The concept of double outlet as a ventriculo-arterial connection has been well accepted for several decades. This is described elsewhere in this textbook (see Chapter 1 ). It may occur with each atrial arrangement, with any atrioventricular connection, and with all possible variations of ventricular morphology. The morphologic arrangement can then be further complicated by the presence of a host of associated defects, some common and some rare. The clinical picture is as inconstant as the anatomical permutations and associations would suggest. In this chapter, we review the combinations in which the outflow tracts arise from only one ventricle, but in the setting of hearts with two ventricles, and in which each ventricle possesses its own atrioventricular connection, in other words, those with biventricular atrioventricular connections. Origin of both arterial trunks from the same ventricle, of course, can also be found in the setting of univentricular atrioventricular connections, but these lesions are considered in the chapters of the book concentrating on the functionally univentricular arrangements ( Chapter 31, Chapter 32 ).
HISTORY
The first example of double outlet right ventricle known to us was described in 1793, by Mr Abernethy of St Bartholomew’s Hospital, who commented that ’both ventricles, the left by means of an opening in the upper part of the septum ventriculorum, projected their blood into the aorta’. 1 Farre 2 regarded this case as being, in most respects, similar anatomically, and in its clinical history, to a number of other cases which were undoubtedly examples of what we would now describe as tetralogy of Fallot, albeit that Farre drew particular attention to the right ventricular origin of the aorta in the case described by Abernethy. The term double outlet right ventricle, however, did not appear until 1957. 3 Prior to that, examples of hearts with both arterial trunks arising from the right ventricle were described as partial transposition since only the aorta was considered to be placed across the ventricular septum. 4 Other hearts which would now be designated thus were included in the collections of Peacock, 5 Von Rokitansky, 6 Spitzer, 7 and Abbott, 4 generally under the terms partial transposition or complete dextroposition of the aorta. 4 It is inappropriate at this point to revisit the tortuous semantic debate that has continued over the past century, and more, with regard to the use of the term transposition , particularly in relation to hearts with both great arteries arising from the right ventricle. Suffice it to say that, for our purposes, we consider discordant ventriculo-arterial connections to be the essence of transposition (see Chapter 38 ). Transposition as thus defined, therefore, is mutually exclusive from double outlet right ventricle.
An equally tortured debate has surrounded the relationship between double outlet right ventricle and tetralogy of Fallot. It is a fact that the extent of right ventricular origin of the aorta is markedly variable in hearts having the phenotypic morphology of tetralogy of Fallot (see Chapter 36 ). In a proportion of such cases, therefore, the aortic valve will be supported predominantly by right ventricular structures. Indeed, cases of this type were included by Fallot himself in his original description of the lesion that now bears his name. 8 As we have explained, however, we consider double outlet right ventricle to represent one form of ventriculo-arterial connection, rather than a malformation defined on the basis of phenotypic anatomy. There is also no question but that, in some hearts having the phenotypic morphology of tetralogy of Fallot, the larger part of the overriding subaortic outlet is supported within the right ventricle. 9,10 Patients having such hearts will be described within this chapter. For quite some time, however, it was suggested that presence of complete muscular infundibulums supporting the entirety of the leaflets of both arterial valves was an essential part of the the diagnosis of double outlet right ventricle. 11 It was subsequently established that one of the most important principles of description of congenitally malformed hearts was that structures should be defined in their own right, and not on the basis of another feature which is itself variable. 12 On the basis of this principle, known as the morphological method, it is inappropriate to define double outlet ventricle, a specific form of ventriculo-arterial connection, on the basis of infundibular morphology, this latter feature being but one of the many variables complicating the morphology of the various entities grouped together because both arterial trunks arise in larger part from the same ventricle.
Double outlet right ventricle itself is but one part of the overall group of hearts to be described in this chapter. The other part, namely double outlet left ventricle, is very much rarer. Indeed, for quite some time distinguished morphologists and embryologists went on record as stating that double outlet from a morphologically left ventricle was an embryological impossibility. 13 Description of a heart with both arterial trunks arising from the left ventricle in the setting of an intact ventricular septum proved beyond doubt that the entity existed. 14 Since then, cases have tended to be described in isolation, rather than in large series, from either the pathological or clinical viewpoints.
