Tetralogy of Fallot

Anatomy

The heart is a muscular organ consisting of four chambers: the right and left atria and the right and left ventricles. The atria are the upper chambers, while the ventricles are the lower chambers. The right and left sides of the heart are separated by muscular walls called the atrial and ventricular septa.

Normally, oxygen-poor (venous) blood enters the right atrium, passes into the right ventricle, and is pumped through the pulmonary artery to the lungs, where it becomes oxygenated. Oxygen-rich blood then returns to the left atrium, flows into the left ventricle, and is pumped through the aorta to supply oxygen to the body’s tissues.

Description of the Disease

Tetralogy of Fallot is a congenital cyanotic heart defect consisting of four characteristic abnormalities:

• Pulmonary valve or right ventricular outflow tract stenosis.
• Ventricular septal defect (VSD).
• Overriding aorta (dextroposition of the aorta), in which the aorta is positioned over the ventricular septal defect.
• Right ventricular hypertrophy.

These structural abnormalities allow oxygen-poor blood from the right ventricle to bypass the lungs and flow directly into the left side of the heart, where it mixes with oxygen-rich blood before being pumped into the systemic circulation. As a result, the body’s tissues receive blood with a reduced oxygen content, causing cyanosis.

Tetralogy of Fallot accounts for approximately 5–8% of all congenital heart defects and is slightly more common in boys than in girls.

Causes of the Disease

Tetralogy of Fallot is primarily associated with genetic factors, including specific gene mutations and chromosomal abnormalities. The risk may also be increased by maternal rubella infection during pregnancy, alcohol consumption during pregnancy, and advanced maternal age (over 40 years).

Symptoms

Symptoms usually become apparent during infancy or early childhood, most commonly between 2 and 5 years of age.

Typical symptoms include:

• Shortness of breath, especially during physical activity.
• Cyanosis (bluish discoloration of the lips, fingers, toes, and skin).
• Poor exercise tolerance.
• Clubbing of the fingers and toes, with enlargement of the fingertips and curved nails, resulting from long-term oxygen deficiency.

Children may experience episodes of severe breathlessness and cyanosis (hypercyanotic or “tet” spells), during which they become restless, cry, and in severe cases may lose consciousness or develop seizures. Older children often instinctively squat during these episodes, which increases blood flow to the lungs and temporarily improves oxygenation.

Diagnosis

Diagnosis is based on the patient’s symptoms, physical examination, and imaging studies.

Investigations include:

• Chest X-ray, which may demonstrate the characteristic boot-shaped heart.
• Echocardiography, the primary diagnostic test, which identifies all four anatomical components of Tetralogy of Fallot.
• Additional tests, such as electrocardiography (ECG), cardiac MRI, or cardiac catheterization, may be performed when necessary.

Treatment

Definitive treatment is surgical repair, which is usually performed during infancy or early childhood. Surgery aims to close the ventricular septal defect and relieve obstruction of blood flow from the right ventricle to the lungs.

Without treatment, the prognosis is poor, and many patients do not survive beyond adolescence. Following successful surgical repair, most patients have a good long-term prognosis, although some may continue to have reduced exercise tolerance or require lifelong follow-up for residual heart abnormalities.

Source | Author Doctor Nikas Samuolis, reviewed by Prof. Virginijus Šapoka | Vilnius University | Faculty of Medicine | Head of the Department of Internal Medicine, Family Medicine, and Oncology