Transposition of the Great Arteries (TGA)

Key Features

Essentials of Diagnosis

• Cyanotic newborn without respiratory distress

• More common in males

General Considerations

• Accounts for 5% of all cases of congenital heart disease

• Male-to-female ratio is 3:1

• Caused by an embryologic abnormality in the spiral division of the truncus arteriosus in which the aorta arises from the right ventricle (RV) and the pulmonary artery from the left ventricle (LV); this is referred to as "ventriculoarterial discordance"

• Left unrepaired, transposition is associated with a high incidence of early pulmonary vascular obstructive disease

• Because pulmonary and systemic circulations are in parallel, survival is impossible without mixing between the two circuits

Clinical Findings

• Many neonates are large (up to 4 kg) and profoundly cyanotic without respiratory distress or a significant murmur

• Patients may have a ventricular septal defect (VSD) or the ventricular septum may be intact

• Infants with a large VSD may be less cyanotic and usually have a prominent murmur

• Obstruction to outflow from either ventricle is possible

• Coarctation must be ruled out

Diagnosis

Imaging

• Chest radiography

  • Usually nondiagnostic

  • Sometimes there is an "egg on a string" appearance because the aorta is directly anterior to the main pulmonary artery, giving the image of a narrow mediastinum

• Echocardiography

  • Two-dimensional imaging and Doppler evaluation demonstrate the anatomy and physiology well

  • The aorta arises from the RV and the pulmonary artery arises from the LV

  • Associated defects (such as RV or LV outflow tract obstruction or VSD) or coarctation must be evaluated

  • The atrial septum should be closely examined, as any restriction could prove detrimental as the child awaits repair

Diagnostic Procedures

• Electrocardiography

  • Looks normal because the newborn ECG normally has RV predominance

• Cardiac catheterization and angiocardiography

  • Rashkind balloon atrial septostomy

    • Frequently performed if the interatrial communication is restrictive

    • Can be done at the bedside with echocardiographic guidance

  • Coronary anatomy can be delineated by ascending aortography if not well seen by echocardiography.

Treatment

• Early corrective surgery is recommended

• The arterial switch operation (ASO) is performed at age 4–7 days

  • Has replaced the previously performed atrial switch procedures (Mustard and Senning operations)

  • The arteries are transected above the level of the valves and switched, while the coronaries are separately reimplanted

  • Small associated VSDs may be left to close on their own, but large VSDs are repaired

  • The atrial septal defect is also closed

• For patients with TGA and an intact ventricular septum

  • Early surgical repair (<14 days of age) is vital to avoid potential deconditioning of the LV as it pumps to the low-resistance pulmonary circulation

  • If a large, unrestrictive VSD is present,

    • LV pressure is maintained at systemic levels

    • LV does not become deconditioned

    • Corrective surgery can be delayed for a few months

• For ...