Overview/Definition
Definition:
• Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect comprising four components: large VSD, overriding aorta, right ventricular outflow tract (RVOT) obstruction, and right ventricular hypertrophy
Accounts for 3-5% of all CHD and 10% of cyanotic CHD with excellent surgical outcomes when managed appropriately.
Epidemiology:
• Incidence of 0.4-0.7 per 1000 live births in India with male predominance (1.3:1)
Associated with chromosomal abnormalities: 22q11.2 deletion syndrome (15-20%), Down syndrome (8%), and CHARGE syndrome
Maternal risk factors include diabetes, phenylketonuria, and rubella infection during pregnancy.
Age Distribution:
• Clinical presentation varies with degree of RVOT obstruction: severe obstruction presents with cyanosis in neonatal period, moderate obstruction at 3-6 months, mild obstruction may remain asymptomatic until childhood
Peak age for hypercyanotic spells is 6-24 months
Optimal surgical age is 6-12 months.
Clinical Significance:
• Essential high-yield topic for DNB Pediatrics and NEET SS focusing on spell management, surgical timing, and long-term complications
Critical for understanding cyanotic CHD physiology, polycythemia consequences, and postoperative arrhythmia risks
Key condition for pediatric emergency management protocols.
Age-Specific Considerations
Newborn:
• Neonatal presentation depends on degree of pulmonary stenosis: severe obstruction causes early cyanosis and may require PGE infusion to maintain ductal patency
Milder cases may appear pink initially
Hypercyanotic spells rare in neonatal period due to higher hemoglobin oxygen affinity and smaller muscular component of RVOT.
Infant:
• Peak period for hypercyanotic spells (6-24 months) due to increasing muscular component of RVOT obstruction and decreasing oxygen affinity of adult hemoglobin
Squatting behavior typically develops after walking age
Growth failure common due to chronic hypoxemia and increased metabolic demands
Clubbing develops by 6-12 months.
Child:
• Established cyanosis with exercise intolerance and squatting after exertion
Risk of cerebral abscess, stroke, and endocarditis increases with age
Polycythemia complications become prominent (hematocrit >65%)
Delayed cognitive development possible due to chronic hypoxemia
School activity restrictions necessary.
Adolescent:
• Unoperated survivors develop severe complications: stroke risk, endocarditis, arrhythmias, and sudden cardiac death
Pregnancy contraindicated in unrepaired females due to high maternal and fetal mortality
Post-operative patients need lifelong cardiology follow-up for arrhythmias, pulmonary regurgitation, and sudden death risk.
Master TOF Pediatrics with RxDx
Access 100+ pediatric videos and expert guidance with the RxDx app
Clinical Presentation
Symptoms:
• Central cyanosis present from birth or develops in infancy depending on RVOT severity
Exercise intolerance with dyspnea, fatigue, and squatting after exertion
Hypercyanotic spells: sudden onset severe cyanosis, irritability, dyspnea, and possible loss of consciousness
Growth retardation and developmental delays in severe cases.
Physical Signs:
• Central cyanosis with clubbing of fingers and toes
Harsh systolic ejection murmur grade 3-4/6 at left sternal border (softer during spells)
Right ventricular heave, single S2 heart sound
Polycythemia signs: conjunctival injection, ruddy complexion
Squatting posture to increase systemic vascular resistance.
Severity Assessment:
• Mild TOF: Oxygen saturation >85%, minimal symptoms, normal growth
Moderate TOF: Oxygen saturation 75-85%, exercise intolerance, some growth delay
Severe TOF: Oxygen saturation <75%, frequent spells, significant growth failure, clubbing by 6 months, hematocrit >65%.
Differential Diagnosis:
• Differential includes other cyanotic CHD: pulmonary atresia with VSD (no murmur, ductal dependent), tricuspid atresia (different murmur pattern), single ventricle lesions
Acyanotic conditions with pulmonary stenosis and intact ventricular septum
Pulmonary atresia with intact ventricular septum in neonates.
