Transposition of the great arteries is a congenital heart defect present at birth in which the aorta arises from the right ventricle and the pulmonary artery from the left ventricle, creating two parallel circulations incompatible with life unless a communication such as a septal defect or patent ductus arteriosus allows mixing of oxygenated and deoxygenated blood, typically presenting with severe cyanosis in the newborn period.

Transposition of the Great Arteries (TGA) — Paediatric Cardiology

Heart diagram of transposition of the great arteries showing the aorta arising from the right ventricle, the pulmonary artery arising from the left ventricle, and mixing through an atrial septal defect and a patent ductus arteriosus — d-TGA — parallel circulations with mixing via ASD and PDA

Transposition of the great arteries (TGA) is a ventriculoarterial discordant congenital heart defect in which the aorta arises from the right ventricle (RV) (anteriorly and to the right) and the pulmonary artery (PA) arises from the left ventricle (LV) (posteriorly and to the left) ^[1]^[2]^[3].

Breaking the name down:

"Transposition" = trans (across) + position → the great arteries have swapped positions
"Great arteries" = the aorta and pulmonary trunk — the two major outflow vessels of the heart

The term d-TGA (dextro-TGA) refers to the classical complete transposition where the aorta is anterior and rightward relative to the PA. This is distinct from l-TGA (levo-TGA / congenitally corrected TGA), where there is both atrioventricular AND ventriculoarterial discordance (a "double discordance" that is physiologically corrected).

This topic focuses exclusively on d-TGA (complete TGA), the common paediatric surgical emergency.

Key Concept — Parallel Circulations

In normal circulation, the systemic and pulmonary circuits function in series — deoxygenated blood goes to the lungs, gets oxygenated, returns to the left heart, and is pumped systemically. In TGA, the two circuits function in parallel — deoxygenated systemic venous blood returns to the RV and is pumped straight back out to the body via the aorta, while oxygenated pulmonary venous blood returns to the LV and is pumped back to the lungs via the PA. Without intercirculatory mixing, this is incompatible with life ^[1]^[2]^[3].

Feature	Detail
Incidence	~4.7 per 10,000 live births ^[1]
Proportion of all CHD	~5% of all congenital heart disease ^[1]^[3]
Sex	Male predominance (M:F ≈ 2–3:1)
Rank	Second most common cyanotic CHD (after Tetralogy of Fallot in older infants); most common cyanotic CHD presenting in the neonatal period
Age at presentation	Typically within hours to days of birth
Without intervention	Fatal in ~90% by 1 year of age without surgical correction

Hong Kong Context

Congenital heart disease affects approximately 8–10 per 1,000 live births in Hong Kong
TGA is one of the "critical" CHDs targeted by pulse oximetry screening in newborn nurseries in Hong Kong public hospitals
Antenatal detection rates have improved with routine 18–22 week anomaly scans, but TGA remains one of the harder lesions to detect antenatally because the four-chamber view appears normal; the outflow tract views are essential
Associated with fewer noncardiac anomalies ( < 10%) compared with other CHD defects ^[2]^[3]

TGA is NOT associated with any one common genetic abnormality ^[2]^[3]. Most cases are sporadic, but recognised risk factors include:

Category	Risk Factors
Maternal	Gestational diabetes mellitus (strongest association), advanced maternal age, maternal rubella exposure, alcohol use, phenylketonuria
Genetic/Syndromic	Associated with DiGeorge syndrome (22q11.2 deletion) — as TGA is a conotruncal abnormality ^[1]; however, this association is less strong than with TOF or truncus arteriosus
Environmental	Herbicides, rodenticides, some teratogens
Familial	Low recurrence risk (~1–2% in siblings); multifactorial inheritance suspected

Why DiGeorge?

DiGeorge syndrome (22q11.2 microdeletion) affects neural crest cell migration into the pharyngeal arches and outflow tract → conotruncal malformations. TGA, TOF, interrupted aortic arch, truncus arteriosus, and double-outlet RV are all conotruncal abnormalities. "CATCH-22" mnemonic: Cardiac anomaly, Abnormal facies, Thymic aplasia, Cleft palate, Hypocalcaemia — chromosome 22.

4. Anatomy and Embryology

To understand TGA, you need to understand how the single primitive outflow tract (truncus arteriosus and conus) normally septates:

The truncus arteriosus is a single outflow channel in the early embryonic heart
Neural crest cells migrate into the outflow tract and contribute to the aorticopulmonary (AP) septum
The AP septum normally grows in a spiral (helical) fashion → this spiral septation divides the single outflow into:
- The aorta (posteriorly and to the left initially, then crossing to the right)
- The pulmonary trunk (anteriorly and to the right initially, then crossing to the left)
The spiral arrangement ensures the aorta connects to the LV and the PA connects to the RV — i.e., the great arteries "wrap around" each other

Abnormal septation of the conus arteriosus ^[1] → the AP septum grows straight (non-spirally) rather than spirally
This results in the aorta arising anteriorly from the RV and the PA arising posteriorly from the LV — a direct swap
The great arteries run parallel to each other rather than crossing

This is surgically critical:

Coronary artery variations are common and must be delineated pre-operatively ^[2]^[3]
The coronary arteries arise from the sinuses of the aorta that face the pulmonary artery (the "facing sinuses")
Normal pattern (~65%): Left coronary artery (LCA) from left-facing sinus, right coronary artery (RCA) from right-facing sinus
Variant patterns (~35%): Circumflex from right coronary, single coronary, intramural course, etc.
Variant coronary anatomy increases surgical complexity of the arterial switch operation (ASO)

5. Pathophysiology

This is the conceptual core of TGA.

In TGA, systemic and pulmonary circulations run in parallel rather than in series ^[1]^[2]^[3]:

Circuit	Normal	TGA
Systemic	LV → Aorta → Body → Vena cavae → RA → RV → PA	RA → RV → Aorta → Body → Vena cavae → RA (closed loop of deoxygenated blood)
Pulmonary	RV → PA → Lungs → Pulmonary veins → LA → LV → Aorta	LA → LV → PA → Lungs → Pulmonary veins → LA (closed loop of oxygenated blood)

Key insight: Oxygenated blood from the lungs keeps recirculating through the lungs, and deoxygenated blood from the body keeps recirculating through the body. Without mixing between these two circuits, there is no way to deliver oxygen to the tissues → incompatible with postnatal life.

Anatomic sites for mixing are essential and must be present to be compatible with postnatal life ^[2]^[3]:

Level of Mixing	Structure	Notes
Atrial level	PFO (patent foramen ovale), ASD	Most common site of mixing in neonates; bidirectional shunting
Ventricular level	VSD	If present, provides additional mixing
Arterial level	PDA	Critical in the first days of life; allows mixing between aorta and PA
Other	Bronchopulmonary collaterals	Minor contribution ^[2]^[3]

The degree of intercirculatory mixing determines the severity of hypoxaemia ^[1]:

More mixing sites / larger communications → better mixing → higher systemic oxygen saturation → less cyanosis
Fewer/smaller mixing sites → poor mixing → profound cyanosis and metabolic acidosis

In the fetus, the ductus arteriosus is patent → allows some mixing between circuits
After birth, the ductus arteriosus begins to close (triggered by ↑PaO₂ and ↓circulating PGE₂ from the placenta)
Severe systemic hypoxaemia occurs with closure of the duct, especially when the interatrial communication is small → can cause cardiac arrest ^[1]
This is why TGA is classified as a ductal-dependent circulation — the neonate depends on the PDA for survival

Clinical Pearl — Ductal Closure = Emergency

A neonate with TGA and an intact ventricular septum (no VSD) who has only a small PFO is critically dependent on the PDA. When the duct closes (typically 24–72 hours), the baby develops sudden, profound cyanosis, metabolic acidosis, and cardiovascular collapse. This is a paediatric emergency requiring immediate prostaglandin E₁ (PGE₁) infusion and urgent balloon atrial septostomy.

5.4 Haemodynamic Consequences by Subtype

Simple TGA describes patients without another cardiac defect ^[2]^[3]:

Only mixing via PFO/PDA → inadequate mixing → severe cyanosis in the neonatal period ^[1]
High risk of neonatal hypoxia and death when PDA closes ^[1]
The LV pumps blood into the low-resistance pulmonary circulation → high pulmonary flow ^[1]
The RV supports the systemic circulation → pressure overloaded (working against systemic vascular resistance)

Complex TGA describes those with an additional cardiac defect ^[2]^[3]:

VSD provides ventricular-level mixing → adequate mixing → minimal cyanosis ^[1]
However, the combination of VSD + low PVR → large left-to-right shunt → pulmonary overcirculation
Heart failure symptoms develop when PVR falls (typically within the first week of life) ^[1]
If untreated, chronic pulmonary overcirculation → pulmonary vascular disease → Eisenmenger syndrome

PS limits pulmonary blood flow → reduced pulmonary overcirculation (less HF)
But PS also limits the amount of oxygenated blood available for mixing → more cyanosis
Physiology resembles TOF more than simple TGA

High pulmonary flow is characteristic because the stronger LV is supplying the pulmonary circulation ^[1]:

In TGA, the LV connects to the PA → pumps blood into the lungs against low PVR
This means pulmonary blood flow is typically increased (unlike TOF where it is decreased)
This is why TGA is classified as a cyanotic CHD with increased pulmonary blood flow

Classification of Cyanotic CHD by Pulmonary Blood Flow

Increased Pulmonary Blood Flow	Decreased Pulmonary Blood Flow
TGA	Tetralogy of Fallot
Truncus arteriosus	Pulmonary atresia
Total anomalous pulmonary venous return (TAPVR)	Tricuspid atresia (without VSD)
Single ventricle (without PS)	Ebstein anomaly

This distinction is critical for CXR interpretation and clinical reasoning ^[4].

A unique consideration in TGA:

After birth, PVR falls → the LV (connected to PA) works against progressively lower resistance
Over weeks, the LV deconditions (loses muscle mass/wall thickness) as it is no longer working against systemic pressure
This has critical surgical implications: the arterial switch operation (ASO) must be performed within the first 2–3 weeks of life (ideally < 2 weeks) while the LV still has enough muscle mass to take over systemic workload
If delayed beyond ~3–4 weeks, the LV may not be able to support systemic circulation after the switch → LV failure

6. Classification

Type	Description
d-TGA (Complete TGA)	Atrioventricular concordance + ventriculoarterial discordance. RA→RV→Aorta, LA→LV→PA. The "classical" TGA.
l-TGA (Congenitally Corrected TGA / cc-TGA)	Atrioventricular discordance + ventriculoarterial discordance (double discordance). RA→LV→PA, LA→RV→Aorta. Physiologically "corrected" but the RV supports systemic circulation → eventual RV failure.

Category	Associated Defect	Frequency	Clinical Impact
Simple TGA	Intact ventricular septum (± PFO/PDA)	~50%	Severe cyanosis, ductal-dependent
Complex TGA	VSD	~50%	Better mixing but risk of HF and pulmonary vascular disease
	LVOT obstruction / Pulmonary stenosis	~25%	Can be anatomical (valvar PS, pulmonary atresia) or dynamic (systemic RV pressure causes interventricular septum to bow into LV cavity → dynamic obstruction between mitral valve and septum) ^[2]^[3]
	Mitral and tricuspid valve abnormalities	Variable	May complicate surgical repair
	Coronary artery variations	~35%	Critical for surgical planning of ASO
	Coarctation of the aorta	~5%	Adds systemic outflow obstruction

Dynamic LVOT Obstruction in TGA

Why does this happen? In TGA, the RV is the systemic ventricle → generates systemic pressure → the interventricular septum bows toward the lower-pressure LV cavity. This septal bowing narrows the LVOT (the subpulmonary region), creating functional obstruction analogous to SAM in HOCM. This is important because it can worsen after birth as the LV pressure drops further.

