Outcome of Mustard Operation for TGA

Dateline: 09/07/97

Your response to my request for feedback about this site has been very encouraging and provided me with many ideas and suggestions for the Featured Article section. This week, I'll deal with one of the first requests - for information on the long term outcome after a Mustard operation for Transposition of the Great Arteries.

What is Transposition of the Great Arteries ?

Transposition or TGA is a condition where both the great blood vessels of the heart - the aorta and the pulmonary artery - are interchanged in position. This means that the aorta, instead of arising from the left ventricle, takes off from the RIGHT ventricle, while the pulmonary artery arises from the LEFT ventricle. To read about what happens in TGA in greater detail, please visit my other sites on this topic.

What is the Mustard Operation ?

The Mustard or Atrial Switch operation was first described in 1964. In this operation, a "baffle" made of dacron or pericardium is used inside the atrium to direct venous blood from the superior and inferior vena cava into the left ventricle through the mitral valve, from where it passes into the pulmonary artery to the lungs to get purified. Oxygenated blood returning from the lungs through the pulmonary veins is then simultaneously guided across the tricuspid valve into the right ventricle which pumps it to the rest of the body through the aorta.

Why bother about outcome after a Mustard operation ?

Today, the Arterial Switch Operation (ASO) described by Jatene is the operation of choice for TGA, and seldom are Mustard operations performed. However, many survivors of the Mustard operation done in the sixties and seventies are now developing complications or ill effects of the repair, and are seeking medical attention. It is thus appropriate to consider some of the issues that affect this population.

What are the problems that might occur LATE after a Mustard operation ?

To simply enumerate them, the complications that may occur are:

• Systemic Venous Obstruction (SVC,IVC)
• Pulmonary Venous Obstruction
• Tricuspid Valve Incompetence
• Baffle Leaks
• Residual or Recurrent VSD
• Residual or Recurrent LVOTO
• Right and left ventricular dysfunction
• Arrhythmias

I'll discuss each of these briefly, along with the treatment options available.

Systemic Venous Obstruction

Obstruction of the Superior Vena Cava (SVC) is common, and occurs in around 8% of Mustard patients. Usually asymptomatic, it is discovered on a routine post-operative evaluation. If it is more severe, it can produce facial puffiness, or collection of fluid in the chest cavity (pleural effusion). SVC obstruction may be diagnosed by Doppler Echocardiography, and cardiac catheterization is advisable before surgery is performed.
Inferior Vena Cava (IVC) block is rarer, but more serious. It can produce liver engorgement, ascites (fluid collection in the abdomen) and leg swelling. It can also be detected by echocardiography.
While asymptomatic SVC obstruction may not require any intervention, when symptoms develop, or if IVC obstruction is detected, immediate correction is warranted. This may be done by either re-operation (at which the narrow area is widened by using a patch of fabric or pericardium across it) or using a balloon catheter to dilate the narrow segment in the catheterization lab under x-ray guidance.

Pulmonary Venous Obstruction

This is a less frequent, but much more serious, complication of the Mustard operation. Usually caused by a shrinking of the atrial baffle, it produces cough, breahtlessness, fatigue and reduced exercise tolerance. While the diagnosis may be suggested by an echocardiogram, it usually requires a cardiac catheterization to confirm and quantify the severity of block.
While balloon dilatation is sometimes useful, most often immediate re-operation is the only solution.

Leaks in the baffle

This is seldom severe enough to produce any kind of symptoms. Rarely, if the leak is large, especially when combined with some kind of venous obstruction, it may require re-operation to correct both complications.

Tricuspid Valve Incompetence (TVI)

Mild to moderate TVI is more common in patients who have had a Mustard operation for TGA with VSD. The TVI may occur due to injury to the valve cusp at the time of VSD repair, or due to right ventricle failure after surgery. This again may cause breathlessness, fatigue, cough, and venous congestion in the lungs. While mild TVI is ignored, when severe it may require replacement of the valve with an artificial valve, or conversion to a Arterial Switch operation as discussed later.

Residual or Recurrent VSD

Unless the shunt from left to right is large (Qp/Qs greater than 1.5), re-operation may not be required for residual VSDs.

Residual or Recurrent Left Ventricular Outflow Tract Obstruction (LVOTO)

Some patients with TGA have LVOTO which is difficult to correct at the time of a Mustard operation in very small infants. And often, this LVOTO is well tolerated. Only in rare cases does it develop late after operation, or progress in severity. The diagnosis is made by a combination of echocardiography and cardiac cath. Re-operation is needed when patients have symptoms, or when in asymptomatic patients, the pressure inside the left ventricle is higher than in the right (systemic) ventricle. The operation may involve relieving the block (by opening up a narrow valve, or excising a membrane), or bypassing it using a conduit (in case of a tunnel type block).

Ventricular Dysfunction

One of the major cause of long term reduction in quality of life after a Mustard operation is the right ventricle failure that develops. The failure may be due to:
Injury to the right ventricle at the time of surgery
Inherent limitations of the right ventricle to act as the systemic ventricle pumping blood to the entire body

Right ventricle failure is more common in TGA with VSD, especially when the VSD is closed through an incision in the ventricle. Ventricular function studies by cath or radio-nuclide scans show imparied function of the right ventricle both at rest and during exercise. While this may affect a significant number of long term survivors (around 35% incidence at 6 years after surgery), surprisingly most of these patients were asymptomatic and leading normal lives.

The development of late RV failure is in fact one of the most convincing arguments in favor of using an arterial switch operation as the first choice procedure for TGA. Roger Mee demonstrated that some patients with impaired RV function after a Mustard operation can be converted to an ASO.

Rhythm Disturbances

Serious arrhythmias are rarer in Mustard operations performed in recent years. In one study, at 6 years after surgery, 72% had normal sinus rhythm, 18% had junctional rhythm and all other arrhythmias accounted for 10%. The incidence of rhythm problems however increases with time after surgery, and in one study, at 9 years after surgery, 70% of survivors had arrhythmias. However, only one fourth of these were symptomatic, and just 7% needed pacemaker implantation. Late deaths reported after the Mustard operation may be caused by serious and sudden rhythm problems, and perhaps long term survivors need to be periodically screened for them. Medical treatment may be required to control the disturbances, and sometimes pacemaker therapy is needed for extreme slow heart rates.

What are the success rates for re-operations ?

This is very difficult to evaluate since many patients refuse operation, and many more are lost to follow up after surgery. The risks of a second operation, however, are higher than the first. For venous obstruction, systemic or pulmonary, reports indicate a mortality rate of around 20%. However, once surgery relieves the block, recurrence of obstruction is very rare.