Tricuspid atresia is a congenital heart defect present at birth in which the tricuspid valve between the right atrium and right ventricle fails to form, preventing normal blood flow to the lungs and requiring mixing of oxygenated and deoxygenated blood through associated septal defects, typically presenting with cyanosis in the neonatal period.

Tricuspid Atresia

Tricuspid atresia (TA) is a congenital heart defect characterised by the complete absence (agenesis) or imperforation of the tricuspid valve, resulting in no direct communication between the right atrium (RA) and the right ventricle (RV). The name breaks down from Latin/Greek: "tricuspid" = the three-leaflet valve between RA and RV; "atresia" = "a-" (without) + "tresis" (perforation) — literally, "no opening."

Because there is no inlet to the RV, the RV is invariably hypoplastic (underdeveloped), and systemic venous blood must cross to the left side of the heart via an obligatory right-to-left shunt at the atrial level (through an ASD or patent foramen ovale) to reach the systemic and pulmonary circulations. This makes tricuspid atresia a form of functional single-ventricle physiology — the left ventricle is the sole effective pumping chamber ^[1]^[2].

Tricuspid atresia is classified as a cyanotic congenital heart disease with decreased pulmonary blood flow (in most subtypes) and is the most common cause of cyanosis with left ventricular dominance on ECG ^[1]^[2].

Key Conceptual Point

Tricuspid atresia is one of the "duct-dependent" lesions in many of its subtypes. When the ductus arteriosus closes in the first hours to days of life, pulmonary blood flow may fall critically, leading to severe cyanosis and cardiovascular collapse. Recognising this early and starting prostaglandin E1 (PGE1) is life-saving.

Incidence: Approximately 1–3% of all congenital heart disease (CHD) ^[1]^[2].
Prevalence: ~0.5–0.8 per 10,000 live births.
Sex ratio: Slight male predominance (M:F ≈ 1.2:1) in some series; others report roughly equal.
Rank: Third most common cyanotic CHD after Tetralogy of Fallot (TOF) and Transposition of the Great Arteries (TGA) ^[2].
Among all forms of univentricular heart physiology, tricuspid atresia is one of the most common subtypes ^[1].

Risk Factors

Like most CHDs, the aetiology is multifactorial (genetic + environmental).
Genetic: Associated with chromosomal abnormalities in a minority of cases; most cases are sporadic. Rarely associated with deletions on chromosome 22q11 (DiGeorge spectrum) if there are conotruncal abnormalities.
Environmental/Maternal: Maternal diabetes, maternal rubella, teratogen exposure (alcohol, retinoic acid, anticonvulsants such as phenytoin/valproate), and advanced maternal age have been implicated as risk factors for CHD in general, though none are specific to tricuspid atresia.
Familial recurrence risk: ~3–5% for any CHD if one sibling affected (standard for most non-syndromic CHDs).

Anatomy and Embryology

The tricuspid valve is the atrioventricular (AV) valve on the right side of the heart, situated between the RA and RV. It has three leaflets (anterior, posterior, septal) supported by chordae tendineae and papillary muscles within the RV. During normal cardiac development:

The AV canal is divided by the endocardial cushions into the mitral and tricuspid orifices.
The tricuspid valve forms through a process of delamination of the inner layers of the RV myocardium to create the valve leaflets.

In tricuspid atresia, there is failure of development of the right AV orifice. The floor of the RA where the tricuspid valve should be is replaced by a fibrous or muscular plate — a dense sheet of tissue with no opening. Several embryological theories exist:

Malalignment/underdevelopment of the AV canal: The endocardial cushions fail to partition the AV canal appropriately, resulting in absence of the right-sided AV connection.
Failure of delamination: Unlike Ebstein's anomaly (where delamination is incomplete, leading to a displaced but present valve), in tricuspid atresia the process fails entirely, and no valve orifice forms.

Because there is no RV inlet, certain features are universally present:

Structure	Status	Why
Interatrial communication (ASD/PFO)	Obligatory	Systemic venous blood has no way to enter the RV → must shunt R→L at atrial level to reach the LA and then LV. Without this, the lesion is incompatible with life.
Hypoplastic RV	Always present	No direct inflow into RV → RV is underfilled and underdeveloped. The degree of hypoplasia varies with the size of the VSD (if present) and the great artery relationship.
VSD (in ~80–90%)	Very common	The VSD is the only route by which blood can pass from the LV to the RV and then to the pulmonary arteries (in normally related great arteries). If no VSD, pulmonary blood flow is entirely duct-dependent.
PDA	Often present and critical	Especially when the VSD is restrictive or absent, the PDA is the lifeline for pulmonary blood flow.

This is the key to subclassification and directly determines the haemodynamics:

Type I (~70–80%): Normally related great arteries (NRGA) — aorta from LV, PA from hypoplastic RV.
- Pulmonary blood flow depends on VSD size → blood must traverse LV → VSD → RV → PA.
- Most common overall subtype.
Type II (~12–25%): D-Transposition of the great arteries (D-TGA) — aorta from RV, PA from LV.
- Here the PA arises from the large, dominant LV → pulmonary blood flow is often increased (unrestricted).
- Systemic blood flow (via the aorta from the hypoplastic RV) depends on VSD size.
Type III (~3–5%): Other great artery relationships (L-TGA, truncus, etc.) — rare.