PREVALENCE
Double outlet right ventricle is a rare cardiac malformation, accounting for fewer than 1% of all congenital cardiac defects. Although infrequent overall, it is sufficiently common for a number of authors to have accumulated large numbers of pathological, clinical or surgical cases. The more frequent variants of the anomaly are well documented, and present a familiar enough problem to the paediatric cardiologist and surgeon.
Double outlet left ventricle is a very much rarer malformation, albeit that the total number of published cases is now substantial. Indeed, it may be more frequent than has previously been recognised. It probably accounts for fewer than 5% of all hearts with double outlet ventriculo-arterial and biventricular atrioventricular connections. This would correspond to an incidence of fewer than 1 in 200,000 births.
MORPHOLOGY AND CLASSIFICATION
The literature relating to hearts in which both arteries arise in their greater part from the same ventricle is extensive, and includes descriptions of a bewildering variety of anatomic variations. So as to avoid confusion, in our review we focus attention, first, on the categorisation of the various malformations, and only then on the details of morphology, concentrating on the commoner, and more important, malformations.
Categorisation
A logical and step-by-step approach to diagnosis and classification proves of immense value when describing the hearts unified because both arterial trunks arise, in their greater part, from the same ventricle. Analysis, be it in the clinical or pathological situation, follows the same careful sequence that has been outlined in Chapter 1 ( Table 40-1 ). Thus, as with any congenitally malformed heart, analysis starts with ascertainment of atrial arrangement and venous connections. Thereafter, the atrioventricular connections must be established with certainty. At the ventricular level, it is the anatomy of the connection between ventricular mass and great arteries that is the diagnostic feature, albeit that note is taken of the inter-relationships 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, which is categorised in the same way as any other hole between the ventricles (see Chapter 28 ), are also of great importance. In this respect, however, when both arterial trunks arise from the same ventricle ( Fig. 40-1 ), the hole between the ventricles serves as the outlet for the other ventricle. Its most important feature, therefore, is its relationship with the subarterial ventricular outlets ( Tables 40-2 and 40-3 ). Attention must also be paid to the integrity and function of the atrioventricular valves, especially the mitral valve, and to the presence of other associated cardiac defects, which are frequent ( Table 40-4 ). It is neither practical nor desirable to use a rigid type of classification for the various malformations united simply because both arterial trunks arise, in their greater part, from the same ventricle. In our view, the categorisation of each case should be individualised, just as the medical and surgical management need to be tailored to cater to the particular problems of the individual patient. Certain anatomic variants in which both arterial trunks arise from the right ventricle, nonetheless, do occur with sufficient frequency to merit separate discussion. We commence our account, therefore, with definition and discussion of the commoner variants, as has also been discussed in a review of double outlet right ventricle nomenclature as part of the Congenital Heart Surgery Nomenclature and Database Project. 15
|
| Site of Defect | Percentage (of 88 defects) |
|---|---|
| Subaortic | 52 |
| Subpulmonary | 24 |
| Non-committed | 14 |
| Doubly committed | 10 |
| Type of Defect | Subaortic | Subpulmonary | Non-committed | Doubly Committed | Total |
|---|---|---|---|---|---|
| Perimembranous | 36 | 13 | 7 | 5 | 61 |
| Muscular | 9 | 9 | 5 | 4 | 27 |
| Total | 45 | 22 | 12 | 9 | 88 |
| Defect | No. | % |
|---|---|---|
| Pulmonary stenosis | 31 | 37 |
| Atrial septal defect | 19 | 23 |
| Coarctation | 16 | 19 |
| Mitral stenosis | 7 | 8 |
| Straddling mitral valve | 6 | 7 |
| Hypoplastic left ventricle | 5 | 6 |
| Aortic stenosis (valvar or subvalvar) | 4 | 5 |
| Restrictive ventricular septal defect | 4 | 5 |
| Juxtaposition of atrial appendages | 4 | 5 |
| Interrupted aortic arch | 3 | 4 |
| Common atrioventricular valve | 3 | 4 |
| Hypoplastic right ventricle | 2 | 2 |
| Criss-cross atrioventricular connection | 2 | 2 |
