Double Outlet Right Ventricle

Morphology

Double outlet right ventricle (DORV) is a partial abnormality of ventriculoarterial connection and intracardiac ventricular septation. It is a congenital anomaly in which both great arteries arise wholly or in large part from the right ventricle. Both the arrangement of the atrioventricular valves and the ventriculoarterial connections are quite variable, and lie somewhere in between those noted in the tetralogy of Fallot and those in D-transposition. The aorta and main pulmonary artery are dextrorotated from the normal arrangement, and are classically side-by-side or nearly so. There is often both a subaortic and a subpulmonary infundibulum, in contrast to classic tetralogy of Fallot in which there is only a subpulmonary conus, or to D-transposition in which there is only a subaortic conus. The great vessel relationships also lie somewhere in between that of the tetralogy of Fallot and of D-transposition, resulting in both aorto-mitral and aorto-tricuspid discontinuity.

The actual diagnosis of  DORV takes into account the morphology of only a very small part of the heart, namely that of the ventriculoarterial junction. There are numerous additional abnormalities of atrial arrangement and atrioventricular connections, any of which can be associated with the abnormal ventriculoarterial connection. When present, these anomalies, such as atrial isomerism or discordant or double-inlet atrioventricular connections, dominate the clinical picture and are referred to in other sections. Only the largest subset of double outlet ventricle are considered in this section, those with the usual atrial arrangement and concordant atrioventricular connections. Within this subsets, there are many anatomical variants, the most important variable feature being the location of the ventricular septal defect. The location of the ventricular septal defect forms the basis for both a morphological and operative classification, although within this spectrum of variability, any position of the aorta can combine with any position of the main pulmonary artery and any location of the ventricular septal defect thereby creating an infinite number of morphological possibilities. Only rarely is DORV found in the presence of an intact ventricular septum, and in almost all such circumstances the features would suggest that intrauterine or postnatal closure of a preexisting ventricular septal defect took place.

The ventricular septal defect was classified by Lev as being subaortic, subpulmonary, doubly-committed, and noncommitted.

(a) Subaortic ventricular septal defect. Double outlet right ventricle with subaortic ventricular septal defect is the most common sub-type, and is morphologically a close cousin to tetralogy of Fallot. The ventricular septal defect, which is the primary outlet from the left ventricle, is located beneath the outflow tract supporting the aortic valve, and as in the tetralogy of Fallot, is positioned between the limbs of the septomarginal trabeculation. In this setting, the leaflets of the aortic valve often override the crest of the ventricular septum, and there can be doubt about which ventricle the aorta is most connected to, particularly when the morphology of tetralogy of Fallot is also present. Then, although there is discontinuity between the aortic valve and both atrioventricular valves, there still remains fibrous continuity between the mitral and tricuspid valves - that is, for the ventricular septal defect to be perimembranous. This feature is of surgical importance, since it indicates that the conduction tissue is closely related to the margin of the interventricular communication at its postero-inferior rim. Only rarely with a subaortic interventricular communication is there discontinuity between the mitral and tricuspid valves.

Irrespective of the infundibular morphology, the interventricular communication is the only direct outlet of the left ventricle. Therefore, stenosis of the interventricular communication effectively produces subaortic obstruction although there is, of course, free access to the aortic outflow tract from the right ventricle. In the majority of cases however, the subaortic outflow tract is widely patent from both ventricles, and the outlet septum, which in this setting is an exclusively right ventricular structure, is deviated in antero-cephalad direction to produce subpulmonary obstruction. Almost always the arterial trunks are normally related when the interventricular communication is subaortic, or side-by-side with the aorta to the right. In one rare variant, however, the aorta can be anterior and to the left of the pulmonary trunk (with usual atrial arrangement and concordant atrioventricular connections). Although the ventricular septal defect is almost always in subaortic position with this rare pattern, making it possible in most cases for the surgeon to connect the aorta directly to the left ventricle, the septal defect can rarely occupy the locations to be described below when the aorta is left-sided.

