Abstract
Double-outlet right ventricle (DORV) describes a ventriculoarterial connection in which both great arteries associate primarily with the right ventricle in an array of possible arrangements that can produce physiologies from concordant to discordant, and systemic oxygenation ranging from cyanotic to congested. Many corrective operations have been devised, all with a common goal of repatriating the aorta to the left ventricle and ensuring unobstructed biventricular outflow tracts. DORV was first surgically corrected in 1957, and there are now several single- and multi-institutional studies of short- and long-term outcomes for DORV that guide best current practices. Long-term survival and freedom from reintervention are excellent in the current era, informed by advances in two-dimensional and three-dimensional imaging and clinical and anatomic data. This chapter describes the anatomy, physiologic spectrum, and current system of classification for the major variants of DORV. Surgical approaches according to anatomic and clinical classification are compared, with their postoperative management priorities and short- and long-term outcome expectations.
Key Words
Congenital, DORV, VSD, Taussig-Bing, Rastelli, Nikaidoh
Double-outlet right ventricle (DORV) includes an array of ventriculoarterial arrangements in which both great arteries associate primarily with the right ventricle (RV). Corrective strategies are varied, aimed at repatriating the aorta to the left ventricle (LV) and providing unobstructed biventricular outflow tracts. Though DORV is only a description of the ventriculoarterial associations, it can occur also with various combinations of atrioventricular arrangement, including atrial isomerism and complex heterotaxy, which can additionally challenge the correction or palliation. In most clinical series, DORV strategies and outcomes have been subgrouped into the typical, more common, biventricular versus the more complex because the latter has different expectations and treatment strategies.
Definition
By simplest definition, DORV refers to both aorta and pulmonary artery (PA) arising from the RV, almost always in combination with a ventricular septal defect (VSD). Association with the RV is commonly defined as an aorta that overrides the septal crest by more than 50% and therefore lies principally over the RV. The great arteries can be positioned in any configuration around one another, and the VSD can be variably positioned beneath the great vessels to result in the phenomenon of both great arteries mostly aligned with the RV. Depending on the configuration of the great arteries and their relationship with the VSD, DORV anatomy and physiology may resemble that of a simple VSD, that of tetralogy of Fallot (TOF), or that of transposition of the great arteries (TGA). An anterior or rightward aorta may put the PA in closer association with the LV, producing transposition-type physiology, whereas a more posterior aorta is associated with the LV and tetralogy-type or VSD-type physiology results, depending on the degree of pulmonary stenosis (PS). Tetralogy of Fallot (anteriorly malaligned VSD and aortic override of the septum) overlaps with DORV and is called DORV if the aortic override of the septum is 51% favoring the RV. At the other end of the rotational spectrum, transposition of the great vessels is instead called DORV if the PA is principally affiliated with the LV.
Historical Perspective
An autopsy specimen with both great vessels arising from the RV was described in the 18th century. Until the 20th century, considered among variations of TGA, DORV-like pathology was referred to as “partial transposition,” in which the aorta is transposed and the PA is not. The Taussig-Bing variant of transposed aorta with leftward malposed PA was described 1949. The anomaly was first called double-outlet ventricle by Braun in 1952, and Witham is credited with first referring to the lesion as double-outlet right ventricle in 1957. The earliest operative repair was performed by John Kirklin in 1957. Landmark descriptions with clinical correlations, with or without PS followed, as survivable pathways of correction were devised and described.
Embryology
As aquatic organisms climbed out of the sea, a separation into pulmonary and systemic circulations required the septation of a formerly single ventricular outflow tract. In embryogenesis, crest cells migrate from neural folds to the forming conotruncus to direct the septation of the ventricles and of the great arteries. In addition to a separation into two distinct vessels, the great arteries reposition around each other as their associated subvalvar conus grows or recedes, leading the arteries to associate with their respective destination ventricles. D -looping of the primitive heart tube places the aorta rightward of the PA. In normal cardiac development a subsequent resorption of the subaortic conus tows the aorta posteriorly and leftward, to achieve fibrous continuity with the mitral valve and proximity with the LV. Persistence of the subaortic conus leaves the aorta rightward or ventral to the PA, muscle maintains separation between the aortic and mitral valves, and the aorta associates with the RV. In DORV, aortic and pulmonary coni rotate incompletely around one another to join the advancing septal crest, and resultant ventriculoarterial alignment can range from concordant (“VSD-type,” “TOF-type”) to discordant (Taussig-Bing, “TGA-type”). The Taussig-Bing arrangement is very similar to arrested progression with bilateral conus and rightward aorta ( Fig. 58.1 ). Attractive as the concept of bilateral persistent conus is in describing DORV development, in fact there is heterogeneity of actual anatomy that defies a single morphogenic explanation. But the bilateral conus serves as a useful heuristic to visualize the relationships.