| Imperforate mitral valve | 1 | 1 |
| Imperforate tricuspid valve | 1 | 1 |
| Parachute mitral valve | 1 | 1 |
| Cleft mitral valve | 1 | 1 |
| Cleft tricuspid valve | 1 | 1 |
| Totally anomalous pulmonary venous connection | 1 | 1 |
Double Outlet Right Ventricle
The commoner variants, in approximate order of frequency, are:
- •
Those with the interventricular communication in subaortic position, with the aorta spiralling from right to left relative to the pulmonary trunk, along with pulmonary stenosis, the so-called Fallot variant (see Fig. 40-2A )
Figure 40-2
The cartoons show the commoner variants of double outlet right ventricle. A, The variant with a subaortic defect, infundibular pulmonary stenosis, and the aorta to the right of pulmonary trunk, a variant also known as the Fallot type. B, The variant with a subpulmonary defect and parallel arterial trunks, also known as the Taussig-Bing type. C, The variant with a subaortic defect, and with the aorta to the right of the pulmonary trunk, but without pulmonary stenosis. The arrow indicates the path of blood from the left ventricle to the aorta with a subaortic defect.
- •
Those with the interventricular communication in subpulmonary position, with the aorta to the right of, and parallel to, the pulmonary trunk, the so-called Taussig-Bing variant (see Fig. 40-2 B)
- •
Those with the interventricular communication in subaortic position, and with the aorta spiralling from right to left relative to the pulmonary trunk, but in the absence of pulmonary stenosis (see Fig. 40-2 C)
Less common variants are:
- •
Those with the interventricular communication uncommitted, often described as non-committed, to either subarterial outlet, and with the aorta to the right of the pulmonary trunk, with either spiralling or parallel arterial trunks ( Fig. 40-3 A)
Figure 40-3
The cartoons show other, less common variants of double outlet right ventricle. A, The variant with a non-committed defect. B, The variant with the aorta to left of pulmonary trunk, parallel arterial trunks, and pulmonary stenosis. C, The variant with discordant atrioventricular connections and usual atrial arrangement. D, The variant with mirror‑imaged atrial arrangement and concordant atrioventricular connections.
- •
Those with the interventricular communication in doubly committed position, with the aorta to the right of the pulmonary trunk, and with spiralling 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 ( Fig. 40-3 B)
- •
Those with usual atrial arrangement and discordant atrioventricular connections, usually with the aorta parallel to and to the left of the pulmonary trunk ( Fig. 40-3 C) (see Chapter 39 )
- •
Those with mirror‑imaged atrial arrangement ( Fig. 40-3 D). Any of the previously mentioned variations may occur.
- •
Those with isomeric atrial appendages and, hence, mixed and biventricular atrioventricular connections (see Chapter 22 )
Specific Anatomy of the Commoner Variants
Subaortic Interventricular Communication, Aorta to Right of Pulmonary Trunk, Spiralling Arterial Trunks, and Pulmonary Stenosis
There can be a complete muscular infundibulum supporting each arterial valve in this variant ( Fig. 40-4 ), although fibrous continuity between the aortic and atrioventricular valves is found in a high proportion of cases ( Fig. 40-5 ). The subpulmonary outflow tract is narrowed, with or without hypoplasia of the infundibulum (see Figs. 40-4 and 40-5 ). Often the valve is additionally involved. The obstructive lesions are similar to those seen in Fallot’s tetralogy. The interventricular communication, cradled within the limbs of the septomarginal trabeculation, is perimembranous in four-fifths (see Figs. 40-4 and 40-5 ), having a muscular postero-inferior rim in the remainder. This feature has major surgical significance, since the atrioventricular conduction axis is not directly related to the margins of the defect in the presence of the muscular postero-inferior rim, being posterior to it, and hence less vulnerable at operation. In many cases, the aortic valve retains part of its connection within the left ventricle, but as long as most of the aorta is supported by the right ventricle, it is appropriate to diagnose the ventriculo-arterial connection as being double outlet ( Fig. 40-6 ). Important associated lesions may include a restrictive interventricular communication, which in essence represents obstruction of the left ventricular outlet, this occurring in up to one-tenth of cases, 10 and mitral stenosis.