Diagnostic Approach
History Taking:
• Detailed prenatal history including maternal diabetes, medications, infections
Birth history and neonatal cyanosis onset
Feeding pattern assessment and growth trajectory
Detailed spell description: triggers, duration, interventions, frequency
Exercise tolerance and developmental milestone achievement
Family history of CHD.
Investigations:
• Chest X-ray shows "boot-shaped" heart with decreased pulmonary markings, right aortic arch in 25%
ECG demonstrates right axis deviation and right ventricular hypertrophy
Echocardiography diagnostic showing all four components, RVOT gradient assessment, and branch pulmonary artery anatomy.
Normal Values:
• Normal oxygen saturation >95% (TOF typically 70-85%)
Normal hemoglobin: neonates 14-20g/dL, infants 10-14g/dL, children 11-13g/dL (TOF often >16g/dL)
Normal RVOT gradient <30mmHg (TOF typically 40-100mmHg)
Normal RV systolic pressure <30mmHg (TOF elevated).
Interpretation:
• RVOT gradient assessment: mild <40mmHg, moderate 40-70mmHg, severe >70mmHg correlates with cyanosis severity
Branch pulmonary artery anatomy critical for surgical planning
Aortopulmonary collateral assessment important in severe cases
Coronary anatomy evaluation essential before surgery (LAD from RCA in 5-10%).
Management/Treatment
Acute Management:
• Hypercyanotic spell management: knee-chest position, oxygen, IV morphine 0.1mg/kg, IV propranolol 0.01-0.25mg/kg, phenylephrine 5-10mcg/kg IV if hypotensive
Volume expansion with normal saline 10ml/kg
Consider bicarbonate if severe acidosis
Emergency Blalock-Taussig shunt if medical management fails.
Chronic Management:
• Medical management until surgery: propranolol 0.5-1mg/kg TID to prevent spells, iron supplementation to maintain hemoglobin 16-18g/dL, avoid dehydration and fever
Surgical options: complete intracardiac repair (ICR) preferred at 6-12 months, Blalock-Taussig shunt as bridge in neonates with severe symptoms.
Lifestyle Modifications:
• Activity restriction appropriate for oxygen saturation: mild TOF may participate in non-competitive sports, severe TOF requires significant limitation
Hydration maintenance crucial especially during febrile illness
Avoid hot environments and prolonged crying
Air travel precautions with supplemental oxygen if saturation <85%.
Follow Up:
• Pre-operative: every 1-3 months depending on severity with echocardiography, CBC, and growth assessment
Post-operative: lifelong follow-up annually with ECG, echocardiography, and Holter monitoring
Exercise testing after adolescence
Genetic counseling for affected families (3-5% recurrence risk).
Age-Specific Dosing
Medications:
• Propranolol: Neonates 0.25mg/kg TID, Infants 0.5mg/kg TID, Children 1mg/kg TID (max 40mg TID)
Morphine for spells: 0.05-0.1mg/kg IV (neonates lower dose)
Phenylephrine: 5-10mcg/kg IV bolus
Iron supplementation: 3-6mg/kg/day elemental iron divided BID-TID.
Formulations:
• Propranolol available as 10mg, 40mg tablets and 4mg/mL oral solution
Morphine 1mg/mL injection for emergency use
Iron sulfate drops 25mg/mL elemental iron for infants, tablets for older children
Phenylephrine 10mg/mL injection for hospital use only.
Safety Considerations:
• Propranolol monitoring: heart rate >100 bpm in infants, >80 bpm in children, avoid in asthma or severe heart failure
Morphine respiratory depression risk especially in cyanotic patients
Iron supplementation: GI upset, constipation, overdose toxicity
Avoid decongestants and stimulants.