(b) Subpulmonary ventricular septal defect. With this arrangement, the ventricular septal defect is between the limbs of the septomarginal trabeculation, but in a subpulmonary (rather than a subaortic) location. This pattern, the second most frequent, is associated with parallel alignment of the arterial trunks, the aorta being to the right and slightly or markedly anterior to the pulmonary trunk. It is the orientation of the outlet septum, an exclusively right ventricular structure, that is the central feature, and the resulting lesion is usually described as the Taussig-Bing heart. Such hearts exhibit a spectrum of malformation determined by the precise connection of the overriding pulmonary valve. In most cases, there is mitral to tricuspid discontinuity, so that the defect has a muscular postero-inferior rim. Rightward deviation of the outlet septum producing subaortic obstruction is also frequent, as is aortic coarctation. Straddling and overriding of the mitral valve is the other malformation frequently associated with this pattern of DORV.

(c) Doubly-committed, juxta-arterial ventricular septal defect. This subgroup of double outlet right ventricle is also closely related to tetralogy of Fallot. The central feature of this subgroup is complete absence of the muscular outlet septum, so that there is fibrous continuity between the facing leaflets of the aortic and pulmonary valves. The large interventricular communication is located immediately beneath both the aortic and valves, which have a marked tendency to override. The defect can be associated with mitral - tricuspid continuity and therefore be perimembranous, or with mitral - tricuspid discontinuity, and have a muscular postero-inferior rim. Reminiscent of the tetralogy of Fallot, the raphe between the arterial valves is deviated in an antero-cephalad direction to produce pulmonary stenosis with overriding of the aortic valve. Hence, this variant can be diagnosed as tetralogy of Fallot, although it is best considered as DORV with a doubly-committed and juxta-arterial ventricular septal defect, and describe the mode of ventriculoarterial connection.

(d) Noncommitted ventricular septal defect. This is the most complex variant of double outlet right ventricle. Most commonly, the defect is noncommitted because it is perimembranous and opens into the right ventricle beneath the septal leaflet of the tricuspid valve, or because the tension apparatus of the atrioventricular valves is interposed between the margins of the defect and the subarterial outflow tracts. The surgical correction of these variants is quite difficult, and complete repair may not be possible. Rarely is the defect noncommitted because it is within the inlet or apical trabecular components of the muscular septum. To this extent, there is a conflict between the anatomical and functional definitions of a noncommitted defect. What is anatomically a committed defect may be rendered noncommitted functionally because of the interposition of vital structures, usually a valvar tension apparatus, between the defect and the arterial valves. These features are of profound surgical important, and must be taken into account in order to decide when a defect is noncommitted or subarterial.

Hemodynamics

The hemodynamics are dependent on the position of the ventricular septal defect, the relationships of the great arteries, and the presence of associated cardiac malformations, such as outflow obstruction and atrioventricular valve abnormalities. Variable degrees of cyanosis are present in all patients, depending on the location of the ventricular septal defect and the volume of pulmonary blood flow. Patients with DORV and unrestricted pulmonary blood flow have hemodynamics indistinguishable from those with an nonrestrictive ventricular septal defect; those with pulmonary stenosis have hemodynamics analogous to tetralogy of Fallot; and those with subaortic stenosis (Taussig-Bing heart) have hemodynamics similar to transposition of the great arteries with a large ventricular septal defect.

Clinical Findings

The clinical findings are also quite variable, although most patients present in early infancy. Patients with double outlet right ventricle and pulmonary stenosis present analogously to those with tetralogy of Fallot, cyanosis may be initially mild but may progress, and young infants may exhibit cyanotic spells. Patients with a large nonrestrictive ventricular septal defect and no outflow tract obstruction usually present at around 3 months of age with congestive heart failure and minimal signs of cyanosis, and finally those with double outlet right ventricle, unrestricted pulmonary blood flow and left ventricular outflow tract obstruction may present with severe congestive signs and poor peripheral perfusion.

Echocardiography localizes the position of the ventricular septal defect, demonstrates the relationships of the outflow tracts and the presence of obstruction(s) if present, and defines any atrioventricular valve abnormalities. Importantly, echocardiography is able to assess the tricuspid-pulmonic valve distance, and define the presence of straddling atrioventricular valves. Cardiac catheterization is performed to further define the anatomy, to obtain data on pulmonary vascular resistance and to identify coexistent conditions.

