Definition

Double outlet right ventricle (DORV) is best defined as an anomaly of cono-truncal development that results in both great arteries arising entirely or predominantly from the right ventricle (RV).¹ Consequently, DORV is not a specific congenital malformation; rather DORV is a descriptive term used to define the relationship of the great arteries to the RV. Most authors agree that the degree of aortic override of the RV has to be at least 50 percent and that the only outlet of blood from the left ventricle (LV) is the ventricular septal defect (VSD).²

Historical Highlights

Although cases of DORV were documented in the mid-19^th century,^3,4 the term “double outlet ventricle” was first used by Braun in 1952 to describe the postmortem anatomy of a heart with complete dextroposition of the aorta, subaortic VSD, and pulmonary stenosis.⁵ Five years later, another series of postmortem examinations described four cases of what were termed “double outlet right ventricle.” The first recognition of DORV on a living patient was made the same year at Mayo Clinic at the time of surgical correction.⁶

During the decades that followed, the complex spectrum of anatomic variations that could be classified as subgroups of DORV became apparent. The importance of distinguishing DORV from simple VSD prior to attempting surgical intervention was emphasized by Engle and Steinberg.⁷ Neufeld was the first to suggest clinicopathologic subsets of DORV when he stratified patients into those with or without pulmonary stenosis.8 In the same original manuscript that distinguished patients without pulmonary stenosis,⁸ he described the location of the VSD relative to the aorta and pulmonary artery (PA). This seminal work was carried forward by Lev when he classified the VSD relative to their position to the subarterial outlets: subaortic, subpulmonary, doubly-committed, and non-committed.¹ The importance of the spacial relationship of the great vessels to each other was also highlighted.^9–11 Although the Taussig-Bing heart was physiologically more similar to TGA with VSD,¹² it was Neufeld who recognized that the Taussig-Bing heart was an anatomic subset of DORV.¹³ Mayo Clinic surgeons were the first to report surgical correction of the Taussig–Bing heart,¹⁴ and intraventricular tunnel repair of this disorder.¹⁵

Embryology

There are two theories that attempt to describe the cono-truncal abnormalities that result in the development of DORV. Lev has proposed that DORV results when there is an abnormal spiraling septation of the aorta from the PA that is more than Fallot’s tetralogy but less than transposition.¹⁶ Alternatively, Van Praagh’s theory proposed that conal underdevelopment results in the great arteries emerging from the RV in a side-by-side arrangement.¹⁷

Classification

Based on the spatial relationship of the VSD to the semilunar valves, DORV can be anatomically classified as subaortic, subpulmonary, doubly-committed, or remote.¹ It should be noted, however, that the pathophysiology and type of surgical repair are influenced not only by the relative location of the VSD to the semilunar valves, but also by the relationship of the great arteries to each other, and any associated abnormalities. Because there is no absolute correlation between the commitment of the VSD to the great arteries and the surgical approach,^18,19 a nomenclature system that defines four types of DORV based on clinical presentation and treatment has been adopted by the STS-EACTS.² The four types are: (1) VSD-type, (2) Fallot-type, (3) TGA-type, and (4) DORV with non-committed VSD. This system offers the advantage of uniformity to DORV nomenclature which allows an accurate and reproducible pediatric cardiac surgery database, resulting in reliable and meaningful outcome studies for the variety of surgical procedures available.