Genetics
Conotruncal dysmorphogenesis is a consequence of an interplay between multiple partially understood gene pathways. Gene alterations in animal models elucidate some mechanisms and identify points where mutation can produce the DORV phenotype. Among genes with demonstrated involvement in the formation of DORV are BMP2 and BMP4, implicated in directing neural crest cell migration, TGFB2, when knocked out, produces DORV in mice, and GATA4, interacting with FOG2 (cardiac cofactor), if inhibited, also yields DORV in an animal model.
Retinoic acid, a vitamin A metabolite, plays a role in cardiac morphogenesis, and gene mutations affecting its ligand-receptor complex can cause DORV, among other defects.
Though TOF is commonly associated with syndromes, DORV is much less so, though some associations of DORV with trisomy 21, trisomy13, trisomy18, and 22q11 deletion have been described.
Surgical Anatomy and Classification
Irrespective of controversies about the mechanisms behind the development of DORV, a classification based on clinical pathology is important to direct patients onto the most successful corrective pathways and expectations. A majority of DORVs are situs solitus with concordant atrioventricular connection. The position of the VSD with respect to the great arteries and the presence or absence of PS, are the relationships most relevant to designing the corrective approach.
Ventricular Septal Defect Position
The VSD can be subaortic, subpulmonic, doubly committed, or uncommitted ( Fig. 58.2 ). Commonest is the subaortic VSD, with a rightward malposed aorta. The relative incidence of subaortic VSD is 42% to 59%, subpulmonary is 21% to 37%, uncommitted is 11% to 26%, and doubly committed is 3% to 9%. The original Taussig-Bing variant includes the combination of subpulmonary VSD, side-by-side great arteries, and bilateral subarterial conus, with or without subaortic stenosis. The term Taussig-Bing is loosely used as synonymous with any DORV with subpulmonary VSD and transposition-like physiology.
Great Artery Position
In normal cardiac development the aorta is positioned posterior to the PA, in continuity with the more posterior LV. In the case of DORV the aortic position can be posterior or rightward and still remain in reach of the LV, but when it is found to lie farther rightward or anterior, the aorta is farther from the LV, the PA closer to the LV, and TGA physiology ensues. Incomplete growth of the pulmonary infundibulum yields stenosis or atresia of the pulmonary valve. Underdevelopment of the subaortic conus may produce aortic stenosis, and downstream effects include coarctation or arch hypoplasia.
Outflow Tract Obstruction
Rightward or leftward deviation of the conal septum determines VSD commitment and affects either outflow tract. Commonest is an anterior and leftward conal septum deviation, defining subaortic VSD, crowding, and PS. In cases of doubly committed VSD, PS is common. With uncommitted VSD, PS is uncommon (see Fig. 58.2 ).
Atrioventricular Abnormalities
Atrioventricular canal defect (AVC) occurs with DORV, is usually unbalanced, and is usually associated with a subpulmonary VSD and with malformed elements of the left heart, including mitral stenosis, mitral atresia, or straddling mitral valve.
AVC with DORV should raise suspicion of heterotaxy. Heterotaxy polysplenia is most commonly associated with AVC and is accompanied by LV hypoplasia and systemic venous anomalies such as interrupted inferior vena cava with azygos continuation. Heterotaxy asplenia is more commonly associated with subpulmonary stenosis, common atrioventricular valve, common atrium, and anomalous pulmonary venous connection.
Associated Obstructive Lesions
Sixty-six percent of patients with a subaortic VSD have PS, with favored flow through the aorta, and subaortic stenosis or arch obstruction is rare. Conversely, among those with a subpulmonary VSD, 30% have arch obstruction, 14% have PS, and 6% have subaortic stenosis. With doubly committed VSD, 59% have PS, 14% have subaortic stenosis, and 9% have arch obstruction, and with uncommitted VSD, 32% have PS, 6% have subaortic stenosis, and 10% have arch anomalies.
