Tetralogy of Fallot

Tetralogy of Fallot (TOF) is a congenital heart defect that occurs during fetal development. It is characterised by a combination of four specific heart abnormalities, which include:

• Ventricular Septal Defect (VSD): This is a hole in the wall that separates the ventricles (two pumping chambers of the heart). This hole is invariably large.
• Pulmonary Stenosis: It is the narrowing of the pulmonary valve or the pulmonary artery, restricting blood flow from the right ventricle to the lungs.
• Overriding Aorta: The aorta, the main artery that carries oxygen-rich blood to the body, is positioned  above the ventricular septal defect, receiving blood from both ventricles.
   
• Right Ventricular Hypertrophy: The right ventricle, responsible for pumping blood to the lungs, becomes thickened due to the increased workload. This muscle thickening will produce a narrowing of variable degrees beneath the pulmonary valve.

Symptoms

• Cyanosis: Cyanosis, commonly referred to as "blue baby syndrome," is a hallmark symptom of Tetralogy of  Fallot. It occurs due to a drop in the oxygen levels in the blood, resulting in a bluish or purplish  discolouration of the skin, lips, and nail beds. This drops in oxygen level occurs because the narrowing of the pulmonary artery prevents an adequate quantity of blood from reaching the lungs to get oxygenated. In addition, the hole (VSD) allows the oxygen-poor blood. In the right ventricle, it is pumped directly into the body. Cyanosis is usually more prominent during physical exertion or episodes of crying.
   
• Heart Murmur: It is an abnormal sound produced by turbulent blood flow within the heart. It occurs due to the structural defects in the Tetralogy of Fallot
   
• Difficulty in Breathing: Children with Tetralogy of Fallot often experience breathlessness or shortness of breath, especially during activities that require increased oxygen supply. This symptom may manifest as rapid breathing, laboured breathing, or struggling to catch one's breath. It can significantly impact a child's ability to engage in physical activities.
   
• Clubbing of Fingers and Toes: Clubbing refers to the abnormal enlargement and rounding of the fingertips and toes. In the Tetralogy of Fallot, the reduced oxygen levels in the blood can lead to clubbing. This symptom is often observed in individuals with long-standing oxygen deprivation and can develop gradually over time.
   
• Poor Growth and Development:  Children with Tetralogy of Fallot may exhibit inadequate growth and development. The compromised oxygen supply to the body's tissues and organs can impair normal growth patterns. They may have difficulties gaining weight or height or achieving developmental milestones at the expected rate.
   
• Tiring Easily: Children with Tetralogy of Fallot often tire quickly and may appear lethargic or fatigued even during routine activities.
   
• Fainting Spells: Dizziness or seizures and episodes of fainting or syncope can occur in individuals with  Tetralogy of Fallot. These episodes are primarily triggered by reduced blood flow to the brain due to abnormalities in the heart's structure. Fainting spells are concerning and require immediate medical attention.    
   
• Long-standing TOF will result in polycythemia (increase in blood cells) which makes the blood thicker and can lead to strokes or tissue and organ damage.

Causes:

• Maternal Factors: Certain maternal factors during pregnancy can contribute to the development of Tetralogy of Fallot in the baby. These include:    

  a. Advanced maternal age (over 35)

     

  b. Maternal illnesses, such as poorly controlled diabetes, rubella (German measles) infection during pregnancy, and certain viral illnesses

     

  c. Maternal substance abuse, such as smoking, alcohol consumption, and illicit drug use during pregnancy

     
• Environmental Factors:Exposure to certain environmental factors during pregnancy may increase the risk of Tetralogy of Fallot. These factors include:        

  a. Some medications, such as certain antiseizure drugs

         

  b. Exposure to certain chemicals and toxins, including solvents, pesticides, and industrial pollutants, may increase the risk.

         

  c.  High levels of radiation exposure during pregnancy

         

  Other Associated Conditions:

     
   
• Genetic Factors:In certain instances, the condition can be inherited from a parent who carries the defective gene. Research suggests that certain genetic syndromes, such as Down syndrome and DiGeorge syndrome (22q11.2 deletion syndrome), have an increased risk of TOF. Someone born with TOF is more likely to have a sibling or child with the disease.    

