Transposition of the great arteries (in this case, dextro-transposition) occurs when the aorta arises directly from the right ventricle and the pulmonary artery arises from the left ventricle, resulting in independent, parallel pulmonary and systemic circulations; oxygenated blood cannot reach the body except through openings connecting the right and left sides of the heart (eg, patent foramen ovale, ventricular septal defect [VSD]). Symptoms are primarily severe neonatal cyanosis and occasionally heart failure, if there is an associated VSD. Heart sounds and murmurs depend on the presence of associated congenital anomalies. Diagnosis is by echocardiography. Definitive treatment is surgical repair.
(See also Overview of Congenital Cardiovascular Anomalies.)
Transposition of the great arteries (TGA) is a broad term that includes both dextro-TGA (d-TGA) and a rarer defect called levo-TGA (l-TGA).
d-TGA: A more common variation in which the aorta is positioned to the right and front of the pulmonary artery, arising from the right ventricle rather than the left.
l-TGA: A less common variation in which the aorta is positioned to the left and front of the pulmonary artery. This anomaly is usually associated with ventricular inversion due to leftward looping of the primitive heart tube, resulting in the condition commonly known as congenitally corrected transposition.
Because d-TGA is by far the most common form, it is often simply called transposition. d-TGA is discussed in this topic, and l-TGA is discussed elsewhere. There are also other rare variants of the transposition of the great arteries, but d-TGA and l-TGA are the most common.
Dextro-transposition of the great arteries (see figure Dextro-transposition of the great arteries) accounts for 5 to 7% of congenital heart anomalies. About 30 to 40% of patients have a ventricular septal defect (VSD); up to 25% have left ventricular outflow tract obstruction (either pulmonic valve or subpulmonary stenosis).
Dextro-transposition of the great arteries
Unoxygenated blood returning to the right heart enters the AO, causing severe cyanosis. Oxygenated blood returning to the LA enters the pulmonary circulation again. The RV is hypertrophied, and the foramen ovale permits minimal mixing. Atrial pressures are mean pressures. AO = aorta; IVC = inferior vena cava; LA = left atrium; LV = left ventricle; PA = pulmonary artery; PV = pulmonary veins; RA = right atrium; RV = right ventricle; SVC = superior vena cava. |
Pathophysiology of TGA
Systemic and pulmonary circulations are completely separated in transposition of the great arteries. After returning to the right heart, desaturated systemic venous blood is pumped into the systemic circulation without being oxygenated in the lungs; oxygenated blood entering the left heart goes back to the lungs rather than to the rest of the body. This anomaly is not compatible with life unless desaturated and oxygenated blood can mix through openings at one or more levels (eg, atrial, ventricular, or great artery level).
Symptoms and Signs of TGA
Severe cyanosis occurs within hours of birth, followed rapidly by metabolic acidosis secondary to poor tissue oxygenation. Patients with a moderate or large atrial septal defect, a large ventricular septal defect, a patent ductus arteriosus, or a combination of these tend to have less severe cyanosis, but symptoms and signs of heart failure (eg, tachypnea, dyspnea, tachycardia, diaphoresis, inability to gain weight) may develop during the first weeks of life.
Except for generalized cyanosis, physical examination is rather unremarkable. Heart murmurs may be absent unless associated anomalies are present. The second heart sound (S2) is single and loud.
Diagnosis of TGA
Chest x-ray and ECG
Echocardiography
Diagnosis of transposition of the great arteries is suspected clinically, supported by chest x-ray and ECG, and established by 2-dimensional echocardiography with color flow and Doppler studies.
On chest x-ray, the cardiac shadow may have the classic egg-on-a-string appearance with a narrow upper mediastinum. ECG shows right axis deviation and right ventricular hypertrophy but may be normal for a neonate.
Image provided by Jeanne Marie Baffa, MD.
Cardiac catheterization is not usually necessary for diagnosis but may be done to enlarge the atrial communication (balloon atrial septostomy) or to further elucidate complex coronary artery anatomy.
