Chapter 9

### Background

Transposition of the great arteries (TGA) is a form of congenital heart defect (CHD) defined by ventricular–arterial discordance with the aorta arising from the right ventricle and the pulmonary artery (PA) arising from the left ventricle. Overall TGA accounts for 5% to 7% of all forms of CHD. The incidence ranges from 21.1 to 30.3 per 100,000 live births. Males are more commonly affected then females, accounting for 60% to 70% of cases. Untreated, 90% of infants will die within the first year of life, and 30% will die within the first week. In 1966, Rashkind and Miller performed the balloon atrial septostomy for the first time in a baby with TGA; this intervention dramatically influenced the survival of neonates with TGA.1 Unlike other forms of CHD that have a high association with extracardiac anomalies, only 10% of patients with TGA have a coexisting extracardiac defect.2

TGA can take on many different anatomic forms with an assorted range of physiologic characteristics. Two of the most common forms of transposition are often referred to as dextro-TGA (d-TGA), or classic transposition, and levo-TGA (l-TGA). The letters d (dextro or rightward) and l (levo or leftward) stem from the Van Praagh segmental nomenclature system and refer to the anatomic position of the aortic valve in relation to the pulmonary valve.

The term d-TGA represents patients who have atria and ventricles in their correct anatomic position but have an aorta arising from the morphologic right ventricle (RV) and a PA originating from the morphologic left ventricle (LV). Patients with d-TGA most commonly have an aorta that is rightward and anterior to the PA (Figure 9-1).

###### Figure 9-1

Dextro-transposition of the great arteries (d-TGA). The aorta (AO) arises from the right ventricle (RV), and the pulmonary artery (PA) arises from the left ventricle (LV). An atrial septal defect (ASD) and patent ductus arteriosus (PDA) are commonly present. The left coronary artery (LCA) and right coronary artery (RCA) can be seen arising from the aorta. LA, left atrium; RA, right atrium. (© 2011 The Children's Hospital of Philadelphia, All Rights Reserved.)

In l-TGA, also known as congenitally corrected TGA (ccTGA), the right atrium drains into the anatomic LV (which is right-sided), and the left atrium drains to the anatomic RV (on the left side of the heart). The aorta arises from the left-sided morphologic RV, and the PA arises from the right-sided morphologic LV (Figure 9-2). Although these patients have the anatomic diagnosis of TGA, patients with l-TGA have “normal physiology,” with an LV pumping deoxygenated blood to the lungs and an RV providing oxygenated blood to the body.

###### Figure 9-2

Levo-transposition of the great arteries (l-TGA). The right atrium drains ...

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