Ventricular Septal Defect

DORV is, for practical purposes, always associated with a VSD. Rarely is DORV not associated with an interventricular communication,²⁰ and this anatomic rarity most likely represents spontaneous closure of a preexisting VSD. The most well known classification of DORV is based on the relative position of the VSD to the arterial outlets.¹ Most often, the VSD is located between the anterior and posterior limbs of the trabecula septomarginalis (TSM) (Fig. 71-1), and as such can be described as “committed.”²¹ The attachment of the infundibular septum to either the anterior or posterior limb predicts which great artery is related to the VSD. Sub-aortic VSD is associated with the infundibular septum being attached or aligned with the anterior limb of the TSM. Conversely, posterior limb alignment of the TSM with the infundibular septum results in a subpulmonary VSD. The infundibular septum is absent or markedly attenuated in cases of doubly-committed VSD. The non-committed VSD is away from the semilunar valve(s) and it has been proposed that this distance be greater than the diameter of the aortic valve.²² The noncommitted VSD is located in the inlet septum (atrioventricular (AV) canal defect or muscular) or the trabecular ventricular septum. The majority of VSDs in DORV are unrestrictive, but restrictive VSDs may be seen in approximately 10 percent of patients. Although restrictive VSDs are diagnosed preoperatively in approximately 1.6 percent, an additional 11 percent of patients require VSD enlargement at the time of repair to prevent subaortic obstruction.^6,19 Multiple VSDs can be seen in 13 percent, and it is extremely rare for no VSD to be present. In the absence of a VSD, there is an ASD, which serves as left-to-right shunt. In this situation, the LV is usually hypoplastic.²

Subaortic VSD

This is the most common type of VSD and occurs in approximately 50 to 55 percent of patients undergoing repair of DORV. The VSD is unrestrictive. Bilateral coni are present in 77 percent of patients and a subpulmonary conus is present in 23 percent (Table 71-1).²² The length of the conus determines the distance of the VSD from the aortic valve. Due to the relationship of the infundibular septum being aligned with the anterior limb of the TSM, the subaortic VSD is located in a posterior position in the ventricular septum (Fig. 71-1A). In the presence of aortic–mitral fibrous continuity (i.e., absent subaortic conus; the left cusp or the base of the anterior leaflet of the mitral valve forms the postero-superior margin of the VSD) the VSD is termed juxta-aortic. Individuals with a subaortic VSD have a relatively normal pattern of circulation.

Subpulmonic VSD

This type of VSD is often seen in the Taussig-Bing anomaly. This VSD is located in a more anterior position in the ventricular septum since the posterior limb of the TSM is rotated and aligned with the infundibular septum (Fig. 71-1B). Pulmonary stenosis is usually absent and the VSD is unrestrictive. A subpulmonary VSD is present in approximately 30 percent of patients with DORV undergoing surgical repair.^6,19 As with the subaortic VSD, the length of the pulmonary conus determines the distance of the VSD from the pulmonary valve. In this situation, the conus forms the anterosuperior margin of the VSD. The absence of subpulmonary conus results in pulmonary–mitral and occasionally pulmonary–tricuspid continuity. This results in the VSD being juxtapulmonary. Individuals with a subpulmonary VSD have a transposition-like circulation because the LV blood is directed to the PA.

Doubly-Committed VSD

This type of VSD is seen in 3 to 10 percent of surgical series.²³ The VSD is usually large due to attenuated or absent infundibular septum. The semilunar valves form the superior border while the limbs of the TSM form the anterior, inferior and posterior margins (Fig. 71-1C).

Noncommitted VSD

This type of VSD is remote from the semilunar valves and is seen in 3 to 20 percent of surgical series.²² Most are associated with DORV and complete AV septal defects. Straddling of the AV valve may be present with this type of VSD (Fig. 71-1D).

Relationship of the Great Arteries

The relationship of the great arteries at the level of the semilunar valves in DORV can be grouped into two broad categories: (1) spiraling and (2) parallel. Spiraling great arteries is the normal anatomic relationship with the aortic trunk positioned posterior and to the right of the pulmonary trunk; this is the most common great vessel relationship in DORV.² When the great arteries are parallel, the aortic trunk is in a more anterior position relative to the pulmonary trunk. There are multiple degrees of variability in the anteroposterior relationship between aortic trunk and pulmonary trunks. In general, however, this relationship can be broken down into the following: (1) aorta located to the right and side-by-side with the PA (Taussig–Bing), (2) aorta located to the right and anterior to the PA (D-TGA), and (3) aorta located anterior and to the left of the PA (L-malposition).

