Fig. 11.1
Congenitally corrected transposition of the great arteries (ccTGA). Definition and associated malformations: the combination of discordant atrioventricular and ventriculo-arterial connections (“duplicated discordance”) results in normal physiology despite the presence of the transposition of the great arteries
The most common anatomical arrangement is situs solitus with L-looping of the ventricles and the aorta anterior and leftward of the pulmonary artery (S,L,L) in 95 percent of cases [2], while situs inversus with D-looping of the ventricles and the aorta anterior and rightward (I,D,D) is also seen in the other 5% of ccTGA cases.
The majority of cases of ccTGA have any associated anatomical abnormalities. The most common lesions include ventricular septal defect (VSD) in 60–80% of patients, the left ventricular outflow tract obstruction (LVOTO) or pulmonary stenosis/atresia (PS/PA) in 40–50% of patients, and abnormalities of the morphologically tricuspid valve in up to 90% of patients with Ebstein’s anomaly in 50% [3–5]. The isolated ccTGA without associated malformation is seen only 1% of cases (Fig. 11.1).
11.2.2 Associated Malformations
11.2.2.1 Ventricular Septal Defect (VSD)
The majority of VSDs are perimembranous, located below the pulmonary valve, with the posterosuperior margin of the defect formed by an extensive area of fibrous continuity between the leaflets of the pulmonary, mitral, and tricuspid valves, most characteristically in this anomaly. Often the perimembranous defects become at least partially obstructed by aneurysmal membranous atrioventricular (AV) septum tissue or the straddling tricuspid valve tissue. Other types of defects are also described including doubly committed subarterial (conal) defects, muscular defects, and AV canal type defects.
11.2.2.2 Left Ventricular Outflow Track Obstruction (LVOTO)
The LVOT obstruction may comprise subpulmonary stenosis and/or pulmonary valve stenosis. Pulmonary atresia (PA) can also be seen. The subpulmonary stenosis is often related to the presence of a fibromuscular shelf on the septum, muscular hypertrophy, tunnellike hypoplasia, or an aneurysmal dilation of fibrous tissue derived from the interventricular component of the membranous septum or an accessory mitral or tricuspid valve tissue.
11.2.2.3 Lesions of the Morphologically Tricuspid Valve
The tricuspid valve has been reported to be abnormal in the great majority of ccTGA patients. There is a wide spectrum of severity. Ebstein’s anomaly of the systemic AV valve also occurs but is different from the typical right-sided Ebstein’s anomaly, only characterized by the septal and posterior leaflets displaced inferiorly toward the cardiac apex [6]. It is rare to find the large “sail-like” deformity of the anterosuperior leaflet, as seen in the setting of concordant atrioventricular connections. And the atrialized portion of the RV inflow is also relatively small.
Another morphological variation is straddling of the tricuspid valve, with overriding the ventricular septum in the presence of VSD. The morphologically mitral valve also straddles and overrides, often in combination with double outlet right ventricle [7].
11.2.3 The Atrioventricular Conduction System in ccTGA: Clinical and Interventional Considerations [1, 8, 9]
With the arrangement of AV discordance, there is reversed offsetting of the attachments of the leaflets of the atrioventricular (the morphological mitral and tricuspid) valves to the septum, with the mitral valve on the right side attached appreciably higher than the tricuspid valve on the left side at the crux of the heart. Almost always there is fibrous continuity between the leaflets of the pulmonary and mitral valves in the roof of the right-sided morphologically left ventricle. The pulmonary outflow tract is deeply wedged between the atrial septum and the mitral valve, thus deviating the atrial septum away from the ventricular inlet septum. Consequently, this gap of septal malalignment is occupied by an extensive membranous septum [1] (Fig. 11.2).
