interventricular communication is usually perimembranous (see Fig. 39.6A ), although it may have a muscular posteroinferior margin (see Fig. 39.6B ). When there is continuity between the leaflets of the aortic and mitral valves, the aortic root usually retains part of its connection with the left ventricle. Although the interventricular communication is often large, it can be restrictive. As emphasized earlier, such a feature produces obstruction to the outflow from the left ventricle.
Other Anatomic Variations
On occasion, there can be multiple interventricular communications. Abnormalities of the atrioventricular valves are found in up to one-quarter of the hearts seen in autopsied series and include mitral stenosis and straddling mitral valve. Obstruction to one or other of the arterial outlets occurs frequently. Pulmonary stenosis, when present, is similar to that seen in tetralogy of Fallot (see Fig. 39.3A ) but is infrequent in the setting of the Taussig-Bing heart. Obstruction of the systemic outlet is much more frequent in the latter setting, with severe coarctation or interruption of the aortic arch found in a significant proportion of such cases. Other associated malformations include juxtaposition of the atrial appendages, totally anomalous pulmonary venous connection, and twisted atrioventricular connections. Variations in coronary arterial anatomy are particularly important in the setting of the Taussig-Bing hearts, since these are now corrected surgically using the arterial switch procedure. The most common arterial variation is 1L2RCx, with the left coronary being rather long. Interatrial communications within the oval fossa are also frequent.
Specific Anatomy of the Less Common Variants
Noncommitted Interventricular Communication
In a minority of patients, the interventricular communication is not directly committed to either arterial outlet. Such defects are usually the ventricular component of an atrioventricular septal defect, typically with a common atrioventricular valve ( Fig. 39.7A ). More rarely, the noncommitted communication is an isolated muscular defect that opens to the inlet or apical part of the right ventricle (see Fig. 39.7B ). Although the ventricular component of an atrioventricular septal defect may seem noncommitted to the anatomist, the surgeon is frequently able to create a long tunnel to one or other outflow tract (see Fig. 39.7A ). The relationships of the defect to the arterial outlets and to other structures within the right ventricle, therefore, require careful analysis. A key feature determining surgical noncommitment will be the presence of leaflet tissue derived from the tricuspid valve interposed between the defect and the arterial outlets (see Fig. 39.7B ).
Doubly Committed Interventricular Communication
The feature of this variant is that the interventricular communication, still opening to the right ventricle between the limbs of the septomarginal trabeculation, is positioned to open directly into both arterial outlets ( Fig. 39.8 ). The defect can again have a muscular posteroinferior rim, which will then protect the atrioventricular conduction axis or can extend to become perimembranous. In most hearts with doubly committed defects, the outlet septum is fibrous or else is no more than a fibrous raphe marking the junction between the leaflets of the arterial valves. On occasion, nonetheless, the outlet septum can be muscular when the interventricular communication is doubly committed. It is also the case that hearts with subaortic or subpulmonary defects can found when the outlet septum is fibrous. When the defect is doubly committed, both outflow tracts tend to override the crest of the muscular ventricular septum, with a spectrum existing between these hearts and double-outlet from the left ventricle. Some have suggested that these hearts are better described as showing double-outlets from both ventricles.
Comparison of the Morphology of the Overall Group
Many diagrams give the impression that, in the different variants, the interventricular communication occupies different locations relative to the muscular ventricular septum. To a certain extent this must be the case, but when examined relative to the overall right ventricular landmarks, its location is relatively constant. Thus, when the defect opens to the outlet of the right ventricle―be it subaortic, subpulmonary, or doubly committed―it is found between the limbs of the septomarginal trabeculation. The variation in morphology then depends on the location of the outlet septum, be it fibrous or muscular, relative to the limbs of the septomarginal trabeculation. When the septal defect is subaortic (see Figs. 39.3 and 39.6 ), the muscular outlet septum is fused with the anterior limb of the trabeculation, as in tetralogy of Fallot. This arrangement walls the subpulmonary outlet off from the interventricular communication. When the defect is in subpulmonary position, in contrast, the muscular outlet septum is fused either to the posterior limb of the septomarginal trabeculation or to the ventriculoinfundibular fold (see Fig. 39.5 ). This walls off the aorta from the defect, with the aorta possessing a complete muscular subaortic infundibulum. The degree of “squeeze” between the muscular outlet septum and the ventriculoinfundibular fold then determines the extent of subaortic obstruction. The smaller the subaortic muscular area, the more likely will be the association with aortic coarctation or interruption. When the defect is doubly committed (see Fig. 39.8 ), the outlet septum is almost always fibrous rather than muscular. This feature, reflecting incomplete formation of the subpulmonary infundibulum, is also a characteristic feature of the doubly committed and juxta arterial ventricular septal defect found with concordant ventriculoarterial connections (see Chapter 32 ). The interrelationships of the various structures forming the margins of the interventricular communication then serve to highlight the danger areas during surgical repair ( Fig. 39.9 ).