With Subpulmonary Interventricular Communication
These hearts are usually described as the Taussig-Bing malformation, recognising the description of the index case in which the pulmonary trunk, which was unobstructed, lay to the left of the aorta and overrode an interventricular communication. 16 In this initial heart, both arterial valves were supported by complete muscular infundibulums. There has subsequently been much discussion as to the most appropriate use of the term Taussig-Bing anomaly, 11 but in our opinion 17 the term is best used for 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. 40-7 ) or discordant ventriculo-arterial connections (see Chapter 38 ). The interventricular communication, again cradled within the limbs of the septomarginal trabeculation, opens beneath the pulmonary trunk because the muscular outlet septum is attached to the ventriculo-infundibular fold. A muscular postero-inferior rim, formed by union of trabeculation and fold in two-fifths of cases, often separates the rim of the defect itself it from the membranous septum (see Fig. 40-7 ). In three-fifths of cases, nonetheless, the defect extends posteriorly, becoming perimembranous ( Fig. 40-8 ).
Double Outlet Right Ventricle with Subaortic Defect and No Pulmonary Stenosis
This malformation is similar in many anatomical respects to the anomaly with subaortic defect and pulmonary stenosis (compare Figs. 40-9, 40-4, and 40-5 ). As in the situation with a stenotic subpulmonary outlet, there can be bilateral infundibulums (see Fig. 40-9 ) or fibrous continuity between the leaflets of the aortic and mitral valves. When there are bilateral infundibulums, the arterial valves are usually side by side (see Fig. 40-9 ), but with fibrous continuity in the roof of the interventricular communication, the aortic valve is typically posterior and to the right of the pulmonary valve. The arterial trunks typically spiral as they exit from the heart. The interventricular communication is usually perimembranous (see Fig. 40-9 ), though it may have a muscular posterior margin ( Fig. 40-10 ). 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 (see Fig. 40-10 ). In such instances, assignment of the overriding valve is made on the basis of the short axis of the root, not the long axis of the ventricular septum (see Fig. 40-6 ). Whilst the ventricular septal defect is often large in this group of cases, restrictive defects may be seen, which effectively produces obstruction to the outflow from the left ventricle, an important clinical consideration.
Other Anatomical Variations
As can be seen in the figures provided thus far, there is much individual variability within the malformations already described. This relates to the site, size and detailed morphology of the interventricular communication, the relationships of the arterial outlets to one another and to the septal defect, and to the frequent presence of additional malformations (see Tables 40-2, 40-3, and 40-4 ). With regard to the interventricular communication, although it usually extends to become perimembranous, irrespective of the infundibular morphology, a muscular postero‑inferior rim is present in a substantial minority of instances (see Table 40-3 ). Perimembranous defects may extend variably to open towards the inlet and trabecular portions of the right ventricle, as well as opening directly into one or other outlet. Restrictive defects, which produce obstruction to the outlet from the left ventricle, are uncommon, but when present are of obvious clinical and surgical importance. Multiple interventricular communications can be found on occasion.
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 Fallot’s tetralogy, 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 interruption of the aortic arch in a significant proportion of these cases. Other major associated malformations include juxtaposition of the atrial appendages, totally anomalous pulmonary venous connection, and criss‑cross atrioventricular connections. The frequent 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. Interatrial communications within the oval fossa are also frequent.
