Tetralogy of Fallot (TOF)

The four parts of tetralogy of Fallot

1. Ventricular septal defect (VSD): a large hole in the wall between the left and right ventricles.
2. Pulmonary stenosis: narrowing at or below the pulmonary valve, restricting blood flow from the right ventricle to the lungs.
3. Overriding aorta: the aorta sits directly above the VSD, so it receives blood from both ventricles.
4. Right ventricular hypertrophy: the right ventricle's wall thickens because it pumps against the narrowing.

Because the outflow to the lungs is narrowed, some oxygen-poor blood from the right ventricle crosses the VSD into the aorta and goes to the body. The more severe the pulmonary narrowing, the bluer the baby. The most severe form, TOF with pulmonary atresia, has no direct connection from the right ventricle to the lungs.

Causes and risk factors

Like most congenital heart defects, TOF develops in the first 8 weeks of pregnancy, and usually no single cause is found. Linked factors include:

• Genetic conditions: 22q11.2 deletion syndrome (DiGeorge syndrome) in about 15% of cases, and Down syndrome
• A parent or sibling with a congenital heart defect
• Diabetes, rubella, phenylketonuria or alcohol use in the mother during pregnancy
• Older maternal age

Genetic testing is usually offered after diagnosis.

Symptoms

Symptoms depend on how narrowed the pulmonary outflow is:

• Cyanosis: a bluish color of the lips, tongue, nails and skin, which may be mild at birth and increase over weeks
• A loud heart murmur, often the first sign noticed
• Fast breathing, poor feeding and tiring during feeds
• Poor weight gain
• Clubbing of the fingers and toes, in older unrepaired children
• In older unrepaired children, squatting after exercise, which raises resistance in the leg arteries and pushes more blood to the lungs

Tet spells

"Tet spells" (hypercyanotic spells) are sudden episodes when the outflow to the lungs tightens further. They often happen after crying, feeding, a bowel movement or waking up. The baby becomes very blue, breathes rapidly and deeply, and may become irritable, then limp or unconscious.

What to do: calm the baby, hold them upright with knees bent up to the chest (the knee-chest position), and call 911 or your local emergency number if it does not settle within a minute or two or the baby becomes floppy. In the hospital, treatment includes oxygen, morphine, fluids and medicines that raise blood pressure.

Diagnosis

• Prenatal ultrasound: many cases are found at the 18 to 22 week anatomy scan and confirmed by fetal echocardiography.
• Newborn pulse oximetry screening: finds low oxygen levels in babies with critical heart defects.
• Echocardiogram: ultrasound of the heart; the key test to confirm TOF and plan surgery.
• ECG and chest X-ray: the X-ray may show a "boot-shaped" heart.
• Cardiac MRI or CT, or catheterization: to map the pulmonary and coronary arteries in complex cases.

Treatment

Complete repair

Open-heart surgery, usually between 3 and 6 months of age, involves:

• closing the VSD with a patch
• widening the narrowed outflow to the lungs by removing thickened muscle and, when needed, placing a patch across the pulmonary valve (transannular patch)

Surgical mortality is now below about 2% at experienced centers.

Temporary procedures

Babies who are very blue or too small for full repair may first have:

• a shunt (a small tube connecting a body artery to a lung artery) to increase lung blood flow
• a stent or balloon to open the outflow or the ductus arteriosus

Full repair follows later.

Life after repair

Most repaired children lead active lives, attend school normally and play sports, often with some limits set by their cardiologist. Problems can develop years later, so lifelong follow-up with a congenital heart specialist is essential.

Long-term issues in adults with repaired TOF include:

• Pulmonary regurgitation: a leaky pulmonary valve after repair, leading over decades to right ventricle enlargement. Many adults need a pulmonary valve replacement, by surgery or a catheter-delivered valve.
• Heart rhythm problems (arrhythmias): atrial and ventricular arrhythmias, which can cause palpitations, fainting and, rarely, sudden death. Some people need an implantable defibrillator.
• Residual narrowing or holes, aortic enlargement and heart failure.
• Infective endocarditis: good dental hygiene matters, and some people need antibiotics before dental work.

Pregnancy

Most women with repaired TOF can have successful pregnancies. Planning ahead with a congenital cardiologist and a high-risk obstetric team is recommended, because pregnancy increases the heart's workload. The child's risk of a congenital heart defect is higher than average, about 3% to 5%, and much higher if 22q11.2 deletion is present. Fetal echocardiography is offered.

Frequently asked questions

What are the four defects of tetralogy of Fallot?

They are a ventricular septal defect (a hole between the lower chambers), pulmonary stenosis (narrowing of the outflow to the lungs), an overriding aorta (sitting above the hole) and right ventricular hypertrophy (a thickened right ventricle wall).

What is the life expectancy with tetralogy of Fallot?

With modern surgical repair, more than 90% of children survive into adulthood, and many live into their 50s, 60s and beyond. Lifelong follow-up and treatment of later problems, such as pulmonary valve replacement and rhythm management, help maintain good health.

What is a tet spell?

A tet spell is a sudden episode in which a baby with unrepaired tetralogy of Fallot becomes much bluer, breathes fast and may become limp, because blood flow to the lungs suddenly drops. Holding the baby in the knee-to-chest position helps; call for emergency help if it does not settle quickly.

Can adults with tetralogy of Fallot exercise?

Most can and should exercise regularly. The type and intensity depend on valve function, ventricle size and rhythm. A congenital cardiologist can advise, sometimes after an exercise test. Competitive or very intense sports may need individual assessment.

Will my child need more surgery after tetralogy of Fallot repair?

Many will. The most common later procedure is pulmonary valve replacement, often in the teens or adulthood, because the valve tends to leak after repair. It may be done by open surgery or through a catheter. Some people also need procedures for rhythm problems.