d-Transposition of Great Arteries

More of fetal d-Transposition of Great Arteries here

Link to CVICU website of Boston Children's Hospital on d-TGA

Summary of d-TGA

Dextro-transposition of the great arteries (d-TGA) is a congenital cardiac defect characterized by an embryological discordance between the aorta and pulmonary trunk. It is the most frequent cyanotic congenital heart pathology observed in neonates. In d-TGA, the aorta arises from the morphologic right ventricle, and the pulmonary trunk emerges from the morphologic left ventricle. This arrangement typically involves the right ventricle positioned to the right of the left ventricle, with the aorta situated anterior and rightward relative to the pulmonary artery. The coronary arteries originate from the aorta (coming out of the RV), and their configuration can be variable. The left ventricle (LV) is exposed to pulmonary vascular resistance (PVR). In the presence of a patent ductus arteriosus (PDA) and elevated PVR, one may observe reverse differential cyanosis, where oxygen saturation in the right arm is lower than in the lower limbs, due to saturated blood preferentially entering the post-ductal aorta. This may also occur with d-TGA+coarctation and d-TGA+interrupted aortic arch. On the parasternal short-axis view, once PVR decreases, the interventricular septum may appear flat or bow toward the left ventricle, reflecting the pressure differential. The standard surgical repair is the arterial switch operation (Jatene procedure), often accompanied by the LeCompte maneuver when anatomical alignment permits. The aorta is re-anastomosed to the left ventricle, and the pulmonary artery to the right ventricle, with the native pulmonary valve becoming the neo-aortic valve. The coronary arteries are carefully detached and reimplanted onto the neoaorta. Delaying surgery can lead to deconditioning of the left ventricle, as it is subjected only to pulmonary afterload. However, in cases with a large PDA, the LV may face near-systemic pressures, preserving its conditioning. Nonetheless, prolonged exposure to excessive pulmonary blood flow may result in pulmonary overcirculation, pulmonary edema, and respiratory distress. For this reason, surgical correction is typically performed between 7 and 14 days of life. The LeCompte maneuver involves repositioning the pulmonary artery anterior to the ascending aorta, which facilitates tension-free anastomoses and optimizes great vessel orientation post-repair.

Anatomy and Physiology

The core issue in d-TGA is ventriculo-arterial discordance, meaning the ventricles are connected to the wrong great arteries. This results in two parallel circulatory circuits:

1. Systemic circuit: Deoxygenated blood from the body returns to the right atrium, flows into the right ventricle, and is pumped into the aorta, which then distributes it back to the body.

2. Pulmonary circuit: Oxygenated blood from the lungs returns to the left atrium, flows into the left ventricle, and is pumped into the pulmonary trunk, which delivers it back to the lungs.

For oxygenated blood to reach the systemic circulation and deoxygenated blood to reach the lungs, there must be mixing between these two parallel circuits. This mixing typically occurs through the Patent Foramen Ovale (PFO) or Atrial Septal Defect (ASD), allowing mixing at the atrial level. One cannot rely solely on the presence of a ventricular septal defect (VSD) or patent ductus arteriosus (PDA) to ensure adequate mixing and systemic oxygenation in d-TGA. This is because pulmonary vascular resistance (PVR) is typically lower than systemic vascular resistance (SVR), resulting in oxygen-rich blood in the left ventricle and pulmonary artery preferentially circulating within the pulmonary circuit, rather than crossing through a VSD or PDA to reach the systemic circulation. Oxygenated blood can only enter the systemic circulation via a PDA when there is a high PVR/SVR ratio, as seen in persistent pulmonary hypertension of the newborn (PPHN), or in the presence of aortic arch obstruction, such as a significant coarctation or interrupted aortic arch. This can lead to the classical finding of reverse differential cyanosis, where the lower limbs are better saturated than the upper body. Even when VSDs are large or multiple, they may permit some degree of mixing; however, this is often insufficient, and one should not rely on ventricular-level mixing alone. Many of these infants still require an atrial septostomy to establish adequate intercirculatory mixing and improve systemic oxygenation. The severity of cyanosis and clinical symptoms depends directly on the degree of mixing. Adequate mixing maintains oxygenation, while restricted mixing leads to severe hypoxemia.