Less Common Variants
Non-Committed Interventricular Communication
In about one-tenth of cases seen in autopsied series, the interventricular communication is not directly committed to either arterial outlet. Such defects are usually perimembranous, and open primarily to the inlet of the right ventricle, often in the presence of a common atrioventricular valve ( Fig. 40-11 ). Isolated muscular interventricular communications can also open directly to the inlet or apical parts of the right ventricle, and then also be non-committed ( Fig. 40-12 ). Such non-committed defects are particularly important surgically, and require careful delineation of the relationships of the defect to the arterial outlets and to other structures within the right ventricle, especially abnormal leaflet tissue derived from the tricuspid valve which may interpose between the defect and the arterial outlets. 18
Doubly Committed Interventricular Communication
In another one-tenth of cases seen in autopsied series, the interventricular communication is positioned so as to open directly into both arterial outlets ( Fig. 40-13 ). As with the majority of the hearts already described, the interventricular communication is cradled between the limbs of the septomarginal trabeculation and is usually perimembranous, although it can have a muscular postero-inferior rim. If the muscular rim is present, it will protect the atrioventricular conduction axis. The essence of these hearts, however, is absence of a muscular outlet septum, with only a fibrous raphe interposing between the leaflets of the arterial valves. This means that both outflow tracts tend to override the crest of the muscular ventricular septum, and a spectrum exists between these hearts and double outlet from the left ventricle. Indeed, the hearts can be considered as showing double outlet from both ventricles ( Fig. 40-14 ). 19
Consistent Variations in Morphology of the Overall Group
When previous accounts of the structure of the variants of double outlet are examined, the impression is often gained that, when the interventricular communication is in subaortic rather than subpulmonary position, it has moved relative to the muscular ventricular septum. To a certain extent, this must be the case, but when examined relative to the overall landmarks of the muscular ventricular septum, its location is remarkably constant. 20,21 Thus, when the defect opens to the outlet of the right ventricle, be it subaortic subpulmonary, or doubly committed, then always it is found between the limbs of the septomarginal trabeculation. The variation in morphology depends upon the connection of the muscular outlet septum relative to the septomarginal trabeculation. When the septal defect is subaortic (see Fig. 40-4 ), then the muscular outlet septum is fused with the anterior limb of the trabeculation, as in tetralogy of Fallot. This fusion walls off the subpulmonary outlet from the ventricular septal defect. 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 ventriculo-infundibular fold (see Fig. 40-7 ). This walls off the aorta from the septal defect and, almost always, produces a complete muscular subaortic infundibulum. The degree of squeeze between the musuclar outlet septum and the ventriculo-infundibular fold determines the extent of subaortic obstruction. The smaller the subaortic muscular area, the more likely it is that there will be aortic coarctation or interruption. The characteristics of the doubly committed defect (see Fig. 40-13 ) are that, almost always, the outlet septum is fibrous rather than muscular, and the adjacent portions of the subaortic and subpulmonary infundibulums are absent. Such absence of the outlet septum, and incomplete formation of the subpulmonary infundibulum, is also a characteristic feature of the doubly committed and juxta-arterial ventricular septal defect found with concordant ventriculo-arterial connections (see Chapter 28 ). The interrelationships of the muscular structures around the interventricular communication (see Fig. 40-12 ) condition other important anatomic features of double outlet. Thus, the size of the ventriculo-infundibular folds determines the extent of the subarterial infundibulums. When the folds are extensive, then long infundibulums are found supporting both arterial valves (see Fig. 40-9 ). In contrast, when the fold is attenuated beneath each arterial valve, then there is atrioventricular-arterial valvar fibrous continuity (see Fig. 40-10 ), but still with double outlet ventriculo-arterial connection. It is then the relationship between the posterior limb of the septomarginal trabeculation and the ventriculo-infundibular fold which determines whether the ventricular septal defect is perimembranous (see Fig. 40-9 ) or has a muscular postero-inferior rim (see Fig. 40-10 ). All of these anatomical details are, nowadays, readily demonstrated using cross sectional echocardiography.
Double Outlet Right Ventricle with Intact Ventricular Septum
When the ventricular septum is intact, which can occur rarely in a patient with double outlet right ventricle, the left ventricle has no direct outlet, and in these circumstances is usually severely hypoplastic.