Medical & Surgical Management

Palliative operative procedures include pulmonary artery banding in cases of excessive pulmonary blood flow, and placement of systemic-pulmonary shunts in cases of pulmonary outflow tract stenosis. Palliative procedures are currently utilized only in cases in which definitive correction is anatomically not feasible. The goal of corrective operative management is to achieve a biventricular repair, in which the left ventricle is connected to the aorta, and the right ventricle to the main pulmonary artery. There are three main variables to be considered when deciding upon the most suitable operation, these being the location of the ventricular septal defect, the degree of tricuspid - pulmonary discontinuity, and the presence of right or left ventricular outflow tract obstruction. Often time, the decision on which operation to perform depends on the intraoperative findings.

Repair with subaortic or doubly-committed ventricular septal defect.

In the spectrum of double outlet right ventricle that is tetralogy of Fallot-like, namely in the presence of a subaortic or doubly-committed, juxta-arterial ventricular septal defect, and adequate tricuspid - pulmonary discontinuity to allow for an unobstructed intraventricular baffle, (usually at least equal to the diameter of the aortic annulus), a Kawashima intraventricular repair can generally be performed, in which the ventricular septal defect is baffled directly to the aorta by use of a tunnel.[306, 310] When the morphology is not favorable for an intraventricular repair, due either to insufficient tricuspid - pulmonary discontinuity or to pulmonary stenosis, then the pulmonary valve may be sacrificed in order to gain sufficient space to place an intraventricular baffle. Right ventricular to pulmonary artery continuity is then established by a conduit, the so-called Rastelli operation. Three other operations, not in common use include réparation à l’étage ventriculaire (REV operation)[61], Nikaidoh’s aortic translocation operation[54], and the pulmonary translocation operation. These operations are described in greater detail below. Resection of the outlet septum or enlargement of the ventricular septal defect may also be necessary to avoid outflow obstruction.

Repair with subpulmonary ventricular septal defect.

In the spectrum of double outlet right ventricle that is D-transposition-like, namely that there is a subpulmonary ventricular septal defect and insufficient tricuspid - pulmonary discontinuity, two options are available for complete repair without the use of a conduit. These include the arterial switch operation, in which an intraventricular patch diverts blood from the ventricular septal defect to the pulmonary valve and a standard arterial switch operation is performed[53], and the pulmonary translocation operation, (see below). A third option is the Damus-Kaye-Stansel operation, in which an intraventricular patch diverts blood from the ventricular septal defect to the pulmonary valve, the main pulmonary artery is divided at its bifurcation, the proximal end is anastomosed to the ascending aorta, and the right ventricular outflow tract reconstructed with a valved conduit from the right ventricle to the distal divided end of the main pulmonary artery. Resection of the outlet septum or enlargement of the ventricular septal defect may also be necessary to avoid outflow obstruction.

Repair with noncommitted ventricular septal defect.

The most common form of noncommitted ventricular septal defect is the atrioventricular septal defect, which extends under the septal leaflet of the tricuspid valve. Several authors have suggested that when this defect occurs with pulmonary stenosis, (which thereby precludes an arterial switch operation), the procedure of choice is patch closure of the ventricular septal defect with creation of a generous anterior and superior extension. The ventricular septal defect extension is then baffled to the aorta as for the standard intraventricular repair described previously. However, in view of the known tendency for surgically created ventricular septal defects to close spontaneously, as well as the inherent risk of creating subaortic stenosis with the tunnel repair, this approach is generally best avoided.

Certain anatomic forms of double outlet right ventricle require surgical approaches that are more closely related to those used for management of a functional single ventricle[538]. In these forms of double outlet right ventricle, the right ventricle is quite hypoplastic, and the defect results in essentially a single functional ventricle. In this subgroup, there is frequently a straddling tricuspid valve and sometimes a superior-inferior ventricular relationship. In other forms of double outlet right ventricle the left ventricle is hypoplastic, and frequently there is hypoplasia or atresia of the mitral valve. However, in still other patients there are two relatively well-formed ventricles, but the ventricular septal defect is of the atrioventricular septal defect type, and construction of a baffle to divert the left ventricular output to the aorta may be extremely difficult without disruption of the tricuspid chordal attachments and anterior enlargement of the ventricular septal defect. Under all of these circumstances, a univentricular palliation may be elected. When a univentricular palliation is considered, the critical surgical features are the function of the atrioventricular valves and obstruction to outflow from both ventricles into the aorta. There is a high incidence of obstruction to either the aorta or the pulmonary artery in patients with double outlet right ventricle, in addition, straddling tricuspid valves and common atrioventricular valves are not infrequently regurgitant in patients with double outlet right ventricle.