Tetralogy of Fallot
Introduction to Tetralogy of Fallot
Tetralogy of Fallot (TOF) is a congenital heart defect characterized by four anatomical abnormalities. It is the most common cyanotic congenital heart defect, accounting for 5-10% of all congenital heart diseases.
Key points:
- Incidence: Approximately 1 in 3,600 live births
- Named after Étienne-Louis Arthur Fallot, who described it in 1888
- Slightly more common in males
- Associated with chromosomal abnormalities (e.g., 22q11 deletion) in about 15% of cases
The four classic components of TOF are:
- Ventricular septal defect (VSD)
- Right ventricular outflow tract obstruction (RVOTO)
- Overriding aorta
- Right ventricular hypertrophy (RVH)
The severity of TOF can vary, primarily based on the degree of RVOTO, ranging from mild ("pink" TOF) to severe ("blue" TOF).
Anatomy and Pathophysiology of Tetralogy of Fallot
Anatomical Features:
- Ventricular Septal Defect (VSD): Large, non-restrictive, subaortic
- Right Ventricular Outflow Tract Obstruction (RVOTO):
- Infundibular stenosis (always present)
- Pulmonary valve stenosis (often present)
- Pulmonary artery hypoplasia (variable)
- Overriding Aorta: Aorta positioned directly over the VSD
- Right Ventricular Hypertrophy (RVH): Secondary to RVOTO
Pathophysiology:
- RVOTO leads to increased right ventricular pressure
- When RV pressure exceeds systemic pressure, right-to-left shunting occurs through the VSD
- Right-to-left shunt results in deoxygenated blood entering the systemic circulation, causing cyanosis
- Degree of cyanosis depends on severity of RVOTO and pulmonary blood flow
Associated Anomalies:
- Right-sided aortic arch (25%)
- Coronary artery anomalies (5-10%)
- Atrial septal defect (ASD)
- Multiple VSDs
- Atrioventricular septal defect (rare)
Clinical Presentation of Tetralogy of Fallot
The clinical presentation of TOF can vary depending on the severity of RVOTO:
Neonatal Period and Infancy:
- Mild TOF ("Pink TOF"):
- Asymptomatic or mildly cyanotic
- Loud systolic murmur
- May present with heart failure symptoms later in infancy
- Severe TOF ("Blue TOF"):
- Cyanosis apparent soon after birth
- Tachypnea and feeding difficulties
- Hypercyanotic "Tet" spells (see below)
Physical Examination:
- Cyanosis (variable)
- Clubbing of fingers and toes (in older infants/children)
- Loud, harsh systolic ejection murmur along left sternal border
- Single S2 heart sound
- "Squatting" position in older children (to increase systemic vascular resistance)
Hypercyanotic "Tet" Spells:
- Sudden onset of deep cyanosis and dyspnea
- Decreased intensity of murmur
- Irritability or altered consciousness
- Can lead to syncope or seizures if prolonged
- Often triggered by agitation, feeding, or dehydration
Diagnosis of Tetralogy of Fallot
Diagnosis of TOF involves a combination of clinical assessment and imaging studies:
1. Prenatal Diagnosis:
- Fetal echocardiography can detect TOF as early as 18-22 weeks gestation
- Allows for planned delivery at a tertiary care center
2. Postnatal Diagnosis:
- Chest X-ray:
- "Boot-shaped" heart due to RV hypertrophy
- Decreased pulmonary vascular markings
- Right aortic arch in 25% of cases
- ECG:
- Right axis deviation
- Right ventricular hypertrophy
- Right atrial enlargement
- Echocardiography:
- Diagnostic modality of choice
- Demonstrates all four components of TOF
- Assesses severity of RVOTO and pulmonary artery anatomy
- Evaluates for associated cardiac anomalies
- Cardiac Catheterization:
- Not routinely required for diagnosis
- May be needed for detailed coronary anatomy
- Useful for preoperative assessment in complex cases
- CT or MRI:
- Provides detailed anatomy of pulmonary arteries and aortopulmonary collaterals
- Useful for surgical planning
3. Genetic Testing:
- Recommended to screen for 22q11 deletion syndrome
- Important for long-term management and family counseling
Management of Tetralogy of Fallot
Management of TOF involves medical stabilization followed by definitive surgical repair:
1. Initial Management:
- Prostaglandin E1 in severely cyanotic neonates to maintain ductal patency
- Beta-blockers (e.g., propranolol) to prevent hypercyanotic spells
- Management of hypercyanotic spells:
- Knee-chest position
- Oxygen administration
- IV fluids
- Morphine
- Phenylephrine to increase systemic vascular resistance
2. Palliative Procedures:
- Modified Blalock-Taussig Shunt:
- Used in symptomatic infants too small for complete repair
- Improves pulmonary blood flow and allows growth before complete repair
- RVOT Stenting:
- Alternative to surgical shunt in selected cases
- Provides temporary palliation before complete repair
3. Definitive Surgical Repair:
- Usually performed between 3-6 months of age
- Earlier repair may be needed in symptomatic infants
- Components of repair:
- VSD closure with patch
- Relief of RVOTO (infundibular resection, pulmonary valvotomy)
- Augmentation of pulmonary arteries if needed
- Closure of any atrial communications
4. Post-operative Care:
