Congenitally Corrected Transposition of the Great Arteries

Congenitally corrected transposition of the great arteries (ccTGA) is a rare defect combining atrioventricular discordance with ventriculoarterial discordance. The atria are connected to the opposite ventricle (left atrium to right ventricle via a tricuspid valve) and the ventricles are connected to the incorrect great artery (right ventricle to aorta). Thus oxygenated blood is circulated systemically by the morphologic right ventricle (RV) and deoxygenated blood returns to the right atrium to be pumped out the left ventricle (LV) to the lungs (Figure 1). The defect is therefore “corrected” because of the physiologic flow of blood through the body. For the purposes of this review, univentricular hearts, those with common atrioventricular (AV) valves and those with aortic atresia will not be discussed.


Introduction
Congenitally corrected transposition of the great arteries (ccTGA) is a rare defect combining atrioventricular discordance with ventriculoarterial discordance.The atria are connected to the opposite ventricle (left atrium to right ventricle via a tricuspid valve) and the ventricles are connected to the incorrect great artery (right ventricle to aorta).Thus oxygenated blood is circulated systemically by the morphologic right ventricle (RV) and deoxygenated blood returns to the right atrium to be pumped out the left ventricle (LV) to the lungs (Figure 1).The defect is therefore "corrected" because of the physiologic flow of blood through the body.For the purposes of this review, univentricular hearts, those with common atrioventricular (AV) valves and those with aortic atresia will not be discussed.

Anatomy
The most common anatomy of ccTGA is that of {S,L,L}, representing atrial and visceral situs solitus (right-sided inferior and superior vena cavae returning deoxygenated blood to a right sided atrium), L-looped ventricles (the morphologic LV with mitral valve positioned on the right), and L-transposed great arteries (aorta arising off the left-sided morphologic RV and therefore situated anterior and leftward of the pulmonary artery).The RV serves as the systemic ventricle and, in the absence of other defects, oxygen saturation is normal.The most common positions of the heart in the chest are levocardia (apex to the left) or mesocardia (midline).Patients with levo-or mesocardia and visceral situs inversus have a high likelihood of ccTGA and therefore must carefully by assessed for atrial, ventricular, and arterial concordance.Dextrocardia, in which the apex of the heart is to the right, occurs in approximately 20% of patients (Graham & Markham, 2010).In cases of dextrocardia with mirror-image anatomy the anatomic designation is {I,D,D}.

Associated defects
The most common associated defects in ccTGA are ventricular septal defects (VSDs), which occur in 60-80% of cases, pulmonary stenosis (PS) in 30-50%, and tricuspid valve (TV) anomalies in 14-56%.The VSDs are usually large, perimembranous, and subpulmonary in location.Muscular inlet defects as well as multiple VSDs may also be seen.Pulmonary stenosis, more appropriately referred to as left ventricular outflow tract obstruction TGA for siblings of ccTGA patients is 2.6% with an overall recurrence risk of 5.2% for ccTGA siblings to have some type of congenital heart defect (Piacentini et al., 2005).A recurrence risk of >5% is higher than expected, as the risk is typically thought to be 1-3% for unaffected parents to have an additional child with congenital heart disease ( Van der Bom et al., 2011).

