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Double Inlet Ventricle and Atretic Atrioventricular Valve
Definition
Double inlet ventricle is a congenital cardiac malformation in which both atria connect to only one ventricular chamber by either two separate atrioventricular (AV) valves or a common AV valve. Closely related to double inlet ventricle are cardiac malformations in which both atria connect to only one ventricular chamber because of atresia of one AV valve that is imperforate or absent. As a group, double inlet ventricles and those with an atretic AV valve are appropriately considered as having a single ventricle or univentricular AV connection, although these phrases are not appropriate for describing morphology of an individual heart.
The ventricular mass in these settings rarely consists only of a solitary ventricle. When, as is usual, there are two ventricles, one is usually incomplete (rudimentary) and hypoplastic. Often the incomplete ventricle is connected to an atrium by overriding of an AV valve. Such arrangements are termed double inlet ventricle only if more than 50% of the overriding valve lies over the main (dominant) ventricle.
Classic tricuspid atresia (univentricular AV connection with atrial situs solitus, ventricular D-loop, single inlet left ventricular main chamber, right-sided AV valve [tricuspid] atresia, and ventriculoarterial [VA] concordant or discordant connection) is separately discussed in Chapter 41 . 1 Most morphologic variants of left-sided AV valve (mitral) atresia with patent aortic outlet are included in this chapter. Mitral atresia in association with either aortic atresia or aortic stenosis, intact ventricular septum, and concordant AV and VA connections represent two of the four classic morphologic forms of hypoplastic left heart physiology and are discussed in Chapter 49 .
1 The adjectives left and right used to modify atrium or ventricle mean morphologically left or right . Position of a chamber or valve is referred to as right sided or left sided .
Historical Note
One of the earliest descriptions of a variety of this congenital anomaly was by Holmes, who in 1824 noted that it was intermediate between a normal heart and one with a solitary ventricular chamber. It is believed that Peacock described a heart with “both auricles opening into the left ventricle” in 1854. Rokitansky described and illustrated a case of double inlet left ventricle in 1875, as did Mann in 1907, describing the heart as cor triloculare biatriatum . Taussig described “single ventricle with a diminutive outlet chamber” in 1939. Lev and colleagues have listed a number of other descriptions of “single (primitive) ventricle” that were published more than 100 years ago.
An important contribution by Van Praagh and colleagues in 1964 at the Mayo Clinic was clear definition of the entity as one in which both AV valves empty into the same ventricle. About the same time, Elliott and colleagues expressed the view, now accepted, that hearts with atresia of one AV valve (and thus a single AV valve) have much in common with hearts with double inlet ventricle. Anderson and colleagues introduced the phrase univentricular AV connection to collate this group of malformations.
Lev clearly established as a different entity hearts with a huge ventricular septal defect (VSD) or common ventricle, in which one side of the common chamber was morphologically right ventricle and the other left ventricle; he thereby excluded them from the single-ventricle category.
Surgical palliation of double inlet ventricle without pulmonary stenosis began with the original description of pulmonary trunk banding by Muller and Damman in 1952. Palliation of double inlet ventricle with pulmonary stenosis has as its basis the original Blalock-Taussig shunt; its application to patients with double inlet ventricle and pulmonary stenosis was only a matter of time. Redo and colleagues may have been the first to show the favorable effect of a Blalock-Hanlon atrial septectomy in patients with left-sided (mitral) valve atresia.
Septating the main chamber to establish two circulations in series emerged from the Mayo Clinic experience of unexpectedly encountering a patient with double inlet ventricle in 1956. Preoperative diagnosis was corrected transposition with VSD, but correct diagnosis was made after opening the ventricle. Septation was accomplished, but the patient died about 6 months after operation, probably during a Stokes-Adams episode. This concept lay dormant for some years, but in 1972 it was further developed by Sakakibara and colleagues and in 1973 by Edie, Malm, and colleagues, who reported four successful septation repairs. Three long-term survivors of septation were reported in 1973 by Arai, Sakakibara, and colleagues, and one was reported by Ionescu and colleagues. McGoon, Danielson, and colleagues began to report successful results from the Mayo Clinic about this same time. The right atrial approach to septation was suggested and applied by Doty and colleagues in 1979.
