Transposition of the great arteries (TGA) is the most common cyanotic congenital heart lesion that presents in neonates. The hallmark of transposition of the great arteries is ventriculoarterial discordance, in which the aorta arises from the morphologic right ventricle and the pulmonary artery arises from the morphologic left ventricle. See the images below.
Although transposition of the great arteries was first described over 2 centuries ago, no treatment was available until the middle of the 20th century, with the development of surgical atrial septectomy in the 1950s and balloon atrial septostomy in the 1960s. These palliative therapies were followed by physiological procedures (atrial switch operation) and anatomic repair (arterial switch operation). Today, the survival rate for infants with transposition of the great arteries is greater than 90%.
The major anatomic classifications of transposition of the great arteries depend on the relationship of the great arteries to each other and/or the infundibular morphology. In approximately 60% of the patients, the aorta is anterior and to the right of the pulmonary artery (dextro-transposition of the great arteries [d-TGA]). However in a subset of patients, the aorta may be anterior and to the left of the pulmonary artery (levo-transposition of the great arteries [l-TGA]). In addition, most patients with transposition of the great arteries (regardless of the spacial orientation of the great arteries) have a subaortic infundibulum, an absence of subpulmonary infundibulum, and fibrous continuity between the mitral valve and the pulmonary valve. Despite these useful classifications, several exceptions are noted, and, hence, discordant ventriculoarterial connection is the only distinguishing characteristic that defines transposition of the great arteries.
From a practical standpoint, the presence or absence of associated cardiac anomalies defines the clinical presentation and surgical management of a patient with transposition of the great arteries. The primary anatomic subtypes are (1) transposition of the great arteries with intact ventricular septum, (2) transposition of the great arteries with ventricular septal defect, (3) transposition of the great arteries with ventricular septal defect and left ventricular outflow tract obstruction, and (4) transposition of the great arteries with ventricular septal defect and pulmonary vascular obstructive disease.
In approximately one third of patients with transposition of the great arteries, the coronary artery anatomy is abnormal, with a left circumflex coronary arising from the right coronary artery (22%), a single right coronary artery (9.5%), a single left coronary artery (3%), or inverted origin of the coronary arteries (3%) representing the most common variants.
The pulmonary and systemic circulations function in parallel, rather than in series. Oxygenated pulmonary venous blood returns to the left atrium and left ventricle but is recirculated to the pulmonary vascular bed via the abnormal pulmonary arterial connection to the left ventricle. Deoxygenated systemic venous blood returns to the right atrium and right ventricle where it is subsequently pumped to the systemic circulation, effectively bypassing the lungs. This parallel circulatory arrangement results in a deficient oxygen supply to the tissues and an excessive right and left ventricular workload. It is incompatible with prolonged survival unless mixing of oxygenated and deoxygenated blood occurs at some anatomic level.
The following are 3 common anatomic sites for mixing of oxygenated and deoxygenated blood in transposition of the great arteries:
Ventricular septal defect (See the images below.)This 2-dimensional echocardiogram (parasternal long-axis view) shows a patient with transposition of the great arteries and ventricular septal defect. The pulmonary artery arises from the posterior (left) ventricular, dives posteriorly, and bifurcates immediately into left and right branch pulmonary arteries. A large ventricular septal defect is present in the outlet septum.This 2-dimensional echocardiogram (apical 4-chamber view) shows a patient with transposition of the great arteries and ventricular septal defect. The anterior aorta arises from the right-sided right ventricle.
One or all of these lesions can be present in concert with dextro-transposition of the great arteries, and the degree of arterial hypoxemia depends on the degree of anatomic mixing.
The etiology for transposition of the great arteries is unknown and is presumed to be multifactorial.
The embryology likely involves abnormal persistence of the subaortic conus with resorption or underdevelopment of the subpulmonary conus (infundibulum). This abnormality aligns the aorta anterior and superior with the right ventricle during development.
United States data
Despite its overall low prevalence, transposition of the great arteries is the most common etiology for cyanotic congenital heart disease in the newborn.  This lesion presents in 5-7% of all patients with congenital heart disease. The overall annual incidence is 20-30 per 100,000 live births, and inheritance is multifactorial. Transposition of the great arteries is isolated in 90% of patients and is rarely associated with syndromes or extracardiac malformations. This congenital heart defect is more common in infants of diabetic mothers.
Race-, sex-, and age-related demographics
No racial predilection is known, but transposition of the great arteries has a 60-70% male predominance.
Patients with transposition of the great arteries usually present with cyanosis in the newborn period, but clinical manifestations and courses are influenced predominantly by the degree of intercirculatory mixing.
The prognosis depends on the specific anatomic substrate and type of surgical therapy used (arterial switch operation, atrial switch operation, or Rastelli procedure).
Overall, perioperative survival following arterial switch operation is greater than 90%. Long-term and arrhythmia-free survival is excellent (approximately 97% at 25 years), and late mortality is predominantly due to sudden death and myocardial infarction. 
The overall mortality rate following an atrial level switch is low; however, long-term morbidity associated with systemic (right) ventricular dilatation and failure, systemic atrioventricular (tricuspid) valve regurgitation, and atrial bradyarrhythmias and tachyarrhythmias is significant.
After arterial switch operation, sequelae may include chronotropic incompetence and neoaortic, pulmonary, and coronary artery complications. However, most patients maintain normal systolic function and exercise capacity.  A subset of patients may experience profound right ventricular failure, but they may do well with left ventricular retraining and late arterial switch. 
Progressive neoaortic root dilation is common and is a risk factor for neoaortic valve regurgitation following arterial switch operation. Continued surveillance of this population is required. 
The mortality rate in untreated patients is approximately 30% in the first week, 50% in the first month, and 90% by the end of the first year. With improved diagnostic, medical, and surgical techniques, the overall short-term and midterm survival rate exceeds 90%.
Long-term complications are secondary to prolonged cyanosis and include polycythemia and hyperviscosity syndrome. These patients may develop headache, decreased exercise tolerance, and stroke. Thrombocytopenia is common in patients with cyanotic congenital heart disease leading to bleeding complications.
Patients with a large ventricular septal defect, a patent ductus arteriosus, or both may have an early predilection for congestive heart failure, as pulmonary vascular resistance falls with increasing age. Heart failure may be mitigated in those patients with left ventricular outflow tract (pulmonary) stenosi.
Arterioplasty in patients with right ventricular outflow tract obstruction (RVOT) following arterial switch surgery may be an effective and durable management option in the immediate term.  In a retrospective study (2004-2013) comprising 223 patients who underwent arterial switch for transposition of the great arteries, 38 patients (16%) developed RVOT within 12.5 months. The surgical morbidity for RVOT management (eg, main pulmonary artery plasty) was 13%, without hospital or late mortality. At the 41.2 months last RVOT postsurgical follow-up, all the patients had NYHA grade 0 or 1 symptoms. 
A small percentage (approximately 5%) of patients with transposition of the great arteries (and often a ventricular septal defect) develop accelerated pulmonary vascular obstructive disease and progressive cyanosis despite surgical repair or palliation. Long-term survival in this subgroup is particularly poor.
Complications include the following:
Congestive heart failure
Eisenmenger syndrome (irreversible and progressive pulmonary vascular obstructive disease)
Rare cases of supravalvular aortic stenosis as a late complication of transposition of the great arteries have been reported. 
Family members should learn cardiopulmonary resuscitation (CPR).
Educate family members about congenital heart disease.
Obtain genetics counseling for future pregnancy, despite the relatively low risk of recurrence.
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