7. Clinical Features

7.1 Symptoms

The clinical presentation depends fundamentally on the degree of intercirculatory mixing ^[1]^[2]^[3]:

Cyanosis soon after birth ^[1] — often within the first hour of life
- Why? Parallel circulations with only a small PFO for mixing → very little oxygenated blood reaches the systemic circuit → profound desaturation (SpO₂ typically 60–80%)
- The cyanosis is central (involving mucous membranes, tongue, lips) and unresponsive to supplemental oxygen (the "hyperoxia test" is positive = stays cyanotic despite 100% FiO₂)
- Why doesn't oxygen help? The problem is not a ventilation/diffusion issue — oxygen is reaching the lungs perfectly well. The problem is that oxygenated blood cannot get to the systemic circulation because of the parallel circuits
Rapid clinical deterioration when the PDA begins to close (24–72h)
- Worsening cyanosis, tachypnoea, metabolic acidosis, lethargy, poor feeding
- Can cause cardiac arrest ^[1]
- Why? Loss of the last significant mixing point → near-complete separation of circuits
Tachypnoea without significant respiratory distress initially
- Why? The lungs are well-perfused (even over-perfused) → no parenchymal lung disease → no significant retractions or grunting at first. The tachypnoea is driven by chemoreceptor stimulation from hypoxaemia and acidosis

Minimal cyanosis — may appear only mildly dusky or even "pink" ^[1]
- Why? The large VSD allows significant bidirectional mixing → reasonable systemic oxygen saturation
Heart failure symptoms within the first week of life ^[1]
- As PVR falls, there is increasing left-to-right shunting through the VSD → pulmonary overcirculation
- Presents with: tachypnoea, feeding difficulty, diaphoresis (especially during feeds), poor weight gain, hepatomegaly
- Why feeding difficulty? Sucking and swallowing are aerobically demanding activities for a neonate; a failing heart cannot increase cardiac output adequately → the baby tires quickly, sweats, and takes smaller volumes
Later: failure to thrive from chronic heart failure and increased metabolic demands

More significant cyanosis than TGA + VSD alone (because PS limits pulmonary blood flow)
Less heart failure (because PS limits pulmonary overcirculation)
Physiology resembles TOF

Coarctation of aorta (CoA) or pulmonary hypertension (pHTN) → reverse differential cyanosis when PA pressure > aortic pressure ^[1]
"Reverse differential" means the upper body is more cyanosed than the lower body — the opposite of what you see in PDA with Eisenmenger (where the lower body is more cyanosed)
Why? If PA pressure exceeds aortic pressure, oxygenated blood from the LV (connected to PA) shunts through the PDA into the descending aorta → the legs get more oxygenated blood than the upper body (which receives purely deoxygenated blood from the RV via the aorta)

Sign	Pathophysiological Basis
Cyanosis (central, unresponsive to O₂)	Parallel circulations → deoxygenated blood in systemic circuit
Heart failure signs (tachypnoea, hepatomegaly, gallop rhythm) — only if adequate mixing with VSD	Pulmonary overcirculation → volume overload
RV impulse (parasternal heave)	RV is the systemic ventricle → pressure overload as it supports systemic circulation against high SVR ^[1]
Loud and single S2	Closure sound of the anteriorly positioned aortic valve — the aorta is anterior and closer to the chest wall → A2 is loud and easily heard. P2 is soft because the PA is posterior. Since A2 is loud and P2 is inaudible, S2 sounds single ^[1]
NO murmur or non-specific ESM/PSM	There is no obstruction or turbulent flow across a stenotic valve in simple TGA — the great arteries are just transposed, not stenotic. If a VSD is present → pansystolic murmur (PSM). If PS is present → ejection systolic murmur (ESM) ^[1]
Tachycardia	Compensatory response to hypoxaemia and/or heart failure
Poor perfusion / shock (late)	Metabolic acidosis from severe hypoxaemia; cardiovascular collapse

Why is There No Murmur in Simple TGA?

Murmurs are caused by turbulent blood flow — usually from blood flowing across a stenotic or regurgitant valve, or through an abnormal communication. In simple TGA with intact ventricular septum, blood flows normally from RV to aorta and from LV to PA — there is no stenosis, no VSD, and no turbulence. The only problem is that the connections are swapped. Hence, the baby can be profoundly cyanotic with a completely silent precordium — a deceptively quiet examination that can catch you off guard.

Exam Pearl — Cyanotic Neonate with No Murmur

A cyanotic neonate with no murmur, loud single S2, and CXR showing increased pulmonary vascular markings = think TGA until proven otherwise. This is a classic OSCE/written exam scenario. Don't be fooled by the absence of a murmur — it doesn't mean the heart is normal!

Feature	TGA	TOF	Tricuspid Atresia
Timing of cyanosis	Hours after birth	Weeks to months (progressive)	At birth
Pulmonary blood flow	Increased	Decreased	Decreased
Murmur	Often absent	ESM at LUSB	Variable
S2	Loud, single	Single (soft P2)	Single
CXR heart shape	"Egg on side"	"Boot-shaped"	Normal/small heart
CXR lung fields	Plethoric	Oligaemic	Oligaemic
Hyperoxia test	Fails (stays cyanotic)	Fails	Fails
Tet spells	No	Yes	No

Age	Typical Presentation
Birth – 24h	Cyanosis detected on routine examination or pulse oximetry screening; may appear well otherwise
24–72h	Worsening cyanosis as PDA closes; metabolic acidosis; tachypnoea
Days – 1 week	Heart failure symptoms if large VSD present (as PVR falls)
> 2 weeks (if untreated)	Chronic cyanosis, failure to thrive, progressive metabolic derangement

8. Investigations (Pre-Diagnosis — Included for Completeness of Clinical Features Section)

While the full diagnostic workup will be covered in the next section, the characteristic investigation findings are closely tied to understanding the clinical features:

Feature	Explanation
"Egg on side" appearance (also called "egg on string")	Oval/egg-shaped cardiac silhouette due to narrowed upper mediastinum ^[1]
Narrowed upper mediastinum	Two reasons: (1) Abnormal anteroposterior relationship of the aorta and pulmonary trunk — normally the great vessels create a wide shadow, but when they are parallel (not crossing), the mediastinal shadow narrows ^[1]; (2) Stress-induced thymic involution — severe neonatal hypoxaemia/stress causes the thymus to shrink ^[1]
Increased pulmonary vascular markings	The stronger LV is supplying the lungs → increased pulmonary blood flow → pulmonary plethora ^[1]

Typically normal for age ^[1] in the neonatal period
Why normal? In the neonate, RV dominance is physiological → the TGA pattern (RV supporting systemic circulation) doesn't look different from normal neonatal RV dominance
Over time: rightward axis deviation and RVH become apparent (as the RV hypertrophies to support systemic circulation)

Diagnostic — the gold standard
Demonstrates ventriculoarterial discordance, identifies associated defects (VSD, PS, CoA), and maps coronary artery anatomy

Neonate placed on 100% FiO₂ for 10 minutes
In cyanotic CHD (including TGA): PaO₂ remains < 150 mmHg (often < 100 mmHg)
In respiratory disease: PaO₂ typically rises > 150 mmHg
Oligaemic lung field on CXR supports cyanotic CHD over respiratory disease ^[4]

AOS Past Paper Point

"Radiograph showing an oligaemic lung field due to reduced pulmonary blood flow" supports cyanotic CHD over respiratory disease ^[4]. Note: This applies to cyanotic CHDs with REDUCED pulmonary blood flow (e.g., TOF). TGA characteristically has INCREASED pulmonary blood flow, so the lung fields would be plethoric, not oligaemic. However, the principle of using CXR lung fields to differentiate cardiac from respiratory cyanosis is key.

Growth: Without correction, infants with TGA develop failure to thrive due to:
- Chronic hypoxaemia → increased metabolic demands
- Heart failure → poor feeding tolerance → inadequate caloric intake
- Increased work of breathing → increased energy expenditure
Neurodevelopment: Chronic hypoxaemia and the haemodynamic instability of the neonatal period can cause neurological injury. Even after successful surgical repair, children with TGA have higher rates of:
- Mild motor delays
- Attention and executive function difficulties
- Learning disabilities
- These are likely related to perioperative brain injury (deep hypothermic circulatory arrest during surgery) and prenatal/postnatal cerebral hypoxia

Breaking the diagnosis: Parents are often overwhelmed — the baby may appear "normal" apart from colour. Use simple language: "Your baby's heart tubes are connected the wrong way around, so the blood isn't getting enough oxygen"
Urgency: Communicate the need for urgent intervention clearly but calmly
Prognosis: After arterial switch operation, long-term survival is excellent (> 95% at 20 years) — this is a key reassurance point
Consent: Informed consent for balloon atrial septostomy and subsequent surgery must come from parents/guardians. Explain risks, benefits, and alternatives in age-appropriate language
Psychosocial: Connect families with cardiac support groups; address parental anxiety and bonding difficulties in the NICU setting

High Yield Summary

TGA = ventriculoarterial discordance: aorta from RV, PA from LV → parallel circulations → incompatible with life without intercirculatory mixing
Intercirculatory mixing occurs at atrial (PFO/ASD), ventricular (VSD), and arterial (PDA) levels — the degree of mixing determines clinical severity
Ductal-dependent circulation: PDA closure → sudden profound cyanosis → cardiac arrest → requires emergent PGE₁
Simple TGA (intact IVS): severe cyanosis within hours, NO murmur, loud single S2, CXR "egg on side" with pulmonary plethora, ECG normal for age
Complex TGA (with VSD): minimal cyanosis but heart failure symptoms ≤1 week as PVR falls
Cyanotic CHD with INCREASED pulmonary blood flow (unlike TOF which has decreased)
CXR: egg on side + narrow mediastinum (parallel great arteries + thymic involution) + increased pulmonary vascular markings
Embryology: failure of spiral septation of the conus → straight septation → transposed great arteries
LV deconditioning: ASO must be performed within first 2–3 weeks before LV loses capacity to support systemic circulation
Coronary artery variants (~35%) are critical for surgical planning

Active Recall - TGA Clinical Features and Pathophysiology

Differential Diagnosis of Neonatal Cyanosis — Approaching TGA

The clinical presentation of TGA is a cyanotic neonate. The differential diagnosis is therefore framed around the question: "Why is this newborn blue?" The approach must distinguish cardiac from non-cardiac causes, then narrow down among the cyanotic congenital heart diseases.

Central cyanosis becomes clinically visible when deoxyhaemoglobin exceeds 5 g/dL ^[6]. Because neonates are relatively polycythaemic (Hb ~15–17 g/dL), cyanosis may be detectable at higher SpO₂ values than in older children or anaemic patients. Check buccal mucosa instead of lip — lip colour can be misleading due to peripheral vasoconstriction ^[6].

GC High-Yield — DDx of Cyanosis in Neonates

The GC 147 lecture and Maksim paediatric notes list the following categories for the differential diagnosis of cyanosis in neonates ^[5]^[6]:

Category	Examples
Cyanotic heart disease	Tetralogy of Fallot, transposition of great arteries, pulmonary atresia, tricuspid atresia, TAPVD, complex heart lesion (e.g. univentricular heart)
Respiratory disorders	Surfactant deficiency, meconium aspiration, pulmonary hypoplasia
Persistent pulmonary hypertension of the newborn (PPHN)	Primary or secondary
Infection	Group B Streptococcal septicaemia
Metabolic	Inborn error of metabolism → metabolic acidosis and shock

The clinical approach to a cyanotic neonate follows a systematic algorithm. The goal is to rapidly identify whether the cause is cardiac or non-cardiac, because the management diverges immediately.

3. Cardiac Causes — Cyanotic Congenital Heart Disease

The major differential diagnoses for TGA are the other cyanotic CHDs. The key discriminating features are the pulmonary blood flow pattern (increased vs. decreased), the CXR silhouette, and the clinical behaviour.

These conditions share the feature of pulmonary plethora on CXR because too much blood is reaching the lungs.