A different surgical concept—using the main (dominant) ventricular chamber for generating systemic blood flow and allowing the vis a tergo of the systemic venous system to generate pulmonary blood flow—was stimulated by the work of Fontan and Baudet (published in 1971 and known as the Fontan operation ) and by the work of Kreutzer and colleagues. Application of this concept to surgical treatment of double inlet ventricle was reported by Yacoub and Radley-Smith in 1976.
Subaortic stenosis became apparent as a major problem when experience with the Fontan operation increased during the early 1970s. In 1973, Neches and colleagues applied the concept of placing the main chamber in direct communication with the aorta by performing an anastomosis of pulmonary trunk to aorta. Others have accomplished this by an anastomosis of the proximal segment of the divided pulmonary trunk to the side of the ascending aorta, a part of a Damus-Kaye-Stansel (DKS) operation. This concept has been revitalized more recently by extensive augmentation of the usually hypoplastic aortic arch in conjunction with the DKS operation in the Norwood I operation and by using the arterial switch operation for this purpose, first by Freedom, Williams, Trusler, and colleagues in 1980 and in neonates by Karl and colleagues in 1991. Penkoske and colleagues approached the problem directly by enlarging the VSD in 1984.
Application of cardiac transplantation to this group of patients was a natural evolution in managing patients with univentricular AV connections and myocardial failure.
Morphology
Generalizations
Ventricular Mass
The main (dominant) chamber making up the ventricular mass in double inlet ventricle with two ventricles may have a left ventricular internal architecture, a right ventricular internal architecture, or an indeterminate architecture. Main chamber volume is largest when there is no pulmonary stenosis but considerably smaller when pulmonary stenosis is present. This is related to the fact that main chamber volume is positively correlated with pulmonary-to-systemic flow ratio ( 
). The nondominant, incomplete (rudimentary) hypoplastic chamber, when present, is always opposite architecture to the dominant chamber. Ventricular topology in double inlet ventricles may be either right-handed (D-loop), left-handed (L-loop), or indeterminate ( Tables 56-1 and 56-2 ). (See “Symbolic Convention of Van Praagh” under Terminology and Classification of Heart Disease in Chapter 1 .)
Table 56-1
Ventricular Architectural Pattern and Atrial Situs in Double Inlet Ventricles a
Data from Stefanelli and colleagues.
| Atrial Situs | n | Solitary Ventricle | Two Ventricles | ||
|---|---|---|---|---|---|
| Indeterminate | Right-Handed (D-Loop) | Left-Handed (L-Loop) | Undetermined Loop | ||
| Solitus | 101 (87) + 89 | 15 | 32 + 89 | 50 | 4 |
| Inversus | 2 (2) | 0 | 2 | 0 | 0 |
| Ambiguus: | 12 (10) | 7 | 5 | 0 | 0 |
| Bilateral right-sidedness | 8 (7) | 5 | 3 | ||
| Bilateral left-sidedness | 4 (3) | 2 | 2 | ||
| Unknown | 1 (1) | 1 | 0 | 0 | 0 |
| T otal | 116 + 89 = 205 | 23 (20) | 39 (34) + 89 | 50 (43) | 4 |
Key: ( ), Percentage of 116.
a Cases of classic tricuspid atresia ( n = 89) are included and underlined.
Table 56-2
Morphologic Findings in 189 Patients with Double Inlet or Common Inlet Ventricle
Modified from Kitamura and colleagues.
