# Transposition of the Great Arteries

## Overview

Transposition of the great arteries (TGA) encompasses lesions where the great arteries arise from the incorrect ventricle. D-TGA (complete transposition) is the most common cyanotic heart defect presenting in the neonatal period. L-TGA (congenitally corrected TGA) is rare and is physiologically corrected but carries long-term structural consequences. The arterial switch operation (ASO) revolutionized the management of D-TGA and is now the gold standard repair.

## D-Transposition of the Great Arteries (D-TGA)

### Anatomy and Pathophysiology

D-TGA is defined by ventriculoarterial discordance, meaning the aorta arises from the RV (anterior and rightward) and the PA arises from the LV (posterior). Atrioventricular concordance is preserved, with the RA connecting to the RV and the LA connecting to the LV. The result is parallel circulations rather than the normal series arrangement. Deoxygenated blood circulates from the RA to the RV to the aorta and back to the systemic circulation without passing through the lungs. Meanwhile, oxygenated blood circulates from the LA to the LV to the PA and back to the lungs without reaching the systemic circulation. Survival requires mixing between the two circuits through an ASD, VSD, or PDA. Without intervention, severe cyanosis and death occur in the neonatal period.

### Associated Lesions

The most common presentation (approximately 60%) is D-TGA with an intact ventricular septum. A VSD is present in 25-30% of cases. A VSD combined with LVOT obstruction occurs in 5-10%. Coronary artery anomalies occur with variable patterns and are critical for surgical planning.

### Initial Management

PGE1 infusion maintains ductal patency and allows mixing at the ductal level. A balloon atrial septostomy (Rashkind procedure) is performed emergently at the bedside or in the catheterization lab to create an atrial communication, improving oxygenation through atrial-level mixing and serving as a bridge to definitive surgical repair.

<image>D-TGA anatomy showing parallel circulations with aorta arising from the RV and PA from the LV, with arrows indicating deoxygenated and oxygenated blood flow in separate circuits</image>

### Arterial Switch Operation (ASO)

#### Timing

The ASO is performed within the first 1-2 weeks of life, before LV "detraining" occurs. In D-TGA with an intact ventricular septum, the LV faces the low-resistance pulmonary circulation and deconditions rapidly, so if repair is delayed beyond 3-4 weeks, the LV may not tolerate systemic pressures after the switch. In D-TGA with a VSD, the LV is maintained at systemic pressures by the VSD, allowing the ASO to be performed later.

#### Technique

The operation proceeds through several steps. Cannulation and CPB are established with aortic and bicaval cannulation under moderate hypothermia. Both the aorta and PA are transected above their respective valves. The most critical step is coronary artery transfer: coronary buttons are excised from the old aortic root (which becomes the neoaortic root) and reimplanted into the neopulmonary root (the new aorta), ensuring they are tension-free without kinking or compression. Coronary transfer is the most technically demanding part of the operation and the main determinant of early outcomes. The Lecompte maneuver brings the PA anterior to the aorta (anterior translocation of the branch PAs) to prevent PA compression behind the aorta. Neoaortic reconstruction places the coronary buttons in the neoaorta with proximal direct anastomosis. Neopulmonary reconstruction converts the old aortic root into the neopulmonary root and patches the defects from coronary button excision with autologous pericardium.

#### Coronary Artery Patterns

The most common pattern (70%) has the LAD and LCx arising from the left-facing sinus and the RCA from the right-facing sinus. Intramural coronary arteries run within the aortic wall before emerging and represent high-risk transfers. A single coronary pattern, where all coronary flow comes from one ostium, requires complex reimplantation. An inverted pattern has the RCA from the left sinus and LAD/LCx from the right sinus. Accurate preoperative and intraoperative identification is essential.

#### Outcomes

Operative mortality is 2-4% overall and less than 2% in experienced centers. Long-term survival exceeds 95% at 20 years. Late complications include neoaortic root dilatation and neoaortic regurgitation (10-15% at 20 years), supravalvar pulmonary stenosis (5-10%, occurring at the suture line or Lecompte site), coronary artery stenosis or occlusion (rare but can cause sudden death), and branch PA stenosis (which may require catheter intervention).

<image>Arterial switch operation steps: great artery transection, coronary button excision and transfer, Lecompte maneuver, and completed neoaortic and neopulmonary reconstructions</image>

### Historical Operations (Largely Abandoned)

#### Atrial Switch (Mustard/Senning)

The atrial switch uses an intra-atrial baffle to redirect systemic and pulmonary venous blood to the opposite AV valve. This restores series circulation but leaves the RV as the systemic ventricle. Problems include systemic RV failure (30-40% at 30 years), atrial arrhythmias (sinus node dysfunction, IART), and baffle leaks or obstruction. This operation is no longer performed for D-TGA, but patients from the 1970s and 1980s are now adults requiring ongoing management, representing a significant adult congenital heart disease population.