Fig. 11.2
The atrioventricular conduction system in ccTGA. (a) Normal heart and (b) ccTGA in situs solitus. AS the atrial septum, VS the ventricular septum, TV tricuspid valve, MV mitral valve, AVS the atrioventricular septum, POT the pulmonary outflow tract
Due to this malalignment of the atrial and inlet ventricular septum, the regular atrioventricular node, which is located at the apex of the triangle of Koch in the base of the atrial septum, is anatomically impossible to connect to the atrioventricular bundle in ccTGA with situs solitus {SLL} arrangement. Instead, the anterior AV node is located beneath the ostium of the right atrial appendages at its junction with the anterior atrial wall and is positioned above the lateral margin of the area of pulmonary to mitral fibrous continuity. The anterior AV node gives rise to a penetrating bundle (PB) through fibrous trigone, and the non-branching bundle (NBB) or the His bundle encircles pulmonary valve anteriorly and descends onto the anterior part of the trabecular septum on the right side (morphologic LV) surface of the septum. (with intimately close relationship to the anterosuperior edge of pm VSD, if present). And then the NBB bifurcates into a cord-like right bundle branch (RBB), which extends leftward to reach the morphologically right ventricle. The fanlike left bundle branch (LBB) cascades down the smooth surface of the morphologically left ventricle (Fig. 11.2). This abnormal course of the conduction system is of crucial significance to the surgeons in the presence of a ventricular septal defect or subpulmonary obstruction (Fig. 11.3).
Fig. 11.3
The relationship of the abnormal course of the AV conduction bundle to the pulmonary valve and a ventricular septal. From the left ventricular view
In contrast, the normal AV conduction bundle from regular posterior AV node is present in situs inversus, which arrangement of ccTGA is associated with better alignment of the atrial and inlet septum with less “wedging” of the pulmonary outflow tract. Furthermore ccTGA in situs inversus and the other variations may have the dual AV node with possible sling, resulting in the occurrence of reentrant supraventricular tachycardia [10, 11].
11.2.3.1 Clinical Implications of Abnormal Conduction System
The long penetrating and non-branching bundle in ccTGA are vulnerable to fibrosis with advancing age. This makes the conduction system somewhat tenuous, with a progressive incidence of complete AV block.
Other conduction disturbances described include sick sinus syndrome, atrial flutter, reentrant atrioventricular tachycardia due to a dual AV node, and an accessory pathway along the atrioventricular junctions.
11.3 Overview of Surgical Intervention
11.3.1 Surgical Management Strategies
11.3.1.1 Physiological Repair vs Anatomical Repair
Figure 11.4 depicts the classification and modifications of surgical procedure for ccTGA: Physiological repair vs anatomical repair. Until recently, patients with associated abnormalities underwent conventional physiological repair. The goal of the operation is to repair the cardiac defects by closing VSD, repairing the tricuspid valve, and reliving LVOTO, while leaving the morphologically right ventricle as the systemic ventricle. The physiologic approach is straightforward but has the shortcomings over time. After this type of repair, the RV remains the systemic ventricle, and long-term results of this type of surgical repair are disappointing with the late occurrence of the right ventricular dysfunction, tricuspid valve regurgitation, and complete heart block. Because of this poor prognosis over the long term, there is an increasing trend toward achieving anatomical correction.
Fig. 11.4
The classification of surgical procedure for ccTGA: Physiological repair (a) vs anatomical repair (b). (a) (1) VSD closure (2) LVOTO relief using LV-PA conduit (conventional Rastelli) with VSD closure (b) (1) The double switch operation (DSO) (2) The Rastelli–Senning/Rastelli–Mustard Operation
The concept of the anatomical correction is the rerouting of the pulmonary venous return to the morphologically left ventricle and aorta and the systemic venous return to the morphologically right ventricle and pulmonary arteries, thus restoring a normal anatomic pattern of circulation. This can be achieved by the combination of atrial switch operation and either arterial or intraventricular switch operation. Anatomic correction for ccTGA is tailored to the patients’ specific anatomies: (1) the arterial–atrial switch procedure or the double switch operation (DSO) for patients with normal LVOTO regardless of the presence of VSD and (2) the Rastelli–atrial switch procedure [the Rastelli/Senning or the Rastelli/Mustard] for patients with an unrestrictive VSD and LVOTO (pulmonary atresia or severe subpulmonary stenosis). Current surgical strategies for ccTGA in relation to the anatomical types are shown in Fig. 11.5.