Condition	Pathophysiology	Key Differentiating Features from TGA
Transposition of Great Arteries (TGA) ^[1]^[2]^[3]	Ventriculoarterial discordance → parallel circulations → survival depends on intercirculatory mixing (PFO, ASD, VSD, PDA)	Cyanosis from birth (D1–2), egg-on-side CXR, narrow mediastinum, no murmur, loud single S2, ECG normal for age
Truncus arteriosus ^[3]^[7]	Aorta, pulmonary arteries, and coronary arteries all arise from a single great vessel → combined output of LV and RV exits through one trunk. Always has a large VSD (the truncal root overrides both ventricles). NOT ductal-dependent ^[3]^[7].	Cyanosis at birth is mild (because mixing occurs freely in the single trunk). HF develops at a few weeks as PVR drops → increased pulmonary flow → marked cardiovascular instability ^[3]^[7]. Systolic ejection click, single S2, truncal regurgitation murmur. CXR: cardiomegaly, increased PVM, absent main PA segment, right aortic arch (30%). Associated with DiGeorge syndrome (22q11.2 deletion) more strongly than TGA
Total Anomalous Pulmonary Venous Return (TAPVR) ^[3]^[7]	All four pulmonary veins drain anomalously — into the RA (supracardiac, cardiac, or infracardiac types) rather than the LA. An ASD/PFO is obligatory for blood to reach the LA and then the systemic circulation	Cyanosis severity depends on obstruction: obstructed TAPVR (especially infracardiac type) → severe cyanosis + pulmonary oedema; unobstructed → mild cyanosis + HF. CXR "snowman" (figure-of-8) in supracardiac type (but only visible after a few months). Fixed split S2. ECG: RAD + RVH
Single ventricle / Univentricular heart without PS ^[6]	Only one functional ventricle receives all systemic and pulmonary venous return → complete mixing → cyanosis	Variable anatomy. Degree of cyanosis depends on PVR and any associated PS. Often presents with balanced cyanosis + eventual HF
Atrioventricular Septal Defect (AVSD) — complete ^[6]	Single 5-leaflet valve spanning both AV junctions + ASD + VSD → common mixing at atrial and ventricular levels	Commonly seen in children with Down syndrome ^[6]. Cyanosis at birth, HF at 2–3 weeks. Superior axis on ECG, RBBB, "goose-neck sign" on angiography ^[6]

How to Distinguish TGA from Truncus Arteriosus

Both present with neonatal cyanosis and increased pulmonary blood flow, but:

TGA: Cyanosis is severe early (parallel circuits, poor mixing) → ductal-dependent → worsens dramatically when duct closes. Egg-on-side CXR. No murmur.
Truncus arteriosus: Cyanosis is mild initially (complete mixing in single trunk) → NOT ductal-dependent → HF predominates as PVR falls. Ejection click, single S2, possible truncal regurgitation murmur. Wide mediastinum (large single trunk), not narrow.

The ductal-dependence distinction is clinically critical: TGA needs PGE₁ urgently; truncus does not.

These conditions show oligaemic lung fields on CXR because there is an obstruction to pulmonary blood flow.

Condition	Pathophysiology	Key Differentiating Features from TGA
Tetralogy of Fallot (TOF) ^[8]	Unequal division of outflow tract → RVOT obstruction + overriding aorta + VSD + RVH ^[8]. R-to-L shunt when RVP > LVP	Cyanosis onset depends on degree of RVOT obstruction — typically progressive over months (infundibular stenosis worsens), not at birth. Hypercyanotic (Tet) spells are characteristic ^[8]. Boot-shaped heart on CXR with oligaemic lung fields. ESM at LUSB (from PS), single S2. ECG: RAD + RVH
Pulmonary atresia (with intact IVS)	Complete obstruction of RVOT → no antegrade flow from RV to PA → ductal-dependent pulmonary circulation	Cyanosis from birth, worse than TGA typically. CXR: dark lung fields (severely oligaemic), small heart or normal size. Continuous PDA murmur may be heard. Ductal-dependent → PGE₁ required
Tricuspid atresia ^[6]	No connection between RA and RV → all systemic venous blood must cross PFO/ASD to LA → common mixing in LA → cyanosis. Only LV is effective; RV is small and non-functional ^[6]	Cyanosis from birth. LV impulse (not RV — because the RV is hypoplastic). Left axis deviation on ECG (unusual in neonatal period, where RAD is normal). Small/absent RV on CXR. Oligaemic lung fields unless VSD is large
Ebstein anomaly	Apical displacement of tricuspid valve → "atrialisation" of RV → massive RA dilatation → R-to-L shunt via PFO	Massive cardiomegaly on CXR ("wall-to-wall" heart). Tricuspid regurgitation murmur. WPW pattern on ECG (accessory pathway). Older children: SVT

Exam Pearl — CXR Discriminator

CXR Finding	Think...
Egg on side + narrow mediastinum + plethoric lungs	TGA ^[1]
Boot-shaped heart + oligaemic lungs	TOF ^[8]
Snowman / figure-of-8 + plethoric lungs	TAPVR (supracardiac)
Wall-to-wall cardiomegaly	Ebstein anomaly
Absent main PA segment + plethoric lungs	Truncus arteriosus
Small heart + very dark (oligaemic) lungs	Pulmonary atresia with intact IVS

These CXR patterns are very high-yield for written papers and OSCEs.

These must be excluded because they are far more common than cyanotic CHD, and some are immediately treatable.

Category	Condition	Key Distinguishing Features from Cardiac Cyanosis
Respiratory disorders ^[6]	Surfactant deficiency (RDS)	Preterm infant, progressive respiratory distress, grunting, retractions. CXR: ground-glass opacification with air bronchograms. Responds to supplemental O₂ (hyperoxia test positive)
	Meconium aspiration syndrome (MAS)	Term/post-term, meconium-stained liquor, respiratory distress from birth. CXR: patchy infiltrates, hyperinflation. May trigger PPHN
	Pulmonary hypoplasia	Associated with prolonged oligohydramnios, CDH, renal agenesis. Severe respiratory failure from birth
	Pneumothorax	Acute deterioration, unilateral decreased air entry, transillumination positive. CXR diagnostic
Persistent Pulmonary Hypertension of the Newborn (PPHN) ^[6]	Failure of the normal postnatal drop in PVR → persistent R-to-L shunting through PDA and/or PFO	Pre- and post-ductal SpO₂ difference > 5–10% (pre-ductal higher). Often secondary to MAS, sepsis, or CDH. Can coexist with parenchymal lung disease. CXR may show underlying cause. Echocardiography shows elevated PA pressures but structurally normal heart
Infection ^[6]	Group B Streptococcal (GBS) septicaemia	Risk factors: maternal GBS colonisation, PROM, intrapartum fever. Presents with respiratory distress, temperature instability, poor perfusion. CXR may mimic RDS. Blood cultures positive. Responds to antibiotics
Metabolic ^[6]	Inborn errors of metabolism (IEM) → metabolic acidosis and shock	Presents with lethargy, poor feeding, metabolic acidosis (high anion gap), hypoglycaemia, hyperammonaemia. Cyanosis is from poor perfusion/shock rather than true R-to-L shunting. Newborn screening may flag

The Hyperoxia Test — First Principles

Why does it work?

In respiratory disease: the problem is V/Q mismatch or diffusion impairment → providing 100% O₂ overwhelms the barrier → PaO₂ rises significantly ( > 150 mmHg)
In cyanotic CHD: the problem is anatomical shunting of deoxygenated blood into the systemic circulation → no amount of supplemental oxygen can fix an anatomical bypass → PaO₂ stays low ( < 100 mmHg)
In PPHN: the problem is functional R-to-L shunting through PDA/PFO → partial response (PaO₂ 100–150 mmHg), and importantly, there is a pre-/post-ductal saturation gradient

Practical points in neonates:

Measure SpO₂ from the right hand (pre-ductal) AND either foot (post-ductal)
A structurally normal heart on echo with a pre-/post-ductal gradient = PPHN
A structurally abnormal heart with no response to O₂ = cyanotic CHD

Some neonates with TGA present not just with cyanosis but with cardiovascular collapse when the PDA closes. This overlaps with other causes of ductal-dependent systemic circulation presenting as cardiogenic shock at Day 4–7 ^[6]:

Condition	Circulation Dependent On	Key Features
TGA (intact IVS)	PDA for intercirculatory mixing	Profound cyanosis, loud single S2, no murmur, egg-on-side CXR
Severe coarctation of aorta (CoA) ^[6]	PDA for lower body perfusion	Cardiogenic shock at D4–7 ^[6]. First presentation: oliguria ^[6]. 4-limb BP: upper limb BP > lower limb BP ^[6]. Generalised pallor, weak peripheral pulses, cold peripheries ^[6]. Differential cyanosis (lower limbs more cyanosed)
Interrupted aortic arch ^[6]	PDA for entire descending aortic flow	Similar to severe CoA but more dramatic collapse. Strong association with DiGeorge syndrome
Hypoplastic left heart syndrome (HLHS) ^[6]	PDA for systemic circulation	Not common in HK / Chinese, but major in Caucasians ^[6]. Absent LV impulse, single S2, no palpable femoral pulses, metabolic acidosis. Hypoplastic LV + aorta on echo
Critical aortic stenosis	PDA for distal systemic perfusion	Harsh ESM at RUSB/apex, weak pulses, cardiomegaly

GC High-Yield — Ductal-Dependent Lesions and PGE₁

All ductal-dependent congenital heart diseases require prostaglandin E₁ (PGE₁) infusion to maintain ductal patency ^[5]^[6]:

Ductal-dependent pulmonary circulation: pulmonary atresia, critical PS, severe TOF
Ductal-dependent systemic circulation: severe CoA, interrupted aortic arch, HLHS, critical AS
Ductal-dependent mixing: TGA

PGE₁ side effects: fever, apnoea, diarrhoea ^[6] — the baby may need intubation for apnoea during PGE₁ infusion.

Management of closing CoA: maintain ductal patency with PGE₁ → re-perfuse abdominal organs and lower limbs → plan for elective corrective surgery ^[6].

The following features, when present in combination, strongly point toward TGA over other differentials:

Feature	Points Toward TGA	Points Away from TGA
Timing	Cyanosis within hours of birth	Cyanosis developing over weeks (TOF)
Murmur	Absent or non-specific	Loud ESM (TOF, AS), continuous (PDA), PSM (VSD)
S2	Loud and single	Widely split and fixed (ASD/TAPVR), paradoxical split
CXR heart shape	Egg on side, narrow mediastinum	Boot-shaped (TOF), snowman (TAPVR), massive (Ebstein)
CXR lung fields	Increased pulmonary vascular markings	Oligaemic (TOF, PA, TA)
ECG	Normal for age	LAD (tricuspid atresia), extreme RAD + RVH (TOF, TAPVR)
Hyperoxia test	Fails (PaO₂ < 100 mmHg)	Passes (respiratory disease)
Pre-/post-ductal gradient	Minimal or absent in simple TGA	Significant gradient suggests PPHN or CoA
Response to PGE₁	Improves mixing → improves SpO₂	No improvement if TAPVR with obstruction

A commonly used mnemonic for cyanotic congenital heart diseases:

T	Condition
Transposition of the Great Arteries	TGA
Tetralogy of Fallot	TOF
Tricuspid Atresia	TA
Total Anomalous Pulmonary Venous Return	TAPVR
Truncus Arteriosus	Truncus

Add Pulmonary Atresia and Ebstein Anomaly to complete the list of major cyanotic CHDs — the 5 T's is a memory aid, not an exhaustive list.

Feature	TGA	TOF	Tricuspid Atresia	TAPVR	Truncus Arteriosus
Pulmonary flow	↑	↓	↓	↑	↑
Cyanosis onset	Birth (hours)	Months (progressive)	Birth	Variable	Birth (mild)
Murmur	None	ESM LUSB	Variable	Systolic flow murmur	Ejection click + systolic
S2	Loud, single	Single (soft P2)	Single	Fixed split	Single (single trunk)
CXR shape	Egg on side	Boot-shaped	Normal/small	Snowman (late)	Cardiomegaly, absent PA
CXR lungs	Plethoric	Oligaemic	Oligaemic	Plethoric	Plethoric
ECG	Normal for age	RAD, RVH	LAD, LVH	RAD, RVH	Biventricular hypertrophy
Ductal-dependent?	Yes (mixing)	If severe	Depends on anatomy	No	No
DiGeorge assoc.	Possible	Strong	No	No	Strong

High Yield Summary — DDx of TGA

Frame the DDx as "Cyanotic Neonate" → cardiac vs. respiratory vs. PPHN vs. infection vs. metabolic
Hyperoxia test: PaO₂ < 100 = cardiac; > 150 = respiratory; 100–150 = PPHN/equivocal
CXR lung fields separate cyanotic CHD into ↑ pulmonary flow (TGA, truncus, TAPVR) vs. ↓ pulmonary flow (TOF, PA, TA, Ebstein)
TGA signature: egg-on-side + narrow mediastinum + plethoric lungs + no murmur + loud single S2 + ECG normal for age
5 T's: TGA, TOF, Tricuspid Atresia, TAPVR, Truncus Arteriosus
Ductal-dependent lesions all need PGE₁; know the side effects (fever, apnoea, diarrhoea)
Distinguish TGA from CoA/HLHS shock: TGA = primarily cyanosis; CoA/HLHS = primarily shock with pallor and weak pulses ± differential cyanosis
Truncus arteriosus is NOT ductal-dependent — a key distinguishing point from TGA

Active Recall - DDx of TGA

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 219) ^[2] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 586–588) ^[3] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 273, 287) ^[5] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (p. 23–30) ^[6] Senior notes: Maksim Paediatric Notes.pdf (p. 55–56, 59–60) ^[7] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 600) — truncus arteriosus and TAPVR sections ^[8] Senior notes: Ryan Ho Cardiology.pdf (p. 187 — TOF; p. 189 — PDA)

Diagnosis of Transposition of the Great Arteries — Criteria, Algorithm, and Investigations

There is no formal "scoring" system for diagnosing TGA (unlike, say, Jones criteria for rheumatic fever). The diagnosis is anatomical and echocardiographic — confirmed by demonstrating ventriculoarterial discordance. However, the clinical pathway to diagnosis follows a very structured approach that integrates clinical suspicion, bedside tests, and definitive imaging.

