Definition and Overview
The transposition of the great arteries (TGA) is a complex congenital heart condition with approximately 3-10% of patients with congenital heart disease born with it. In TGA, the main pulmonary artery arises from the left ventricle and the aorta arises from the right ventricle. Thus, instead of the normal flow of blood, wherein the pulmonary and systemic circulations are in series, the blood flow in patients with TGA are in a parallel circuit: the deoxygenated blood gets pumped to the rest of the body without passing through the lungs, while oxygenated blood is directed repeatedly to the lungs. A shunt, typically a hole in the atrial or ventricular septum or a connection between the aorta and pulmonary artery, allows the mixing of blood, which is necessary for survival. In effect, patients with TGA present with cyanosis (so-called “blue baby”) and poor oxygen saturation. Patients eventually experience symptoms of heart failure, such as breathing difficulty, in about a month.
Two techniques are commonly used to repair this condition: the arterial switch operation (ASO), which is the standard surgical treatment for the transposition of the great arteries, and the less commonly performed atrial switch.
Who Should Undergo and Expected Results
Patients with TGA need to undergo surgical intervention. If left untreated, up to 50% of patients with this condition die within the first month of life and up to 90% die before they reach one year of age.
Early surgical intervention is recommended, even in neonates as young as a few days old. Ideally, the procedure should be conducted in good candidates within the first few weeks or the first month of life, before the left ventricle loses its ability to work as the systemic pump. In some cases, a series of interventions may have to be performed before the actual repair, depending on the anatomy of the disease and the overall health condition of the patient. In patients with poor oxygen saturations, the shunt may have to be maintained or augmented via the infusion of prostaglandin or a procedure known as balloon atrial septostomy.
TGA repair is a complicated procedure but outcomes have greatly improved in recent years. At present, large studies have shown mortality rates as low as 2% to 3%. Higher operative risk is associated with complicated anatomies of the coronary arteries and problems with the aortic arch. The function of the left ventricle in the long-term has also been shown to be superior in patients undergoing the ASO compared to those subjected to the atrial switch. Late survival has been reported to be good, with 80% of patients alive ten years after undergoing the procedure.
How is the Procedure Performed?
The aim of TGA repair is to reroute the blood and approximate the normal pathway of blood flow. There are several ways to accomplish this, but the ASO is the treatment of choice nowadays.
The basic premise of the arterial switch operation is an anatomic correction of the disease. The pulmonary artery and the aorta are divided and “switched” back to the normal anatomic position: the pulmonary artery is connected to the right ventricle and the aorta is connected to the left ventricle. The shunt that enables the mixing of the blood is then closed off during the procedure to bring back the systemic and pulmonary circulations in series.
One of the most difficult and crucial parts of TGA repair is the management of the coronary arteries, the blood vessels that supply the heart. This entails the excision of the openings of the coronary arteries and reimplanting them to the vessel that is connected to the systemic circulation (neoaorta).
Although this is the very basic principle of the procedure, the surgery may involve many other steps, depending on the anatomic variations of the disease. Different operations, such as the Rastelli procedure, may be needed for TGA patients with more complex anatomies.
Possible Risks and Complications
As with any kind of open-heart surgery, there are many possible risks associated with TGA repair. These include bleeding, myocardial ischemia, and infection, to name a few. Cardiac rhythm abnormalities occur less with the ASO than with the atrial switch procedure. Early death with the ASO has been associated with problems in the coronary arteries and failure of the right ventricle.
More commonly encountered, however, is the development of pulmonary stenosis or narrowing after the procedure. This is the most common cause of reintervention after an arterial switch operation, occurring in approximately 10% of patients who underwent repair. In some patients, this may require a repeat operation while in others, it can be managed by less invasive means, specifically endovascular dilatation. There have also been rare reports of reoperations after ASO for other reasons, such as a residual defect in the septum, obstruction of the aorta, and stenosis of the coronary arteries.
[Guideline] Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: guidelines from the American Heart Association: a guideline from the American Heart Association Rheumatic Fever, Endocarditis and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group. J Am Dent Assoc. 2007 Jun. 138(6):739-45, 747-60.
Takeuchi D, Nakanishi T, Tomimatsu H, Nakazawa M. Evaluation of Right Ventricular Performance Long After the Atrial Switch Operation for Transposition of the Great Arteries Using the Doppler Tei Index. Pediatr Cardiol. 2005 Aug 17.