Transposition of the Great Arteries

51

Transposition of the Great Arteries TIM HORNUNG  ❘  CLARE O’DONNELL

Definition and Morphology The term transposition of the great arteries (TGA) describes the anatomic arrangement in which the aorta arises from the right ventricle (RV) and the pulmonary artery from the left ventricle (LV). This malformation was first described in 1797 by Baillie and later in 1814 by Farre. Associated abnormalities are relatively common, occurring in approximately 50% of patients. The most frequently associated lesions are ventricular septal defect (VSD), left ventricular outflow tract (LVOT) obstruction, and coarctation of the aorta. Although patients with more complex intracardiac anatomy (eg, tricuspid atresia or doubleinlet LV) may be described as having TGA, this terminology may be confusing and should be avoided. In these complex hearts the anatomy is most reliably described using the sequential analysis concept where the term ventriculoarterial discordance would be used to describe the arrangement of the great arteries. Therefore this chapter will be restricted to those patients with TGA as described previously. GREAT ARTERY ORIGINS In the great majority of patients with TGA the aorta arises from the RV via a subaortic infundibulum, in a fashion analogous to the pulmonary artery in the normal heart. Conversely, the transposed pulmonary artery arises directly from the LV without a subpulmonary infundibulum; therefore there is fibrous continuity between the mitral and pulmonary valves but no continuity between aortic and tricuspid valves. The abnormal origins of the great arteries result in an altered relationship between the ascending aorta and main pulmonary artery. Instead of the normal crossover or spiral relationship, in transposition hearts the two vessels run parallel to each other, an echocardiographic feature that helps to make the diagnosis of TGA in the cyanosed neonate. There is some morphologic variation in terms of the relative positions of the great arteries. The most common relationship of the great arteries is an anterior and rightward position of the aorta relative to the pulmonary artery. This occurs in approximately 95% of all patients. Many other arrangements have been recognized, the most common being an anterior but leftward position of the aorta. In rare cases of TGA the aorta is the posterior vessel.  CORONARY ARTERIES The anatomy of the coronary arteries is quite variable in patients with TGA. As shown in Fig. 51.1, the coronary ostia arise from the aortic sinuses closest to the pulmonary artery, the so-called facing sinuses. The figure shows the most common arrangement of the coronary arteries, with the left main arising from the left

facing sinus and bifurcating to give rise to the left anterior descending and circumflex arteries, and the right coronary artery arises from the right facing sinus. This arrangement is present in 67% of all patients with TGA. There are many possible variations on this theme, including the circumflex arising from the right coronary artery, a single left or right coronary artery giving rise to all three branches, or an inverted coronary pattern.1 Perhaps the most important variation from a management perspective occurs when one or other coronary artery takes an intramural course between the aorta and pulmonary artery. This variation occurs in approximately 3% of all cases and, although outcome has improved for patients with this arrangement, it continues to be associated with an increased surgical mortality from the arterial switch procedure in many centers.2  ASSOCIATED DEFECTS Ventricular Septal Defect This is the most common abnormality to coexist with TGA, occurring in 40% to 45% of cases. The size and position of such defects within the ventricular septum are variable, but the most common types are perimembranous defects and muscular defects, occurring with approximately equal frequency. Associated malalignment of the outlet septum is common in these types of defect, with some degree of malalignment in up to 75% of cases. Less common types of defect are atrioventricular septal defects and doubly committed subarterial defects, each making up approximately 5% of the total. Small defects, especially in the muscular septum, are likely to close spontaneously, but larger defects will generally need surgical management.  Left Ventricular Outflow Tract Obstruction This abnormality is second in frequency to VSDs, occurring to some degree in up to 25% of patients. It is more likely to occur in patients who also have a VSD. The anatomy of the obstruction is somewhat variable but most commonly involves either a subvalvar fibrous membrane or a combination of valvar and muscular subvalvar stenosis. Less common types of obstruction are due to abnormal chordal attachments of the mitral valve into the ventricular septum below the pulmonary valve or aneurysm formation of the membranous septum. In patients who have undergone atrial baffle repair of TGA, there is commonly a gradient across the LVOT due either to bulging of the ventricular septum into the outflow tract or to systolic anterior motion of the mitral valve. In most cases, the gradient is relatively mild, although in a minority it may be more severe, leading to the development of systemic pressures within the LV. Such pressure loading of the LV may be 513

514

PART VIII  Cyanotic Conditions LAD Ao

Body

Cx

RA

LA

RV

LV

RA

LA

RV

LV

Lungs

A

RCA Body PA Figure 51.1  Coronary artery pattern in transposition of the great arteries (TGA). The aortic sinuses in TGA are described in terms of their relationship to the pulmonary artery (PA). Therefore the left- and rightfacing sinuses face the PA and the nonfacing sinus does not. The figure shows the most frequent coronary pattern seen in TGA. The left main coronary artery arises from the left-facing sinus and gives rise to the left anterior descending (LAD) and circumflex (Cx) arteries. The right coronary artery (RCA) arises from the right-facing sinus. Ao, Aorta.

potentially beneficial in that it may render the patient suitable for a late arterial switch conversion (see later).  Coarctation of the Aorta Aortic coarctation is seen in approximately 5% of patients with TGA. It may be a discrete shelflike lesion or may be associated with hypoplasia of the distal aortic arch. Coarctation is more common in patients with malalignment-type VSDs and may be associated with some degree of subaortic narrowing in this situation. 

Genetics and Epidemiology TGA is the most common form of cyanotic congenital heart disease (CHD) presenting in the neonatal period. Of all forms of cyanotic CHD, only tetralogy of Fallot is more common. TGA represents approximately 5% to 7% of all CHD and has a birth incidence of 20 to 30 per 100,000 live births, with a male preponderance of approximately 2:1. There have been a small number of reports of possible genetic associations in individual cases of TGA, involving deletions at chromosome 22q11, and in one family the ZIC3 gene on the X chromosome. Nevertheless, in the great majority of cases, TGA is not currently known to be associated with any specific single gene defects. In mice, great arterial septation abnormalities have been induced by the administration of retinoic acid to the developing embryo, and very high incidence of TGA has also been observed in the perlecan-null mouse. There has been some suggestion that TGA in human fetuses may be related to maternal intrauterine hormonal imbalance, a possible association has been identified with older maternal age, and there is also a higher than expected incidence of TGA in infants of diabetic mothers. In one large study of patients with transposition, the incidence of congenital heart defects in both siblings and parents of affected children was less than 1%. An accurate recurrence rate in offspring of parents with TGA is not available, but this would appear to be approximately 1% to 2%. 

