Congenital corrected transposition of the great arteries (cc-TGA)

Congenital corrected transposition of the great arteries (cc-TGA or l-TGA) is a very rare and complicated heart defect (it affects 0.5–1% of all congenital heart defects). 

As with d-TGA, the large arteries originate from the wrong pumping chamber, i.e., the aorta from the right ventricle and the pulmonary artery (PA) from the left ventricle. In addition, in cc-TGA, the pumping chambers are also connected to the wrong atrium, i.e., the right atrium to the left pumping chamber and the left atrium to the right chamber. Overall, this means that the venous oxygen-poor (blue) blood from the body enters the right atrium, then the left ventricle, and from there is correctly ejected into the pulmonary artery. From the lungs, where the blood is enriched with oxygen, it flows back into the left atrium, from there into the right ventricle, and is then ejected into the body via the aorta. 

If there are no additional congenital heart defects, this “double switch” initially results in a functioning circulation, which is why we refer to this heart defect as “congenitally corrected,” because blood circulation is normal and oxygen enrichment in the lungs and blood and oxygen transport to the organs function properly, even though the large vessels and the two ventricles are reversed. 

However, this “corrected” system has a weak point, because the right ventricle is now on the side of the “systemic circulation” and thus on the side of higher pressure. The right ventricle cannot withstand this increased strain in the long term, as it is not designed for this purpose in the same way as the left ventricle. As a result, this “anatomically right ventricle” fails. Increasing leakage of the tricuspid valve (which belongs to the right ventricle) is often a sign of right ventricular failure in the systemic circulation.

In this heart defect, a “left rotation” of the heart, which initially develops as a tube, occurs during the fourth to eighth week of pregnancy, in contrast to a “right rotation” that occurs in healthy hearts. Because of this left rotation, it is also referred to as l-TGA (laevo = left). In a quarter of children with cc-TGA, there may also be a malposition of all the internal organs in the chest and abdominal cavity. All organs that are normally located on the right side are then located on the left side, which is referred to as “situs inversus.”

In addition to cc-TGA, there is often a defect in the ventricular septum (ventricular septal defect, VSD), a narrowed outflow tract to the lungs or a narrowing of the pulmonary valve itself, or changes to the tricuspid valve (valve belonging to the right ventricle). 

The right ventricle can withstand the higher strain in the systemic circulation for varying lengths of time. In most cases, this ventricle ultimately fails after 20 to 30 years. 

Together with a large ventricular septal defect and a certain narrowing of the outflow tract to the lungs (pulmonary stenosis), this heart defect may remain undetected for a long time, as the blood is enriched with oxygen in the lungs, as mentioned above, and the left ventricle supports the right ventricle.

The right ventricle can usually only withstand the increased pressure of the systemic circulation for a limited time. The symptoms in children with cc-TGA can vary greatly depending on the additional congenital heart defects present. Children may also be completely symptom-free for a long time.

If there is no pulmonary stenosis, symptoms may occur much earlier. If, for example, there is still a large VSD, much more blood flows from left to right and from there into the lungs, leading to flooding of the lungs even in infancy.

In cases of very severe pulmonary stenosis, cyanosis (blue discoloration of the skin) may also be observed.

If the right ventricle fails and the tricuspid valve leaks, blood backs up into the lungs, which can cause breathing difficulties. At the same time, too little blood is pumped into the body's circulation, leading to heart failure, which can manifest itself in your child as a significant reduction in performance, shortness of breath during minor exertion, increased respiratory infections, difficulty drinking, and delayed growth. Cardiac arrhythmias may also occur.

Due to the diversity of accompanying heart defects and the resulting symptoms, a reliable diagnosis and appropriate treatment at a center with experience in this type of heart defect are extremely important.

The reasons for the development of this complex heart defect are not yet fully understood, but it is assumed that many different factors and environmental influences play a role (multifactorial).

At the German Heart Center at Charité, we have set ourselves the goal of performing the complicated double switch operation on patients when the conditions are right. After correction, the left ventricle can then support the systemic circulation, which is the task for which it was actually intended. 

Of course, the left ventricle must also be suitable for this. We have examined the “ideal conditions” for a double switch operation very carefully and in collaboration with pediatric heart surgeons and pediatric cardiologists in order to be able to make the best possible decision for each patient. To do this, we use precise ultrasound findings, but also MRI of the heart to better assess the muscle mass of the anatomically left ventricle and thus its “existence in the systemic circulation.” 

In a study we conducted, we arrived at new thresholds that we can now apply to all future patients. It has been shown that lower muscle mass and volume of the left ventricle than previously recommended in earlier studies are sufficient to successfully perform a double switch operation.

Since cc-TGA is associated with a very complex clinical picture, which presents itself in each child with different accompanying anomalies and different functions of both ventricles, the decision as to which therapy is most suitable in terms of quality of life and life expectancy must be made on an individual basis. 

There are basically two treatment concepts: “anatomical” and “physiological” correction. At the German Heart Center at Charité, we prefer anatomical correction, provided that the necessary conditions are met. 

