What Is Transposition of the Great Arteries (TGA)?

Congenital defect in which major structures of the heart are switched

Diagram of Heart
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Transposition of the great arteries (TGA) is a group of congenital defects in which the position of major blood vessels of the heart are switched. In rare cases, even the chambers of the heart will be swapped. TGA causes the diversion of normal blood circulation, robbing the body of the oxygen and nutrients that it needs. Depending on which structures are switched, TGA can range in severity from subclinical (without notable symptom, at least until later in life) to life-threatening. TGA can be readily diagnosed with X-ray and other studies. Surgery is an essential part of the treatment plan in most cases.

Also known as transposition of the great vessels (TGV), TGA is a rare but serious disorder that affects one of every 4,000 to 10,000 births.

Types of TGA

There are two types of TGA that differ by the vessels and heart chambers involved:

  • Dextro-transposition of the great arteries (d-TGA) occurs when the position of the main pulmonary artery and aorta are switched.
  • Levo-transposition of the great arteries (l-TGA) is a rarer condition in which not only are the aorta and pulmonary arteries are switched but also the lower chambers of the heart (called the ventricles).

TGA is usually accompanied by other defects, such as a ventricle septal defect (a hole between the lower chambers of the heart), atrial septal defect (a hole between the upper chambers of the heart), or patent ductus arteriosus (a hole in the aorta).

Symptoms

The symptoms of TGA can vary by the type of defect involved. Those associated with d-TGA are more immediate and severe, while those associated with l-TGA are often subclinical (with few observable symptoms) until later in life.

Dextro-TGA

Of the two types, d-TGA is considered more serious because the switching of the aorta and pulmonary artery interferes with the normal flow of blood. Rather than following the normal pattern (body-heart-lung-heart-body), d-TGA will follow two separate and distinct "circular" patterns:

  1. Deoxygenated blood intended for the lungs is instead diverted out of the heart via the aorta (body-heart-body).
  2. Oxygenated blood intended for circulation is instead diverted back to the lungs via the pulmonary artery (body-lungs-body).

The depletion of blood oxygen (hypoxia) in infants with d-TGA can cause serious and potentially life-threatening symptoms, including:

  • Cyanosis (blueish skin color due to the lack of oxygen)
  • Dyspnea (shortness of breath)
  • A pounding heart
  • Weak pulse
  • Poor feeding

Moreover, delivering too much oxygen-rich blood to the lungs can cause damage by placing oxidative stress (an imbalance between antioxidants and free radicals) on lung tissues.

Without surgery, the only way for a baby to survive d-TGA is for blood to pass through holes in the heart—such as a septal defect or patent ductus arteriosus—allowing oxygenated blood to mix with deoxygenated blood, albeit at inadequate volumes.

Levo-TGA

With l-TGA, the switching of both the aorta and pulmonary artery, as well as the left and right ventricles, will not stop blood circulation. Instead, it will cause the blood to flow in the opposite direction.

Because oxygenated blood is still available, the symptoms of l-TGA tend to be less severe. This doesn't mean, however, that the condition is benign. Because the flow of blood is reversed, the right ventricle has to work harder to counteract the force of normal circulation, putting excessive strain on the heart.

Simple l-TGA (in which no other congenital heart defects are involved) may not manifest with easily identifiable symptoms, although blood pressure may be elevated. Over time, the stress placed on the right ventricle can cause ventricular hypertrophy (the abnormal enlargement of the heart chamber).

This can reduce the outflow of blood from the heart and trigger symptoms of heart failure, including:

  • Difficulty breathing on exertion
  • Angina (chest pain) on exertion
  • Syncope (fainting, typically on exertion)
  • Heart palpitations (skipped heartbeats)
  • General fatigue
  • Upper abdominal fullness
  • Discomfort or pain in the upper right abdomen
  • Loss of appetite

Complex l-TGA (in which additional heart defects are involved) may lead to identifiable symptoms early on, including mild cyanosis and extreme fatigue with exertion. Abnormal passages in the heart can reduce the heart's ability to pump blood both to and from the lungs and to and from the rest of the body.