| DIRV ( n = 31) | DILV ( n = 45) | CIRV ( n = 93) | CILV ( n = 20) | |
|---|---|---|---|---|
| Atrial Arrangement | ||||
| Usual | 19 (61%) | 40 (89%) | — | 2 (10%) |
| Mirror image | 1 (3%) | 1 (2%) | — | — |
| Right isomerism | 8 (26%) | 4 (9%) | 89 (96%) | 16 (80%) |
| Left isomerism | 3 (10%) | — | 4 (4%) | 2 (10%) |
| Ventricular Loop | ||||
| D-loop | 21 (68%) | 18 (40%) | ||
| L-loop | 10 (32%) | 27 (60%) | ||
| Ventriculoarterial Connections | ||||
| SORV | 18 (58%) | 5 (11%) | 42 (45%) | 7 (35%) |
| DORV | 12 (39%) | 1 (2%) | 39 (42%) | 6 (30%) |
| DOLV | — | 2 (4%) | — | 2 (10%) |
| Discordant | 1 (3%) | 30 (67%) | 8 (9%) | 4 (20%) |
| Concordant | — | 7 (16%) | 4 (4%) | 1 (5%) |
| Pulmonary Pathway | ||||
| Pulmonary atresia with nonconfluent PA | 5 (16%) | — | 3 (3%) | 1 (5%) |
| Pulmonary atresia with confluent PA | 13 (42%) | 5 (11%) | 39 (42%) | 6 (30%) |
| Pulmonary stenosis | 6 (19%) | 16 (36%) | 43 (46%) | 9 (45%) |
| No obstruction | 7 (23%) | 24 (53%) | 8 (9%) | 4 (20%) |
| Aortic Pathway | ||||
| Coarctation/interruption | 2 (6%) | 4 (9%) | 1 (1%) | 1 (5%) |
| No obstruction | 29 (94%) | 41 (91%) | 92 (99%) | 19 (95%) |
Key: CILV, Common inlet left ventricle; CIRV, common inlet right ventricle; DILV, double inlet left ventricle; DIRV, double inlet right ventricle; DOLV, double outlet left ventricle; DORV, double outlet right ventricle; PA, pulmonary arteries; SORV, aorta arising from right ventricle with pulmonary atresia.
The nondominant chamber is called incomplete (or rudimentary ) because it lacks one or more of its component parts, usually the inlet portion but occasionally also the outlet, leaving only the apical trabeculated part. The incomplete chamber is always smaller than the dominant chamber and is connected to the dominant chamber by a VSD. The VSD is sometimes called a bulboventricular foramen, but this term applies only when the incomplete chamber is of right ventricular morphology. Rarely, such as when there is double inlet to one chamber and double outlet from the other, both chambers are incomplete. The ventricular septum is malaligned and incomplete in nearly all hearts with double inlet ventricle, or is completely absent.
Some consider a solitary ventricle with double inlet to be an indeterminate ventricle, and some consider it to be a right ventricle.
Atria
Any type of atrial situs can be present. However, with double inlet left ventricle, there is usually atrial situs solitus, and with double inlet right and indeterminate ventricles, about half have situs solitus and half have a heterotaxy pattern, right atrial isomerism predominating (see Chapter 58 ). Situs inversus (mirror image) is unusual (see Tables 56-1 and 56-2 ).
Atrioventricular Connection
There are usually two perforate AV valves positioned entirely in the dominant ventricle. Their morphologic characteristics are frequently indeterminate, neither tricuspid nor mitral, and it is therefore best to call them left-sided (draining the left-sided atrium) and right-sided (draining the right-sided atrium) ( Fig. 56-1 ). Alternatively, there may be a common AV valve ( Fig. 56-2 ), although this is rare in double inlet left ventricle. When the AV valve is a common one, valvar abnormalities are common, including important regurgitation.
In about 20% of cases, one of the perforate valves or the common valve overrides the remnant of ventricular septum, or the tension apparatus of one or both valves straddles the septum. Rarely, a common patent AV valve overrides or straddles the septum.
Atresia of an AV valve usually involves total absence of the AV connection, but occasionally there is an imperforate membrane with a miniature tension apparatus beneath it. Typically (as in classic tricuspid atresia; see Morphology in Chapter 41 ) the small, incomplete ventricular chamber is on the same side as the atretic valve, but it may be on the opposite side.
Ventriculoarterial Connections
VA connections can be of any type, except in the case of a solitary ventricle, where there can only be a single or double outlet. In double inlet left ventricle, the most frequent connection is discordant, with aorta and subaortic incomplete right ventricle (outlet chamber) to the left, but sometimes to the right, of the pulmonary trunk; concordant, double outlet, and single outlet connections occur ( Table 56-3 ).