High Yield

The great artery relationship determines whether the child presents with decreased pulmonary blood flow and severe cyanosis (Type I with restrictive VSD — the classic presentation) or increased pulmonary blood flow with mild cyanosis and heart failure (Type II or Type I with large VSD). This distinction is critical for management.

The most widely used classification is the Edwards and Burchell / modified classification based on:

Great artery relationship (Type I, II, III)
Presence and size of VSD (subtype a, b, c)

Type	Great Arteries	Subtype a	Subtype b	Subtype c
Type I (NRGA, ~70–80%)	Normally related	IVS intact (no VSD) → pulmonary atresia	Small/restrictive VSD → ↓pulmonary blood flow (PS)	Large VSD → ↑pulmonary blood flow (no PS)
Type II (D-TGA, ~12–25%)	D-Transposed	VSD absent + PA atresia (very rare)	Small/restrictive VSD → subaortic stenosis (↓systemic flow)	Large VSD → ↑pulmonary blood flow
Type III (~3–5%)	Other (L-TGA, truncus, etc.)	Variable	Variable	Variable

Clinical Significance of Subtypes

Type Ia: No VSD → pulmonary blood flow is entirely PDA-dependent → severe cyanosis at birth, duct-dependent circulation, will die without PGE1 and intervention.
Type Ib (most common subtype overall): Small VSD → restricted pulmonary blood flow → cyanosis from birth, degree depending on VSD size → most require a systemic-to-pulmonary artery shunt (e.g., modified Blalock-Taussig shunt).
Type Ic: Large VSD → unrestricted pulmonary blood flow → presents more like a mixing lesion with mild cyanosis but significant heart failure (pulmonary over-circulation) → may need pulmonary artery banding.
Type IIb: D-TGA + small VSD → systemic outflow obstruction (the aorta arises from the hypoplastic RV, and the VSD is the route for blood to reach the aorta) → presents with systemic hypoperfusion and shock, similar to critical coarctation or interrupted aortic arch.
Type IIc: D-TGA + large VSD → unrestricted pulmonary blood flow → HF + mild cyanosis.

The most common presentation of tricuspid atresia is Type Ib (normally related great arteries with a restrictive VSD), presenting with cyanosis and decreased pulmonary blood flow ^[1]^[2].

Aetiology

Most cases are sporadic with no identifiable single gene defect.
Multifactorial inheritance: combination of genetic susceptibility (polygenic) and environmental triggers.
Associated syndromes: Tricuspid atresia is less commonly syndromic than some other CHDs (e.g., AVSD with Down syndrome). However, occasionally associated with:
- Heterotaxy syndromes
- 22q11.2 deletion (if conotruncal anomalies coexist)
Hong Kong context:
- Hong Kong has one of the lowest birth rates in the world, but with advancing maternal age and more IVF pregnancies, the population-level number of CHD diagnoses per year remains relatively stable.
- Antenatal screening by fetal echocardiography at 18–22 weeks is increasingly routine in Hong Kong, particularly at centres like Queen Mary Hospital (QMH), Prince of Wales Hospital (PWH), and Queen Elizabeth Hospital (QEH). This allows prenatal diagnosis and planned delivery at a centre with paediatric cardiac surgery capability.
- The incidence of CHD in Hong Kong is similar to international figures (~8 per 1,000 live births for all CHD; tricuspid atresia ~0.5–0.8 per 10,000).
- Post-natal detection via the pulse oximetry screening programme for critical CHD (SpO₂ < 95% in the first 24–48 hours of life) is an important public health measure to detect duct-dependent lesions like tricuspid atresia before catastrophic ductal closure.

Pathophysiology

Understanding the pathophysiology requires tracing the blood flow step by step, since the normal route through the right heart is completely blocked.

Systemic venous return (deoxygenated blood from SVC and IVC) enters the RA normally.
Atretic tricuspid valve → blood cannot enter the RV directly.
Obligatory R-to-L shunt at atrial level: Blood must cross from RA → LA through the ASD/PFO. This is the only exit for systemic venous blood.
- If the ASD is restrictive → RA pressure rises markedly → RA dilatation → systemic venous congestion → hepatomegaly, oedema → and inadequate delivery of blood to the LA → low cardiac output.
In the LA, deoxygenated systemic venous blood mixes with oxygenated pulmonary venous blood → the LA acts as a mixing chamber.
- The degree of oxygen saturation in the LA (and hence the systemic arterial saturation) depends on the ratio of pulmonary to systemic blood flow (Qp:Qs).
Mixed blood enters the LV (the sole effective ventricle).
From the LV:
- Most blood is ejected into the aorta (systemic circulation).
- Some blood passes through the VSD into the hypoplastic RV and then into the PA (pulmonary circulation).
- The size of the VSD (and any associated pulmonary stenosis) determines how much blood reaches the lungs.