Natural history and outcome
The natural history of ccTGA depends largely on the presence of associated defects.Patients under 5 years old who also have VSD, LVOTO, and/or TV abnormalities represent the highest frequency of non-surgical deaths.However patients w i t h i s o l a t e d c c T G A ( n o associated lesions) may survive into their 4 th and 5 th decades (Hoffman, 2009;Presbitero et al., 1995).Many patients will demonstrate one or more complications including heart block, tricuspid regurgitation (TR), and congestive heart failure (CHF).Approximately 2-4% of ccTGA patients have ventricular pre-excitation (Wolff-Parkinson-White syndrome) and should undergo radiofrequency ablation of accessory pathways in cases of symptomatic reentrant tachycardia.Atrial tachycardia such as atrial fibrillation and flutter often occur with increasing age, atrial enlargement, and after surgical repair where suture lines and scars may support focal reentrant circuits.By 45 years of age 67% of ccTGA patients with associated defects will have developed CHF, as shown in Figure 2, whereas only 25% of ccTGA patients without associated lesions will have progressed to CHF by this age (Graham et al., 2000).Prieto et al suggests that outcome is dependent on morphology of the TV (the systemic AV valve), as this was the only predictor of severe regurgitation and RV dysfunction in a cohort of ccTGA patients described after mean follow-up of 20 years.The authors concluded that severe TV insufficiency leading to RV dysfunction has the greatest impact on long-term survival in both operated and unoperated patients.In patients who underwent surgical intervention for ccTGA, 20-year survival rate was 90% for patients with competent TVs, whereas survival was only 35% for patients with severe TV insufficiency.Furthermore, patients who were diagnosed with severe TV insufficiency demonstrated a rapid deterioration in clinical status with RV failure occurring on average 5 years after onset of insufficiency (Prieto et al., 1998).Overall natural history in the ccTGA patient without associated defects is promising, as patients may remain relatively asymptomatic through early and mid-adulthood.However the frequent development of complications in the 4 th and 5 th decades often culminates in the progressive development of RV (systemic) dysfunction and heart failure, requiring aggressive medical management and possible surgical intervention (Presbitero et al., 1995).

Diagnosis
Just as the natural history is largely dependent on defects associated with ccTGA, so is timing of presentation and diagnoses.

Prenatal diagnosis
Fetal diagnosis of many forms of CHD continues to improve.However the fetus with ccTGA and mild or no additional intracardiac anomalies may be overlooked by routine ultrasound screening.Distinct features notable on prenatal ultrasound that may improve detection of ccTGA are parallel course of the great arteries in combination with dextrocardia, abnormal insertion of the papillary muscles, and/or an abnormal TV (McEwing & Chaoui, 2004;Paladini et al., 2006;Shima et al., 2009).A retrospective review by Wan et al. found no difference in the number of cardiac interventions, timing of surgery, or survival between a cohort of ccTGA patients diagnosed prenatally (n = 14) and postnatally (n = 26).However, because 70% of this cohort required cardiac intervention prior to 3 years of age, the authors suggest prenatal diagnosis is important for preparation and counseling of the family (2009).A recent review of 11 cases of fetal ccTGA diagnoses describes the use of four-dimensional echocardiography and spatiotemporal image correlation (STIC), in which the relationship of the great arteries can be assessed in several different orthogonal planes by placement of a reference dot on images reconstructed from acquired volume data sets (Zhang et al., 2011).

Early presentation and diagnosis
Diagnoses of infants and children may occur after murmur evaluation, as VSDs are commonly associated lesions.In cases of large VSDs or severe TV regurgitation, some infants may present in CHF with diaphoresis, pallor, tachypnea, inability to gain weight, hepatomegaly, and a gallop on exam.Auscultation of the ccTGA patient may also reveal a loud, single second heart sound (S2) at the left 2 nd intercostal space, with absence of S2 over the right 2 nd intercostal space (Friedberg & Nadas, 1970).The presence of VSD combined with LVOTO may lead to a cyanotic presentation from decreased pulmonary blood flow.However, some degree of LVOTO may be protective of the lung bed in patients with large VSDs, and may delay a CHF presentation despite the normal decrease in pulmonary vascular resistance.

Late presentation and diagnosis
Interestingly, if there are no additional associated defects ccTGA may go unnoticed until adolescence or adulthood.Case reports have even cited incidental findings and late diagnoses of ccTGA in adults in the fifth to eighth decades of life (Chang et al., 2009;Jennings et al., 1984;Orchard et al., 2010;Scardi et al., 1999).A cohort of patients with ccTGA over 18 years of age who presented to an adult CHD clinic over a 15 year period is described by Beauchesne et al (2002).Sixty-six percent of these patients were over 18 years of age when diagnosed, and 17% of the cohort was over 60 years old at the time of diagnosis.Common reasons for referral in such patients range from abnormal ECGs and cardiomegaly on chest radiographs to complete heart block and murmurs (Presberito et al., 1995).

