Tetralogy of Fallot (Year of the Zebra)

Summary

Tetralogy of Fallot (TOF) is a congenital heart defect involving four abnormalities: stenosis of the right ventricular outflow tract, right ventricular hypertrophy, a ventricular septal defect, and an overriding aorta. These defects can cause cyanosis and oxygen deprivation, particularly when right ventricular outflow obstruction leads to deoxygenated blood being shunted into the systemic circulation. Babies with TOF may experience feeding difficulties, failure to thrive, and tet spells, during which they may squat to temporarily alleviate symptoms. Diagnosis is made via echocardiography, and surgical repair typically occurs within the first year of life, resolving most issues and improving oxygenation.

Takeaways

• 😀 Tetralogy of Fallot (TOF) is a congenital heart condition characterized by four major heart abnormalities.
• 😀 The first abnormality is stenosis of the right ventricular outflow tract, which makes it difficult for deoxygenated blood to reach the pulmonary circulation.
• 😀 The second feature is right ventricular hypertrophy, where the right ventricle thickens to pump harder against the obstruction.
• 😀 A large ventricular septal defect is the third abnormality, which causes shunting of blood between the ventricles.
• 😀 The fourth feature is aortic override, where the aorta is positioned over the septal defect, allowing deoxygenated blood to enter the systemic circulation.
• 😀 The severity of right ventricular outflow obstruction affects whether oxygenated blood is shunted from left to right or deoxygenated blood is shunted from right to left.
• 😀 Cyanosis, a bluish discoloration of the skin, can occur if deoxygenated blood enters systemic circulation, leading to a drop in oxygen saturation below 80%.
• 😀 TOF is often linked to chromosome 22 deletions and DiGeorge syndrome, but the exact cause is unclear.
• 😀 Babies with TOF can show symptoms like feeding difficulties, poor weight gain, and clubbing of fingers and toes, with cyanosis being evident around their lips and nail beds.
• 😀 Tet spells, or hypercyanotic episodes, occur when oxygen demand increases, leading to a sudden decrease in oxygen saturation, and the baby may squat to temporarily relieve the cyanosis.
• 😀 Treatment for tet spells includes calming the baby, administering oxygen, IV fluids, and medications to improve pulmonary blood flow, while surgical repair is often needed within the first year of life to correct the defects.

Q & A

What are the four main abnormalities associated with Tetralogy of Fallot (TOF)?

The four main abnormalities in Tetralogy of Fallot (TOF) are: 1) Stenosis of the right ventricular outflow tract, 2) Right ventricular hypertrophy, 3) Ventricular septal defect (VSD), and 4) Aortic override of the ventricular septal defect.

How does the stenosis in the right ventricular outflow tract affect blood flow?

Stenosis in the right ventricular outflow tract makes it harder for deoxygenated blood to reach the pulmonary circulation, causing an obstruction that leads to increased pressure in the right ventricle.

What is the consequence of right ventricular hypertrophy in TOF?

Right ventricular hypertrophy occurs as the right ventricle becomes thickened due to the extra effort required to pump blood past the narrowed outflow tract. This thickening causes the heart to take on a boot-shaped appearance on X-ray.

What role does the ventricular septal defect (VSD) play in TOF?

The VSD creates a gap between the ventricles, allowing blood to shunt between them. In TOF, deoxygenated blood is shunted from the right ventricle to the left ventricle due to the high pressure in the right side of the heart, leading to oxygen-poor blood entering the systemic circulation.

How does the aortic override contribute to the symptoms of TOF?

The aorta sits over the VSD, which allows deoxygenated blood to flow from the right ventricle directly into the aorta and out to the body, contributing to systemic cyanosis and low oxygen levels.

What is cyanosis, and how is it related to TOF?

Cyanosis is the bluish or purple discoloration of the skin, typically seen in the lips and fingernail beds. In TOF, cyanosis occurs because deoxygenated blood is shunted into the systemic circulation, reducing oxygen levels in the body.

What is the significance of right ventricular outflow obstruction in TOF?

The degree of right ventricular outflow obstruction determines the severity of symptoms. With less obstruction, oxygenated blood may still reach the lungs. With more obstruction, deoxygenated blood is shunted from the right to the left side, leading to cyanosis.

What are tet spells, and why do they occur in TOF patients?

Tet spells are episodes of sudden cyanosis that occur when the oxygen demand exceeds the blood flow to the lungs, such as during physical activity. They are characterized by a sudden drop in oxygen saturation, causing the patient to become cyanotic.

How do patients with TOF reduce cyanosis during a tet spell?

Patients may squat down or assume a knee-chest position, which increases vascular resistance in the legs, raising pressure in the systemic circulation. This helps reverse the blood shunt, allowing more blood to flow to the lungs for oxygenation.

What are the treatment options for severe TOF?

Severe TOF is treated with cardiac repair surgery, typically performed in the first year of life. The surgery involves closing the VSD and enlarging the right ventricular outflow tract, which resolves the associated defects and allows the heart to function more normally.