What is transposition of the great arteries? 

Transposition of the Great Arteries (TGA) is a serious and rare congenital heart defect where the two main arteries leaving the heart the aorta and the pulmonary artery are swapped or ‘transposed.’ In a healthy heart, the pulmonary artery carries deoxygenated blood to the lungs, and the aorta carries oxygenated blood to the body. In TGA, this arrangement is reversed, creating two separate circulatory loops that prevent oxygen-rich blood from reaching the body’s vital organs. Without immediate medical intervention and surgery, TGA is life-threatening. 

TGA affects approximately 1 in 3,500 to 5,000 live births in the UK. Because the body cannot receive the oxygen it needs to function, newborns with this condition often appear ‘blue’ (cyanotic) shortly after birth. While the diagnosis is critical, advancements in neonatal cardiac surgery specifically the ‘arterial switch’ operation have transformed the outlook for these infants. Today, more than 90% of babies born with TGA survive into adulthood and lead healthy, active lives. 

What We will cover in this Article 

• The anatomical difference between a healthy heart and TGA. 

• Recognising the early signs of cyanosis in newborns. 

• Immediate medical stabilisations, including PGE1 and balloon septostomy. 

• The surgical ‘Arterial Switch’ procedure and its timing. 

• Long-term monitoring and clinical outcomes for TGA patients. 

• Differentiation between D-TGA and L-TGA (Congenitally Corrected). 

Anatomy: The Swapped Arteries 

In a baby with TGA, the ‘plumbing’ of the heart is incorrectly connected. In a normal heart, the right-side pumps blood to the lungs and the left side pumps blood to the body. In TGA, the aorta is connected to the right ventricle, and the pulmonary artery is connected to the left ventricle. This creates a dangerous situation where oxygen-poor blood is continuously pumped back to the body, and oxygen-rich blood is continuously pumped back to the lungs. 

For a baby with TGA to survive the first few days of life, there must be a way for the two blood loops to mix. This usually happens through naturally occurring ‘holes’ like a Patent Foramen Ovale (PFO) or a Patent Ductus Arteriosus (PDA). If these holes are too small, the baby will become severely oxygen-deprived very quickly. 

Symptoms and Immediate Clinical Stabilisation 

The most common symptom of TGA is cyanosis, a bluish tint to the skin, lips, and tongue, which is usually noticed within minutes or hours of birth. Unlike some other heart defects, babies with TGA often have normal birth weights and may initially appear healthy apart from their colour. Other signs include rapid breathing, a fast heart rate, and difficulty feeding. 

Once TGA is suspected, the NHS clinical team moves rapidly to stabilise the infant. This often involves: 

• Prostaglandin (PGE1) Infusion: A medication given via a drip to keep the ductus arteriosus open, allowing oxygenated blood to mix and reach the body. 

• Balloon Atrial Septostomy (BAS): A bedside procedure where a cardiologist uses a small balloon to enlarge the hole between the upper heart chambers to improve mixing. 

• Monitoring: Intensive care monitoring of oxygen saturations and blood gases to ensure the baby remains stable until surgery. 

The Arterial Switch Operation 

The definitive treatment for TGA is the ‘Arterial Switch’ operation, which is typically performed within the first two weeks of life. During this complex open-heart surgery, the surgeon disconnects the aorta and pulmonary artery and reattaches them to their correct ventricles. A vital part of this surgery involves moving the tiny coronary arteries (which supply blood to the heart muscle itself) to the new aorta. 

Differentiation: D-TGA vs. L-TGA 

It is important to distinguish between the common form of TGA (D-TGA) and a rarer version called ‘Congenitally Corrected’ TGA (L-TGA). While they sound similar, their impact on the heart is very different. 

Feature	D-TGA (Complete)	L-TGA (Corrected)
Circulation	Two separate, non-mixing loops	Anatomically swapped, but blood flows correctly
Symptoms	Severe blueness at birth	Often no symptoms in childhood
Emergency?	Yes, life-threatening at birth	No, but may cause issues later in life
Surgery	Arterial Switch in infancy	Depends on associated defects
Detection	Prenatal scan or at birth	Often found during adulthood

To Summarise 

Transposition of the Great Arteries is a critical heart defect where the main arteries are connected to the wrong chambers. While it presents a life-threatening emergency at birth, modern surgery has made it a highly treatable condition. The ‘arterial switch’ procedure effectively restores normal circulation, allowing the vast majority of children to grow up with normal heart function. Lifelong follow-up with a cardiologist is essential to monitor the coronary arteries and valve health as the child matures. 

If your baby has blue-tinged lips, tongue, or skin, or is struggling to breathe, call 999 immediately. 

If your newborn is unusually lethargic, cold to the touch, or grey in appearance, call 999 immediately. 

Authority Snapshot (E-E-A-T Block) 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician (MBBS) with postgraduate certifications in ACLS and BLS. Dr. Petrov has extensive clinical experience in general medicine and emergency care, having worked in hospital wards and intensive care units where neonatal cardiac stabilisations are performed. His expertise ensures this information on Transposition of the Great Arteries is accurate, safe, and aligned with current NHS and British Congenital Cardiac Association (BCCA) standards.