- Close monitoring in pediatric cardiac ICU
- Management of potential complications (arrhythmias, low cardiac output)
- Early extubation and mobilization when possible
Long-term Outcomes of Tetralogy of Fallot
Long-term outcomes for patients with repaired TOF have improved significantly over the past decades:
Survival:
- Overall survival >90% at 30 years after repair
- Near-normal life expectancy for many patients
Long-term Complications:
- Pulmonary Regurgitation:
- Most common long-term sequela
- May require pulmonary valve replacement
- Right Ventricular Dysfunction:
- Due to chronic volume overload from pulmonary regurgitation
- May lead to exercise intolerance and arrhythmias
- Arrhythmias:
- Atrial and ventricular arrhythmias
- Risk of sudden cardiac death
- Residual RVOTO: May require re-intervention
- Aortic Root Dilation: Requires monitoring and possible intervention
Follow-up:
- Lifelong cardiology follow-up is essential
- Regular echocardiography and ECG monitoring
- Cardiac MRI for detailed assessment of RV function and pulmonary regurgitation
- Exercise stress testing to assess functional capacity
- Holter monitoring for arrhythmia detection
- Counseling regarding pregnancy and contraception for female patients
With appropriate surgical repair and ongoing management, many patients with TOF can lead normal, productive lives. However, they require lifelong specialized cardiac care to monitor for and address potential long-term complications.
Tetralogy of Fallot
- What are the four main components of Tetralogy of Fallot (TOF)?
Ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy, and overriding aorta - What percentage of congenital heart defects is TOF?
Approximately 5-10% - Which gender is more commonly affected by TOF?
Males (slight predominance) - What is the primary embryological defect in TOF?
Anterior and cephalad deviation of the infundibular septum - What is the characteristic clinical sign of TOF in infants?
Cyanosis - What is a "tet spell" in patients with TOF?
A hypercyanotic episode caused by decreased pulmonary blood flow - Which diagnostic test is considered the gold standard for diagnosing TOF?
Echocardiogram - What is the classic chest X-ray finding in TOF?
"Boot-shaped" heart due to right ventricular hypertrophy and a concave pulmonary arterial segment - Which ECG finding is common in patients with TOF?
Right axis deviation and right ventricular hypertrophy - What is the preferred age for elective surgical repair of TOF?
Between 3-6 months of age - What is the name of the surgical procedure used to temporarily increase pulmonary blood flow in TOF?
Blalock-Taussig shunt - What is the mortality rate for complete surgical repair of TOF in infants?
Less than 2% - Which genetic syndrome is associated with a higher incidence of TOF?
22q11 deletion syndrome (DiGeorge syndrome) - What is the risk of recurrence of TOF in offspring if a parent has TOF?
Approximately 3-4% - What is the most common long-term complication after TOF repair?
Pulmonary valve regurgitation - Which arrhythmia is more common in adults with repaired TOF?
Ventricular tachycardia - What is the recommended follow-up interval for patients after TOF repair?
Annual follow-up with a cardiologist specializing in adult congenital heart disease - Which imaging modality is often used for long-term follow-up of TOF patients?
Cardiac MRI - What is the name of the surgical technique used to enlarge the right ventricular outflow tract in TOF repair?
Transannular patch - Which medication might be used to treat cyanotic spells in infants with unrepaired TOF?
Propranolol (beta-blocker) - What is the life expectancy for patients with repaired TOF?
Majority survive into adulthood, but life expectancy is reduced compared to the general population - Which complication can occur due to chronic right ventricular volume overload in repaired TOF?
Right ventricular dysfunction and failure - What is the most common indication for reoperation in adults with repaired TOF?
Pulmonary valve replacement due to severe regurgitation - Which non-invasive test is used to assess exercise capacity in TOF patients?
Cardiopulmonary exercise testing - What is the name of the transcatheter procedure used to replace the pulmonary valve in some TOF patients?
Percutaneous pulmonary valve implantation (Melody valve) - Which biomarker is used to assess right ventricular function in TOF patients?
B-type natriuretic peptide (BNP) - What is the recommended frequency of cardiac MRI in adults with repaired TOF?
Every 2-3 years, or more frequently if clinically indicated - Which pregnancy-related complication is more common in women with repaired TOF?
Increased risk of arrhythmias and right heart failure - What is the name of the surgical technique that preserves the pulmonary valve during TOF repair?
Pulmonary valve-sparing repair - Which factor is associated with increased risk of sudden cardiac death in adults with repaired TOF?
QRS duration >180 ms on ECG
