S Raja, S Nayak, M Kaarne
arterial switch operation, congenital cardiac defects, transposition of the great arteries
S Raja, S Nayak, M Kaarne. Arterial Switch Operation for Simple Transposition: Three Decades Later. The Internet Journal of Thoracic and Cardiovascular Surgery. 2003 Volume 6 Number 2.
Without intervention, babies born with transposed great arteries (TGA) are doomed to a rapid death. Although the Mustard and Senning atrial switch procedures achieved widespread acceptance and success during the past three decades, the search for an operation to return the great arteries to their normal anatomic positions continued. This was stimulated primarily by the accumulating observations at mid- to long-term follow-up studies of an increasing frequency of important arrhythmic complications, including sudden unexplained death; the spectre of late right ventricular dysfunction and major tricuspid regurgitation in a ventricle unsuited for a lifetime of systemic function; and dissatisfaction with the operative mortality and results in the subgroup of infants with TGA and large ventricular septal defect (VSD). Starting in 1954, a number of innovative procedures to achieve an anatomic correction were described, but clinical success was not achieved until 1975 by Jatene and coworkers, who had the distinction of performing the first successful arterial switch operation (ASO) in a patient with TGA and VSD. ASO is now the procedure of choice in most medical centres. It represents a major improvement since it does not introduce any additional intracardiac anomaly, restores the left ventricle to its natural systemic function, and maintains the sinus node function. The long-term success of this procedure depends on adequate reconstruction of the pulmonary artery, adequate growth of these anastomotic sites, capability of the native pulmonary valve and root to function in the systemic circulation, and adequate function of the left ventricle.
This review article attempts to briefly summarize the historical aspects of arterial switch operation and assess the outcome after this procedure.
Transposition of the great arteries (TGA) is a severe cardiac malformation in which the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle. An alternative terminology describes this malformation as a cardiac anomaly with the combination of concordant atrioventricular and discordant ventriculoarterial connections.1,2,3TGA is a lethal and relatively frequent malformation accounting for 5-7% of all congenital cardiac malformations.4,5With a concordant atrioventricular connection, the physiologic effects are acute and cyanosis and distress are usually obvious soon after birth. Survival depends on the mixing of blood between pulmonary and systemic circulations, mainly through a patent foramen ovale and assisted by a patent ductus arteriosus (PDA) and sometimes a co-existent ventricular septal defect. If left untreated many infants die in the first week of life, and most die by 1 year of age.6
The arterial switch operation (ASO) ensures “anatomic correction” of transposition of the great arteries at the arterial level. The term anatomic correction of transposition of the great arteries applies to all repairs connecting the right ventricle with the pulmonary artery and the left ventricle with the aorta. This can be accomplished at the ventricular level7,8,9or at the arterial level, either with coronary transfer10or without coronary transfer.11,12,13,14This article reviews the procedure that is now called the arterial switch operation (ASO) - that is, anatomic correction of TGA at the arterial level with coronary transfer.
Mustard and colleagues in 1954 were the first to unsuccessfully attempt ASO.15They used monkey lung as an oxygenator and transferred only the left coronary artery. None of the patients survived. In the pre-cardiopulmonary bypass era, both experimental16as well as clinical17,18, attempts to switch the great arteries without coronary transfer failed.
Attempts to switch the great arteries along with the coronary arteries were continued despite impressive results of the physiologic repair.19,20Senning reported three patients with TGA who had en bloc transfer of pulmonary valve and artery and diversion of the left ventricle to the aorta through a VSD.20Apart from efforts of Idriss and colleagues21other experimental techniques for switching great arteries with coronary transfer were also reported.22,23
The credit for performing the first successful arterial switch operation in a patient with TGA and a large VSD goes to Jatene and associates.24This operation was restricted to patients with TGS and VSD, large PDA, or left ventricular outflow tract obstruction whose left ventricular pressure was at or close to systemic levels after birth.25A number of techniques, avoiding mobilization of coronary arteries, were developed to reduce the high early operative mortality attributed partly to technical difficulties related to transfer of the coronary arteries. These included baffling of the coronary arteries to a surgically created aorto-pulmonary window26; end-to-side anastomosis of the proximal pulmonary artery to the ascending aorta with placement of a conduit from right ventricle to the distal pulmonary artery.13,14,27; translocation of the entire aortic root including the proximal coronary arteries.28However, the ASO with coronary artery transfer retained its original appeal. Lecompte and colleagues devised an important maneuver of transferring the distal pulmonary artery anterior to the ascending aorta thus facilitating direct anastomosis of the neopulmonary artery without conduit interposition.7
For patients with TGA and intact ventricular septum (IVS), with a few exceptions29,30, most earlier attempts at performing primary ASO failed, mainly because of left ventricular dysfunction. Yacoub and associates devised a two-stage approach for patients with TGA-IVS by first banding the main pulmonary artery (with or without systemic-pulmonary shunt) to stimulate the development of the left ventricular muscle mass, followed by an ASO several months later.31The “rapid two-stage ASO” for TGA-IVS was later introduced by surgeons at the Children's Hospital in Boston who after performing the PA banding and systemic-pulmonary shunt as the first stage did ASO within an average interval of 7 days.32
Outcomes after Arterial Switch Operation for simple transposition and TGA with VSD
The neonatal arterial switch operation (ASO) has become the surgical procedure of choice for correction of transposition of the great arteries (TGA) with or without ventricular septal defect (VSD), as demonstrated by encouraging early and mid-term cardiac results33,34,35,36as well as normal exercise capacity in most patients.37,38This section reviews outcomes after ASO for simple transposition and TGA with VSD.
