CONGENITALLY CORRECTED TRANSPOSITION OF THE GREAT ARTERIES
(L-TGA)

The congenitally corrected transposition of the great arteries (L-TGA) is a rare congenital heart disease characterized by an abnormal ventricular and arterial arrangement. In this condition, the aorta arises from the right ventricle, while the pulmonary artery arises from the left ventricle, with a concomitant ventricular inversion. The right ventricle is positioned on the left side and receives blood from the left atrium, while the left ventricle is on the right side and receives blood from the right atrium. This compensatory inversion allows for a physiological blood flow and normal oxygenation, avoiding the cyanosis typical of other congenital heart diseases. However, in the long term, the systemic right ventricle, not being designed to withstand high-pressure loads, tends to dilate and deteriorate, progressively leading to heart failure and valvular insufficiency.

Clinical Presentation

The symptoms of L-TGA vary depending on the presence of associated defects and the progression of systemic right ventricular dysfunction.
In the neonatal and infant stages, many patients remain asymptomatic, especially in the absence of additional structural abnormalities. Diagnosis at this stage is often incidental, discovered during prenatal screening or following a cardiology examination due to the presence of a heart murmur.
In children with associated defects, such as ventricular septal defect or pulmonary stenosis, early signs of heart failure may appear, including tachypnea, feeding difficulties, and poor growth. During adolescence and early adulthood, the disease progression becomes more evident.
The systemic right ventricle, not being designed to withstand high pressures, begins to show signs of functional deterioration. Patients may experience fatigue, reduced exercise tolerance, and exertional dyspnea, sometimes accompanied by palpitations or arrhythmic episodes. The failure of the right atrioventricular valve, anatomically corresponding to the tricuspid valve, may worsen over time, causing venous congestion and peripheral edema.
In adulthood, the clinical picture may evolve into overt heart failure, with paroxysmal nocturnal dyspnea, orthopnea, dependent edema, and ascites.
Ventricular arrhythmias and atrial fibrillation become more frequent, increasing the risk of embolic events. In more advanced cases, deterioration of the cardiac conduction system often leads to complete atrioventricular block, which may present with syncopal episodes and require pacemaker implantation.

Complications

Beyond progressive heart failure, L-TGA is associated with several complications.
The systemic right ventricle, not structurally suited to sustain high pressures for decades, tends to dilate, progressively reducing ejection fraction and predisposing to right atrioventricular valve insufficiency.
Tricuspid valve regurgitation, in particular, is one of the main causes of heart failure, as annular dilation and leaflet dysfunction lead to atrial overload and progressive venous congestion. Another common complication is complete atrioventricular block, which occurs due to the abnormal positioning of the His bundle.
Progressive deterioration of the cardiac conduction system, related to myocardial fibrosis and right ventricular dilation, may necessitate pacemaker implantation. In patients with advanced ventricular dysfunction, the risk of malignant ventricular arrhythmias significantly increases, sometimes requiring an implantable defibrillator to prevent sudden cardiac death.

Diagnosis

The diagnosis of L-TGA can occur prenatally, in the neonatal period, or later in life, depending on the presence of symptoms or associated cardiac defects.
Fetal echocardiography can identify ventriculo-arterial discordance and ventricular inversion as early as the second trimester of pregnancy, especially in cases where other congenital defects are present. However, in isolated cases without associated abnormalities, diagnosis may be more challenging and occur later. In neonates and young children, postnatal echocardiography is the primary diagnostic tool, particularly in the presence of heart murmurs or signs of heart failure.
In asymptomatic patients, the condition may be incidentally detected during routine examinations or in response to findings of conduction abnormalities on electrocardiographic studies.

Treatment

Treatment aims to prevent and manage complications associated with disease progression.
Heart failure therapy relies on the use of beta-blockers, SGLT2 inhibitors, diuretics, and ARNI to reduce ventricular load and improve systemic right ventricular function.
In patients with complete atrioventricular block, pacemaker implantation is necessary to ensure proper electrical conduction.
In those at high risk for malignant ventricular arrhythmias, an implantable defibrillator serves as a key preventive strategy.
In selected cases, surgical interventions such as atrioventricular valve replacement or the double-switch operation may be considered.
In patients with advanced heart failure unresponsive to medical therapy, heart transplantation remains the only long-term treatment option.

References
1. Baruteau AE, et al. Cardiac conduction system in congenitally corrected transposition of the great arteries and its clinical relevance. J Am Heart Assoc. 2017;6(12):e007759.
2. Cohen MS, et al. Echocardiographic assessment of transposition of the great arteries and congenitally corrected transposition of the great arteries. Echo Res Pract. 2019;6(4):R107-R119.
3. Graham TP, et al. Long-term outcome in congenitally corrected transposition of the great arteries: a multi-institutional study. J Am Coll Cardiol. 2000;36(1):255-261.
4. Hutter PA, et al. Twenty-five years' experience with the arterial switch operation. J Thorac Cardiovasc Surg. 2002;124(4):790-797.
5. Marino B, et al. Trasposizione delle grandi arterie. Qualche spiraglio nell'inquadramento patogenetico. G Ital Cardiol. 2003;4(3):237-241.
6. Martins P, et al. Transposition of the great arteries. Orphanet J Rare Dis. 2008;3:27.
7. Warnes CA, et al. Transposition of the great arteries. Circulation. 2006;114(24):2699-2709.