Tetralogy of Fallot: Clinical Case Discussion & Key Points
Model Case Presentation
Patient Demographics
Name: Master Arjun, Age: 8 months, Gender: Male, Informant: Mother (Reliable)
Chief Complaints
- Bluish discoloration of lips and fingertips since 2 months of age
- Episodic crying with worsening bluish discoloration and limpness – 3 episodes in last 1 month
- Poor weight gain since birth
History Summary
Baby was born pink at birth. Bluish discoloration appeared at around 2 months and has been gradually worsening. Mother noticed the baby turns more blue during crying, feeding, or playing. In the last month, there have been 3 episodes of sudden, severe blueness with loss of tone and brief unconsciousness — each lasting 2–5 minutes, self-resolving (hypercyanotic "Tet" spells). During these spells, the mother noticed the baby instinctively pulls up its knees (fetal position). The child prefers to squat when playing now. No fever, no edema, no prior cardiac surgery.
Born at term via NVD, cried immediately. Birth weight 2.9 kg. Antenatal period unremarkable. No maternal infections (rubella), no teratogenic drug exposure. Non-consanguineous marriage. No family history of CHD. No features of Down syndrome or DiGeorge syndrome noted.
Examination Summary
| Parameter | Finding | Significance |
|---|---|---|
| Weight | 5.2 kg | Failure to Thrive (expected ~8 kg) |
| SpO₂ | 78% (room air) | Severe hypoxemia |
| RR | 46/min | Tachypnea |
| HR | 142/min | Tachycardia |
| Cyanosis | Central + Peripheral | Right-to-left shunt |
| Clubbing | Grade 2 (early) | Chronic hypoxia |
| Pallor | Absent | Compensatory polycythemia |
Precordium: No precordial bulge. Normal apex at 4th ICS at MCL (no cardiomegaly — RV does not dilate in TOF). Systolic thrill at left upper sternal border (LUSB). Parasternal heave present (RV hypertrophy).
Auscultation: Single S2 (absent P2). Loud, harsh, Grade 4/6 Ejection Systolic Murmur (ESM) at left upper sternal border (pulmonary area), radiating to the back. No apical mid-diastolic murmur (no left-to-right shunt, no flow across mitral valve).
Other systems: Lungs clear (no pulmonary plethora — decreased pulmonary blood flow). No hepatomegaly (no CCF — TOF rarely causes CCF). No pedal edema.
✅ Complete Diagnosis
Cyanotic Congenital Heart Disease — Tetralogy of Fallot with severe Right Ventricular Outflow Tract Obstruction, with Hypercyanotic (Tet) Spells, Failure to Thrive, and Chronic Hypoxia (Grade 2 Clubbing, SpO₂ 78%).
📝 History — Exam Q&A
Tetralogy of Fallot (TOF) is the most common cyanotic CHD, accounting for approximately 5–7% of all congenital heart defects and ~10% of all CHDs in symptomatic infants in the first year of life.
Mnemonic: PROVE
- P — Pulmonary stenosis (Right Ventricular Outflow Tract Obstruction — infundibular ± valvular)
- R — Right Ventricular Hypertrophy (secondary, due to RVOTO)
- O — Overriding Aorta (aorta straddles the VSD, receiving blood from both ventricles)
- V — Ventricular Septal Defect (large, perimembranous/malalignment type)
💡 Key Concept
All four defects arise from a single embryological cause: anterosuperior malalignment of the infundibular (conal) septum. RVH is secondary and not a primary defect.
At birth, the patent ductus arteriosus (PDA) and high PVR provide additional pulmonary blood flow. As the PDA closes (within days to weeks) and as infundibular hypertrophy progressively worsens with age and growth, pulmonary blood flow decreases, the right-to-left shunt through the VSD increases, and cyanosis becomes apparent — usually by 2–6 months of age.
The degree and timing of cyanosis directly correlates with the severity of RVOTO.
A sudden, paroxysmal episode of severe cyanosis due to acute worsening of right-to-left shunting. Typically occurs in children 2 months to 2 years of age.