Subaortic Interventricular Communication with Left-Sided Aorta
The key point in diagnosing this variant is that, despite the aorta being left sided, the heart exhibits usual atrial arrangement with concordant atrioventricular connections. The lesions were of more significance when arguments raged concerning the significance of the so-called loop rule, left-sided aortas being presumed only to exist with left hand ventricular topology when there was the usual atrial arrangement. Nowadays there is no problem in defining with precision the atrial arrangement and the atrioventricular connections, and in recognising the left-sided location of the aorta. 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 makes surgical repair relatively easy, 22 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. When encountered, left juxtaposition of the atrial appendages is frequent, as is straddling mitral valve. 22,23
Double Outlet Right Ventricle with Discordant Atrioventricular Connections
This complex malformation has been described in association with both usual and mirror-image atrial arrangements. When seen, many patients with usual atrial arrangement have their hearts placed in the right chest, while those with mirror-imaged atriums have left-sided hearts. Pulmonary stenosis was present in four-fifths of the largest reported series, 24 with the interventricular communication being subpulmonary more frequently than subaortic. Despite the discordant atrioventricular connections, there was marked variability in the relationships of the great arteries, with the aorta to the left of the pulmonary trunk in only two-thirds of cases. This variant of double outlet right ventricle has much in common with congenitally corrected transposition, and is discussed further in Chapter 39 .
Double Outlet Right Ventricle with Either Mirror-Imaged Atrial Arrangement or Isomeric Atrial Appendages
We have already made mention of double outlet right ventricle in the setting of mirror‑imaged atrial arrangement. Very few cases have been reported, but the same variability must be anticipated as for double outlet right ventricle when found with usual atrial arrangement. Double outlet right ventricle is much more frequent in the presence of isomeric atrial appendages, 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 22 ). This means that the complexity and multiplicity of the malformations seen in the presence of isomerism with double outlet right ventricle may be expected to be extreme. One combination in particular deserves mention, that of biventricular and mixed atrioventricular connections and a common atrioventricular orifice. 25 This combination is found with both right and left isomerism, and with either right hand or left hand ventricular topologies. The interventricular communication opens to the inlet of the right ventricle, and usually there are bilateral infundibulums. As shown in Figure 40-11 , nonetheless, it is often possible to construct a tunnel between the interventricular communication and the subaortic outlet, so providing the associated malformations are not too severe, biventricular repair remains a possibility.
Double Outlet Left Ventricle
Because of the rarity of this malformation, pathological, clinical, or surgical series of any size have rarely been reported from individual institutions. Moreover, reviews of the subject, and reports of individual cases, have frequently included material relating to functionally univentricular hearts.26–28 The largest review of which we are aware collected a total of 100 cases, with biventricular atrioventricular connections in four-fifths. The reviews reveal that, as might be expected, double outlet left ventricle most commonly occurs in hearts with usual atrial arrangement and concordant atrioventricular connections, making up nine-tenths of the series. Discordant atrioventricular connections with usual atrial arrangement were noted in one-twentieth of cases, and mirror-imaged atrial chambers were reported in the remaining cases, albeit that no mention was made of isomeric atrial appendages. Variability, as with double outlet right ventricle, depends on the site of the interventricular communication, its relationship to the subarterial outlets, and the relationships of the arterial trunks. Infundibular morphology has also varied dramatically, albeit that bilaterally deficient infundibulums are more frequently found with double outlet left ventricle than in any other situation. This arrangement, nonetheless, does not occur in the majority of cases, the commonest finding being a subpulmonary infundibulum with fibrous continuity between the leaflets of the aortic and mitral valves. Associated abnormalities are the rule rather than the exception. A particularly high frequency of obstruction in the pulmonary outflow tract is found when the interventricular communication is subaortic. Those with a subpulmonary defect have a high incidence of systemic obstruction, usually coarctation, with about half the reported cases being thus affected. As might be expected, there is a low incidence of pulmonary obstruction when the defect is subpulmonary. Anomalies of the atrioventricular valves occur in up to one-third of cases, and include hypoplasia, stenosis, straddling and Ebstein-like malformations. The tricuspid valve is more often abnormal than the mitral. Hypoplasia of the right ventricle is also a frequent finding. As with double outlet right ventricle, therefore, extreme heterogeneity exists. It is doubtful whether it is justifiable to seek to make groupings or categories. Each reported type is individually extremely rare, and is subject to a host of associated defects and problems. It is these features that dominate the clinical picture, and determine the surgical options.
In each case, therefore, the problem should be analysed in the same logical sequence required for any complex defect. Investigation and categorisation need to be individualised, 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.
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