Annex A > Chapter 3 - Developments in the UK, in the Diagnosis and Treatment of Congenital Heart Abnormalities in Children, 1984-1995 > The specific heart abnormalities and procedures referred to in the Inquiry > Transposition of the Great Arteries (TGA)

Transposition of the Great Arteries (TGA)

Figure 8: Transposition of the Great Arteries

The problem

70 This is one of the commonest of the cyanotic congenital heart abnormalities. For a clearer understanding of the abnormality, a brief recapitulation may be helpful. The great arteries are the aorta and the pulmonary artery. The left ventricle normally connects to the aorta into which it pumps oxygenated blood, and the right ventricle connects to the pulmonary artery into which it pumps deoxygenated blood. When the great arteries are transposed, the left ventricle connects to the pulmonary artery and the right ventricle to the aorta. Deoxygenated blood returns from the body to the right side of the heart and should then flow to the lungs to be oxygenated. Instead it is again pumped out to the body. Similarly, oxygenated blood returning from the lungs to the left side of the heart is pumped again to the lungs. In order for the baby with TGA to survive, it is essential that some of the oxygenated blood should cross over to the right side of the heart and then to the body. Similarly some of the deoxygenated blood should cross over to the left side of the heart in order to flow to the lungs to become oxygenated. In the fetus there is normally a hole in the wall between the left and right atriums, and there is also an arterial duct [11] connecting the aorta and the pulmonary artery. These fetal structures normally remain open for several hours after birth and the blood flow through them allows for the necessary crossover of blood between the left and right sides of the heart. The baby is usually slightly blue at birth, and the cyanosis increases as the communications between the two sides of the heart become smaller. Unless emergency measures are undertaken the baby's condition deteriorates rapidly and he does not survive. Some babies with TGA are born with additional abnormalities, one of the commonest being VSD. In that case, an additional communication between the two sides of the heart may result in the cyanosis being quite mild but the baby then suffers from the additional problems associated with a VSD. The term `Taussig-Bing' syndrome is used to describe a VSD which is just beneath the pulmonary artery so that there tends to be a considerable flow of blood to the lungs. [12] Other associated abnormalities that occur not uncommonly are pulmonary stenosis, and Coarctation of the Aorta, and they add additional problems in the overall progress and management of the baby.

71 There is a particular problem relevant to the management of TGA which is important. The heart requires a blood supply to the heart muscle. This comes from the coronary arteries, which branch off from the aorta almost as soon as that great artery arises from the left ventricle in the normal heart, or from the right ventricle in TGA. The flow into the coronary arteries depends on the blood pressure in the aorta being at least normal, and it is important that oxygenated blood flows to the heart muscle. The logical operation in TGA is one in which the great arteries are disconnected from their transposed positions and reconnected so that they receive blood respectively from the correct ventricles. Therefore it is clear that during the operation the coronary arteries need to be moved over together with the aorta. There are technical difficulties associated with this delicate part of the operation and it is important that the cardiologist and the surgeon both have as clear an understanding as possible of the branching of the coronary arteries in each individual case.

Diagnosis

72 Transposition of the Great Arteries was one of the earliest of the diagnoses that could be made confidently using echocardiography. Throughout the period covered by the Inquiry's Terms of Reference, almost all centres in the UK would have used echocardiography alone in order to obtain a complete diagnosis of TGA together with most of the other associated abnormalities. The sensitivity and accuracy of detecting the associated abnormalities have been enhanced by the use of ultrasound Doppler and colour-flow mapping. An important element of the echocardiographic diagnosis is to try to visualise the origins and branching of the coronary arteries in order to alert the surgeon if there is likely to be anything unusual. There are always a few cases in which cardiac catheterisation still becomes necessary as, for example, when there is any uncertainty about certain diagnostic details.