Clinical features:
- Sudden onset of deep cyanosis (worsening baseline cyanosis)
- Hyperpnea (rapid, deep breathing — not due to lung disease)
- Agitation or inconsolable crying → may progress to
- Limpness, loss of consciousness, seizures (if prolonged)
- Murmur becomes softer or disappears during a spell (less blood crossing RVOT)
Triggers: Crying, feeding, defecation, awakening, fever, anemia, tachycardia, morning (after overnight fast)
Mechanism (vicious cycle): Trigger → ↑HR/↓SVR → ↑right-to-left shunt → ↓PaO₂ → respiratory center stimulated → hyperpnea → ↑venous return to RV → ↑RVOT spasm → ↑right-to-left shunt → further ↓PaO₂ (worsening cycle)
Squatting is a pathognomonic compensatory maneuver in older children with TOF. It relieves hypoxia by:
- Kinking the femoral arteries → increases systemic vascular resistance (SVR)
- ↑SVR → reduces the right-to-left shunt across the VSD (more blood pushed to pulmonary circulation)
- Also traps desaturated blood in the lower limbs, reducing its return to the heart
In infants, the equivalent behavior is the knee-chest (fetal) position — mother notices baby draws up its knees when cyanosed.
💡 Exam Pearl
Squatting occurs in children old enough to walk. Infants reflexively adopt the knee-chest position. Both increase SVR → decrease right-to-left shunt.
- No signs of CCF (no hepatomegaly, no edema) — TOF rarely causes heart failure
- No prior surgery or shunt — assess if previously palliated
- No fever — to exclude IE or infectious precipitant of spells
- Antenatal: No maternal rubella, diabetes, phenylketonuria, retinoic acid exposure
- Genetics: Features of DiGeorge syndrome (22q11.2 deletion) — conotruncal defects, hypocalcemia, immunodeficiency, palatal abnormalities, characteristic facies
- Features of Down syndrome — associated with AVSD but occasionally TOF
- Family history — recurrence risk ~3% for siblings
A form of TOF where the RVOTO is mild enough that blood preferentially flows to the pulmonary circulation (net left-to-right shunt). The child appears pink and may even present with features of heart failure (like a large VSD).
- Also called "Acyanotic TOF" or "Fallot's pink spell"
- As infundibular stenosis worsens with growth, these children gradually become cyanotic
- Murmur in pink TOF may be pansystolic (from VSD component) rather than ESM
- Diagnosis confirmed on echocardiography
| Variant | Feature | Significance |
|---|---|---|
| TOF with Pulmonary Stenosis | Classical TOF (most common) | Infundibular ± valvular PS |
| TOF with Pulmonary Atresia | Complete RVOT obstruction, pulmonary blood supply from PDA or MAPCAs | Most severe; PGE1 urgent |
| TOF with Absent Pulmonary Valve | Massively dilated PAs compress bronchi → respiratory distress | Rare; worst prognosis |
| TOF with AVSD | Associated AV canal defect | Common in Down syndrome |
| Pentalogy of Cantrell | TOF + ASD | Some classify the 5th component as ASD |
💡 MAPCAs
Major Aortopulmonary Collateral Arteries — abnormal vessels arising from the aorta or its branches to supply the lungs when RVOT is completely obstructed (TOF with PA). These require unifocalization surgery before complete repair.
- General population risk: ~0.1%
- One sibling affected: ~3%
- Father affected: ~2%
- Mother affected: ~6–10%
- Associated with 22q11.2 deletion (DiGeorge/velocardiofacial syndrome) in ~15% of TOF cases — genetic counseling essential
- Also associated with Trisomy 21, VACTERL association
🩺 Examination — Exam Q&A
| Feature | TOF (ESM) | VSD (PSM) |
|---|---|---|
| Type | Ejection Systolic Murmur (ESM) | Pansystolic Murmur |
| Timing | Starts after S1, ends before S2 (gap) | Starts with S1, continues to S2 (no gap) |
| Location | Left Upper Sternal Border (pulmonary area, 2nd ICS) | Left Lower Sternal Border (3rd-4th ICS) |
| Radiation | To the back / lung fields | To right sternal border |
| Origin | RVOT obstruction (infundibular/pulmonary stenosis) | Across VSD |
| S2 | Single (absent P2) | Loud P2 (if PAH) |
💡 Key Point
In TOF, the murmur is from the RVOTO, not from the VSD. The VSD in TOF is large and non-restrictive — no gradient across it — hence no VSD murmur. The louder the ESM, the more pulmonary blood flow (milder RVOTO). A very soft murmur = severe RVOTO = severe TOF.