Table 56-3
Summary of Morphologic Features of the Ventriculoarterial Connections in 97 Specimens of Double Inlet Left Ventricle
Modified from Uemura and colleagues.
| Feature | Right Ventricle Leftward | Right Ventricle Rightward |
|---|---|---|
| Ventriculoarterial Connection a | ||
| Concordant | 2 | 13 |
| Discordant | 51 | 16 |
| Double outlet RV | 1 | 3 |
| Aorta from RV/pulmonary atresia | 6 | 1 |
| Double outlet LV | 2 | 1 |
| Aorta from LV/pulmonary atresia | — | 1 |
| Infundibular Morphology | ||
| Subpulmonary | 2 | 13 |
| Subaortic | 58 | 17 |
| Subpulmonary and subaortic | 1 | 3 |
| Markedly attenuated | 1 | 2 |
| Aortic Valve in Relation to Pulmonary Valve | ||
| Right posterior | 2 | 14 |
| Right anterior | 2 | 17 |
| Right side-by-side | 2 | 3 |
| Left anterior | 54 | — |
| Left side-by-side | 2 | 1 |
| Arterial Trunks | ||
| Spiraling | 2 | 14 |
| Parallel | 60 | 21 |
Key: LV, Left ventricle; RV, right ventricle.
a For overriding of the aortic or pulmonary valve, the so-called 50% rule was applied.
Conduction Tissue
Morphology of the AV node and conduction system is abnormal. Position of the AV node is determined primarily by whether the ventricular septal remnant reaches the crux (see “Atrioventricular Node” under Conduction System in Chapter 1 ). From the surgeon's standpoint, it is important to know that the AV node can be anywhere around the perimeter of the right-sided AV valve.
Coronary Arteries
Terminology of the coronary artery branches is arguable. Left and right coronary arteries usually arise from the two aortic sinuses facing the pulmonary trunk. There are usually prominent descending branches (encircling coronary arteries) that indicate points of attachment of septum to free ventricular wall, and therefore the boundaries of the incomplete ventricle.
Types
Double Inlet Left Ventricle
In double inlet left ventricle, the most common double inlet connection, the dominant ventricle is of left ventricular morphology. Apical trabeculations beyond insertions of the papillary muscles display a delicate criss-cross pattern. The septal surface is typically smooth in its superior half, and the crescentic margin bounding the VSD is smooth ( Fig. 56-3 ). VSD morphology, however, can be variable. Of 46 patients with double inlet left ventricle carefully evaluated by Bevilacqua and colleagues, 24 had VSDs separated from the semilunar valves and completely surrounded by muscle (muscular defects), 19 had VSDs adjacent to the anterior semilunar valve (subaortic defect) in association with malalignment or hypoplasia of the infundibular septum, and 3 had multiple muscular defects.
The small incomplete (rudimentary) ventricle is of right ventricular morphology, with coarse apical trabeculations and frequently a recognizable trabecula septomarginalis (septal band) bounding the VSD anteriorly. A smooth-walled infundibulum is present when one or both great arteries arise from this chamber ( Fig. 56-4 ). Otherwise, and rarely, the chamber exists as a blind pouch. It is always positioned on the anterosuperior shoulder of the dominant left ventricle ( Fig. 56-5 ), usually to the left but sometimes to the right. The septum thus lies obliquely and never extends to the crux.
The typical morphology of double inlet left ventricle, with ventricular L-looping, left-sided incomplete right ventricle, and VA discordant connections, occurs in about half of all cases, with a wide variety of VA connections in the remainder (see Table 56-3 ). The relatively uniform internal cardiac architecture of the AV valves and myocardium in typical double inlet left ventricle may be more variable when double outlet right ventricle occurs with it. Atrial situs is usually solitus, occasionally ambiguus, but rarely situs inversus.