Clinical Presentation

D-TGA is a leading cause of cyanotic heart disease in neonates. The main symptom is cyanosis.

• In infants with an intact ventricular septum (no VSD) and a restrictive PFO or ASD, severe cyanosis and metabolic acidosis develop rapidly, often within the first hours of life.

• When there is a large ASD or PFO, allowing adequate atrial mixing, cyanosis may be mild, and the infant may show minimal signs of heart disease initially. Physical examination findings like heart size and murmurs may be minimal.

• In infants with a VSD, clinical presentation varies based on the VSD size and associated lesions, as well as the PVR/SVR ratio allowing some mixing. A large VSD may allow significant mixing but can lead to increased pulmonary blood flow. Infants with a large VSD may present with signs of heart failure.

Diagnosis

Several imaging modalities are used for the diagnosis and evaluation of d-TGA:

• Echocardiography (Transthoracic): This is the primary imaging modality for d-TGA. It provides essential information about the heart's morphology, function, and hemodynamics. Echocardiography is used to visualize the ventriculo-arterial connections, assess the size of the ASD/PFO and VSD (if present), determine the direction and magnitude of shunting, evaluate ventricular function, and examine the pulmonary venous return. It clearly demonstrates the aorta arising from the right ventricle.

• Chest Radiography: The classic chest X-ray finding in d-TGA is the "egg on a string" appearance, due to the narrow superior mediastinum (transposed great arteries) and enlarged cardiac silhouette. It can also show patterns of pulmonary vascularity which correlate with pulmonary blood flow.

• Electrocardiography (ECG): The ECG usually appears normal in the newborn period, but often shows right-axis deviation and right ventricular hypertrophy (RVH). An upright T wave in the right precordial leads might persist beyond the first few days.

• Cardiac Catheterization: While rarely used for initial diagnosis, catheterization can be essential for therapeutic intervention, such as balloon atrial septostomy to enlarge a restrictive atrial communication and improve mixing in severely cyanotic neonates. Catheterization with angiography is considered the gold standard for defining the origins and anatomy of the coronary arteries, which is crucial for surgical planning. However, these can typically be well defined by echocardiography in most cases. 

• Computed Tomography (CT) Imaging: CT is valuable for detailed imaging of cardiovascular structures, especially in post-surgical patients or when MRI is contraindicated. It can delineate the anatomy of baffles, conduits, and is used for evaluating coronary artery anatomy. CT provides morphological details but not hemodynamics or blood flow quantification. It is rarely used. 

• Cardiac Magnetic Resonance Imaging (MRI): MRI provides comprehensive anatomical and hemodynamic information, allowing quantification of ventricular size, function, and valvular performance. It is effective for assessing coronary arteries and post-surgical anatomy. It is also rarely used since echocardiography can provide sufficient information. 

Management

Initial management focuses on ensuring adequate mixing:

• Infusion of Prostaglandin E1 (PGE1) is often initiated to maintain the patency of the ductus arteriosus. This is particularly important if there is a concomittant coarctation, hypoplastic arch or interrupted aortic arch. It is also used to promote mixing by increasing pulmonary blood flow, pulmonary venous return and left atrial preload. This favours the left to right inter-atrial shunt, allowing for oxygen to enter the systemic circulation (RA and RV to Aorta). The PDA itself is not a reliable source of mixing, but would allow for Oxygen to enter the aorta if there is a Pulmonary (high O2) to Aortic (low O2) shunt. This is only seen when PVR exceeds SVR, or there is Coarctation, or there is Interrupted Aortic arch. 

• In cases of severe cyanosis with restrictive atrial communication, an urgent balloon atrial septostomy is performed to create a larger opening between the atria, facilitating mixing.

The definitive treatment for d-TGA is typically surgical correction:

• For classical d-TGA: the Arterial Switch Operation (ASO) is the preferred corrective procedure. First performed by Jatene in 1975, this operation involves transecting and switching the great arteries to their appropriate ventricles and re-implanting the coronary arteries onto the neo-aorta.