Treatment of TGA
Prostaglandin E1 (PGE1) infusion
Sometimes balloon atrial septostomy
Surgical repair
Unless arterial oxygen saturation is only mildly decreased and the atrial communication is adequate, a PGE1 infusion may help by opening and maintaining patency of the ductus arteriosus; this infusion increases pulmonary blood flow, which may promote left-to-right atrial shunting, leading to improved systemic oxygenation. However, if the patent foramen ovale has a small opening, PGE1 may have the opposite effect because the increased blood return to the left atrium may close the flap of the foramen ovale, leading to decreased mixing, along with elevation of left atrial pressure and pulmonary edema. Also, opening the ductus may decrease systemic blood flow. Thus, PGE1 must be used with caution, and patients must be monitored closely.
Pulmonary edema and respiratory failure may require mechanical ventilatory support.
Pearls & Pitfalls
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For severely hypoxemic neonates who do not immediately respond to PGE1 or who have a very restrictive foramen ovale, cardiac catheterization and balloon atrial septostomy (Rashkind procedure) can immediately improve systemic arterial oxygen saturation. A balloon-tipped catheter is advanced into the left atrium through the patent foramen ovale. The balloon is inflated and abruptly withdrawn to the right atrium to enlarge the opening in the atrial septum. As an alternative to taking the neonate to the catheterization laboratory, the septostomy procedure can be done at the bedside under echocardiographic guidance.
Definitive repair of d-TGA is the arterial switch (Jatene) operation, typically done during the first week of life. The proximal portions of the great arteries are transected, the coronary arteries are transplanted to the native pulmonary root, which will become the neoaortic root, the aorta is connected to the left ventricle, and the pulmonary artery is connected to the right ventricle. Survival rate after surgery is > 95%. An associated VSD should be closed at the time of primary repair unless it is small and hemodynamically insignificant. Native pulmonic stenosis is problematic unless it is mild because pulmonic stenosis will effectively become aortic stenosis after the arterial switch procedure. If pulmonic stenosis is moderate or severe, other surgical options may need to be considered.
Because of the technical difficulties of transplanting the coronary arteries in neonates and infants, the arterial switch procedure could not be done before the early 1980s (1). Prior to that era, patients with D-TGA were treated with an "atrial switch" operation, referred to as either a Mustard or Senning procedure. This operation reconstructed the atrial septum and placed an intra-atrial baffle to divert the superior vena cava and inferior vena cava return to the left ventricle and the pulmonary venous return to the right ventricle. There are many adults with D-TGA born before 1980 who had this repair (2, 3). However, these patients have a very high incidence of the long-term sequelae of dysfunction of the systemic right ventricle, atrial arrhythmias, and baffle obstructions. Because of those sequelae, the arterial switch procedure became the preferred approach once it was technically feasible.
Endocarditis prophylaxis is recommended preoperatively but is required only for the first 6 months after repair unless there is a residual defect adjacent to a surgical patch or prosthetic material.
Treatment references
1. Castaneda AR, Norwood WI, Jonas RA, et al: Transposition of the great arteries and intact ventricular septum: Anatomical repair in the neonate. Ann Thorac Surg 38:438–443, 1984. doi: 10.1016/s0003-4975(10)64181-1
2. Kempny A, Dimopoulos K, Uebing A, et al: Outcome of cardiac surgery in patients with congenital heart disease in England between 1997 and 2015. PLoS One 12(6):e0178963, 2017. doi:10.1371/journal.pone.01789631
3. Meadows AK: Transposition of the Great Arteries after Mustard/Senning Repair. Adult Congenital Heart Association June 15, 2016. Accessed November 3, 2011. https://www.achaheart.org/your-heart/health-information/transposition-of-the-great-arteries-after-mustardsenning-repair/
Key Points
In dextro-transposition of the great arteries (d-TGA), the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle, resulting in independent pulmonary and systemic circulations.
d-TGA is incompatible with life unless mixing of the circulations occurs through an atrial and/or ventricular septal opening, or a patent ductus.
Severe cyanosis occurs within hours of birth, followed rapidly by metabolic acidosis; there are no murmurs unless other anomalies are present.
Relieve cyanosis by giving prostaglandin E1 infusion to keep the ductus arteriosus open and sometimes by using a balloon catheter to enlarge the foramen ovale.
Do definitive surgical repair during the first week of life.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
American Heart Association: Common Heart Defects: Provides overview of common congenital heart defects for parents and caregivers
American Heart Association: Infective Endocarditis: Provides an overview of infective endocarditis, including summarizing prophylactic antibiotic use, for patients and caregivers
