Transposition of the Great Arteries

What is transposition of the great arteries (TGA)?

Transposition of the great arteries (TGA) is a congenital heart defect in which the main arteries that pump blood to the lungs and to the body connect to the heart abnormally. 

When looking at the normal circulation of the heart:

• The right side of the heart pumps blood that is low in oxygen (blue) through the pulmonary artery and into the lungs, where it picks up oxygen and becomes oxygen-rich (red).
• The left side of the heart receives oxygen-rich (red) blood from the lungs and pumps it out to the body through the aorta. The body then uses up the oxygen and the blood becomes blue and goes back to the right side of the heart.

In babies with TGA, the two arteries are switched (transposed):

• The aorta (body artery) attaches to the right side of the heart instead of the left
• The pulmonary artery (lung artery) attaches to the left side of the heart instead of the right

This means that the body receives blood that is low in oxygen, and the lungs receive blood that is high in oxygen.  This type of blood flow cannot support the body in the way it needs to survive and requires surgery or other procedures soon after birth.

Other defects in babies with TGA

Babies with TGA often have other heart defects, such as:

• A hole between the bottom chambers of the heart (ventricular septal defect).
• A hole between the upper chambers of the heart (atrial septal defect).
• The patent ductus arteriosus (PDA) is a normal connection between the lung (pulmonary) and body (aorta) artery that exists in babies before they are born. This connection goes away after birth between the first few hours to days after birth, when babies begin breathing on their own.

These holes allow for mixing of the red (oxygen-rich) and blue (oxygen-poor) blood, so that the body is able to receive some oxygen-rich blood. The body requires some mixing of red & blue blood in order to survive.

Causes of transposition of the great arteries

The causes of congenital heart defects such as TGA are unknown. Babies with differences in their genes or chromosomes are often more likely to have certain types of heart defects; however, TGA is not commonly found in these babies.

Diagnosing TGA

Before Birth

TGA is a heart defect that can be diagnosed by ultrasound before babies are born, typically after 18 weeks gestation during the 2^nd or 3^rd trimester. A provider may suspect a baby has TGA based on indications from an ultrasound, and can request a fetal echocardiogram, which is a detailed ultrasound of a baby’s heart.

Diagnosing TGA in babies before birth is important because they require special care soon after birth. Babies with TGA should be born in a high-risk birth center where there is access to neonatal and cardiology services at the time of delivery.

After Birth

Babies who are born with TGA will show symptoms at birth or shortly after. Depending on how much mixing of red and blue blood is present through the ductus arteriosus, patent foramen ovale, and any ventricular septal defects, symptoms will vary in severity.

• Newborn pulse oximetry screening can help detect TGA by measuring the amount of oxygen in a baby’s blood. If oxygen levels are low, this can signal to the care team to perform further testing to assess for undiagnosed conditions such as congenital heart disease.
• Similar to prenatal testing, the most common test used to diagnose TGA is an echocardiogram.
• Other common tests used to help diagnose and assess babies with TGA include:
  • Cardiac catheterization
  • EKG
  • Chest X-Ray
    
    

Signs and symptoms of TGA

When babies are born with TGA, there is not enough oxygen getting out to their body. This can lead to severe symptoms, complications and death if left untreated.

Common signs of TGA:

• Cyanosis (bluish-tinted skin) caused by a low amount of oxygen getting out to the body
• Difficulty breathing
• Poor feeding

Treatment

On average, Children’s Mercy sees around 10 babies per year with TGA.

Treatment for TGA begins shortly after birth. Babies with TGA will require monitoring in the neonatal intensive care unit (NICU) before surgery and will go to the pediatric intensive care unit (PICU) following surgery for close monitoring. Once the baby is stable, they will then go to our inpatient cardiac unit on 4 Sutherland.

Treatment options include:

Medication

Shortly after birth, a medication called Prostaglandin is given continuously to babies through an IV line. The purpose of this medication is to keep the patent ductus arteriosus (PDA) open and prevent from closing in order to allow for mixing of the red and blue blood, so that the body will receive some oxygen-rich blood. Babies may stay on this medication until they undergo surgery.

Babies with TGA will likely need oxygen after birth as well. If a baby has a low oxygen level or has difficulty breathing on their own, a breathing tube may be needed.

Cardiac Catheterization

If the hole between the upper chambers of the heart (atrial septal defect) is not big enough after birth, a catheter procedure called an atrial septostomy may be needed to make the hole larger in order to allow for mixing of the red and blue blood. It is common for babies with TGA to need this procedure and is performed in a catheterization lab by cardiologists who specialize in interventional pediatric cardiology. This procedure is often performed sometime within the first few hours to days after birth, depending on the severity of baby’s symptoms and how big the atrial septal defect is.

Surgery

Every baby born with TGA will require heart surgery in the newborn period, typically between the first 3 to 14 days after birth. The most common surgery with the best outcomes is the arterial switch operation. This operation involves switching the main arteries as well as the coronary arteries and large blood vessels, where the pulmonary artery connects to the right side of the heart, and aorta connects to the left side of the heart.