Lungs

B Figure 51.2  Blood flow in transposition of the great arteries (TGA). The anatomic arrangement of the TGA heart causes blood to circulate in (A) two separate parallel circuits rather than (B) the normal single series circuit. In patients with TGA, oxygenated blood (dark) circulates continuously around the pulmonary circuit, whereas deoxygenated blood (light) circulates around the right side of the heart without picking up oxygen from the lungs. LA, Left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

Early Presentation and Management Antenatal diagnosis of TGA is becoming more frequent; however, most commonly the infant with complete transposition will be diagnosed after being recognized as a “blue baby,” often within the first day of life. Examination of these infants reveals a varying degree of cyanosis; the remainder of the cardiac examination reveals a murmur-less heart in the absence of associated lesions. The second heart sound is single and loud because of the relationship of the great arteries, the aortic valve being anterior. The anatomic arrangement of the TGA heart causes blood to circulate in two separate parallel circuits rather than the normal single series circuit (Fig. 51.2). The systemic arteries receive blood that has not passed through the pulmonary circulation and therefore remains deoxygenated. Mixing of blood between the two parallel circuits is essential for small amounts of oxygenated blood to enter the systemic circuit and supply vital organs. Mixing can take place at the level of the atrial septum via a patent oval foramen and at the level of the great arteries via a patent arterial duct. From the time that a diagnosis of TGA is suspected, patients are managed with intravenous prostaglandin E1 to restore and/or maintain patency of the arterial duct and allow mixing between the circuits. BALLOON ATRIAL SEPTOSTOMY To maintain acceptable systemic arterial oxygen saturations prior to definitive surgery, the early management of these patients at most centers includes balloon atrial septostomy. This procedure disrupts the foramen flap, thus creating a larger communication between the atria and allowing better atrial-level mixing between the two parallel circuits.3

51  Transposition of the Great Arteries

515

Pulmonary trunk TV

Ao

MV

SVC

A

B

SA node

C

CS

Pericardial baffle

Limbus

Large patch

D

E

Closure

Figure 51.3  The Mustard operation for transposition of the great arteries. A, Surgeon’s view of the right atrium. B, The right atrium is opened, and the atrial septum is excised. C, The pericardial baffle is initially sutured around the left pulmonary veins. D, The baffle is completed. E, The right atrium is closed. Ao, Aorta; CS, coronary sinus; MV, mitral valve; SA, sinoatrial; SVC, superior vena cava; TV, tricuspid valve. (Modified from Kirklin JW, Barrett-Boyes BG. Complete transposition of the great arteries. In: Kirklin JW, Barrett-Boyes BG, eds. Cardiac Surgery. 2nd ed. New York, NY: Churchill Livingstone, White Plains; 1993:1383-1467).

The procedure is performed using an angulated balloontipped Fogarty or Miller–Edwards catheter, the reinforced latex balloons having a volume of 1.8 or 4 mL. The catheter is introduced via a femoral venous or umbilical venous approach and passed into the right atrium, across the oval foramen and into the left atrium under echocardiographic or angiographic control. The balloon is then inflated and drawn back sharply across the oval foramen to the junction of the right atrium and inferior caval vein, producing a tear of the foramen flap. After successful balloon atrial septostomy, most infants can be weaned off intravenous prostaglandin and will maintain a systemic arterial oxygen saturation of between 50% and 80%. In the era of atrial baffle repairs, this procedure allowed adequate oxygenation for growth until such time as the atrial baffle operation was performed—often beyond 6 months of age. In the current era, most infants undergo definitive repair with the arterial switch operation within the first 2 weeks of life.  ATRIAL BAFFLE REPAIR Mustard and Senning Operations The first definitive operations for TGA were described by Senning4 in 1959 and Mustard5 in 1964. Both of these procedures “correct” the physiological abnormality of the transposed great arteries by forming a baffle within the atria to “switch” the flow of blood at inflow level. This results in a reversion to the normal flow of blood with the heart and lungs being in series; however, the LV remains the subpulmonary ventricle and the RV the systemic ventricle.

The main difference between the two procedures is that in the Senning operation the baffle is created from right atrial wall and atrial septal tissue without the use of extrinsic materials; however, the Mustard operation involves resection of the atrial septum and the creation of a baffle from pericardium or synthetic material (Fig. 51.3). These operations were performed at varying stages of life but usually between 1 month and 1 year of age.6 In experienced hands the early mortality rate associated with these procedures is low, with a surgical mortality rate generally between 1% and 10% (Box 51.1).  Arterial Switch Operation The successful anatomic correction of TGA was first described in 1975 by Jatene et  al.7 This procedure involves transection of the aorta and pulmonary artery at a level above the valve sinuses. The coronary arteries are detached from the aorta with a surrounding “button” of aortic wall and sutured into place in the neoaorta. Finally, the pulmonary trunk is moved forward into its new position anterior to the aorta, and the switched great arteries are sutured into place (Fig. 51.4). The arterial switch is a technically challenging operation, but has the great advantage over the Mustard or Senning procedure in that the LV becomes the systemic ventricle. The procedure is usually performed within the first 2 weeks of life and should be undertaken at the latest by 4 to 6 weeks of life. After this time the patient with TGA and intact ventricular septum will have suffered significant regression of left ventricular muscle mass due to its functioning at low pressure in the pulmonary circuit. This thinning of the left ventricular myocardium increases the potential for left ventricular failure after the arterial switch procedure and increases surgical risk. 

516 BOX

51.1

PART VIII  Cyanotic Conditions

Complications After Repair

Mustard and Senning Operations • Endocarditis • Sinus node dysfunction • Intraatrial reentrant tachycardia • Sudden cardiac death • Baffle leaks • Baffle obstruction • Tricuspid valve regurgitation • Right ventricular systolic and diastolic dysfunction • Residual hemodynamic lesions • Pulmonary hypertension  Rastelli Operation • Endocarditis • Atrial and ventricular tachycardias • Sudden death • Complete heart block • Left and right ventricular dysfunction • Conduit stenosis • Residual hemodynamic lesions  Arterial Switch Operation • Endocarditis • Pulmonary outflow obstruction • Neoaortic dilation and valvar regurgitation • Coronary artery stenosis

Rastelli Operation The most frequently used surgical option for patients with the combination of TGA, pulmonary outflow tract obstruction, and VSD is the Rastelli operation (Fig. 51.5), which was originally described in 1969.8 Concern about the long-term outcome of Rastelli patients has led to the development of the related Reparation a l’etage ventriculaire (REV) procedure,9 Metras modification,10 and Nikaidoh procedure.11 The Rastelli operation uses the VSD as part of the LVOT and involves placement of a baffle within the RV, directing blood from the VSD to the aorta. The pulmonary valve or subpulmonary region is oversewn, and a conduit is inserted between the RV and the pulmonary artery. Suitability for the Rastelli operation is dependent on appropriate VSD anatomy: the defect should be large and subaortic in position. Surgical enlargement of the VSD may be undertaken but carries with it a risk of inducing complete heart block and has been shown to be associated with less good long-term outcomes. The main advantage of this operation is that the LV becomes the systemic ventricle. The most important limitation is that the patient is committed to further operations because the pulmonary conduit is likely to need replacing several times during the patient’s life. There is continuing debate regarding the most appropriate timing of the Rastelli operation. Some believe that the procedure should be performed during early infancy, citing the advantages of early physiological correction, less time spent with systemic hypoxemia, and avoidance of a left-to-right shunt from palliative procedures. Others believe that a palliative procedure is the most appropriate first intervention, usually a modified Blalock-Taussig shunt. The reasons cited would be the higher risks associated with early repair and that a smaller conduit will require earlier reoperation. 