1.1 Clinical Diagnostic Criteria (Suspicion → Confirmation)

A neonate should be suspected of having TGA when the following constellation is present:

Criterion	Detail	Pathophysiological Basis
1. Central cyanosis within hours of birth	SpO₂ < 85–90% on pulse oximetry; visible cyanosis of mucous membranes	Parallel circulations → deoxygenated blood recirculates systemically
2. Cyanosis unresponsive to supplemental oxygen	Hyperoxia test: PaO₂ remains < 100 mmHg on 100% FiO₂	Anatomical shunt — O₂ cannot cross the parallel circuit barrier
3. No significant respiratory distress (initially)	No grunting, minimal retractions; tachypnoea is chemoreceptor-driven, not from lung disease	Lungs are well-ventilated and well-perfused (even over-perfused); the problem is circulatory, not ventilatory
4. Quiet precordium	No murmur or non-specific ESM/PSM ^[1]; loud and single S2 ^[1]	No turbulent flow (transposed but unobstructed great arteries); anteriorly placed aortic valve → loud A2
5. CXR: egg-on-side + narrow mediastinum + plethoric lungs	Classic but not always present in first hours ^[1]^[9]^[10]	Parallel great arteries narrow the vascular pedicle; stress-related thymic involution; strong LV → lungs
6. ECG: normal for age	Typically normal for age ^[1]^[9]^[10]	Neonatal RV dominance is physiological → TGA-pattern RV dominance is indistinguishable
7. Echocardiography: ventriculoarterial discordance	Confirms diagnosis by demonstrating parallel arrangement of great arteries with the pulmonary trunk arising posteriorly from LV and aorta arising anteriorly from RV ^[9]^[10]	Definitive anatomical demonstration

The Diagnosis is Echocardiographic

Echocardiography is the definitive diagnostic test ^[9]^[10]. CXR and ECG raise suspicion; echo confirms. In many centres with experienced neonatal echocardiographers, the diagnosis can be made within minutes at the bedside, allowing immediate initiation of PGE₁ and planning for balloon atrial septostomy.

Before any clinical suspicion arises, many cases of TGA are now detected through routine newborn pulse oximetry screening, which is standard practice in Hong Kong public hospital newborn nurseries.

Aspect	Detail
Timing	Performed at 24–48 hours of life (before discharge)
Method	SpO₂ measured on the right hand (pre-ductal) and either foot (post-ductal)
Positive screen	SpO₂ < 95% in either limb, OR > 3% difference between pre- and post-ductal readings
Why right hand?	Right hand is supplied by the right subclavian artery, which branches off the aorta proximal to the ductus → pre-ductal blood. The feet receive post-ductal blood
Sensitivity for TGA	Good but not perfect — TGA with a large VSD may have near-normal SpO₂ and be missed

Why is pulse oximetry screening important for TGA specifically?

TGA with intact IVS and adequate PDA may have SpO₂ in the high 70s–low 80s → detectable
The baby may appear "well" apart from subtle colour change → clinical examination alone misses cases
Early detection → early PGE₁ → prevents catastrophic collapse when the duct closes

Critical Management Point — Start PGE₁ Before Echo

In a cyanotic neonate with a failed hyperoxia test and CXR suggesting cyanotic CHD, start prostaglandin E₁ (PGE₁/alprostadil) infusion IMMEDIATELY — do NOT wait for echocardiographic confirmation. The risk of the duct closing while waiting for echo is far greater than the risk of PGE₁. This is a time-critical intervention.

4. Investigation Modalities — Detailed Findings and Interpretation

The CXR is the first imaging modality obtained in a cyanotic neonate. In TGA, it shows a characteristic triad:

Finding	Description	Pathophysiological Explanation
"Egg-on-side" appearance	Oval cardiac silhouette ^[9]^[10] — the heart looks like an egg lying on its side	The shape results from the combination of: a globally enlarged heart (both ventricles working at high output) + the narrow superior vascular pedicle
Narrow mediastinum / narrow vascular pedicle	The upper mediastinal shadow is unusually thin	Two reasons: (1) Abnormal AP relationship of the aorta to the pulmonary trunk — normally these vessels cross and create a wide shadow on PA film; in TGA they run parallel (one directly in front of the other), so on PA view the pedicle appears narrow ^[1]^[9]^[10]. (2) Stress-related thymic involution — severe hypoxaemia and stress in the neonate causes the thymus to shrink, further narrowing the mediastinal shadow ^[1]^[9]^[10]
Increased pulmonary vascular markings	Pulmonary plethora — the lung fields appear "whiter" with more prominent vascular markings	The stronger LV is supplying the pulmonary circulation ^[1] → increased pulmonary blood flow → engorgement of pulmonary vessels

Important caveats:

The classic "egg-on-side" may not be visible in the first few hours of life — the CXR may look relatively normal early on
Cardiomegaly develops over hours to days as both ventricles work at high output
If TGA is associated with PS → pulmonary vascular markings may be normal or decreased (not plethoric)

"Egg-on-side" is a high-yield CXR finding for exams — always mention the narrow mediastinum and plethoric lung fields together ^[1]^[9]^[10].

Finding	Interpretation
Typically normal for age ^[1]^[9]^[10]	In the neonatal period, right axis deviation and RVH are physiological → the ECG findings of TGA (RV supporting systemic circulation → RVH) are indistinguishable from normal neonatal ECG
Right axis deviation and RVH are normal in the first few days of life and may be the only findings present on a newborn ECG ^[9]^[10]	This is a key trap — do NOT dismiss a normal neonatal ECG as reassuring in a cyanotic baby. TGA can have an entirely normal ECG
Later findings (weeks–months, if uncorrected)	Progressive RVH (as RV continues to work against systemic afterload), possible RA enlargement
With large VSD	Combined ventricular hypertrophy (biventricular hypertrophy) may develop

Why is the ECG normal?

Let's think from first principles:

At birth, the RV is already the dominant ventricle (it has been pumping against high PVR in utero and supplying most of the cardiac output via the ductus)
In TGA, the RV continues to work against systemic resistance — but this is the same workload the RV was already doing in utero
Therefore, the neonatal ECG cannot distinguish "pathological RV dominance from TGA" from "physiological RV dominance of a normal newborn"
Only as the child ages would the RVH become abnormally persistent (normally the LV takes over dominance by ~6 months)

Exam Trap — Normal ECG ≠ Normal Heart

A normal ECG in a cyanotic neonate does NOT exclude cyanotic congenital heart disease. TGA classically has a normal neonatal ECG. Always correlate with clinical findings, CXR, and echocardiography.

Echocardiography is the gold standard for diagnosis of TGA. It provides:

Information	Echo Findings	Clinical Significance
Ventriculoarterial discordance	Parallel arrangement of great arteries — PA arising posteriorly from LV, aorta arising anteriorly from RV ^[9]^[10]	Confirms the diagnosis of TGA
Great artery relationship	Aorta is anterior and usually rightward (d-TGA); great arteries run parallel rather than crossing	Distinguishes d-TGA from l-TGA and from normal anatomy
Atrial septum	Size of PFO/ASD; direction and velocity of shunting	Determines adequacy of atrial mixing → guides decision for balloon atrial septostomy
Ventricular septum	Presence, location, and size of VSD	Classifies simple vs. complex TGA; influences surgical approach
Outflow tracts	LVOT/subpulmonary obstruction (dynamic or anatomical PS)	LVOT obstruction present in ~25% ^[2]^[3] — affects surgical planning
Coronary artery anatomy	Origin, branching pattern, and course of coronary arteries	Critical for arterial switch operation — the coronary arteries must be transferred to the neo-aorta. Variant anatomy (intramural course, single coronary) increases surgical risk
Associated anomalies	CoA, aortic arch abnormalities, valve abnormalities	Comprehensive pre-surgical assessment
Ventricular function	LV and RV systolic function; LV mass and wall thickness	Assesses whether the LV has sufficient mass to support systemic circulation after ASO (LV "preparedness")
Ductus arteriosus	Size and direction of flow through PDA	Confirms ductal patency and its contribution to mixing

Subcostal views are particularly useful in neonates because of the horizontal heart position and good acoustic windows through the liver.

Fetal echocardiography:

TGA can be detected antenatally on the outflow tract views during the 18–22 week anomaly scan
The four-chamber view is typically normal in TGA (both ventricles and AV valves are normal) → this is why TGA is one of the harder lesions to detect prenatally
The three-vessel view (3VV) and three-vessel-trachea view (3VT) show the abnormal parallel arrangement of the great arteries

Parameter	Method	Interpretation
Purpose	Differentiate cardiac from respiratory cause of cyanosis	Based on whether supplemental O₂ can overcome the cause of desaturation
Method	Place neonate on 100% FiO₂ for 10 minutes → measure PaO₂ from right radial artery (pre-ductal)	Right radial artery samples pre-ductal blood
PaO₂ < 100 mmHg	Cyanotic CHD very likely	Anatomical shunt → O₂ cannot cross the shunt barrier
PaO₂ > 150 mmHg	Respiratory cause likely	V/Q mismatch or diffusion limitation overcome by high FiO₂
PaO₂ 100–150 mmHg	Equivocal — consider PPHN, CHD with large VSD (some mixing improves with O₂), or methemoglobinaemia	Check pre-/post-ductal gradient, proceed to echo

In TGA specifically:

Simple TGA (intact IVS): PaO₂ typically 25–50 mmHg on 100% FiO₂ → grossly abnormal
TGA with large VSD: PaO₂ may be 50–80 mmHg → still below threshold but less dramatically

Measurement	Site	What It Tells You
Pre-ductal SpO₂	Right hand (or right ear lobe)	Saturation of blood from aorta proximal to ductus
Post-ductal SpO₂	Either foot	Saturation of blood from aorta distal to ductus
Interpretation in TGA	Usually no significant gradient in simple TGA (both pre- and post-ductal blood come from the same deoxygenated RV output)	Distinguishes from PPHN (where gradient > 5–10% with pre-ductal higher) and from CoA with Eisenmenger (where post-ductal is lower)

Pre-/Post-Ductal Gradient — Key Interpretations

Pattern	Likely Diagnosis
Both low, no gradient	TGA (parallel circuits — aorta carries deoxygenated blood throughout) or cyanotic CHD with intracardiac mixing
Pre-ductal high, post-ductal low ( > 5% difference)	PPHN or CoA
Pre-ductal low, post-ductal higher (reverse differential)	TGA with CoA or pHTN (reverse differential cyanosis when PA pressure > aortic pressure ^[1])

Finding	Interpretation
Low PaO₂ (despite supplemental O₂)	Anatomical R-to-L shunting / parallel circulation
Metabolic acidosis (low pH, low HCO₃⁻, high lactate)	Tissue hypoxia → anaerobic metabolism → lactic acidosis. This is a sign of decompensation and demands urgent intervention
PaCO₂ may be normal or low	Hyperventilation driven by chemoreceptors responding to hypoxaemia/acidosis. Lung ventilation is usually normal in TGA

Indication	Detail
Gold standard for elucidating coronary artery courses and origin ^[9]^[10]	Invasive catheterisation with contrast injection into aortic root
When used	For patients with coronary artery anatomy that cannot be determined confidently with echocardiography prior to surgical intervention ^[9]^[10]
Why important	The arterial switch operation requires transferring coronary arteries from the native aorta (arising from RV) to the neo-aorta (the former PA). Variant coronary anatomy (intramural course, single coronary, coronary crossing behind the PA) increases surgical difficulty and risk
Trend	With improving echocardiographic and CT angiography resolution, invasive coronary angiography is used less frequently but remains the definitive test when non-invasive imaging is inconclusive

Modality	Role in TGA
CT angiography	Excellent spatial resolution for coronary artery anatomy; fast acquisition (important for neonates). Used when echo is insufficient for coronary delineation. Radiation exposure is a consideration
Cardiac MRI	Gold standard for post-operative follow-up (assessing neo-aortic root, coronary patency, ventricular function). Not typically used for initial neonatal diagnosis (long acquisition time, need for sedation/anaesthesia)