The murmur becomes softer or disappears during a Tet spell.
Reason: During a spell, acute infundibular spasm causes near-complete RVOT obstruction. Virtually no blood crosses the RVOT → no turbulence → no murmur. Blood is diverted entirely right-to-left through the VSD into the aorta. This is a clinical sign that the spell is severe.
Normally, S2 has two components: A2 (aortic valve closure) and P2 (pulmonary valve closure). In TOF:
- The pulmonary artery pressure is very low (due to RVOTO)
- The pulmonary valve may be absent, stenotic, or close very softly
- P2 is absent or inaudible → only A2 is heard → single S2
A single S2 in a cyanotic child is an important pointer towards TOF (or pulmonary atresia).
- Central cyanosis — bluish discoloration of lips, tongue, buccal mucosa
- Peripheral cyanosis — fingertips, toes
- Clubbing — hypertrophic periosteal reaction due to chronic hypoxemia (takes weeks to months to develop, usually absent in neonates)
- Plethora/polycythemia — ruddy complexion due to compensatory erythrocytosis
- Failure to thrive — poor weight gain due to increased metabolic demand and reduced cardiac output
- Prominent superficial veins — secondary to polycythemia
TOF is an obstructive + right-to-left shunt lesion. Key reasons:
- RVOTO prevents excess pulmonary blood flow → no volume overload of left heart
- The RV undergoes hypertrophy (concentric, pressure overload) but not dilatation
- Concentric hypertrophy does not significantly increase cardiac silhouette size on CXR
- Left heart is not volume overloaded (less pulmonary venous return)
This is in contrast to VSD/ASD, where volume overload causes cardiomegaly. Normal heart size + cyanosis = think TOF.
A parasternal (left sternal border) heave is a lifting, sustained impulse felt by the heel of the hand placed along the left sternal border in systole. It signifies Right Ventricular Hypertrophy (RVH).
In TOF, the RV works against the obstructed RVOT (pressure overload) → concentric RVH → parasternal heave. Unlike volume overload (which produces a diffuse, thrusting apex), pressure overload produces this sustained heave.
A repaired TOF child may show:
- Midline sternotomy scar — evidence of prior open-heart surgery
- Pink, well-perfused, no cyanosis or clubbing (if fully repaired)
- Normal growth for age
- Early diastolic murmur (EDM) at LUSB — due to pulmonary regurgitation (PR) from transannular patch or disrupted pulmonary valve, the most common post-repair sequel
- Residual ESM — if residual RVOTO remains
- Wide, fixed split S2 — if RBBB from VSD closure (common post-repair ECG finding)
- Signs of RV failure (hepatomegaly, raised JVP) — if severe chronic PR has caused RV dilatation
🚨 Key Long-Term Issue
Pulmonary regurgitation (PR) after TOF repair is the most important long-term complication → leads to progressive RV dilatation → RV failure and arrhythmias → requires pulmonary valve replacement (surgical or transcatheter).