Other Anatomic Considerations
Coronary anomalies occur in 50% of DORV cases. Most clinically relevant are cases with the left coronary artery crossing a pulmonary or neopulmonary outflow tract, posing challenges to its enlargement.
With discordant atrioventricular connection, the aorta is anterior and leftward of the PA, and the VSD position is subpulmonary more commonly than subaortic. Juxtaposed atrial appendages, Ebstein malformation of the tricuspid valve, tricuspid atresia, double-inlet RV, and double-chamber RV have all been described in association with DORV.
Classification
A current and widely accepted system of classification for DORV, based on clinical presentation and treatment strategy, was developed by the Society of Thoracic Surgeons–European Association for Cardio-Thoracic Surgery (STS-EACTS) Congenital Heart Surgery Nomenclature and Database Project and consists of four types of DORV. In the absence of PS, DORV with a subaortic VSD is termed VSD-type . In the presence of PS, it is TOF-type . In variants where the PA associates more closely with the LV, it is considered TGA-type , and when the VSD is remote from both semilunar valves, it is noncommitted VSD-type. Relative prevalence by type is VSD-type, 25%; TOF-type, 35%; TGA-type, 20%; and noncommitted VSD-type, 20%.
Pathophysiology
Perfusion Balance
A spectrum of physiologies matches the spectrum of anatomic variants of DORV. An unrestrictive VSD means equivalent pressures in the LV and RV and pulmonary blood flow that is gated by the degree of PS. In the absence of PS the balance between pulmonary and systemic circulations is dictated by the pulmonary vascular resistance (PVR). In the neonate, postnatal changes in PVR exacerbate or ameliorate pulmonary blood flow extremes, producing a moving target for management. All influences taken together, DORV physiology can range from congestive heart failure in cases of unrestricted pulmonary blood flow, to cyanosis from pulmonary hypoperfusion. In TGA-type DORV the presence of subaortic stenosis may further exacerbate congestive failure and systemic hypoperfusion.
Mixing/Oxygenation Balance
The commitment of the VSD determines streaming. Whereas in TOF-type DORV, hypoxia may result from PS, the TGA-type DORV, with subpulmonary VSD, will also exhibit hypoxia but due instead to inadequate mixing and RV-aorta streaming. In the single-ventricle variants, mixing is more complete, and oxygenation is more reflective of relative pulmonary and systemic flows.
Patent Ductus Arteriosus
A patent ductus arteriosus (PDA) may circumvent PS to produce pulmonary overcirculation and congestive failure despite the presence of PS. Conversely, severe PS or pulmonary atresia may require maintenance of ductal patency to achieve adequate pulmonary blood flow. Aortic stenosis or arch obstruction may render the systemic circulation dependent on ductal patency. In transposition physiology, ductal patency represents one of three levels where mixing can improve hypoxia.
Presentation and Preoperative Management
The infant with VSD-type DORV (subaortic VSD and no PS) will have excessive pulmonary blood flow and symptomatic congestive failure in the first weeks of life, worsening along with the fall of PVR. Examination may reveal tachypnea, tachycardia, a holosystolic murmur, and a mid-diastolic rumble (mitral flow murmur). Cardiomegaly and prominent pulmonary vascularity is seen on chest x-ray examination. The mainstay of nonoperative, anticongestive management includes diuretics and afterload reduction, escalating as necessary to mechanical ventilation and pulmonary vasoconstrictive strategies such as permissive hypercapnia and low inspired O 2 concentration. When conservative measures fail, operative management can include a palliative PA band or definitive operative repair ( Table 58.1 ).
