Transposition of the Great Arteries

TGA is an important duct-dependent cardiac defect. A patient may be present in the exam following BT shunt placement or after corrective surgery.

Transposition of the great arteries (TGA) –  the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. TGA may be associated with VSD (50%), left ventricular outflow tract obstruction (25%) or abnormalities of the mitral and tricuspid valves .

Less common than ToF as a cause for cyanotic heart disease.

Survival after birth depends on the mixing of the systemic/RV circuit and the pulmonary/LV circuit. This can occur at the PFO and ductus, but when the ductus closes (1-14 days) there is usually insufficient mixing to allow systemic oxygenation and the baby will become progressively cyanotic and then acidotic.
This process will be less dramatic if there is a coexistant VSD.
As there is no pulmonary overcirculation and blood flow (volume) to the body is not affected, there are no signs of heart failure.

Diagnosis using hyperoxic test and exclusion of causes of respiratory cyanosis. Prostaglandin E1 to maintain duct patency and transfer to centre for anatomical diagnosis.
Balloon atrial septostomy (via umbilical vein/ femoral vein) to allow mixing. Once patient is stabilised, corrective surgery ( arterial switch operation) is carried out before 2 weeks of age.
If discovered after neonatal period: 2 stage procedure with pulmonary artery banding to train left ventricular muscles, followed by switch operation.

Clinical (post-op in examination)
Not cyanosed. Median sternotomy scar.
Possible scar in groin from catheter procedure.
Ejection systolic mumur on left upper sternal edge radiating to left axilla and back but not so much on right axilla. This is due to left pulmonary artery narrowing due to compression by aorta after the switch operation.

ECG – Normal or Right Axis Deviation/Right Ventricular Hypertrophy
CXR – Normal or ‘egg-on-side’ appearance.

Exam vignette
I examined Tom, a 7-year-old boy who looks well-grown for his age and I would like to plot his height and weight on a growth chart.
He is pink and not in respiratory distress. There are no dysmorphic features or finger clubbing.
There is a median sternotomy scar on his chest.
He has a grade 3/6 ejection systolic murmur on audible on left upper sternal edge which is radiating to left axilla and the back.
The findings  are consistent with repaired complex congenital heart condition. My differential diagnosis include transposition of great artery which was repaired and complicated by left pulmonary artery narrowing following switch operation.

Filed in Cardiovascular
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