| Feature | TOF | Eisenmenger (e.g., large VSD) |
|---|---|---|
| Murmur | ESM at LUSB | PSM absent/soft; Graham-Steell murmur (PR) |
| S2 | Single (absent P2) | Loud, single S2 (A2 = P2) |
| P2 | Absent/soft | Very loud (palpable) |
| Cardiomegaly | Absent (normal/small heart) | Present (cardiomegaly) |
| History | Cyanotic from birth/early infancy | Previously acyanotic; cyanosis developed later |
| Squatting | Present (characteristic) | Absent |
| Polycythemia | Present | Present |
🔬 Investigations — Exam Q&A
- "Boot-shaped heart" (Coeur en Sabot) — due to upturned RV apex (RVH) + concave main pulmonary artery segment (small/absent PA)
- Decreased pulmonary vascular markings (oligemic lung fields) — reduced pulmonary blood flow
- Normal heart size or mildly enlarged (not cardiomegaly)
- Right aortic arch in 25% of cases (aorta indents the trachea on the right side)
- Concavity of left heart border (at the site of main pulmonary artery)
💡 Boot-Shaped Heart Explained
The "boot" or "wooden clog" silhouette: the toe points upward (elevated RV apex due to RVH) and the instep is concave (absent main pulmonary artery segment). This is the classic CXR appearance of TOF.
- Right Axis Deviation (RAD) — due to RVH
- Right Ventricular Hypertrophy (RVH) — tall R waves in V1, deep S waves in V5-V6; upright T wave in V1 beyond neonatal period
- Right atrial enlargement (tall P waves) in some cases
- Qr pattern in V1 (in severe RVH)
Post-repair ECG:
- Right Bundle Branch Block (RBBB) — almost universal after transventricular repair (ventriculotomy)
- Prolonged QRS duration — important: QRS ≥ 180 ms is associated with risk of ventricular tachycardia and sudden cardiac death
2D Echocardiography with Color Doppler — the investigation of choice. It demonstrates:
- All four components of TOF (VSD, overriding aorta, RVOTO, RVH)
- Site and severity of RVOTO (infundibular, valvular, or combined)
- Pulmonary valve annulus size and morphology
- Branch pulmonary artery anatomy (size, confluency)
- Coronary artery anatomy (especially LAD from RCA — important pre-surgically)
- Associated anomalies (ASD, additional VSDs, right aortic arch)
| Investigation | Expected Finding | Significance |
|---|---|---|
| CBC | ↑Hb, ↑Hct, ↑RBC (polycythemia) | Compensatory erythrocytosis due to chronic hypoxia |
| Arterial Blood Gas | ↓PaO₂, ↓SaO₂, normal/↓PaCO₂ | Confirms cyanosis; does not improve with 100% O₂ (hyperoxia test) |
| Serum ferritin / Iron studies | May show iron deficiency | Iron-deficient polycythemia worsens viscosity paradoxically |
| Coagulation (PT, aPTT) | May be deranged | Polycythemia → coagulation defects |
| Calcium | Hypocalcemia (if DiGeorge) | 22q11.2 deletion association |
| Uric acid | May be elevated | Increased cell turnover in polycythemia |
The child is given 100% oxygen for 10–15 minutes, and ABG is checked.
| PaO₂ Response | Interpretation |
|---|---|
| PaO₂ rises to > 150 mmHg | Pulmonary cause of cyanosis (V/Q mismatch correctable with O₂) |
| PaO₂ remains < 100 mmHg | Cardiac cause (fixed right-to-left shunt — O₂ cannot reach blood bypassing lungs) |
In TOF, the PaO₂ does not improve significantly with 100% O₂ → confirms cyanotic CHD. This is one of the earliest bedside tests to differentiate cardiac from pulmonary cyanosis in a neonate.
