COMPLETE TRANSPOSITION OF THE GREAT ARTERIES (d-TGA)

The complete transposition of the great arteries (d-TGA) is a cyanotic congenital heart disease characterized by a discordant ventriculo-arterial connection, where the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. This configuration results in two parallel and separate circulatory circuits, making the condition incompatible with life without interventions that allow the mixing of oxygenated and deoxygenated blood.

d-TGA accounts for approximately 5-7% of all congenital heart diseases. In a significant percentage of cases, associated anomalies may be present, including ventricular septal defects (VSD) and left ventricular outflow tract obstruction.

In d-TGA, the connection of the great vessels is reversed compared to normal cardiac anatomy. The aorta arises from the right ventricle instead of the left, while the pulmonary artery arises from the left ventricle instead of the right. This results in two separate circulatory circuits, where the right ventricle pumps deoxygenated blood directly into the systemic circulation, while the left ventricle receives oxygenated blood and recirculates it to the lungs without distributing it to the organs.
Without an intracardiac or extracardiac shunt, d-TGA would rapidly become fatal in the neonatal period.
Neonatal survival depends on the presence of natural shunts that allow blood mixing between the two circuits. The main compensatory mechanisms include the patent foramen ovale (PFO) or atrial septal defect (ASD), which enables blood flow between the atria, the patent ductus arteriosus (PDA), which connects the pulmonary artery and the aorta to facilitate blood mixing, and the ventricular septal defect (VSD), which allows communication between the ventricles.
When these shunts are absent or insufficient, severe cyanosis occurs, which does not respond to oxygen therapy, leading to rapid clinical deterioration.

Clinical Presentation

Newborns with d-TGA present with severe cyanosis within a few hours of birth, unresponsive to oxygen therapy. They may exhibit tachypnea, feeding difficulties, progressive metabolic acidosis, and neonatal heart failure.
The severity of the clinical presentation depends on the presence and adequacy of intracardiac or extracardiac shunts. Severe hypoxia due to circuit separation leads to reduced systemic oxygenation, resulting in metabolic acidosis and multi-organ dysfunction. Additionally, the right ventricle, having to pump against a greater resistance than its normal function, undergoes progressive hypertrophy, while the left ventricle, inadequately stimulated, tends to become hypotrophic.
After birth, the ductus arteriosus tends to close, worsening cyanosis. Although pulmonary vascular resistance gradually decreases, this is insufficient to compensate for the altered systemic circulation. Oxygen therapy is ineffective as it does not alter the separation of the circuits.

Prenatal Diagnosis

d-TGA can be diagnosed prenatally through fetal echocardiography during the second-trimester morphology scan. Early diagnosis allows optimal planning of delivery and neonatal care.

Management and Treatment

The management and treatment of newborns with complete transposition of the great arteries involve two phases:

1. Neonatal stabilization: Initial management includes the administration of prostaglandins (PGE1) to keep the ductus arteriosus open and balloon atrial septostomy (Rashkind procedure), a palliative procedure that creates an artificial ASD to improve systemic oxygenation.
2. Definitive surgical correction (Jatene procedure): This consists of an arterial switch operation to be performed within the first two weeks of life. During surgery, the aorta and pulmonary artery are transected and reattached to their corresponding ventricles, restoring normal circulation. Additionally, the coronary arteries are transferred to the neo-aorta, ensuring adequate myocardial perfusion. This intervention restores normal cardiac physiology and has survival rates exceeding 95% in specialized centers.

With early diagnosis and timely intervention, the prognosis is excellent. However, long-term follow-up is essential to monitor potential complications such as ventricular dysfunction, residual obstructions, or arrhythmias.

References
1. Marelli AJ, Mackie AS, Ionescu-Ittu R, Rahme E, Pilote L. *Congenital Heart Disease in the General Population: Changing Prevalence and Age Distribution.* Circulation. 2007;115(2):163-172.
2. Marino B, Digilio MC, Toscano A, Giannotti A, Dallapiccola B. *Trasposizione delle grandi arterie: aspetti embriologici e considerazioni fisiopatologiche.* G Ital Cardiol. 1999;29(6):681-688.
3. Pasquini L, Mellander M, Seale A, Matsui H, Roughton M, Ho SY. *Diagnosi prenatale della trasposizione delle grandi arterie.* Heart. 2007;93(11):1431-1436.
4. Mocumbi AO, Sliwa K, Soma-Pillay P. *Cardiopatie congenite nel neonato: presentazione clinica e diagnosi.* Cardiovasc J Afr. 2012;23(3):112-117.
5. Fraser CD Jr, Jaquiss RD, Rosenthal DN, Humpl T. *Early Survival After Pediatric Heart Transplantation: Effect of Center Volume, Pulsatile Perfusion, and VAD Strategy.* Ann Thorac Surg. 2012;93(2):637-644.
6. Jatene AD, Fontes VF, Paulista PP, Souza LC, Neger F, Galantier M, Sousa JE.** *Anatomic correction of transposition of the great vessels.* J Thorac Cardiovasc Surg. 1982;83(1):20-26.
7. Yuan SM, Shinfeld A, Mishaly D, Raanani E. *Anatomic repair of transposition of the great arteries: a review of the Jatene procedure in the current era.* Isr Med Assoc J. 2008;10(6):511-515.
8. Bonhoeffer P, Boudjemline Y, Saliba Z, Merckx J, Aggoun Y, Bonnet D, Sidi D, Kachaner J.** *Percutaneous replacement of pulmonary valve in a right-ventricle to pulmonary-artery prosthetic conduit with valve dysfunction.* Lancet. 2000;356(9239):1403-1405.