In transposition of great arteries (TGA), pulmonary artery arises from the left ventricle and aorta arises from the right ventricle. Aorta is anterior and to the right of aorta in D-TGA, which is the variety which we mean when we say just transposition of great arteries. L-TGA is a physiological corrected transposition with aorta to the left of the pulmonary artery, also called C-TGA. In L-TGA, in addition to ventricular arterial discordance, there is also atrioventricular discordance so that systemic venous blood flows from the right atrium to the morphological left ventricle and to the pulmonary artery. Similarly pulmonary venous flow reaches the morphological right ventricle from the left atrium and further into the aorta.
In D-TGA, initial treatment is to have the ductus patent by prostaglandin infusion and further improve systemic saturation by balloon atrial septostomy. Atrial switch repair is known as Mustard procedure in which superior and inferior vena caval blood is baffled to the left atrium and onto the left ventricle and pulmonary artery. Pulmonary venous flow is baffled the right atrium right ventricle and the aorta. Symptom free survival until 2nd-3rd decade of life is feasible with Mustard procedure. The better option if diagnosed early in the neonatal period is an arterial switch operation or Jatene’s procedure. Long term data on arterial switch operation is being reported now. Competence of the pulmonic valve which becomes the neo-aortic valve is a question. Development of ostial stenosis in the reimplanted coronaries is also a concern. Long term complications of atrial based repair include arrhythmias and sudden cardiac death. Only eighteen percent maintain sinus rhythm and most go on to develop sick sinus syndrome atrial flutter/fibrillation and implantation of a permanent pacemaker may be needed in some. Systemic (tricuspid) atrioventricular valve regurgitation can develop in some. Whether tricuspid valve regurgitation is the final answer for this is not yet known. Systemic (RV) ventricular failure is another important problem. 15% have symptoms of heart failure by 2nd-3rd decade. Cardiac transplant or staged arterial switch with pulmonary banding to “train” the left ventricle may be an option in this case. Baffle obstructions are a rare (5%) but serious complication. Systemic venous obstruction is more common and should be suspected if new upper extremity edema develops. Pulmonary venous obstruction will manifest with new onset heart failure symptoms. Echocardiogram or cardiac catheterization is needed for further evaluation. Pulmonary venous obstruction can be treated surgically. Systemic venous obstruction may be treated with angioplasty/stents.
Most cases of L-TGA are asymptomatic for many years, often into adult life. Even though it is a physiologically corrected state, studies have shown that one fourth may die by a mean age of thirty eight years. Progressive heart failure, sudden cardiac death, AV block and atrial arrhythmias may occur in them. Severe tricuspid valve regurgitation requiring tricuspid valve replacement may occur. It may be difficult to image using echocardiograms and MRI may be needed, more so for better evaluation of right ventricular function.
Arterial switch operation for transposition of great arteries (D-TGA)
Transposition of great arteries (D-TGA) with intact ventricular septum is one of the few conditions which require surgical intervention in the early neonatal period. If a successful balloon atrial septostomy can be done to improve the mixing at the atrial level, surgery need by done within two to three weeks. Otherwise the neonate may have to be taken up within the first week itself, if there is severe hypoxemia.
Arterial switch operation (Jatene’s) is done under cardiopulmonary bypass and involves the restoration of ventriculo-arterial concordance. Sternotomy is done under general anaesthesia. The ventilation may be suspended momentarily during sternotomy to prevent lung injury with the sternotomy saw. In case the right ventricle is opened inadvertently during sternotomy (quite rare) urgent pecutaneous femoro-femoral bypass may be instituted.
Arterial duct is dissected, ligated and divided. Pulmonary artery and its proximal branches are also dissected for mobilization.
Cardiopulmonary bypass is instituted after total body heparinisation. Arterial cannula is inserted into the aorta as distally as possible and venous cannula can be inserted in the right atrial appendage and inferior vena cava. Cardioplegia can be either cold blood or crystalloid, the former being better. Cardioplegia solution is rich in potassium to produce cardiac arrest in diastole. External cooling of the heart with cold saline is done prior to administration of cardioplegia. Cardioplegia may be administered through a cannula inserted proximal to the aortic cross clamp. The right atrium is vented to drain the coronary venous blood which would otherwise distend the heart during administration of cardioplegia. Cardioplegia can be repeated administered every 20 minutes. Circulatory cooling is done using the hypothermia unit attached to the heart lung machine. Cardioplegia ensures myocardial protection due to the lowered oxygen demand. Venting of the left ventricle can be done by a catheter placed across the interatrial septum through the right atriotomy.
Aorta and pulmonary arteries are transected and transferred to the corresponding ventricles by the LeCompte manouevre. Coronaries are transferred along with a button of tissue to the neo-aorta. The arterial suturing can be done with 6-0 Prolene.
Occasionally it may be difficult to close the sternum initially due to tissue swelling in extreme neonates. In that case skin closure with bandaging and secondary closure may have to be resorted to.
