Congenitally corrected transposition of the great arteries (levo-Transposition of the Great Arteries, L-TGA) is a rare congenital heart disease characterized by a double discordance: the atrioventricular connection is reversed (atrioventricular discordance), as is the connection between the ventricles and great arteries (ventriculo-arterial discordance). Due to this double anomaly, the blood flow sequence is paradoxically preserved: systemic venous blood is still oxygenated, and oxygenated blood reaches the peripheral tissues, despite passing through ventricles that are morphologically inverted.
The right atrium empties into the morphologic left ventricle, which pumps blood into the pulmonary artery, while the left atrium connects to the morphologic right ventricle that empties into the aorta.
Circulation is thus functionally “correct,” but the underlying anatomical anomaly carries significant consequences over time. Specifically, the morphologic right ventricle, structurally designed for low pressures, is required to support systemic circulation, resulting in a progressive risk of ventricular dysfunction. Moreover, the right atrioventricular valve (which in this anatomy corresponds to the tricuspid valve) is prone to regurgitation, contributing to heart failure.
In about 90% of cases, L-TGA is associated with other structural cardiovascular anomalies, including:
L-TGA accounts for less than 1% of all congenital heart defects. It may remain asymptomatic for many years, particularly in patients without associated anomalies, and is sometimes diagnosed in adulthood during evaluations for heart failure or arrhythmias. However, in many cases, its natural history involves progressive deterioration of right ventricular function and severe hemodynamic and arrhythmic complications. Early recognition and accurate anatomical-functional characterization are crucial to plan appropriate management and prevent functional decline.
The genetic causes of L-TGA are not fully understood, but early embryonic disturbances in the development of the heart, particularly the conotruncal region, are believed to play a role. Mutations in the NKX2.5, GATA4, TBX5, and ZIC3 genes have been linked to conotruncal defects; however, most cases of L-TGA are sporadic and isolated. Some occur in syndromic contexts, such as heterotaxy or cilia-related dysplasias.
Congenitally corrected transposition of the great arteries arises early in cardiac embryogenesis, between the fifth and eighth weeks of gestation, during the formation and looping of the primitive heart tube. Normally, the heart undergoes a rightward rotation ("D-looping"), positioning the right ventricle on the right and the left ventricle on the left. In L-TGA, however, there is a leftward looping (L-looping), leading to inversion of the ventricular chambers and their connections with the great arteries.
The final result is a double discordance:
Unlike Complete Transposition of the Great Arteries (d-TGA), this double discordance results in a “physiologically” corrected circulation:
right atrium → left ventricle → lungs → left atrium → right ventricle → aorta
Systemic blood is thus oxygenated and appropriately distributed, yet the morphology of the ventricular chambers and atrioventricular valves is inverted, leading to significant pathophysiological consequences due to the pressure overload mismatch imposed on the ventricles.
Functionally, the main problem in L-TGA is that the right ventricle lies in the systemic position and must sustain the pressure load of the entire systemic circulation, for which it is not structurally suited. Over time, this may lead to progressive dysfunction of the systemic right ventricle, initially compensated but eventually decompensating. Additionally, the atrioventricular valve separating the left atrium from the right ventricle (i.e., the tricuspid valve, now in systemic position) may develop significant regurgitation, further exacerbating heart failure.
Another key pathophysiological feature is the frequent involvement of the conduction system. In L-TGA, the His bundle follows an abnormal and vulnerable course, predisposing to progressive atrioventricular blocks that may develop at any age and eventually require permanent pacemaker implantation.
The clinical presentation of congenitally corrected transposition of the great arteries is highly variable and depends on three main factors: associated cardiac malformations, systemic right ventricular function, and integrity of the atrioventricular conduction system. In patients without associated defects, the condition may remain silent for years and be diagnosed incidentally. However, most patients have concomitant anomalies that lead to earlier clinical manifestations.
In the newborn, isolated L-TGA is often asymptomatic and may go undiagnosed in the absence of obvious heart murmurs or signs of hemodynamic overload.
The presence of a ventricular septal defect or pulmonary stenosis may instead cause central cyanosis, signs of pulmonary overcirculation, or respiratory difficulties in the first weeks of life. In such cases, the condition may mimic other complex congenital heart diseases, making early diagnosis less straightforward.
During childhood and adolescence, some patients begin to show signs of progressive heart failure, due to gradual decline in systemic right ventricular function. Symptoms may include fatigue, growth delay, reduced exercise tolerance, and, in more advanced stages, signs of venous congestion. Tricuspid regurgitation often contributes to the worsening hemodynamic status.
In adulthood, L-TGA may present late, with symptoms initially misattributed to dilated cardiomyopathy or arrhythmias. Common clinical pictures include:
The medical history should explore episodes of syncope, decline in physical performance, and any family history of congenital heart disease. It is also important to document signs of progressive ventricular dysfunction, prior cardiac surgeries, and symptoms suggestive of rhythm disorders.
On physical examination, heart murmurs due to septal defects or valvular regurgitation may be heard, along with signs of overt right-sided heart failure. In advanced cases, a diastolic gallop or muffled heart sounds may be present. A thorough assessment is essential, as about one-third of patients—especially those with isolated forms—may have apparently normal cardiac auscultation findings.
Progressive dysfunction of the systemic right ventricle is the main negative prognostic factor. Without monitoring and timely interventions, L-TGA can progress to irreversible advanced heart failure.
The diagnosis of congenitally corrected transposition of the great arteries requires high clinical and instrumental accuracy, especially in asymptomatic patients or those with subtle presentations. Suspicion may arise in the neonatal period based on heart murmurs or signs of pulmonary overcirculation, or later in the context of unexplained arrhythmias or heart failure. In many cases, the disease is initially misdiagnosed as a form of dilated cardiomyopathy, highlighting the critical role of detailed echocardiographic assessment.