Two variants of double inlet left ventricle warrant further description: (1) double inlet left ventricle with ventricular L-loop, left-sided incomplete right ventricle, and VA discordant connection and (2) double inlet left ventricle with ventricular D-loop, right-sided incomplete right ventricle, and VA concordant connection.
With Ventricular L-Loop, Left-Sided Incomplete Right Ventricle, and Ventriculoarterial Discordant Connection
This is the largest subset of hearts with double inlet ventricle, comprising half the cases (see Figs. 56-3 through 56-5 ). The large left ventricular main chamber lies to the right and receives left-sided and right-sided AV valves, which usually are of tricuspid and mitral morphology, respectively, although both may be bicuspid. There may be some straddling and overriding (but <50%) of the AV valves. The majority of AV valves function normally, but the most common abnormality is stenosis of the left-sided “tricuspid” valve. A heavy trabecula often separates insertion of the papillary muscles into the diaphragmatic free wall of the left ventricle. The left-sided tricuspid valve commonly has attachments of the subvalvar tension apparatus to the ventricular septum.
The aorta arises above the short infundibulum of the incomplete left-sided right ventricle (see Fig. 56-4 ). The pulmonary trunk arises from the base of the left ventricle, anterior and superior to the right-sided AV (“mitral”) valve, usually with pulmonary-mitral fibrous continuity. Subvalvar and valvar pulmonary stenoses occur but are not common, and pulmonary atresia occurs only occasionally.
The VSD is usually large and lies beneath the infundibular septum, but it may be restrictive, producing subaortic stenosis (see “ Subaortic Stenosis ” later under Natural History). As noted, the VSD may be in an atypical position within the apical septal trabeculations, and occasionally it is multiple. Muscular defects are more likely than subarterial defects to be restrictive.
The AV node is anterior and away from the atrial septum, lying in the right atrial wall adjacent to the superior commissural tissue between anterior and posterior leaflets of the right-sided AV valve. This arrangement also pertains to ventricular D-loop when the left ventricle is the main chamber, because again there is no ventricular septum extending to the crux. The bundle of His passes anterior to the pulmonary valve to reach the ventricular septum (see later Figs. 56-19 and 56-21 ).
Configuration of coronary arteries is similar to that in congenitally corrected transposition of the great arteries (see “Atrioventricular Node and Bundle of His” and “Coronary Arteries” under Morphology in Section I of Chapter 55 ).
With Ventricular D-Loop, Right-Sided Incomplete Right Ventricle, and Ventriculoarterial Concordant Connection
This occurs in about 10% of cases and most resembles the normal heart. The large left ventricle lies to the left and posteriorly, and the small right ventricle lies to the right, anteriorly and superiorly. It was first described by Holmes and is often called the Holmes heart .
There are usually two AV valves (often with the right-sided one straddling but with less than 50% override) or a common valve. The incomplete right ventricle is similar to that present in classic tricuspid atresia, with an extensive infundibulum leading to a pulmonary valve that is normally related to the aortic valve. Pulmonary stenosis is common, and the VSD may be restrictive.
The AV node is again anterior at about the 11-o’clock position relative to the right AV valve, as seen by the surgeon from the right atrium. The bundle of His descends from the anteriorly positioned AV node directly onto the ventricular septum without coming into relation with the ventricular outflow tract. Rarely the AV node and bundle encircles the anterior aspect of the right AV orifice.
Double Inlet Right Ventricle
In double inlet right ventricle, both atria connect to a morphologically right ventricle. Apical trabeculations are coarse, and the trabecula septomarginalis is recognizable on the septal surface, with the VSD contained between its anterior and posterior limbs. The incomplete left ventricle is always positioned posteriorly and inferiorly (“in the hip pocket”) in relation to the main chamber and usually lies to the left (D-loop; Fig. 56-6 ) or rarely to the right (L-loop). More often than not, it is very small and slitlike, communicating with the main chamber by a tiny VSD, with no connection to a great artery. In other cases, the left ventricle is of reasonable size and the obliquely placed septum is well formed; in contrast to that in double inlet left ventricle, it extends superiorly to the crux. In these cases, fine apical trabeculations are recognizable, and the superior septal surface beneath the VSD is smooth.
