Tetralogy of Fallot is the most common cyanotic congenital heart defect, typically presenting in infancy, characterized by ventricular septal defect, right ventricular outflow tract obstruction, overriding aorta, and right ventricular hypertrophy, leading to mixing of deoxygenated blood into the systemic circulation and "blue spells" in affected children.

Tetralogy of Fallot (TOF) — Paediatric Cardiology

"Tetra" = four (Greek); "Fallot" = Étienne-Louis Arthur Fallot, who first described the four features in 1888. The name literally tells you: four things going wrong together.

Tetralogy of Fallot (TOF) is the most classic cyanotic congenital heart disease (CHD), characterised by four anatomical abnormalities that arise from a single embryological defect — anterocephalad malalignment of the infundibular (conal/bulbar) septum:

Right ventricular outflow tract (RVOT) obstruction (pulmonary stenosis — the key determinant)
Ventricular septal defect (VSD) — large, malalignment type, non-restrictive
Overriding aorta — aortic root straddles the VSD
Right ventricular hypertrophy (RVH) — secondary consequence of chronic RV pressure overload

The main haemodynamic determinant is the degree of RVOT obstruction ^[1]^[2]. Everything else — the degree of cyanosis, the direction of shunt, whether the child is "pink" or "blue" — flows from how tight the RVOT is.

Core Concept

TOF is really a monology (one embryological defect) that produces a tetralogy (four features). The anterocephalad deviation of the infundibular septum causes RVOT narrowing and VSD simultaneously; aortic overriding and RVH are downstream consequences.

Parameter	Detail
Incidence	4–5 per 10,000 live births ^[1]^[2]
Proportion of all CHD	~7–10% of all CHD ^[2] (some sources cite 3.5% ^[1]; GC slides cite ~7–10%)
Sex ratio	M:F = 1:1 ^[1]^[2]
Key distinction	Most common cause of cyanosis in infancy at 1 year of age ^[1]^[2] — note: in the neonatal period, d-TGA is more common as a cause of cyanosis; TOF typically manifests cyanosis later as RVOT obstruction is progressive
Association	~15% associated with 22q11.2 deletion (DiGeorge / velocardiofacial syndrome); also associated with trisomy 21, CHARGE syndrome, Alagille syndrome

Most common cause of cyanosis in infancy at 1y ^[1]^[2] — this is an extremely high-yield exam fact.

Hong Kong Context

In Hong Kong, congenital heart disease screening is routine in neonates. Pulse oximetry screening (SpO₂ < 95% or > 3% difference between pre- and post-ductal) catches many cases. TOF with severe RVOT obstruction presents neonatally; milder forms may be picked up at routine 6-week checks when a murmur is heard.

3. Embryology and Anatomy

Understanding TOF requires understanding normal conotruncal septation:

The bulbar (conal/infundibular) septum normally grows in a spiral fashion within the conotruncus (the common outflow tract of the embryonic heart)
This spiral growth separates the single outflow tract into two great arteries — the pulmonary trunk (anteriorly and to the left) and the aorta (posteriorly and to the right)
The bulbar septum then grows proximally (inferiorly) to fuse with the interventricular septum (IVS), completing the separation of the two ventricles at the outflow level

Bulbar septum normally grows spirally to septate the outflow tract into pulmonary trunk and aorta → grows proximally to fuse with IV septum ^[1]^[2]

Unequal division of outflow tract with failure to fuse with IVS (VSD) → overriding aorta + subvalvar pulmonary stenosis → RV hypertrophy ^[1]^[2]

In TOF, the infundibular septum deviates anteriorly and cephalad (superiorly). This single malalignment causes:

Anatomical Feature	Mechanism
RVOT obstruction	Anterocephalad shift of the infundibular septum directly narrows the subpulmonary infundibulum (subvalvar stenosis). Additional levels of obstruction can co-exist (see below).
VSD	The malaligned infundibular septum fails to meet and fuse with the muscular IVS → large perimembranous (malalignment-type) VSD
Overriding aorta	The aortic root, no longer anchored entirely over the LV, straddles the malaligned VSD — it "overrides" both ventricles. Degree of override varies (< 50% override = TOF; > 50% override = double outlet right ventricle, DORV)
RVH	The non-restrictive VSD equalises pressures between RV and LV; the RV faces systemic pressure → concentric RVH develops (this is a secondary, adaptive response, not a primary defect)

Pulmonary stenosis: usually infundibular narrowest ^[1]^[2]

The RVOT obstruction in TOF can occur at multiple levels (often combined):

Level	Description
Subvalvar (infundibular)	Most common and most important level. Dynamic muscular narrowing that can worsen with catecholamine surges (this is why tet spells occur)
Valvar	Can be valvar due to hypoplastic PV annulus and bicuspid PV ^[1]^[2] — the pulmonary valve is often thickened, bicuspid, with a small annulus
Supravalvar	Can be supravalvar at main pulmonary artery at sinotubular ridge ^[1]^[2]
Branch PA stenosis	Can be associated with branch PA stenosis ^[1]^[2] — hypoplasia of one or both branch pulmonary arteries

In the most extreme form — TOF with pulmonary atresia — there is complete absence of luminal continuity between RV and pulmonary arteries; pulmonary blood flow is entirely dependent on the PDA or major aortopulmonary collateral arteries (MAPCAs).

Always large (typically as large as the aortic root) and non-restrictive
Malalignment type, perimembranous
Because it is non-restrictive, RV and LV pressures are essentially equalised — the direction of shunting depends entirely on the relative resistances downstream (i.e., RVOT obstruction vs. systemic vascular resistance)

Association	Frequency / Detail
Right aortic arch	~25% of TOF patients (important for surgical planning; identified on CXR)
22q11.2 microdeletion	~15%; screen with FISH or microarray. Associated with DiGeorge sequence (thymic hypoplasia → T-cell immunodeficiency, hypocalcaemia from parathyroid hypoplasia, palatal abnormalities)
ASD / PFO	When present → "Pentalogy of Fallot"
Coronary anomalies	~5%; aberrant LAD arising from RCA crossing the RVOT — crucial for surgery (must not cut through it!)
AVSD	Especially in trisomy 21 with TOF
Absent pulmonary valve syndrome	Variant of TOF with massive aneurysmal dilation of PAs causing airway compression

4. Pathophysiology — The Haemodynamic Story

This is the most important section to understand. Every clinical feature of TOF is explained by understanding the haemodynamics.

Think of it this way: the heart has two parallel outflow paths from the RV:

Path 1: Through the RVOT → pulmonary arteries → lungs (this is the "correct" path)
Path 2: Through the VSD → overriding aorta → systemic circulation (this is the "shunt" path)

Blood, like water, takes the path of least resistance. The balance between these two paths determines whether the child is pink or blue.

Main haemodynamic determinant is RVOT obstruction ^[1]^[2]

Degree of RVOT Obstruction	Haemodynamic Consequence	Clinical Phenotype
Mild obstruction	SVR > PVR + mild RVOT obstruction → net L-to-R shunting ('pink Fallot') → presents with heart failure as in large VSD ^[1]^[2]	Acyanotic, may present at 4–6 weeks with signs of heart failure (this is when PVR drops physiologically)
Moderate obstruction	No significant shunting ^[1]^[2] — balanced	Minimally symptomatic, may have mild exertional desaturation
Significant obstruction	Equalization of RV and LV pressure → R-to-L shunting occurs when RVP > LVP → cyanosis ^[1]^[2]	Progressive cyanosis, typically manifesting in infancy as RVOT obstruction worsens
Severe / Critical obstruction	Near-complete or complete RVOT obstruction → almost all RV output shunts R-to-L → profound cyanosis. If pulmonary atresia, entirely duct-dependent	Neonatal cyanosis, duct-dependent pulmonary circulation

The infundibular stenosis in TOF is not static — it has a muscular, dynamic component:

The infundibular muscle hypertrophies over time (reactive to pressure overload)
Relative infundibular narrowing worsens as the child grows but the RVOT does not grow proportionally
This is why most TOF children are initially "pink" at birth and become progressively cyanotic over the first few months of life

This is a classic exam concept:

The ejection systolic murmur (ESM) in TOF is caused by turbulent flow through the stenotic RVOT (not the VSD — the VSD is too large to generate significant turbulence)
When RVOT obstruction worsens (e.g., during a tet spell), less blood flows through the RVOT → less turbulence → the murmur gets softer or disappears
This is paradoxical: the child is getting sicker (more cyanotic) but the murmur is getting quieter

Unlike valvar PS, ↑obstruction → ↑shunting → ↓pulmonary flow → ↓murmur ^[1]^[2]

Exam Pearl

A common mistake: students assume a louder murmur means the child is worse. In TOF, the opposite is true. A disappearing murmur during a tet spell is an ominous sign — it means near-complete RVOT obstruction with R-to-L shunting.

Fallot's sign: symptoms alleviated by squatting on exercise. Characteristic in older children. Mechanism: ↑SVR → ↓R-to-L shunt; ↑VR → ↑pulmonary flow ^[1]^[2]

Why does squatting help?

↑ Systemic vascular resistance (SVR): Squatting compresses the femoral arteries → increases afterload on the left side → makes it harder for blood to go through the VSD into the aorta → redirects blood through the RVOT into the lungs
↑ Venous return (VR): Squatting compresses the large veins in the legs → increases preload → more blood returns to the right heart → more blood is pushed through the RVOT

Both mechanisms increase pulmonary blood flow and reduce R-to-L shunting → improved oxygenation.

This is a self-learned behaviour in older children with uncorrected TOF — they instinctively squat during exertion or tet spells.

5. Classification

Type	RVOT Obstruction	Presentation
"Pink" TOF	Mild	Acyanotic; presents like a large VSD with L-to-R shunt and heart failure
Classic TOF	Moderate to severe	Progressive cyanosis in infancy; tet spells
TOF with pulmonary atresia	Complete	Duct-dependent cyanotic newborn; requires PGE₁ to maintain ductal patency
TOF with absent pulmonary valve	Variable (regurgitant rather than stenotic)	Massive PA dilation → airway compression → respiratory distress

TOF with ASD ("Pentalogy of Fallot")
TOF with AVSD (common in trisomy 21)
TOF with right aortic arch
TOF with coronary anomalies
TOF with MAPCAs (major aortopulmonary collateral arteries)

6. Aetiology and Risk Factors

Genetic Association	Detail
22q11.2 microdeletion	Most important genetic association (~15%); DiGeorge / velocardiofacial syndrome. Screen all TOF patients.
Trisomy 21	TOF (especially TOF-AVSD) is associated
Trisomy 13, 18	Less commonly associated
JAG1 mutations	Alagille syndrome — TOF + peripheral PS + bile duct paucity
NKX2.5, GATA4, TBX1	Transcription factor mutations implicated in conotruncal defects
CHARGE syndrome	CHD7 mutations

Factor	Mechanism
Maternal diabetes (pre-gestational)	Teratogenic effect of hyperglycaemia on cardiac neural crest cell migration
Maternal rubella	Classic association with PDA and peripheral PS, but also conotruncal defects
Maternal phenylketonuria	Elevated phenylalanine is teratogenic
Retinoic acid exposure	Affects neural crest cell migration → conotruncal defects
Alcohol	Fetal alcohol spectrum disorder includes CHD
Folic acid deficiency	Some evidence for increased CHD risk

The conotruncal region of the heart is populated by cardiac neural crest cells during embryogenesis. These cells are essential for proper outflow tract septation. Disruption of neural crest cell migration (genetic — e.g., 22q11.2 deletion affecting TBX1; or environmental — e.g., retinoic acid) leads to conotruncal defects including TOF, truncus arteriosus, interrupted aortic arch, and DORV.