Late Outcome NATURAL HISTORY Without surgical intervention the survival rates of patients with TGA are poor. Most patients will die in the first few months of life, with approximately 90% of patients dying in infancy.12 Patients with isolated TGA and no associated lesions (approximately 50% of the total) have the worst outcome— only 30% survive beyond the first month of life (Fig. 51.6). Patients with a large VSD have a somewhat better outcome, but fewer than 50% will survive the first year of life. The subset of patients with coexistent LVOT obstruction and VSD has the best outcome, with approximately 50% surviving to 3 years of age. These patients may occasionally be seen as cyanosed adults with “balanced” circulation despite no previous surgical intervention.  ATRIAL BAFFLE REPAIRS Survival and Functional Status Surgical mortality rates after the Mustard and Senning operations were low in most centers that performed large numbers of these operations. A review of the literature concerning operations performed between 1971 and 1979 showed a mean hospital mortality rate of 4.8%.13 A large single-center review showed that the surgical mortality rate fell significantly in the second half of the series, with a mortality rate of 10.4% between 1963 and 1973 and 0.9% between 1974 and 1985.14 Early mortality after repair of patients with associated lesions is significantly higher. In the literature review quoted above, the average mortality for patients with TGA and VSD was 23%,13 and although more recent results show improved outcome for this population, the surgical risk is clearly higher. The Mustard and Senning procedures were superseded by the arterial switch operation in the mid to late 1980s in most surgical centers, and the population of patients who have undergone these procedures is therefore essentially complete. Unfortunately these patients have several issues leading to late morbidity and mortality, especially as the population ages. Late survival data after atrial baffle repair show a small but ongoing attrition rate, with the most frequent causes of death being sudden death and systemic right ventricular failure. In one large single-center series, the 5-year survival rate was 89% and the 20-year survival rate 76%.15 Another large series showed a 90% 10-year and an 80% 20-year survival rate.16 A large study showed a 30-year survival rate of 60%.17 Some studies have suggested somewhat better long-term survival in Senning patients compared with Mustard patients. Survival rates after repair of TGA and VSD are again less good, with 5-year survival rates of 60% to 70%. Risk of late death after atrial baffle repairs is 2.7 times greater in patients with a VSD, relative to those with an intact ventricular septum. Functional status is reasonably good in this population, with around 60% to 80% of patients in many series being in functional class I and the majority of the remainder being in class II.14,16 Nevertheless, overall functional class does appear to be declining with increasing length of follow-up.18 Formal testing demonstrates that the exercise capacity of the atrial baffle population as a whole is reduced relative to the normal population, with the most significant cause of limitation appearing to be chronotropic incompetence.19 The stroke volume response to exercise is also reduced secondary to a failure to augment ventricular filling rates during tachycardia, presumably due to the abnormal

51  Transposition of the Great Arteries Incision to enlarge VSD Subpulmonary stenosis Pulmonary trunk

517

Closure of subpulmonary stenosis VSD

MV

A

B

Ao

Aortic valve

C

TV

Dacron patch

Dacron patch

VSD

D

E Dacron Dacron patch

Homograft Pledgets

Pulmonary artery Ao

F

G

Figure 51.4  The Rastelli operation for transposition of the great arteries with ventricular septal defect (VSD) and pulmonary outflow obstruction. A, Surgeon’s view of the right ventricle. B, The right ventricle is opened and the VSD enlarged if necessary. C, The entrance to the pulmonary artery is closed. D and E, A patch is sewn into place to create a tunnel from the left ventricle across the VSD to the aortic valve. F, A valved conduit is prepared and sutured to the pulmonary artery. G, The proximal end of the conduit is sutured to the right ventriculotomy. Ao, Aorta; MV, mitral valve; SVC, superior vena cava. (Modified from Kirklin JW, Barrett-Boyes BG. Complete transposition of the great arteries. In: Kirklin JW, Barrett-Boyes BG, eds. Cardiac Surgery. 2nd ed. New York, NY: Churchill Livingstone, White Plains; 1993:1383-1467).

characteristics of the atrial baffles.20 Peak oxygen uptake is also reduced in this population, being 65% predicted in one large study, with peak oxygen uptake and minute ventilation-carbon dioxide production relationship (VE/VCO2 slope) predicting event-free survival.21  Arrhythmias and Sudden Cardiac Death Patients who have undergone the Mustard or Senning procedure are at risk of both bradyarrhythmias and tachyarrhythmias. The most common tachyarrhythmia is an incisional atrial reentry tachycardia, sometimes described as atypical atrial flutter. The most common bradyarrhythmia is sinus node dysfunction leading to sinus bradycardia with a junctional escape rhythm. Bradyarrhythmias Resting bradycardia is frequently seen in atrial baffle patients, representing a sinus bradycardia often with a slow junctional escape rhythm, typically 40 to 60 beats per minute. This is

usually asymptomatic. Sinus node dysfunction in this group appears to be more likely with increasing time from operation. One series demonstrated a probability of being in sinus rhythm of 77% at 5 years, 61% at 10 years, 52% at 15 years, and 40% at 20 years.15 A recent study showed that less than a quarter of patients were in sinus rhythm 20 years after their surgery.22 Histologic examination of the sinus node region demonstrates abnormalities of the sinus node and sinus node artery, and electrophysiological studies show that abnormal function of the sinus node is present in at least 50% of patients.23 The chronotropic response to exercise is variable in this situation: a minority of patients has a very poor response with maximum rates of 70 to 80 per minute, whereas many will achieve a maximum rate between 100 and 150 per minute. A normal exercise chronotropic response is relatively unusual in this population, and indeed maximum exercise heart rate is the most important predictor of exercise capacity for these patients. For those with a poor chronotropic response to exercise, rate

518

PART VIII  Cyanotic Conditions (Sinus 1) Circumflex artery LPA

PA

Cardioplegic infusion line

LAD

Level of aortic transection

PA transection level

Ductus arteriosus

Ao

A

SVC

RCA (sinus 2)