The VA connection is usually double outlet or single outlet (pulmonary atresia) from the right ventricle ( Fig. 56-7 ; see also Fig. 56-1 ). A concordant connection sometimes occurs, with the aorta arising from the incomplete left ventricle. Pulmonary stenosis can be present.
Two AV valves may enter the large right ventricle, with the left one straddling, or frequently a common AV valve. Atrial situs inversus, and particularly right atrial isomerism, is more common in double inlet right ventricle than in double inlet left ventricle. Double inlet right ventricle associated with right atrial isomerism seems to be particularly prevalent in the Chinese.
In the presence of a D-loop and a ventricular septum reaching the crux, the AV node has its usual posterior position in the atrial septum with its normal relation to the ostium of the coronary sinus. The perforating bundle of His passes through the AV anulus and on to ventricular myocardium, either on the ventricular septum or on a trabecula on the posterior ventricular wall. In rare L-loop, the conduction system is variable, but a conventionally located AV node may be present, as well as a more rudimentary node located more anteriorly and superiorly along the right-sided AV anulus. The nonbranching bundle then descends onto a free-running trabecula in the main chamber.
Double Inlet Indeterminate Ventricle
Double inlet indeterminate ventricle includes hearts in which both atria connect to a solitary ventricle. Prevalence of this subset depends on the care with which a search is made for the possibility that the malformation is actually double inlet right ventricle, because a tiny isolated accessory ventricular chamber may be missed by cardiac imaging and may be found only on careful autopsy examination. Even when the ventricle is truly solitary, it may represent a morphologically right ventricle without a rudimentary left ventricle, because apical trabeculations are always coarse, and there may be a freestanding column posteriorly reminiscent of the trabecula septomarginalis (see Fig. 56-7 ).
There is a higher prevalence of heterotaxy in double inlet indeterminate ventricle than in the other types of double inlet ventricle. With it, as well as with atrial situs solitus and inversus, two perforate AV valves are usually present. The only VA connection possible is double or single (pulmonary atresia) outlet ventricle. Pulmonary stenosis is common. The great arteries are often more or less normally related.
The AV node is usually posterior when there is a rudimentary ridge in the ventricle and distinct papillary muscles to both AV valves. In this case, the AV node passes down a free-running trabecula. When a ridge is absent, the AV node is usually situated laterally (away from the atrial septum) and anteriorly, and the nonbranching bundle descends into the right parietal wall of the indeterminate ventricle.
Common Ventricle
Rarely an apparently common (solitary) ventricle has no ventricular septum or a diminutive apical ridge, but importantly, one side of the ventricular mass is morphologically right ventricle and the other morphologically left. Lev and colleagues consider this to be a heart with a huge VSD rather than double inlet common ventricle.
Left Atrioventricular (Mitral) Valve Atresia and Patent Aortic Outlet
Left-sided AV (mitral) valve atresia with patent aortic outlet has a widely varying morphology. All variants are discussed here, with one exception: mitral atresia with patent aortic outlet (aortic stenosis) with intact ventricular septum, atrial situs solitus, levocardia, single inlet right ventricle with D-loop, and hypoplasia of all left cardiac segments, together with VA concordant connection. This variant is considered one of the four classic morphologic variants of hypoplastic left heart physiology, along with mitral atresia–aortic atresia, mitral stenosis–aortic atresia, and mitral stenosis–aortic stenosis (see “Left Ventricle and Mitral Valve” under Morphogenesis and Morphology in Chapter 49 ).
The atretic valve may be imperforate, in which case there is a hypoplastic membrane, sometimes with a miniature chordal apparatus beneath it; or the AV connection may be absent, with the floor of the atrium being separated from the ventricle by fibrofatty tissue. In a study of 23 patients with patent aortic outlet and atresia of the left AV valve, 15 had absence of the left AV connection, 5 had an imperforate left AV valve, and 3 had atrial isomerism. Those with imperforate left AV valve demonstrated concordant AV connections.
