Anatomy and physiology

For a more detailed review, the reader is invited to read any of the outstanding anatomic reports already devoted to the malformation,^1–3 along with the review of echo-morphologic correlations which precedes our own review in this supplement.⁴ In the heart with usual atrial arrangement, the right-sided morphologically right atrium connects through the mitral valve to the right-sided morphologically left ventricle, while the left-sided morphologically left atrium connects to the left-sided morphologically right ventricle through its tricuspid valve. The key feature is mirror-imaged arrangement of the ventricles, so-called left-hand ventricular topology, or “l-looping”. The morphologically left ventricle supports the pulmonary trunk, and the morphologically right ventricle gives rise to the aorta, which in most instances is anterior and leftward relative to the pulmonary trunk. In some patients with discordant atrioventricular connections, there may be double outlet from the morphologically right ventricle, or a single outlet with pulmonary atresia. These variants are not strictly “double discordance”, albeit closely related because of the discordant atrioventricular connections. All of these patterns can also be found in mirror-imaged form when there is mirror-imagery of the atrial chambers and the other organs of the body, so-called “situs inversus.” In this setting, however, the ventricles are usually arranged with right-hand topology, or “d-looping.” The anatomic situation can be further complicated when the heart is right-sided, with its apex pointing to the right. This is the usual pattern with mirror-imaged atrial arrangement, and a frequent finding with the usual atrial arrangement. The heart, however, can also be left-sided, with the apex pointing to the left, when the atrial chambers are mirror-imaged. These discrepancies between atrial arrangement and cardiac position can further complicate diagnosis and surgical management.

It was the work by Anderson et al.⁵ that elucidated the anatomy of the conduction tissue in congenitally corrected transposition, albeit that, as they explained, they did no more than rediscover work previously published in the German literature.⁶ Rather than the atrioventricular node being located in its anticipated position at the apex of the triangle of Koch, the node and penetrating bundle of His are displaced anteriorly, being found in the vestibule of the right atrium inferior to the mouth of the right atrial appendage. The atrioventricular bundle penetrates to pass anterior to the orifice of the pulmonary valve before extending to branch on the crest of the ventricular septum, the bundle branches then being mirror-imaged in the setting of usual atrial arrangement, along with the ventricles. In the presence of a ventricular septal defect, the non-branching part of the atrioventricular bundle is located anterior and superior to the defect itself. Dual atrioventricular nodes, with dual penetrating bundles, may be found in some patients, with the second node and bundle occupying their anticipated positions relative to the triangle of Koch. In these settings, there is typically a “sling” of conduction tissue joining the nodes together along the crest of the ventricular septum.⁷ Rarely, there can be a solitary node and bundle in regular position, but this is very much the exception rather than the rule. Such regular nodes, and “slings”, are found when there is better alignment between the atrial and ventricular septal structures, as in double outlet right ventricle or pulmonary atresia. It had been thought that the node reverted to its regular position within the apex of the triangle of Koch in the presence of mirror-imaged atrial arrangement, but Hosseinpour and colleagues⁸ pointed out that this is almost certainly because all cases studied thus far had better alignment between the septal structures because of co-existing pulmonary stenosis or atresia. Straddlingof the mitral valve could be another of the reasons of better alignment of the atrial and ventricular septal structures.³