IVC

Ao

B

C

Sinus 1

RV branch

Sinus 2

Commissure

E

D

F PA

Ao

Neoaorta

Pericardial patches

Lecompte maneuver

G

H

I

Neopulmonary artery

Figure 51.5  The arterial switch operation for transposition of the great arteries (TGA). A, Surgeon’s view of the heart. Sinus 1, left-facing sinus; sinus 2, right-facing sinus. B, Dashed lines indicate the sites of transection of the aorta and main pulmonary artery. C, The aorta is transected. D, The pulmonary trunk is transected. E, A button of aorta is excised around the ostium of the left main coronary artery. F, An incision is made in the left-facing sinus of the neoaorta, into which the left coronary button will be sutured. G, The right coronary artery button is excised and sutured on to the neoaorta in similar fashion. H, The distal ascending aorta is brought under the pulmonary bifurcation (the Lecompte maneuver) and is anastomosed to the proximal portion. Pericardial patches are sewn into the neopulmonary trunk to fill the defects left by the coronary buttons. I, The proximal and distal portions of the neopulmonary trunk are anastomosed. Ao, Aorta; IVC, inferior vena cava; LAD, left anterior descending artery; LPA, left pulmonary artery; PA, pulmonary artery; RCA, right coronary artery; RV, right ventricle; SVC, superior vena cava. (Modified from Kirklin JW, Barrett-Boyes BG. Complete transposition of the great arteries. In: Kirklin JW, Barrett-Boyes BG, eds. Cardiac Surgery. 2nd ed. New York, NY: Churchill Livingstone, White Plains; 1993:1383-1467).

responsive atrial pacing may result in a symptomatic improvement in terms of exercise capacity. Pacemaker implantation has been required in 15% to 25% in series with long-term follow-up.17,22 

procedural success in many cases but can be technically challenging and may require transbaffle puncture.25 There does appear to be a risk of high-grade atrioventricular block as a result of this procedure.26,27 

Tachyarrhythmias Intraatrial reentry tachycardia occurs in up to 50% of patients after atrial baffle repair of TGA. A study with a mean follow-up of 23 years after the Mustard procedure demonstrated that 48% of patients had had at least one episode of supraventricular tachycardia.24 Of these patients, 73% had “atrial flutter.” Catheter radiofrequency ablation of these arrhythmias has produced

Sudden Death Sudden death is a well-documented occurrence after atrial baffle repair, occurring in 7% to 15% of patients.16,28 A multicenter Dutch paper exploring predictors of sudden death found that symptoms of arrhythmia or heart failure, as well as previous documented atrial flutter or fibrillation, increased the risk of sudden death.29 Other data have suggested that

51  Transposition of the Great Arteries

519

100 90 80 Survival (%)

70 60 50 40 30 20 10 0 0

1

2

3

4

5

6

7

8

Age (years) PFO (±PDA) (n = 127) VSD + PVD (n = 29)

ASD (±PDA) (n = 41) VSD + IPBF (n = 32)

VSD + PS (n = 17) VSD + PVD + IPBF (n = 61)

Figure 51.6  Actuarial survival curves of various subsets of patients with transposition of the great arteries. ASD, Atrial septal defect; IPBF, increased pulmonary blood flow; PDA, patent ductus arteriosus; PFO, patent foramen ovale; PS, pulmonary stenosis; PVD, pulmonary vascular disease; VSD, ventricular septal defect ≥3 mm.

loss of sinus rhythm may also be a predictor. Sudden death is likely to be arrhythmic in most cases, and in the Dutch study ventricular fibrillation or ventricular tachycardia were the most frequent arrhythmias in documented cases. Implantable cardioverter defibrillator (ICD) implantation has been undertaken in these patients and has a clear indication for secondary prevention. Indications for primary prevention ICD implantation have been less clear, and our own experience has matched that of others, with a low rate of appropriate shocks.30,31  Ventricular Function The main concern regarding the long-term outlook for patients with atrial baffle repairs of TGA has been the function of the systemic RV. Although it is clear that the RV can tolerate functioning at systemic pressures in the short to medium term without difficulty, it may potentially fail when required to do this in the long term. Studies using magnetic resonance imaging (MRI) and echocardiography have consistently shown significant rates of right ventricular dysfunction in this population. A study from the Netherlands reviewing 91 patients after the Mustard operation showed that all patients had good function or mild dysfunction 14 years after repair. However, when the group was restudied at a median follow-up of 25 years, 61% had moderate or severe dysfunction.18 At most recent follow-up, a mean of 35 years since surgery, only one of 47 patients had normal right ventricular function.32 Therefore our concern is that patients with mild right ventricular dysfunction in the third decade of life may progress to more severe dysfunction over the decades to come. We have observed several patients in our own clinic who have had quite rapid

progression of right ventricular systolic dysfunction to the stage in which this becomes severe. As yet there are no clear risk factors that predict the development of severe right ventricular dysfunction in this population, although research in our group suggests that there may be a relationship with the degree of right ventricular hypertrophy: those with the most severe hypertrophy having less good ventricular function. This research potentially fits in with the finding that the great majority of atrial baffle patients have right ventricular myocardial perfusion abnormalities.33 It is possible that the greatly increased coronary demand of the systemic RV outstrips the available coronary supply from a morphologic right coronary artery system. Several small studies assessing the use of ACE inhibitors or angiotensin receptor blockers have not demonstrated any significant benefit.  Tricuspid Valve Function Mild-to-moderate tricuspid regurgitation is relatively common in patients after atrial baffle repair of TGA. The reversal of the right and left ventricular pressure relationship results in altered geometry of the ventricular septum. Therefore the tricuspid valve takes on a more rounded shape, which in combination with the displaced septal chordal attachments of the valve results in an increased tendency to tricuspid regurgitation. Severe tricuspid regurgitation in patients without associated lesions is unusual in most series and when present may reflect severe ventricular dysfunction and dilatation. In patients with associated VSD the incidence of important tricuspid regurgitation is higher (approximately 5% to 10%) partly due to damage to the valve and its support apparatus during operation. In this case, repair or replacement of the valve may be justified to