The patent right-sided AV valve may occasionally override the remnant of ventricular septum, but with more than 50% of the anulus committed to the larger right ventricular chamber. The tension apparatus may straddle the septum, which reaches the crux.
In this most common arrangement (“mitral” atresia), there is atrial situs solitus, ventricular D-loop, and a dominant right ventricle connected to the right atrium by a patent right-sided (usually tricuspid) AV valve and a small and incomplete left ventricle lying posteriorly and to the left ( Figs. 56-8 and 56-9 ). The left ventricle may be a blind chamber connecting to the right ventricle by a small VSD (in which case the VA connection is either double or single outlet right ventricle), but more commonly it functions as an outlet chamber giving origin to the aorta (concordant VA connection) and rarely to the pulmonary artery. The left ventricle is often smaller than suggested by the position of the left anterior descending coronary artery (see Fig. 56-9 ). Characteristically, when the aorta arises from the small left ventricle, the VSD is restrictive and the aorta small in association with coarctation or aortic arch hypoplasia. Interatrial obstruction is also common.
Alternatively, and less commonly, the arrangement is atrial situs solitus and ventricular L-loop with single inlet and more or less right-sided left ventricle, in which case the right atrium is connected to the dominant left ventricle by a patent AV valve with either mitral or indeterminate morphology. There is an incomplete left-sided right ventricle situated anteriorly and to the left, above which is the atretic left-sided AV valve, and the VSD may be restrictive. The septum does not reach the crux. The usual VA connection is discordant with the right ventricle giving origin to the aorta, but double outlet left ventricle also occurs.
Right Atrioventricular (Tricuspid) Valve Atresia
Excluding cases of classic right-sided (tricuspid) valve atresia (see Chapter 41 ), right-sided AV valve atresia can occur with single inlet and more or less left-sided right ventricle (ventricular L-loop). Right AV valve atresia has also been reported in association with an indeterminate solitary ventricle. The patent left-sided AV valve may occasionally override the septum and may have multiple leaflets.
Associated Cardiac Anomalies
Associated cardiac anomalies occur in at least one third of patients with double inlet ventricle. AV valve malformations are common and include leaflet dysplasia, leaflet cleft and tags, and anular hypoplasia, in addition to straddling. These can produce either valvar regurgitation or stenosis. The pulmonary valve may be stenotic from anular hypoplasia and leaflet thickening, or it may be atretic. Subvalvar pulmonary stenosis is common and results from either infundibular narrowing (muscle hypertrophy, hypoplasia, or occasionally a deviated septum) (see Fig. 56-1 ) or, more commonly, a restrictive VSD leading to an outflow chamber from which the pulmonary trunk arises (see Fig. 56-4 ). Aortic arch anomalies (coarctation, aortic arch interruption, or arch hypoplasia) also sometimes coexist with single ventricle (see Table 56-2 ). Multiple VSDs are not rare.
Subaortic stenosis is one of the most important coexisting cardiac anomalies. Because of the variable time of its appearance, it is discussed later under Natural History.
Clinical Features And Diagnostic Criteria
Clinical manifestations vary with morphology. Patients without pulmonary stenosis or atresia, about one third of the total, present in a manner similar to those with tricuspid atresia and normally related great vessels without pulmonary stenosis or atresia (see Clinical Features and Diagnostic Criteria in Chapter 41 ).
When mild or moderate pulmonary stenosis coexists, early years of life may be without important symptoms. A 
of approximately 2 or less results in only moderate cardiomegaly and mild pulmonary overcirculation on the chest radiograph and good functional status, albeit with mild cyanosis. Presentation in early or middle childhood rather than in infancy is common and is usually precipitated by cyanosis, a cardiac murmur, or typical findings on a chest radiograph. Clinical presentation is similar to that of tricuspid atresia and normally related great arteries with mild to moderate pulmonary stenosis (see Chapter 41 ).
When pulmonary stenosis is severe or pulmonary atresia is present, important cyanosis usually results in presentation in the early days or weeks of life, similar to that of tricuspid atresia and normally related great vessels with severe pulmonary stenosis or pulmonary atresia.