Associated malformations are almost always present, being found in approximately nine-tenths of patients.⁹ A ventricular septal defect, pulmonary stenosis, malformations of the morphologically tricuspid valve, and disturbances of atrioventricular conduction represent the most common and most important associated lesions. Because the flow of blood in congenitally corrected transposition is normal in the absence of associated malformations, such patients are often asymptomatic. The presence of a haemodynamically significant ventricular septal defect, however, will result in pulmonary hypertension, congestive cardiac failure, and failure to thrive, just as would be expected in patients with ventricular septal defects in the setting of concordant atrioventricular connections. When important pulmonary stenosis coexists with a ventricular septal defect, the physiology is often similar to that of tetralogy of Fallot, and cyanosis may be the presenting symptom. The morphologically tricuspid valve is frequently afflicted by Ebstein's malformation, with resulting regurgitation from the morphologically right ventricle to the left atrium. Regurgitation across the morphologically tricuspid valve can also occur because of shift of the ventricular septum. When the pressure is higher in the morphologically right ventricle than in the left ventricle, as may be seen in patients without associated anomalies or following surgical closure of a ventricular septal defect and/or relief of pulmonary stenosis, the shift of the ventricular septum towards the morphologically left ventricle produces distortion of the subvalvar apparatus of the tricuspid valve, and promotes regurgitation across the valve. This explains the not infrequent occurrence of tricuspid regurgitation following “uncomplicated” closure of the ventricular septal defect in infants. The long and tortuous pathway of the conduction tissue has been implicated in the occurrence of spontaneous complete heart block.⁴ Perhaps most importantly, over the longer term patients may develop significant dysfunction of the systemic morphologically right ventricle. Although this appears commonly in the presence of regurgitation across the morphologically tricuspid valve, it is not always clear which condition is the primary problem, and which is secondary.

Outcomes following traditional repair

A number of recent studies have investigated the long-term outcomes in patients who have not undergone any surgical procedures, and in others following traditional surgical techniques used for repair of the associated malformations that leave the morphologically right ventricle supporting the systemic circulation.^10–13 Prieto et al. from Columbia University¹¹ reported a poor survival rate once the diagnosis of tricuspid regurgitation had been made. In their report, survival was only 60 percent 5 years later. Importantly, surgery had no beneficial effect, perhaps reflecting the poor function of the morphologically right ventricle in many of these patients. In another report from the Mayo Clinic,¹⁴ survival was significantly improved when patients underwent replacement of the tricuspid valve before the onset of advanced right ventricular dysfunction. Both of these reports^{11, 14} underscore the poor prognosis in patients with tricuspid regurgitation, especially when the performance of the morphologically right ventricle is reduced. Similarly, another report from Laennec Hospital in Paris¹⁵ demonstrated that, for those patients with an associated ventricular septal defect and pulmonary stenosis, freedom from late replacement of the tricuspid valve, and/or insertion of a pacemaker, was a disappointing 40 percent at 5 years following repair. Overall survival was also low at 69 percent. A recent review from Children's Hospital in Boston,¹⁶ which included all patients presenting to that institution, demonstrated that freedom from right ventricular dysfunction was less than 60 percent 10 years after presentation. Survival following traditional repair was only 70 percent at 10 years. These reports highlight an immutable fact following traditional reparative techniques, namely that in significant numbers of patients, the morphologically right ventricle and the tricuspid valve function poorly when left in the systemic circulation. Although it cannot be stated with certainty from these reports whether morphologically right ventricular dysfunction precedes, and ultimately results in, tricuspid valvar regurgitation, or the other way round, it is likely that the morphologically right ventricle tolerates tricuspid regurgitation poorly when left at systemic workloads, and that dysfunction occurs fairly rapidly following its inception. In either case, however, the onset of either right ventricular dysfunction or tricuspid regurgitation predicts a poor prognosis. Both are more likely to occur following traditional repair, perhaps due to septal shift once left ventricular pressure is reduced. Because of all these considerations, there is now an increasing tendency to seek to achieve anatomic surgical repair, either by the so-called “double switch”, or by combining an atrial redirection procedure with redirection of left ventricular blood to the aorta.