Early mortality and survival
In recent years, major changes as regards timing for operation, surgical technique, and perioperative care have resulted in a considerable improvement in the early outcome following ASO. Institutions with extensive experience and properly prepared for ASO in neonates, report less than 5% early operative or hospital mortality in both simple TGA and TGA with VSD.39,40,41,42,43,44This is a major improvement compared with about 15% reported in earlier eras.33,39,40,42,45,46,47,48,49Death rate is extremely low by 6 to 12 months after ASO, and survival declines minimally after that time.405- and 10-year survival is 90% even for high-risk patients.33,50,51,52,53,54Although figures for 15- to 20-year survival are still not available, but it can be reasonably speculated that it will be about 90%.
Death following ASO is usually secondary to ventricular dysfunction resulting from imperfect transfer of coronary arteries to the neoaorta. In fact, translocation of the coronary arteries remains one of the most crucial aspects of the operation and late mortality for the ASO appears to coincide with coronary artery events.55,56,57,58Sudden death secondary to acute myocardial infarction has been reported in 1-2% of hospital survivors following the ASO and usually occurs within the first six months after repair.59Right ventricular dysfunction secondary to severe pulmonary vascular disease is the only other important mode of death accounting for less than 1% of all deaths.40
Right ventricular outflow tract obstruction
The most commonly encountered long-term morbidity following ASO is right ventricular outflow tract obstruction (RVOTO) with a reported incidence from 7% to 40%.33,39,41,43,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76Postoperative obstruction may occur at multiple levels following anatomic correction. Usually obstruction is in the pulmonary trunk. Less frequently, RVOTO is at the bifurcation of the pulmonary trunk. Circumferential narrowing at the suture line may also occur. Pulmonary artery stenosis may be related to the technique of reconstruction of the proximal pulmonary arteries with a patch to fill the defects in the posterior wall where the coronary artery buttons were excised71,77,78or to distortion of the main and peripheral pulmonary arteries as a result of the anterior placement of the bifurcation (Lecompte's maneuver).7Supravalvular pulmonary stenosis is often associated with growth failure of the valve annulus and neopulmonary valve stenosis. It also induces a disturbed vascularization with asymmetrical distribution of the pulmonary flow between the two pulmonary branches43, so that a significant stenosis should be relieved early, either by balloon angioplasty or surgical patchplasty, in order to promote branch growth. Balloon dilation of these stenotic areas has met with limited success and pulmonary arterioplasty often requires operative reintervention which carries with it a significant mortality rate.77,79,80,81,82
Neopulmonary valve regurgitation
Neopulmonary valve regurgitation occurs after ASO with most studies using Doppler echocardiographic evaluation reporting incidence varying from 9% to 80%.75,83,84,85
Neoaortic valve regurgitation and stenosis
Post-ASO neoaortic valve regurgitation is commonly an underestimated complication of anatomic repair of TGA. The anatomic pulmonary valve, with thin leaflets and little collagen and elastic tissue, must function as the neoaortic valve after ASO. Mild regurgitation has been found in about 35% of patients86,87,88with moderate to severe regurgitation being demonstrated in 5% or fewer patients.35,84,85,86,87,88,89,90Prevalence of aortic regurgitation in patients who have reached 20 years of age is not known but may be appreciable.91More importantly, the frequency of the regurgitation after ASO seems to increase with time62,66,69,72,73,92,93and isolated cases have had significant regurgitation requiring valve replacement.41,94,.95,.96,97
Left ventricular outflow tract and neoaortic stenosis are very rare in the literature.33,41,44,62,64,66,70,73,98,99,100
Coronary artery obstruction and myocardial perfusion
Mobilization and translocation of the coronary arteries remain the most technically challenging aspect of the ASO. It carries the combined risk of primary ischemic injury and late problems with coronary artery kinking or ostial stenosis. The long-term patency and growth of the coronary arteries are crucial for the ASO to be considered the procedure of choice for the surgical management of TGA. Coronary artery obstruction has been documented in a disturbingly high number of asymptomatic TGA patients evaluated prospectively by angiography at 5- to 10-year follow-up.56,101The prevalence of coronary events in literature varies from 2% to 11%.47,53,55,69,102,103The coronary events most often occur immediately after the ASO and are the main cause of death33,47,48,50,51,53,102,103or morbidity.104In the early postoperative period, coronary events are related to coronary anatomy and to surgical technique difficulties.33,47,48,55,69,102,103,104Causes are probably anatomical kinking or torsion and extrinsic compression by biological glue that necessitated immediate coronary revision or reoperation.55Late coronary mortality and myocardial infarction are rare and have a prevalence of less than 2% in most studies.47,48,59,69,101,102,103,104Coronary revascularizations occur late, at least 1 year after ASO and most often after 3 years48,55,56,101Late coronary events are not related to intraoperative problems or early ischemic symptoms.56,101Causes are probably progressive fibrocellular intimal thickening or stretching of the coronary artery with growth.57