7. Clinical Features

Symptom	Pathophysiological Basis	Detail
Cyanosis	R-to-L shunt through VSD due to RVOT obstruction → deoxygenated blood enters systemic circulation	Timing depends on degree of RVOT obstruction: neonatal in those with profound RVOT obstruction; infancy/childhood as majority of RVOT obstruction is progressive ^[1]^[2]. Central cyanosis (lips, tongue, mucous membranes)
Progressive exercise intolerance	With exertion, increased oxygen demand + decreased SVR (peripheral vasodilation) → worsened R-to-L shunt → desaturation	Older infants may become breathless, irritable, or limp with activity
Fallot's sign (squatting)	Symptoms alleviated by squatting on exercise. Characteristic in older children. Mechanism: ↑SVR → ↓R-to-L shunt; ↑VR → ↑pulmonary flow ^[1]^[2]	Self-learned compensatory posture. Pathognomonic for TOF in an older child.
Hypercyanotic (Tet/Fallot) spells	Transient near-complete RVOT obstruction (infundibular spasm) → almost all blood shunts R-to-L → profound cyanosis, metabolic acidosis	See dedicated section below. Typically occur in the morning or after crying, feeding, straining, or fever
Heart failure symptoms (in "pink" TOF)	Heart failure at 4–6 weeks in those with mild RVOT obstruction ^[1]^[2] — behaves like a large VSD with L-to-R shunt once PVR drops	Tachypnoea, feeding difficulty, poor weight gain, diaphoresis
Failure to thrive	Chronic hypoxia → increased metabolic demand + poor feeding → inadequate caloric intake	Common in unrepaired TOF

Sign	Pathophysiological Basis	Detail
Central cyanosis	Deoxygenated blood in systemic circulation due to R-to-L shunt	Degree varies with RVOT obstruction severity. May be absent in "pink" TOF
Clubbing	Chronic hypoxia → release of VEGF and other growth factors → soft tissue hypertrophy of nail beds	Develops after months of chronic hypoxia; not present in neonates
Failure to thrive	Chronic hypoxia + increased metabolic demands	Growth faltering, low weight-for-age
RV impulse ± systolic thrill	RVH → forceful RV contraction palpable at left sternal border; turbulent flow through RVOT → thrill at LUSB	RV impulse ± systolic thrill ^[1]^[2]
Single S2 (single second heart sound) due to soft/inaudible P2	The pulmonary valve closure sound (P2) is diminished because of reduced flow through the pulmonary valve and often a hypoplastic/thickened valve; A2 is prominent and heard as a single S2	Single S2 due to soft inaudible P2 ^[1]^[2] — contrast with normal physiological splitting of S2 in healthy children
Ejection systolic murmur (ESM) at left upper sternal border (LUSB) radiating posteriorly	Due to PS, NOT VSD (too wide → PSM very soft) ^[1]^[2]. Turbulent flow through the narrowed RVOT creates this harsh crescendo-decrescendo murmur	Loudness is inversely proportional to severity: louder murmur = milder obstruction (more flow through RVOT). Will disappear with Tet's spell ^[1]^[2]
No significant VSD murmur	The VSD is large and non-restrictive → minimal pressure gradient across it → little turbulence → very soft or absent pansystolic murmur	This distinguishes TOF from a restrictive VSD (where you hear a loud PSM)
VSD-like murmur in "pink" TOF	VSD-like in those with mild RVOT obstruction ^[1]^[2] — when there is significant L-to-R shunting	May hear a louder PSM and apical diastolic rumble (due to increased flow across the mitral valve)

7.3 Hypercyanotic ("Tet") Spells — Detailed Mechanism

Hypercyanotic (Tet, Fallot) spells: transient spells of near-occlusion of RVOT with profound cyanosis ^[2]

These are life-threatening emergencies that occur most commonly between 2–4 months of age (can occur from 1 month to school age).

Crying, agitation, feeding
Straining (e.g., defaecation)
Fever, dehydration
Morning (after prolonged sleep → mild dehydration + lower SVR)
Any cause of ↓SVR or ↑HR

This is a vicious cycle — the acidosis and hyperpnoea worsen the shunting, which worsens the acidosis. Without intervention, it can lead to seizures, stroke, and death.

Sudden onset of deep cyanosis (may become grey/ashen)
Hyperpnoea (deep, rapid breathing — NOT typical respiratory distress pattern)
Inconsolable crying initially, then limpness / loss of consciousness if prolonged
Murmur disappears — because there is no flow through the RVOT
Metabolic acidosis on blood gas
May lead to seizures, CVA, or death if untreated

Why the Murmur Disappears During a Tet Spell

The ESM in TOF is generated by turbulent flow through the stenotic RVOT. During a tet spell, infundibular spasm near-completely occludes the RVOT → virtually no blood flows through it → no turbulence → murmur becomes softer or vanishes entirely. This is an ominous sign indicating critical obstruction.

8. Additional Clinical Considerations

A radiograph showing an oligaemic lung field due to reduced pulmonary blood flow SUPPORTS cyanotic CHD rather than respiratory disease as the cause of cyanosis ^[3]

Feature	Cyanotic CHD (e.g., TOF)	Respiratory Disease
Respiratory effort	Usually comfortable (unless in tet spell)	Tachypnoea, subcostal/intercostal recession, grunting
Hyperoxia test (100% O₂)	PaO₂ remains < 150 mmHg (fails to rise significantly)	PaO₂ usually rises > 150 mmHg
CXR	Oligaemic lung fields	Hazy/opacified lung fields
SpO₂ response to O₂	Minimal improvement	Significant improvement

Failure to thrive is common in unrepaired TOF due to chronic hypoxia
Polycythaemia develops as a compensatory response to chronic hypoxia (EPO-driven erythropoiesis) → increases viscosity → risk of thromboembolic events (stroke, cerebral abscess)
Brain abscess risk: R-to-L shunting bypasses the pulmonary capillary filter → bacteraemia can directly seed the brain
Developmental delay may occur if chronic hypoxia is severe and prolonged

Age	Likely Presentation
Neonate	Profound cyanosis (if severe RVOT obstruction / pulmonary atresia); duct-dependent
4–6 weeks	Heart failure if "pink" TOF (as PVR drops, L-to-R shunt increases)
2–6 months	Progressive cyanosis; onset of tet spells
Older child (if unrepaired)	Squatting, clubbing, polycythaemia, exercise intolerance, brain abscess

9. Key Paediatric-Specific Considerations

TOF is a treatable condition — families need early reassurance that surgical repair is possible and outcomes are excellent
Explain the concept of "blue spells" and when to seek emergency care
Discuss genetic testing (especially 22q11.2 deletion screening) and its implications for recurrence risk

Parental consent for investigations and surgery in infants
For older children (e.g., re-do surgery in adolescence for pulmonary valve replacement), involve the child in discussions appropriate to their developmental stage

Parameter	Relevance in TOF
SpO₂	Normal for age: > 95%. In cyanotic TOF, baseline may be 75–85%. Post-repair, should normalise to > 95%
Haemoglobin	Polycythaemia is compensatory — Hb may be 180–220 g/L in chronic cyanosis. Normal infant Hb varies (see paediatric haematology ranges)
Heart rate	Tachycardia during tet spells; age-specific normal ranges apply (infant: 100–160 bpm)

High Yield Summary

Tetralogy of Fallot — Key Points for Exams:

Four features: RVOT obstruction (PS), VSD (large, malalignment), overriding aorta, RVH — all from one defect: anterocephalad malalignment of the infundibular septum
Most common cause of cyanosis in infancy at 1 year ^[1]^[2]
Main haemodynamic determinant is RVOT obstruction — this determines pink vs. blue
Mild obstruction → "pink Fallot" (L-to-R shunt, heart failure at 4–6 weeks); significant obstruction → R-to-L shunt → cyanosis
Murmur is ESM at LUSB due to PS, NOT VSD — murmur gets SOFTER with worsening obstruction (paradoxical)
Single S2 (inaudible P2) — because pulmonary valve closure is diminished
Squatting (Fallot's sign): ↑SVR + ↑VR → ↓R-to-L shunt → improved oxygenation
Tet spells: infundibular spasm → vicious cycle of ↓pulmonary flow → acidosis → hyperpnoea → ↑shunting
22q11.2 deletion: screen ALL TOF patients
CXR clue: oligaemic lung fields + boot-shaped heart; supports cardiac (not respiratory) cause of cyanosis ^[3]
Complications of chronic cyanosis: polycythaemia, brain abscess, stroke, clubbing, FTT

Active Recall - Tetralogy of Fallot

Differential Diagnosis of Tetralogy of Fallot

The differential diagnosis of TOF is best approached by thinking about why the child is presenting the way they are and then systematically considering what else could produce that same picture. TOF can present in three broad clinical modes — each with its own differential:

Cyanotic neonate/infant (the classic presentation)
Heart failure in early infancy ("pink Fallot" mimicking acyanotic CHD)
Asymptomatic murmur detected incidentally

The most important differential framework is cyanotic CHD categorised by pulmonary blood flow, which is how exam questions are structured.

Cyanotic CHD can be categorised according to the underlying physiology: ↓ Pulmonary blood flow, ↑ Pulmonary blood flow, Severe heart failure ^[4]^[5]

This is the master classification. The CXR is your best bedside tool to distinguish these categories — look at the lung fields (oligaemic vs. plethoric) and the heart size/shape.

This is the group that TOF sits in. All conditions here share the same fundamental haemodynamic problem: obstruction to pulmonary blood flow → R-to-L shunting → cyanosis.

DDx of cyanosis in neonates — Cyanotic heart disease: Tetralogy of Fallot, transposition of great arteries, pulmonary atresia, tricuspid atresia, TAPVD, complex heart lesion (e.g., univentricular heart) ^[6]

Condition	Key Features Distinguishing from TOF	Ductal Dependence	Pathophysiology
Tetralogy of Fallot (TOF)	VSD + overriding aorta + RVH + RVOT obstruction ^[4]^[5]. Boot-shaped heart on CXR. ESM at LUSB. Progressive cyanosis.	√/✗ — Only if severe RVOT obstruction ^[4]^[5]	Anterocephalad malalignment of infundibular septum → RVOT obstruction → R-to-L shunt through VSD
TOF with Pulmonary Atresia (TOF/PA)	Most extreme variant of TOF in which pulmonary stenosis is replaced by complete atresia of pulmonary valve ^[4]^[5]. No antegrade flow from RV to PAs. Requires PDA as alternative source of pulmonary blood flow. Development of major aortopulmonary collateral arteries (MAPCAs) arising directly from aorta ^[4]^[5].	√ (Always) ^[4]^[5]	Complete obstruction → zero antegrade pulmonary flow → entirely duct-dependent (or MAPCA-dependent)
Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)	No VSD (intact septum). Small, hypertensive RV (unlike TOF where RV is large). May have RV-dependent coronary circulation (sinusoids). Continuous murmur of PDA.	√ (Always) ^[4]^[5]	Atretic PV + intact IVS → blood cannot exit RV antegradely → RA blood shunts R-to-L through PFO/ASD → duct supplies pulmonary flow
Critical Pulmonary Stenosis	Severe but not atretic PV. Tiny jet of antegrade flow on echo. Neonatal cyanosis similar to PA/IVS but less severe.	√ (Only in critical PS) ^[4]^[5]	Near-complete PV obstruction → ↑ RV pressure → R-to-L shunt at atrial level through PFO
Tricuspid Atresia (TA)	Absent tricuspid valve → no direct RA-to-RV communication. Ductal dependent only if severe RVOT obstruction ^[4]^[5]. ECG classically shows left axis deviation + LVH (unusual in a cyanotic neonate — most cyanotic CHD shows RVH). Small/absent RV.	√/✗ ^[4]^[5]	No RA→RV flow → obligatory R-to-L shunt at atrial level (ASD/PFO) → all blood enters LA/LV → pulmonary flow depends on VSD size + RVOT patency (or PDA)
Ebstein Anomaly	Apical displacement of tricuspid valve leaflets → "atrialized" RV. Massive cardiomegaly on CXR ("wall-to-wall" heart). Severe TR. WPW on ECG (~20%).	√/✗ — Only if severe RVOT obstruction ^[4]^[5]	Displaced TV → massive TR → functional RVOT obstruction → R-to-L shunt at atrial level through ASD/PFO

How to Remember the ↓ Pulmonary Flow Group

Think: "The Right side is blocked" — the obstruction is always somewhere along the RV → PA pathway (infundibulum, PV, PA, or TV). Blood cannot get to the lungs easily, so it shunts R-to-L, and the CXR shows oligaemic (dark) lung fields.

Key Distinguishing Points: TOF vs. Other ↓ Pulmonary Flow Lesions

Feature	TOF	PA/IVS	Tricuspid Atresia	Ebstein
VSD	Large, malalignment type	Absent (intact IVS)	Variable (usually present)	Usually ASD, not VSD
RV size	Normal/large, hypertrophied	Small, hypertensive	Small/hypoplastic	Large but "atrialized"
ECG axis	RAD + RVH	RVH	LAD + LVH (classic!)	RAD, tall P waves, RBBB, delta waves
CXR heart shape	Boot-shaped (coeur en sabot)	Normal/small heart	Normal or mildly enlarged	Massive cardiomegaly
Level of shunt	Ventricular (VSD)	Atrial (PFO/ASD)	Atrial (ASD)	Atrial (ASD)
Age at presentation	Variable (days to months)	First days of life	First days to weeks	Variable

DDx (↑ Pulmonary blood flow) (3Ts): Transposition of great vessels (TGA), Truncus arteriosus, Total anomalous pulmonary venous return (TAPVR) ^[4]^[5]

These conditions are cyanotic but have increased pulmonary blood flow — the lungs are flooded but the mixing is inadequate. This is the opposite haemodynamic to TOF.