Techniques of anatomic repair as used at the University of Michigan

Atrial redirection: the Senning procedure

With some modifications, we use the techniques established by Senning many years ago for the treatment of transposition with concordant atrioventricular connections. Perhaps the most significant difference between patients with regular transposition, as opposed to those with congenitally corrected transposition, is the size of the left atrium. For those patients with decreased pulmonary blood flow, the left atrium is often small, making the surgical reconstruction of the new pulmonary venous atrium more difficult. Thus, we routinely enlarge the pulmonary venous atrium with a patch (Fig. 1). The potential to injure the atrioventricular node must be kept in mind when constructing the pathways for systemic venous return, as the node is located in a more anterior position, and may be crossed by the suture line. The increased prevalence of right-sided hearts can further complicate the Senning procedure but has not, in our experience, led to greater technical difficulties. We do not recommend the use of a bidirectional Glenn anastomosis to reduce the likelihood of obstruction along the superior caval venous pathway.

Figure 1. Construction of the pulmonary venous atrium during the Senning procedure. A patch of autologous pericardium or cryopreserved homograft is inserted to augment the pulmonary venous pathway.

The arterial switch

As with the atrial switch, the techniques employed for the arterial switch are generally the same as those used for repair of regular transposition in the setting of concordant atrioventricular connections. The accepted principles for transfer of the coronary arteries apply, and are not substantially different (Fig. 2). We use the Lecompte manoeuvre, but the leftward position of the proximal neopulmonary trunk makes the connection to the bifurcation more difficult. Closure of the bifurcation, and extension of the incision towards the left, facilitates that anastomosis (Fig. 3).

Figure 2. Transfer of the coronary arteries during the arterial switch procedure.

Figure 3. The pulmonary arteries are reconstructed by shifting the anastomosis to the bifurcation leftward to achieve better alignment of the proximal pulmonary trunk. A trouser-shaped patch of autologous pericardium is used to augment the sinuses of Valsalva where the coronary arterial buttons were removed.

Outcomes

Numerous recent reports have reviewed the less than satisfactory results for traditional surgical repair, leaving the morphologically right ventricle supporting the systemic circulation.^18–20 Because of this, many centres have now opted for anatomic repair, restoring the morphologically left ventricle to supporting the systemic circulation.^21–29 We present here a brief review of the outcomes from our own institutions in Tokyo and Ann Arbor.

Experience at Tokyo Women's Medical University

Between January1972 and September 2005, a total of 195 patients, with a median age of 8.3 years, and a range from 2 months to 47 years old, with either congenitally corrected transposition, or discordant atrioventricular connections and double outlet right ventricle, underwent definitive repairs at the Heart Institute of Japan at Tokyo Women's Medical University. Since 1990, anatomic repair or definitive palliation has been performed in a total of 88 patients, either by means of the double switch, atrial redirection combined with the Rastelli procedure, the reversed Patrick-McGoon procedure combined with atrial redirection for those patients with double outlet right ventricle and suitable intracardiac anatomy (Fig. 4), or a Fontan procedure. For the purposes of this review, we evaluated the long-term results of surgery, performed before the age of 15 years, in those patients who underwent the double switch operation, the conventional Rastelli procedure, the Fontan procedure, along with those undergoing conventional repair for tricuspid regurgitation, simple closure of the ventricular septal defect, or relief of pulmonary stenosis, analyzing the results in those patients who were now older than 18 years at the time of the review. Actuarial survival rate was 50 percent at 25 years for the patients undergoing conventional repair, 80 percent at 25 years for those undergoing the Rastelli procedure, 85 percent at 20 years for those converted to the Fontan circulation, and 90 percent at 15 years in those having the double switch (Fig. 5). Long-term survival was low after conventional repair, but similar after a double switch, the Rastelli procedure, or conversion to the Fontan circulation. Freedom from re-intervention was similar in all groups, but re-intervention increased with time after the operations.

Figure 4. The cartoon shows the site of placement of the intraventricular baffle to achieve rerouting by the technique of Patrick and McGoon in suitable patients with discordant atrioventricular connections and double outlet ventricle. Abbreviations: MV: mitral valve; TV: tricuspid valve; A: aorta; PA: pulmonary trunk.