Monitoring:
• Regular CBC monitoring for polycythemia (target hematocrit 55-65%), iron studies every 3-6 months
Growth parameters monthly in infants
Oxygen saturation monitoring at rest and with activity
Blood pressure and heart rate monitoring on propranolol therapy
Renal function if on ACE inhibitors.
Prevention & Follow-up
Prevention Strategies:
• Primary prevention limited as most TOF cases are sporadic
Periconceptional folic acid supplementation may reduce overall CHD risk
Maternal diabetes control important during organogenesis
Avoid teratogenic medications including thalidomide, phenytoin, and alcohol during pregnancy.
Vaccination Considerations:
• Standard immunization schedule with additional influenza vaccine annually
Pneumococcal vaccination important due to functional asplenia risk
Live vaccines generally safe in post-operative patients without immunosuppression
COVID-19 vaccination recommended as high-risk group
RSV prophylaxis in select high-risk infants.
Follow Up Schedule:
• Pre-operative: monthly in symptomatic infants, every 3 months in stable patients
Post-operative: 1 week, 1 month, 6 months, then annually lifelong
More frequent follow-up for arrhythmias, heart failure, or other complications
Transition to adult congenital heart disease specialist by age 16-18.
Monitoring Parameters:
• Growth velocity and developmental milestones
Exercise tolerance using age-appropriate functional assessment
Hemoglobin and hematocrit levels for polycythemia monitoring
Echocardiographic assessment of residual defects, ventricular function, and valve regurgitation
ECG and Holter for arrhythmia detection.
Complications
Acute Complications:
• Hypercyanotic spells most dangerous acute complication, can lead to seizures, stroke, or death if untreated
Cerebral abscess risk due to right-to-left shunting bypassing pulmonary filter
Dehydration rapidly worsens cyanosis due to increased blood viscosity
Infective endocarditis risk especially with poor dental hygiene.
Chronic Complications:
• Polycythemia complications: stroke, seizures, bleeding tendency, gout
Eisenmenger syndrome in unrepaired cases with progressive pulmonary hypertension
Post-operative complications: arrhythmias (10-15%), sudden cardiac death (1-2%), pulmonary regurgitation requiring valve replacement, residual VSD.
Warning Signs:
• Spell indicators: increased cyanosis, irritability, hyperpnea followed by lethargy or loss of consciousness
Neurological symptoms: headache, confusion, focal deficits suggesting cerebral complications
Bleeding tendency with severe polycythemia
Fever or new murmur suggesting endocarditis.
Emergency Referral:
• Immediate referral for hypercyanotic spells not responding to initial management
New onset neurological symptoms or signs of stroke
Suspected endocarditis with fever and new murmur
Severe dehydration or illness requiring hospitalization
Any sudden deterioration in exercise tolerance or consciousness.
Parent Education Points
Counseling Points:
• Explain TOF as "four heart problems together" causing mixing of blue and red blood
Emphasize excellent surgical outcomes with >95% survival and good quality of life
Discuss spell recognition and immediate management techniques
Address activity limitations and gradual improvement after surgery
Provide genetic counseling for family planning.
Home Care:
• Spell management: place child in knee-chest position, remain calm, provide comfort
Maintain adequate hydration especially during illness or hot weather
Monitor for signs of dehydration: decreased urination, dry mouth, lethargy
Ensure adequate rest and avoid overexertion
Maintain good dental hygiene to prevent endocarditis.
Medication Administration:
• Give propranolol with food at consistent times, monitor for slow heart rate or breathing
Iron supplements between meals for better absorption, with vitamin C if tolerated
Never stop cardiac medications abruptly without consulting cardiologist
Keep emergency medications (morphine) readily available if prescribed.
When To Seek Help:
• Call 911 for spell lasting >15 minutes, loss of consciousness, or seizure activity
Seek immediate care for: sudden increase in cyanosis, severe breathing difficulty, neurological changes, high fever >38.5°C
Contact cardiologist for: decreased exercise tolerance, new symptoms, missed medications >24 hours, or any parental concerns about child's condition.