| ANATOMY | STS-EACTS Classification | Physiology | PALLIATION | Surgical Corrections | |||
|---|---|---|---|---|---|---|---|
| VSD Position | PS/No PS | AS/No AS | Medical | Interventional/Surgical | |||
| Subaortic or doubly committed VSD | No pulmonary stenosis | No aortic stenosis | VSD-type | Congestion (Q p > Q s ) | Diuretics, afterload reduction, mechanical ventilation, hypercapnia | Pulmonary artery band | VSD baffle to aorta, Kawashima |
| Pulmonary stenosis | No aortic stenosis | TOF-type | Cyanosis (Q p < Q s ) | Beta-blockade, hydration, sedation, PGE 1 | Aortopulmonary shunt, ductal stent | VSD baffle to aorta, RVOT procedure (Rastelli or REV) | |
| Subpulmonary VSD | No pulmonary stenosis | No aortic stenosis | TGA-type | Cyanosis (streaming) | PGE 1 , mechanical ventilation | Balloon atrial septostomy | VSD baffle to pulmonary valve, arterial switch |
| Aortic stenosis | VSD baffle to pulmonary valve, arterial switch + RVOT procedure (Rastelli or REV) | ||||||
| Pulmonary stenosis | No aortic stenosis | Cyanosis (Q p < Q s ) | PGE 1 , mechanical ventilation | Aortopulmonary shunt, ductal stent | Yasui, Nikaidoh, Yamagishi truncal switch | ||
| Noncommitted VSD | No pulmonary stenosis | No aortic stenosis | Non-committed VSD-type | Congestion (Q p > Q s ) | Diuretics, afterload reduction, mechanical ventilation, hypercapnia | Pulmonary artery band | Any of above, depending on pathway between VSD and suitable great artery, ± RVOT procedure |
| Aortic stenosis | |||||||
| Pulmonary stenosis | No aortic stenosis | Cyanosis (Q p < Q s ) | PGE 1 , mechanical ventilation | Aortopulmonary shunt, ductal stent | |||
The infant with TOF-type DORV (subaortic VSD with PS) will have restricted pulmonary blood flow and a balance of circulation governed by the degree of PS. Presentation may range from asymptomatic to cyanotic, and hypercyanotic spells may occur with dynamic, muscular sub-PS. The physical examination reveals the harsh systolic murmur of PS and a single second heart sound. The chest x-ray examination may show a small cardiac silhouette and dark lung fields. Medical management includes hydration, sedation, and mechanical ventilation. When present, a PDA can circumvent the effects of PS to result in balanced or excessive pulmonary blood flow. Cyanotic infants or those with ductal dependent pulmonary blood flow are maintained on prostaglandin (PGE 1 ) and may additionally undergo palliative ductal stenting, operative aortopulmonary shunt construction, or definitive operative repair ( Table 58.2 ).
| Procedure Name | Description | Conditions |
|---|---|---|
| IVR | Intraventricular LV-aorta tunnel | Aorta posterior, sufficient TV-PA separation to accommodate baffle |
| Rastelli | Intraventricular LV-aorta tunnel after VSD enlargement, with RV-PA reconstruction | Aorta posterior, rightward or anterior, pulmonary stenosis |
| Kawashima | Intraventricular LV-aorta tunnel, circumnavigating the pulmonary valve | Aorta anterior or rightward (TGA), no pulmonary stenosis |
| Jatene arterial switch (IVR-ASO) | Intraventricular LV-PA tunnel with coronary transfer to pulmonary artery | |
| Double root translocation | Aortic root translocation to LV with pulmonary root translocated to RV | |
| REV | Intraventricular LV-aorta tunnel after resection of conal septum, with direct RV-PA connection | Aorta anterior or rightward (TGA), pulmonary stenosis, Taussig-Bing |
| Nikaidoh (aortic root translocation) | Aortic root translocation to LV with RV- PA conduit | |
| Yamagishi (half-turn truncal switch) | En bloc rotation of aorta and PA, coronary reimplantation | |
| Yasui | Intraventricular LV-PA tunnel, Damus-Kaye-Stansel anastomosis, RV-PA conduit |
A patient with TGA-type DORV (subpulmonary VSD) will exhibit hypoxia from inadequate mixing. The physical examination will reveal cyanosis, tachypnea, a systolic murmur if stenosis is present, and a diastolic rumble if the patient is primarily congested. The chest x-ray examination may reveal cardiomegaly and prominent pulmonary vascular markings. Preoperative management is directed at optimizing intracardiac mixing, which can occur at the VSD, atrial septal defect (ASD), and PDA levels. Therapies may include PGE 1 infusion, mechanical ventilation, and balloon atrial septostomy.
DORV with absent VSD is rare, and adequate systemic circulation will depend on mitral insufficiency and an ASD that can produce enough left-to-right shunting to support the RV and its dual output. A restrictive VSD can cause the physiologic equivalent of aortic stenosis. Preoperative management may include PGE 1 infusion and balloon atrial septostomy.
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