74: Transposition of the Great Arteries

Epidemiology

• Transposition of the great arteries (TGA) is the most common cyanotic cardiac anomaly, accounting for approximately 10 percent of congenital cardiac malformations.

Morphology

• The aorta arises from the right ventricle (RV) and the pulmonary artery (PA) from the left ventricle (LV). More than 50 percent of patients have an intact ventricular septum (IVS), while the remainder is split between a ventricular septal defect (VSD) with and without pulmonary stenosis (PS). The coronary artery pattern is variable; the most common one involves the left circumflex and left anterior descending (LAD) coronary arteries arising from the leftward and the right coronary artery (RCA) from the rightward sinus, respectively.

Pathophysiology

• Systemic and pulmonary circuits are in parallel, with the degree of cyanosis depending on mixing at the atrial septal defect (ASD), patent ductus arteriosus (PDA), or VSD level, as well as with the degree of coexisting PS.

Clinical features

• In the absence of PS, pulmonary overcirculation ensues, with variable cyanosis determined by the adequacy of mixing. Cases of TGA with adequate PS and VSD can remain asymptomatic for a prolonged period. Infants with late presentation exhibit LV deconditioning from prolonged exposure of the LV to low pulmonary pressures.

Diagnosis

• Electrocardiography (ECG) and chest x-ray (CXR) suggest the diagnosis in the cyanotic newborn. Echocardiography defines the relationship between the great vessels, associated ASD/VSD/PDA/coronary patterns and estimates LV pressures. Cardiac catheterization is rarely required in the current era.

Treatment

• In patients with an IVS, severe cyanosis can be improved with percutaneous intervention (balloon or blade atrial septostomy). The arterial switch operation (ASO) with or without VSD closure is the operation of choice, performed after LV training with PA banding in patients with a deconditioned LV. In patients with significant PS and cyanosis, temporary palliation with a modified Blalock–Taussig shunt can be performed before repair with a Rastelli or Nikaidoh operation.

Outcomes

• Excellent outcomes are reported, with an operative mortality of less than 5 percent; long-term complications are represented by supravalvar PS, neoaortic regurgitation or stenosis, and coronary insufficiency.