Chest radiograph
The CXR in ccTGA patients with mesocardia or levocardia typically demonstrates a straightened upper-left cardiac border from the leftward-positioned ascending aorta.Dextrocardia usually occurs with normal situs and, as stated previously, occurs in 20% of ccTGA patients (Figure 3).The presence of abdominal situs solitus and dextrocardia should raise suspicion of ccTGA.In the patient without any associated defects, an atypical cardiac position in an otherwise normal CXR may be the only indication of ccTGA.However marked cardiomegaly, left atrial enlargement, and an increase in pulmonary vasculature may be present in patients with a large VSD and significant left to right shunt.A CXR with impressive cardiomegaly and left atrial enlargement may also be indicative of an Ebstein-like malformation of the TV.The presence of pulmonary stenosis or atresia will demonstrate darkened lung fields from attenuated pulmonary blood flow.Overall, the degree of cardiomegaly and amount of visible pulmonary vascularity is dependent on the presence and direction of shunting, as well as the severity of LVOTO (Carey & Ruttenberg, 1964).

Electrocardiogram
The ECG in patients with ccTGA is most significant for a superior QRS axis and atypical septal activation.As discussed previously, the conduction system in ccTGA consists of inverted AV bundles.Therefore the septum is activated from right to left, demonstrating presence of septal Q waves in the right precordial leads (QR pattern in leads V4R and V1) a n d a b s e n c e o f Q w a v e s i n t h e l e f t p r e c o r d i a l l e a d s ( r S p a t t e r n i n l e a d V 6 ) .I n f a c t , undiagnosed ccTGA patients with such a pattern on ECG have been diagnosed with remote inferior infarcts (Jennings et al., 1984;Warnes, 2006).Preexcitation may be observed in those patients with ccTGA and Wolff-Parkinson-White.Finally, varying degrees of AV block may be present, as well as patterns of right or left-sided chamber enlargement.

Echocardiography
Transthoracic echocardiography (TTE) as an imaging modality is relatively inexpensive, widely available, and noninvasive.As with many types of CHD, TTE is the first line and most useful modality in the diagnosis of ccTGA.The anatomical designation (most commonly {S,L,L} as discussed previously), is first assigned by demonstrating atrial position, ventricular looping, and arterial looping.Morphology of the RV is seen on TTE by the presence of coarse trabeculations and a moderator band, whereas the LV has a smoothwalled endocardium and a funnel-shaped appearance.The level of the TV is inferior to the MV, which may also give a clue to ventricular inversion.In evaluation of the outflow tracts, the aorta in ccTGA is usually anterior and to the left of the PA.Once the diagnosis of ccTGA is made through demonstration of discordance between atria and ventricles as well as ventricles and great arteries, several anatomic objectives should be defined in the TTE evaluation.Semilunar and AV valve morphology as well as presence and severity of regurgitation warrant full description.Coronary origins should be identified and their proximal courses described.The degree of LVOTO is important as well as any additional defects present, as these will impact whether and what type of surgical repair is necessary (Oechslin, 2009).Transesophageal echocardiography (TEE) has been shown to have greater accuracy over TTE in correctly defining atrial situs and chordal AV valve attachments in adult patients with ccTGA (Caso et al., 1998).TEE is also more useful for investigation of intracardiac vegetations in cases of suspected endocarditis and in evaluation of thrombus in the atrial appendages, which may be applicable to the ccTGA patient with sustained atrial arrhythmias.

Cardiac catheterization
Rather than a modality for diagnosis, cardiac catheterization (Figure 4) is typically reserved for the post-surgical patient who would benefit from an intervention such as LV to pulmonary artery (PA) conduit dilation or stent placement.For patients undergoing surgical palliation for single-ventricle ccTGA anatomy, catheterization is performed to assess pressure, function, and valve regurgitation prior to surgery.Most interesting, however, is the adult patient who presents with ischemic heart disease and is discovered on cardiac catheterization to have ccTGA after abnormal catheter passes or inversion of coronary arteries on angiography (Jennings et al., 1984).