In anatomical correction, the blood from the body and lungs is diverted in the atrium so that it reaches the correct ventricle (i.e., blood from the body to the right ventricle and blood from the lungs to the left ventricle). The aorta and pulmonary artery are then repositioned so that they now originate from the correct ventricle: the aorta from the left ventricle and the pulmonary artery from the right ventricle. This is done with a procedure known as a “double switch operation,” which is one of the most complicated operations in pediatric heart surgery. 

In contrast to double switch surgery (DSO), in physiological correction the two ventricles remain in their respective positions and only accompanying anomalies such as a VSD are corrected by closing the VSD with a patch or narrowing of the right outflow tract by removing the thickened muscle tissue. However, the right ventricle and its associated tricuspid valve are not permanently suitable for supporting the systemic circulation and will not be able to withstand this increased strain in the long term. However, when this “failure” of the right ventricle and tricuspid valve occurs varies greatly and is individual to each patient. 

Therefore, if the anatomical situation allows, we prefer early anatomical correction to prevent the progression of right ventricular and tricuspid valve failure. However, this anatomical correction (DSO) is not possible in every patient, as the anatomical left ventricle must be sufficiently prepared to perform its tasks in the systemic circulation. The literature specifies certain criteria that must be met in order to successfully perform this DSO. We examined all of the criteria mentioned in our patients who had already undergone surgery and identified the following influencing factors: patient age, muscle mass, volume and function of the left ventricle and mitral valve.

If these conditions are not met, the anatomical left ventricle can be “trained” by applying a pulmonary artery band (PAB) and creating an atrial septal defect (ASD). The PAB forces the left ventricle to build up higher pressure, which transports more blood volume through the ASD. This ultimately leads to an increase in muscle mass and volume in the anatomically left ventricle.

If there is an additional VSD, the creation of a pulmonary artery band may also be necessary to prevent pulmonary congestion. 

If there is a pronounced narrowing of the (anatomically left) outflow tract toward the lungs, this can lead to a significant lack of oxygen in the blood, as mentioned above, which can cause cyanosis in the child. This may require palliative surgery in the form of a “shunt” that directs more blood to the pulmonary circulation via a connection between the aorta and the pulmonary artery until a definitive correction can be performed. 

If one of the two ventricles is significantly underdeveloped, correction may not be possible. In this case, univentricular palliation can be performed according to the Fontan principle, as with a single-chamber heart, but this may be associated with the known complications of Fontan circulation in the long term (see Univentricular Heart/Fontan Palliation).

Due to the wide variety of congenital heart defects and the resulting diversity and complexity of possible corrective surgeries, double switch surgery is not offered in all pediatric cardiac surgery clinics in Germany, but only in larger ones. As an alternative to correction, it is often suggested to wait and see as long as no symptoms are visible, or to perform symptom-oriented surgery (physiological correction). These are usually less complicated operations that also work for a certain period of time. 

At the German Heart Center at Charité (DHZC), we have extensive experience in caring for patients after complex corrective procedures. Our intensive care unit is staffed by pediatricians, pediatric intensive care physicians, and pediatric intensive care nurses with years of experience. They are knowledgeable about the treatment and possible complications and can therefore avoid them or detect them early and treat them in a timely manner. In the rare case that heart failure occurs after corrective surgery that cannot be remedied with medication, we have heart support systems of all sizes available. The artificial heart treatment team at the DHZC has the most experience worldwide in the use, handling, and removal of such artificial heart systems in children and adults. Our extensive experience with such rare and complex heart defects is reflected in the excellent postoperative progress of our patients. Further information can be found in our externally validated quality assurance standards and annual quality reports.

To the pediatric heart surgery quality report

Depending on the type of surgery performed (palliative or corrective), the child can in most cases resume normal activities after a varying recovery period. 

If a shunt is initially created as a “palliative measure” until complete correction, the oxygen saturation in the blood must be closely monitored during this time. For this purpose, we also use home monitoring with pulse oximetry after discharge.

If a pulmonary artery band has been placed, the increasing muscle mass of the anatomically left ventricle must be closely monitored; otherwise, there are no restrictions for the patient.

If it was possible to perform a double switch operation, there is nothing to prevent normal physical activity after the hospital stay and an appropriate recovery period. However, in the weeks, months, and even years following the operation, precise checks must be carried out by a pediatric cardiologist in private practice in order to closely monitor the child's further development and also to monitor the function of the left ventricle, which is now in the systemic circulation.

If univentricular palliation in the form of a Fontan circulation was necessary, there are various complications (pulmonary effusions, cardiac arrhythmias, liver dysfunction) that could occur after the operation. In principle, even with a Fontan circulation, an acceptable quality of life can often be achieved today, albeit with a reduced life expectancy. In order to maintain this in the long term, close monitoring by a pediatrician is necessary.

The sternum, which we have to cut lengthwise during this operation, usually takes about four to six weeks to heal completely and become stable. After that, there is nothing to prevent normal physical activity.