It must be noted that the relationship of the great arteries and the type of VSD present are independent of each other. In general terms, however, spiraling and L-malposition of the great arteries are most commonly associated with a subaortic VSD. Side-by-side (parallel) great arteries are most often associated with a subpulmonic VSD.²

Other Cardiac Anomalies

Associated cardiac anomalies are common with DORV, and almost any type of congenital cardiac anomaly can be present. At the Mayo Clinic, 179 patients with a diagnosis of DORV were operated on between 1972 and 1992, and 87 (48.6 percent) had concomitant congenital anomalies. Table 71-2 shows the concomitant anomalies present in this series. ASD was the most common associated anomaly, followed by persistent left SVC and coronary artery anomalies. Multiple VSDs were seen in approximately 12 percent of patients and are a risk factor for early mortality.²⁴ Coarctation of the aorta is a commonly associated anomaly in approximately 50 percent of patients with the Taussig–Bing form of DORV.²⁵

Overriding and/or straddling of the AV valve apparatus may be present in DORV, making biventricular repair difficult. Straddling of the right AV valve may permit a biventricular repair.²⁶ Significant overriding of the right AV valve may result in a small inlet portion of the RV after VSD closure and a concomitant bidirectional cavopulmonary shunt may be necessary.²⁷ Left AV (mitral) valve anomalies include mitral atresia, parachute valve, straddling, and supravalvular stenosing ring.

Pulmonary stenosis occurs commonly in DORV, particularly in those cases with subaortic and doubly-committed VSDs. The stenosis is most often at the level of the infundibulum.

Coronary Artery Anatomy

The coronary artery anatomy in DORV is predominantly the normal pattern.²⁸ However, anomalous coronary patterns can be seen in up to 16 percent of patients undergoing operation. The most common abnormality is anomalous origin of the left anterior descending artery from the right coronary artery. This pattern is typically seen in the subgroup of DORV with subaortic VSD and right ventricular outflow tract obstruction (RVOTO).²⁹ Coronary arterial patterns that are seen with transposition of the great arteries are also present in patients with DORV.

Conduction Tissue

The AV node and His bundles follow pathways that are specific for the type of AV connections. In AV concordance, the VSD is usually perimembranous (conoventricular) and the conduction tissue is along the posterior-inferior border of the defect. In the presence of AV discordance, the conduction pathways are anterior and adjacent to the PA.

Epidemiology

DORV is a rare congenital cardiac anomaly. Its frequency is approximately 0.09 per 1000 births. There is no racial or gender predominance.^30,31

Pathophysiology and Clinical Manifestation

Subaortic VSD

The position of the infundibular septum and the presence of RVOTO determine the clinical presentation. Anterior deviation of the infundibular septum producing RVOTO presents with cyanosis, similar to tetralogy of Fallot. Concomitant pulmonary stenosis may be present. Other findings that can be seen as a result of RVOTO include failure to thrive, dyspnea on exertion, squatting and polycythemia.

Management is similar to that of tetralogy of Fallot. In the absence of RVOTO, the clinical presentation is like that of a large VSD with heart failure being the presenting symptom.

Subpulmonary VSD

Clinical presentation is usually cyanosis due to unfavorable streaming of deoxygenated blood into the aorta and oxygenated blood into the PA via the subpulmonary VSD. This presentation is very similar to that of patients with D-TGA. Subaortic stenosis may be present in up to 35 percent of patients with Taussig–Bing anomaly.²⁵ Concomitant coarctation or arch hypoplasia may occur in up to 50 percent of infants with DORV and subpulmonary VSD. Patients are seen in early infancy with cyanosis, heart failure, failure to thrive and frequent respiratory infections. High pulmonary blood flow in this subgroup of DORV results in pulmonary vascular obstructive disease at an early age if surgical correction is not undertaken.

Doubly-Committed VSD

This lesion is uncommon and presentation depends on the presence of favorable or unfavorable streaming. Pulmonary stenosis may also be present.

Remote VSD

Clinical presentation is similar to patients with single ventricle. Oxygen saturations are usually that of complete mixing due to the remoteness of the VSD from the great arteries. Pulmonary blood flow may be balanced, increased or decreased.

There are no specific findings on physical exam that are pathognomonic of DORV. Patients in heart failure can present with tachypnea and failure to thrive, while cyanosis is seen in patients with inadequate pulmonary blood flow.