Aspect	Detail
Diagnostic	Measures intracardiac pressures, oxygen saturations in each chamber, quantifies shunt ratios (Qp:Qs), assesses PVR
Therapeutic	Balloon atrial septostomy (Rashkind procedure) is performed during catheterisation — this is both a diagnostic confirmation and a life-saving intervention (covered in management section)
Timing	Often performed urgently when echo confirms TGA and atrial mixing is inadequate

Investigation	Simple TGA (Intact IVS)	TGA + Large VSD	TGA + VSD + PS
SpO₂	Very low (60–80%)	Mildly low (80–90%)	Moderately low (70–85%)
Hyperoxia test	PaO₂ < 50 mmHg	PaO₂ 50–80 mmHg	PaO₂ < 60 mmHg
Pre-/post-ductal gradient	Minimal or absent	Minimal or absent	Minimal or absent
CXR	Egg-on-side, narrow mediastinum, plethoric lungs	Cardiomegaly, plethoric lungs, may not have classic egg shape	Variable; may have less plethora
ECG	Normal for age	Biventricular hypertrophy (later)	RVH
Echo	Parallel great arteries, intact IVS, restrictive PFO	VSD with bidirectional shunting	VSD + subpulmonary stenosis
ABG	Severe hypoxaemia + metabolic acidosis	Mild hypoxaemia, less acidosis	Moderate hypoxaemia

Aspect	Detail
Routine screening	18–22 week anomaly scan — four-chamber view, outflow tract views
Key antenatal finding	Parallel outflow tracts on the three-vessel view (3VV) — the aorta and PA do not cross
Four-chamber view	Normal in TGA → this is why TGA is frequently missed prenatally
Detection rate	Historically 30–50% in many centres; improving with mandatory outflow tract views
Benefit of antenatal diagnosis	Planned delivery at tertiary centre with paediatric cardiac surgery → immediate PGE₁ and balloon septostomy on standby → significantly reduced morbidity and mortality

Why is TGA Hard to Detect Antenatally?

The four-chamber view — the most commonly obtained cardiac view during routine obstetric ultrasound — is normal in TGA. Both ventricles are normal in size, both AV valves are present and functional, and the atria look normal. The abnormality is only in the outflow tracts, which require the sonographer to deliberately sweep superiorly from the four-chamber view. If outflow tract views are not obtained or are suboptimal, TGA will be missed.

Strategy	Implementation
Pulse oximetry screening	Standard in Hong Kong public hospitals; performed before discharge at 24–48h
Clinical examination	Neonatal examination by paediatrician within 24h of birth — includes assessment of colour, heart sounds, femoral pulses
Challenge	TGA with adequate mixing (large VSD or widely patent PDA) may have SpO₂ > 95% and pass screening
Follow-up	Any neonate with failed pulse oximetry screen → immediate clinical assessment + hyperoxia test + CXR + urgent echo

High Yield Summary — Diagnosis of TGA

Clinical suspicion: Cyanotic neonate within hours of birth, no murmur, loud single S2, unresponsive to O₂
Pulse oximetry screening: SpO₂ < 95% → triggers workup
Hyperoxia test: PaO₂ < 100 mmHg on 100% FiO₂ = cyanotic CHD likely
CXR triad: Egg-on-side + narrow mediastinum + pulmonary plethora ^[1]^[9]^[10]
ECG: Typically normal for age — do NOT be falsely reassured ^[1]^[9]^[10]
Echo is definitive: Parallel great arteries; PA from LV posteriorly, aorta from RV anteriorly ^[9]^[10]
Coronary anatomy: Must be delineated pre-operatively; echo first, coronary angiography is gold standard if echo inconclusive ^[9]^[10]
Start PGE₁ BEFORE echo if clinical + CXR suspicion is high — do not wait
Pre-/post-ductal gradient: Usually minimal in TGA (unlike PPHN or CoA)
Antenatal detection: Four-chamber view is normal in TGA → outflow tract views are essential → frequently missed prenatally

Active Recall - Diagnosis of TGA

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 219) ^[2] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 586–588) ^[3] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 273) ^[4] AOS material: AOS - Paeds.pdf (Question 6) ^[6] Senior notes: Maksim Paediatric Notes.pdf (p. 55–56, 59–60) ^[9] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 590–592) ^[10] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 277)

Management of Transposition of the Great Arteries

The management of TGA is one of the great success stories of paediatric cardiac surgery. An untreated neonate with TGA has ~90% mortality by 1 year; with modern management the operative survival of the arterial switch operation exceeds 97%. The management follows a clear temporal sequence: resuscitate → stabilise → bridge → definitive repair.

This phase begins the moment cyanotic CHD is suspected — often within hours of birth.

Intervention	Detail	Rationale
Airway and breathing	Supplemental O₂ via nasal cannula or hood; intubation if apnoeic or in respiratory failure	Oxygen may marginally improve mixing by causing mild pulmonary vasodilation → ↑pulmonary flow → ↑volume of oxygenated blood available for mixing. However, oxygen alone cannot fix the parallel circulation
IV access	Peripheral IV (or umbilical venous catheter in neonates)	For PGE₁ infusion, fluid resuscitation, and blood sampling
Monitoring	Continuous SpO₂ (pre- and post-ductal), ECG, BP, temperature	Track response to PGE₁; detect deterioration
Correct metabolic acidosis	IV sodium bicarbonate if pH < 7.1; cautious volume expansion with 10 mL/kg normal saline if poor perfusion	Severe hypoxaemia → lactic acidosis → further myocardial depression → vicious cycle. Correcting acidosis improves myocardial function and responsiveness to PGE₁
Avoid excessive oxygen	Target SpO₂ 75–85% (not > 95%)	In TGA, excessive O₂ → ↓PVR → ↑pulmonary blood flow → pulmonary overcirculation without improving systemic oxygenation (the problem is mixing, not ventilation). Also, hyperoxia can accelerate ductal closure
Temperature management	Maintain normothermia (36.5–37.5°C)	Hypothermia → ↑metabolic demand → ↑O₂ consumption → worsens hypoxaemia. Hyperthermia → same effect
Nil by mouth	NBM with IV maintenance fluids (D10% with electrolytes at neonatal rates)	Pre-operative preparation; risk of aspiration in a critically ill neonate

Key Concept — O₂ Target in TGA

Do NOT aim for SpO₂ > 95% in a neonate with TGA. The target is 75–85%. Pushing for higher saturations with excessive O₂ is futile (the problem is anatomical mixing, not V/Q mismatch) and potentially harmful (accelerates ductal closure, causes pulmonary overcirculation).

3. Phase 2 — Prostaglandin E₁ (PGE₁) Infusion: Maintaining Ductal Patency

This is the single most important initial intervention. Initial management aims at promoting intercirculatory mixing at two levels: ductal level by IV prostaglandin E (PGE₁) (e.g. alprostadil) infusion ^[11]^[12].

Aspect	Detail
Drug	Alprostadil (prostaglandin E₁ / PGE₁) — a synthetic prostaglandin
Name breakdown	"Alprostadil" = a synthetic analogue of prostaglandin E₁, which is the endogenous prostanoid that keeps the ductus arteriosus patent in fetal life
Mechanism	PGE₁ acts on smooth muscle EP₄ receptors in the ductal wall → relaxation of ductal smooth muscle → reversal of ductal constriction → maintains or re-opens the ductus arteriosus
Why it works in TGA	The PDA provides arterial-level mixing between the aorta and PA → deoxygenated blood in the aorta can mix with oxygenated blood in the PA → improves systemic SpO₂
Route	Continuous IV infusion via central or peripheral line (ideally dedicated lumen)
Starting dose	0.01–0.05 mcg/kg/min
Maintenance dose	0.01–0.02 mcg/kg/min (titrate to lowest effective dose once duct is patent)
Higher dose for re-opening	Up to 0.1 mcg/kg/min if duct has already closed and needs to be re-opened
Onset	Minutes to hours (usually 15–30 min for improvement in SpO₂)

These are critical to know for exams ^[6]:

Side Effect	Mechanism	Management
Apnoea (10–12%)	PGE₁ acts on brainstem respiratory centres → central apnoea	Must have intubation equipment at bedside. If apnoea occurs → intubate and ventilate. Some centres electively intubate before starting PGE₁, especially for transport
Fever	Direct pyrogenic effect of prostaglandins on hypothalamic thermoregulation	Monitor temperature; antipyretics if needed; do NOT stop PGE₁
Hypotension	PGE₁ is a vasodilator → ↓SVR	Volume resuscitation; inotropes if severe
Diarrhoea	PGE₁ stimulates intestinal smooth muscle and secretion	Usually mild; manage supportively
Flushing, oedema	Vasodilation + capillary leak	Usually mild
Seizures (rare)	CNS effect at higher doses	Reduce dose; anticonvulsants if needed

GC High-Yield — PGE₁ Side Effects

PGE₁ side effects: fever, apnoea, diarrhoea ^[6]. This triad is commonly examined. The most dangerous is apnoea — always have the baby near intubation equipment when starting PGE₁.

	Detail
Indications	Any ductal-dependent congenital heart lesion: (1) ductal-dependent pulmonary circulation (e.g. pulmonary atresia, critical PS, severe TOF), (2) ductal-dependent systemic circulation (e.g. severe CoA, interrupted aortic arch, HLHS), (3) ductal-dependent mixing (TGA)
Contraindications	Relative: persistent pulmonary hypertension of the newborn (PPHN) where PDA contributes to R-to-L shunting (but clinical judgement needed). There are no absolute contraindications if the neonate is ductal-dependent — the risk of NOT giving PGE₁ (death) outweighs all side effects

4. Phase 3 — Balloon Atrial Septostomy (BAS / Rashkind Procedure)

Initial management aims at promoting intercirculatory mixing at atrial level by performing balloon atrial septostomy (BAS) ^[11]^[12]. Balloon atrial septostomy increases atrial mixing and increases systemic oxygenation ^[11]^[12].

Aspect	Detail
What	A balloon-tipped catheter is passed through the femoral vein or umbilical vein → advanced into the RA → across the PFO into the LA → the balloon is inflated → pulled back sharply through the atrial septum → tears the septum primum → creates a large, non-restrictive atrial communication
Name	Rashkind procedure (after William Rashkind, who developed it in 1966)
Where	Can be performed at the bedside in NICU under echocardiographic guidance (no need for cardiac catheterisation lab in emergency)
Effect	Creates a large ASD → allows bidirectional mixing of oxygenated (LA) and deoxygenated (RA) blood → increases systemic oxygen saturation typically by 10–15%

Indication	Explanation
Inadequate mixing despite PGE₁	SpO₂ remains < 75% or clinical deterioration despite PGE₁ → the PFO is too restrictive to allow adequate atrial mixing
~20% of TGA neonates require BAS ^[6]	Most neonates improve with PGE₁ alone (PDA provides sufficient mixing), but those with very restrictive PFO/intact atrial septum need BAS
Bridge to surgery	Stabilises the baby for days to weeks while awaiting the arterial switch operation

Contraindication / Risk	Detail
Not needed if adequate mixing	If SpO₂ is acceptable (> 75–80%) on PGE₁ alone, BAS is not performed
Risk of atrial arrhythmia	Tearing the septum can trigger transient arrhythmias
Risk of vessel injury	Femoral/iliac vein injury during catheter passage
Risk of cardiac perforation	Rare but potentially fatal; echo guidance mitigates this

5. Phase 4 — Definitive Surgical Repair

Arterial switch operation is the STANDARD choice of surgery ^[11]^[12]^[13]^[14].