- Cardiac catheterization:
- Suspected coronary artery anomaly not delineated by echo (e.g., LAD arising from RCA — crosses RVOT, may be cut during surgery)
- Assessment of branch PA anatomy and pressures
- MAPCAs assessment in TOF with pulmonary atresia
- Interventional: balloon dilation of RVOT/PA, RVOT stenting (palliation), transcatheter pulmonary valve replacement
- Cardiac MRI:
- Post-repair assessment of RV volumes and function (gold standard for quantifying PR and RV size pre-PVR)
- Branch PA anatomy
- Coronary artery anatomy
- CT Angiography: Branch PA anatomy, MAPCAs, aortic arch anomalies
💊 Management — Exam Q&A
Tet spells are medical emergencies. Management follows a stepwise approach:
| Step | Intervention | Mechanism |
|---|---|---|
| 1st | Knee-chest position (infants) / Squatting (children) — calm the child | ↑SVR → ↓right-to-left shunt |
| 2nd | Supplemental Oxygen (though limited benefit in fixed shunt) | Pulmonary vasodilation; reduces hyperpnea drive |
| 3rd | IV Morphine sulfate (0.1–0.2 mg/kg SC/IV) | Suppresses hyperpnea, reduces infundibular spasm, sedation |
| 4th | IV Fluids (normal saline bolus 10–20 mL/kg) | ↑preload → ↑pulmonary blood flow |
| 5th | IV Propranolol (0.01–0.2 mg/kg slow IV) | ↓HR, reduces infundibular spasm (β1-blockade) |
| 6th | IV Phenylephrine or Norepinephrine | ↑SVR → ↓right-to-left shunt |
| 7th | Sodium Bicarbonate (if metabolic acidosis: 1 mEq/kg IV) | Corrects acidosis → breaks the vicious cycle |
🚨 Avoid
DO NOT give digoxin during a spell (increases RVOT contractility and worsens spasm). Avoid tachycardia-inducing drugs.
Oral propranolol (1–4 mg/kg/day in 3 divided doses) is used as:
- Prophylaxis against Tet spells — reduces frequency and severity
- Reduces infundibular spasm (β₁ blockade → reduces RVOT dynamic obstruction)
- Reduces heart rate → more time for ventricular filling
- Used as a bridge to surgery in symptomatic infants who cannot undergo immediate definitive repair
It does NOT cure TOF — it is only a temporizing measure.
Complete intracardiac repair under cardiopulmonary bypass (open-heart surgery), typically performed at 3–6 months of age (electively) or earlier if symptomatic.
The repair consists of:
- VSD closure with a Dacron/pericardial patch
- Relief of RVOTO — infundibular muscle resection, pulmonary valvotomy, pulmonary valve replacement if needed
- Transannular patch (TAP) — if pulmonary annulus is small; widens RVOT but inevitably causes pulmonary regurgitation
Approach: Transatrial-transpulmonary (preferred) OR transventricular (older approach — causes RBBB).
Palliative procedures create a systemic-to-pulmonary artery shunt to increase pulmonary blood flow and relieve cyanosis until definitive repair.
| Shunt | Vessels Connected | Notes |
|---|---|---|
| Modified Blalock-Taussig (mBT) Shunt | Subclavian artery → Ipsilateral PA (via Gore-Tex tube graft) | Most common palliative procedure today |
| Classic BT Shunt | Subclavian artery end-to-side to PA | Historic; no longer used |
| Waterston Shunt | Ascending aorta → Right PA | Historic; complications of PA distortion |
| Potts Shunt | Descending aorta → Left PA | Historic; high complication rate |
| RVOT Stenting | Stent placed in RVOT via catheter | Newer; avoids surgery in small infants |
Indications for palliation: Severe hypoxia or Tet spells in a neonate or small infant with unfavorable anatomy (small PAs, anomalous coronary crossing RVOT) not suitable for immediate complete repair.
PGE1 (Alprostadil) maintains or reopens the ductus arteriosus, ensuring additional pulmonary blood flow in:
- TOF with pulmonary atresia — critically dependent on PDA for pulmonary blood supply
- Severe TOF with critical hypoxia in the immediate neonatal period (SpO₂ < 70%)
Dose: 0.05–0.1 mcg/kg/min IV infusion
Side effects: Apnea (most dangerous — have intubation ready), fever, hypotension, jitteriness, cortical hyperostosis with long-term use
🚨 Remember
PGE1 is a temporizing measure. It buys time until surgical palliation or complete repair can be performed.