Fig. 11.5
Current surgical strategies for ccTGA in relation to the anatomical types
Despite anatomical repair may improve long-term prognosis, this operation represents major and technically challenging surgical procedures. The physiological repair may be still indicated to a certain group of patients with associated lesion who are contraindicated to anatomical repair.
11.3.1.2 Operative Indication for ccTGA
In general the diagnosis of ccTGA is not in itself an indication for surgical correction. The operative indication should be based on the hemodynamic impact of the associated lesions and the potential of the systemic RV to fail. Definitive indication includes the patients with heart failure due to a large VSD or a VSD with significant LVOTO/PS. When a VSD is present, the indications for operation will be determined by its hemodynamic impact (i.e., Qp/Qs, pulmonary arterial pressure, and pulmonary resistance), as well as the specific morphology of the defect itself. In the presence of pulmonary stenosis the indication for surgery is dictated by the severity of the obstruction (i.e., transpulmonary pressure gradient >50 mmHg) and the degree of cyanosis, hypoxemia, and polycythemia. Other major indications for surgery include the severity and progression of tricuspid valve regurgitation (TR). Replacement of the morphologically tricuspid valve is usually recommended, if the regurgitation is more than grade 2/4 at the time of intracardiac repair of other lesions [12]. Systemic AV valve replacement is relatively common in the adult age.
If the decision is made to achieve the anatomic correction in order to retain anatomically normal physiology to avoid the future deterioration of the systemic RV and TR, the timing and strategies of surgery are always difficult decision, especially in asymptomatic patients with the isolated ccTGA or with hemodynamically well-balanced lesions. Most centers would not recommend a prophylactic double switch operation for patients without associated abnormalities in whom the RV and tricuspid valve function are normal. Instead, pulmonary arterial banding (PAB) is indicated to the isolated ccTGA to retrain the LV for the subsequent anatomical correction in childhood, especially in patients with the presence of significant TR or RV dysfunction. Some centers consider the anatomical repair is their institutional first choice for the patients who have a balanced systemic and pulmonary blood flow due to VSD and pulmonary stenosis without clinically significant cyanosis to treat [13].
11.3.1.3 PAB for Retraining the Left Ventricle in Isolated ccTGA for DSO [14–16]
In the isolated ccTGA without associated abnormalities, LV pressure will be at pulmonary artery pressure; thereby the LV should be retrained in younger children by the placement of a pulmonary artery band (PAB) to increase LV pressure for DSO. This strategy is thought to be particularly required in pediatric patients with significant tricuspid regurgitation. Some report proposed the early prophylactic pulmonary artery banding in neonate with isolated ccTGA considering the future application of DSO.
In childhood the LV can be successfully retrained using a strategy of progressive pulmonary artery banding in order to provide an increased pressure load on the LV and promote LV hypertrophy. The possible predictors for a successful LV retraining include an LV systolic pressure of at least 70–80% of systemic pressure in childhood or 100% in adolescence and an LV wall thickness or LV mass index that is equivalent to that in a systemic LV. One of the best predictors of failure of retraining is age, with most successfully retrained patients being <10 years of age [17].
11.3.1.4 Pulmonary Artery Banding as a Definitive Palliation
Pulmonary artery banding intended to train the LV has been shown simultaneously to reduce the tricuspid regurgitation and subsequently to improve the RV dysfunction [18]. As regards the mechanism of this phenomenon, it has been speculated that an increase in the LV to RV pressure ratio also may reduce the degree of TR by the shift of the interventricular septum toward the RV [18, 19]. Recently Cools et al. [20] proposed PAB as “open-end” palliation for systemic RV dysfunction and progressive tricuspid regurgitation in 14 patients aged 0.9–14.9 years. Whether this strategy will be applied to adults with isolated ccTGA remains to be seen.
