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KEY POINTS
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Key Points

  • Transposition of the great arteries is a relatively rare congenital cardiac malformation that has potential to cause major morbidity and mortality in the neonatal period.

  • Complete TGA results in separation of the systemic and pulmonary circulations, because of ventriculoarterial discordance, and leads to severe hypoxia in the early neonatal period.

  • Corrected TGA has both atrioventricular and ventriculoarterial discordance, so that effectively pulmonary and systemic circulations are normal, thereby rarely resulting in pediatric morbidity.

  • Prenatal diagnosis of complete TGA is achieved by noting a parallel path of the ventricular outflow tracts, with lack of the normal crossover of these vessels.

  • Prenatal recognition of complete TGA is critical, as immediate pediatric cardiology intervention in the early neonatal period will be required.

  • The surgical treatment of choice for complete TGA has changed from the atrial switch to the arterial switch procedure, and is associated with excellent long-term survival.

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CONDITION
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Transposition of the great arteries (TGA) may be either complete or corrected. Complete TGA is also known as d-transposition, simple transposition, or atrioventricular concordance with ventriculoarterial discordance. This anomaly probably occurs because of failure of the aorticopulmonary septum to follow a spiral course during embryogenesis, resulting in the aorta arising from the right ventricle and the pulmonary artery arising from the left ventricle (de la Cruz et al., 1981). Atrial septal defect (ASD) and ventricular septal defect (VSD) are commonly seen with complete TGA and may also be associated with pulmonary artery obstruction. This is a potentially critical abnormality because, without a persistent communication between right and lefts sides of the heart, both the systemic and pulmonary circulations will run in parallel thereby preventing adequate oxygenation. Complete TGA usually causes no significant hemodynamic compromise when the fetus is in utero, but rapid deterioration occurs soon after birth in those cases without sufficient mixing of the right- and left-sided circulations.

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In a cohort of 130 neonates delivered with TGA, Jouannic et al. (2004) noted that 13 of 130 neonates (10%) with TGA had profound hypoxemia (defined as a Pao2 < 25 mmHg) and metabolic acidosis (pH < 7.15) in the first 30 minutes of life (Jouannic et al., 2004). Fortunately, concurrent cardiac structural anomalies such as VSDs may allow for communication between right and left sides of the heart to allow adequate mixing of blood. Even in infants with an intact ventricular septum, a nonrestrictive foramen ovale and patent ductus arteriosus may also allow for adequate mixing of systemic circulation and oxygenated venous return to avoid significant hypoxemia early in the neonatal course. However, neonates with an intact ventricular septum and either a restrictive foramen ovale or constricted ductus arteriosus may experience significant preoperative morbidity due to inadequate intracardiac mixing. In these cases, severe hypoxemia may necessitate immediate balloon atrioseptostomy in order to prevent end organ damage from ongoing hypoxemia.

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In order to optimally plan for delivery and neonatal management, efforts have been directed at identifying fetal echocardiographic predictors of fetuses who will ...

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