520

PART VIII  Cyanotic Conditions

reduce volume loading and prevent progressive deterioration of right ventricular function. However, tricuspid valve repair in the context of moderate or severe RV dysfunction is unlikely to be successful, and valve replacement is unlikely to be beneficial and may carry significant risk.  Baffle Obstruction and Baffle Leaks Baffle obstruction is an infrequent but important late complication after the Mustard and Senning operations. Superior limb systemic venous baffle obstruction occurs with a frequency of approximately 5% to 10% in Mustard patients, whereas inferior limb obstruction occurs infrequently, with an incidence of only 1% to 2%. Mild obstruction can be managed expectantly, although more severe stenosis may require surgical or catheter intervention. Pulmonary venous baffle obstruction is also infrequent, occurring with a frequency of approximately 2%. Severe obstruction of the pulmonary venous channel will lead to the development of pulmonary hypertension and therefore pressure loading of the morphologic LV, which in turn may render the patient suitable for consideration of late arterial switch conversion. Baffle leaks are more common than obstruction, the most common site being at the suture line of the superior limb of the systemic venous baffle. Baffle leaks have been shown to be present in up to 25% of patients,34 although most are not hemodynamically significant. Shunting may be either left to right or right to left. In patients with a large left-to-right shunt, the consequent volume loading of the systemic RV may necessitate reintervention to close the defect. In patients with important right-to-left shunts, systemic arterial desaturation will develop, likewise necessitating closure. However, these large shunts are rare, and only approximately 1% to 2% of atrial baffle patients will require reintervention for baffle leaks.  Pulmonary Hypertension The late development of pulmonary vascular disease is a recognized complication after atrial baffle procedures, occurring with a frequency of approximately 7%. This complication is more common after late repair and in patients with an associated VSD.  ARTERIAL SWITCH OPERATION Survival and Functional Status Operative survival after the arterial switch in the current era is very good, with a surgical mortality rate of between 1% and 5% for patients without associated lesions.6,35,36 The operative mortality rate is higher in patients with an associated VSD but is still less than 5% in some series.37 Functional status is normal in the great majority of patients, and aerobic exercise capacity has been shown to be normal or low-normal relative to age- and sex-predicted values.38 Mid- to long-term follow-up studies for the arterial switch operation are reassuring at this relatively early stage in the history of this procedure. A review of more than 1000 survivors showed an overall survival rate of 88% at both 10 and 15 years, with no deaths later than 5 years after operation.39 The results are somewhat less good in patients with associated lesions, with a survival rate of 80% at both 10 and 15 years, although the difference largely represents differing operative risk. Data on late morbidity for the arterial switch are accruing, with many centers now able to examine outcomes for patients who are completing their third decade. Cardiac residua and sequelae have been reported in 25% to 40% of patients,

including aortic root dilation, neoaortic regurgitation, right ventricular outflow tract obstruction, coronary abnormalities, and arrhythmia. Late residua are more common in those who required cardiac reintervention in childhood.40,41,42  Arrhythmias and Sudden Cardiac Death Sinus rhythm with normal conduction is maintained at mediumto long-term follow-up in 95% to 98% of arterial switch patients. There is a low incidence, less than 2%, of complete heart block, usually in patients who had an associated VSD. In one study the incidence of supraventricular tachycardia at medium-term follow-up was 4%, the majority occurring more than 1 year after the surgery. The incidence of late sustained ventricular arrhythmias was less than 0.5%.43 Sudden death is unusual in most series and is usually related to myocardial infarction secondary to coronary artery obstruction.  Ventricular Function Good left ventricular function is the norm after the arterial switch operation, with more than 95% of patients having normal left ventricular systolic function at medium- to longterm follow-up. Severe ventricular dysfunction is an occasional complication in a small proportion of patients and is often associated with coronary artery abnormalities. Left ventricular dysfunction is a recognized cause of death in less than 1% of patients.  Pulmonary Artery Stenosis Reintervention is required in at least 10% of patients after the arterial switch operation and in many cases is due to supravalvar main pulmonary artery stenosis or branch pulmonary artery stenosis. This occurs in at least 5%—and in as many as 25% of patients in some series—although recent results appear better. One large multicenter study showed freedom from pulmonary artery stenosis of 95%, 90%, and 86% at 1, 5, and 10 years, respectively. Surgical or catheter intervention to address pulmonary arterial stenosis is required in a significant minority of arterial switch patients. Small numbers of patients to date have required neopulmonic valve replacement as a late consequence of attention to relieve right outflow tract obstruction.41  Neoaortic Valve Regurgitation There appears to be an ongoing risk of the development of important aortic regurgitation, although only a small proportion has needed intervention at current stages of follow-up. In one large study the incidence of all grades of aortic regurgitation was 16% at a median follow-up of 4.9 years; however, only 3.8% had regurgitation of grade 2 or more.39 Freedom from reoperation for aortic regurgitation was 99.1%, 97.6%, and 96.2% at 5, 10, and 15 years, respectively. Risk factors for the development of important neoaortic valve regurgitation include size discrepancy between the great arteries, bicuspid pulmonary valve, LVOT obstruction, follow-up duration, and aortic root dilation.42,44,45 Some degree of aortic root dilatation is almost universal in this population, and several studies have shown serial increases in aortic root Z scores with serial follow-up.46 Early data suggested that aortic dilatation may stabilize in adult life, but follow-up is too short at this stage to be certain of the natural history of this complication in adulthood. To date we have not seen complications, such as aortic dissection or rupture, but patients with severe aortic dilatation clearly need careful follow-up. 

51  Transposition of the Great Arteries

Coronary Arterial and Vascular Complications In a large study of 1198 hospital survivors of the arterial switch 7.2% had coronary events, defined as death from myocardial ischemia/infarction, sudden death, nonfatal infarction or reoperation for coronary stenosis. The great majority of these events occurred in the first 3 months after the surgery. In a subset of 324 who underwent coronary angiography, 6.8% had significant lesions, 13 with coronary occlusions, and 9 with stenosis. A further 4% had minor coronary stenosis.47 Several other series have also reported coronary abnormalities and late deaths due to coronary events. Because of the denervation of the heart at the time of the arterial switch operation, the symptoms of myocardial ischemia may be atypical, without classic angina, and it is therefore important to remain vigilant for the possibility of this complication. Abnormalities of vascular function, including decreased arterial distensibility and increased pulse wave velocity have been demonstrated in late follow-up.48 Considered with the known risk of neoaortic root pathology and potential for increased late coronary vulnerability, these findings are now highlighting the potential need for proactive management of risk factors, including weight, physical activity, and smoking in this population.  Neurologic Outcomes Follow-up studies have demonstrated increased neurodevelopmental risk in the arterial switch population. Although most scores on neuropsychological testing fall into the average range, studies have demonstrated substantial proportions below the expected mean. Magnetic resonance brain imaging studies in adolescents have demonstrated abnormalities in approximately one-third of adolescents. Preoperative acidosis, hypoxia, and perioperative seizures have been shown to be associated with later neurologic concerns.49  RASTELLI OPERATION Survival and Functional Status Operative survival after the Rastelli operation was poor early in the surgical experience, with mortality rates of up to 30%; however, this has improved substantially such that more recent series report an operative mortality rate of 5% or less.13,50 There is a significant incidence of late mortality after Rastelli repair, with a large single center series reporting a survival rate of 82% at 5 years, 80% at 10 years, 68% at 15 years, and 52% at 20 years.50 The most common causes of late death or transplantation were left ventricular failure and sudden death. In a more recent European multicenter report including related operations, results were somewhat better in terms of short-medium term survival, with survival rates of 88% at 5 and 10 years, 85% at 15 years, and 58% at 20 years.51 A large single-center series suggests that long-term outcomes may be better after the REV procedure.52 Functional status is often good in these patients, although the presence of conduit stenosis or important ventricular dysfunction may be limiting factors. Exercise capacity in the Rastelli population overall is reduced compared with that in the normal population.  Arrhythmias and Sudden Cardiac Death There is a significant incidence of sudden death after the Rastelli operation, which is considered likely to be arrhythmic in nature.

