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Transpssitiol~ of the Great Arteries

Indications for Surgery

Simple Transposition in Neonates


A baby with this malformation needs to be operated without delay. A very cyanosed infant will require palliation by balloon atrial septostonly (BAS). When indicated arterial switch operation is done in the first few weeks of life. It shoi~ld not he clelayed more than Sour weelts as the left ventriclc would have regressed and will Fdil to support the systemic circulation on switching.

Siittyle Traizsyosition of tlze Great Arteries Present after 30 Days A switch operation will have poor results, as the ventricle that has regressed will not be able to maintail1 systemic circulation. The alternative is rapid two-stage switch operation. This prepares the left ventricle for supporting systelllic circulution. The steps of thc operation are: (1) Pulmonary trunk banding along
with systenlic pulmonary artery shunt. (2) Arterial switch operation after 1-2 weeks when by echo the left ventricle has become suitable. Another approach to the problem is atrial switch operation (Senning or Mustard Procedure).

Tra~tsposition c# tlt e Great Arteries witlz Ve~ztricular Scptal Defect Transposition of the great arteries with VSD is an indication lor surgery. It is prelerable to do VSD closure and aterial switch operation within the first few weeks of life. However as the ventricle does not regress because of the presence of VSD it can be done after four weeks also.Transpositiort of the Great Arteries with VSD and Left Ventl-icular Ou#Zow

Tract Obstruction
The presence of such a condition has to be surgically corrected. T11el.e is difference of opillion about the timing and definitive procedure to be carried out.When symptoms and cyanosis are severe systemic pulmonary artery shunt is indicated. Thc alternate approach is a Le Complc procedure. Le Compte called this operation REV procedure (Reparation la etage Ventriculare). It is not very clear as to the youngest age at which Le Comple procedure can be done. When the baby is around six months of age it is a fairly safe operation.

Technique of Surgery

Arterial Switch Operation

This is the operation of choice for simple transposition of the great arteries as it ensures anatomical correction. The approach is through midline incision and median sternotomy. It is usually done with a high ascending aortic cannula anddirect cannulation of SVC and IVC. Patient is cooled down to 18 to 25°C and pel-fusion flow reduced. There is no need for resorting to circulatory arrest.Alternately, the operation could be done with single light atrial cannula and resorting to biief period of circulatory arrest. Heart is a~rested by cold cardioplegic solution administered ante-grade through the aortic root. It could also be supplemented by retrograde cardioplegia through the coronary sinus. Atrial and vei~ti-iculw pacing wires are inserted.

Transoesophageal echocardiogram will help in deciding adequacy of coronary circulation by assessing global and regional wall motion. The success of arterial switch operation depends on coronary arleiy button tnunsfel; which in turn varies according to the type of oiigin of coronary artesies in transposjtion of the great arteries.

Atrial Switclz Operatiolz (Sclzniizg or Mustard Operation)
In transposition of the great arlcrics there is ventriculo arlerial discordailce whereby aorta arises Trom right ventricle and pulmonal-y ;u.Lesy froin left ventricle. In atrial switch operation a baflle js placcd in he alriuin in such a way that blood from SVC and IVC flows under the baffle to milral valve ilnd left vent icle and to the pulmoilary artery. Pulmonary venous rcturn flows over thc patch to tricuspid valve and RV and then to aorta.

Senning Procedure

Operation is peiforined by ascending aorlic and separate SVC and IVC cannulation. If the operation is done under deep hypolhcrinic circulatory arrest(DHCA) a single right atrial cannula is used. After aorta is cross-clamped and cold cardioplegia is given into the aortic root, a trap door incision is made on the right atiium. Another longitudiilal incisioil is made on the lest atriuin in front of right superior and inferior pulmonary veins. Foramen OvaIe is closed and cutting back on to the corollary sinus and on to the atrial septuin a flap is luised. The septa1 flap is sewn to the posterior atrial wall on to the lcft and superior to the left pulnlonary vein openings. The right margin of right atriotomy is then suturcd to the medial flap of the septa1 incision so that the SVC and IVC blood will flow to the milral valve. Finally the medial flap of trap door like right aldotomy is sutured to the lateral flap of the leTt atriolomy to complete the operation.Alternatively, in situ pericardiuill could be utilized to make lateral wall of the pathway for pulmonary veilous blood to the tiicuspid valve. Tnlerrupled sutures are used in places so as to allow growth as the child grows. The advantage of Senning over Mustard operatioil is that the babies own atrial tissue is used and it grows with the baby.
 
Mustard Operation

The difference in Mustard operation is that either pericardium or polyester patch is used for making the inter atrial baffle. The b'affle complications are less if a~ltologus pericardiurn is used. The size and shape of the baffle has to be accurately measured and designed. As the baby's atrial septum is not used in this operation, it is completely excised. s u t ~ ~ r i n of g the baffle as in the case of Senning operation is done. The problems of atrial switch operation could be due to obstructioil to systemic or pulmonmy venous flow as the baby grows. Ultimately as right ventricle is the systemic pumping chamber it will fail.

Results

Arterial switch Operation


The operation is highly specialised. When carried out in experienced centers the mortality for simple TGA and TGA with VSD is 2 to 7 per cent. Among babies who survive the operation the survival up to one year is vely good. Five yeas survival is higher than 90 per cent.Most of the deaths are related to poor left ventricular function caused by imperfect transfer of coronary arteries. Right ventricular outflow tract obstruction is another complication requi ing reoperation in about 10 per cent of cases.

Atrial Switch Operation
The hospital mortality reported varies between 0 and 15 per cent. Late survival isn worse for TGA with VSD compared to simple TGA. 15 year survival after Mustard and Senning operations are 64 per cent and 86 per cent respctively. In a large series from Toronto Hospital for sick children the 20 year survival for Mustard procedure was 80 per cent with 10 per cent having RV dysfunction. 172.ansposition with VSD and Pulmonary Stenosis

In the early years Rastelli and le Compte operations had 20 to 30 per cent mortality. This has been reduced to 5 per cent in good centers. 10 year survival during follow-up is around 95 per cent. However, 15 <and 20 year survival fall to 68 per cent and 52 per cent.When operation is done at younger age re-operation rate is higher. For Le Compte procedure it is around 26 per cent and for Rastelli 67 per cent when followed up for longer periods.

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