What is Double Outlet Right Ventricle (DORV) ?
Some of the defects I have described are “simple”, some are a little “complex” – but DORV is something else.
It is a common term that actually describes a wide spectrum of heart disease, ranging from something similar to a Ventricular Septal Defect (VSD), through Tetralogy of Fallot (ToF) to Transposition of the Great Arteries (TGA).
It is sometimes like one, at other times like another, and occasionally a mixture of some of them. So if at first you are baffled, don’t worry. I too was, and figured it out only after a long hard struggle.
What is Double Outlet Right Ventricle ?
Normally, a ventricle has just ONE outlet. For the left ventricle, this is the aorta. For the right ventricle it is the pulmonary artery. In DORV, both of these “outlet” blood vessels – aorta and pulmonary artery – arise from the RIGHT VENTRICLE, either totally or to a great extent.
That sounds simple. What’s so complex about that ?
Well, the complexity lies in the extreme variability of the position of the outlet vessels in relation to each other, and the presence of additional defects. These include VSD, narrowing of the pulmonary valve (Pulmonary Stenosis), abnormal attachments of the mitral or tricuspid valves and abnormalities in the structure of the ventricles themselves.
The number of combinations possible are simply mind boggling. I will try and explain how exactly this affects the outcome, and decision about surgical repair.
What happens in DORV ?
Most cases of DORV have a VSD. DORV is classified based on the relationship between the VSD and the blood vessels.
- If the VSD is right under the aorta, it is called DORV with Sub-Aortic VSD.
- If it lies under the pulmonary artery, it becomes DORV with Sub-Pulmonary VSD – also called the Taussig-Bing anomaly.
- If the VSD is under both the arteries, it is called DORV with Doubly Committed VSD.
- And sometimes, the VSD is remote from the arteries, and is known as DORV with Non-Committed VSD.
This has a bearing on how the child with DORV behaves.
When the VSD is right under the aorta, the features are like that of a simple VSD. This means that the child is likely to get frequent chest colds, and become breathless on exertion.
When in addition to this, there is narrowing of the pulmonary valve (Pulmonary Stenosis), the course is similar to Tetralogy of Fallot (ToF). There is a “blue” discoloration – cyanosis. Paradoxical embolism, squatting, and easy fatigue on exercise may be seen.
If the VSD is sub-pulmonary, the features are just like those of Transposition of Great Arteries (TGA). Cyanosis, giddiness, fainting, and chest infections may occur.
When the VSD is doubly committed or non committed, clinical features are variable. In either instance, the presence of pulmonary stenosis modifies the picture.
What factors affect treatment of DORV ?
In addition to the location of the VSD, other factors also affect surgical decision making.
1. The distance between the aorta and the tricuspid valve
Surgical repair of DORV involves connecting the left ventricle to the aorta, while leaving the right ventricle attached to the pulmonary artery.
To do this, the surgeon must create a tunnel from the VSD to the aorta. Blood from the left ventricle will then pass across the VSD into the tunnel, and finally into the aorta. This is called the Intra-Ventricular Tunnel operation.
There are however certain limitations to this operation.
The tunnel will pass through the right ventricle cavity, between the tricuspid and pulmonary valves. If these two valves are placed very close together, it will not be possible to create a tunnel of an adequate size without blocking one or the other of these valves.
The surgeon and cardiologist always decide before operation by tests including echocardiography about whether this distance is adequate for an intra-ventricular tunnel operation. If not, other alternatives must be sought.
2. The size of the VSD
The VSD will be a part of the tunnel leading out of the left ventricle. So it must be large enough to permit blood flow without obstruction. A small VSD may need to be enlarged at the time of surgery.
3. Any abnormal attachments of the mitral or tricuspid valves
The mitral and tricuspid valves are themselves marvels of structural design. They have leaflets supported by struts – called “chordae tendineae” – attached to muscles called “papillary muscles“.
Together this unique system keeps blood flow directed one-way in the normal heart.
Sometimes in DORV, either of these valves may be abnormal. Instead of connecting with one ventricle, they may over-ride the wall (septum) between the two ventricles. At times, even the supporting structures – the chordae and papillary muscles – will cross the ventricular septum. This condition is called “straddling“.
Both of these situations are of importance to the surgeon. During the operation, if these structures are injured or divided, the valve cannot work well, and will become leaky – valve regurgitation. It is also of great importance to detect valves that are leaky before surgery, since the choice of operation will vary.
4. Size of the ventricles
The reason for requesting this information is to decide if, after repair, the left ventricle will be able to sustain the future workload of supplying blood to the entire body.