Condition	Key Features	Ductal Dependence	Why Cyanotic Despite ↑ Pulmonary Flow?
d-Transposition of Great Arteries (d-TGA)	Aorta arises from RV, PA arises from LV → two parallel circuits. Cyanosis from birth. Egg-on-a-string CXR (narrow mediastinum). Most common cause of cyanotic CHD in the first day of life.	√ (Always) ^[4]^[5]	Parallel circuits: deoxygenated blood recirculates through body, oxygenated blood recirculates through lungs. Survival requires mixing (PDA, ASD, or VSD).
Truncus Arteriosus	Single great artery arising from both ventricles (common truncal valve). Bounding pulses. Wide pulse pressure. Truncal valve click.	✗ (No mixing required — common trunk provides mixing) ^[4]^[5]	Single outflow → complete mixing of oxygenated and deoxygenated blood → mild cyanosis + HF (volume overload of lungs).
Total Anomalous Pulmonary Venous Return (TAPVR)	All 4 pulmonary veins drain to systemic venous system (SVC, coronary sinus, IVC, etc.) rather than LA. Obligatory R-to-L shunt at ASD. Obstructed TAPVR = surgical emergency (infradiaphragmatic type).	✗ (No mixing required — ASD provides mixing) ^[4]^[5]	All oxygenated pulmonary venous blood returns to RA → mixes with deoxygenated blood → some goes to LA via ASD. If mixing is poor (small ASD) or obstructed, severe cyanosis.

Why these are NOT TOF:

CXR shows plethoric (not oligaemic) lung fields
Heart failure features are prominent (unlike TOF where HF is absent unless "pink")
d-TGA: cyanosis is from parallel circuits, not R-to-L shunting
Truncus / TAPVR: cyanosis is from incomplete mixing, not obstruction

DDx (Severe heart failure): Critical Coarctation of aorta, Interrupted aortic arch, Critical aortic stenosis, Hypoplastic left heart syndrome (HLHS) ^[4]^[5]

These present with cardiogenic shock rather than isolated cyanosis. They are duct-dependent for systemic (not pulmonary) perfusion.

Condition	Key Features	Ductal Dependence
Critical Coarctation of Aorta	Normal ductus arteriosus closes 48hr after birth → kidney is first organ to be affected → oliguria/anuria ^[6]. 4-limb BP: lower limb BP lower than upper limb ^[6]. Radio-femoral delay.	√ (Only in critical) ^[4]^[5]
Interrupted Aortic Arch	Complete discontinuity of aortic arch. Presents with acute collapse when duct closes. Associated with 22q11.2 deletion (like TOF).	√ (Always) ^[4]^[5]
Critical Aortic Stenosis	Severe LV outflow obstruction → low cardiac output → shock.	√ (Only in critical) ^[4]^[5]
Hypoplastic Left Heart Syndrome (HLHS)	Underdeveloped LV, mitral valve, aortic valve. Rare in Chinese ^[6]. Single S2. Duct-dependent systemic circulation.	√ (Always) ^[4]^[5]

Cardiogenic shock usually occurs in ductal-dependent CHD, typically at D4–7 after delivery when the ductus closes ^[6]

Why Coarctation Presents with Shock, Not Cyanosis

In critical coarctation, the obstruction is in the systemic outflow (aortic arch), not the pulmonary outflow. When the duct closes, the lower body loses its blood supply → renal failure (oliguria is the first sign), gut ischaemia, metabolic acidosis → cardiogenic shock. The cyanosis in coarctation is differential cyanosis (lower body only — because pre-ductal saturation is normal but post-ductal is low).

Not all cyanotic neonates have CHD. The hyperoxia test and CXR help distinguish:

DDx of cyanosis in neonates — Respiratory disorders: surfactant deficiency, meconium aspiration, pulmonary hypoplasia; PPHN; Infection: Group B Streptococcal septicaemia; Metabolic: IEM → metabolic acidosis and shock ^[6]

Category	Examples	How to Distinguish from TOF
Respiratory	RDS (surfactant deficiency), meconium aspiration, congenital diaphragmatic hernia, pulmonary hypoplasia	Respiratory distress signs (tachypnoea, grunting, retractions). CXR shows parenchymal disease. Hyperoxia test: PaO₂ rises significantly with 100% O₂
Persistent Pulmonary Hypertension of the Newborn (PPHN)	Elevated PVR → R-to-L shunt at ductal/foramen ovale level	Pre-/post-ductal SpO₂ difference > 5%. Echo shows elevated PA pressures without structural CHD. Responds to inhaled nitric oxide.
Infection	GBS sepsis, pneumonia	Fever, inflammatory markers, positive cultures. CXR may show infiltrates.
Metabolic	Inborn errors of metabolism	Severe metabolic acidosis out of proportion to clinical picture. Ammonia, lactate, organic acids elevated.
Haematological	Methaemoglobinaemia (rare)	Chocolate-brown blood that doesn't turn red with O₂. Measured SpO₂ ~85% but PaO₂ normal.
CNS	Central hypoventilation, birth asphyxia	Apnoea/irregular breathing rather than tachypnoea. Neurological signs.

When TOF has minimal RVOT obstruction, it presents like a large VSD with L-to-R shunt and heart failure:

Minimal obstruction = ↑ P. flow = L-to-R shunt = HF ^[4]^[5]

Condition	Key Distinguishing Feature
Large VSD	No RVOT obstruction. Normal S2 splitting. Loud PSM at LLSB. Plethoric CXR.
AVSD (complete)	Common in trisomy 21. AV valve regurgitation. Superior axis on ECG.
Large PDA	Continuous "machinery" murmur. Bounding pulses. Wide pulse pressure.
Aortopulmonary window	Rare. Continuous murmur. Direct communication between ascending aorta and PA.

The ESM at LUSB of TOF must be differentiated from:

Murmur	Condition	Key Distinguishing Feature
ESM at LUSB	Valvar pulmonary stenosis	Ejection click (absent in infundibular stenosis of TOF). Normal S2 splitting (delayed P2 but still audible, unlike TOF where P2 is absent). No cyanosis unless critical.
ESM at LUSB	ASD	Wide, fixed split S2 (vs. single S2 in TOF). Flow murmur, not turbulence through obstruction.
ESM at RUSB	Aortic stenosis	Radiates to carotids. Ejection click. Normal S2 or paradoxical split.
Innocent murmur	Still's murmur / flow murmur	Musical/vibratory quality. Normal S2 splitting. No thrill. Changes with position. Normal CXR/ECG.

Early recognition and emergent stabilization is critical to ensure optimal outcome in patients with cyanotic congenital heart disease ^[4]^[5]

Step-by-step clinical reasoning:

Confirm cyanosis — central, not peripheral; confirm with pulse oximetry (SpO₂ < 95%)
Hyperoxia test — give 100% O₂; if PaO₂ remains < 150 mmHg → likely cardiac cause
Pre- and post-ductal SpO₂ — significant difference suggests PPHN or duct-dependent lesion with differential perfusion
CXR — look at lung fields (oligaemic vs. plethoric), heart size, heart shape, situs
ECG — axis, hypertrophy pattern (RVH vs. LVH vs. biventricular)
Echocardiography — definitive anatomical diagnosis

For cyanotic CHD: Investigations include CXR, ECG, Echocardiography + Doppler USG ^[6]

High Yield Summary — Differential Diagnosis of TOF

TOF sits in the ↓ pulmonary blood flow group of cyanotic CHD (oligaemic CXR, boot-shaped heart, ESM at LUSB, single S2)
Cyanotic CHD is categorised by: ↓ pulmonary flow, ↑ pulmonary flow (3Ts), severe heart failure ^[4]^[5]
↓ Pulmonary flow DDx: TOF, TOF/PA, PA/IVS, critical PS, tricuspid atresia, Ebstein anomaly
↑ Pulmonary flow DDx (3Ts): d-TGA, truncus arteriosus, TAPVR
Heart failure DDx: Critical CoA, interrupted aortic arch, critical AS, HLHS
Non-cardiac DDx: respiratory (RDS, MAS), PPHN, GBS sepsis, IEM ^[6]
"Pink Fallot" DDx: Large VSD, AVSD, large PDA
Ductal-dependent lesions require PGE₁ to maintain patency — know which lesions are duct-dependent for pulmonary vs. systemic flow
Tricuspid atresia is the classic cyanotic CHD with LAD + LVH on ECG — distinguishes it from TOF (RAD + RVH)
Boot-shaped heart (coeur en sabot) on CXR is characteristic of TOF but not pathognomonic

Active Recall - Differential Diagnosis of TOF

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (Section 6.2.3 — Cyanosis and Cyanotic Heart Disease, p.213) ^[2] Senior notes: Ryan Ho Cardiology.pdf (Section 3.7.2 — Tetralogy of Fallot, p.187) ^[3] AOS material: AOS - Paeds.pdf (Question 6 — cyanotic CHD vs respiratory disease) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Cyanotic CHD differential diagnosis tables, p.280–284) ^[5] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Cyanotic CHD differential diagnosis tables, p.593–599) ^[6] Senior notes: Maksim Paediatric Notes.pdf (DDx of cyanosis in neonates, p.55–56)

Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Tetralogy of Fallot

TOF does not have a "scoring-based" diagnostic criterion like rheumatic fever or SLE. Instead, the diagnosis is anatomical — confirmed when echocardiography demonstrates all four defining features arising from a single embryological defect. The diagnosis is made when the following are present:

Four features of TOF: ^[7]

A large ventricular septal defect (opening between the ventricles)

An aorta positioned over / "overriding" the ventricular septal region

Narrowing of the right ventricular outflow tract / pulmonary valve region

Markedly thickened right ventricular muscular wall

Criterion	Explanation from First Principles
VSD	Malalignment-type, perimembranous, large and non-restrictive. Must be subaortic. If the VSD is restrictive, think of isolated VSD with incidental PS rather than true TOF.
Overriding aorta	The aortic root straddles the crest of the IVS, receiving blood from both ventricles. Degree of override determines whether it is TOF ( < 50% override) or DORV ( > 50% override).
RVOT obstruction	Can be at any level — infundibular (most common and most important), valvar, supravalvar, or branch PA. Must be significant enough to cause haemodynamic consequence.
RVH	Secondary to chronic pressure overload from RVOT obstruction + systemic-pressure VSD. Not a primary defect but an obligate consequence.

Diagnostic Standard

Echocardiography is the gold standard for anatomical diagnosis of TOF. It defines the VSD, aortic override, RVOT obstruction (level and severity), PA anatomy, and associated anomalies. Cardiac catheterisation is reserved for complex cases requiring detailed haemodynamic data or coronary/PA anatomy delineation before surgery.

2. Diagnostic Algorithm — Clinical Approach to the Cyanotic Infant

The practical question is: "A baby is blue — how do I work out it's TOF?"

The approach follows a logical sequence from bedside assessment to definitive imaging.

Cyanosis is usually clinically apparent when 3–5 g/dL of deoxygenated haemoglobin is present → may be influenced by Hb concentration (e.g., anaemia masks cyanosis, polycythaemia may cause apparent cyanosis) ^[1]

Differentiation between causes — Clinical: shallow breathing and apnoea → CNS; respiratory distress → respiratory; normal breathing pattern (± murmurs) → CVS ^[1]

Why pulse oximetry first?

Central cyanosis needs > 3–5 g/dL of deoxyhaemoglobin to be visible — in anaemic neonates, you can miss it. Pulse oximetry objectively detects desaturation before clinical cyanosis is apparent.
In Hong Kong, pulse oximetry screening is performed on all neonates (pre- and post-ductal) as part of the newborn examination.

Why the hyperoxia test?

Hyperoxia (nitrogen washout) test: 100% O₂ × 10 min → monitor PaO₂ from right radial artery (pre-ductal). PaO₂ > 15 kPa (≈150 mmHg) for lung pathologies; remains low for cyanotic CHD ^[1]

The logic: in a normal lung or one with parenchymal disease, flooding the alveoli with 100% O₂ will overcome any V/Q mismatch and raise PaO₂ substantially. In cyanotic CHD, the problem is intracardiac shunting — the blood bypasses the lungs entirely, so no amount of inspired O₂ can fix it.