Diagnosis:

Clinical Evaluation: 

• Medical History: The doctor will inquire about any symptoms or signs of heart problems, family history of congenital heart defects, and the presence of other associated conditions.   
• Physical Examination: The healthcare provider will assess vital signs, listen to the heart sounds, and check for any abnormal physical findings, such as a heart murmur or cyanosis (bluish discolouration of the skin).

Diagnostic Tests:

Following the clinical evaluation, several diagnostic tests may be employed to confirm the diagnosis of TOF. Common diagnostic tests include:

   
• Pulse oximetry is a non-invasive test in which a small sensor is placed on the fingertips, toe or ear, ideally to measure how much oxygen is in the blood. Ideally, all newborn babies should have a pulse oximeter test before going home to make their blood level oxygen levels are normal.   
• Electrocardiogram (ECG): An ECG records the electrical activity of the heart, providing information about heart rate, rhythm, and any abnormalities. In TOF, an ECG may reveal characteristic findings, such as right ventricular hypertrophy and right axis deviation.   
• Chest X-ray: A chest X-ray can provide valuable information about the heart's size and shape. In TOF, a chest X-ray may show a characteristic "boot-shaped" heart due to the enlarged right ventricle.   
• Echocardiography: This is the mainstay of the diagnostic tests. This non-invasive imaging technique uses ultrasound waves to create images of the heart. Echocardiography allows visualisation of the heart's structure, blood flow patterns, and any abnormalities, enabling accurate diagnosis of TOF.   
• Cardiac MRI or CT Scan: These advanced imaging techniques offer detailed three-dimensional images of the heart and its surrounding structures. Cardiac MRI or CT scans provide precise information about the size, position, and abnormalities associated with TOF.   
• Cardiac Catheterization: In certain cases, cardiac catheterisation may be performed to obtain additional information about the heart's anatomy and blood flow. During this procedure, a thin tube is inserted into a blood vessel and guided to the heart to measure pressure and assess the severity of the defects.   
• Genetic Testing: In some instances, genetic testing may be recommended, especially when there is a family history of congenital heart defects or suspected genetic syndromes associated with TOF.   

Treatment

The management of the Tetralogy of Fallot typically involves a multi-disciplinary approach. Surgery is the mainstay of management, with medical management being used to stabilise patients till surgery is done. Doctors repair TOF through surgery soon after birth or later in infancy, depending on the baby's health, weight and severity of the defects and symptoms. The overwhelming majority should have a surgical correction by one year of age.

Medication-based Treatment:   

• Prostaglandin E1 (PGE1): Administered to maintain or reopen the connection between the aorta and pulmonary artery (ductus arteriosus) in newborns with severe cyanosis while awaiting surgery.   
• Beta-blockers: are used to reduce right ventricular infundibular spasm, reduce the incidence of hypoxemic spells and control the heart rate.

Surgical Interventions:

Surgery is the primary treatment for tetralogy of Fallot, aiming to correct the underlying cardiac defects and improve circulation. The most common surgical interventions include:   

• Complete Intracardiac Repair: This procedure, also known as primary repair, is performed during infancy or early childhood. It involves opening the chest to access the heart, repairing the ventricular septal defect (VSD), widening the narrowed pulmonary valve, and, if necessary, addressing any right ventricular outflow tract obstruction.   
• Palliative Shunt: In cases where the child is too young or too ill for complete intracardiac repair, a palliative shunt may be created. The shunt redirects blood flow from the aorta to the pulmonary artery, alleviating cyanosis and improving oxygenation.   
• Transcatheter Interventions: In certain cases, less invasive procedures such as balloon valvotomy or stenting may be performed using catheter-based techniques. These interventions can help alleviate right ventricular outflow tract obstruction and delay or avoid open-heart surgery.

Follow-up Care and Long-term Management:

After surgical intervention, long-term management and follow-up care are crucial to monitor the patient's condition and ensure optimal cardiac health. These include:

   
• Regular Cardiac Check-ups: Routine visits to a cardiologist to assess cardiac function and monitor the growth and development of the pulmonary artery and its branches. In most cases, an Echo on a yearly basis suffices. However, the doctor may also admire a CT angiography or a cardiac MRI during these visits and detect any potential complications.   
• Lifestyle Modifications: Encouraging a heart-healthy lifestyle, including regular exercise, a balanced diet, and avoiding tobacco smoke exposure, can help maintain overall cardiovascular health.   
• Education and Support: This may include guidance on recognising symptoms, managing medications, and accessing resources for emotional and social support.

Prognosis