Aspect	Detail
Name	Arterial Switch Operation (ASO); also called the Jatene operation (after Adib Jatene, 1975) ^[11]^[12]
Type of correction	Anatomical correction ^[11]^[12] — restores normal ventriculoarterial concordance
What it involves	Involves transection and reanastomosis of great arteries so the LV supports the neoaorta and the RV supports the neopulmonary trunk ^[11]^[12]
Coronary transfer	Coronary arteries are reimplanted in the neoaortic root ^[11]^[12]. Coronary artery has to be transposed as well ^[13]^[14]. This is the most technically demanding part of the operation
Timing	Usually performed within 2 weeks of life (early neonatal period) ^[11]^[12]
Why early?	After birth, PVR drops → LV (connected to PA) works against progressively lower resistance → LV deconditions (loses wall thickness and muscle mass). If surgery is delayed beyond ~3–4 weeks, the LV cannot generate systemic pressure after the switch → acute LV failure. The "window" is approximately 2–3 weeks
Operative mortality	< 3% in experienced centres (excellent outcomes)
Long-term survival	> 95% at 20 years

Step-by-step summary of the ASO:

Median sternotomy, cardiopulmonary bypass with deep hypothermia
Transect the aorta and pulmonary artery above their respective valves
Excise the coronary artery ostia from the native aortic root (which arises from RV) as "buttons" of tissue
Reimplant the coronary artery buttons into the native pulmonary root (which arises from LV — this will become the neo-aorta)
Reconnect: PA root (from LV) → ascending aorta (now neo-aorta); aortic root (from RV) → pulmonary trunk (now neo-PA)
This is the LeCompte manoeuvre — the branch PAs are brought anterior to the neo-aorta to reduce tension
Close ASD/VSD if present
Result: LV → neo-aorta → systemic circulation; RV → neo-PA → lungs — normal physiology restored

Why Coronary Transfer is Critical

The coronary arteries originally arise from the aorta (which in TGA comes from the RV). During ASO, the native PA root becomes the neo-aorta. If you simply reconnect the great arteries without transferring the coronaries, the coronaries would end up connected to the neo-PA (low-pressure, deoxygenated blood) → myocardial ischaemia and death. Therefore, coronary arteries must be excised as buttons and reimplanted into the neo-aortic root ^[11]^[12].

Complication	Mechanism	Frequency
Pulmonary artery stenosis (most common)	Stretching or distortion of the branch PAs during the LeCompte manoeuvre → supravalvular PS	5–10%; may require balloon dilation or re-operation
Coronary artery insufficiency	Kinking, stretching, or thrombosis of the reimplanted coronary arteries → myocardial ischaemia	Rare but potentially fatal; higher risk with variant coronary anatomy (intramural course)
Neo-aortic root dilation	The native pulmonary root (now the neo-aorta) was designed for low-pressure pulmonary circulation → progressive dilation under systemic pressure	Progressive; may develop over years; usually well-tolerated
Neo-aortic regurgitation	Dilation of the neo-aortic root → annular dilation → AR	Usually mild; severe AR may eventually require valve replacement

Scenario	Management Modification
TGA + intact IVS, presenting late ( > 3–4 weeks)	LV has deconditioned → cannot support systemic circulation after ASO. Options: (1) LV retraining with PA banding ± systemic-to-PA shunt to increase LV afterload for weeks, then perform ASO as a "two-stage switch"; (2) atrial switch operation (Senning/Mustard) as fallback
TGA + large VSD	The VSD keeps LV pressure high (LV pumps against both pulmonary and partial systemic resistance via VSD) → LV does NOT decondition → ASO can be performed later (up to ~8 weeks). VSD is closed during the same operation
TGA + VSD + PS	Severe PS prevents adequate pulmonary blood flow. ASO alone cannot address the PS. Options: (1) Rastelli operation — close VSD with a baffle directing LV outflow to the aorta + RV-to-PA conduit; (2) Nikaidoh procedure (aortic translocation). Performed at 1–2 years of age
Complex TGA with unrepairable anatomy	Atrial switch (palliative) or heart transplantation

Venous (atrial) switch operation is a physiological correction — obsolete nowadays ^[11]^[12], but important to know because some adult patients with TGA who had surgery in the 1970s–1990s will have had this operation.

Aspect	Detail
Senning procedure	Uses atrial septal tissues as baffles to redirect systemic venous blood to the LV (→ PA) and pulmonary venous blood to the RV (→ aorta) ^[11]^[12]
Mustard procedure	Uses pericardium and synthetic material as baffles ^[11]^[12]
Problem	RV continues to function as a systemic ventricle after the operation ^[11]^[12] → Less favourable because RV is NOT designed physiologically to support systemic circulation ^[11]^[12]
Why RV fails	The RV has a crescent-shaped cavity, thinner walls, and different myofibre orientation compared to the LV. It is designed for low-pressure pulmonary work. Under chronic systemic pressure, it develops progressive dilatation, dysfunction, tricuspid regurgitation, and eventual failure (typically in the 3rd–4th decade of life)

Late complications of atrial switch are common ^[11]^[12]:

Complication	Mechanism
Atrial arrhythmia (atrial tachycardia / flutter)	Extensive atrial surgery → scarring → re-entrant circuits; loss of sinus node function
RV (systemic) dysfunction	Progressive failure of the morphological RV under systemic pressure
Baffle leak	Gaps in the intra-atrial baffle → R-to-L or L-to-R shunting
Baffle obstruction	Narrowing of the systemic or pulmonary venous pathway → systemic or pulmonary venous congestion ^[11]^[12]

GC High-Yield — ASO vs. Atrial Switch

Feature	Arterial Switch (ASO)	Atrial Switch (Mustard/Senning)
Type	Anatomical correction	Physiological correction
Status	Standard of care	Obsolete
Systemic ventricle	LV (normal)	RV (abnormal → eventual failure)
Coronary transfer	Yes	No
Key complication	Supravalvar PS, coronary issues	Arrhythmia, RV failure, baffle problems
Timing	Within 2 weeks	Was done later

For neonates with TGA + VSD who develop heart failure while awaiting surgery, or for complex cases:

Intervention	Indication	Detail
Diuretics (furosemide 1 mg/kg/dose IV/PO)	Pulmonary congestion / volume overload from large L-to-R shunt via VSD	Reduces preload → ↓pulmonary congestion. Monitor electrolytes (K⁺, Na⁺)
ACE inhibitors (captopril 0.1–0.5 mg/kg/dose PO TDS)	Afterload reduction in HF	↓SVR → ↓afterload → improves forward flow. Use with caution — neonates are sensitive to hypotension
Digoxin (loading then maintenance 5–10 mcg/kg/day)	HF with reduced systolic function	Seldom used due to narrow therapeutic index ^[1]. Enhances contractility via Na⁺/K⁺ ATPase inhibition. Monitor digoxin levels
Nutritional support	All TGA neonates	High caloric feeds (fortified breast milk or high-calorie formula up to 100–120 kcal/100 mL) via NG tube if oral feeding insufficient. High caloric diet due to increased metabolic demand ^[1]
Inotropes (dopamine, dobutamine, milrinone)	Cardiogenic shock, post-operative low cardiac output syndrome	Dopamine 5–10 mcg/kg/min; milrinone 0.25–0.75 mcg/kg/min ("inodilator" — inotrope + vasodilator) ^[1]

All patients after ASO require lifelong paediatric and adult congenital cardiology follow-up:

Follow-up Aspect	What to Monitor	Frequency
Echocardiography	Neo-aortic root size, neo-aortic regurgitation, supravalvular PS, branch PA stenosis, ventricular function	Every 6–12 months in childhood; annually in adulthood
ECG	Arrhythmias, ST changes (coronary insufficiency)	At each visit
Exercise testing	Functional capacity, exercise-induced ischaemia (rare), chronotropic competence	From school age onwards; annually or biannually
Cardiac MRI	Quantitative assessment of ventricular volumes, function, great artery anatomy, coronary artery patency	Every 2–5 years from adolescence
Coronary assessment	CT coronary angiography or stress testing if concern for coronary insufficiency	As indicated
Neurodevelopment	Screening for developmental delay, ADHD, learning difficulties	Particularly in first 5 years
Endocarditis prophylaxis	Required for 6 months post-operatively; long-term only if prosthetic material used or residual defect adjacent to prosthetic patch	Per latest guidelines
Pregnancy counselling	Female patients: pre-conception cardiology review; TGA post-ASO is generally well-tolerated in pregnancy if good ventricular function	Reproductive age

Timepoint	Action
Birth – minutes	Recognise cyanosis → pulse oximetry → hyperoxia test → clinical assessment
Minutes – hours	Start PGE₁ infusion → stabilise → urgent CXR, ECG, echo
Hours	Echo confirms TGA → assess adequacy of mixing → BAS if restrictive PFO (~20%)
Days 1–14	Stabilise on PGE₁ ± post-BAS → optimise nutrition, metabolic status → ASO within 2 weeks
Surgery	Arterial switch operation: transect great arteries, reimplant coronaries, reanastomose
Post-operative	PICU: inotropes, ventilation, monitoring for low cardiac output syndrome, arrhythmia
Months – years	Serial echo, growth monitoring, neurodevelopmental screening
Lifelong	Annual cardiology follow-up: neo-aortic root, valve function, coronary patency

High Yield Summary — Management of TGA

PGE₁ (alprostadil) is the first-line emergency treatment — maintains ductal patency for intercirculatory mixing. Side effects: apnoea, fever, diarrhoea ^[6]
Balloon atrial septostomy (Rashkind) — ~20% of neonates need this to create adequate atrial-level mixing. Done at bedside under echo guidance
Arterial switch operation (Jatene) — standard of choice, anatomical correction, within 2 weeks of life ^[11]^[12]
ASO involves transection and reanastomosis of great arteries + coronary artery reimplantation ^[11]^[12]
ASO complications: supravalvular PS (most common), coronary insufficiency, neo-aortic root dilation, neo-aortic regurgitation ^[11]^[12]
Atrial switch (Mustard/Senning) is obsolete — RV as systemic ventricle fails long-term. Late complications: arrhythmia, RV dysfunction, baffle problems ^[11]^[12]
LV deconditioning is the reason ASO must be done early — the LV loses capacity to support systemic circulation as PVR falls
TGA + VSD + PS → Rastelli operation (LV-to-aorta baffle + RV-to-PA conduit) rather than ASO
Lifelong follow-up is mandatory for all post-ASO patients

Active Recall - Management of TGA

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 200, 219) ^[6] Senior notes: Maksim Paediatric Notes.pdf (p. 59) ^[11] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 591–593) ^[12] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 278) ^[13] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 600) ^[14] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 287)

Complications of Transposition of the Great Arteries

Complications of TGA can be organised into three temporal categories: (1) pre-operative complications (from the disease itself before surgical repair), (2) early post-operative complications (days to weeks after ASO), and (3) late post-operative complications (months to decades after ASO or atrial switch). Understanding these from first principles requires linking back to the underlying haemodynamics and surgical anatomy.

1. Pre-Operative Complications (Untreated or Pre-Surgical TGA)

These are the complications of the disease itself — the consequences of parallel circulations and chronic hypoxaemia in the neonate.

Aspect	Detail
Mechanism	Parallel circulations → deoxygenated blood recirculates systemically → tissue hypoxia → anaerobic metabolism → lactic acidosis
Why it matters	Severe metabolic acidosis depresses myocardial contractility, impairs PGE₁ responsiveness, and perpetuates a vicious cycle of worsening cardiac output and tissue perfusion
Clinical impact	Can cause cardiac arrest ^[1], especially when the duct closes in neonates with intact ventricular septum and restrictive PFO
Management	Urgent PGE₁, BAS, correction of acidosis with sodium bicarbonate if pH < 7.1

Sustained hypoxaemia before diagnosis or intervention causes end-organ damage:

Organ	Consequence	Mechanism
Brain	Hypoxic-ischaemic encephalopathy (HIE), seizures, white matter injury	Inadequate cerebral oxygen delivery → neuronal injury. The neonatal brain is especially vulnerable due to high metabolic demand and incomplete myelination
Kidneys	Acute kidney injury (AKI), oliguria	Renal tubular cells are highly oxygen-dependent → tubular necrosis from hypoxaemia + poor renal perfusion
Liver	Hepatic dysfunction, coagulopathy	Hepatocyte ischaemia → transaminitis, impaired synthetic function
Gut	Necrotising enterocolitis (NEC) risk	Gut mucosal ischaemia → bacterial translocation → intestinal necrosis. Risk increased by low cardiac output states and umbilical catheterisation

Brain Injury in TGA — Even Before Surgery

Studies show that up to 30–50% of neonates with TGA have evidence of pre-operative white matter injury on MRI, even before any surgical intervention. This occurs because of chronic in-utero and neonatal cerebral hypoxia — the brain is perfused with relatively deoxygenated blood from the moment of ductal closure. This is why early diagnosis and rapid intervention are so important — every hour of severe hypoxaemia counts.