Problem: ↑FiO₂ can promote ductal closure in duct-dependent circulation → potentially dangerous! ^[1]

Clinical Safety Warning

The hyperoxia test must be performed with caution in any neonate with suspected duct-dependent circulation. High FiO₂ promotes PDA closure, which can precipitate cardiovascular collapse in duct-dependent lesions (e.g., severe TOF, TOF/PA, critical PS, d-TGA, critical CoA). Have PGE₁ (prostaglandin E₁) readily available before performing the test. In practice, many centres now go straight to bedside echocardiography instead.

Why the CXR?

CXR: Hazy lung fields → respiratory parenchymal disease or TAPVC (with PV drainage obstruction). Dark oligaemic lung fields → cyanotic CHD (majority associated with ↓ pulmonary flow) ^[1]

The CXR simultaneously tells you:

Lung fields: oligaemic (↓ pulmonary flow group, e.g., TOF) vs. plethoric (↑ pulmonary flow, e.g., TGA) vs. parenchymal infiltrates (respiratory disease)
Heart shape: boot-shaped (TOF), egg-on-a-string (TGA), wall-to-wall (Ebstein), snowman/figure-of-8 (supracardiac TAPVR)
Heart size: normal-to-mildly-enlarged (TOF) vs. massive (Ebstein)
Situs and laterality: dextrocardia, abnormal abdominal visceral arrangement

Why echocardiography is definitive?

Bedside echo: directly visualise cardiac defects if any ^[1]

Echocardiography provides real-time anatomical and haemodynamic information:

All four TOF features
Level and severity of RVOT obstruction (infundibular, valvar, supravalvar)
PA branch size and confluence
Direction and magnitude of shunt (colour Doppler)
Associated anomalies (ASD, right aortic arch, coronary anomalies, AVSD)
Ventricular function

3. Investigation Modalities — Detailed Findings and Interpretation

Finding	Interpretation
SpO₂ < 95% (pre-ductal, i.e., right hand)	Abnormal — warrants further evaluation
SpO₂ 75–85%	Typical for moderate-severe TOF
Pre-ductal = post-ductal desaturation	Intracardiac R-to-L shunt (as in TOF) — the shunt occurs at the ventricular level, proximal to the duct
Pre-ductal > post-ductal by > 3%	Suggests ductal-level or post-ductal shunting (more typical of PPHN or coarctation)

Why pre-ductal = post-ductal in TOF? Because the R-to-L shunt in TOF occurs through the VSD into the overriding aorta — this is proximal to the ductus arteriosus insertion point. Both pre- and post-ductal blood are equally desaturated.

CXR findings in CHD: heart may be in right or left hemithorax; heart size normal in PS and enlarged in no PS; pulmonary vascular marking is oligaemic in PS and plethoric in no PS ^[1]

CXR Feature	Finding in TOF	Explanation
Heart shape	"Boot-shaped" heart (coeur en sabot)	Upturned apex due to RVH + concavity in the region of the main PA segment (underfilled/hypoplastic PA). The combination creates a boot silhouette.
Heart size	Normal or mildly enlarged	Unlike conditions with volume overload (e.g., large VSD), TOF has pressure overload only → concentric RVH without significant chamber dilation
Pulmonary vascular markings	Oligaemic (decreased)	RVOT obstruction → reduced pulmonary blood flow → lungs appear "dark" and underperfused
Aortic arch	Right-sided in ~25%	Look for the aortic knuckle on the right rather than left. Important for surgical planning.
Mediastinum	Normal width	Contrasts with d-TGA (narrow mediastinum → "egg-on-a-string")

The Boot-Shaped Heart — Why?

The "boot shape" has two components: (1) The apex is tilted upwards because the hypertrophied RV pushes it superiorly. (2) The main PA segment is concave (the normal slight convexity of the left heart border formed by the PA is absent or scooped out) because the pulmonary trunk is hypoplastic with reduced flow. Together, this looks like a boot (or wooden shoe — "sabot" in French).

ECG Feature	Finding in TOF	Explanation
Axis	Right axis deviation (RAD)	RVH shifts the mean QRS vector rightward
RV hypertrophy	Tall R in V1 (R > S), deep S in V5–V6; upright T in V1 beyond neonatal period (normally inverted after ~1 week of age in children)	Chronic RV pressure overload → increased RV muscle mass → dominant rightward and anterior forces
Right atrial enlargement	Tall, peaked P waves (P pulmonale) in lead II, > 2.5 mm	RA dilation secondary to increased RV filling pressure
Comparison with tricuspid atresia	TOF: RAD + RVH. TA: LAD + LVH	This is the key ECG discriminator between the two most important cyanotic CHDs with ↓ pulmonary flow

Age-appropriate interpretation note: In neonates, physiological RVH is normal (the RV is dominant in utero). Therefore, RVH on ECG is hard to diagnose in the first few days of life. The persistence of RVH pattern beyond the neonatal period, or extreme RVH (e.g., pure R wave in V1 > 20mm), suggests pathological RVH as in TOF.

This is the definitive diagnostic investigation. It provides both anatomical and haemodynamic information.

Echocardiographic Feature	What to Assess	Clinical Significance
VSD	Size, location (perimembranous, malalignment), restrictive vs. non-restrictive	Should be large and non-restrictive in TOF. Malalignment type is diagnostic.
Aortic override	Degree of override ( < 50% = TOF, > 50% = DORV)	Determines whether this is TOF or DORV (Taussig-Bing type)
RVOT obstruction	Level (infundibular, valvar, supravalvar), severity (gradient by Doppler), PV annulus size, morphology	Guides surgical strategy (transannular patch vs. infundibulectomy alone). Peak gradient across RVOT by continuous-wave Doppler.
PA anatomy	Main PA size, branch PA size and confluence, presence of stenosis	Adequate PA size is critical for successful complete repair. McGoon ratio and Nakata index quantify PA adequacy.
Coronary anatomy	Aberrant LAD from RCA crossing RVOT	Present in ~5%. Critical for surgery — an anomalous LAD across the RVOT precludes a transannular patch at that site
Aortic arch	Side (left vs. right), patency of PDA	Right arch in ~25%. PDA patency determines duct-dependence.
Associated anomalies	ASD, AVSD, additional muscular VSDs	Alters surgical plan and prognosis
Ventricular function	RV and LV systolic function	Baseline assessment; usually preserved pre-operatively
Shunt direction and magnitude	Colour Doppler across VSD	Confirms R-to-L (cyanotic TOF), bidirectional (balanced), or L-to-R (pink TOF)

Echocardiography demonstrates intracardiac anatomy, arterial relationship with the heart, systemic/pulmonary venous return ^[1]

Not routinely performed for diagnosis in the current era (echocardiography suffices in most cases). Reserved for specific indications:

Indication	Rationale
Delineation of PA anatomy	When echo windows are suboptimal or PAs are severely hypoplastic — need to determine if PAs are adequate for repair
Coronary anatomy	If echo is inconclusive regarding aberrant coronary course
MAPCA delineation	In TOF with pulmonary atresia — MAPCAs arise from the aorta and must be mapped before unifocalisation surgery
Haemodynamic assessment	Measure RV pressure, PA pressure, Qp:Qs, RVOT gradient directly
Interventional	Balloon dilation of branch PA stenosis; stenting of PDA or RV-PA conduit

Increasingly used in older children and pre-surgical planning:

Modality	Advantage	Common Use in TOF
Cardiac MRI	No radiation; excellent for quantifying RV volumes, function, and pulmonary regurgitation (post-repair). Gold standard for RV assessment.	Pre-redo surgery (PVR timing); quantify PR fraction; assess RV volumes/function
CT angiography	Fast; excellent spatial resolution for vascular anatomy. Radiation exposure is a concern in children.	PA anatomy, MAPCA mapping, coronary anatomy when MRI/echo inconclusive

Test	Indication	Rationale
22q11.2 FISH / chromosomal microarray	All TOF patients	~15% have 22q11.2 deletion. Implications: immunodeficiency (thymic hypoplasia), hypocalcaemia (parathyroid hypoplasia), developmental delay, palatal issues. Affects anaesthetic and surgical management (irradiated blood products if T-cell deficient).
Karyotype	If dysmorphic features	Trisomy 21, 13, 18
Whole exome/genome sequencing	Selected cases with multiple anomalies	Identifies rare monogenic causes

Test	Finding in TOF	Explanation
ABG / VBG	Metabolic acidosis during tet spells (↑ lactate)	Tissue hypoxia from profound desaturation → anaerobic metabolism
Full blood count	Polycythaemia (↑ Hb, ↑ Hct) in chronic cyanosis	Compensatory EPO-driven erythropoiesis. Hb can reach 180–220 g/L. Increases viscosity → thrombotic risk
Iron studies	May show microcytic polycythaemia (relative iron deficiency)	High RBC production depletes iron stores → microcytic but still polycythaemic. Microcytic red cells are less deformable → ↑ viscosity → ↑ risk of tet spells and stroke
Calcium	May be low if 22q11.2 deletion present	Parathyroid hypoplasia → hypocalcaemia. Check ionised calcium.
Renal function	Usually normal unless duct-dependent lesion with compromised renal perfusion	Baseline assessment
Coagulation	May be deranged in severe polycythaemia	Polycythaemia → platelet dysfunction + consumption coagulopathy

Iron Deficiency in Cyanotic CHD

A common and dangerous pitfall: relative iron deficiency in cyanotic CHD. The child may have a high Hb (e.g., 180 g/L) but low ferritin and microcytic red cells. Microcytic polycythaemia is MORE viscous than normocytic polycythaemia (small, rigid RBCs don't deform well in microcirculation). This paradoxically increases the risk of tet spells and cerebrovascular events. Always check iron studies in cyanotic CHD and supplement iron if deficient — even if the Hb looks "high enough."

Investigations: CXR, ECG, Echocardiography + Doppler USG ^[6]

Investigation	Key Findings in TOF	Primary Purpose
Pulse oximetry	SpO₂ 75–90% (depending on severity); equal pre- and post-ductal	Screening, monitoring
Hyperoxia test	PaO₂ remains < 150 mmHg on 100% O₂	Distinguish cardiac from respiratory cyanosis
CXR	Boot-shaped heart, oligaemic lung fields, right aortic arch (25%)	Bedside assessment, pattern recognition
ECG	RAD, RVH (tall R in V1, upright T in V1 after neonatal period), P pulmonale	Supportive evidence, distinguish from TA (LAD + LVH)
Echocardiography	All 4 features + level/severity of RVOT obstruction + PA anatomy + coronary anatomy + shunt direction	Gold standard — definitive diagnosis
Cardiac catheterisation	PA pressures, RVOT gradient, MAPCA anatomy	Pre-surgical planning in complex cases
Cardiac MRI	RV volumes, function, PR fraction	Post-repair surveillance; pre-redo surgery
CT angiography	PA anatomy, MAPCAs, coronary anatomy	Complex anatomy delineation
Genetic testing	22q11.2 deletion (FISH/microarray), karyotype	All TOF patients; affects peri-operative care
Blood tests	Polycythaemia, ABG (acidosis in tet spell), iron studies, calcium	Baseline, monitoring, complication detection

Presentation Age	Most Likely Scenario	Key Investigations
Neonate (Day 0–7)	Severe TOF or TOF/PA; duct-dependent	SpO₂ screening, hyperoxia test (with caution), urgent echo, PGE₁ if duct-dependent
4–6 weeks	"Pink Fallot" presenting with heart failure as PVR drops	Echo (to distinguish from isolated large VSD), ECG (RVH favours TOF over VSD)
2–6 months	Classic progressive cyanosis, onset of tet spells	Echo (confirm diagnosis, plan surgery), CXR (boot-shaped heart), genetic testing
Older child (if unrepaired)	Squatting, clubbing, polycythaemia, exercise intolerance	FBC (polycythaemia), iron studies, echo, cardiac MRI (if pre-surgical)

High Yield Summary — Diagnosis of TOF

TOF is diagnosed anatomically by echocardiography demonstrating all four features: large malalignment VSD, overriding aorta, RVOT obstruction, RVH
Investigations: CXR, ECG, Echocardiography + Doppler USG ^[6] — this is the core investigation triad
CXR: boot-shaped heart (coeur en sabot) + oligaemic lung fields — the classic radiological pattern. Dark oligaemic lung fields point to cyanotic CHD with ↓ pulmonary flow ^[1]
Hyperoxia test: PaO₂ remains < 150 mmHg (< 15 kPa) on 100% O₂ → cardiac cause. Caution: may promote ductal closure in duct-dependent circulation ^[1]
ECG: RAD + RVH (contrast with tricuspid atresia: LAD + LVH)
Echo is gold standard — defines anatomy, RVOT obstruction severity, PA size, coronary anatomy, shunt direction, associated anomalies
22q11.2 genetic testing in ALL TOF patients — ~15% prevalence; affects peri-operative and long-term care
Iron studies are essential — microcytic polycythaemia is more dangerous than normocytic polycythaemia (increased viscosity → tet spells and stroke)
Cardiac catheterisation reserved for complex anatomy (MAPCAs, inadequate PA size, inconclusive coronary anatomy)
Cardiac MRI is the gold standard for post-repair RV assessment and timing of pulmonary valve replacement

Active Recall - Diagnosis of TOF

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (Section on Cyanosis — differentiation and classification, p.195; investigations of univentricular heart, p.222) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Cyanotic CHD differential diagnosis tables, p.267–284) ^[5] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (TOF overview and cyanotic CHD classification, p.580–599) ^[6] Senior notes: Maksim Paediatric Notes.pdf (DDx of cyanosis in neonates, investigations, p.55–56) ^[7] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (p.11 — schematic anatomy of TOF)

Management of Tetralogy of Fallot

The management of TOF spans a spectrum from emergency neonatal stabilisation through palliative procedures to definitive surgical repair and lifelong follow-up. The approach is determined by the severity of RVOT obstruction and the clinical presentation at each stage.

