Tetralogy of Fallot

Overview

Tetralogy of Fallot (TOF) is a congenital heart defect that comprises four anatomical abnormalities of the heart, which together result in oxygen-poor blood being pumped out to the body. It is the most common cyanotic congenital heart disease, accounting for approximately 10% of all congenital heart defects. First described by French physician Étienne-Louis Arthur Fallot in the late 19th century, the condition is typically diagnosed in infancy or early childhood due to its hallmark feature - cyanosis (a bluish discoloration of the skin and lips). With timely surgical repair and medical management, the long-term outlook for individuals with TOF has improved significantly.

Causes

Tetralogy of Fallot arises due to abnormal development of the heart during fetal growth, particularly affecting the outflow tract of the heart. While the exact cause is not always known, several risk factors have been identified:

• Genetic mutations – Some cases are associated with chromosomal abnormalities, such as 22q11.2 deletion syndrome (DiGeorge syndrome).

• Maternal factors – Poorly controlled diabetes, alcohol use, or rubella infection during pregnancy may increase the risk of congenital heart defects.

• Familial history – A family history of congenital heart disease can raise the risk of TOF in offspring.

• Sporadic cases – Many occur without an identifiable cause or family history.

Symptoms

The clinical presentation of Tetralogy of Fallot varies depending on the severity of the anatomical defects and degree of oxygen deprivation. Common symptoms include:

• Cyanosis – Bluish skin, lips, and fingernails, especially noticeable during crying or feeding.

• Heart murmur – A loud, harsh murmur is often heard on auscultation due to turbulent blood flow.

• Clubbing of fingers and toes – A later sign resulting from chronic hypoxia.

• Difficulty feeding – Infants may tire easily and fail to gain weight appropriately.

• Irritability and fatigue – Especially during exertion or crying.

• Tet spells – Sudden episodes of deep cyanosis, rapid breathing, and fainting caused by a temporary worsening of the right-to-left shunt.

Symptoms often become evident within the first few weeks of life but may vary based on the severity of the defect.

Diagnosis

Diagnosis of Tetralogy of Fallot involves clinical assessment and advanced imaging techniques. Steps include:

• Physical examination – Detection of cyanosis, clubbing, and heart murmur.

• Pulse oximetry – Measures oxygen saturation in the blood; often low in TOF patients.

• Chest X-ray – May show a “boot-shaped” heart (coeur en sabot) due to right ventricular hypertrophy.

• Electrocardiogram (ECG) – Reveals right axis deviation and signs of right ventricular hypertrophy.

• Echocardiography – The primary diagnostic tool; shows the four characteristic defects and evaluates blood flow.

• Cardiac catheterization – Sometimes performed to further assess heart anatomy and pulmonary pressures before surgery.

• Genetic testing – May be considered if syndromic features are present or there’s a family history.

Treatment

Treatment for Tetralogy of Fallot is primarily surgical, with the goal of correcting the defects and improving blood oxygenation. Treatment approaches include:

1. Initial Stabilization:

• Prostaglandin E1 infusion – In newborns, this keeps the ductus arteriosus open, allowing more oxygenated blood to reach the body.

• Management of tet spells – Includes placing the infant in a knee-chest position, administering oxygen, morphine, or beta-blockers.

2. Surgical Repair:

• Complete repair – Usually performed within the first year of life. It includes:

  • Closure of the ventricular septal defect (VSD) with a patch

  • Removal of obstructive muscle and widening of the right ventricular outflow tract and pulmonary valve

• Temporary shunt surgery – In very small or unstable infants, a palliative shunt (e.g., Blalock-Taussig shunt) may be placed to increase pulmonary blood flow until complete repair is feasible.

3. Long-Term Management:

• Lifelong cardiology follow-up – To monitor heart function, valve integrity, and rhythm disturbances.

• Medications – Such as beta-blockers or diuretics in some patients with residual symptoms.

• Activity restrictions – May be recommended based on the individual’s cardiac function and rhythm stability.

Prognosis

The prognosis for individuals with Tetralogy of Fallot has improved dramatically with advances in surgical techniques and neonatal care. Key aspects include:

• Post-surgical survival – Over 90% of children who undergo complete repair survive into adulthood.

• Residual issues – Some individuals may develop complications such as arrhythmias, right ventricular dysfunction, or pulmonary valve regurgitation later in life, requiring additional interventions.

• Quality of life – Most patients lead active, relatively normal lives, though periodic monitoring is essential.

• Pregnancy – Women with repaired TOF can often have successful pregnancies but require specialized care and preconception counseling.

With proper management and follow-up, the long-term outlook for patients with Tetralogy of Fallot is excellent, especially when treated early in life.