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In one large series there was a high incidence of documented late arrhythmias, with approximately equal rates of ventricular and supraventricular tachycardia.50 There is also a risk of early or late development of heart block in these patients. The occurrence of ventricular tachycardia in particular may be associated with conduit obstruction and right ventricular hypertension and should direct the physician towards a detailed hemodynamic assessment of the patient.  Ventricular Function Left ventricular dysfunction is present in approximately 25% of Rastelli patients at late follow-up and is a cause of late death in a significant minority. Right ventricular dysfunction is also common, often secondary to the abnormal pressure and/or volume load related to conduit dysfunction.  Conduit Stenosis and Outflow Tract Obstruction Development of stenosis of the RV-pulmonary artery conduit after childhood Rastelli procedure is inevitable. Most patients who undergo the Rastelli procedure will require multiple conduit replacements during a normal lifespan because the longevity of currently used bioprosthetic conduits is between 10 and 20 years. The use of percutaneous implantable valves in these situations is now widespread, but concerns exist about the increased risk of endocarditis associated with these valves. Vigilance for the development of conduit stenosis or regurgitation is important throughout life in this population. LVOT obstruction is less common but equally important and should be detected by careful clinical and echocardiographic evaluation. 

Outpatient Assessment ATRIAL BAFFLE AND RASTELLI PATIENTS • Regular clinical examination: In atrial baffle patients focusing on signs of atrioventricular valve regurgitation and congestive cardiac failure. Audible splitting of the second heart sound may indicate development of pulmonary hypertension. In Rastelli patients the character of the pulmonary ejection murmur should be noted to exclude conduit stenosis. • Electrocardiogram (ECG): Cardiac rhythm should be noted; there is a significant incidence of loss of sinus rhythm in the Mustard and Senning populations, with junctional rhythm being a common baseline rhythm. Right-axis deviation and right ventricular hypertrophy are present owing to the systemic pressure in the RV in this population. Patients after the Rastelli operation will have a surgical right bundle branch block pattern and are also at risk of late development of complete heart block. • Chest x-ray: Patients with TGA have a narrow mediastinal shadow owing to the parallel relationship of the great arteries. Cardiothoracic ratio is normal in the patient without ventricular dilatation, and pulmonary vascular markings should be normal in the absence of pulmonary hypertension or significant baffle leaks. •  Echocardiogram: Echocardiography in the atrial baffle population allows assessment of the degree of tricuspid regurgitation, as well as interrogation for baffle stenosis and baffle leaks (although more detailed analysis may require transesophageal echo). Two-dimensional echocardiography also allows an approximate estimation of systemic right ventricular function, and early experience suggests that transthoracic three-dimensional echocardiography will allow volumetric measurement of right ventricular ejection

522 BOX

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Observations

Echocardiography • Quantify tricuspid regurgitation in atrial baffle patients • Color Doppler assessment for atrial baffle stenosis and baffle leaks • Quantify aortic regurgitation and branch pulmonary artery stenosis (where possible) after arterial switch operation • Assess pulmonary conduit gradient after Rastelli operation • Estimation of right and left ventricular function • Exclude other residual lesions (eg, residual VSDs)  Magnetic Resonance Imaging (see Figs. 51.7 to 51.9) • Quantitative assessment of right and left ventricular function and dimensions. Serial measurements of systemic right ventricular function—particularly valuable in Mustard and Senning patients • Assessment of systemic and pulmonary venous inflow channels for baffle stenosis and baffle leaks • Exclusion of supravalvar or branch pulmonary artery stenosis in arterial switch patients • Measurement of aortic root size and quantification of aortic regurgitation in arterial switch patients • Coronary artery imaging in arterial switch patients • Assessment of conduit stenosis and gradient in Rastelli patients fraction (RVEF) in those with good transthoracic echo windows. The use of speckle tracking to assess right ventricular myocardial deformation may predict adverse outcomes in this population. In Rastelli patients, echocardiography will exclude residual VSDs, allow assessment of left ventricular function and exclude LVOT obstruction, as well as estimating right ventricular systolic pressure and degree of conduit stenosis. • MRI: MRI is the most valuable imaging modality in these patients (see Observations Box 51.2 and Figs. 51.7 to 51.9). This allows detailed quantitative assessment of RV and LV systolic function, as well as assessment of baffle anatomy in the atrial baffle population and conduit flow imaging in the Rastelli population. • Radionuclear ventriculography: This can be a useful imaging modality for analysis of systemic right ventricular function in patients who are unable to undergo MRI. • Cardiopulmonary exercise testing: Regular exercise testing is useful in terms of recognizing change of clinical status in the individual patient. In Mustard and Senning patients the chronotropic response to exercise is frequently impaired, and these patients may occasionally benefit from pacemaker implantation. • 24-hour Holter recording: This can detect heart block or severe sinus node dysfunction resulting in prolonged pauses, as well as episodes of atrial or ventricular tachyarrhythmia. We perform Holter monitoring as a routine part of follow-up and also to obtain baseline information prior to initiating negative chronotropic medications.  ARTERIAL SWITCH PATIENTS • Regular clinical examination: Focusing on signs of pulmonary artery stenosis and neoaortic valve regurgitation.

Figure 51.7  Magnetic resonance imaging scan of a patient after the arterial switch operation, showing the branch pulmonary arteries straddling the ascending aorta after the LeCompte maneuver. The arrow indicates stenosis of the left pulmonary artery as it passes the aorta.

SVC

IVC

Figure 51.8  Magnetic resonance imaging scan of a patient after the Mustard operation showing the superior and inferior vena cava draining into the systemic venous baffle. The arrow indicates stenosis of the superior limb of the systemic venous baffle.

• ECG: Care should be taken to exclude signs of myocardial ischemia and right ventricular hypertrophy, suggesting pulmonary outflow obstruction. •  Echocardiogram: Regular echocardiography to exclude supravalvar and branch pulmonary artery stenosis, neoaortic regurgitation, and left ventricular dysfunction. However, note that the branch pulmonary arteries may be difficult to image with echo in this population, necessitating MRI or computed tomography (CT) assessment in some patients. Exercise or dobutamine stress echocardiography may be beneficial if there are concerns regarding possible coronary abnormalities.

