What is Transposition of the Great Arteries?
Transposition of the great arteries (TGA) is a heart defect in children, present at birth, where the two main arteries leaving the heart are reversed. These arteries are the aorta and pulmonary trunk. Normally, during heart development in an embryo, a specific structure called the conotruncal septum follows a spiral path to split the main artery of the heart into two separate ones – the aorta and the pulmonary arteries. In cases of TGA, this doesn’t happen as it should, and both arteries come from the wrong place. This condition happens when the aorta originates from the right lower chamber of the heart, instead of the left, and the pulmonary artery comes from the left lower chamber, not the right one.
Most cases of TGA involve a form known as Dextro-TGA (D-TGA). In this form, the right lower chamber of the heart (right ventricle) is positioned to the right side of the left lower chamber of the heart (left ventricle), with the aorta being positioned forward and to the right of the pulmonary artery. This results in two separate and parallel blood circuits, instead of the desired single, interconnected one. In one circuit, blood lacking oxygen from the body returns to the right side of the heart and is then pumped right back out to the body without receiving any fresh oxygen. In the other, oxygen-rich blood from the lungs returns to the left side of the heart, and is then pumped right back to the lungs.
Babies with this condition often show signs of having low oxygen levels, like bluish skin, within the first 30 days of life. Because two separate circuits won’t sustain life, the only way for them to survive is if they have some other birth defects that allow the oxygen-rich and oxygen-poor blood to mix together.
What Causes Transposition of the Great Arteries?
We’re not really sure what causes Transposition of the Great Arteries (TGA), but we think it’s likely due to a combination of factors. Two theories have been put forward to try and explain how TGA occurs during the early stages of a baby’s development in the womb:
-The first theory, suggested by De la Cruz, is that TGA may occur because a certain part of the baby’s heart, called the aortopulmonary septum, doesn’t twist like it should during development. This could lead to the septum growing in a straight line instead, which could cause TGA.
-The second theory, proposed by Goor and Edwards, suggests that TGA might be due to improper absorption or lack of development of a part of the heart called the subpulmonary conus. In this case, another part of the heart, known as the subaortic conus, continues to persist. This could also lead to TGA.
It’s important to remember these are just theories and we still need to learn more to truly understand the causes of TGA.
Risk Factors and Frequency for Transposition of the Great Arteries
Transposition of the great arteries (TGA) is a heart condition that occurs in approximately 4.7 out of every 10,000 live births. This represents about 3% of all birth defects affecting the heart and 20% of heart diseases that cause a bluish coloration in the skin due to low oxygen.
Signs and Symptoms of Transposition of the Great Arteries
Transposition of the great arteries (TGA) is a heart condition that can be hard to diagnose before a baby is born, since regular ultrasound scans might not clearly show it. Most symptoms of dextro-TGA (D-TGA), one type of this condition, show up during the first month of a baby’s life (the neonatal period). The symptoms are all related to how much mixing there is between the two main pathways of blood flow in the heart. Here are the typical symptoms:
- Cyanosis: This is a bluish tint to the skin, lips, and nail beds, which is caused by low oxygen levels. The degree of cyanosis varies depending on how much the two circuits in the heart mix. This can be influenced by the size and presence of an atrial septal defect (ASD) or ventricular septal defect (VSD), which are holes in the walls between heart chambers. This blue coloration doesn’t get worse with exertion or extra oxygen.
- Tachypnea: This is a faster than normal breathing rate, usually over 60 breaths a minute. But despite this rapid breathing, babies with D-TGA don’t show signs of respiratory distress like pulled-in muscles, grunting sounds, or flared nostrils, and they seem comfortable.
- Murmurs: A heart murmur, or extra heart sound, is not usually present unless there is a small VSD or narrowing of the pulmonary valve (pulmonic stenosis). A murmur from a VSD would be present throughout the heartbeat cycle and noticeable at the lower left edge of the breastbone. Pulmonic stenosis would cause a murmur during the “systolic” or contracting phase of the heartbeat, noticeable at the upper left edge of the breastbone.
Patients with another type of this condition, levo-TGA (L-TGA), usually don’t experience negative effects until later in life. Over time, the right chamber of the heart can’t manage the increased force needed to push blood through the body’s circulation. Eventually, these individuals will show signs and symptoms of heart failure.
Testing for Transposition of the Great Arteries
D-TGA, also known as ‘transposition of the great arteries’, can be hard to spot during an ultrasound while the baby is still in the womb. This is because there are no noticeable differences in the size of the heart’s ventricles. However, if a doctor suspects there might be a problem with the baby’s heart based on a clinical examination, they will perform an echocardiogram once the baby is born. This is a type of ultrasound scan that looks specifically at the heart.
The echocardiogram can show if the main arteries – the aorta and the pulmonary trunk – have started from the wrong place. It can also spot any other problems within the heart.
Other tests that might be completed include:
– An electrocardiogram (ECG): this measures the electrical activity of the heart and can show whether the heart’s right side is overworked.
– A chest X-ray: the typical X-ray of someone with TGA has a very specific look, known as ‘egg on a string’.