Atresia of the left-sided AV valve, when combined with a restrictive foramen ovale, results in severe pulmonary venous hypertension with its typical chest radiographic appearance and severe respiratory distress in early life. The presentation can mimic that of classic hypoplastic left heart physiology with restrictive or intact atrial septum (see Chapter 49 ). This situation may be masked initially by pulmonary stenosis and small pulmonary blood flow, only to become apparent after a systemic–pulmonary artery shunt is created. Severe AV valve regurgitation results in elevated atrial pressure and early appearance of heart failure.
Double inlet single left ventricle with AV and VA discordant connections, restrictive VSD (bulboventricular foramen), and aortic arch hypoplasia typically mimics hypoplastic left heart physiology in its presentation (see Chapter 49 ).
The electrocardiogram and chest radiograph may raise suspicion of the presence of double inlet ventricle, but echocardiography usually is the first definitive diagnostic procedure. Absence of the posterior (inlet) septum between the AV valves, one of the hallmarks of double inlet ventricle, can usually be diagnosed from the echocardiogram, particularly when associated with apposition of the unsupported septal leaflets of the two AV valves. Echocardiography with Doppler color flow imaging can provide all the necessary diagnostic information ( Figs. 56-10 and 56-11 ).
Cineangiography may be performed ( Figs. 56-12 and 56-13 ) but currently is not necessary for planning therapy in the neonate or infant, and may be disadvantageous to the condition of the patient. It should be recalled that the Holmes heart is easily misdiagnosed as tetralogy of Fallot. Cardiac catheterization and cineangiography can provide important information about the patient presenting in older infancy or later, or about the patient who has previously undergone surgery, primarily by defining pulmonary vascular resistance and morphology of the branch pulmonary arteries.
Magnetic resonance imaging and computed tomography have little diagnostic role in the neonate.
Natural History
Double Inlet Ventricle
Estimated overall survival without treatment is about 57% at 1 year and 45% at 5 years ( Fig. 56-14 ). The monumental study by Franklin and colleagues documented the relatively favorable prognosis of certain subsets. Specifically, patients with atrial situs solitus and double inlet left ventricle, ventricular L-loop, discordant VA connection without systemic outflow obstruction, 
of about 1 to 2 (due to mild to moderate pulmonary stenosis), and presentation between 14 and 60 days of age have about a 90% chance of surviving for at least 10 years without intervention ( Fig. 56-15 ). Estimated survival without intervention of other commonly encountered subsets is illustrated in Figs. 56-15 and 56-16 . Although the natural history impact of differing AV connections has not been clearly defined, evidence exists that differences in left ventricular function are present depending on whether the inlet connection has two patent valves or one ( Fig. 56-17 ).
Presentation with severe acidosis and low cardiac output has been a particularly severe risk factor for early death without intervention. Systemic outflow obstruction at any level, particularly aortic atresia, is also a strong risk factor for early death.
Mitral Atresia
When atresia of the left AV valve coexists with a restrictive opening in the atrial septum, such as in mitral atresia (atrial situs solitus, ventricular D-loop, right ventricular main chamber, and absent or imperforate left AV valve), the situation is rapidly fatal; death usually occurs within the first few months of life. Prognosis is the same in patients with ventricular L-loop and left-sided AV valve atresia (i.e., left-sided tricuspid atresia). Even when the foramen ovale is not restrictive in early life, in this condition there is a strong tendency for it to become restrictive later in infancy or in early childhood.
Subaortic Stenosis
The tendency to develop subaortic stenosis when the aorta arises from the incomplete ventricle (outlet chamber) poses a serious threat. This category includes patients with (1) double inlet left ventricle and VA discordant connection, (2) tricuspid atresia and VA discordant connection, and (3) mitral atresia and VA concordant connection. The subaortic obstruction is usually caused by a restrictive VSD; however, sometimes muscle within the incomplete subaortic ventricle is the cause, not a small VSD per se. The three morphologic variants have a similar natural history, which is discussed in detail for tricuspid atresia and VA discordant connection in Chapter 41 .
Technique Of Operation
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