Occurs in 0.03-0.07/1,000 live births.

Failure of proper development of the outflow tracts will cause both outflow tracts to emerge from the right ventricle.

Normal outflow tract development is as following:

Kramer (1942) suggested that there are three embryological areas, the conus, the truncus and the pulmonary arterial segments. Each segment develop two opposing ridges of endocardial tissue, the opposing pair of ridges and those from various segments meet to form the septum separating the two outflow tracts and the aortopulmonary trunks. The aortopulmonary septum is formed by ridges separating the fourth (future aortic arch) and the sixth (future pulmonary arteries) aortic arches. The truncus ridges are formed at the area where the semilunar valves are destined to be formed, therefore forming the septum between the ascending aorta and the main pulmonary artery. The conus ridges form just below the semilunar valves and from the septation between the right and left ventricular outflow tracts.

Van Mierop (1979), agrees that there are three pairs of ridges forming in the aortopulmonary, truncus and conus regions, however, he states that the pairs of ridges fuse independently and later on fuse with each other to complete the septation. His theory indicate that the truncus ridges form first, and as they fuse they form a truncal septum which then fuses with the aortopulmonary septum which is formed by invagination of the dorsal wall of the aortic sac between the fourth and the sixth aortic arch arteries.

Asami(1980), follow Van Mierop’s theory, however, he believes that these ridge fuse in the opposite direction of what Van Mierop has indicated, i.e. from the outflow tract to the aortopulmonary region.

Pexieder(1978, 1984) and Orts Llorca et al (1982), believe that there are only tow septa, a conotruncal (or bulbar) and an aortopulmonary septum.

The border between the myocardial wall of the outlet and the mesenchymal vessel wall is very well demarcated. The endocardial cushion tissue forms six valve swellings, underneath which two ridges are formed which are opposed to the myocardial layer. A mesenchymal arch forms within the endocardial tissue, the two limbs of the arch are in contact with the myocardium of the ventricular outflow. These bulges within the outflow tract are positioned dextroposteriorly on the parietal wall and sinsitroanteriorly on the right side of the primary septum.

 Double outlet right ventricle is diagnosed when one great vessel and all or the majority of the other great vessels emerge from the right ventricle. The great vessels relationship to each other may be in any of the various possibilities but usually they are side by side and parallel. The aortic valve could be to the right or left of the pulmonic valve or in an anteroposterior relationship. Three-quarter of cases have pulmonary stenosis. The VSD could be subaortic, subpulmonic or non-committed or far away from the semilunar valves (as in muscular or AV canal type VSD’s). Many other congenital anomalies may be present, for example, hypoplastic left heart, however, this would be with good aortic valve size and ascending aorta and mitral atresia may sometimes be present.

Three types of great vessels arrangement are observed:

The aorta to the right and posterior of the pulmonary valve, the two great vessels intertwine, i.e., normal relationship. This is the most frequent.

The aorta and pulmonary artery are side by side and the great vessels are parallel without intertwining. The aorta is to the right of the pulmonary artery. This is the second most common and also known as the Taussig-Bing variety.

Great vessels are again parallel with aorta to the left. This is the lest common. The VSD and double outlet right ventricle does not change in its location, however, it is in between the two arms of the tribiculo-septal marginalis. The anatomy of the great vessels and conal tissue determine to which arterial valve the VSD is committed.

Taussig-Bing Anomaly:

This is double outlet right ventricle with aortic valve being anterior and to the right of the pulmonary valve, i.e., transposition of the great vessels arrangement. The great vessels are parallel to each other. The VSD is subpulmonic and there is no pulmonary stenosis.

VSD in double outlet right ventricle could be muscular or of the AV canal type and therefore non-committed to any arterial valve.

When the great vessels are normally related the line dissecting the short axis of the arterial valves is parallel to the interventricular septum. Therefore the outlet septum is perpendicular to the interventricular septum and if the outlet septum is well formed and fuses with the interventricular septum this will lead to subaortic VSD but if the outlet septum is hypoplastic than the VSD will be doubly committed.

When the great vessels are of the Taussig-Bing variety the line dissecting the short axis of the arterial valve is perpendicular to the interventricular septum and the infundibulum fold fuses with the interventricular septum and this will determine if the VSD is committed to the pulmonary artery (well fused fold and trabeculoseptal marginalis) were doubly committed (no fusion). Therefore, if the great vessels are normally related a VSD could be subaortic or doubly committed and if great vessels are transposed then the VSD is subpulmonic or doubly committed. The boundaries of the VSD is important to the surgeon since the posterio-inferior border of the VSD may be muscular (when the ventriculo infundibulum both fuses with the trabeculoseptal marginalis) therefore making it safe for the surgeon to close the VSD. However, if these structures are not fused the conduction system will lie close to the rim of the VSD and therefore there is increased risk of AV block when VSD baffle is placed.

 In DORV, both great vessels emerge from the RV.  This will cause:
Cyanosis, as the well oxygenated blood from the LV mixes with the de-oxygenated blood from the RA.
Increase in pulmonary blood flow, the right ventricle, due to large VSD and the fact that the aorta emerges from the RV will cause the RV pressure to be systemic.  Therefore, the pulmonary blood flow will be significantly increased, causing CHF.  The extent of increased pulmonary valve is determined by the frequently accompanying pulmonary stenosis (valvar or subvalvar).  Pulmonary blood flow can be increased, normal or decreased depending upon the extent of stenosis.

 Presentation depends upon pulmonary stenosis.  If severe, the clinical picture will be that of cyanosis due to decreased pulmonary blood flow similar to patients with TOF.  On the other hand, mild or no pulmonary stenosis will result in CHF with less cyanosis.

The RV will be hypertrophied with right axis deviation and possible RAE.

This is valuable in assessing the nature of the defect.  Subxipjoid views show the defect nicely.  The origin of both great vessels can be seen from the RV in this view.  The relationship of the two great vessels to each other is also appreciated from the sub-xiphoid views.  Assessment of the sub-pulmonic conus is possible.  The relationship of the VSD to the aortic valve is evident in this view as well.

The extent of pulmonary stenosis can be studied from the sub-xiphoid and parasternal short axis.

Diagnostic cardiac catheterization is typically not needed prior to B-T shunt placement in cases of severe pulmonary stenosis.  Angiography and/or assessment of PVR may be needed, particularly prior top complete repair.

 The initial consideration is the extent of pulmonary blood flow:
Increased:  if there are no signs of valvar or subvalvar pulmonary stenosis together with increased pulmonary blood flow, then banding of the main pulmonary artery to restrict blood flow should be considered.  Complete repair may be an option if the cardiac anatomy is amenable to neonatal surgery such as with normally related great vessels and subaortic VSD.
Normal:  Period of 4-6 months of observation is best, particularly if the pulmonary blood flow is slightly increased allowing adequate oxygen saturation (75-85%).  This is followed by complete repair, in which the VSD is baffled to connect the LV to aorta with or without placement of RV to PA conduit.
Decreased:  A B-T shunt followed by complete repair at about 6 months of age.