Finally, there’s a procedure called cardiac catheterization. This involves inserting a tube, known as a catheter, into one of the blood vessels that leads to your heart. While this procedure isn’t normally used to diagnose TGA, it is considered the ‘gold standard’ for clarifying where the coronary arteries (which supply blood to the heart) are starting from. It is also routinely used in severe cases of TGA to perform a procedure known as a balloon septostomy, which can help to improve the levels of oxygen in the blood.
Treatment Options for Transposition of the Great Arteries
If a patient is diagnosed with Transposition of the Great Arteries (D-TGA), immediate steps need to be taken to ensure the patient is getting enough oxygen. A common medicine called Prostaglandin E1 is given to the patient. This medicine helps in keeping a certain blood vessel in the heart (ductus arteriosus) open. Along with this, a medical procedure called balloon atrial septostomy (BAS) is performed. In this procedure, a tiny balloon is used to create an opening between the two upper chambers of the heart which helps stabilize the patient. Once the patient’s condition is stable, corrective surgery is planned.
This surgery is generally performed within the first week of life in patients with D-TGA. There are two main types of surgeries currently used:
1. Arterial Switch Operation (ASO): This is the standard surgical procedure for patients with D-TGA who don’t have severe pulmonary stenosis (a condition causing the narrowing of the pulmonary valve). During this operation, the surgeon cuts both major vessels of the heart – the aorta and the pulmonary trunk – and then moves them to their correct positions. The blood vessels that supply blood to the heart muscle (coronary arteries) are also moved and reattached in the correct location on the aorta. If a Ventricular Septal Defect (VSD) (a hole in the wall separating the two lower chambers of the heart) is present, it is also fixed during this procedure.
2. Rastelli Procedure: This procedure is indicated when a patient with D-TGA also has a large VSD and stenosis of the pulmonary artery. In this procedure, the VSD is closed using a baffle, which guides oxygen-rich blood from the left chamber of the heart into the aorta. A tube is placed from the right chamber of the heart to the pulmonary artery to allow oxygen-poor blood to flow to the lungs.
There are also other corrective procedures such as the Mustard and Senning procedure, Nakaidoh procedure, Réparation à l’Etage ventriculaire (REV procedure), and Yasui procedure. However, these surgeries are performed less often.
What else can Transposition of the Great Arteries be?
When diagnosing the heart condition called transposition of the great arteries, doctors need to consider other similar conditions that could present the same kinds of symptoms. These include:
- Double-Outlet Right Ventricle: a condition where both the body’s main blood vessels come out of the right side of the heart.
- Tricuspid Atresia: a condition where the tricuspid heart valve is missing or abnormally developed.
- Pulmonary Atresia: a condition where the pulmonary valve doesn’t form properly, inhibiting blood flow from the heart to the lungs.
- Tetralogy of Fallot: a rare condition caused by a combination of four heart defects that are present at birth.
- Total Anomalous Pulmonary Venous Return: a condition where the veins bringing blood back from the lungs don’t connect to the left atrium like they are supposed to.
- Truncus Arteriosus: a rare heart defect present at birth where a single blood vessel comes out of the heart instead of the usual two.
Each of these conditions would require different treatment approaches, making it important to correctly identify the issue.
What to expect with Transposition of the Great Arteries
Patients with D-TGA, which is a heart condition where the two main arteries leaving the heart are reversed, are likely to do really well after surgery. The current survival rates are over 90%, which is quite promising. The surgery known as ASO (Arterial Switch Operation) has shown the best long-term survival and results in terms of quality of life. Some research even shows a survival rate higher than 95%, covering a span of 15 to 25 years after being discharged from the hospital.
Possible Complications When Diagnosed with Transposition of the Great Arteries
Corrective surgeries for heart conditions can lead to several complications. These might include:
- Having an irregular heart rhythm
- Blockage or leakage from the constructed tunnel (in a Rastelli Procedure)
- Narrowing of the arteries that lead to the lungs
- Narrowing of the arteries that supply blood to the heart
- Widening of the base of the aorta, the main vessel carrying blood out of the heart
- Leaking of the aortic valve, which controls the flow of blood from the heart to the aorta
Preventing Transposition of the Great Arteries
People who have had their ‘D-TGA’ condition fixed may find they’re a bit less capable when it comes to exercise. D-TGA, or Dextro-Transposition of the Great Arteries, is a serious heart condition that is present from birth. Certain factors can further bring down this exercise capacity. These include having had a VSD repair (fixing a hole in the heart), a weaker left section of the heart, and getting the repair done before the ASO procedure (another type of heart surgery) developed. Even with reduced ability to exercise, it doesn’t seem to affect routine activities in daily life.
Studies have highlighted that people who’ve undergone ASO (Arterial Switch Operation – a type of heart surgery) are more prone to suffer from neurodevelopmental issues. In other words, they may have problems with things like learning, behavior, and skills. One hospital found that nearly two-thirds of teenagers who had the ASO procedure as babies later needed special education help. This hospital also found that people who had ASO were more likely to suffer from ADHD (Attention-Deficit/Hyperactivity Disorder), which makes it difficult to pay attention and control impulsive behaviors.
Given these concerns, the American Heart Association suggests ongoing checks for kids who’ve had D-TGA surgery. This will help identify early if they’re having any neurodevelopmental issues, so that appropriate help can be provided.