• For d-TGA associated with a VSD and significant left ventricular outflow tract obstruction (LVOTO), alternative repair strategies such as the Rastelli procedure or other anatomical repairs like REV or Nikaidoh procedures are often employed. The Rastelli procedure involves closing the VSD to direct the left ventricle to the aorta and placing a conduit from the right ventricle to the pulmonary artery.

• Atrial switch / Mustard was previously used and is no longer favoured since the ASO procedure. 

Outcomes

Outcomes after surgical correction of d-TGA have significantly improved with the advent of the ASO.

• Studies on ASO outcomes report high survival rates, approximately 92.0% in the short-term (0-1 year), 90.0% in the medium-term (1-20 years), and 87.0% in the long-term (>20 years). Survival rates have improved over time.

• Freedom from reoperation is also high in the short-term (93.0%), but the need for subsequent procedures decreases over medium (81.0%) and long (78.0%) follow-up, primarily for issues related to the neo-aorta or pulmonary arteries.

• Potential long-term complications can include neo-aortic root dilation and aortic insufficiency, pulmonary artery stenosis (often supravalvar above the neo-pulmonary valve), and issues related to the reimplanted coronary arteries.

• Neuropsychological outcomes and quality of life in long-term survivors have been studied, with variable findings across different reports. Generally excellent. 

The long-term management of individuals with d-TGA after surgical repair involves regular follow-up to monitor ventricular function, valve status, coronary arteries, and potential outflow tract obstructions.

References: 

1. Dipchand AI, editor. Manual of Cardiac Care in Children. Springer Nature Switzerland AG; 2024.

2. Park IS, editor. An Illustrated Guide to Congenital Heart Disease: From Diagnosis to Treatment – From Fetus to Adult. Springer Nature Singapore Pte Ltd.; 2019.

3. Rudolph AM. Congenital Diseases of the Heart: Clinical-Physiological Considerations. 3rd ed. Blackwell Publishing; 2009.

4. Rigby ML, Anderson RH. Echocardiography in Congenital Heart Disease Made Simple. TFM Pub.; 2005.

5. Klienman CS, Seri I, editors. Hemodynamics and Cardiology: Neonatology Questions and Controversies. Saunders, an imprint of Elsevier Inc.; 2008.

6. Szymanski MW, Sharma S, Kritzmire SM, Forero F. Transposition of the Great Arteries [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan- [updated 2025 Mar 16; cited 2024 May 15]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538434/.

Morphological considerations

1. Great Artery Relationship and Position

• Typical Parallel Arrangement: In the most common form of d-TGA, the aorta and pulmonary artery are positioned parallel to each other. This is the characteristic finding. Sometimes there might be an illusion of crossing in antenatal ultrasound, but anatomically they are almost always parallel.

• Vessel Crossing (Rare): While extremely rare, there can be a transposition where the outflow tracts cross after surgical correction (Arterial Switch Operation), or in very rare original anatomies where the vessels themselves might appear to cross in certain views.

• Aorta Position: The aorta is typically anterior and rightward relative to the pulmonary artery. This is the most frequent position. However, the aorta can also be positioned more posteriorly. Even with a posterior aorta, the vessels are usually parallel. The position of the aorta (anterior or posterior) needs to be added to the segmental analysis of the heart.

2. Conus Anatomy

• Subaortic Conus & Mitral-Pulmonary Continuity: The typical finding in the right ventricle is the presence of a subaortic conus (infundibulum), a muscular structure separating the tricuspid valve from the aortic valve. In the left ventricle, there is typically mitral-pulmonary continuity, meaning the anterior leaflet of the mitral valve is in fibrous continuity with the posterior pulmonary valve without intervening muscle (no subpulmonary conus).

• Bilateral Conus: Less commonly, a bilateral conus can exist, where muscular tissue separates both the tricuspid valve from the aortic valve (subaortic conus) and the mitral valve from the pulmonary valve (subpulmonary conus). This bilateral conus is often, though not always, associated with a posterior aorta. The relative sizes of the subaortic and subpulmonary conuses can influence the anterior/posterior position of the great arteries even in the presence of bilateral conus. A bilateral conus appears as mitral-pulmonary discontinuity on echocardiography.

3. Associated Ventricular Septal Defects (VSDs)

• Frequency: Approximately half of d-TGA cases are associated with a VSD (of various sizes and location).