Usually, both ventricles are moderately developed, with the left being much smaller than the right. Sometimes, the left ventricle may be very small, and then DORV becomes a form of the “Single Ventricle” anomaly.
5. Any other obstruction in the “outlet” arteries
Sometimes other abnormalities like coarctation of the aorta or pulmonary artery stenosis may coexist. If not detected at or before surgery, they can contribute to a poor outcome. These co-existing anomalies need to be repaired too at the time of surgery.
The feasibility of surgery is never decided on the basis of just one factor, but is based on a comprehensive evaluation by various tests, including sometimes a cardiac catheterization study.
What are the surgical options for DORV ?
There are two basic types of repair for DORV
- Anatomic Repair, which restores a circulation with two ventricles
- Univentricular Repair, in which only one ventricle is functional. I will explain this situation in the section on Fontan operation for Tricuspid Atresia.
When can an anatomic repair be performed ?
The only criterion for suitability for an anatomic repair is the presence of two well-developed ventricles that will be capable of tolerating the workload after repair. It requires fine judgement after thorough investigation to make this decision.
What are the types of anatomic repair ?
There are three techniques of anatomic repair
- Intra-Ventricular Repair
This operation has been described earlier. A tunnel is created between the VSD and aorta, directing blood from the left ventricle across the VSD into the aorta. The major requirement for this is an adequate distance between the tricuspid and pulmonary valves. If this distance is very small, one of the other alternative must be employed.
- “REV” or Lecompte Operation
In this operation, a tunnel is created in the same way as in the intra-ventricular repair. But the tunnel may block the pulmonary valve. So continuity is achieved by directly sewing the pulmonary artery to the right ventricle, bypassing the blocked pulmonary valve.
- Arterial Switch with Tunnel Procedure
Here a tunnel is created inside the right ventricle, between the VSD and the Pulmonary Valve. Following this, an arterial switch operation (see the section on TGA for further details) is performed to restore normal circulation.
What are the difficulties in creating a tunnel ?
The surgeon aims to create a non-obstructive passage between the left ventricle and aorta. There may be hurdles at different levels.
- VSD size – If the VSD is very small, it may need to be enlarged at the time of surgery.
- Abnormal attachments of chordae tendineae – When the tricuspid valve chordae run across the path of the tunnel, it may be possible to divide them and re-attach them to the wall of the tunnel. If the mitral valve chordae are abnormal, an anatomic repair is better avoided because of the risk of mitral valve leak if the supporting tissue is damaged.
- Narrowing of the valves or great arteries – This may need to be relieved at the time of repair.
In summary then, a simple way to decide upon the choice of repair would be
- NORMAL tricuspid valve to pulmonary valve distance with
a. Normal pulmonary valve – Intra-Ventricular Repair
b. Narrow pulmonary valve – Intra-Ventricular Repair with Pulmonary Valve Enlargement
- DECREASED tricuspid valve to pulmonary valve distance with
a. Normal pulmonary valve – Arterial Switch with Tunnel to Pulmonary Artery
b. Narrow pulmonary valve – REV operation
What is the best age to repair DORV ?
Since DORV is not a single entity, the best age for repair depends on the type of DORV.
- When there is no pulmonary stenosis, DORV with sub-aortic or sub-pulmonary VSD can be repaired electively at 6 months of age.
- For DORV with non-committed VSD, later repair at 3 to 5 years age is advisable.
- When pulmonary stenosis is present, DORV with sub-aortic VSD is treated exactly as Tetralogy of Fallot. DORV with sub-pulmonary or non-committed VSD is electively repaired at 3 to 5 years age.
However, none of these suggestions are absolute ones. Decision making in individual cases depends on the specific nature of each patient.
What is the outcome after DORV repair ?
These are still uncharted waters. Most published operation series have a mixture of all the subtypes of DORV. In a complex and variable condition like this, such reports on a non-homogenous group are not predictive.
For instance, the outcome of DORV with sub-aortic VSD, good ventricular function and no pulmonary stenosis will differ considerably from DORV with sub-pulmonic VSD, small left ventricle and pulmonary stenosis. Much more analysis, particularly after categorizing cases according to their anatomy, is needed.
In general, there is a 5% risk of operative mortality, and about 80% of patients are alive 5 years after surgery.
Late complications are uncommon if the operation has been properly designed and executed. Rarely, rhythm disturbances – arrhythmias – have caused sudden death, but the risk of this varies in different reports.
Complications are more common in the non-committed VSD group, since usually more complex repair techniques are needed in these patients.
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