51  Transposition of the Great Arteries

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yet demonstrated statistically significant benefit from drugs, such as ACE inhibitors or β-blockers, and have been limited by small patient numbers at individual centers. In our own practice we have used these agents for patients with decompensated heart failure or for those with moderate or severe systemic right ventricular dysfunction. In most cases these drugs will be welltolerated, but β-blockers in particular need to be initiated carefully in the context of the sinus bradycardia that is frequently seen in this population. 

RV

Figure 51.9  Magnetic resonance imaging scan of a patient after the Rastelli operation. The arrow indicates severe stenosis of the pulmonary conduit.

• Exercise stress testing: We would perform routine exercise testing in the early teenage years or earlier if there are concerns of possible myocardial ischemia. In general, exercise tolerance is good; however, in addition to ischemic changes, exercise assessment should be attentive to subtler abnormalities of heart rate and blood pressure response. In one study of young adults operated for TGA, TGA with VSD, or Taussig-Bing anomaly, peak oxygen uptake was 86%, predicted with a chronotropic index less than 80% in 34% of patients.53 •  Selective coronary angiography (or coronary CT): In patients in whom there is a suspicion of coronary artery stenosis these investigations should be performed. There is currently no consensus as to the utility of routine aortography or coronary angiography after the arterial switch operation. • MRI: Useful for assessing the anatomy of the branch pulmonary arteries to exclude stenosis. With improvements in technology, this is also becoming a valuable tool for assessment of the coronary arteries and myocardial perfusion in this population although in the absence of symptoms or ECG changes myocardial perfusion assessment appears to have low yield.54 

Late Management Options MEDICAL THERAPY For patients with dysfunction of the systemic RV after the Mustard and Senning operations, standard drug treatment has been widely used as for a failing systemic LV. Studies have not

SURGICAL AND CATHETER INTERVENTIONS Atrial Baffle Patients Atrial Baffle Revision Patients with important baffle stenosis may require surgical or catheter intervention. The procedure of choice is a transcatheter intervention using either balloon dilatation or primary implantation of self-expanding or balloon expandable stents. These procedures have been widely used in patients with systemic venous baffle obstruction.55 In most centers, hemodynamically important baffle obstruction will have been treated at a younger age, and new cases will be relatively unusual. In our own practice one of the more frequent indications at this stage is to improve more moderate baffle obstruction to facilitate transvenous pacemaker or defibrillator implantation. Transcatheter dilatation of pulmonary venous baffle obstruction has been performed successfully but is more technically challenging, and these patients, as well as those with complete obstruction of a systemic venous baffle limb, may require surgical revision. Baffle leaks are also amenable to transcatheter therapy in many cases. Most reports have documented the successful use of septal occluder devices, although covered stents have also been used for this purpose.  Arterial Switch Conversion The arterial switch operation is likely to have medium- and long-term benefits over atrial baffle repairs, the most important of which is that the LV is returned to the systemic circulation. In atrial baffle patients with systemic right ventricular failure, the ideal option would be to convert the patient to an arterial switch operation with takedown of the atrial baffle and closure of the atrial septum. Although this procedure has been successful in some pediatric patients, its success in adult patients is less encouraging. In most atrial baffle patients the left ventricular pressure is low and the left ventricular myocardium is thin, appropriate to its functioning at pulmonary pressure. Therefore the LV requires “retraining” to function at systemic pressures. Retraining of the LV is accomplished by the application of a pulmonary artery band to increase left ventricular pressure and induce myocardial hypertrophy, a procedure that may need to be staged. This procedure has been used with some success in the analogous population with congenitally corrected TGA but generally only in young children. In older children and adult patients in particular it is usually unsuccessful due to the frequent development of left ventricular failure and for this reason is usually not applicable to the adult atrial baffle patient.56 There is a small subgroup of atrial baffle patients with systemic left ventricular pressure due to either LV outflow tract obstruction or pulmonary venous baffle obstruction; these patients are likely to be have a more favorable outcome from late arterial switch conversion. 

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Pulmonary Artery Banding Some observers have advocated the use of pulmonary artery banding as a therapeutic measure in its own right for patients with important tricuspid regurgitation. The rise in left ventricular pressure induced by banding results in a resetting of ventricular septal geometry, the ventricular septum moving towards the RV and thus closer to its position in the normal heart. The tricuspid valve therefore assumes a geometry closer to normal, and this has been shown to result in a reduction of tricuspid regurgitation in the short term. Despite this, there are risks associated with pulmonary artery banding in this population. This strategy has not been widely adopted at this stage, and its long-term benefits remain unclear.  Radiofrequency Ablation of Arrhythmias Intraatrial reentry tachycardias and other supraventricular tachycardias in atrial switch patients have been addressed by both surgical and catheter radiofrequency ablative techniques.25-27 Procedural success rates up to 70% to 90% have been reported and have improved with the application of newer three-dimensional mapping in combination with entrainment mapping techniques. Recent reports have also reported success with remote magnetic navigation techniques. The widespread scarring present in the atria of these patients makes assessment and treatment of reentrant tachycardia a complex procedure requiring detailed knowledge of the surgical anatomy and may require transbaffle puncture; these procedures should be performed only by electrophysiologists familiar with this patient population. There is a significant recurrence rate, necessitating a second procedure in 30% of patients in a series.57 Some series have reported an important risk of highdegree atrioventricular block complicating radiofrequency ablation in this population.  Implantable Cardiac Defibrillators ICD implantation has been used in this population with varying success. Secondary prevention following cardiac arrest due to ventricular fibrillation or hemodynamically unstable ventricular tachycardia is a class I indication according to the Adult Congenital Heart Disease arrhythmia consensus statement of the pediatric and congenital electrophysiology society.30 ICD implantation for primary prevention is a class IIB indication, and several groups have reported low rates of appropriate shocks, coupled with high rates of inappropriate shocks. At this stage, further work is required to clarify indications for primary prevention ICD implantation in this population.31  Resynchronization Therapy Data regarding cardiac resynchronization therapy for the failing systemic RV are limited to case reports and small case series. Nevertheless, these suggest that in some patients improvement may be gained by this technique either as definitive therapy or as a bridge to transplantation.  Arterial Switch Patients Pulmonary Artery Dilatation or Surgery Balloon angioplasty of pulmonary artery stenosis after the arterial switch operation has a relatively high failure rate, with most series quoting success rates of approximately 50%. The best results appear to be in patients with branch pulmonary artery stenosis.58 Primary stent implantation appears to have higher initial success rates, although most operators would reserve the use of stents for older children and adolescents. Proximal pulmonary artery stents