Management

73 From the late 1970s, the initial emergency management of almost all newborn babies with severe cyanotic congenital heart disease has been to treat with prostaglandin E in order to keep the arterial duct open. In TGA this is usually rapidly effective in improving the blood oxygenation by encouraging more blood flow to the lungs and more flow through the hole between the two atriums. Then, by means of a cardiac catheterisation technique, a larger hole is created in the wall between the atriums. This is known as `balloon atrial septostomy'. Improvements in the design of the equipment for this procedure have simplified it significantly and it is now regarded as relatively safe and routine. There have been minor developments related to balloon atrial septostomy between the mid-1980s and mid-1990s. They have been influenced largely by improvements in intensive care management. Instead of moving the baby to the cardiac catheterisation theatre, the procedure is often performed in the intensive care unit using echocardiography in order to visualise the cardiac catheter and the cardiac structures. Most babies with an adequate hole in the atrial septum can survive and thrive for many months.

74 In the mid-1980s the standard approach after balloon atrial septostomy was to discharge the baby home, then plan further investigations with a view to an operation at around 6 months of age. The precise timing depended on the general condition of the baby and on the degree of cyanosis during the period of follow-up. Although it was recognised that the logical operation would have been to `switch' the great arteries to their `correct' ventricles, the technicalities of moving the coronary arteries had not been adequately mastered. Therefore the type of operation that had been performed since the mid-1960s was undertaken, namely the Mustard procedure or the Senning procedure.

75 Both of these operations employ the same principle. Deoxygenated blood returning from the body is diverted so that it flows to the left ventricle (instead of the right), then to the lungs. Similarly, oxygenated blood returning from the lungs is diverted so that it flows to the right ventricle and then to the aorta. Thus instead of the left ventricle pumping blood to the body, the right ventricle continues to do this work and the left ventricle continues to pump blood to the lungs. Since the operation was first designed, it has been questioned as to whether the right ventricle was capable of sustaining the demands of pumping at a higher pressure than if it were providing blood flow to the lungs. The operation is very effective and enables children to lead normal lives but in the longer term, complications have been reported, mostly during late adolescence or early adult life. Therefore considerable efforts were made during the 1980s to perfect the more logical Arterial Switch operation.

76 During the 1980s there were some isolated reports of Arterial Switch operations being done in the United Kingdom but virtually all centres continued to rely on the Mustard and Senning procedures. Meanwhile, considerable advances in the Arterial Switch technique were made in a few centres in the United States and in Europe and Australia. Towards the end of the 1980s a few centres in the UK were obtaining good or satisfactory results by using the Switch procedure and by the early 1990s the operation had become well established in most of the major centres. By the mid-1990s it was expected that all major centres would have been performing the Arterial Switch operation instead of the Mustard or the Senning procedure with a reasonable expectation of good results. It was recognised that the major technical problem with the Switch procedure continued to be related to the difficulty of relocating the coronary arteries. Surgeons began to appreciate that if the coronary artery anatomy was particularly difficult, it was advisable to ask for help, if at all possible, from one of the few surgeons with a wide experience of dealing with the problem. Great reliance was ordinarily placed on the paediatric cardiologist to recognise that a coronary abnormality might be present in an individual case.

77 Associated additional abnormalities create more work for the surgeon and consequently complicate the technical procedure. Each of the additional abnormalities must be repaired in addition to the Arterial Switch being carried out. There is one notable exception. Some children with TGA also have a VSD together with pulmonary stenosis. If the VSD is high in the ventricular septum and just below both great arteries it is often more convenient to perform the so-called Rastelli operation. In this procedure a patch is placed on the defect in such a way that flow from the left ventricle is diverted through the VSD and into the aorta. This process necessitates closing the connection between the left ventricle and the pulmonary artery. Then a valved conduit is placed between the right ventricle and the pulmonary artery.

78 Most patients who have survived the Arterial Switch operation have an uncomplicated course but it is essential that they are kept under regular review and are assessed by echocardiography for evidence of any of the later complications. Some of these patients need further operations or cardiac catheter interventions in order to remedy problems such as narrowing of the pulmonary arteries or very occasionally significant leaking of the aortic valve. Although there is the expectation that children undergoing the Arterial Switch operation are likely to have better long-term results that those with the Mustard or Senning operation, not many patients have had a sufficiently long post-operative period in order to be able to confirm that belief.

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Footnotes

[11] See the section on the management of Tetralogy of Fallot in this chapter

[12] See the section on the diagnosis of Ventricular Septal Defect (VSD) in this chapter