- Hypercyanotic spells — can be fatal if untreated
- Cerebral thrombosis/Stroke — polycythemia → hyperviscosity → thrombosis; paradoxical embolism through VSD
- Brain abscess — paradoxical embolism of bacteria bypassing pulmonary filter (via right-to-left shunt); often polymicrobial
- Infective Endocarditis (IE) — turbulent flow at RVOT
- Polycythemia complications — gout (hyperuricemia), coagulation defects
- Relative iron deficiency — iron-deficient polycythemia paradoxically worsens thrombotic risk (microcytes are less deformable)
- Death — 50% mortality by age 6 years without surgery
💡 Brain Abscess in TOF
Any cyanotic CHD child presenting with focal neurological deficits, fever, and raised ICP should be suspected for brain abscess. It occurs because infected emboli bypass the pulmonary filter (which normally traps bacteria) via the right-to-left shunt. Most common organisms: Streptococcus, Staphylococcus, mixed organisms.
As per AHA 2007 guidelines:
- IE prophylaxis IS recommended for unrepaired cyanotic CHD including TOF (unlike isolated VSD/ASD where it's not recommended)
- Recommended for:
- Unrepaired cyanotic CHD (including TOF)
- Repaired CHD with residual defects near prosthetic material
- First 6 months after complete repair with prosthetic material
- Previous IE
- Cardiac transplant with valvulopathy
- Drug: Amoxicillin 50 mg/kg (max 2g) PO 1 hour before dental procedures
- Pulmonary Regurgitation (PR) — most common; especially after transannular patch; leads to RV dilatation, RV failure, arrhythmias
- Right Bundle Branch Block (RBBB) — almost universal after transventricular repair
- Ventricular tachycardia / Sudden cardiac death — risk increases with QRS duration ≥ 180 ms, severe PR, severe RV dilatation
- Residual RVOTO — needs surveillance; may require re-intervention
- Aortic root dilatation and aortic regurgitation — due to intrinsically abnormal aortic root
- Atrial arrhythmias — atrial flutter, fibrillation
- Pulmonary valve replacement (PVR) — eventually needed in most patients; can be surgical or transcatheter (Melody/SAPIEN valve)
- Neurodevelopmental issues — increasingly recognized; require multidisciplinary follow-up
🔭 Recent Advances — Exam Q&A
A catheter-based approach to replace the dysfunctional pulmonary valve without open surgery, avoiding the need for cardiopulmonary bypass.
- Melody Valve (Medtronic) — a bovine jugular vein valve mounted on a balloon-expandable stent; first approved TPVR device; used in RVOT conduits
- SAPIEN XT / SAPIEN 3 (Edwards Lifesciences) — balloon-expandable transcatheter heart valve; used in larger RVOT
- Indications: Severe PR with RV dilatation/dysfunction after TOF repair; residual RVOT obstruction
- Advantage: No sternotomy, shorter hospital stay, preserves future surgical options
- Limitation: Requires adequate conduit anatomy; risk of infective endocarditis on the valve device (IE prophylaxis mandatory lifelong)
RVOT stenting is a catheter-based palliative intervention — a stent is placed in the RVOT/pulmonary valve area to relieve obstruction and increase pulmonary blood flow.
- Alternative to surgical systemic-to-pulmonary shunt (mBT shunt) in small infants with severe TOF
- Promotes branch PA growth before complete repair
- Avoids a thoracotomy
- Studies show comparable outcomes to mBT shunt with potentially fewer complications
- The stent is removed during subsequent complete intracardiac repair
Fetal echocardiography is an ultrasound of the fetal heart, typically performed at 18–22 weeks gestation.
- TOF can be diagnosed prenatally with high accuracy
- Allows prenatal genetic counseling — testing for 22q11.2 deletion by amniocentesis/CVS
- Enables planned delivery at a tertiary care center with pediatric cardiac surgery capabilities
- Allows immediate neonatal stabilization with PGE1 if TOF with PA is anticipated
- Improves outcomes by preventing metabolic acidosis and hemodynamic compromise at birth
- Indicators for fetal echo: family history of CHD, maternal diabetes, maternal rubella, teratogenic drug exposure, abnormal obstetric scan, chromosomal abnormalities
Traditional TOF repair often required a transannular patch (TAP) to widen the RVOT, which destroys the pulmonary valve — leading to severe PR and its long-term consequences (RV failure, arrhythmias, sudden death).