Cardiac Magnetic Resonance Imaging (cMRI)
Cardiac MRI is now used in many types of CHD to further define anatomy and to quantify ventricular function and volume (Figure 5).For initial diagnosis, cMRI may be helpful in patients with restricted TTE windows, to define visceroatrial situs, and to delineate complex associated defects.In patients with interruption of the inferior vena cavae, systemic return from the lower body can be difficult to delineate by echocardiography, but is well defined by cMRI.Because echocardiographic evaluation of RV function in ccTGA patients is limited by geometric assumptions, cMRI has become the gold standard for RV function and volume assessment.TV morphology as well as degree of regurgitation can also be determined through cMRI.Prior to performing anatomic surgical repair in a ccTGA patient beyond infancy, cMRI may be useful in evaluation of LV mass, volume, and ejection fraction.Furthermore, if there are concerns about degree of LV dysfunction, perfusion studies with delayed enhancement MRI may be performed to directly investigate scarring of the LV myocardium prior to committing this ventricle to systemic workload.Cardiac MRI may therefore be a useful modality for evaluation of ccTGA patients not only as an adjunct to TTE for initial diagnosis, but also for assessment prior to surgical repair and serial follow-up of the systemic RV.If the presence of MRI-incompatible pacemaker or prosthetic valve precludes assessment by MRI, computed tomography (CT) scans can depict anatomy but cannot yield functional data as does MRI (Schmidt et al., 2000;Teo & Hia, 2011).

Exercise and stress testing
Cardiopulmonary exercise testing by treadmill is an important adjunct for ccTGA patient evaluation and management.In those patients able to perform treadmill tests, exercise capacity is determined through minute ventilation, carbon dioxide production, and oxygen consumption.Impaired exercise capacity in ccTGA patients has been shown to correlate with diastolic dysfunction in the form of increased RV filling pressures as measured by tissue Doppler imaging (Tay et al., 2011).Cardiopulmonary exercise testing in combination with gadolinium-enhanced MRI has been utilized to demonstrate RV myocardial fibrosis hypothesized to be responsible for RV dysfunction (Giardini et al., 2006).Systemic RV function can also be evaluated by dobutamine stress testing, in which MRI is performed at baseline and with dobutamine infusion.Objectively defining the capacity of the systemic RV to respond to stress may guide treatment on both initial and follow-up evaluations (Dodge-Khatami et al., 2002;Fratz et al., 2008).Sequential testing, performed either by exercise testing or by dobutamine stress test, is useful to assess overall cardiopulmonary function and response to medical or surgical therapy.

Management
7.1 Medical management CHF medical management for the ccTGA patient with systemic RV has been extrapolated from CHF therapy for LV failure.This primarily includes β-adrenergic receptor blockade (βblockers), diuretics and afterload-reducing agents with an angiotensin-converting enzyme (ACE) inhibitor (Winter et al., 2009).Digoxin may also be useful for its inotropic and antiarrhythmic effects.Angiotensin receptor blockade with losartan was evaluated in a multicenter, randomized, placebo-controlled clinical trial by Dore and colleagues (2005) but found to have no improvement on exercise capacity and no reduction in neurohormonal levels in patients with systemic right ventricles.Overall, evidence-based therapy for optimal CHF treatment in patients with systemic RV is lacking.Beyond medication, cardiac resynchronization has emerged as a therapy for patients with impaired systemic RV function and widened QRS morphology on ECG.Increased QRS duration as a result of bundle branch block or conventional pacemaker is typically greater than 120-140 ms with some patients having QRS duration >200 ms.Such electromechanical dyssynchrony creates inefficiency in ventricular ejection, whereas restoring synchrony has been shown to decrease QRS duration with improvement in RV filling time, ejection fraction, and overall CHF symptoms (Diller et al., 2006;Janousek et al., 2004;Kordybach et al., 2009).Takemoto et al. ( 2010) reports the use of transvenous permanent para-Hisian pacing in an 8 year old with ccTGA.Restoration of cardiac synchrony decreased the QRS duration from 198 ms to 94 ms, decreased interventricular conduction delay from 137 ms to 37 ms, and improved the patient's CHF symptoms from NYHA (New York Heart Association) class III to NYHA class II over a period of 6 months.Limitations in cardiac resynchronization therapy include difficulty in percutaneous lead delivery, although this has successfully been accomplished even in ccTGA cases of dextrocardia (Malecka et al., 2010).

