This is one of the most complex morphological diagnoses in congenital heart disease as it requires clear 3D understanding of the intra-cardiac anatomy and consists of a spectrum of lesions that may require a variety of surgical solutions to achieve anatomical repair. The term ‘double-outlet right ventricle’ (DORV) means that there is a VSD and that both the great arteries are (predominantly) arising from the right ventricle. The aorta often overrides the VSD, but at least 50 per cent of the aorta must be committed to the RV in order to classify as a DORV. Usually, both ventricles are well developed, and complete biventricular repair depends on (1) the extent (if any) of any pulmonary or sub-pulmonary stenosis and (2) the relationship of the great vessels to the VSD. The essential components of the morphological spectrum of DORV are often best considered by appreciating the relationship of the aorta to the mitral valve – in the normal heart, these two structures are in direct fibrous continuity, but as the aorta moves anteriorly, it becomes more committed to the RV and further away from the mitral valve (Figure 17.1). Thus, the aorta sits on a complete skirt of muscle (an infundibulum). As the aorta moves further forward, it becomes even further away from the VSD than the pulmonary artery (PA) – continuing this anterior and rotational movement – and the great vessels become transposed in extreme cases of DORV.
Figure 17.1 Long-axis parasternal view of DORV emphasizing the loss of continuity between the aortic (Ao) and mitral valve (MV).
Another way of classifying DORV is through the position of the VSD. The commonest orientation is the sub-aortic VSD, and the rarest is when the VSD is remote from both the great vessels – the non-committed VSD. Occasionally, the VSD is double committed, straddling beneath both the great vessels, and finally, as described earlier, the VSD can be sub-pulmonary, implying that the aorta is very anterior and distant from the LV.
Part of the definition of tetralogy of Fallot is that the aorta overrides the ventricular septum; however, if the override is such that more than 50 per cent of the aorta is committed to the RV, then this is categorized as DORV. Often there is still direct continuity of the aorta to the MV, and the DORV is created in response to the deviation of the ventricular septum rather than the malposition of the aorta.
These patients will be in heart failure as for any patient with an unrestrictive VSD. Repair will depend on the relationship of the aorta to the VSD and requires an appreciation of the 3D pathway that will be created within the heart to commit the aorta back to the LV. In more severe cases, such a pathway may risk obstructing the outflow to the PA.
DORV with Sub-Pulmonary VSD.
This implies a more severe form of DORV in that the aorta has moved so anteriorly that it is actually further away from the VSD than the PA (Figure 17.2). As a result, the great arteries are often malposed, being more side by side or even with the aorta anterior to the PA. This is known as the ‘Taussig-Bing anomaly’. A decision has to be made as to whether the aorta can be baffled through to the VSD or an arterial switch would be preferable, then closing the VSD over to the (original) PA to achieve correction. The condition may also be associated with coarctation, aortic arch hypoplasia or aortic interruption (in around 50 per cent of cases).
This is rare, but occasionally the VSD is situated more in the inlet septum and is remote from the great vessels. The possibility of correction will depend on whether or not it is possible to create an adequate-sized pathway from the VSD to the aorta – thus correction depends on the size and exact position of the VSD. Some cases may not be septatable and need to consider a Fontan-type pathway.