The fundamental principle: Surgery is the definitive treatment ^[6]. Medical therapy is a bridge — it buys time until the child is an appropriate size and condition for repair.

Age group: Neonates (Day 0–28)

When TOF presents with profound cyanosis in the neonatal period, it means the RVOT obstruction is severe enough that pulmonary blood flow depends on the PDA. As the PDA closes physiologically (usually within 24–48 hours of birth), the neonate becomes critically cyanotic.

IV PGE₁ with early shunting in neonates with profound obstruction presenting with cyanosis ^[1]

2.1 Prostaglandin E₁ (PGE₁ / Alprostadil)

Aspect	Detail
Drug	Prostaglandin E₁ (alprostadil) — "prostag-landin" = prostaglandin mediator; acts on smooth muscle of the ductus arteriosus
Mechanism	Relaxes the smooth muscle of the ductus arteriosus wall → maintains or re-opens the PDA → allows aortic blood to flow retrogradely into the pulmonary arteries → provides pulmonary blood flow for oxygenation
Route	Continuous IV infusion (central or peripheral — but central preferred for stability)
Dose	Start at 0.05 µg/kg/min; can reduce to 0.01–0.02 µg/kg/min once duct opens (maintenance)
Side effects	Apnoea (up to 12% — monitor in NICU, may need intubation), fever, hypotension, jitteriness, diarrhoea, flushing
Key point	This is a temporising measure — it keeps the baby alive until surgical intervention can be performed

PGE₁ and Apnoea — Paediatric Safety Point

PGE₁ causes apnoea in ~10–12% of neonates. Always have resuscitation equipment and intubation readiness when starting PGE₁. This is especially important during neonatal transport (e.g., from a district hospital to a tertiary centre with cardiac surgery capability like Queen Mary Hospital / Grantham Hospital in Hong Kong).

Duct-dependent pulmonary circulation: blood flows from aorta to pulmonary arteries via duct for oxygenation in lungs. Ductal closure will result in severe hypoxemia and infants will present shortly after birth with cyanosis. E.g., PA + Critical PS + Severe TOF ^[4]^[5]

3. Acute Management of Hypercyanotic (Tet) Spells

This is a paediatric emergency. The child is having near-complete RVOT obstruction from infundibular spasm → vicious cycle of desaturation → acidosis → hyperpnoea → worsened shunting.

Step	Action	Mechanism / Rationale
1. Knee-chest position	Place infant in knee-chest position (or parent holds infant with knees tucked to chest)	Mimics squatting → ↑SVR → ↓R-to-L shunt; ↑VR → ↑pulmonary flow ^[1]^[2] — compresses femoral arteries (↑SVR) and femoral veins (↑VR)
2. Calm the child	Minimal handling, keep parent present, avoid painful stimuli initially	Reduce catecholamine surge → reduce infundibular spasm
3. Oxygen	High-flow O₂ via face mask	Maximises alveolar PO₂ for whatever pulmonary blood flow exists (limited benefit since the problem is shunting, but still given)
4. IV fluid bolus	Normal saline 10–20 mL/kg	Increases preload → increases RV filling → pushes more blood through the narrowed RVOT
5. Morphine	0.1–0.2 mg/kg IV/IM/SC	Sedation (breaks the crying/agitation cycle), reduces catecholamine drive, mild SVR increase. Also suppresses the hyperpnoeic response (reduces the vicious cycle).
6. IV phenylephrine	5–20 µg/kg IV bolus	Pure α₁-agonist → potent vasoconstriction → ↑SVR → ↓R-to-L shunt by making it "harder" for blood to flow through the aorta relative to the RVOT
7. IV sodium bicarbonate	1–2 mEq/kg IV	Corrects metabolic acidosis → breaks the acidosis → hyperpnoea → worsened shunting cycle
8. IV propranolol / esmolol	Propranolol 0.01–0.1 mg/kg slow IV (max 0.15 mg/kg); or esmolol infusion	β-blocker: relaxes the infundibular muscle spasm (the infundibular obstruction is dynamic and responsive to β-adrenergic stimulation). Also reduces heart rate → longer diastolic filling time → improved coronary perfusion of the hypertrophied RV
9. General anaesthesia / intubation	If refractory to above measures	Positive pressure ventilation ↑SVR; deep anaesthesia abolishes catecholamine surge and infundibular spasm
10. Emergency surgical shunt	If all medical measures fail	Modified Blalock-Taussig shunt ^[1] or emergency complete repair if anatomy suitable

Why β-Blockers Work in Tet Spells

The infundibular stenosis in TOF has a dynamic muscular component. During a tet spell, catecholamines (from crying, distress, acidosis) cause the infundibular muscle to contract even more forcefully, nearly obliterating the RVOT. β-Blockers oppose this catecholamine-driven spasm → relax the infundibulum → re-open the RVOT → restore pulmonary blood flow.

Aspect	Detail
Indication	Children with TOF awaiting surgical repair who have had tet spells or are at high risk
Dose	Propranolol 1–4 mg/kg/day PO in 3–4 divided doses
Mechanism	Sustained β-blockade → reduces infundibular reactivity → prevents spasm; also lowers heart rate → reduces oxygen demand
Duration	Bridge to surgery; continue until repair is performed
Monitoring	Heart rate, blood pressure, blood glucose (β-blockers can mask hypoglycaemia in infants — an important paediatric concern)

4.1 "Pink Fallot" with Heart Failure

Heart failure at 4–6 weeks in those with mild RVOT obstruction ^[1]^[2]

When RVOT obstruction is mild, the haemodynamics resemble a large VSD with L-to-R shunt → volume overload → heart failure as PVR drops in the first weeks of life.

Treatment	Detail
Diuretics	Furosemide 1–2 mg/kg/day PO (loop diuretic → reduces preload and pulmonary congestion)
Digoxin	Sometimes used for its inotropic effect; narrow therapeutic index in paediatrics — monitor levels
Avoid ACEI/ARB	Avoid ACEI/ARB → ↓SVR → trigger tet spells ^[1]. This is critical: in a child with TOF (even if currently "pink"), reducing SVR increases the R-to-L shunt gradient. Unlike heart failure from other causes, ACEI/ARB can be dangerous here.
Nutritional support	High caloric diet due to ↑metabolic demand ^[1] — use fortified breast milk or high-calorie formula

ACEI/ARB Contraindication in TOF

Avoid ACEI/ARB in TOF ^[1]. This is a commonly tested exam point. The logic: ACEI/ARB reduce SVR (systemic afterload). In TOF, reducing SVR makes the systemic circuit "easier" to flow into compared to the obstructed RVOT → blood preferentially shunts R-to-L through the VSD → worsened cyanosis or precipitation of a tet spell. This is true even in "pink Fallot" because the RVOT obstruction can become critical at any time.

5. Surgical Management

Palliative procedure before definitive repair. Indications: severe cyanosis or uncontrolled tet spells in neonates, pulmonary artery hypoplasia that would not tolerate biventricular repair ^[1]

Modified Blalock-Taussig shunt (mBTS): synthetic graft from innominate/subclavian to ipsilateral PA → allow L-to-R shunting → provide adequate pulmonary flow ^[1]

Aspect	Detail
Name origin	Alfred Blalock (surgeon) and Helen Taussig (paediatric cardiologist) — pioneers of the first cyanotic CHD palliation in 1944
Classic BTS	Direct anastomosis of subclavian artery to ipsilateral PA (no longer used — sacrifices the subclavian artery, difficult to control flow)
Modified BTS	Synthetic graft (Gore-Tex) from innominate or subclavian artery to ipsilateral PA ^[1] — preserves the subclavian artery; graft size determines shunt flow
Mechanism	Creates an artificial L-to-R shunt → systemic arterial blood enters the PA → increases pulmonary blood flow → improves oxygenation
Indications	(1) Severe cyanosis or uncontrolled tet spells in neonates ^[1]; (2) Pulmonary artery hypoplasia — the shunt provides flow to promote PA growth before complete repair; (3) Neonates too small for complete repair
Murmur	Continuous "machinery" murmur (similar to PDA) — systemic-to-PA flow throughout cardiac cycle
Critical follow-up	Always listen for shunt murmur on follow-up → blocked BT shunt can kill ^[1]. If the murmur disappears, it means the shunt is thrombosed → acute loss of pulmonary blood flow → death. This is an emergency requiring urgent re-intervention.

Pre-repair TOF with severe cyanosis or uncontrolled tet spell: modified Blalock-Taussig shunt ^[1]

Transcatheter ductal/RVOT stenting in some centres ^[1]

Procedure	Mechanism	Indication
Ductal stenting	Percutaneous stent placed in the PDA to maintain patency without PGE₁	Alternative to mBTS in duct-dependent neonates; avoids sternotomy
RVOT stenting	Balloon-expandable stent placed across the infundibulum / PV	Relieves RVOT obstruction, improves antegrade pulmonary flow; buys time for PA growth before definitive repair

Complete repair: usually at 6–12 months (ideal) ^[1]

This is the curative operation. The goal is to close the VSD and relieve the RVOT obstruction completely, restoring normal biventricular circulation.

Aspect	Detail
Timing	Usually 6–12 months ^[1] (ideal). Some centres perform primary repair in the neonatal period for severe cases. In Hong Kong, elective repair is typically planned around 4–6 months if the child is stable.
Approach	Median sternotomy, cardiopulmonary bypass, cardioplegic arrest

Components of the repair:

Procedure: (1) Repair of VSD by patch closure; (2) Enlargement of RVOT by resecting infundibular and subinfundibular muscle bundles ± transannular patch ^[1]

Component	Technique	Rationale
VSD patch closure	Dacron or pericardial patch sewn to close the VSD, directing LV outflow exclusively to the aorta	Eliminates the R-to-L (or L-to-R) shunt; separates the two circulations. Must avoid the conduction tissue (bundle of His runs along the posteroinferior rim of the perimembranous VSD).
Infundibular muscle resection	Resection (cutting away) of the hypertrophied muscle bundles in the RVOT	Relieves subvalvar obstruction — the muscular component of the RVOT narrowing
Pulmonary valvotomy	Commissurotomy of fused or dysplastic PV leaflets	Relieves valvar stenosis if present
Transannular patch (TAP)	If the PV annulus is too small (hypoplastic), a patch is sewn across the annulus to widen it, extending from the RV across the PV annulus into the MPA	Widens the RVOT beyond the native annulus size. Obligatory pulmonary regurgitation results because the PV annulus is disrupted ^[1].
RV-PA conduit	In cases with coronary artery crossing the RVOT (aberrant LAD) or pulmonary atresia	A valved conduit (homograft or bioprosthetic) bridges the RV to the PA, bypassing the obstructed native RVOT

Perioperative outcome: mortality 0–3% (but ↑↑↑ for smaller kids) ^[1]

Transannular Patch — The Trade-Off

A transannular patch effectively eliminates RVOT obstruction but at the cost of obligatory pulmonary regurgitation (PR). This PR is well-tolerated initially (the low-pressure RV can handle volume overload for years), but over decades leads to progressive RV dilation and dysfunction. This is why lifelong follow-up is mandatory. The art of TOF surgery is balancing adequate relief of obstruction against minimising PR.

