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Transposition of the Great Arteries
Transposition of the great arteries 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 (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 vary depending on the presence of associated congenital anomalies. Diagnosis is by echocardiography. Definitive treatment is surgical repair.
Transposition of the great arteries (TGA—see Figure: Transposition of the great arteries.) accounts for 5 to 7% of congenital heart anomalies. About 30 to 40% of patients have a VSD; 5% have subpulmonary stenosis.
Transposition of the great arteries.
Systemic and pulmonary circulations are completely separated. 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).
Severe cyanosis occurs within hours of birth, followed rapidly by metabolic acidosis secondary to poor tissue oxygenation. Patients with a large VSD, a patent ductus arteriosus, or both are less cyanotic, 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 2nd heart sound (S 2 ) is single and loud.
Diagnosis 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 ventricular hypertrophy but may be normal for a neonate.
Cardiac catheterization is not usually necessary for diagnosis but may be done to enlarge the atrial communication.
Unless arterial O 2 saturation is only mildly decreased and the atrial communication is adequate, a PGE 1 infusion (0.01 to 0.1 mcg/kg/min IV) 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, PGE 1 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. Also, opening the ductus may decrease systemic blood flow. Thus, PGE 1 must be used with caution and patients must be monitored closely. Metabolic acidosis is treated with NaHCO 3 . Pulmonary edema and respiratory failure may require mechanical ventilatory support.
For severely hypoxemic neonates who do not immediately respond to PGE 1 or who have a very restrictive foramen ovale, cardiac catheterization and balloon atrial septostomy (Rashkind procedure) can immediately improve systemic arterial O 2 saturation. A balloon-tipped catheter is advanced into the left atrium through the patent foramen ovale. The balloon is inflated with diluted radiopaque dye 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 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, and 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. Pulmonic stenosis is problematic unless it is mild and can be addressed surgically at the time of the arterial switch procedure.
Endocarditis prophylaxis is recommended preoperatively but is required only for the first 6 mo after repair unless there is a residual defect adjacent to a surgical patch or prosthetic material.
In transposition of the great arteries (TGA), the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle, resulting in independent pulmonary and systemic circulations.
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 PGE 1 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.
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