Concern remains as to the long-term effect on myocardial perfusion from coronary artery mobilization and reimplantation. When compared with the intraatrial repair, the ASO offers the advantage of normalizing the reversed role of the two ventricles. The importance of this advantage depends on the assumption that the left ventricle is not affected by the operative procedure or postoperative complications. Myocardial perfusion studies following the ASO have shown a surprisingly high incidence of perfusion defects.105,106,107,108,109,110These abnormalities suggest a reduction of regional coronary flow reserve, a physiologic variable that assesses the ability of coronary flow to increase under hyperemic stimulation. However, these perfusion defects generally lessen with exercise108and are rarely correlated with electrocardiographic, echocardiographic, or angiographic changes, so that their clinical significance is questionable. The precise etiology of those abnormalities is undefined, but may be more related to the insult of open heart surgery itself than to the coronary manipulation involved in the arterial switch procedure. According to one study these abnormalities reflect arteriolar or capillary processes below the resolution of coronary angiography, resulting from inhomogeneous myocardial protection, embolism, or other intraoperative insults.107The rarity of regional left ventricular wall motion abnormalities is reassuring in comparison with scintigraphic studies.105,108,111,112However, reduction of regional coronary flow reserve is a functional disorder which in pediatric patients is not accurately detected by echocardiography and angiocardiography. Exercise testing appears to be useful in detecting ischemic damage or exercise-induced ventricular arrhythmias possibly secondary to reduced coronary flow reserve.113Many questions remain about long-term development of the coronary circulation after coronary reimplantation, including the evolution of atherosclerosis and coronary flow reserve.
Left ventricular function is usually normal after the arterial switch operation. A comparative study between the arterial and atrial switch showed that late postoperatively left ventricular ejection fraction was within the normal range in 98% of patients with simple TGA undergoing the arterial switch repair but in 79% of those who underwent an arterial switch repair.114Similar results have been shown by other studies.44,115,116,117
Interestingly, preoperative dynamic left ventricular outflow tract obstruction, even with a gradient of up to 120 mm Hg, disappears after the arterial switch operation.118,119
Growth of arteries
Although all currently available information indicates that aortic, pulmonary, and coronary anastomoses grow at a rate comparable to growth of the child44,99,120yet there is some concern that the technique of the arterial switch introduces possible growth interference at different levels, such as the pulmonary-aortic anastomosis and the introduction of aortic tissue due to coronary transfer. Each growth interference may have an impact on the aortic valve, the neo-aortic (pulmonary) sinuses and the aortic root.121Similar concerns have been raised about the growth of the main and branch pulmonary arteries.43Disproportionate dilatation of the neo-aortic root has been reported after the arterial switch operation.93,121According to Hutter and associates after the arterial switch, the neo-aortic valve and sinus are larger than normal. In the first year of life, there is rapid dilatation of the new aorta followed by active growth with tendency towards normalization of the valve and sinus size. However, this aortic dilatation by itself is rarely associated with significant insufficiency.121
The use of an intraatrial baffling procedure such as the Mustard19or Senning20repairs for transposition of the great arteries (TGA) has been associated with a high incidence of cardiac rhythm abnormalities.122,123,124,125,126,127,128Sinus bradycardia, complicated by recurrent atrial flutter, is the most common management issue in this population and may contribute to late sudden death. These rhythm disturbances are thought to arise from trauma to the sinus node and atrial muscle from the extensive intraatrial suture lines required in the baffling procedure.129 During the arterial switch operation there is little intraatrial manipulation other than the repair of the atrial septal defect (either congenital or caused by balloon atrial septostomy). One of the major theoretical advantages of anatomic correction is that the limited atrial procedure should result in a significantly improved rhythm status of the survivors. The reported incidence of arrhythmias after arterial switch is 3% to 734,130,131which is much less compared to the 13% to 100% frequency of rhythm disturbances following atrial switch repair.34,122,131,132,133,134,135,136,137However, as the follow-up is relatively short, one must remain vigilant in this regard, since such problems may become apparent after many years.