The size of the ventriculoinfundibular fold determines the length of the subarterial infundibula. When the folds are extensive, long infundibula are found supporting both arterial valves. Attenuation of the fold beneath either arterial valve produces atrioventricular–arterial valvar fibrous continuity, but still with double-outlet ventriculoarterial connection. Incisions through the fold take the surgeon outside the ventricular cavity, potentially placing in danger the major branches of the coronary arteries. This is not the case with the outlet septum, which is always an intracavitary structure. It can be resected without fear of damaging the conduction tissues. The relationship between the posterior limb of the septomarginal trabeculation and the ventriculoinfundibular fold determines the vulnerability of the conduction axis, depending on whether the defect is perimembranous or has a muscular posteroinferior rim. Should the defect need to be enlarged, it is safest to resect the anterocephalad limb of the septomarginal trabeculation, remembering that the septal perforating arteries are located within the septal crest in this area. All of these anatomic details are today readily demonstrated using clinical imaging (discussed later).
Intact Ventricular Septum
In a small minority of cases the ventricular septum can be intact in the setting of double-outlet right ventricle. In these instances, the left ventricle has no direct outlet and is usually severely hypoplastic. Patients with such hearts are unlikely to be candidates for biventricular surgical correction.
Subaortic Interventricular Communication With Left-Sided Aorta
In a minority of hearts, the aorta can be left-sided and anterior even in the setting of the usual atrial arrangement with concordant atrioventricular connections. When there is the usual atrial arrangement, left-sided aortas are more often found with discordant atrioventricular connections and left-sided ventricular topology. Distinction of the variant with concordant atrioventricular connections and right-sided topology should no longer be a problem. When found, the interventricular communication is typically subaortic, although it can be subpulmonary or doubly committed. Infundibular morphology is also variable. The usual subaortic location of the interventricular communication facilitates surgical repair, although the presence of a coronary artery passing anteriorly relative to the subpulmonary outlet can complicate the situation in the presence of pulmonary stenosis, which may be both valvar and subvalvar. Left juxtaposition of the atrial appendages is frequent, as is straddling of the tension apparatus of the mitral valve.
Discordant Atrioventricular Connections
In this setting it is more frequent to find the aortic root in an anterior and left-sided location. The discordant atrioventricular connections, however, can also be found with mirror-imaged atrial arrangement, when the aortic root will typically be anterior and right-sided. When seen with the usual atrial arrangement, many hearts are placed in the right chest, whereas patients with mirror-imaged atria have left-sided hearts. The interventricular communication is subpulmonary more often than subaortic. There is variability in the relationships of the great arteries, with the aorta to the left of the pulmonary trunk in only two-thirds of reported cases. The dominant feature is the discordant nature of the atrioventricular connections (see Chapter 38 ).
Mirror-Imaged Atrial Arrangement or Isomeric Atrial Appendages
Comparable variability, as found with usually arranged atrial chambers, must be anticipated when the atrial chambers are mirror-imaged. Double-outlet right ventricle, however, is much more frequent in the presence of isomeric atrial appendages rather than mirror imagery, being particularly common in the overall group of patients having isomeric right appendages. In the syndromes of isomerism, of course, variability occurs at all levels of the heart (see Chapter 26 ). This means that the complexity and multiplicity of the malformations are extreme. The combination of biventricular and mixed atrioventricular connections with a common atrioventricular orifice can be found with both right and left isomerism and with either right-side or left-side ventricular topologies. The interventricular communication typically opens to the inlet of the right ventricle and there are usually bilateral infundibula. As shown in Fig. 39.7 , these are the situations in which it is often possible to construct a tunnel between the interventricular communication and one or other of the arterial roots. Provided that the associated malformations are not too severe, biventricular repair remains a possibility.