Laid-back aortogram for visualization of coronary arteries
Laid-back aortogram is a technique described by Mandell VS et al [Am J Cardiol. 1990;65:1379-83] for the visualization of coronary arteries in d-transposition of great arteries in infants prior to surgery. This technique has also been used for the visualization of coronary arteriovenous fistulas in infants. Balloon occlusion aortography (dye is injected proximal to the balloon which is inflated to occlude the aorta) is done through the venous route. In d-transposition, the catheter is passed from the right ventricle to the aorta. In cases without transposition, as in coronary arteriovenous fistula, the catheter is passed to the left heart via the foramen ovale.
The visualization of coronary arteries is optimized by a 40 – 45 degrees caudal tilt of the camera / image intensifier (laid-back). 1 ml/Kg of contrast is delivered in half to one second to provide best images. The caudal view is easier to interpret than standard views. The relation between the great vessels and origins of coronary arteries and the territory supplied by each artery are better visualized. The caudal view is better for the demonstration of coronary anatomy in infants with transposition of great arteries and double outlet right ventricle.
Long term problems after arterial switch (Jatene’s) operation
Arterial switch operation is the standard of care for the management of transposition of great arteries (TGA) detected in early neonatal period. Even though it is currently the ideal treatment for TGA, there are certain potential long term problems with this approach as well. The most frequent long term sequelae is supravalvar pulmonary stenosis, though supravalvar aortic stenosis can also occur with lesser frequency. Yacoub MH and associates [Yacoub MH et al. Supravalvular pulmonary stenosis after anatomic correction of transposition of the great arteries: causes and prevention. Circulation 1982;66(Suppl):I193-7] noted that three of their twenty two patients who underwent arterial switch operation developed supravalvar pulmonary stenosis at a follow up of 1-4.6 years (mean 2.0 years). They had used homologous duramater in the majority of cases to bridge the gap between the proximal pulmonary route and the distal pulmonary artery and a Dacron tube in a few cases. Gradients ranged from 45 to 95 mm Hg in those with supravalvar pulmonary stenosis. Two of them were corrected by pericardial patch repair. Carrel T and associates described the results of direct reconstruction of the pulmonary artery during the arterial switch procedure [Carrel T et al. Direct reconstruction of the pulmonary artery during the arterial switch operation: an interesting surgical option with excellent hemodynamic results. Ann Thorac Surg. 1998;65:1115-9]. Forty seven of their one hundred and eighty nine patients underwent direct pulmonary artery reconstruction. Extensive mobilization of both pulmonary arteries into the hilum was needed for this approach. They performed a large anastomosis without any tension between the remnant of the aortic sinus of Valsalva and pulmonary artery. Early mortality was 8.5 percent in this group. Thirty seven of the forty three survivors had a pulmonary gradient of less than 15 mm Hg. Mild pulmonary stenosis with gradient between 15 to 30 mm Hg was noted in four and severe supravalvar pulmonary stenosis with gradient more than 30 mm Hg was noted in two. One patient underwent reoperation for widening of right ventricular outlow tract. The mean follow up period in this report was thirty six months.
Some patients develop dilatation and annuloectasia of the anatomic pulmonary root (neo aortic root). This can lead on to post operative aortic regurgitation. Another important concern with arterial switch operation is the potential for damage to coronary arteries during transfer to the neo aortic root.
The incidence of stenosis or occlusion of main coronary arteries in the survivors is significant [Tanel RE et al. Coronary artery abnormalities detected at cardiac catheterization following the arterial switch operation for transposition of the great arteries. Am J Cardiol 1995;76:153-7; Bonhoeffer P, et al. Coronary artery obstruction after the arterial switch operation for transposition of the great arteries in newborns. J Am Coll Cardiol 1997;29:202-6]. Sudden death several years after surgery has also been reported [Tsuda E et al. Late death after arterial switch operation for transposition of the great arteries. Am Heart J 1992;124:1551-7].
Atrial arrhythmias after atrial based repair of transposition of great arteries
Atrial scarring following an atrial based repair of transposition of great arteries is an important concern which has lead to the introduction and acceptance of arterial switch as the better choice. The likelyhood of maintenance of sinus rhythm decreases progressively as years pass by after a Mustard operation, being seventy two percent at one year, fifty six percent at five years and just forty three percent at thirteen years. The reason could be damage to the sinus node area during surgery as well as damage to the internodal conduction pathways and scars acting as nidus for reentry circuits [Gillete PC, Kugler JD, Garson Ajr, Gutgesell HP, Duff DF, McNamara DG. Mechanisms of cardiac arrhythmias after the Mustard operation for transposition of the great arteries. Am J Cardiol 1980;45:1225-30]. Recurrent atrial flutter may need ablation, though it may require a retrograde arterial approach because the focus may be in the pulmonary venous canal.