Enlarged bronchial arteries
Abnormally enlarged bronchial arteries are frequently identified at postoperative catheterization after arterial switch operation despite early repair and may explain continuous murmurs or persistent cardiomegaly in patients with otherwise normal noninvasive findings.44, 138,139,140These vessels are probably intrinsic to transposition and not related to the duration or degree of cyanosis before repair, or to a decreased pulmonary blood flow to one lung or the other because of hypoplastic pulmonary artery. The shunt is sometimes significant, necessitating catheter-directed therapy with coil embolization.138
Exercise performance is significantly reduced after the Mustard or Senning atrial baffle operation for transposition of the great arteries.141,142One of the expected benefits of the arterial switch operation is that exercise performance would be improved after a more anatomically correct repair of this defect. Available data on exercise performance in this population demonstrates that cardiopulmonary performance during exercise is generally excellent after the arterial switch operation.108,109,113,143However, even though essentially all surviving patients are fully active and without limitation143,144evidence of stress-induced myocardial ischemia continues to be a concern in this population.38,110,143Continued monitoring of exercise performance, especially for ischemia, would appear to be warranted as this population ages and begins to participate in more vigorous athletic activities.143
Neonatal arterial switch operation with combined circulatory arrest and low flow bypass is associated with neurological impairment, but not with reduced development as assessed by formal testing of motor, cognitive, language, and behavioral functions.145At 8-year follow-up in one patient cohort, overall physical and psychosocial health status was similar to that of general population, according to the Mean Physical Health Summary, and the Mean Psychosocial Summary scores; however, increased problems with attention, learning, speech, and developmental delay are reported by parents.146A recently published, single center, randomized controlled trial to assess developmental, neurologic, and speech outcomes 8 years after arterial switch operation has revealed that the use of total circulatory arrest to support vital organs while performing ASO is generally associated with greater functional deficits than is use of low-flow cardiopulmonary bypass, although both strategies are associated with increased risk of neurodevelopmental vulnerabilities.147
Reoperative probability for a variety of complications has ranged from 5% to 30% in the literature.33,48,80,81,97,104,148,149,150,151,152Neopulmonary stenosis or RVOTO is the single most common complication requiring reintervention.97Complications other than neopulmonary stenosis after the arterial switch operation severe enough to require reintervention are distinctly uncommon.153Compression of esophagus153and left main bronchus154,155have been reported after arterial switch.The mechanism of left bronchial compression after an arterial switch operation may relate to the placement of the proximal ascending aorta posterior to the transected pulmonary artery.154,155The left main bronchus is intimately related to the left pulmonary artery and the descending thoracic aorta as it courses beneath the aortic arch. The mobilization and posterior displacement of the ascending aorta behind the left pulmonary artery as the neoaorta may allow it to impinge upon the left main bronchus, or may permit compression of the bronchus between the ascending and descending aorta.154,155
Other reported complications requiring reintervention are aortic arch obstruction80 and neoaortic insufficiency.41,94,95,96,97Aortic arch obstruction seems to be limited to that patient population in whom an aortic coarctation was present and an extensive aortic reconstruction comprised a portion of the initial operation. This problem appears, at least in the short term, amenable to balloon angioplasty techniques for correction.80
The arterial switch operation has been universally recognized as the therapy of choice for children born with transposition of the great arteries. As experience with this operation has increased, mortality has been lowered and is consistently below 10% in most contemporary series. Most children who have undergone the ASO have also enjoyed normal growth, development, and cardiac function. In contrast to the former atrial switch procedures, the ASO has the advantages of maintenance of sinus node function, preservation of the left ventricle as the systemic ventricle, and the mitral valve as the systemic atrioventricular valve. However, the ASO involves translocation of the coronary arteries, the pulmonary valve becomes the systemic outflow valve, and the pulmonary arteries may become distorted because of their atypical relationship to the great vessels. All these are associated with early as well as delayed complications. Incidence of late reintervention, whether in the form of therapeutic cardiac catheterization or operation, is not uncommon in this patient population. Therefore, it is important to realize that even though it is almost three decades since the first ASO was performed and morbidity and mortality has been lowered yet one must remain vigilant to identify newly emerging problems, since such unrecognized problems may become apparent only after follow-up of many years.
Dr. Shahzad G. Raja Department of Paediatric Cardiac Surgery Alder Hey Children's Hospital Liverpool L12 2AP United Kingdom Fax: +44(0)151 252 5643 Tel: +44(0)151 252 5635 Email: email@example.com