• Location: VSDs in d-TGA are not necessarily restricted to the outflow tract region ("conotruncal") but can be located anywhere in the septum. Four anatomical types (corresponding to three surgical locations) are recognized.

• Specific Types:

  • Perimembranous VSDs: Located below the septal band's "Y". They are in the position of the membranous septum and show septo-arterial continuity with the pulmonary artery in the left ventricle view (not with the aortic or non-coronary commissures as in a normal heart).

  • Trabeculated Muscular VSDs: Located within the muscular septum. They can be anterior, posterior, or apical.

  • Inlet VSDs: Located in the inlet septum, often associated with straddling and overriding of the tricuspid valve which inserts into the left ventricle through the defect. A tricuspid valve straddling always passes through an inlet VSD. These VSDs may become functionally closed as the tricuspid leaflet adheres to the septal crest.

  • Outflow Tract (Outlet / Conoventricular) VSDs: Located below the semilunar valves. These VSDs are associated with malalignment of the conal septum. An anterior malalignment of the conal septum causes a VSD that results in subaortic stenosis in d-TGA. A posterior malalignment of the conal septum causes a VSD that results in subpulmonary stenosis. Outflow tract VSDs in d-TGA show septo-arterial discontinuity (the septum does not align with the artery above the VSD). It can also sometimes be classified in the spectrum of double outlet right ventricle with TGA physiology - Taussig-Bing anomaly.

4. Outflow Tract Obstructions

• Left Ventricular Outflow Tract Obstruction (LVOTO) / Subpulmonary Stenosis: Can occur due to various mechanisms:

  • Posterior malalignment of the conal septum (with outlet VSD).

  • A bicuspid pulmonary valve (similar to a normal heart with bicuspid aortic valve). This bicuspid pulmonary valve is within the LVOT since the LV is sub-pulmonary.

  • A muscular membrane in the LV outflow tract (e.g., "muscle of Moulaert").

  • A fibrous circumferential membrane developing subpulmonary, sometimes originating from the conal septum, particularly seen after switch surgery.

  • A cleft of the mitral valve directed towards the outflow tract.

  • Straddling tricuspid valve displacing or impacting the mitral valve.

  • An enormous dilated coronary sinus pushing on the mitral valve and obstructing filling/outflow.

• Right Ventricular Outflow Tract Obstruction (RVOTO) / Subaortic Stenosis: Occurs primarily due to anterior malalignment of the conal septum (with outlet VSD).

5. Other Associated Anomalies

• Coronary Artery Anatomy: The origins and courses of the coronary arteries are highly variable and critically important for surgical planning (Arterial Switch Operation). Variations mentioned include right and left coronaries arising from posterior sinuses, single coronary artery, right coronary arising from the left sinus with an anterior loop. Issues with post-switch re-implantation sites (e.g., small or slit-like ostia, tension) can occur.

• Atrioventricular (AV) Valve Anomalies:

  • Mitral Valve: Can have a cleft directed towards the outflow tract, be hypoplastic, straddle or override the ventricular septum, have a parachute morphology (single papillary muscle), or present with other "bizarre" morphologies.

  • Tricuspid Valve: Can be hypoplastic or straddle/override the ventricular septum through an inlet VSD.

• Aortic Arch Anomalies: Association with coarctation of the aorta or interruption of the aortic arch can occur, sometimes related to abnormalities in aortic flow during fetal life (e.g., hypoplastic right ventricle).

• Atrial Appendage Juxtaposition: Anomalous positioning of the atrial appendages, such as left juxtaposition of the right appendage, can occur in d-TGA. In left juxtaposition, both atrial appendages are on the left side of the great arteries and may have a similar narrow-based implantation resembling a left appendage. This anomaly increases the risk of inadvertently entering the right atrial appendage during a balloon atrial septostomy procedure.

• Pulmonary Valve Anomalies: A bicuspid pulmonary valve is a possible finding, which is analogous to a bicuspid aortic valve in a normal heart configuration.

These variations highlight the anatomical complexity of d-TGA beyond the primary ventriculo-arterial discordance and are crucial considerations for diagnosis, assessment, and surgical planning.

