Congenital Heart Disease: What Is Dextro-Transposition Of The Great Arteries (d-TGA)?

Normally, the heart contains two major arteries, blood vessels that carry blood away. One artery takes oxygen-poor blood to the lungs so that it can become oxygen-rich again, while the other takes oxygen-rich blood from heart (after it returns from the lungs) and sends it to the body. Thus, the pattern of blood flow is body-heart-lung-heart-body.

Dextro-Transposition Of The Great Arteries (d-TGA) is a birth defect in which the two main arteries become switched. When this occurs, the blood flow becomes abnormal since the arteries are connected to the wrong part of the heart. This causes the blood flow to either:

• Get stuck in a body-heart-body loop, causing oxygen-poor blood to constantly travel around the body without getting oxygen
• Or get stuck in a lung-heart-lung loop, which means oxygen-rich blood doesn’t get delivered to the body.

The only way that people can survive this condition without undergoing surgery is through leaks of oxygen-rich blood into oxygen-poor blood, allowing some delivery of oxygen to the rest of the body. If a child is unable to undergo surgery, doctors can perform a procedure called catheterization (which encourages mixing of oxygenated and deoxygenated blood). This helps buy time and delays surgery until the child is ready.

Why does d-TGA occur?

The cause of most cases d-TGA is not known. The condition emerges over the course of fetal development. Some maternal risk factors associated with d-TGA include:

• Age. If the mother is over the age of 40 when she’s pregnant, that increases the risk of d-TGA.
• Diseases during pregnancy. If the mother has certain illnesses during pregnancy, such as diabetes, rubella or other viral diseases, that increases the risk of d-TGA.
• Environment. If the mother drinks alcohol or smokes during pregnancy, that can lead to d-TGA.
• Genetics. Congenital heart defects often run in families.

What are the symptoms of d-TGA?

Symptoms associated with d-TGA include:

• A bluish tint to the skin or lips, which indicates cyanosis or a lack of oxygen to the tissue.
• Being short of breath or breathing harder.
• The baby has trouble gaining weight and growing.
• Child has a lack of appetite.

What are the potential complications of d-TGA?

Several complications can develop in patients with d-TGA, particularly if the condition is left untreated:

• Hypoxia, a condition in which the child’s body does not receive the oxygen they need to survive.
• Heart failure, a condition in which the heart is not able to pump adequate blood because the heart muscle is too weak or stiff.
• Lung damage caused by excess blood volume.
• Arrhythmia (heart rhythm abnormalities).
• Narrowing of the coronary arteries (which supply blood to heart).

How can you prevent d-TGA?

In the vast majority of cases, d-TGA cannot be prevented. However, it is important for pregnant women to make healthy lifestyle choices. Do not drink or smoke and make sure you are up to date with all your vaccinations. You should also take 400 micrograms of folic acid a day.

How is d-TGA diagnosed?

Usually, d-TGA is not diagnosed prior to birth as that would be quite difficult. However, once the baby is born, a doctor may suspect a congenital heart defect if they observe that the baby has trouble breathing, cyanosis, or they can hear a heart murmur.

The following tests can be administered to diagnose d-TGA:

• An echocardiogram, which uses ultrasound waves to make a moving picture of the heart that can be seen on a screen. This can allow the doctor to see if the arteries are switched.
• Cardiac catheterization, in which the doctor puts in a catheter (a thin tube) into a blood vessel which goes up to the baby’s heart. Once there, a dye is injected to help create detailed pictures of structures within the heart, allowing for the identification of a defect.
• Chest x-ray, which allows doctors to visualize structures of the chest . This can also help determine if the positions of the two arteries are switched.
• An electrocardiogram, a test that measures the electrical activity of the baby’s heart and helps detect any abnormalities.

What are the treatments for d-TGA?

All children with d-TGA will need surgery to correct this defect. Prior to surgery, the babies may be given some medication or undergo a cardiac catheterization procedure known as atrial septostomy to manage the condition until they are ready for surgery. The following surgeries may be conducted in babies with d-TGA:

• Arterial switch operation, the most common surgery for d-TGA. During this surgery, the two switched arteries are moved back to their original positions.
• Atrial switch operation, a surgery in which the surgeon makes a type of tunnel between the two upper regions of the heart to divert oxygen-poor blood to the artery that goes to the lungs so that it can become oxygen-rich. Similarly, the oxygen-rich blood is diverted to the region of the heart that pumps blood to the rest of the body.