11.4 Clinical Manifestation in Adulthood
11.4.1 Clinical Manifestation of Adult Unoperated ccTGA and the Timing of Diagnosis
The adult with ccTGA presents in various ways, and the clinical course is quite variable depending on the presence and severity of associated lesions. If there are no associated defects, or well-balanced circulation due to the combination of the lesions, the patient will typically be asymptomatic early in life. Diagnosis can be made later in adulthood, when patients present with complete heart block or congestive heart failure, or incidentally when an ECG, chest X-ray, or echocardiogram is performed for other reasons.
According to the report from the Mayo Clinic adult congenital heart disease database from 1986 to 2000 of the unoperated adult (≧18 years old) with ccTGA, the correct diagnosis was first made at the age older than 18 years old in 66% of patients, 17% of whom were more than 60 years old at the time of diagnosis [21]. And more strikingly, adult patients with unoperated ccTGA are often misdiagnosed in adulthood and are referred late with the presence of symptomatic systemic AV valve (SAVV) regurgitation, significant right ventricular dysfunction, and AV block. Beauchesne et al. reported that 53% of adult unoperated patients had advanced systemic ventricular dysfunction at the time of referral, and, often, they have had severe SAVV regurgitation ≧3/4 in 59% of them [21] and therefore were deemed as “referred late.”
11.4.2 Natural History
The natural history of patients with ccTGA is largely dictated by the function of the systemic RV and by the presence or absence of associated abnormalities.
In general, ccTGA is known to have an unfavorable natural history. Most patients with lesions will develop progressive RV dysfunction, relatively early in life, and may not, in great majority, live over 50 years of age. A single center database review from the Toronto Congenital Cardiac Centre for Adults of 131 patients with ccTGA showed a mortality rate of 21% in patients >18 years of age, with a mean age at death of 33 years. Several studies documented an increasing incidence of cardiac failure with advancing age; this late consequence is extremely common by the fourth and fifth decades. A multicenter study conducted by the International Society for Adult Congenital Cardiac Disease of 182 patients with adult ccTGA (≧18 years old) has demonstrated that by the age of 45 years, 67% of patients with associated lesions and 25% of patients without significant associated lesions had congestive heart failure [22].
In contrast, in the setting of ccTGA without any other associated anomalies, the ventricular function is adequate to maintain a “normal” physical activity into adulthood [23, 24]. Some patients, but very rare, may survive to the seventh and eighth decades when no associated anomalies exist being discovered as a chance finding at autopsy [25, 26].
11.4.2.1 Mechanism of Systemic Right Ventricular Failure
The exact mechanism of SV failure is unknown but may relate to microscopic structural features and fiber orientation of the RV myocardium. The morphologically RV lacks the helical myocytic arrangement, essential to the twisting or torsion of the ventricle, and thus being unable to sustain the demands of a systemic ventricle, unlike LV [27].
Other possibilities include coronary perfusion mismatch, because the cardiac hypertrophy caused by the pressure overload on the morphological right ventricle may surpass the coronary artery oxygen supply, which comes mainly from the right coronary artery. A high incidence of myocardial perfusion defects with regional wall-motion abnormalities and impaired ventricular contractility has been reported [28]. Systemic ventricular dysfunction is also caused by volume overload due to AV valve regurgitation or complete AV block.
11.4.2.2 The Left-Sided Morphologically Tricuspid Valve
The natural history of the left-sided morphologically tricuspid valve is variable. The valve tends to remain competent during the first decade of life but slowly becomes progressively incompetent during the second to fifth decades of life. If there is an Ebsteinoid malformation of the valve, the regurgitation can be seen at birth. In the majority of patients, the SAVV is morphologically abnormal, and with time, there is increasing regurgitation. Beauchesne et al. [21] reported that adult unoperated ccTGA obtained prevalence of systemic valvar regurgitation of 59%, and 68% of them underwent systemic AV valve replacement.
11.4.2.3 Rhythm Abnormality: Complete Atrioventricular Block and Atrial Tachyarrhythmias
Approximately one-tenth of infants born with congenitally corrected transposition have complete heart block [29, 30]. In patients born with normal cardiac conduction, the risk of developing heart block over time increases by 2% per year until it reaches a prevalence of 10–15% by adolescence and 30% in adulthood [31].