Transthoracic echocardiography plays a central role, allowing the identification of double discordance. Ventricular anatomy must be carefully analyzed using morphological indices (trabeculation, location of chordae tendineae, atrioventricular valve insertion).
Diagnostic confirmation is based on the identification of:
When transthoracic acoustic windows are suboptimal, particularly in adults, transesophageal echocardiography may be necessary to better characterize the atrioventricular connections and origins of the great arteries.
In complex or previously operated patients, cardiac magnetic resonance imaging (MRI) is especially useful for precise assessment of ventricular function, intracardiac flows, and right-sided chamber dilation.
The electrocardiogram (ECG) may provide indirect clues: the cardiac axis is often left-deviated, with intraventricular conduction abnormalities and bundle branch block patterns. In advanced cases, high-degree atrioventricular blocks may be detected, requiring monitoring or pacemaker implantation.
Chest X-ray is not diagnostic but may show cardiomegaly, increased pulmonary vascular markings in cases of overcirculation, or signs suggestive of heart failure.
Arterial blood gas analysis may reveal hypoxemia in the presence of associated defects with right-to-left shunting, but is nonspecific.
Cardiac catheterization plays a limited role in the initial diagnosis today but may be indicated in patients with suspected pulmonary hypertension, for preoperative evaluation, or to define vascular resistance in those considered for surgery. It can also provide direct measurement of pressure in the systemic right ventricle, which is useful in the setting of dysfunction.
The definitive diagnosis is based on integration of echocardiographic, MRI, and clinical data. Timely recognition of the double discordance—especially in the absence of cyanosis or obvious signs—is essential to establish an appropriate therapeutic plan and ensure long-term follow-up.
Treatment of congenitally corrected transposition of the great arteries is closely dependent on the functional status of the systemic right ventricle and the presence and severity of associated anomalies. In the rare isolated and well-compensated cases, careful clinical and instrumental monitoring may be sufficient. However, in most patients, a proactive therapeutic approach is required to prevent progression toward heart failure or major arrhythmias.
Management is structured into three main areas: medical therapy, corrective or palliative surgery, and arrhythmia management.
Medical treatment is indicated in symptomatic patients or those showing signs of systemic right ventricular function decline, aiming to support ventricular performance. It is based on the use of diuretics, ACE inhibitors or angiotensin receptor blockers, and sometimes beta-blockers, with the goal of reducing afterload and improving systemic ventricular function. However, while these drugs are commonly used in left ventricular heart failure, their efficacy in L-TGA is less well established.
In patients with significant associated defects, surgical correction is appropriate. Examples include closure of VSDs, valvuloplasty or tricuspid valve replacement in cases of significant regurgitation, and relief of right ventricular outflow tract obstruction when present.
In cases of progressive deterioration of systemic right ventricular function or severe tricuspid regurgitation, a double switch procedure (atrial switch combined with arterial switch) may be considered to restore the normal atrio-ventriculo-arterial sequence, placing the left ventricle in the systemic position. This complex surgery is preferably performed in childhood before the left ventricle loses its capacity to sustain systemic afterload. In adults, the procedure is only feasible after gradual left ventricular retraining, often with pulmonary artery banding.
Arrhythmias are a major aspect of L-TGA management. Advanced atrioventricular blocks are common and may develop at any age. Permanent pacemaker implantation is often necessary, even in young patients. For those with supraventricular tachyarrhythmias, specific antiarrhythmic therapy or catheter ablation may be indicated.
The long-term prognosis of L-TGA is strongly influenced by the presence of associated defects and the function of the systemic right ventricle. In unoperated patients, survival may extend into adulthood, but with progressive hemodynamic decline. Following early corrective surgery, prognosis improves significantly, especially when the left ventricle is adequately trained to sustain systemic pressure. However, even in surgically treated patients, lifelong specialized follow-up is essential, with close monitoring of ventricular function, valvular status, and electrical activity.
Although congenitally corrected transposition of the great arteries allows for functionally effective circulation in early life, it can evolve over time into serious complications. These are largely related to the systemic position of the morphologic right ventricle and frequent involvement of the conduction system. Such complications may occur even in the absence of associated anomalies and can significantly affect survival and quality of life in adulthood.
The most common and prognostically significant complication is progressive dysfunction of the systemic right ventricle. Without the structural capacity to withstand systemic afterload, the ventricle undergoes dilatation, hypertrophy, and eventual contractile failure, leading to symptoms of heart failure, reduced exercise tolerance, and systemic congestion. This evolution may remain silent for years, but once established, it is often irreversible.
Another important complication is tricuspid valve regurgitation, which in L-TGA separates the left atrium from the systemic right ventricle. Structural or functional changes in the valve, often due to ventricular dilatation, contribute to volume overload and hemodynamic decline.
Atrioventricular conduction disorders are extremely common in L-TGA, with an annual risk of complete AV block exceeding 1–2% in unoperated patients. The anomalous and superficial course of the His bundle makes it vulnerable to mechanical or degenerative damage. Permanent pacemaker implantation is frequently necessary, sometimes even in childhood.
Postoperative complications in patients undergoing double switch or other surgical correction (e.g., septal or valvular repair) include:
Finally, in patients with advanced refractory heart failure, heart transplantation may become necessary. This represents the last therapeutic option when pharmacologic or surgical management is no longer effective. The timing of transplantation should be evaluated early, before the onset of multi-organ deterioration.
A multidisciplinary approach with regular follow-up in adult congenital heart disease centers is essential to monitor ventricular function, prevent arrhythmic complications, and schedule timely therapeutic interventions. The complex evolution of L-TGA requires long-term surveillance, even in initially asymptomatic patients.