Surgical management
Indications for surgical management in ccTGA patients of all ages continue to evolve and most often are determined on a case-by-case basis.Beauchanese et al. (2002) described a cohort of 44 unrepaired adult ccTGA patients.Of these, the 30 patients who required surgical intervention had significantly larger pre-operative cardiothoracic ratios on chest radiographs, and had moderate to severe or severe systemic AV valve regurgitation.The ejection fraction of the systemic ventricle between the operated and unoperated groups was not statistically significant (Beauchesne et al., 2002).As discussed previously and depicted in Figure 2, nearly 2/3 of unrepaired ccTGA patients with associated defects will have developed CHF by the age of 45 years.Even asymptomatic adults with ccTGA have been shown by echocardiography to have RV dysfunction through the use of tissue Doppler quantification techniques (Bos et al. 2006).Thus the natural evolution of ccTGA for the majority of patients is eventual RV dysfunction and TV regurgitation.It is postulated that progression to failure in a systemic RV is unavoidable because the RV and TV are not anatomically suited to withstand the systemic pressure for which the LV and MV are intended.One mechanism thought to contribute to progressive RV decompensation is worsening TR from annular dilation and/or displacement of the septal leaflet of the TV as the RV remodels to accommodate systemic afterload.
Table 1.ccTGA {S,L,L} Surgical Repair and Palliation.VSD, ventricular septal defect; PS, pulmonary stenosis; PA, pulmonary artery; PV, pulmonary valve; RV, right ventricle; TR, tricuspid regurgitation; BDG, Bidirectional Glenn Depending on the age of presentation and extent of associated lesions, surgical repair may include one or more of several approaches (Table 1).In patients with a VSD and no LVOTO, "classic" or "physiologic" repair may include VSD closure only.Specific techniques must be employed in ccTGA patients to avoid damage to the conduction system during VSD closure.Because the AV conduction bundle descends along the anterior rim of the VSD and travels along the septal side of the right-sided morphologic LV, it is recommended to suture the VSD patch along the morphological right ventricular aspect of the septum.The surgical approach should be via right atriotomy and right-sided mitral valve.Ideally the VSD patch will lie partially on the morphologic LV septal aspect (to avoid damage to the TV superiorly) and partially on the morphologic RV aspect of the septum inferiorly (to avoid damage to the main conduction bundle) (Jonas, 2004).Physiologic repair may also include relief of pulmonary stenosis (PS) and/or LV to PA conduit placement.There is, however, the possibility that decreasing LV pressure by VSD closure and/or PS relief may allow the ventricular septum to realign towards the LV, resulting in displacement of the TV septal leaflet and increasing TR (Kral Kollars et al. 2010;Said et al. 2011).In a cohort of 123 patients with ccTGA presenting for classic biventricular repair over 33 years, the surgical group undergoing repair of VSD + PS demonstrated the greatest survival whereas patients requiring TV replacement at their initial operation exhibited the shortest survival.Risk factors for death in the VSD +/-PS relief groups included pre-operative RV end diastolic pressure greater than 17mmHg and complete heart block.Survival rates at 1-, 5-, 10-, and 15years for patients who underwent classic repair were 84%, 75%, 68%, and 61%, respectively, although 17 of the 113 patients in this subgroup underwent Fontan and achieved 100% survival in short-term follow-up (Figure 6).The univentricular pathway with Fontan was assigned to ccTGA patients for which biventricular repair was contraindicated, as in patients with straddling AV valve tissue, inaccessible or multiple VSDs, or unbalanced complete AV canals (Hraska et al. 2005).More recently Bogers et al. (2010) confirmed that classic repair in which the RV remains the systemic ventricle results in significant incidence of reoperation and overall suboptimal survival.The "anatomic" or "Double Switch" (DS) operation was developed in response to unsatisfactory outcomes after the classic repair.Components of the DS (Figure 7A) include arterial switch with coronary artery transfer, VSD closure if necessary, and interatrial baffle by Senning or Mustard procedure.The Senning and Mustard operations, referred to as an "atrial switch," serve to direct systemic venous flow to the TV and RV and pulmonary venous flow to the mitral valve and LV.The purpose of the DS is to improve long term outcome by restoring the LV and MV to the systemic circulation.Requirements for this repair before committing the LV to the systemic workload include pre-operative LV pressure that is 80-100% systemic and normal LV wall thickness and function for a systemic LV (Duncan & Mee, 2005;Poirier et al., 2004).In the absence of LVOTO, pulmonary hypertension, or an unrestrictive VSD, the morphologic LV requires training prior to committing it to the systemic ventricle in the DS.LV training has been performed by placement of a pulmonary artery band (PAB) which is then serially tightened to introduce a greater pressure load nearing that of systemic pressure to the