11.4: Transposition of the Great Arteries
- Page ID
- 42788
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Introduction
Transposition of the great arteries (TGA) accounts for 5-8% of all congenital heart defects and occurs 2-3 times more frequently in males. TGA is best defined as a normal atrioventricular connection with an abnormal ventricular–arterial connection; the morphological left atrium is connected through the left ventricle with the pulmonary artery and the morphological right atrium through the right ventricle with the aorta. (Figure 11.4.1)The aorta is often located on the right side and in front of the pulmonary artery (D-TGA). In 70 percent there is an isolated form of TGA, in 30 percent the TGA is accompanied by other heart defects, like VSD or obstruction of the left ventricle outflow tract.
Pathophysiology
The circulation in TGA patients is not serial but parallel (Figure 11.4.2); the venous blood is returned to the systemic circulation through the right atrium and ventricle, while the arterial oxygenated blood is directed back into the pulmonary artery through the left atrium and ventricle. Due to this abnormal circulation there is severe cyanosis directly after birth, therefore it is critical for the ductus arteriosus and foramen ovale to remain open. Without treatment there is a mortality of 30% within one week, 50% within one month and 90% within one year. When an associated VSD is present the chances of survival are higher due to more shunting thus more oxygenated blood in the systemic circulation. These patients are able to reach early adulthood without corrective surgery or intervention. However the pulmonary hypertension that develops in this situation will eventually lead to severe problems.
Treatment
Mortality of TGA has dramatically improved from 90 percent for unoperated patients to rates of less than 5 percent following corrective surgery using the arterial switch operation. Most patients are referred for surgical repair during the first three to five days of life. The choice of surgical procedure is dependent on the presence and nature of other cardiac anomalies. In patients without any other cardiac defect (simple D-TGA), arterial switch operation is the recommended procedure. In general, the arterial switch operation has replaced the earlier atrial switch procedures developed by Mustard and Senning. In patients with D-TGA and a ventricular septal defect (VSD), the preferred procedure is arterial switch operation and VSD closure. In patients with D-TGA, large VSD, and significant pulmonary stenosis, the Rastelli procedure, an alternative surgical approach, should be considered. In some cases, arterial switch operation with or without repair of the left ventricular outflow obstruction is used. Both the arterial switch operation and Rastelli procedures are surgical anatomic corrections resulting in a morphologic left ventricle as the systemic ventricle. In comparison to atrial switch procedures, which involved the rerouting of venous return in the atria and are now only rarely performed, the arterial switch operation appears to have similar long-term survival rates with reduced long-term morbidity primarily due to a lower risk of atrial arrhythmias and heart failure. As a result, it is the recommended procedure in most patients with D-TGA.
Outcome
The long-term survival rates for patients with D-TGA following surgical correction are excellent for both arterial switch operation and atrial switch procedures. The long-term survival 20 years after discharge is about 95 and 80 percent for arterial switch and atrial switch respectively. Progressive congestive heart failure and sudden death are the principal causes of death. Perioperative mortality is greater in patients with complex (additional cardiac anomaly) D-TGA compared to those with simple D-TGA. There are no clinical trials comparing outcomes of arterial switch and atrial switch procedures. Reintervention is common following both approaches.
Patients who undergo surgical repair for D-TGA have a reduced exercise capacity primarily due to pulmonary disease. Patients after arterial switch operation appear to have better exercise capacity than those who underwent atrial switch procedures. The decrease in exercise capacity, however, does not limit ordinary activity as most patients meet the criteria for New York Heart Association functional class I.
It appears that patients with D-TGA may have mild long-term neurodevelopmental impairment, most likely due to perioperative factors including hypoxemia, acidosis, cardiopulmonary bypass, and hemodynamic instability.