Scenario	Surgical Strategy
Neonate, duct-dependent	PGE₁ → mBTS (or ductal stent) → complete repair at 4–6 months
Neonate, uncontrolled tet spells	mBTS: severe cyanosis or uncontrolled tet spells in neonates ^[1] → complete repair
Infant with progressive cyanosis, adequate PA size	Complete repair at 6–12 months ^[1]
Infant with hypoplastic PAs	mBTS first (to promote PA growth) → complete repair once PAs adequate
"Pink Fallot" with heart failure	Anti-failure medication (avoid ACEI/ARB) → complete repair at 6–12 months
Asymptomatic	Elective complete repair at 6–12 months
Aberrant coronary crossing RVOT	RV-PA conduit (cannot do transannular patch at that site)

6. Post-Operative Management and Long-Term Follow-Up

Pulmonary regurgitation as principal late complication ^[1]

After complete repair, TOF patients require lifelong cardiac follow-up. They are never truly "cured" — they are "repaired."

Complication	Mechanism	Monitoring
Pulmonary regurgitation (PR)	Cause: ↑aggressive repair → ↑risk of PV damage (especially if transannular patch used → obligatory PR) ^[1]	Cardiac MRI (quantify PR fraction), echocardiography
RV dilation and dysfunction	PR → chronic RV volume overload → progressive RV dilation → RV failure ^[1]	Cardiac MRI (RV volumes — gold standard), exercise testing
Arrhythmias	VT, atrial flutter, AF ^[1] — scar tissue from VSD patch and RVOT reconstruction creates re-entrant circuits	Holter monitoring, exercise testing
Sudden cardiac death	Late arrhythmia (VT) in the setting of dilated, dysfunctional RV	Risk stratification, consider ICD in high-risk patients
↓ Exercise tolerance	RV dysfunction + PR + residual RVOT obstruction	Exercise testing every 3–4 years ^[1]

Management of PR: by pulmonary valve replacement in (1) MRI showing RVH + > 25% regurgitant fraction; (2) Symptomatic (RV failure, arrhythmia) ^[1]

Aspect	Detail
Indications	(1) MRI: RV dilatation + > 25% regurgitant fraction ^[1]; (2) Symptomatic: RV failure, exercise intolerance, arrhythmia ^[1]; (3) Progressive RV dilation on serial imaging (RVEDVi > 150–170 mL/m², RVESVi > 80 mL/m²); (4) Significant residual RVOT obstruction ( > 60 mmHg gradient)
Timing	Before irreversible RV dysfunction occurs (RV should still be recoverable)
Options	Surgical PVR (bioprosthetic valve, homograft) or transcatheter PVR (Melody valve / Sapien valve)
Transcatheter PVR	Percutaneous — valve deployed via femoral vein into the RVOT. Requires a suitable "landing zone" (usually a pre-existing conduit or bioprosthetic ring). Less invasive, shorter recovery. Increasingly used.

Require long-term follow-up and exercise testing Q3–4y ^[1]

Assessment	Frequency	Purpose
Cardiology clinic	At least annually for life	Symptom review, examination (PR murmur, RV function signs)
Echocardiography	Annually	RV size and function, RVOT gradient, PR severity, residual VSD
Cardiac MRI	Every 3–5 years (or more frequently if concerns)	Gold standard for RV volumes, PR quantification (regurgitant fraction), RV function
Exercise testing	Every 3–4 years ^[1]	Assess functional capacity, detect exercise-induced arrhythmias
Holter monitoring	As indicated (symptoms or screening)	Detect arrhythmias (VT, atrial flutter)
Pregnancy counselling	Pre-conception for female patients	Most repaired TOF patients tolerate pregnancy well, but those with significant RV dysfunction or arrhythmias need specialist care
Endocarditis prophylaxis	For 6 months post-surgery; indefinitely if residual defects or prosthetic material	Prosthetic patches and conduits are at risk for endocarditis

Prognosis: good after complete repair (93% 25-year survival) ^[1]

Unrepaired TOF is compatible with survival to adulthood → CAN present in adulthood ^[1]

Scenario	Prognosis
Repaired TOF	Excellent: 93% 25-year survival. Most lead normal or near-normal lives. Lifelong follow-up required for late complications.
Unrepaired TOF	Natural history: ~50% mortality by age 6 without surgery; ~10% survive to age 20. However, some adults with balanced haemodynamics survive unrepaired into adulthood.
TOF with pulmonary atresia	More complex; outcomes depend on PA anatomy and MAPCAs. Multi-stage surgery required.

8. Special Paediatric Considerations

TOF is a surgically treatable condition with excellent long-term outcomes — families need early reassurance
Teach parents to recognise tet spells (sudden deep cyanosis, rapid breathing, going limp) and what to do (knee-chest position, call ambulance)
Explain the concept of lifelong follow-up — the child is not "cured" after surgery, but most live full, active lives
Discuss genetic testing implications (22q11.2 deletion) and recurrence risk counselling

Avoid agitation pre-operatively (may trigger tet spell) — use sedative premedication
Maintain SVR — avoid agents that drop SVR (e.g., volatile anaesthetics at high concentration, propofol bolus)
Phenylephrine should be available in the operating theatre
If 22q11.2 deletion confirmed: use irradiated blood products (to prevent transfusion-associated GVHD due to T-cell immunodeficiency) and check calcium (parathyroid hypoplasia → hypocalcaemia → arrhythmia risk)

Pre-operative: many TOF infants have failure to thrive → high-calorie feeds, dietitian involvement
Post-operative: catch-up growth typically occurs after successful repair

High Yield Summary — Management of TOF

IV PGE₁ for duct-dependent neonatal TOF to maintain PDA patency. Side effects: apnoea (10–12%), fever, hypotension ^[1]^[4]^[5]
Tet spell management (stepwise): Knee-chest position → calm child → O₂ → IV fluid bolus → morphine → phenylephrine → sodium bicarbonate → IV propranolol → intubation/GA → emergency surgery
Oral propranolol 1–4 mg/kg/day as bridge to surgery to prevent tet spells
Avoid ACEI/ARB in TOF — ↓SVR → triggers/worsens R-to-L shunting ^[1]
Modified Blalock-Taussig shunt: synthetic graft from innominate/subclavian to ipsilateral PA → L-to-R shunt → increases pulmonary flow. Indications: severe cyanosis, uncontrolled tet spells, hypoplastic PAs ^[1]
Always listen for shunt murmur on follow-up → blocked BT shunt can kill ^[1]
Complete repair at 6–12 months: VSD patch closure + RVOT reconstruction ± transannular patch. Mortality 0–3% ^[1]
Transannular patch → obligatory pulmonary regurgitation — the principal late complication ^[1]
Pulmonary valve replacement indicated when: MRI RVH + > 25% regurgitant fraction; or symptomatic (RV failure, arrhythmia) ^[1]
Prognosis: 93% 25-year survival after complete repair. Lifelong follow-up required ^[1]
Exercise testing every 3–4 years post-repair ^[1]

Active Recall - Management of TOF

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (Section on TOF management, p.214; heart failure management, p.200) ^[2] Senior notes: Ryan Ho Cardiology.pdf (Section 3.7.2 — Tetralogy of Fallot, p.187) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (TOF overview — duct-dependent circulation, p.267–284) ^[5] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (TOF overview — duct-dependent circulation, p.580–599) ^[6] Senior notes: Maksim Paediatric Notes.pdf (CHD treatment — surgery is definitive, p.55–56)

Complications of Tetralogy of Fallot

Complications of TOF are best understood by dividing them into two temporal phases: pre-operative complications (related to the uncorrected disease and chronic cyanosis) and post-operative complications (related to the surgical repair itself and long-term sequelae). This distinction is clinically crucial because a child sitting in your clinic may fall into either category depending on whether repair has been performed.

1. Pre-Operative (Unrepaired) Complications

These arise from the fundamental pathophysiology of TOF: chronic cyanosis due to R-to-L shunting, reduced pulmonary blood flow, and compensatory mechanisms that themselves become pathological over time.

This was discussed in detail in the management section, but it is the most acute and life-threatening pre-operative complication.

Aspect	Detail
Mechanism	Infundibular spasm → near-complete RVOT obstruction → profound R-to-L shunt → severe desaturation → metabolic acidosis → hyperpnoea → vicious cycle
Peak age	2–4 months (can occur 1 month to school age)
Triggers	Crying, feeding, straining, fever, dehydration, morning waking
Consequence if untreated	Seizures, cerebrovascular accident (stroke), death
Key clinical sign	Disappearing ESM (no flow through RVOT) — paradoxically, a quieter child with no murmur is sicker

Aspect	Detail
Mechanism	Chronic hypoxia → renal hypoxia-sensing cells detect low PaO₂ → increased erythropoietin (EPO) production → stimulates bone marrow → increased RBC production → polycythaemia
Consequence	Haemoglobin may reach 180–220 g/L; haematocrit > 0.65. This massively increases blood viscosity.
Clinical effects	Headache, lethargy, visual disturbances, dizziness in older children; microvascular sludging
Thrombotic risk	Hyperviscous blood predisposes to venous sinus thrombosis, stroke, and pulmonary thrombosis

Systemic complications: polycythemia ^[1] — a direct consequence of chronic cyanosis driving compensatory erythropoiesis.

Iron Deficiency Makes Polycythaemia More Dangerous

As explained in the investigations section: relative iron deficiency in the setting of polycythaemia produces microcytic red blood cells that are less deformable. Small, rigid RBCs navigate microcirculation poorly, increasing viscosity disproportionately to the haematocrit. This increases the risk of tet spells and cerebrovascular events. Always check iron studies and supplement iron if ferritin is low, even if Hb appears "adequately elevated."

Systemic complications: cerebral embolism/abscess ^[1]

Complication	Mechanism	Detail
Brain abscess	In normal circulation, venous blood passes through the lungs, where the pulmonary capillary bed acts as a filter — trapping bacteria and small thrombi. In TOF, the R-to-L shunt bypasses this filter → bacteraemia can directly seed the cerebral vasculature → brain abscess	More common in older children with longstanding cyanosis. Organisms: often oral flora (Streptococcus, anaerobes). Presents with headache, fever, focal neurological deficit, seizures.
Cerebral thromboembolism / stroke	Polycythaemia + hyperviscosity + paradoxical embolism (venous thrombi crossing R-to-L shunt) → cerebral arterial or venous thrombosis	Risk increases with haematocrit > 0.65 and with dehydration (further concentrating blood). Even small venous thrombi (e.g., from peripheral IV lines) can cross the VSD and embolise to the brain.

Why Brain Abscess in Cyanotic CHD?

Think of the lungs as a "bacterial sieve." Normally, any transient bacteraemia (e.g., from dental procedures, skin breaks) is filtered by the pulmonary capillary bed before reaching the systemic arterial circulation. In TOF, the R-to-L shunt provides a direct highway from the venous system to the systemic arteries, bypassing the lungs entirely. Bacteria enter the cerebral circulation unfiltered → brain abscess. This is why infective endocarditis prophylaxis and good dental hygiene are important in cyanotic CHD.

Systemic complications: stunted growth from hypoxia ^[1]

Mechanism	Detail
Chronic hypoxia → increased basal metabolic rate + decreased appetite + poor feeding tolerance	The heart and respiratory muscles work harder under chronic hypoxia, consuming more calories. Simultaneously, the infant feeds poorly (tires during feeds due to desaturation). The combination of increased demand and decreased intake results in failure to thrive.
Post-repair	Growth typically catches up after successful complete repair, especially if done early (before 12 months).

