Transposition of the great arteries

Transposition of the great arteries (TGA) is a rare and critical heart defect present at birth whereby the two main arteries, aorta and pulmonary artery, are reversed. 

In a healthy heart, the oxygen-rich blood flows through the aorta while oxygen-poor blood flows through the pulmonary artery 

In a healthy heart, the left side of the heart pumps oxygen-rich blood to the rest of the body via the aorta while the right side of the heart pumps oxygen-poor blood to the lungs through the pulmonary artery. However, in babies with TGA, this becomes reversed; oxygen-poor blood gets pumped to the rest of the body by the aorta while oxygen-rich blood gets pumped to the lungs by the pulmonary artery. This causes a change in blood circulation and oxygen will be unevenly distributed from the heart to the rest of the body. Due to insufficient oxygen in the blood, one’s body will not be able to function properly, often resulting in serious complications, which can lead to death if left untreated. TGA is most often detected prenatally or within the first hours to weeks of the child’s life and is usually associated with other heart defects such as a ventricular septal defect (VSD). Having defects like VSD or atrial septal defect (ASD) creates a pathway for the baby’s blood to mix, allowing some oxygen-rich blood to still be pumped to the body. 

Possible complications from Transposition of the great arteries (TGA)

Complications to look out for depends on any operations previously performed.

1) Mustard or Senning procedure
Patients who previously underwent the Mustad or Senning procedure might face possible complications like: 

• Heart failure
  
• Baffle obstruction / leaks 
• Abnormal heart rhythms 
  

• Rastelli conduit stenosis or regurgitation
  
• Right heart failure
• Abnormal heart rhythms
  

Symptoms for babies with Transposition of the great arteries (TGA) usually occur at or soon after birth. Babies that have TGA can have the following symptoms:

• Breathlessness
• Palpitations (abnormal sensation of the heart beating)
• Bluish skin colour (cyanosis)
• Poor appetite 
• Weak pulse 
  

However, severity of the symptoms can vary depending on whether the baby has other congenital heart defects like ventricular septal defect (VSD) or atrial septal defect (ASD), both of which create a pathway for oxygen-rich blood to be pumped to the rest of the body. As such, babies with TGA and VSD or ASD may not have such severe symptoms.

It is thus possible for people to only discover their TGA condition in adulthood. If you develop breathlessness, palpitations, lower limb swelling, syncope (fainting), giddiness or chest pain you should visit your doctor as soon as possible.

​Transposition of the Great Arteries (TGA) is a congenital heart disease and usually cannot be prevented. However, you can take the following steps towards a healthy pregnancy which can reduce the risks of having a baby with TGA:

• Avoid harmful substance like alcohol, tobacco and illicit drugs.
• Make sure you keep up to date with your vaccinations to avoid infections that can be harmful to a developing fetus.
• Speak with your doctor early to get prenatal care and supplements even before you get pregnant. Discuss your current health, lifestyle and medications with your doctor. He/she will then provide you with advice for a healthy pregnancy. 
• Eat a balanced diet and exercise regularly. 
• Manage diabetes well if you have the condition and work closely with your doctor to keep it under control before getting pregnant. 
  

More importantly, if you have a family history of congenital heart defects or other genetic disorders, speak with your doctor before getting pregnant. 

There is no clear cause for Transposition of the great arteries (TGA), though it is mostly associated with abnormalities in certain genes or chromosomes. There are certain risk factors that increase the likelihood of TGA such as:

• Genetics: A family history of congenital heart defects increases the chances of TGA in your biological children. 
• Pregnancy-related issues: drinking alcohol, smoking, bad management of diabetes, taking certain medications or suffering from infections. 
  

Diagnosis of Transposition of the great arteries (TGA) can be done either during pregnancy or after the baby is born. 

During pregnancy
Pregnant mothers can go for prenatal tests to check for birth defects. Signs of TGA such as heart murmurs might be detected during an ultrasound scan of the mother, and the doctor might order a fetal echocardiogram (ultrasound scan of the baby’s heart) to see if there are problems with the heart’s structure and function. 

For adults, diagnosis usually starts with a physical examination by a doctor, assessing your medical history and routine tests. If the doctor hears a heart murmur during the physical examination, he/she might order other tests to confirm the diagnosis of TGA. The recommended tests may include:

• Chest X-ray: Allows the doctor to see if there is blood flow building up in the lungs. 
• Electrocardiogram (ECG): This can show the heart’s activity and heart rate by recording the heart’s electrical activity. 
  
• Echocardiogram: Accurately shows the position of the aorta and pulmonary artery to determine if there is TGA. It can also detect other congenital heart defects such as ventricular septal defect (VSD) or atrial septal defect (ASD).
  
• Cardiac catheterisation: A flexible, thin tube (catheter) will be inserted into the heart through a blood vessel in the leg or abdomen to diagnose TGA. 
  

Transposition of the great arteries (TGA) needs to be treated by corrective surgery. Before babies with TGA undergo their corrective surgeries, doctors might give them medications to increase blood flow and improve the mixing of oxygen-poor and oxygen-rich blood.