naïve LV.Median banding time for the purpose of LV retraining has been reported on average to be 13-14 months (Ly et al., 2009;Poirier et al., 2004;Winlaw et al., 2005).Morphologic LV reconditioning with PAB in patients with systemic RV after atrial switch for dextrotransposition of the great arteries (dTGA) has been described by Poirier et al (2004).PAB was performed in this population prior to anatomic correction or as bridge to transplant, and the success rate of completing adequate LV retraining was significantly less in patients beyond 12 years of age (20% of patients over 12 years completed the protocol, whereas 62% of patients less than 12 years were able to complete the PAB protocol, p = 0.02).Although a well defined standard for age of PAB placement in this setting is yet to be realized, it is apparent that candidacy for LV training with PAB beyond adolescence is questionable.Also concerning is report of late LV dysfunction in ccTGA patients who underwent DS operation after successful LV retraining by PAB placement (Quinn et al., 2008).Rather than performing pulmonary artery banding in symptomatic ccTGA patients with intention of anatomic repair, Metton and associates (2010) advocate the use of PAB in asymptomatic ccTGA neonates and infants with intact ventricular septum to maintain rather than train the LV.In Metton's group the TV was not repaired at PAB placement, as it was thought that PAB placement may improve TR that was present prior to banding (Ly et al., 2009).This mechanism is described by Kral Kollars et al. (2010) in 14 patients who underwent PAB for LV retraining (median age 1.1 years, range 0 to 12 years).Eleven of the 14 patients had an increase in LV pressure of ≥2/3 systolic RV pressure with PAB and demonstrated significantly decreased TR as the LV geometry became more spherical and the interventricular septum shifted toward the morphologic RV.Patients who underwent classic ccTGA repair with procedures that reduced LV pressure below that of the RV, such as VSD closure with LV to PA conduit placement, demonstrated significantly increased TR postoperatively.Although it is reasonable to medically manage mild TR with anticongestive therapy and afterload reduction, surgical intervention is indicated in cases of moderate or moderate to severe TR.TV repair for ccTGA patients is rarely successful, and most patients require valve replacement, which can be problematic in young children because of the relatively large prosthesis needed to allow for growth.Palliation with PAB may therefore be reasonable in infants and young children, since it has been shown that severe TV insufficiency leading to RV dysfunction has the greatest impact on long-term survival (Kral Kollars et al., 2010;Prieto et al., 1998).Several groups have concluded that TV replacement should be considered at the earliest sign of RV dysfunction, with recommendations to consider operation before systemic ventricular ejection fraction (EF) decreases below 40 and 44% (Mongeon et al., 2011;Van Son et al., 1995).The combination of progressive systemic RV dysfunction and TR has lead to the consideration of a variation in DS operation for patients with LVOTO.Rather than combining the atrial and arterial switches, the Senning or Mustard atrial switch procedure is combined with a Rastelli operation, in which the LV outflow is channeled from the LV through a large VSD to the aorta and an RV to PA conduit is placed (Figure 7B).This operation is technically challenging and subject to the need for conduit replacements as well as possible reoperation for interatrial or interventricular baffle obstructions.Specific to the Senning / Rastelli operation, risk factors associated with death include longer cardiopulmonary bypass and aortic cross-clamp times, and there is an increased risk of complete heart block and ventricular dysfunction if the existing VSD requires enlargement (Gaies et al., 2009;Shin'oka et al., 2007).Nevertheless, intermediate results in a small group of ccTGA patients with VSD and LVOTO who underwent this form of anatomic repair suggest good biventricular function and mild or no AV valve insufficiency up to 17 years post-operatively (Hörer et al., 2007).An additional variation in the DS for patients with severe RV dysfunction, hypoplasia of the RV, or abnormal right atrial anatomy includes a modified atrial switch termed the "hemi-Mustard/bidirectional Glenn," which is performed in combination with either an arterial switch or a Rastelli procedure.In this operation the interatrial baffle only includes the IVC return, as the SVC is reimplanted into the pulmonary artery to create a cavo-pulmonary Glenn shunt, and the SVC portion of the RA is oversewn.Midterm outcomes from the hemi-Mustard/Glenn as reported by Malhotra et al. (2011) are favorable and hold several advantages over the traditional Senning or Mustard atrial switch.The authors report a prolonged lifespan of the RV to PA conduit due to volume-unloading the RV, increased intra-atrial space for pulmonary venous return (and therefore less risk of pulmonary venous obstruction), and less risk for arrhythmia with the reduction in intra-atrial suture lines.It remains to be seen if the hemi-Mustard / bidirectional Glenn variant of the DS will prove favorable in long-term studies.