Around two-fifths of adult patients, nonetheless, will have normal cardiac conduction throughout their lives. As time passes, the PR interval prolongs, until complete heart block becomes manifest [2].
11.4.2.4 Impact of Atrial Situs on Natural History
Oliver et al. [32] reviewed the long-term outcome of 38 adult ccTGA patients (≧18 years old) to compare the natural history of two anatomic arrangements, situs inversus vs situs solitus, and concluded that the natural prognosis was significantly better in situs inversus than that in situs solitus. Ebstein-like anomaly or spontaneous complete atrioventricular block was rare, and late complications are uncommon in patients with ccTGA with situs inversus. It has been speculated that the good septal alignment in ccTGA with situs inversus might preclude of AV conduction disorders and tricuspid valve abnormalities.
11.4.3 Unnatural History of Operated Patients
11.4.3.1 Long-Term Outcome and Complications After the Physiological Repair
Long-term results of this type of surgical repair are disappointing [33, 34]. Hraska et al. [33] reported the outcomes of 123 patients with ccTGA who underwent a variety of surgical procedures. The 10-year survival after physiological repair was only 67%, and systemic RV dysfunction occurred in 44% of patients. Freedom from RV dysfunction was approximately 40% at 15 years with factors predicting RV dysfunction being Ebstein’s anomaly, tricuspid valve replacement, and postoperative complete heart block.
As regards the impact of the individual procedures, Bogers et al. [35] reviewed the long-term outcome of Rastelli-type and non-Rastelli-type physiological repairs for ccTGA. Actuarial survival at 20 years was 62% for the non-Rastelli group and 67% for the Rastelli group. Freedom from reoperation was 47% at 20 years in the non-Rastelli group and 21% at 19 years for the Rastelli group. Tricuspid valve regurgitation was more often seen in the non-Rastelli group, whereas redo operations were performed predominantly in the Rastelli group mainly for conduit obstruction.
The impact of preoperative TR is crucial in the physiological repair, and it has been documented that when no tricuspid valve regurgitation is present preoperatively, a survival rate of 72% at 30 years can be reached with the physiological repair [36].
11.4.3.2 Long-Term Outcome and Complications After the Anatomical Repair: The DSO and the Rastelli/Senning Procedure
Series of the DSO and the Rastelli/Senning procedure have been published by several groups in large centers with early mortality currently of 0–10% and long-term survival at 10 years of 80–95% [14, 36–41]. Another factor to be considered for interpreting the outcome of anatomical repair is the learning curve for such complex operations and the recent progress in technical modification.
As regards the type of anatomical repair (the DSO vs Rastelli/Senning), more recently it has been reported that the long-term outcome of the DSO was more favorable than the other with an excellent reoperation-free survival, and this procedure should be considered as the optimal procedure of choice [38, 39]. Hiramatsu et al. [38] reviewed 90 patients with ccTGA from 1983 to 2010 underwent the Rastelli–Senning/Mustard procedure (group I) and the DSO (group II). Although survival, including hospital and late mortality at 20 years, was similar (75.7% in group I vs. 83.3% in group II), freedom from reoperation was 77.6% in group I vs. 94.1% in group II. Similarly, Gaies et al. [39] demonstrated that the 10-year survival was superior in the patients who underwent the DSO compared to the Rastelli–Senning.
In contrast, the outcome of the Rastelli/Senning operation for ccTGA with LVOTO and VSD has been improved with the technical modification and the improvement in the materials for extracardiac conduit. For patients with pulmonary stenosis and restrictive VSD, additional DKS anastomosis seems to be an effective approach to avoid postoperative systemic ventricular outflow tract obstruction and surgical heart block, as reported by Hoashi et al. [13].