Coronary Anatomy

Understanding the coronary artery anatomy is critical for surgical planning, particularly for the arterial switch operation (ASO). While the coronary arteries arise from the aortic sinuses, their origins and proximal courses can vary significantly compared to a normal heart. These variations can make surgical repair technically challenging and are associated with worse outcomes. The coronary arteries typically arise from the aortic sinuses that are adjacent to, or "facing," the pulmonary trunk. Using the Leiden Convention, where one imagines standing in the non-coronary aortic cusp facing the pulmonary trunk, these facing sinuses are designated as sinus 1 (to the right) and sinus 2 (to the left). Coronary arteries arise from both, or one, of these facing sinuses. Several variations in coronary artery patterns exist in d-TGA:

• The "Usual" Pattern: This is the most common configuration, seen in approximately two-thirds of patients. The left anterior descending (LAD) and circumflex (Cx) arteries originate from the left-facing sinus (sinus 2), and the right coronary artery (RCA) originates from the right-facing sinus (sinus 1). This is sometimes notated as 1L/Cx2R.

• Circumflex Artery from the RCA: This is the most frequently observed anomalous pattern in complete TGA, occurring in about 20% of individuals and contributing to the estimated 25-30% of patients with an unusual coronary course. In this variation, the Cx artery arises from the RCA and typically passes posterior to the pulmonary root as it courses to the left atrioventricular groove. This pattern is notated as 1L2R, Cx.

• Single Coronary Artery: This anomaly occurs in approximately 10% of patients with transposition and around 1% of congenital heart defects overall. It can present as a single left or a single right coronary artery, or arise from the non-coronary (posterior) sinus. The presence of a single coronary ostium is associated with a worse prognosis.

• Intramural Course: One of the coronary arteries (often the LAD) may run for a distance within the wall (adventitia) of the aorta. This is seen in 2-5% of cases and can pose significant surgical difficulties during the ASO. An intramural course is associated with a worse prognosis. Echocardiographic clues suggesting an intramural course include the artery arising from the contralateral sinus, segments of the artery not being visible, high velocity or turbulent flow at the origin, and early branching.

• Coronary Artery Crossing the RVOT: While mentioned specifically in the context of Tetralogy of Fallot where it can limit surgical options, a coronary artery crossing the right ventricular outflow tract (RVOT) is also a significant variation in TGA that influences surgical approach. For example, the RCA can cross in front of the narrowed RVOT.

• Dual LAD: Some variations include the presence of dual anterior descending coronary arteries.

• Other Variations: Less common patterns include inverted origins of the RCA and LCA, and variations in the origin of the LAD from the RCA.

Surgical Significance for ASO: During the ASO, the coronary arteries must be carefully mobilized from the native aorta (harvested as "buttons" with a cuff of aortic wall) and reimplanted onto the neoaorta (the former pulmonary trunk). An intramural course may require specific techniques like unroofing the intramural segment. Careful technique is paramount to minimize complications such as kinking, stretching, torsion, or stenosis at the reimplantation site. Coronary artery abnormalities are a primary cause of early mortality and morbidity after the ASO, and complications like ostial stenosis can also occur years later.

Imaging and Diagnosis: Pre-operative evaluation of coronary anatomy is crucial. Echocardiography is the primary imaging modality for diagnosing TGA and can often evaluate coronary artery anatomy, identifying variations like a single ostium or intramural course, although defining the anatomy can be challenging. Cardiac catheterization with angiography remains the gold standard for definitively determining coronary artery origins. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are also effective methods for evaluating the coronary arteries and are often necessary for detailed visualization, especially in complex cases or for follow-up post-ASO. CT angiography can provide a reliable evaluation.

References:

• Gittenberger-de Groot AC, Sauer U, Oppenheimer-Dekker A, Quaegebeur J. Coronary arterial anatomy in transposition of the great arteries: a morphologic study. Pediatr Cardiol. 1983;4:15– 24. 

• Martins P, Castela E. Transposition of the great arteries. Orphanet J Rare Dis. 2008;3:27. 

• Pasquali SK, Hasselblad V, Li JS, et al. Coronary artery pattern and outcome of arterial switch operation for transposition of the great arteries: a meta-analysis. Circulation. 2002;106(20):2575–80. 