Mechanism	Detail
Severe polycythaemia (Hct > 0.65–0.70) → consumption of clotting factors and platelets	In extreme polycythaemia, the expanded red cell mass consumes clotting factors disproportionately. Platelet function is also impaired. This creates a paradox: the child is simultaneously at risk of both thrombosis (from hyperviscosity) and bleeding (from coagulopathy).
Clinical relevance	Increased surgical bleeding risk; easy bruising; mucosal bleeding in severe cases

Mechanism	Detail
Turbulent flow across the RVOT and abnormal intracardiac anatomy create endothelial damage → nidus for bacterial colonisation	Risk exists in unrepaired TOF, during and after palliative shunts, and for at least 6 months post-repair (or indefinitely if residual defects/prosthetic material remain)
Prevention	Antibiotic prophylaxis before dental procedures and selected invasive procedures per current guidelines

Always listen for shunt murmur on F/U → blocked B-T shunt can kill ^[1]^[2]

Complication	Mechanism	Management
Shunt thrombosis	Synthetic graft has thrombogenic surface; low-flow states (dehydration, hypotension) promote clotting → acute loss of pulmonary blood flow	Emergency — if shunt murmur disappears, urgent re-intervention (surgical thrombectomy or new shunt). Low-dose aspirin is often given prophylactically post-mBTS.
Shunt stenosis	Progressive intimal hyperplasia within the graft → narrowing over time → decreasing pulmonary flow → progressive cyanosis	May need revision or complete repair
Pulmonary artery distortion	The shunt anastomosis can cause kinking or stenosis of the branch PA at the insertion site	May complicate subsequent complete repair; may need intraoperative PA plasty
Heart failure	If the shunt is too large, it creates excessive L-to-R shunting → pulmonary overcirculation → volume overload → heart failure	Graft size is chosen carefully to balance adequate oxygenation without overcirculation

2. Post-Operative (Post-Repair) Complications

After complete repair, the haemodynamics are vastly improved, but the child is NOT "normal." Surgical scars, residual lesions, and iatrogenic consequences create a new set of long-term issues.

Pulmonary regurgitation as principal late complication ^[1]^[2]

Cause: ↑aggressive repair → ↑risk of PV damage (esp if transannular patch used → obligatory PR) ^[1]^[2]

This is the single most important long-term complication and is essentially an expected, accepted trade-off of complete TOF repair.

Aspect	Detail
Mechanism	During RVOT reconstruction, the pulmonary valve leaflets may be damaged or excised. If a transannular patch is used (patching across the PV annulus to widen a hypoplastic annulus), the valve becomes incompetent by definition — the patch disrupts the annular ring → obligatory pulmonary regurgitation ^[1]^[2]
Haemodynamic consequence	The pulmonary valve normally prevents backflow from the PAs into the RV during diastole. Without a competent PV, blood regurgitates into the RV with each cardiac cycle → chronic RV volume overload → progressive RV dilation
Tolerance	PR is well-tolerated for years to decades because the RV operates in a low-pressure system. However, the RV eventually fails from chronic volume overload.
Timeline	Clinically significant RV dilation typically develops 15–25 years after repair, though it can be earlier

Problems: RV dilation and dysfunction, ↓ET, arrhythmia (VT, AFlu, AF), sudden cardiac death ^[1]^[2]

Aspect	Detail
Mechanism	Chronic PR → RV volume overload → progressive RV dilation → myocardial fibrosis → contractile dysfunction → RV failure
Clinical features	Exercise intolerance (↓ET), peripheral oedema, hepatomegaly, elevated JVP (in older patients), fatigue
Detection	Cardiac MRI is the gold standard for quantifying RV volumes (RVEDVi, RVESVi) and ejection fraction. Echocardiography can assess RV function but is less accurate for volumes.
Significance	RV dysfunction is the primary driver of morbidity and mortality in repaired TOF long-term

Arrhythmia (VT, AFlu, AF) ^[1]^[2]

Arrhythmia Type	Mechanism	Clinical Significance
Ventricular tachycardia (VT)	Scar tissue from VSD patch and RVOT incision/infundibulectomy creates macro-re-entrant circuits in the RV myocardium. A dilated, fibrosed RV is the perfect substrate for re-entry.	Most dangerous arrhythmia — can degenerate into VF → sudden cardiac death
Atrial flutter (AFlu)	Right atrial scarring from suture lines + chronic RA dilation (from RV dysfunction and TR) → atrial macro-re-entry	Poorly tolerated in a compromised RV; rapid ventricular response can precipitate haemodynamic collapse
Atrial fibrillation (AF)	Similar substrate to AFlu; more common in older adults with repaired TOF	Loss of atrial contribution to RV filling further compromises cardiac output
Complete heart block	The bundle of His runs along the posteroinferior rim of the perimembranous VSD — suturing the VSD patch can damage it → complete heart block	Occurs in < 2% of modern repairs; may require permanent pacemaker

Risk stratification for sudden cardiac death:

QRS duration > 180 ms (indicates severe RV dilation — the wider the QRS, the bigger the RV, the worse the prognosis)
Inducible sustained VT on electrophysiology study
Severe RV dilation (RVEDVi > 170 mL/m²)
RV dysfunction (RVEF < 45%)
Severe PR
Consider ICD implantation in high-risk patients

Sudden cardiac death ^[1]^[2]

Aspect	Detail
Incidence	~0.5–1% per decade of follow-up; cumulative lifetime risk ~2–6%
Mechanism	Ventricular tachyarrhythmia (VT → VF) in the context of a dilated, scarred RV
Risk factors	QRS > 180 ms, prior sustained VT, severe RV dilation, poor RV function, older age at repair, use of transannular patch, previous ventriculotomy
Prevention	Timely pulmonary valve replacement to prevent progressive RV dilation; ICD in selected high-risk patients; catheter ablation of VT circuits

↓ET (exercise tolerance) ^[1]^[2]

Mechanism	Detail
Multifactorial: PR → RV volume overload → reduced forward stroke volume during exercise; residual RVOT obstruction limits augmentation of pulmonary flow; chronotropic incompetence (some patients have impaired heart rate response to exercise); deconditioning	Most repaired TOF patients have subnormal peak VO₂ (typically 60–85% of predicted) even when asymptomatic
Monitoring	Exercise testing every 3–4 years ^[1]^[2] — detects declining functional capacity and exercise-induced arrhythmias

Lesion	Mechanism	Consequence
Residual VSD	Incomplete patch closure or patch dehiscence	L-to-R shunt → volume overload; continuous murmur at left sternal border
Residual RVOT obstruction	Incomplete infundibular resection, recurrent muscular hypertrophy, or suboptimal transannular patch	RV pressure overload → progressive RVH → exercise intolerance
Branch PA stenosis	Native hypoplasia or distortion from prior shunt or surgical manipulation	Limits pulmonary blood flow to one lung → V/Q mismatch → effort desaturation
Aortic root dilation	The overriding aorta in TOF is exposed to increased volume flow (receives blood from both ventricles pre-repair). Post-repair, the aortic root may remain dilated or progressively dilate.	Aortic regurgitation (AR) — an increasingly recognised late complication. Can eventually require aortic root/valve surgery.
Tricuspid regurgitation (TR)	RV dilation → tricuspid annular dilation → secondary (functional) TR	Worsens RV volume overload → further dilation → a vicious cycle

Management: by pulmonary valve replacement in (1) MRI show RVH + > 25% regurgitant fraction (2) symptomatic (RV failure, arrhythmia) ^[1]^[2]

Require long-term F/U and exercise testing Q3–4y ^[1]^[2]

Indication	Detail
Imaging-based	Cardiac MRI: RV dilatation + PR regurgitant fraction > 25%; RVEDVi > 150–170 mL/m²; RVESVi > 80 mL/m²; RVEF declining
Symptom-based	RV failure symptoms, exercise intolerance declining on serial testing, new arrhythmias
Combined	Current guidelines increasingly favour earlier PVR (before RV is irreversibly dilated) to preserve long-term RV function
Options	Surgical PVR (bioprosthetic valve, homograft — most common); Transcatheter PVR (Melody valve, SAPIEN valve — for patients with a suitable landing zone such as a pre-existing RV-PA conduit or bioprosthetic ring)
Outcome	PVR generally results in significant improvement in RV volumes and exercise capacity if done before irreversible RV dysfunction. Bioprosthetic valves have a finite lifespan (~10–15 years) → most patients will need repeat PVR during their lifetime.

Aspect	Detail
Risk	Prosthetic VSD patch, transannular patch material, RV-PA conduits, and any residual turbulent flow sites create ongoing endocarditis risk
Prophylaxis	Antibiotic prophylaxis before dental procedures and other high-risk invasive procedures for the first 6 months post-surgery (prosthetic material not yet endothelialised); indefinitely if there are residual defects adjacent to prosthetic material. Per AHA/ESC guidelines (2021 update).
Organisms	Viridans streptococci (dental origin), Staphylococcus aureus, HACEK group

Category	Complication	Timing	Mechanism
Pre-op	Tet spells	Infancy (peak 2–4 months)	Infundibular spasm → near-complete RVOT obstruction
Pre-op	Polycythaemia / hyperviscosity	Chronic	Compensatory EPO-driven erythropoiesis
Pre-op	Brain abscess	Childhood (longstanding cyanosis)	R-to-L shunt bypasses pulmonary capillary filter
Pre-op	Cerebral thromboembolism / stroke	Any age	Polycythaemia + paradoxical embolism
Pre-op	Growth failure	Infancy onwards	Chronic hypoxia + increased metabolic demand
Pre-op	Coagulopathy	Severe polycythaemia	Consumption of clotting factors + platelet dysfunction
Pre-op	Infective endocarditis	Any age	Turbulent flow → endothelial damage → bacterial colonisation
Palliative	Shunt thrombosis	Post-mBTS	Thrombogenic graft surface + low-flow
Post-op	Pulmonary regurgitation	Years to decades post-repair	Transannular patch → obligatory PR; PV damage ^[1]^[2]
Post-op	RV dilation and dysfunction	Progressive	Chronic PR → RV volume overload ^[1]^[2]
Post-op	Arrhythmia (VT, AFlu, AF)	Years to decades	Surgical scar re-entry circuits + dilated RV ^[1]^[2]
Post-op	Sudden cardiac death	Any time post-repair	VT → VF in dilated, scarred RV ^[1]^[2]
Post-op	↓ Exercise tolerance	Progressive	Multifactorial: PR, RV dysfunction, residual lesions ^[1]^[2]
Post-op	Residual VSD / RVOT obstruction	Immediate to progressive	Incomplete repair / recurrence
Post-op	Aortic root dilation / AR	Decades	Chronic aortic root volume overload from overriding aorta
Post-op	Complete heart block	Immediate post-op	Surgical damage to bundle of His
Post-op	Infective endocarditis	Lifelong	Prosthetic material, residual turbulent flow

Consideration	Detail
Developmental impact	Chronic cyanosis before repair can affect neurodevelopmental outcomes. Early repair (before 6–12 months) is associated with better cognitive outcomes. Children with 22q11.2 deletion are at additional risk for developmental delay regardless of cardiac repair timing.
Adolescent transition	Repaired TOF patients must transition from paediatric to adult congenital heart disease (ACHD) services. This is a vulnerable period — adolescents may disengage from follow-up. Education about lifelong surveillance need is essential.
Pregnancy counselling (female patients)	Most repaired TOF patients tolerate pregnancy, but those with significant PR, RV dysfunction, or arrhythmias need pre-conception cardiac MRI and risk stratification. Pregnancy increases blood volume (40–50%) → can unmask RV dysfunction.
Exercise and sport	Most repaired TOF patients can participate in moderate physical activity. High-intensity competitive sports may be restricted depending on residual lesions, RV function, and arrhythmia risk. Individualised exercise testing guides recommendations.
Dental hygiene	Emphasise to families: good oral hygiene is critical to reduce bacteraemia episodes and brain abscess / endocarditis risk — both pre- and post-repair

High Yield Summary — Complications of TOF

Pre-operative complications (unrepaired TOF):

Tet spells — life-threatening; infundibular spasm → R-to-L shunt → cyanosis → acidosis vicious cycle
Polycythaemia — compensatory; increases viscosity and thrombotic risk ^[1]
Brain abscess — R-to-L shunt bypasses the pulmonary capillary "filter" ^[1]
Cerebral thromboembolism/stroke — polycythaemia + paradoxical embolism ^[1]
Growth failure (stunted growth from hypoxia) ^[1]
Coagulopathy — from severe polycythaemia
Infective endocarditis — turbulent flow + abnormal intracardiac anatomy

Post-operative complications (repaired TOF):

Pulmonary regurgitation — the principal late complication ^[1]^[2]; obligatory if transannular patch used
RV dilation and dysfunction — from chronic PR volume overload ^[1]^[2]
Arrhythmias: VT, atrial flutter, AF — from surgical scar re-entry + dilated RV ^[1]^[2]
Sudden cardiac death — VT/VF in dilated, scarred RV; QRS > 180 ms is a risk marker ^[1]^[2]
Decreased exercise tolerance — multifactorial ^[1]^[2]
Management of PR: pulmonary valve replacement when MRI shows RVH + > 25% regurgitant fraction OR symptomatic ^[1]^[2]
Lifelong follow-up with exercise testing every 3–4 years ^[1]^[2]
Prognosis: 93% 25-year survival after complete repair ^[1]^[2]