will press onto the ascending aorta and may potentially compromise the coronary arteries and therefore may not be suitable in all cases. Surgical relief of pulmonary stenosis, often requiring the use of a patch, may be required in those who do not respond to interventional catheter techniques.  Coronary Artery Interventions Coronary artery lesions after the arterial switch have been treated successfully using surgical bypass grafting, as well as percutaneous catheter procedures.47  Repair of Residual Lesions Severe neoaortic regurgitation may require surgical attention. There have been reports of valve replacement, valve repair, and autograft replacement using the neopulmonary valve. Other hemodynamically significant residual lesions will also require repair (eg, residual VSDs, LVOT obstruction, and mitral valve regurgitation).  Rastelli Patients Conduit Replacement and Dilatation All patients with an RV to pulmonary artery conduit will eventually require conduit replacement. Although gaining initial surgical access to the heart in this situation may be technically challenging, surgical mortality from conduit replacement is low. The more recently developed transcatheter implantable valves have shown good medium-term results and may substantially reduce the number of operative interventions required for these patients. Nevertheless, concerns exist around the increased rates of bacterial endocarditis that have been seen with these valves, and further follow-up is required.  Repair of Residual Lesions There is a risk of both LVOT obstruction and residual VSDs after the Rastelli operation. In some cases residual VSDs may be amenable to transcatheter device closure, but many patients with hemodynamically important residual lesions will need surgical revision.  Palliative Atrial Baffle Procedure Rarely, adult patients are encountered with unoperated TGA and a large VSD. These patients have pulmonary vascular disease that precludes closure of the VSD. If these patients are found to have a pulmonary arterial oxygen saturation significantly higher than their aortic saturation, a palliative Mustard or Senning operation without closure of the VSD is likely to be beneficial by improving their systemic oxygenation. The operative mortality rate from this procedure in one series was 7%, with a survival rate of 92% at 7 years.  Transplantation For many atrial baffle patients with a failing systemic RV, or Rastelli patients with a failing LV, heart transplantation will be the only available surgical option. Assessment of pulmonary artery pressures is particularly important in the atrial baffle patient with evidence of pulmonary venous baffle obstruction. 

Pregnancy MATERNAL RISK Mustard and Senning Patients There is a significant risk of maternal pregnancy complications in this population, although the majority will have uncomplicated

51  Transposition of the Great Arteries

pregnancies. A US multicenter review of 70 pregnancies in 40 women reported 10 miscarriages and 6 therapeutic abortions, with live births in the remaining 54. Cardiac complications occurred in 36% of pregnancies, including arrhythmia, heart failure, and hemoptysis, these complications largely developing in the third trimester but some developing in the first 2 weeks after delivery. One patient who developed heart failure died, and one required transplantation during the postpartum period.59 The Toronto Congenital Cardiac Centre for Adults reported 25 pregnancies in women with atrial baffle repairs of TGA with cardiac complications in six, including congestive cardiac failure, arrhythmia, and death from postpartum heart failure in one patient.60 In patients with good or mildly impaired ventricular function and no previous arrhythmias, the maternal risk from pregnancy is likely to be relatively low; however, there is a risk of deterioration of systemic right ventricular function during pregnancy in patients with atrial baffle repairs, which may not recover following the pregnancy. In patients with symptomatic congestive heart failure or those with previous arrhythmia, the risk from pregnancy is clearly higher. We would actively discourage pregnancy in patients with moderate or severe ventricular dysfunction or symptomatic heart failure. Obstetric care should be provided in a unit experienced in the management of pregnancy in women with CHD. Ideal management is in a program run jointly between a high-risk obstetric service and a congenital cardiology service, with regular follow-up during the pregnancy. Potential mothers should be counseled before becoming pregnant, and detailed up-to-date imaging including MRI assessment of RV function should be available to aid the counseling process. This process should include discussion of the uncertain maternal longevity in this population. If residual hemodynamic lesions are present, consideration should be given to addressing these lesions before conception. Patients can have normal vaginal deliveries, and other than trying to minimize pain and keep the second stage short, labor and delivery usually do not need to be modified for cardiac reasons.  FETAL RISK There is an increased risk of prematurity and small-for-gestational-age birthweight. In the multicenter US study described above, prematurity was frequent (39%) and the average birth weight was 2.7 kg, with 31% of infants weighing less than 2.5 kg. The risk of CHD in children of parents with TGA is thought to be 1% to 2%, although accurate rates are not available. All mothers should be offered detailed fetal echocardiography at approximately 16 to 18 weeks of gestation. 

Level of Follow-up All patients who have had repair of TGA in addition to the rare unoperated survivors should be followed at a center specializing

525

in adult CHD. Most Mustard, Senning, and Rastelli patients can be seen annually, although those with complicating factors, such as severe systemic right ventricular dysfunction, will require more frequent visits. Arterial switch patients may be able to be seen less frequently unless there are specific reasons for concern such as severe aortic root dilatation. Patients should have a clinical history taken and examination performed, as well as ECG and echocardiography at each visit. The “gold standard” imaging modality for atrial baffle patients is cardiac MRI, and as this modality becomes more widely available it should be performed at least every 3 years for these patients. In patients who are unable to undergo MRI, radionuclide ventriculography may be a suitable alternative for the assessment of right ventricular function in centers experienced in its use for the assessment of the systemic RV. 

Endocarditis Prophylaxis The most recent revisions (2008–2015) of the various international guidelines for endocarditis prophylaxis would not support the use of prophylaxis in most repaired transposition patients, although many would continue to recommend prophylaxis for Rastelli patients because of the bioprosthetic pulmonary valve. 

Exercise For atrial baffle patients with good or mildly impaired systemic ventricular function, few restrictions need to be imposed. We would advocate avoidance of isometric exercise to protect the systemic RV, although there is no evidence that any form of exercise is detrimental. It is worth noting that in the Dutch multicenter study of sudden death in this population, 81% of deaths occurred during exercise.29 Patients with moderate or severe right ventricular dysfunction should be advised to avoid more strenuous and competitive exercise but encouraged to pursue regular light-to-moderate social exercise. Rastelli patients without residual hemodynamic lesions and with good ventricular function should receive similar advice to the atrial baffle group. Patients with moderate or severe ventricular dysfunction or outflow obstruction should likewise avoid more strenuous exercise. Arterial switch patients without residual hemodynamic lesions and with good ventricular function should not be restricted in terms of exercise. In patients with significant aortic root dilatation isometric and competitive exercise should probably be avoided. Exercise testing should be undertaken in all arterial switch patients in their early teenage years to exclude ischemia resulting from coronary arterial complications. In all groups of transposition patients, as for all patients with CHD, regular aerobic exercises, such as walking, cycling, and swimming, should be encouraged.

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