Double-Outlet Left Ventricle
Because of the rarity of this malformation, it is unusual to find pathologic, clinical, or surgical series of any size. The largest review of which we are aware collected a total of 100 cases, with biventricular atrioventricular connections in 80%. As might be expected, double-outlet left ventricle most commonly occurs in hearts with the usual atrial arrangement and concordant atrioventricular connections. Discordant atrioventricular connections with the usual atrial arrangement and mirror-imaged atrial chambers have been reported, although no mention was made of isomeric atrial appendages. As with double-outlet right ventricle, the interventricular communication can vary in its relationship to the subarterial outlets, with further variability in the relationships of the arterial trunks and infundibular morphology. Bilaterally deficient infundibula, however, are more frequently found with double-outlet left ventricle than in any other situation. The commonest finding, nonetheless, has been a subpulmonary infundibulum with fibrous continuity between the leaflets of the aortic and mitral valves. Associated abnormalities are the rule rather than the exception. Obstruction in the pulmonary outflow tract is frequent when the interventricular communication is subaortic. Patients with a subpulmonary defect, in contrast, have a high incidence of systemic obstruction, usually coarctation. Reported anomalies of the atrioventricular valves include hypoplasia, stenosis, straddling, and Ebstein-like malformations, with the tricuspid valve more often abnormal than the mitral. Hypoplasia of the right ventricle is also frequent. Because of this marked heterogeneity, it is doubtful whether it is justifiable to seek to make groupings or categories. It is the combinations that dominate the clinical picture and determine the surgical options. In each patient, therefore, the arrangements should be analyzed in the same logical sequence as required for any complex defect. Investigation and categorization must be individualized, with each patient having his or her defects systematically documented in terms of atrial arrangement, atrioventricular connection, morphology of the interventricular communication and its relationship to the outlets, arterial relations, obstruction to the ventricular outlets, atrioventricular valvar abnormalities, and other associated malformations.
Morphogenesis
During early embryonic development, the outflow tract of the heart arises exclusively from the developing right ventricle. For the embryo, therefore, double-outlet right ventricle can be considered the default option ( Fig. 39.10A ). But before the ventricular septum can be closed, the subaortic outflow tract must be transferred to the developing left ventricle (see Fig. 39.10B ). The stage of transfer is analogous to the situation found postnatally in the setting of tetralogy of Fallot (see Fig. 39.2 ).
This process of transfer, therefore, demonstrates most clearly the anatomic differences between the initial embryonic interventricular communication, which becomes the outflow tract for the left ventricle, and the eventual area of septation, which is closed by formation of the membranous septum (see Fig. 39.10 ). However, the fundamental cause of the embryologic error or errors leading to retention of the origin of both arterial roots from the right ventricle remains unclear. In the experimental situation, double-outlet right ventricle has been created in chick embryos by placing a loop around the infundibulum prior to its septation. Many genetically modified mice exhibit double-outlet right ventricle, or else a common arterial trunk arising exclusively from the right ventricle. Examples are now encountered with the interventricular communication in subaortic, subpulmonary, and doubly committed positions. The findings provide evidence for the pathologic continuum found between concordant ventriculoarterial connection and double-outlet right ventricle when the interventricular communication is a subaortic defect ( Fig. 39.11A ).
A similar spectrum of development in mice with knockout of Pitx2 shows the change from double-outlet right ventricle with subpulmonary defect to discordant ventriculoarterial connections with ventricular septal defect. The finding of still further genetically modified mice with failure of muscularization of the outflow cushions reveals the mechanism underscoring formation of the doubly committed defect (see Fig. 39.11B ). In these mice with absence of a muscular outlet septum, it is also easy to appreciate how both outflow tracts can become incorporated into the left ventricle. Although the failure of muscularization of the outflow cushions means that there is absence of the subpulmonary infundibulum (see Fig. 39.11B ), the inner heart curvature remains myocardial. This is also the case in normal development even after the aortic root has been transferred to the left ventricle and the interventricular communication closed. Leftward shift of the arterial valves relative to the ventricular septum, therefore, is not dependent on absorption and shortening of the infundibula.
Pathophysiology
The pathophysiology of the double-outlet ventricle is as variable as its anatomy. Depending on the degree of override of the arterial valves, the position and size of the interventricular communication, potential obstruction of an arterial outlet, and the arrangement of the great arteries themselves, the pathophysiologic picture can range from that seen in simple ventricular septal defects to that of discordant ventriculoarterial connections, or even functionally single ventricle physiology. Many patients with double-outlet ventricles also have associated cardiac lesions that may affect the physiology, thus further complicating clinical management.
Intraventricular Streaming
A very characteristic feature of double-outlet right ventricle physiology is intraventricular streaming. Based on the underlying anatomy, oxygenated blood entering the right ventricular cavity through the interventricular communication may show preferential flow to one of the arterial trunks. Interventricular communications are commonly unrestrictive. However, restriction can occur and may then necessitate surgical enlargement of the communication. Streaming may vary significantly between patients.
Subaortic interventricular communications allow for preferential blood flow of oxygenated blood to the aorta, thereby limiting the amount of right-to-left shunting ( Fig. 39.12A ). Pathophysiologically similar to large ventricular septal defects, double-outlet right ventricle and subaortic interventricular communication show increased pulmonary blood flow and little cyanosis, although systemic saturations may be decreased to some degree based on intracardiac mixing. If an obstruction to the pulmonary outflow is present, the physiology mimics that of tetralogy of Fallot. The severity of cyanosis depends on the extent of obstruction. The dynamic obstruction in tetralogy of Fallot, presenting with characteristic spells, can be seen in patients with double-outlet right ventricle as well.