Outcomes: Physiologic vs. anatomic repair
Alghamdi and associates ( 2006) published a meta-analysis of 11 nonrandomized studies totalling 124 ccTGA patients and compared in-hospital mortality between physiologic and anatomic repair.Patient age at time of repair ranged from 3 months to 55 years with 41% of patients undergoing definitive repair prior to 1995.Thirty patients underwent physiologic repair, 69 underwent Rastelli-type anatomic repair, and 25 received anatomic repair with arterial switch.The Rastelli-type anatomic repair had significantly lower hospital mortality while era of operation before 1995 demonstrated an increased mortality risk.A large risk analysis performed by Shin'oka et al. (2007) combined ccTGA patients with a group of systemic RV patients with discordant AV connections, (n=189) and compared long-term results of definitive surgical repair with respect to hospitalization, late mortality, and reoperation.Risk factors for hospital death included preoperative moderate TR and intraoperative cardiopulmonary bypass time of over 240 minutes.The presence of TR was also a risk factor for late mortality.Reoperation risks included preoperative cardiomegaly (cardiothoracic ratio of >0.6) and presence of TR, operative need for VSD enlargement, and patient size of <10 kg.Although survival of classic repair in patients without TR was satisfactory in comparison to anatomic repair, patients with ccTGA and discordant AV connections with TR demonstrated improved survival with anatomic repair.More recently Lim and colleagues (2010) report results from a multicenter study including 167 patients who underwent biventricular ccTGA repair.Of the patients studied, 123 underwent physiologic repair (ASD or VSD closure, TV surgery, and/or pulmonary ventricle to PA conduit placement), and 44 underwent anatomic repair (atrial + arterial switch or atrial + interventricular re-routing procedure) over the years 1983 -2009.Long-term results of biventricular repair revealed an estimated survival of 83.3% ± 0.05% at 25 years.The incidence of complete heart block was lower for the anatomic repair group, and there was a late mortality of 5.9% after physiologic repair in comparison to 0% after anatomic repair.
Freedom from systemic AV valve regurgitation and ventricular dysfunction was significantly higher after anatomic repair.The authors concluded that anatomic is superior to physiologic repair in patients with two adequately sized ventricles.However high risk groups such as those patients with RV dysfunction or the need for LV training warrant careful selection prior to undergoing anatomic repair.Taken together, these outcomes favor anatomic over classic /physiologic repair with careful preoperative assessment of TR for the purpose of risk stratification.