Aspect	Detail
Mechanism	Heart failure in ≤1 week ^[1] in those with adequate mixing. As PVR falls postnatally → massive L-to-R shunting through VSD → pulmonary overcirculation → volume overload of the LV
Presentation	Tachypnoea, feeding difficulty, diaphoresis, hepatomegaly, failure to thrive
Why it's a complication	While the VSD paradoxically "helps" by providing mixing (less cyanosis), the cost is heart failure from pulmonary flood

Eisenmenger syndrome develops if TGA + large VSD is left unrepaired ^[15]:

Step	Mechanism
1	Large VSD → chronic pulmonary overcirculation (large L-to-R shunt component through VSD)
2	Destruction of pulmonary arterioles → irreversible pulmonary vascular disease with ↑PVR and pulmonary hypertension ^[15]
3	PVR approaches or exceeds SVR → reversal of shunt (now R-to-L) → systemic hypoxia and cyanosis ^[15]
4	Irreversible — once established, surgical repair is contraindicated (removing the VSD would leave the RV without an outlet for its high-pressure output → acute RV failure)

Eisenmenger complications in children and adolescents ^[1]^[15]:

Cardiac: progressive right heart failure, arrhythmia, infective endocarditis (rare) ^[1]^[15]
Pulmonary: pulmonary artery thrombosis, massive haemoptysis due to rupture of major vessel ^[1]^[15]
Systemic: stunted growth from hypoxia, polycythaemia, cerebral embolism/abscess ^[1]^[15]

Eisenmenger in TGA — Now Rare

With modern neonatal diagnosis and early ASO (within 2 weeks), Eisenmenger syndrome from TGA is essentially preventable and now very rare in developed settings including Hong Kong. It remains a concern in resource-limited settings where delayed presentation occurs.

Mechanism	Chronic hypoxaemia → ↑EPO from kidneys → reactive erythrocytosis → ↑haematocrit → hyperviscosity
Complications	Polycythaemia ^[1]^[15] → headache, fatigue, stroke risk. Hyperviscosity → microvascular thrombosis, cerebral infarction. In neonates, haematocrit > 65–70% is particularly dangerous
Relevance	Mainly an issue in delayed or unrepaired TGA; rarely seen in the era of early ASO

Aspect	Detail
Risk	Any structural heart lesion → turbulent flow → endothelial damage → nidus for infection. In TGA, risk particularly from VSD jet lesion or PDA
Prevention	Endocarditis prophylaxis is recommended peri-operatively and for 6 months post-operatively; long-term prophylaxis only if prosthetic material adjacent to residual defect

2. Early Post-Operative Complications (After ASO — Days to Weeks)

Aspect	Detail
Frequency	Most common early post-ASO complication; occurs in ~25% of neonates
Timing	Typically 6–18 hours post-operatively
Mechanism	Myocardial stunning from cardiopulmonary bypass + cardioplegic arrest + reperfusion injury + coronary artery manipulation → transient myocardial dysfunction
Signs	Tachycardia, poor perfusion (prolonged CRT > 3 seconds), oliguria ( < 1 mL/kg/hr), metabolic acidosis, rising lactate
Management	Inotropes (milrinone is first-line — an "inodilator" that improves contractility and reduces afterload), dopamine/dobutamine, volume optimisation, afterload reduction. Mechanical support (ECMO) if refractory

Aspect	Detail
Mechanism	Coronary artery reimplantation is the most technically challenging part of the ASO. Kinking, stretching, external compression, or thrombosis of the reimplanted coronary ostia → myocardial ischaemia or infarction
Presentation	Acute LV dysfunction, ST changes on ECG, elevated troponin, cardiogenic shock
Risk factors	Variant coronary anatomy (intramural course, single coronary, coronary crossing behind the PA)
Management	Emergency coronary re-implantation or ECMO as a bridge

Type	Mechanism
Junctional ectopic tachycardia (JET)	Most common arrhythmia post-ASO. Arises from the AV junction due to surgical manipulation near the AV node and bundle of His. Narrow complex tachycardia with AV dissociation
Complete heart block	Rare; from direct injury to the conduction system during VSD closure (if VSD present)
Supraventricular tachycardia	Less common; atrial manipulation

Post-operative bleeding is a general risk of any open-heart surgery in neonates, exacerbated by:

Immature coagulation system in neonates
Heparin use during cardiopulmonary bypass
Hypothermia-induced coagulopathy
Multiple suture lines (great artery anastomoses, coronary buttons)

Mediastinitis, sepsis, and wound infection — standard risks of neonatal cardiac surgery. Managed with prophylactic antibiotics and aseptic technique.

3. Late Post-Operative Complications (After ASO — Months to Decades)

These are the complications that paediatric and adult congenital cardiologists monitor for throughout life.

Pulmonary artery stenosis ^[11]^[12]^[16]:

Aspect	Detail
Frequency	5–10% of ASO patients; most common late complication
Mechanism	During ASO, the branch PAs are mobilised and brought anterior to the neo-aorta (LeCompte manoeuvre) → stretching, distortion, or compression of the branch PAs → supravalvular or branch PA stenosis
Why supravalvular?	The stenosis occurs at the anastomotic site where the native aortic root (now the neo-PA) was reconnected, or at the branch PA origins due to geometric distortion
Presentation	May be asymptomatic (murmur only) or cause exercise intolerance, RV pressure overload → RVH on ECG, ESM at LUSB
Management	Balloon dilation (catheter-based) for discrete stenosis; surgical revision or stenting for complex stenosis

Coronary artery insufficiency ^[11]^[12]^[16]:

Aspect	Detail
Mechanism	Progressive fibrosis, intimal proliferation, or kinking at the reimplanted coronary ostia → chronic coronary insufficiency → silent myocardial ischaemia
Frequency	Clinically significant in 2–7% of patients
Why it matters in children	Unlike adults with IHD, children with post-ASO coronary stenosis may not develop collaterals. Sudden cardiac death can be the first manifestation — particularly during exercise
Screening	Exercise stress testing from school age; coronary CT angiography or invasive angiography if concern
Management	Coronary revascularisation (surgical reimplantation, CABG, or PCI); activity restriction if significant stenosis

Silent Coronary Ischaemia Post-ASO

Children and adolescents post-ASO may have asymptomatic coronary artery stenosis. Unlike adults who develop angina, children may not recognise or report symptoms. Sudden cardiac death during exercise can be the first presentation. This is why regular exercise testing and coronary surveillance are mandatory throughout childhood and adolescence.

Neo-aortic root dilation ^[11]^[12]^[16]:

Aspect	Detail
Mechanism	The native pulmonary root (now the neo-aorta) was designed for low-pressure pulmonary circulation. Under chronic systemic pressure, its wall structure — thinner, more elastic, fewer smooth muscle layers — leads to progressive dilation
Frequency	Progressive in many patients; moderate dilation is common, severe dilation requiring intervention is uncommon
Clinical significance	Dilation itself is usually well-tolerated, but may lead to neo-aortic regurgitation (see below). Risk of aortic dissection is very low but theoretically possible
Monitoring	Serial echocardiography measuring neo-aortic root dimensions (Z-scores for age and body surface area)

Neo-aortic regurgitation ^[11]^[12]^[16]:

Aspect	Detail
Mechanism	Neo-aortic root dilation → annular dilation → failure of leaflet coaptation → aortic regurgitation. The native pulmonary valve (now neo-aortic valve) has thinner, more pliable leaflets than a normal aortic valve → more prone to regurgitation under systemic pressures
Frequency	Mild AR is common (up to 30%); moderate-severe AR requiring intervention is uncommon ( < 5% at 20 years)
Monitoring	Serial echocardiography
Management	If severe → aortic valve repair or replacement (Ross procedure or mechanical valve)

Aspect	Detail
Where	Great artery anastomotic lines (neo-aorta or neo-PA), coronary reimplantation sites
Mechanism	Scar tissue formation, intimal fibrosis, or neointimal hyperplasia at suture lines
Management	Balloon dilation, stenting, or surgical revision

These complications are seen in adult patients who had venous switch operations in the 1960s–1990s. They present to adult congenital heart disease (ACHD) clinics and are important to know.

Late complications of atrial switch are common ^[11]^[12]^[5]^[16]:

Complication	Mechanism	Clinical Presentation
Atrial arrhythmia (atrial tachycardia/flutter) ^[11]^[12]^[5]	Extensive atrial surgery → scarring → loss of sinus node function → re-entrant atrial circuits	Palpitations, syncope, sudden death. Sinus node dysfunction → bradycardia requiring pacemaker. May alternate between bradycardia and tachycardia (tachy-brady syndrome)
RV (systemic) dysfunction ^[11]^[12]^[5]	RV is NOT designed physiologically to support systemic circulation ^[11]^[12]. Under chronic systemic pressure → progressive RV dilation, hypertrophy, and eventual failure. Tricuspid regurgitation (now the systemic AV valve) worsens RV volume overload	Exercise intolerance, dyspnoea, oedema, hepatomegaly. Resembles adult heart failure. May require heart transplantation
Baffle leak ^[11]^[12]^[5]	Dehiscence or gaps in the intra-atrial baffle → mixing of systemic and pulmonary venous blood	Cyanosis (if R-to-L shunt through baffle), paradoxical embolism risk
Baffle obstruction ^[11]^[12]^[5]	Narrowing of the systemic or pulmonary venous pathway by the baffle → systemic or pulmonary venous congestion ^[11]^[12]	SVC/IVC obstruction → superior vena cava syndrome, hepatic congestion, oedema. Pulmonary venous obstruction → pulmonary oedema, dyspnoea

The GC 147 lecture slide specifically references "previous venous switch operations (Mustard/Senning operations)" ^[5] with reference to long-term outcomes data (Farooqi et al. JACC Heart Fail 2016), emphasising that these historical patients now present as adults with significant morbidity from RV failure and arrhythmias.

Aspect	Detail
Frequency	Up to 30–50% of ASO survivors have some neurodevelopmental difficulty
Types	Motor delays (fine and gross), attention deficit/hyperactivity, executive function difficulties, learning disabilities, lower full-scale IQ (by ~5–10 points compared to population mean)
Causes	Multifactorial: (1) pre-operative cerebral hypoxia from parallel circulations, (2) pre-operative white matter injury, (3) cardiopulmonary bypass → cerebral microembolism, (4) deep hypothermic circulatory arrest (DHCA) → global cerebral ischaemia during surgery, (5) post-operative LCOS → further cerebral hypoperfusion
Monitoring	Neurodevelopmental screening at 6, 12, 18, 24 months, then school-age assessments
Intervention	Early physiotherapy, occupational therapy, speech therapy; educational support; psychology input for ADHD/executive function

Family Communication — Neurodevelopmental Outcomes

When counselling families pre-operatively, it is important to mention that while survival after ASO is excellent ( > 97%), there is a meaningful risk of neurodevelopmental difficulties (~30–50%). This is NOT primarily a complication of surgery — much of the brain injury occurs before surgery from chronic hypoxaemia. Early intervention services should be offered proactively. Frame this positively: "Most children do well and attend mainstream school, but we monitor development closely so we can provide extra support early if needed."

Issue	Detail
Pre-operative	Failure to thrive from hypoxaemia + heart failure + high metabolic demand
Post-ASO	Most children achieve normal growth and development after successful repair. Catch-up growth is expected within the first 1–2 years
Exercise	Most post-ASO patients can participate in normal physical activities including competitive sports, provided there is no significant residual lesion (PS, coronary stenosis, ventricular dysfunction). Individual exercise prescriptions should be guided by exercise stress testing

Timing	Complication	Key Mechanism
Pre-operative	Severe hypoxaemia → cardiac arrest	Parallel circulations, duct closure
	Multi-organ hypoxic injury	Inadequate tissue O₂ delivery
	Heart failure (with VSD)	Pulmonary overcirculation after PVR drops
	Eisenmenger syndrome (unrepaired)	Irreversible pulmonary vascular disease
	Polycythaemia / cerebral events	Reactive erythrocytosis from chronic hypoxia
Early post-ASO	Low cardiac output syndrome	CPB + cardioplegia → myocardial stunning
	Coronary kinking/thrombosis	Technical complication of coronary transfer
	Arrhythmia (JET)	Surgical manipulation near AV node
	Bleeding, infection	Neonatal cardiac surgery risks
Late post-ASO	Pulmonary artery stenosis (most common)	LeCompte manoeuvre → PA distortion
	Coronary artery insufficiency	Ostial fibrosis/kinking at reimplantation sites
	Neo-aortic root dilation	Native PA root under systemic pressure
	Neo-aortic regurgitation	Annular dilation, thin pulmonary valve leaflets
	Neurodevelopmental difficulties	Pre-op hypoxia + CPB + DHCA
Late post-atrial switch	Atrial arrhythmia	Atrial scarring, sinus node damage
	RV (systemic) dysfunction	RV not designed for systemic circulation
	Baffle leak/obstruction	Dehiscence or narrowing of intra-atrial baffles