### D-TGA Surgical Options by Anatomy

| Anatomy | Preferred Operation | Key Features |
|---------|-------------------|-------------|
| D-TGA with intact septum | Arterial switch operation (ASO) | Within 1-2 weeks; coronary transfer critical |
| D-TGA with VSD | ASO + VSD closure | Can be performed later (LV maintained at systemic pressure) |
| D-TGA with VSD + LVOT obstruction | Rastelli, Nikaidoh, or REV | ASO precluded by fixed subpulmonary stenosis |
| D-TGA (historical) | Atrial switch (Mustard/Senning) | No longer performed; adults with systemic RV require lifelong follow-up |

### D-TGA with VSD and LVOT Obstruction

When a VSD coexists with fixed LVOT obstruction (subpulmonary stenosis), the standard ASO is precluded. The Rastelli procedure closes the VSD with a baffle directing LV blood to the aorta and places an extracardiac RV-PA conduit, providing biventricular repair but requiring conduit replacement as the patient grows. The Nikaidoh (aortic translocation) procedure mobilizes the aortic root and translocates it over the LV, providing better LVOT anatomy. The REV procedure (Repairation a l'Etage Ventriculaire) uses an intraventricular baffle with a direct RV-PA connection without a conduit.

## L-Transposition of the Great Arteries (Congenitally Corrected TGA / cc-TGA)

### Anatomy

L-TGA is defined by double discordance -- both atrioventricular discordance and ventriculoarterial discordance. Blood flows from the RA to the morphologic LV to the PA (pulmonary circulation) and from the LA to the morphologic RV to the aorta (systemic circulation). While blood flow is physiologically "corrected" with series circulation maintained, the morphologic RV supports the systemic circulation.

### Associated Lesions (Present in > 90%)

Associated lesions include VSD (the most common), pulmonary stenosis (LVOT obstruction), tricuspid (systemic AV valve) regurgitation with an Ebstein-like malformation being common, and complete heart block with a progressive risk of approximately 2% per year.

### Natural History

The morphologic RV is not designed for lifelong systemic pressure work, and progressive dilation and dysfunction typically develop by the fourth or fifth decade. Systemic AV (tricuspid) valve regurgitation worsens as the RV dilates, and complete heart block develops progressively.

### Surgical Management

#### Physiologic Repair (Conventional)

Physiologic repair involves VSD closure with an LV-PA conduit if LVOT obstruction is present. This addresses associated lesions but leaves the morphologic RV as the systemic ventricle, failing to fix the fundamental problem.

#### Anatomic Repair (Double Switch)

The anatomic repair aims to restore the morphologic LV as the systemic ventricle. For cc-TGA without LVOT obstruction, an atrial switch (Mustard or Senning) is combined with an arterial switch. For cc-TGA with LVOT obstruction and a VSD, an atrial switch is combined with a Rastelli procedure. The LV may require "training" through PA banding if LV pressure is low, preparing it for systemic work. This is a more complex operation but provides better long-term ventricular function. Patient selection is critical -- the LV must be trainable and of adequate size.

<image>Congenitally corrected TGA (L-TGA) anatomy showing double discordance with systemic RV, and comparison of physiologic repair versus anatomic repair (double switch) approaches</image>

## Adult Management Considerations

A growing population of adults exists with both repaired D-TGA (ASO survivors) and atrial switch survivors (Mustard/Senning). Atrial switch patients require systemic RV monitoring with serial echocardiography and cardiac MRI, baffle surveillance for leaks and obstruction, arrhythmia management (often requiring a pacemaker and antiarrhythmic medications), heart failure management (though evidence is limited and HF therapies may be less effective for a systemic RV), and ultimately heart transplantation for end-stage systemic RV failure. ASO survivors require neoaortic root surveillance for progressive dilatation, coronary artery assessment through stress testing and CT coronary angiography, assessment of supravalvar PS with catheter intervention if needed, and exercise recommendations (most ASO patients have near-normal exercise capacity).

## Clinical Pearls

D-TGA is a neonatal emergency, and any cyanotic neonate unresponsive to supplemental oxygen should have TGA in the differential -- PGE1 saves lives. Balloon atrial septostomy (Rashkind) is the key temporizing measure before surgical repair. Coronary transfer is the make-or-break step of the arterial switch operation, and anomalous coronary patterns must be meticulously defined preoperatively. The Lecompte maneuver (anterior PA translocation) prevents branch PA compression and is a critical step in the ASO. Atrial switch survivors (Mustard/Senning) face lifelong risk of systemic RV failure and arrhythmia and require specialized adult congenital care. In cc-TGA, the anatomic (double switch) repair addresses the fundamental problem of a systemic RV but is a complex operation best performed at high-volume centers. Late sudden death in ASO patients, though rare, can occur from coronary artery complications, making screening important.

## References
- Jatene AD et al. "Anatomic correction of transposition of the great vessels." *J Thorac Cardiovasc Surg*. 1976.
- Losay J et al. "Late outcome after arterial switch operation for transposition of the great arteries." *Circulation*. 2006.
- Baumgartner H et al. "2020 ESC Guidelines for the management of adult congenital heart disease." *Eur Heart J*. 2021.
- Warnes CA. "Transposition of the great arteries." *Circulation*. 2006.
- Hraska V et al. "Long-term outcome of the double switch operation." *Eur J Cardiothorac Surg*. 2017.
- Stout KK et al. "2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease." *Circulation*. 2019.