Tetralogy of Fallot

Introduction

Tetralogy of Fallot is one type of cyanotic congenital heart disease. It comprises of four defects that are present at birth. The four defects are:

• Pulmonary stenosis: Narrowing of the valve and passage between the right ventricle and the pulmonary artery (main blood vessel leading to the lungs) which reduces blood flow to the lungs.
• Ventricular septal defect: A ventricular septal defect is a hole in the wall (septum) that separates the left and right ventricles.
• Overriding aorta: Normally the aorta branches off the left ventricle. In tetralogy of Fallot, the aorta is shifted to the right and lies directly above the ventricular septal defect. As a result, the aorta receives a mix of oxygen-poor and oxygen-rich blood from both the right and left ventricles respectively.
• Right ventricular hypertrophy: Enlargement and thickening of the right ventricle occurs because the right ventricle has to work harder than normal to pump the blood to the pulmonary artery.

Some children or adults who have tetralogy of Fallot may have other heart defects such as atrial septal defect, a right-sided aortic arch or abnormal course of coronary arteries. Together, these defects lead to problems in blood flow, causing oxygen-poor blood to flow to the body.

Causes and Risk Factors

Tetralogy of Fallot develops in an unborn baby while the heart is developing early in pregnancy. Usually, the exact cause is unknown. However, the following factors might increase the risk of having tetralogy of Fallot:

• Woman who is older than age 40 during pregnancy
• Woman who drinks a lot of alcohol during pregnancy
• Parent has tetralogy of Fallot
• Woman who has poor nutrition during pregnancy
• Woman who has a viral illness during pregnancy, such as rubella (German measles)
• The presence of Down syndrome or 22q microdeletion in the baby

Signs and Symptoms

The symptom or signs usually occur while the patient is an infant or soon after. Sometimes, depending on the severity of the defects, the symptoms may not be noted until adulthood.

• Cyanosis: Infants and children with tetralogy of Fallot usually have bluish tint to the skin, fingertips, or lips because their blood does not carry enough oxygen.
• Heart murmur: Tetralogy of Fallot is usually discovered within the first year of life when a healthcare provider hears a heart murmur.
• Getting tired easily during play or exercise.
• Squatting: Toddlers or older children with unrepaired tetralogy of Fallot might instinctively squat when they are short of breath. Squatting increases blood flow to the lungs.
• Digital clubbing: An abnormal, rounded shape of the nail bed in the fingers and toes may develop in children with tetralogy of Fallot.

Tet (hypercyanotic) spells

Sometimes, babies who have tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying or feeding, or when agitated. These episodes are called tet (or hypercyanotic) spells. Tet spells are caused by a rapid drop in the amount of oxygen in the blood. Tet spells are most common in young infants, around two to four months old. There would also be other symptoms including tiredness and limpness, fussiness, or seizure. Tet spells are potentially life-threatening due to low oxygen content.

Complications

A possible complication of tetralogy of Fallot is bacterial infection of the inner lining of the heart or heart valve (infective endocarditis). Another possible complication is stroke due to blockage of blood vessels of the brain. People with untreated tetralogy of Fallot usually develop more complications over time, which might result in death or disability before adulthood.

Diagnosis

Generic tests

Nowadays this condition is usually diagnosed with cardiac echocardiography. Additional tests may be performed to confirm the diagnosis, assess the severity, or prepare for surgical repair. They may include:

• Pulse oximetry: this test checks the amount of oxygen in your child’s blood
• Chest X-ray
• Electrocardiogram (ECG): this checks for irregular heartbeats (arrhythmias)

Special investigations available in HKCH

• Computerized tomography (CT scan): this may be performed to check the size of the pulmonary arteries or the location of the coronary arteries before the cardiac surgery
• Cardiac catheterization: in some situations, this invasive test may be involved. This involves putting a narrow tubing through the skin into the blood vessel and the inside of the heart. This would obtain information about the pressure, blood flow and size of the cardiac and vascular structures such as pulmonary arteries or coronary arteries.
• Genetic test: the doctor may order blood tests to check if your child has genetic abnormalities such as Down syndrome or 22q microdeletion.

Treatment

Currently, all paediatric cardiac surgeries in Hong Kong are performed in the Hong Kong Children’s Hospital.

Surgical repair of tetralogy of Fallot

Open heart surgery to repair tetralogy of Fallot can be performed between 6 months old and 1 year old. This involves:

• Closing the ventricular septal defect
• Widening the pulmonary stenosis and the right outflow tract
• Repairing other defects

Shunt operation

Sometimes open-heart reparative surgery cannot be performed for various reasons. For example, babies who are very small for their age, or it may be too risky for some to have open heart surgical repair. These babies may need a palliative operation called shunt operation in which a tube is placed between a branch of the aorta and a branch of the pulmonary artery to allow more blood to go to the lungs.

Medication

Sometimes a medication is prescribed to prevent the recurrence of hypercyanotic spell for children who have not received surgery.

Possible complications after tetralogy of Fallot surgery

While most babies do well after open heart surgical repair of tetralogy of Fallot, some may develop problems in the long term after the surgery, including:

• Leaking pulmonary valve (pulmonary regurgitation), in which blood leaks through the valve back into the right ventricle and increases burden of right heart
• Leaking tricuspid valve, in which blood leaks through the tricuspid valve from the right ventricle to right atrium
• Residual ventricular septal defects
• Enlargement and / or dysfunction of the right ventricle or left ventricle
• Arrhythmias
• Enlargement of the ascending aorta

Therefore, it is very important to have long term and regular checkups with the cardiologist even after reparative surgery.

Care and Precautions

General instructions

The HKCH Cardiology team will provide medical follow-up for paediatric patients with tetralogy of Fallot in need of surgical intervention or after surgical repair. Your child will need to see a cardiologist throughout his or her life even after successful surgical repair. This is important because doctors will check for any new problems in your child and make sure that any existing problems are under control. When your child reaches adulthood, the care will be transferred from the paediatric cardiology team to adult congenital heart disease specialists.

Certain types of physical activities may be limited. Please check with your child’s cardiologist for advice on physical activities and exercises.

Dental care

Maintaining good dental care is important for patients with congenital heart disease. Arrange routine dental care with the dentist to check for and treat dental caries. Ask your child’s cardiologist if antibiotic is needed before dental procedures.

Situations for seeking immediate medical attention

Go see a doctor right away if your child:

• Becomes more bluish-tinge cyanotic than usual
• Has trouble breathing
• Becomes tired and limp
• Decreased exercise capacity

Tet (or hypercyanotic) spell

If your child develops a tet (or hypercyanotic) spell, you should:

• Attempt to calm your child.
• Place your child on his or her side and bring the knees up tight against the chest (the knee-chest position). This helps increase blood flow to the lungs and relieve the spell.

If symptoms do not improve within minutes or if your child passes out, seek urgent medical consultation or emergency services.

Acknowledgement

Principal author: Dr Chow Pak-cheong on behalf of Cardiology Team, HKCH
Initial posting: Mar 2024

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