Pulmonary valve-sparing repair aims to preserve or reconstruct a competent pulmonary valve during TOF repair, using:
- Limited infundibular muscle resection without crossing the annulus
- Monocusp patch reconstruction at the pulmonary valve level
- Ultrasound-guided catheter balloon dilation of the pulmonary valve prior to repair (to allow a smaller transannular patch)
Advantage: Significantly reduces long-term PR → fewer re-operations for PVR, better RV function preservation, reduced arrhythmia risk.
TOF is a conotruncal defect primarily due to abnormal neural crest cell migration affecting the cardiac outflow tract development.
- 22q11.2 deletion (DiGeorge/Velocardiofacial syndrome): Found in ~15% of TOF patients; most common genetic syndrome in TOF
- Features: Cardiac defects (conotruncal), Hypocalcemia (absent parathyroids), Immune deficiency (absent thymus), Cleft palate, Characteristic facies
- Mnemonic: CATCH-22 (Cardiac, Abnormal facies, T-cell deficiency, Cleft palate, Hypocalcemia — chromosome 22)
- JAG1 mutations — Alagille syndrome (TOF + peripheral PS + liver disease)
- NKX2.5, GATA4, TBX1 mutations — sporadic TOF
- Trisomy 21 — associated AVSD more common, but can have TOF
⚡ Key Points — Quick Revision
One-Liners for Exam
- Most common cyanotic CHD: TOF
- Four components (PROVE): Pulmonary stenosis, RVH, Overriding aorta, VSD
- Single cause of all four: Anterosuperior malalignment of infundibular septum
- Murmur: ESM at LUSB (from RVOTO, NOT VSD)
- S2: Single (absent P2)
- Softer murmur = more severe TOF (less blood crossing RVOT)
- CXR: Boot-shaped heart + oligemic lung fields (decreased pulmonary vascular markings)
- ECG: RVH + Right axis deviation; post-repair: RBBB
- No cardiomegaly in TOF (RVH is concentric; no volume overload)
- Gold standard: 2D Echo with Color Doppler
- Squatting: ↑SVR → ↓right-to-left shunt (pathognomonic in older children)
- Tet spell management: Knee-chest position → O₂ → Morphine → IV fluids → Propranolol → NaHCO₃
- Avoid digoxin in Tet spells (worsens infundibular spasm)
- PGE1: For TOF with pulmonary atresia (duct-dependent) in neonates
- Palliative shunt: Modified Blalock-Taussig shunt (mBT shunt)
- Definitive surgery: VSD closure + RVOT relief at 3–6 months
- Most common post-repair complication: Pulmonary Regurgitation (PR) → RV dilatation
- QRS ≥ 180 ms post-repair: Risk of sudden cardiac death
- Transcatheter PVR: Melody valve or SAPIEN (for post-repair PR)
- 22q11.2 deletion (DiGeorge): In ~15% TOF; CATCH-22 features
- Brain abscess in cyanotic CHD: Paradoxical embolism bypassing pulmonary filter
- Iron deficiency + polycythemia: Worsens thrombotic risk; monitor iron in TOF
- IE prophylaxis: Required in unrepaired TOF (cyanotic CHD)
📊 TOF vs VSD — Quick Comparison
| Feature | TOF | Large VSD |
|---|---|---|
| Type | Cyanotic CHD | Acyanotic CHD |
| Shunt | Right-to-Left | Left-to-Right |
| Murmur | ESM at LUSB | PSM at LLSB |
| S2 | Single (absent P2) | Loud P2 |
| CXR heart size | Normal/small | Cardiomegaly |
| Lung fields | Oligemic | Plethoric |
| CCF | Absent (rarely) | Present |
| Clubbing | Present (chronic) | Absent |
| Squatting | Present | Absent |