Follow-up and special considerations
Patients with ccTGA require outpatient follow-up every 1-2 years by a pediatric or adult congenital cardiologist.Symptomatology, ventricular function, and valvar insufficiency should further guide frequency of follow-up.It is recommended an ECG be performed at each visit to monitor for AV block with periodic consideration of Holter monitor.Cardiopulmonary exercise testing is performed to assess overall function as well as response to medical or surgical therapy.RV function in the unrepaired or physiologically repaired ccTGA patient must be closely monitored with serial echocardiography even in asymptomatic patients (Bos et al., 2006).Cardiac MRI with cine data used to quantify RV volume, mass, and ejection fraction is the best modality to serially quantify RV function, and should be performed every 3-5 years.

Pregnancy
Pregnancy in the ccTGA patient is generally well tolerated except in the presence of maternal NYHA class III-IV symptoms, moderate or severe AV valve regurgitation, or poor ventricular function (EF<40%).Evaluation of pregnancy outcome in 22 women with ccTGA revealed 50 live births in 60 total pregnancies (83%).However, the rate of miscarriage in the ccTGA mothers was higher than the general population (Connolly et al., 1999).A recent cohort of patients by Gelson and colleagues (2011) revealed high maternal and neonatal morbidity in women with systemic right ventricles with a significant number of babies born small for gestational age.Although cyanosis in women with ccTGA has been shown to be a risk factor for miscarriage, the women in the cohort of Gelson et al. were normally saturated (Gelson et al., 2011;Thierrien et al. 1999).The risk of congenital heart defects in the offspring of mothers with ccTGA has not been defined.

Heart transplant
Patients for which heart transplantation may be considered are those with end-stage RV failure, significant LV dysfunction and pulmonary valve abnormalities precluding successful DS operation, or uncontrollable arrhythmia (Duncan & Mee, 2005).For patients undergoing surgical intervention, poor preoperative EF of the systemic ventricle has been shown to predict the eventual need for transplantation (Beauchesne et al., 2002).

Conclusions and special considerations
Although debate continues over efficacy and long-term follow-up of physiologic vs. anatomic repair for ccTGA, recent outcomes data favor anatomic correction in which systemic function is restored to the LV.Management considerations specific to this population of complicated patients include type and timing of surgical intervention to

Fig. 2 .
Fig. 2. Freedom from CHF in group I (associated lesions, n=125) and group II (no significant associated lesions, n=50) as a function of increasing age.(Reprinted from Journal of the American College of Cardiology, Vol.36, No. 1, Long-term outcome in congenitally corrected transposition of the great arteries: A multi-institutional study, pp.255-261, Copyright 2000 with permission from Elsevier).

Fig. 3 .
Fig. 3. CXR of infant with dextrocardia, abdominal situs solitus, and ccTGA.Note the position of the cardiac apex pointed to the right.The left heart border demonstrates the prominent leftsided ascending aorta.The thymic shadow is seen over the right mediastinum.

Fig. 4 .
Fig. 4. Cardiac catheterization of ccTGA infant with dextrocardia, pulmonary stenosis, and VSD (same infant as in Fig. 3).(A.) Anterior-posterior projection.A catheter is positioned in the right-sided morphologic left ventricle (LV).Contrast fill the LV, pulmonary trunk, and pulmonary arteries.Contrast flows right to left across the VSD (arrow) and fills the aorta.(B.) Lateral projection.Contrast from the LV flows through the LV outflow tract, across the pulmonary valve, and fills the pulmonary arteries.The aorta fills by right to left shunting through the VSD.Note the aorta is anterior to the pulmonary artery.(C.) Anterior-posterior projection.A catheter is positioned retrograde into the left-sided morphologic right ventricle (RV).Contrast fills the trabeculated RV and the leftward aorta.(D.) Lateral projection.Contrast fills the large RV, ascending, and descending aorta.LV, left ventricle; RV right ventricle; Ao, Aorta; aAo, ascending aorta; dAo, descending aorta; MPA, Main pulmonary artery; PA, Pulmonary artery.

Fig. 5 .
Fig. 5. Oblique cut T2-weighted MRI image of 4-chamber cardiac view of ccTGA patient with levocardia.The RA empties into a right-sided, smooth-walled, morphologic LV.A star (*) labels the entrance of a right pulmonary vein into the left atrium, which empties into a trabeculated, left-sided, morphologic RV.RA, right atrium; LV, left ventricle; LA, left atrium; RV, right ventricle.