A balloon atrial septostomy might also be performed before these corrective procedures. This is a minimally invasive procedure which involves inserting a flexible, thin tube (catheter) into the heart to create or increase the size of a hole between the two atria (upper chambers). This allows more blood to mix and thus, more oxygen-rich blood gets pumped around the body. However, this is only a temporary solution and corrective surgeries are still required later on.

Corrective surgery will treat the transposition of the great arteries (TGA) and this treatment can be carried out soon after the child’s birth. While having a baby with this serious condition is alarming, TGA can be alleviated and treated with operation.

There are a few procedures that treat TGA:

1) Arterial Switch Operation

This procedure is usually done within the first month of the baby’s life. The pulmonary artery and aorta are switched back to their correct positions – pulmonary artery connected to the right ventricle and aorta connected to the left ventricle. The coronary arteries that provide blood to the heart will also be reattached to the aorta. 

2) Atrial Switch Operation

This procedure is not commonly performed because of the higher risks of complications. In this procedure, a tunnel is created between the two atria (upper chambers) of the heart. This allows oxygen-poor blood to move from the right atrium to the left ventricle and out of the pulmonary artery to the lungs. Oxygen-rich blood then moves through the tunnel from the left atrium to the right ventricle and out of the aorta to the body. Although the arteries are not shifted, this causes the right ventricle to work harder to pump blood to the entire body which can lead to complications in the future. 

3) Rastelli procedure 

For babies with both TGA and ventricular septal defect (VSD), this procedure might be recommended. The surgeon will close the defect (hole) and redirect blood flow from the left ventricle to the aorta which leads to the rest of the body. The connection between the left ventricle and pulmonary artery is blocked. A connection is then made with a prosthetic (artificial) valve from the right ventricle to the pulmonary artery. 

Complications after operation should be monitored for and can be treated. Medications (ACE inhibitors and beta blockers) can be useful in the event of heart failure. Abnormal heart rhythms can be managed with medications or ablation procedures. Baffle or conduit stenosis or regurgitation may require intervention with surgery or percutaneous techniques.

​Living with Transposition of the great arteries (TGA)

Activity
You may need to restrict your activity especially if your heart function is weak or there is presence of abnormal heart rhythm or valve issues. Your cardiologist will determine the limitations to your activities.

Prevention of endocarditis
You will need antibiotics to prevent endocarditis (infection of the inner layer of the heart) before any dental procedures if there are residual problems after operation. Antibiotics may also be required if you should go for body piercing or tattooing. Please consult your cardiologist.

Family planning and pregnancy 
There are some associated risks with pregnancy even after TGA repair is done. Please consult your cardiologist for advice.

National Heart Centre Singapore (NHCS) and the Department of Obstetrics & Gynaecology from Singapore General Hospital run a monthly specialised joint Cardiac-Obstetric Clinic on the last Monday morning of the month to see all pregnant patients with heart disease. Over the last 10 years, we have managed 200 to 300 pregnant patients with varying severity of cardiac problems through their pregnancy with successful outcomes.

NHCS Adult Congenital Heart Disease (ACHD) Programme

This programme was first started in 2003 and currently offers:

• ACHD clinic on every Wednesday and Thursday afternoon, and on the first and third Fridays of the month in which an average of 20-30 patients are seen at each session. Besides offering care and follow up of ACHD patients, NHCS also does screening of suspected Marfan patients; close monitoring of ACHD patients during pregnancy (see Pregnancy and Women with CHD) and a monthly joint Cardiac Obstetric Clinic (every last Monday of the month) with obstetricians from Singapore General Hospital (SGH) ; Monthly Transition Clinic in KK Women's and Children's Hospital (KKH) run jointly with paediatric cardiologists from KKH for patients above the age of 16. The aim is to give paediatric patients a smooth transition from paediatric cardiology to adult cardiology services. An average of 100-150 teenagers with congenital heart disease are transferred from KKH to NHCS every year. There is also a monthly Pulmonary Hypertension Clinic (every second Friday of the month) run jointly with a respiratory physician and a rheumatologist from SGH for general as well as congenital patients with severe pulmonary hypertension.
  
• Dedicated twice weekly congenital echocardiography sessions. 
  
• Dedicated weekly congenital cardiac catheterisation and intervention (particularly atrial septal defect (ASD), patent foramen ovale (PFO), patent ductus arteriosus (PDA) device closure).
• Surgical interventions including extra-cardiac Fontan procedures for uni-ventricular hearts, pulmonary homograft replacements for Tetralogy of Fallot of patients with severe pulmonary regurgitation, Rastalli conduit for patients with pulmonary atresia.
• Expertise in nuclear imaging, magnetic resonance imaging (MRI) and multi-slice computed tomography (CT) imaging.
• Expertise in pacing, arrhythmia treatment and ablation in congenital patients.
• Expertise in cardiopulmonary and exercise testing.
• Expertise in heart and lung transplantation for selected patients with end-stage congenital heart disease.
• Dedicated ACHD nurse for education, support and care of ACHD patient and their families.
  

Adult Congenital Heart Disease (ACHD) Clinic

This clinic looks after patients with operated as well as unoperated congenital heart conditions from age 16 onwards. Adults with congenital heart disease need regular monitoring and sometimes further surgical interventions. It also screens suspected Marfan patients and monitors ACHD patients closely during pregnancy.

For more information on NHCS Adult Congenital Heart Disease (ACHD) Programme, visit here.