The Complication of the Anatomical Repair
There is a definite incidence of late occurrence of various complications relating to anatomical repair. The complications after the atrial switch include sinus nodal dysfunction, supraventricular arrhythmias, and problems with the atrial baffle obstruction. If the ventricular switch is used, the left ventricular outflow obstruction due to the stenosis of VSD or intracardiac rerouting baffle, aortic regurgitation, or RV-PA conduit obstruction and regurgitation can occur. After the DSO, coronary arterial obstruction or stenosis, aortic valvar regurgitation, and pulmonary arterial stenosis may be evidenced.
Outcome of Retraining the Morphological Left Ventricle for Isolated ccTGA
In the isolated ccTGA, during childhood, the subpulmonary LV has been successfully retrained using a strategy of multi-staged PAB in order to provide an increased pressure load on the LV and promote LV hypertrophy. Recent studies documented that the failure rate of LV training before anatomical repair from 0 to 20% is mainly due to LV dysfunction. One of the best predictors of failure of retraining is age, with most successfully retrained patients being <10 years of age [14, 16, 17]. Devaney et al. [16] reported that the two oldest patients, aged 12 and 14 years, had LV failure necessitating removal of the band PAB among 15 patients who underwent PAB for the LV retraining. Poirier et al. demonstrated that the success rate was only 20% in patients older than 12 years old, whereas 62% of the patients less than 12 years old successfully completed LV retraining [17]. Therefore, surgical retraining of the LV is an option in children but not in adults due to unfavorable outcomes. LV retraining is even a challenging task in older children.
LV Dysfunction After DSO
Systolic dysfunction of the LV is relatively common after the double switch procedure [15, 40, 41]. In a retrospective, single-institution study of a total of 113 ccTGA patients, Murtuza et al. [41] demonstrated that freedom from death, transplantation, or poor LV function at 10–14 years was significantly lower in the DSO compared to the Rastelli–Senning group, despite the better actuarial survivals at 10 years in the former group. Quinn et al. [15] reported that patients requiring LV retraining prior to the DSO may be more at risk of developing significant LV dysfunction (6 of 11 patients: 55 %) than patients whose the left ventricle remains at systemic pressure at birth (6 of 33 patients 16 %).
LV dysfunction has been also noticed by several groups, regardless of the proceeded PAB to retrain LV, and is attributed to various factors including complete AV block, aortic regurgitation, and mitral regurgitation [41, 42]. LV function in patients who did not have a large left to right shunt preoperatively demonstrated to be better than in the group who had a large VSD or patent ductus arteriosus as a cause of LV preparedness [40].
The occurrence of LV dysfunction indicates that the DSO is still fraught with imperfections. The Rastelli group apparently more often required conduit revisions but has otherwise performed well.
11.4.3.3 Anatomical vs Physiological Repair
As regards the benefit of the anatomical repair in the actuarial survival rate, Shin’oka et al. [36] reported that there were no statistical differences in the long-term survival rates between the physiological and anatomic surgical repairs. Nevertheless, the outcome of the physiological repair was much worse in patients with significant preoperative TR (the survival at 30 years: 71.9% without TR vs 19.1% with TR). In contrast, results of the anatomical repair were favorable even for patients with significant TR (71.8% 30 years), and, therefore, the anatomical repair should be a procedure of choice for those patients with significant TR. Conversely, the physiological repair still remains a viable option with an acceptable long-term survival when patients do not have significant TR before their operation.
In 2010 Lim et al. [43] analyzed 167 patients with ccTGA who underwent biventricular repairs and demonstrated the superiority of anatomical repair compared to the physiological repair in the long-term outcome for systemic AV valve and ventricular function.
Freedom from TR and RV dysfunction was significantly higher in the anatomical repair than in the physiological repair (74.5% at 18 year vs 7.4% at 22 year for freedom from TR and 86.3% at 18 years vs 19% at 23 years for freedom from RV dysfunction, respectively). The reoperation-free ratio was 10.1% at 22 years after the physiological repair and 46.2% at 15 years after the anatomical repair. Meta-analysis of individual patient data reported by Alghamdi et al. [44] including 11 studies revealed superiority of the anatomical repair for in-hospital mortality.
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