Figure 5. Actuarial survival following surgery at Tokyo Women's Medical University for patients with congenitally corrected transposition or discordant atrioventricular connections undergoing repair at less than 15 years of age, and who were more than 18 years old at the time of this review.

Experience at the University of Michigan with anatomic repair

To date, a total of 44 patients have undergone anatomic repair at the University of Michigan. The Senning procedure combined with the arterial switch procedure has been performed in 24 patients, ranging in age from 6 weeks to 8 years. One patient, a two year old male undergoing a double switch procedure combined with closure of a ventricular septal defect died when the heart became asystolic immediately following a rapid administration of amiodarone. No other patients have died, either early or late. Two patients needed support by extracorporeal membrane oxygenation, one preoperatively. There were no new permanent arrhythmias, although 4 patients had preexisting complete heart block. In one patient, who underwent retraining of the morphologically left ventricle at 7 years of age, we resorted eventually to cardiac transplantation due to persistent left ventricular diastolic dysfunction. Following the double switch, regurgitation across the tricuspid valve decreased in all those patients with significant tricuspid regurgitation preoperatively, without the need for surgical intervention on the tricuspid valve (Fig. 6). Reoperation was required in three patients, replacing a conduit in one, relieving obstruction in the superior caval venous pathway in another, and relieving pulmonary venous obstruction in the final one. Anatomic repair was achieved by combined Senning and Rastelli procedures in an additional 20 patients, ranging in age from 5 months to 5 years, with a median of 17 months. Of this group, two patients died before they could be discharged from the hospital, both secondary to neurologic complications. In both patients, early dysfunction of the right heart resulted in decreased cerebral perfusion pressure and subsequent brain death. Both patients had fully recovered their cardiac function after 48 hours, but were removed from life support when their neurologic state was confirmed.

Figure 6. The function of the morphologically tricuspid valve following the double switch procedure as assessed from the experience at the University of Michigan.

Conclusions

It is now accepted that the traditional surgical approaches to patients with congenitally corrected transposition or discordant atrioventricular connections are associated with less than satisfactory late outcomes. The association of tricuspid valvar regurgitation has been a poor prognostic indicator in all studies that have evaluated the natural history of this condition. The reduction of pressure in the morphologically left ventricle after traditional repair promotes an increase in regurgitation across the tricuspid valve, likely from septal shift, and this certainly contributes to the overall poor late outcomes. Replacement of the tricuspid valve once morphologically right ventricular function is significantly impaired is also associated with poor outcomes.

Anatomic repair has been shown to be associated with satisfactory early and intermediate outcomes, although late follow-up remains to be determined. Obstruction of the superior caval or pulmonary venous pathways, atrial arrhythmias, and regurgitation across the neoaortic valve are all potential late consequences of this approach. The latter may be particularly important following preliminary banding of the pulmonary trunk. The experience at the University Michigan, in addition to that of others, indicates that older patients are less likely to undergo satisfactory left ventricular retraining, although the precise cut-off in terms of age cannot be determined. Older patients with failing right ventricles, however, are probably optimally treated by cardiac transplantation.

At the University of Michigan, patients with congenitally corrected transposition and a ventricular septal defect undergo an elective double switch combined with closure of the ventricular septal defect. Infants and young children with moderate or more than moderate tricuspid valvar regurgitation are considered for banding of the pulmonary trunk to retrain the morphologically left ventricle for an eventual double switch. In those patients with a pulmonary valve deemed unsuitable for an arterial switch procedure, we seek to achieve repair by combing the Senning and Rastelli procedures, providing this is anatomically feasible. Early right ventricular dysfunction has been common in our experience following this procedure, likely due to the need to perform a right ventriculotomy, place a generous patch within the right ventricle, and insert a conduit between the right ventricle and the pulmonary arteries. Early support of the right heart with extracorporeal membrane oxygenation is likely to improve the outcomes in this group, particularly when cerebral perfusion pressure is low, and should be utilized until right ventricular function recovers.