Attrition rate in transposition of great arteries
Transposition of great arteries is the most common cyanotic congenital heart disease at birth. It is in fact the first condition to be thought of if cyanosis, especially with heart failure, is detected on day one. It contributes to about five to eight percent of the congenital heart diseases [Carlgren LE. The incidencie of congenital heart disease in children born in Goteborg, 1941-1950. Br Heart J 1959;21:40] and the survival is poor without early intervention. Untreated, thirty percent of them die in the first week, fifty percent in first month, seventy percent in first six months and ninety percent in the first one year. [Liebman J, Cullum L, Belloc NB. Natural history of transposition of the great arteries: anatomy and birth an death characteristics. Circulation 1969;40:237-62] But there are also rare cases of unusual longevity without surgical intervention and such cases may present in adult life. [Gallego P, Oliver JM, Benito F, Mesa JM, Sanz E, Moreno I, et al. Unusual longevity without surgical intervention in complete transposition of the great arteries. Pediatr Cardiol 1998;19:358-60] This happens most often when there is a large atrial septal defect with good mixing of the circulations. It may be noted that pulmonary and systemic circulations are in parallel in transposition of great arteries unlike the series arrangement in normal individuals. Hence good mixing is mandatory for good survival. Mixing at atrial level permits good systemic oxygenation without the development of significant pulmonary hypertension. A balanced shunt with ventricular septal defect and pulmonary stenosis (left ventricular outflow tract obstruction) also may permit survival into adult life without surgery. This can be considered as a tetralogy of Fallot equivalent circulation.
Why the systemic right ventricle can fail in operated TGA
There are various reasons why a systemic right ventricle can fail in operated transposition of the great arteries in case of atrial based repairs. Basically the structure of the right ventricle is not meant to be a systemic pump. It is meant to be a low pressure generating pump for the pulmonary circulation. In atrial based repair of transposition of great arteries or in congenitally corrected transposition of great arteries, the systemic right ventricle has to face the high pressure high resistance circuit of the systemic circulation instead of the low pressure low resistance pulmonary circulation. More over coronary circulation maintained by a right coronary artery may not be adequate for the right ventricle to function as a systemic pump. Myocardial damage produced by severe hypoxia prior to surgery is another potential factor leading to myocardial dysfunction. Insufficient perioperative myocardial protection can also be another contributory factor in some cases.
Systemic AV valve replacement in cTGA
Congenitally corrected transposition of the great arteries (CCTGA or cTGA) is a condition in which there is atrioventricular and ventricular arterial discordance so that the circulation is physiological. The right atrium connects to the morphological left ventricle, which in turn connects to the pulmonary artery so that systemic venous blood reaches the pulmonary circulation. The left atrium is connected to the morphological right ventricle which ejects to aorta, thereby ensuring that pulmonary venous drainage reaches the systemic circulation. Since the atrioventricular (AV) valves are a property of the ventricles, the systemic right ventricle in this case has a tricuspid valve. Hence it is prone for deformities affecting the tricuspid valve. In upto 70% cases of CCTGA, systemic AV valve (SAVV) may be displaced inferiorly, the Ebstein’s anomaly. This abnormal SAVV is an important cause for regurgitation rather than ventricular dilatation and dysfunction. SAVV was the only independent predictor of death in congenitally corrected transposition of the great arteries in certain series (Prieto LR, Hordof AJ, Secic M, Rosenbaum MS, Gersony WM. Progressive tricuspid valve disease in patients with congenitally corrected transposition of the great arteries Circulation 1998;98:997-1005). The prognosis becomes poor when SAVV replacement is delayed and the systemic ventricular ejection fraction falls significantly. Ten year survival after SAVV replacement was only about twenty percent when the pre operative systemic ventricular ejection fraction (SVEF) was below 44% in earlier studies (van Son JA, Danielson GK, Huhta JC, et al. Late results of systemic atrioventricular valve replacement in corrected transposition J Thorac Cardiovasc Surg 1995;109:642-652). In a recent series from Mayo Clinic, Mongeon F et al ( J Am Coll Cardiol, 2011; 57:2008-2017) it was found that late SVEF beyond one year was preserved in 63% of those who underwent surgery with SVEF of 40% or more while it was seen in only 10.5% of those who underwent surgery with SVEF less than 40%. An SVEF of 40% or less, subpulmonary ventricular systolic pressure of 50 mm Hg or more, atrial fibrillation and a poor NYHA class III or IV were the pre operative factors associated with late mortality. The authors recommend that SAVV replacement in those with cTGA and SAVV regurgitation should be recommended before the SVEF falls below 40% and the subpulmonary ventricular systolicpressure rises above 50 mm Hg.
Mesocardia with L-TGA
X-ray chest PA showing mesocardia and L-posed aorta in levo transposition of great arteries (L-TGA)
Important differential diagnosis for a shadow along the left upper cardiac border are:
1. L – posed aorta (ascending aorta arising on the left side)
2. Dilated main pulmonary artery
3. Aneurysm of arch or upper descending thoracic aorta
4. Vertical vein in total anomalous or hemi-anomalous pulmonary venous connection
5. Aneursym of the ductus arteriosus
6. Partial absence of left pericardium causing bulge of cardiac structures to the left
7. Left atrial appendage and submitral aneurysm (a little lower on the silhouette)