High Yield Summary — Complications of TGA

Pre-operative: Severe hypoxaemia → cardiac arrest when PDA closes (especially with intact IVS) ^[1]; heart failure within 1 week if large VSD; Eisenmenger syndrome if unrepaired (now rare)
Eisenmenger triad: congenital L-to-R shunt + pulmonary arterial disease + cyanosis ^[15]. Complications: RHF, arrhythmia, polycythaemia, cerebral embolism/abscess, haemoptysis ^[1]^[15]
ASO late complications (the four to know): pulmonary artery stenosis (most common), coronary artery insufficiency, neo-aortic root dilation, neo-aortic regurgitation ^[11]^[12]
Atrial switch late complications: atrial arrhythmia, RV (systemic) dysfunction, baffle leak, baffle obstruction ^[11]^[12]^[5]
Neurodevelopmental complications affect up to 30–50% of ASO survivors — mainly from pre-operative cerebral hypoxia and CPB
Coronary artery insufficiency post-ASO can cause sudden cardiac death in children during exercise — regular exercise testing and coronary surveillance mandatory
Lifelong cardiology follow-up is required for all patients regardless of surgical technique

Active Recall - Complications of TGA

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 193, 219–220) ^[5] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (p. 26–30) ^[11] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 591–593) ^[12] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 278) ^[15] Senior notes: Ryan Ho Cardiology.pdf (p. 186 — Eisenmenger syndrome) ^[16] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 220 — ASO late complications, venous switch complications)

High Yield Summary

TGA = ventriculoarterial discordance: aorta from RV, PA from LV → parallel circulations → incompatible with life without intercirculatory mixing
Intercirculatory mixing occurs at atrial (PFO/ASD), ventricular (VSD), and arterial (PDA) levels — the degree of mixing determines clinical severity
Ductal-dependent circulation: PDA closure → sudden profound cyanosis → cardiac arrest → requires emergent PGE₁
Simple TGA (intact IVS): severe cyanosis within hours, NO murmur, loud single S2, CXR "egg on side" with pulmonary plethora, ECG normal for age
Complex TGA (with VSD): minimal cyanosis but heart failure symptoms ≤1 week as PVR falls
Cyanotic CHD with INCREASED pulmonary blood flow (unlike TOF which has decreased)
CXR: egg on side + narrow mediastinum (parallel great arteries + thymic involution) + increased pulmonary vascular markings
Embryology: failure of spiral septation of the conus → straight septation → transposed great arteries
LV deconditioning: ASO must be performed within first 2–3 weeks before LV loses capacity to support systemic circulation
Coronary artery variants (~35%) are critical for surgical planning

High Yield Summary — DDx of TGA

Frame the DDx as "Cyanotic Neonate" → cardiac vs. respiratory vs. PPHN vs. infection vs. metabolic
Hyperoxia test: PaO₂ < 100 = cardiac; > 150 = respiratory; 100–150 = PPHN/equivocal
CXR lung fields separate cyanotic CHD into ↑ pulmonary flow (TGA, truncus, TAPVR) vs. ↓ pulmonary flow (TOF, PA, TA, Ebstein)
TGA signature: egg-on-side + narrow mediastinum + plethoric lungs + no murmur + loud single S2 + ECG normal for age
5 T's: TGA, TOF, Tricuspid Atresia, TAPVR, Truncus Arteriosus
Ductal-dependent lesions all need PGE₁; know the side effects (fever, apnoea, diarrhoea)
Distinguish TGA from CoA/HLHS shock: TGA = primarily cyanosis; CoA/HLHS = primarily shock with pallor and weak pulses ± differential cyanosis
Truncus arteriosus is NOT ductal-dependent — a key distinguishing point from TGA

High Yield Summary — Diagnosis of TGA

Clinical suspicion: Cyanotic neonate within hours of birth, no murmur, loud single S2, unresponsive to O₂
Pulse oximetry screening: SpO₂ < 95% → triggers workup
Hyperoxia test: PaO₂ < 100 mmHg on 100% FiO₂ = cyanotic CHD likely
CXR triad: Egg-on-side + narrow mediastinum + pulmonary plethora ^[1]^[9]^[10]
ECG: Typically normal for age — do NOT be falsely reassured ^[1]^[9]^[10]
Echo is definitive: Parallel great arteries; PA from LV posteriorly, aorta from RV anteriorly ^[9]^[10]
Coronary anatomy: Must be delineated pre-operatively; echo first, coronary angiography is gold standard if echo inconclusive ^[9]^[10]
Start PGE₁ BEFORE echo if clinical + CXR suspicion is high — do not wait
Pre-/post-ductal gradient: Usually minimal in TGA (unlike PPHN or CoA)
Antenatal detection: Four-chamber view is normal in TGA → outflow tract views are essential → frequently missed prenatally

High Yield Summary — Management of TGA

PGE₁ (alprostadil) is the first-line emergency treatment — maintains ductal patency for intercirculatory mixing. Side effects: apnoea, fever, diarrhoea ^[6]
Balloon atrial septostomy (Rashkind) — ~20% of neonates need this to create adequate atrial-level mixing. Done at bedside under echo guidance
Arterial switch operation (Jatene) — standard of choice, anatomical correction, within 2 weeks of life ^[11]^[12]
ASO involves transection and reanastomosis of great arteries + coronary artery reimplantation ^[11]^[12]
ASO complications: supravalvular PS (most common), coronary insufficiency, neo-aortic root dilation, neo-aortic regurgitation ^[11]^[12]
Atrial switch (Mustard/Senning) is obsolete — RV as systemic ventricle fails long-term. Late complications: arrhythmia, RV dysfunction, baffle problems ^[11]^[12]
LV deconditioning is the reason ASO must be done early — the LV loses capacity to support systemic circulation as PVR falls
TGA + VSD + PS → Rastelli operation (LV-to-aorta baffle + RV-to-PA conduit) rather than ASO
Lifelong follow-up is mandatory for all post-ASO patients

High Yield Summary — Complications of TGA

Pre-operative: Severe hypoxaemia → cardiac arrest when PDA closes (especially with intact IVS) ^[1]; heart failure within 1 week if large VSD; Eisenmenger syndrome if unrepaired (now rare)
Eisenmenger triad: congenital L-to-R shunt + pulmonary arterial disease + cyanosis ^[15]. Complications: RHF, arrhythmia, polycythaemia, cerebral embolism/abscess, haemoptysis ^[1]^[15]
ASO late complications (the four to know): pulmonary artery stenosis (most common), coronary artery insufficiency, neo-aortic root dilation, neo-aortic regurgitation ^[11]^[12]
Atrial switch late complications: atrial arrhythmia, RV (systemic) dysfunction, baffle leak, baffle obstruction ^[11]^[12]^[5]
Neurodevelopmental complications affect up to 30–50% of ASO survivors — mainly from pre-operative cerebral hypoxia and CPB
Coronary artery insufficiency post-ASO can cause sudden cardiac death in children during exercise — regular exercise testing and coronary surveillance mandatory
Lifelong cardiology follow-up is required for all patients regardless of surgical technique

Transposition Of The Great Arteries

Transposition of the Great Arteries (TGA) — Paediatric Cardiology

Hong Kong Context

4. Anatomy and Embryology

5. Pathophysiology

5.4 Haemodynamic Consequences by Subtype

6. Classification

7. Clinical Features

7.1 Symptoms

8. Investigations (Pre-Diagnosis — Included for Completeness of Clinical Features Section)

Active Recall - TGA Clinical Features and Pathophysiology

Differential Diagnosis of Neonatal Cyanosis — Approaching TGA

3. Cardiac Causes — Cyanotic Congenital Heart Disease

Active Recall - DDx of TGA

References

Diagnosis of Transposition of the Great Arteries — Criteria, Algorithm, and Investigations

1.1 Clinical Diagnostic Criteria (Suspicion → Confirmation)

4. Investigation Modalities — Detailed Findings and Interpretation

Active Recall - Diagnosis of TGA

References

Management of Transposition of the Great Arteries

3. Phase 2 — Prostaglandin E₁ (PGE₁) Infusion: Maintaining Ductal Patency

4. Phase 3 — Balloon Atrial Septostomy (BAS / Rashkind Procedure)

5. Phase 4 — Definitive Surgical Repair

Active Recall - Management of TGA

References

Complications of Transposition of the Great Arteries

1. Pre-Operative Complications (Untreated or Pre-Surgical TGA)

2. Early Post-Operative Complications (After ASO — Days to Weeks)

3. Late Post-Operative Complications (After ASO — Months to Decades)

Active Recall - Complications of TGA

References

On this page

Transposition Of The Great Arteries

1. Definition

2. Epidemiology

3. Risk Factors

4. Anatomy and Embryology

4.1 Normal Embryology of the Outflow Tract

4.2 Pathological Embryology in TGA

4.3 Coronary Artery Anatomy in TGA

5. Pathophysiology

5.1 The Parallel Circulation Problem

5.2 Intercirculatory Mixing — The Lifeline

5.3 Why the Duct is Critical (Ductal-Dependent Circulation)

5.4 Haemodynamic Consequences by Subtype

5.4.1 Simple TGA (Intact Ventricular Septum — ~50%)

5.4.2 Complex TGA (with VSD — ~50%)

5.4.3 TGA with VSD and Pulmonary Stenosis

5.5 Pulmonary Flow in TGA

5.6 The LV "Deconditioning" Problem

6. Classification

6.1 By Anatomy

6.2 By Associated Defects [2][3]

7. Clinical Features

7.1 Symptoms

7.1.1 TGA with Inadequate Mixing (Simple TGA, Intact Ventricular Septum)

7.1.2 TGA with Adequate Mixing (TGA + Large VSD)

7.1.3 TGA with VSD and PS

7.1.4 Reverse Differential Cyanosis (Rare, Specific Scenario)

7.2 Signs

7.3 Comparison with Other Cyanotic CHDs (Clinical Differentiation)

7.4 Presentation by Age

8. Investigations (Pre-Diagnosis — Included for Completeness of Clinical Features Section)

8.1 Chest X-Ray [1]

8.2 ECG [1]

8.3 Echocardiography

8.4 Hyperoxia Test [4]

9. Growth and Developmental Considerations

10. Family-Centred Care and Communication

Active Recall - TGA Clinical Features and Pathophysiology

References

1. Framework: Why is the Neonate Cyanotic?

2. Step-by-Step Diagnostic Approach

3. Cardiac Causes — Cyanotic Congenital Heart Disease

3.1 Cyanotic CHD with Increased Pulmonary Blood Flow (Like TGA)

3.2 Cyanotic CHD with Decreased Pulmonary Blood Flow (Unlike TGA)

4. Non-Cardiac Causes of Neonatal Cyanosis

5. Differentiating TGA from Other Causes of Neonatal Cardiogenic Shock

6. Approaching the Differential — Clinical Decision Points

7. "Cyanotic Neonate" Mnemonic: The 5 T's of Cyanotic CHD

8. Summary Table: Key Differential Features of Major Cyanotic CHDs

Active Recall - DDx of TGA

1. Diagnostic Criteria

2. Pulse Oximetry Screening — The First Step

3. Diagnostic Algorithm

4. Investigation Modalities — Detailed Findings and Interpretation

4.1 Chest X-Ray (CXR) [1][9][10]

4.2 Electrocardiogram (ECG) [1][9][10]

4.3 Echocardiography (Echo) — The Definitive Test [9][10]

4.4 Hyperoxia Test [4][6]

4.5 Pre- and Post-Ductal Oxygen Saturation [6]

4.6 Arterial Blood Gas (ABG)

4.7 Coronary Angiography [9][10]

4.8 Cardiac CT Angiography (CTA) and Cardiac MRI

4.9 Cardiac Catheterisation (Diagnostic and Therapeutic)

5. Summary of Investigation Findings in TGA

6. Antenatal Diagnosis

7. Newborn Screening and Early Detection in Hong Kong

Active Recall - Diagnosis of TGA

1. Overview — Management Phases

2. Phase 1 — Immediate Resuscitation and Stabilisation (Neonates)

3. Phase 2 — Prostaglandin E₁ (PGE₁) Infusion: Maintaining Ductal Patency

3.1 Pharmacology of PGE₁ (Alprostadil)

3.2 Side Effects of PGE₁

3.3 Indications and Contraindications for PGE₁

4. Phase 3 — Balloon Atrial Septostomy (BAS / Rashkind Procedure)

4.1 Procedure

4.2 Indications

4.3 Contraindications and Risks

5. Phase 4 — Definitive Surgical Repair

5.1 Arterial Switch Operation (ASO / Jatene Operation) — The Standard of Care

5.2 Complications of the Arterial Switch Operation [11][12]