Transposition of the great arteries

Question 1

TGA - background

Answer 1

1. Aorta and pulmonary arteries arise from incorrect ventricles
2. Two parallel circulations
3. Systemic venous blood flowing through R side of heart back into aorta
4. Pulmonary venous blood through left side of heart into pulmonary circulation
5. Not compatible with life. Survival dependent on mixing of blood between these two parallel circuits via foramen ovale, ductus arteriosus or a septal defect

Question 2

TGA - clinical features

Answer 2

1. Infants usually present in the first few hours or days with worsening duct dependent
   cyanosis
2. Hypoxia is usually severe, but heart failure is not a feature
3. This is a medical emergency and early diagnosis and intervention are required to avoid severe hypoxia

Is there SOB?

Question 3

TGA - ix (3)

Answer 3

Bedside

1. ECG
   - Shows normal ventricular complexes
   - May manifest T-wave abnormalities (?)

Imaging

2. CXR
   - Shows normal-sized/mildly enlarged heart with contour that sometimes resembles an egg on its side
   - Pulmonary vascular markings are usually increased (why?)
3. Echo
   - **Dx

Does an oxygen test (?) need to be performed?

Question 4

TGA - mx (3->5)

Answer 4

A. Balloon atrial septostomy

1. May be required as an emergency procedure to improve systemic arterial oxygen saturation Venous access typically through umbilical vein/femoral vein. Inflatable balloon-tipped catheter passed into LA via foramen ovale under U/S guidance
2. Balloon is then inflated and forcefully withdrawn into RA, in order to tear the atrial septum and create an ASD - results in an increase in highly saturated pulmonary venous blood flow into the right atrium and then into the systemic circulation

B. Can also improve systemic arterial oxygenation with prostaglandin E infusion

C. Surgery

4. After successful balloon septostomy, most infants will manage comfortably for many days or weeks. Surgical correction involves transecting the great arteries and re-anastomosing them to the appropriate ventricle
5. The arterial switch procedure is preferably performed in the first few weeks of life. After this time, the normal decline in pulmonary vascular resistance (why?) leads to atrophy of the LV such that it becomes less accustomed to working at a higher workload, which is problematic when restored to the systemic circulation postoperatively. If operation is delayed and there is concern regarding ability of LV to support the systmeic ciruclation, then strategies such as preparatory banding of pulmonary artery (?)/postoperative mechanical support may be employed