• Szymanski MW, Sharma S, Kritzmire SM, et al. Transposition of the Great Arteries. [Updated 2025 Mar 16]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. (This source was cited for the definition of d-TGA and the role of imaging modalities). 

• Pasquini L, Sanders SP, Parness IA, et al. (1994) Coronary echocardiography in 406 patients with d-loop transposition of the great arteries. J Am Coll Cardiol, 24, 763–768. 

• Mahle WT, Martin GR, Beekman RH III,, et al. (2012) Endorsement of health and human services recommen-dation for pulse oximetry screening for critical congenital heart disease. Pediatrics, 129, 190–192. 

• Khairy P, Clair M, Fernandes SM, et al. (2013) Cardiovascular outcomes after the arterial switch operation for D-transposition of the great arteries. Circulation, 127, 331–339.

d-TGA with PPHN, coarctation or interrupted aorta (reverse differential saturations)

In d-transposition of great arteries, there are 3 scenarios during which there can be reversed differential saturations. 

1. Scenario 1 - d-TGA with Coarctation of the Aorta or Scenario 2 - d-TGA with Interrupted Aortic Arch: 

   1. Deoxygenated blood enters the Right Atrium, the Right Ventricle, and reaches the ascending aorta.

   2. Oxygenated blood enters the Left Atrium, the Left Ventricle, the Pulmonary Artery. Because the duct is patent and there is a coarctation or interrupted aortic arch with underfilling / empty descending post-ductal aorta, this promotes PA to Aorta shunting. Hence, more oxygenated blood (relative to the ascending aorta) enters the descending aorta. 

2. Scenario 3 - TGA with Suprasystemic Pulmonary Vascular Resistance: 

   1. Deoxygenated blood enters the Right Atrium, the Right Ventricle, and reaches the ascending aorta.

   2. Oxygenated blood enters the Left Atrium, the Left Ventricle, the Pulmonary Artery. Because the duct is patent and the PVR >> SVR, this favours PA to Aorta shunting. Hence, more oxygenated blood (relative to the ascending aorta) enters the descending aorta. 

d-TGA - Case and Echocardiography images

From: "Describing Congenital Heart Disease by Using Three-Part Segmental Notation" 

By: Erica K. Schallert, MD • Gary H. Danton, MD, PhD • Richard Kardon, DO Daniel A. Young, MD

If the aorta is anterior to and rightward of the MPA, the anomaly is described as dextrotransposition, or d-transposition, of the great vessels, which is denoted as “{_, _, d-TGV}”; if the aorta is anterior to and leftward of the MPA, the anomaly is described as levotransposition (l-transposition) or congenitally corrected transposition, which is denoted as “{_, _, l-TGV}.” If the aorta is neither anterior nor posterior to the MPA, the great vessels are usually described as malpositioned: If the aorta is rightward of the MPA, the anomaly is described as d-malposition, which is denoted as “{_, _, d-MGV}”; if the aorta is leftward of the MPA, the anomaly is described as l-malposition, which is denoted as “{ _, _, lMGV}.” 

Great vessels are seen parallel to each other, with a mostly left to right PDA.

Atrial septostomy (Rashkind balloon procedure)

Some patients may require atrial septostomy, which allows for increased mixing. In our centre, the procedure is done at the bedside in the neonatal intensive care unit. A catheter is introduced in the right atrium by an umbilical approach (or femoral approach if the umbilical one is unsuccessful). The balloon goes through the foramen ovale and is inflated and then pulled in order to open the inter-atrial septum. One may need to pay attention to the mitral valve, and avoid avulsion of the valve when pulling the balloon. 

D-TGA presentation by Satit Manopunya and Thien-An Lam (Montreal Children's Hospital)

Images by Dr Oung Savly from a d-TGA requiring a Senning procedure

Dr Oung Savly  is a pediatric cardiologist, Head of division of pediatric cardiology/CICU, Kantha Bopha Children’s Hospital, Phnom Penh, Cambodia. Twitter/X account of Dr Savly

Contact information: oungsavly007@gmail.com 

Online: November 2nd, 2023