Active Recall - Complications of TOF

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (TOF management and complications, p.214; Eisenmenger complications, p.193; duct-dependent circulation, p.193) ^[2] Senior notes: Ryan Ho Cardiology.pdf (TOF management and complications, p.188)

High Yield Summary

Tetralogy of Fallot — Key Points for Exams:

Four features: RVOT obstruction (PS), VSD (large, malalignment), overriding aorta, RVH — all from one defect: anterocephalad malalignment of the infundibular septum
Most common cause of cyanosis in infancy at 1 year ^[1]^[2]
Main haemodynamic determinant is RVOT obstruction — this determines pink vs. blue
Mild obstruction → "pink Fallot" (L-to-R shunt, heart failure at 4–6 weeks); significant obstruction → R-to-L shunt → cyanosis
Murmur is ESM at LUSB due to PS, NOT VSD — murmur gets SOFTER with worsening obstruction (paradoxical)
Single S2 (inaudible P2) — because pulmonary valve closure is diminished
Squatting (Fallot's sign): ↑SVR + ↑VR → ↓R-to-L shunt → improved oxygenation
Tet spells: infundibular spasm → vicious cycle of ↓pulmonary flow → acidosis → hyperpnoea → ↑shunting
22q11.2 deletion: screen ALL TOF patients
CXR clue: oligaemic lung fields + boot-shaped heart; supports cardiac (not respiratory) cause of cyanosis ^[3]
Complications of chronic cyanosis: polycythaemia, brain abscess, stroke, clubbing, FTT

High Yield Summary — Differential Diagnosis of TOF

TOF sits in the ↓ pulmonary blood flow group of cyanotic CHD (oligaemic CXR, boot-shaped heart, ESM at LUSB, single S2)
Cyanotic CHD is categorised by: ↓ pulmonary flow, ↑ pulmonary flow (3Ts), severe heart failure ^[4]^[5]
↓ Pulmonary flow DDx: TOF, TOF/PA, PA/IVS, critical PS, tricuspid atresia, Ebstein anomaly
↑ Pulmonary flow DDx (3Ts): d-TGA, truncus arteriosus, TAPVR
Heart failure DDx: Critical CoA, interrupted aortic arch, critical AS, HLHS
Non-cardiac DDx: respiratory (RDS, MAS), PPHN, GBS sepsis, IEM ^[6]
"Pink Fallot" DDx: Large VSD, AVSD, large PDA
Ductal-dependent lesions require PGE₁ to maintain patency — know which lesions are duct-dependent for pulmonary vs. systemic flow
Tricuspid atresia is the classic cyanotic CHD with LAD + LVH on ECG — distinguishes it from TOF (RAD + RVH)
Boot-shaped heart (coeur en sabot) on CXR is characteristic of TOF but not pathognomonic

High Yield Summary — Diagnosis of TOF

TOF is diagnosed anatomically by echocardiography demonstrating all four features: large malalignment VSD, overriding aorta, RVOT obstruction, RVH
Investigations: CXR, ECG, Echocardiography + Doppler USG ^[6] — this is the core investigation triad
CXR: boot-shaped heart (coeur en sabot) + oligaemic lung fields — the classic radiological pattern. Dark oligaemic lung fields point to cyanotic CHD with ↓ pulmonary flow ^[1]
Hyperoxia test: PaO₂ remains < 150 mmHg (< 15 kPa) on 100% O₂ → cardiac cause. Caution: may promote ductal closure in duct-dependent circulation ^[1]
ECG: RAD + RVH (contrast with tricuspid atresia: LAD + LVH)
Echo is gold standard — defines anatomy, RVOT obstruction severity, PA size, coronary anatomy, shunt direction, associated anomalies
22q11.2 genetic testing in ALL TOF patients — ~15% prevalence; affects peri-operative and long-term care
Iron studies are essential — microcytic polycythaemia is more dangerous than normocytic polycythaemia (increased viscosity → tet spells and stroke)
Cardiac catheterisation reserved for complex anatomy (MAPCAs, inadequate PA size, inconclusive coronary anatomy)
Cardiac MRI is the gold standard for post-repair RV assessment and timing of pulmonary valve replacement

High Yield Summary — Management of TOF

IV PGE₁ for duct-dependent neonatal TOF to maintain PDA patency. Side effects: apnoea (10–12%), fever, hypotension ^[1]^[4]^[5]
Tet spell management (stepwise): Knee-chest position → calm child → O₂ → IV fluid bolus → morphine → phenylephrine → sodium bicarbonate → IV propranolol → intubation/GA → emergency surgery
Oral propranolol 1–4 mg/kg/day as bridge to surgery to prevent tet spells
Avoid ACEI/ARB in TOF — ↓SVR → triggers/worsens R-to-L shunting ^[1]
Modified Blalock-Taussig shunt: synthetic graft from innominate/subclavian to ipsilateral PA → L-to-R shunt → increases pulmonary flow. Indications: severe cyanosis, uncontrolled tet spells, hypoplastic PAs ^[1]
Always listen for shunt murmur on follow-up → blocked BT shunt can kill ^[1]
Complete repair at 6–12 months: VSD patch closure + RVOT reconstruction ± transannular patch. Mortality 0–3% ^[1]
Transannular patch → obligatory pulmonary regurgitation — the principal late complication ^[1]
Pulmonary valve replacement indicated when: MRI RVH + > 25% regurgitant fraction; or symptomatic (RV failure, arrhythmia) ^[1]
Prognosis: 93% 25-year survival after complete repair. Lifelong follow-up required ^[1]
Exercise testing every 3–4 years post-repair ^[1]

High Yield Summary — Complications of TOF

Pre-operative complications (unrepaired TOF):

Tet spells — life-threatening; infundibular spasm → R-to-L shunt → cyanosis → acidosis vicious cycle
Polycythaemia — compensatory; increases viscosity and thrombotic risk ^[1]
Brain abscess — R-to-L shunt bypasses the pulmonary capillary "filter" ^[1]
Cerebral thromboembolism/stroke — polycythaemia + paradoxical embolism ^[1]
Growth failure (stunted growth from hypoxia) ^[1]
Coagulopathy — from severe polycythaemia
Infective endocarditis — turbulent flow + abnormal intracardiac anatomy

Post-operative complications (repaired TOF):

Pulmonary regurgitation — the principal late complication ^[1]^[2]; obligatory if transannular patch used
RV dilation and dysfunction — from chronic PR volume overload ^[1]^[2]
Arrhythmias: VT, atrial flutter, AF — from surgical scar re-entry + dilated RV ^[1]^[2]
Sudden cardiac death — VT/VF in dilated, scarred RV; QRS > 180 ms is a risk marker ^[1]^[2]
Decreased exercise tolerance — multifactorial ^[1]^[2]
Management of PR: pulmonary valve replacement when MRI shows RVH + > 25% regurgitant fraction OR symptomatic ^[1]^[2]
Lifelong follow-up with exercise testing every 3–4 years ^[1]^[2]
Prognosis: 93% 25-year survival after complete repair ^[1]^[2]

Tetralogy Of Fallot

Tetralogy of Fallot (TOF) — Paediatric Cardiology

3. Embryology and Anatomy

4. Pathophysiology — The Haemodynamic Story

5. Classification

6. Aetiology and Risk Factors

7. Clinical Features

7.3 Hypercyanotic ("Tet") Spells — Detailed Mechanism

8. Additional Clinical Considerations

9. Key Paediatric-Specific Considerations

Active Recall - Tetralogy of Fallot

Differential Diagnosis of Tetralogy of Fallot

Key Distinguishing Points: TOF vs. Other ↓ Pulmonary Flow Lesions

Active Recall - Differential Diagnosis of TOF

References

Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Tetralogy of Fallot

2. Diagnostic Algorithm — Clinical Approach to the Cyanotic Infant

3. Investigation Modalities — Detailed Findings and Interpretation

Active Recall - Diagnosis of TOF

References

Management of Tetralogy of Fallot

2.1 Prostaglandin E₁ (PGE₁ / Alprostadil)

3. Acute Management of Hypercyanotic (Tet) Spells

4.1 "Pink Fallot" with Heart Failure

5. Surgical Management

6. Post-Operative Management and Long-Term Follow-Up

8. Special Paediatric Considerations

Active Recall - Management of TOF

References

Complications of Tetralogy of Fallot

1. Pre-Operative (Unrepaired) Complications

2. Post-Operative (Post-Repair) Complications

Active Recall - Complications of TOF

References

On this page

Tetralogy Of Fallot

1. Definition

2. Epidemiology

3. Embryology and Anatomy

3.1 Normal Embryological Development of the Outflow Tract

3.2 Pathogenesis of TOF

3.3 Anatomy of the RVOT Obstruction — Levels

3.4 The VSD in TOF

3.5 Associated Anomalies

4. Pathophysiology — The Haemodynamic Story

4.1 The Central Concept: A Large VSD with Variable RVOT Obstruction

4.2 Spectrum of Severity

4.3 Why RVOT Obstruction Is Progressive

4.4 Why the Murmur Gets Softer as the Child Gets More Blue

4.5 Squatting Physiology (Fallot's Sign)

5. Classification

5.1 By Severity of RVOT Obstruction (Clinical Spectrum)

5.2 By Associated Anomalies

6. Aetiology and Risk Factors

6.1 Genetic Factors

6.2 Environmental / Maternal Risk Factors

6.3 Neural Crest Cell Connection

7. Clinical Features

7.1 Symptoms

7.2 Signs

7.3 Hypercyanotic ("Tet") Spells — Detailed Mechanism

Trigger Factors

Pathophysiological Cascade

Clinical Features of a Tet Spell

8. Additional Clinical Considerations

8.1 Cyanosis vs. Respiratory Disease — How to Distinguish

8.2 Growth and Development Impact

8.3 Age-Specific Presentation Summary

9. Key Paediatric-Specific Considerations

9.1 Communication with Families

9.2 Consent and Assent

9.3 Normal Values for Age — Context

Active Recall - Tetralogy of Fallot

References

1. Framework: Differential Diagnosis of Cyanotic Congenital Heart Disease

2. Decreased Pulmonary Blood Flow Group (Oligaemic Lung Fields)

3. Increased Pulmonary Blood Flow Group (Plethoric Lung Fields) — "The 3 Ts"

4. Severe Heart Failure Group (Systemic Outflow Obstruction)

5. Non-Cardiac Differential Diagnosis of Neonatal Cyanosis

6. Differential of the "Pink Fallot" Presentation (Heart Failure at 4–6 Weeks)

7. Differential of the Murmur in TOF

8. Summary Approach: The Cyanotic Neonate

Active Recall - Differential Diagnosis of TOF

1. Diagnostic Criteria — Defining TOF

2. Diagnostic Algorithm — Clinical Approach to the Cyanotic Infant

2.1 Step-by-Step Approach

2.2 Key Decision Points Explained

3. Investigation Modalities — Detailed Findings and Interpretation

3.1 Pulse Oximetry

3.2 Chest X-Ray (CXR)

3.3 Electrocardiogram (ECG)

3.4 Echocardiography (Gold Standard)

3.5 Cardiac Catheterisation and Angiography

3.6 Cardiac MRI / CT Angiography

3.7 Genetic Testing

3.8 Blood Tests

4. Investigations Summary Table — Putting It All Together

5. Approach by Age of Presentation

Active Recall - Diagnosis of TOF

1. Management Algorithm — Overview

2. Emergency Management of the Cyanotic Neonate (Duct-Dependent TOF)

3. Acute Management of Hypercyanotic (Tet) Spells

3.1 Step-by-Step Management

3.2 Prevention of Tet Spells — Oral Propranolol

4. Medical Management — Specific Situations

5. Surgical Management

5.1 Palliative Surgery — Modified Blalock-Taussig Shunt (mBTS)

5.2 Transcatheter Alternatives to Palliative Surgery

5.3 Definitive Surgery — Complete Intracardiac Repair

5.4 Surgical Indications Summary

6. Post-Operative Management and Long-Term Follow-Up

6.1 Late Complications (will be discussed further in Complications section)

6.2 Pulmonary Valve Replacement (PVR)

6.3 Follow-Up Schedule

7. Prognosis