Some people with l-TGA may not have symptoms or even be aware of their condition until adulthood when signs of heart failure appear. In these adults, medical management is often preferred over surgery.

Causes

The transposition of the great arteries occurs during fetal development. The reason why this occurs is still unknown, although it is believed that certain health conditions alter the way in which embryonic cells specialize and differentiate. In some cases, they may "flip" the genetic coding, causing a reversal of the position of the great arteries and ventricles.

Among some of the maternal risk factors believed associated with TGA are:

  • Poorly control diabetes during pregnancy
  • Drinking alcohol during pregnancy
  • Having rubella (German measles) or other viral infections during pregnancy
  • Smoking during pregnancy
  • A family history of congenital heart defects

TGA is more likely to occur if any of these things occur during the first trimester of pregnancy when cells are just starting to specialize.

Having these risk factors does not mean your child will be born with TGA. Other factors may contribute, and further research is needed before the genetic and environmental triggers are clearly defined.

With that said, every effort should be made to avoid smoking and alcohol during pregnancy, to control diabetes and other chronic health conditions, and to seek necessary vaccinations before getting pregnant.

Diagnosis

TGA is usually suspected if a baby is born with signs of hypoxia (low blood oxygen characterized by cyanosis and labored breathing). However, the signs may be missed if the child is born with l-TGA or d-TGA is accompanied by a septal defect. Often, prenatal investigations will not be performed unless there are clear signs of a heart or circulatory defect.

If TGA is suspected, the doctor will first check the baby's heart with a stethoscope. A common sign is a heart murmur in which blood makes an abnormal swishing sound as it moves through the heart.

TGA can be confirmed with a combination of diagnostic tests:

  • Electrocardiogram (ECG), which measures the heart's electrical activity during heartbeats to detect structural abnormalities
  • Echocardiogram, which uses sound waves to visualize the heart as it pumps blood
  • Chest X-ray, which uses ionizing radiation to visualize the position of the aorta and pulmonary artery
  • Computed tomography (CT), which takes multiple X-ray images to create three-dimensional "slices" of the heart
  • Cardiac catheterization, in which a narrow tube is run from a vein in the baby's groin to the heart to better visualize the heart on X-ray and to measure the internal pressure of the heart

If TGA is suspected before birth, a fetal echocardiogram can be performed while the baby is still in the womb. At present, fetal heart surgery and catheterization are reserved for life-threatening situations as their effectiveness has yet to be proven.

Treatment

The treatment of TGA varies by the type involved as well as the age of the patient at the time of diagnosis.

Dextro-TGA

Because d-TGA is generally more overt at birth and, as such, more likely to be diagnosed, treatment would be focused on correcting the heart defect.

However, because the heart of a newborn is so small, surgery is often delayed until at least two weeks after birth. During this waiting period, the baby's survival is usually dependent upon having one or more holes in the heart (i.e., septal defects, patent ductus arteriosus) to maintain adequate circulation.

Prior to corrective surgery, the pediatric cardiac surgeon will recommend several options to better stabilize the newborn's condition:

  • Medications: Shortly after birth, the baby will receive an intravenous (IV) infusion of Alprostadil (prostaglandin E1) which helps keeps the abnormal holes in the heart open.
  • Balloon atrial septostomy (BAS): For this procedure, a thin catheter is run from the baby's groin to the heart. A balloon the end of the catheter is then inflated to enlarge the hole in the heart.

In the past, these procedures were performed so that corrective surgery could be delayed for around a month.

In recent years, surgeons have opted to forego the BAS due to the risk of complications (such as stroke, embolism, atrial perforation, vascular damage, and cardiac tamponade) and perform corrective surgery two weeks after birth.

There are several options a surgeon can pursue to correct d-TAG. Both are open surgeries that access the heart by entering the chest. The two primary choices are:

  • Arterial switch operation: This surgery involves severing the aorta and pulmonary artery and switching them to their correct positions. It is considered the preferred option in most cases. During the surgery, any holes in the heart may be sutured or allowed to close on their own if they are small.
  • Atrial switch operation: This surgery involves the creation of a tunnel (baffle) between the two upper chambers of the heart (atria). This allows deoxygenated blood to reach the lungs and oxygenated blood to access the aorta for delivery to the rest of the body. While effective, the surgery may cause leaks and heart rhythm disorders and often requires additional corrective surgeries later in life.

Even if the surgery is considered successful, the heart will need to be regularly monitored by a cardiologist throughout the individual's life. Certain physical activities may need to be avoided, such as weightlifting or extreme sports, as they can place excessive strain on the heart.

Levo-TGA

Because the symptoms of l-TGA are often subtle, the condition may not be recognized until the baby is older. In some cases, the condition may only be diagnosed in later life when symptoms of heart failure develop.

Generally speaking, most children with l-TGA will not require surgery unless there is a septal defect or obstruction of the right ventricular valve. Instead, the child will be monitored throughout life and into adulthood to identify and treat any heart problems that may arise.

If surgery is needed, it may involve:

  • Heart valve repair: This surgery may either be performed as an open surgery or corrected via a catheter into the heart.
  • Heart valve replacement: This surgery, performed either as an open surgery or via heart catheterization, will replace the damaged valve with a prosthetic one.
  • Double switch operation: This is a technically complex surgery that reroutes oxygenated blood to the left ventricle and aorta and deoxygenated blood to the right ventricle and pulmonary artery.

Whether surgery is performed or not, a child with l-TGA may be faced with numerous heart problems as they get older, including heart valve problems, bradycardia (slowed heart rhythms), and heart failure. Medications and procedures like a heart block and pacemaker surgery may be needed to correct these concerns.

Adults diagnosed with l-TGA rarely need double-switch surgery, although valve repair or replacement is not uncommon. Efforts instead will be made to appropriately treat symptoms of heart failure and heart rhythm disorders.

Prognosis

The prognosis (predicted outcome) of TGA can vary. However, with advances in the surgical and pharmaceutical management of d-TGA and l-TGA, survival times and quality of life measures have increased enormously in recent years. In some cases, a normal life expectancy can be achieved.

Dextro-TGA

Clearly, the greatest challenge is improving outcomes involves newborns with d-TGA who invariably require surgery. A 2018 study published in the Annal of Thoracic Surgery reported that babies who underwent arterial or atrial switch surgery had, respectively, an 86.1% or 76.3% chance of surviving for at least 20 years.

Excluding those who had died during the operation, the likelihood of survival for those with an arterial switch jumped to 97.7%, while those with atrial switch has a 20-year survival rate of 86.3%. Long-long medical management and additional surgeries, when needed, will likely extend those survival times for many more years.

Levo-TGA

In people with l-TGA, survival times are generally greater but are influenced by the extent of structural abnormalities in the heart as well as the medical interventions taken.

For instance, a 2015 review published in the Oscher Journal reported that people with l-TGA who had leakage of the tricuspid valve (one of the two valves on the right side of the heart) had a 20-year-survival rate of 43% compared to those without valve leakage whose 20-year-survival was 93%.

On the other hand, the replacement of the tricuspid valve in people with TGA corresponds to a 5- and 10-year survival rate of 100% and 94%, respectively.

Even people with TGA who require a heart transplant have a 5-year survival rate of 69% due to improved surgical techniques and postoperative therapies.

A Word From Verywell

If your baby has transposition of the great arteries, you may be understandably worried. It may help to know that most babies born with TGA can survive well into adulthood without serious complications if treated appropriately.

Until the mid-20th century, the majority of babies born with TGA did not survive more than a few months. With the advent of newer, better surgical techniques and improved post-surgical care, the picture has changed for the better.

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