Key Haemodynamic Concepts

All systemic venous and pulmonary venous blood mixes in the LA → the systemic arterial oxygen saturation is determined by the relative volumes of pulmonary vs systemic venous return mixing.
If Qp:Qs is low (e.g., restrictive VSD, pulmonary stenosis/atresia) → more deoxygenated blood relative to oxygenated blood → more cyanosis.
If Qp:Qs is high (e.g., large VSD, no PS) → more oxygenated blood in the mix → less cyanosis but more pulmonary over-circulation and HF.

The LV must handle both the systemic and pulmonary circulations → chronic volume overload.
Over time, this leads to LV dilatation and dysfunction if untreated.
On examination, the apex beat is displaced and hyperdynamic (LV dominance) ^[1]^[2].

The RA empties entirely through the ASD/PFO.
If the interatrial communication is restrictive (too small), RA pressure rises dramatically → systemic venous congestion, hepatomegaly, and critically reduced cardiac output.
A balloon atrial septostomy (Rashkind procedure) may be urgently needed to enlarge the ASD if it is restrictive.

In Type Ia (no VSD → pulmonary atresia) or Type Ib with very restrictive VSD:
- Pulmonary blood flow is PDA-dependent.
- As the ductus arteriosus closes (normally within 24–72 hours of birth), pulmonary blood flow drops catastrophically → profound cyanosis → metabolic acidosis → death if untreated.
- PGE1 (prostaglandin E1 / alprostadil) infusion is life-saving — it keeps the ductus arteriosus open.

In Type II with small VSD, the aorta arises from the hypoplastic RV.
Systemic blood flow depends on the VSD for blood to reach the RV → aorta.
If the VSD is restrictive → subaortic obstruction → reduced systemic blood flow → shock.
This is a less common but critically important variant.

Subtype	Pulmonary Blood Flow	Systemic Blood Flow	Main Problem	Clinical Picture
Type Ia (NRGA, no VSD)	PDA-dependent (very low)	Adequate	Severe cyanosis	Duct-dependent, profound cyanosis at birth
Type Ib (NRGA, small VSD)	Reduced (restricted by VSD ± PS)	Adequate	Cyanosis	Most common; moderate-severe cyanosis
Type Ic (NRGA, large VSD)	Increased (unrestricted)	Adequate	Pulmonary over-circulation + HF	Mild cyanosis, HF symptoms
Type IIb (D-TGA, small VSD)	Increased (PA from LV)	Restricted (aorta from RV, small VSD)	Systemic outflow obstruction	Shock, poor perfusion, ± mild cyanosis
Type IIc (D-TGA, large VSD)	Increased	Adequate	Pulmonary over-circulation + HF	Mild cyanosis, HF

Clinical Features

The clinical presentation of tricuspid atresia depends heavily on the subtype (great artery relationship and VSD size). The most common presentation is a cyanotic neonate with decreased pulmonary blood flow.

Symptoms (with Pathophysiological Basis)

Mechanism: Obligatory R-to-L shunting at the atrial level → mixing of deoxygenated and oxygenated blood in the LA → reduced systemic arterial oxygen saturation → central cyanosis.
Cyanosis is typically present from birth or within the first few hours of life ^[1]^[2].
Severity depends on the amount of pulmonary blood flow:
- Type Ia/Ib: Marked cyanosis (SpO₂ often 65–85%), worsening as PDA closes.
- Type Ic/IIc: Mild cyanosis (SpO₂ may be 85–92%) with signs of HF predominating.
Progressive cyanosis: In Type Ib, as the infant grows, the VSD may become relatively more restrictive (or the muscular VSD may partially close), worsening cyanosis over weeks to months.

Not as classic as in Tetralogy of Fallot, but can occur.
Mechanism: Dynamic infundibular (subpulmonary) spasm → further reduction in pulmonary blood flow → acute worsening of cyanosis.
Triggered by crying, feeding, defecation (anything that increases oxygen demand or decreases systemic vascular resistance).

Tachypnoea, feeding difficulty, diaphoresis (sweating during feeds), failure to thrive ^[1]^[2].
Mechanism: Excessive pulmonary blood flow → pulmonary congestion → increased work of breathing; LV volume overload → decreased cardiac efficiency → poor systemic perfusion → failure to thrive.
Onset typically at 2–6 weeks of age as pulmonary vascular resistance falls postnatally, allowing more blood to flood the lungs.

Mechanism: Combination of chronic hypoxaemia (impaired tissue oxygen delivery → impaired growth) and increased metabolic demand (increased work of breathing, increased cardiac work).
Very common in both cyanotic and HF-predominant subtypes.

In Type Ia (pulmonary atresia) or Ib with very restrictive VSD:
- As the PDA closes in the first 24–72 hours → dramatic fall in pulmonary blood flow → severe hypoxaemia → metabolic acidosis → cardiovascular collapse ^[1].
- Symptoms: deepening cyanosis, tachypnoea, lethargy, poor feeding, acidotic breathing, seizures, shock.
- This is a paediatric emergency.

In the rare child who survives without intervention (e.g., naturally balanced circulation), chronic hypoxaemia and limited cardiac reserve lead to exercise intolerance.

In children with decreased pulmonary blood flow who are not surgically palliated:
- Squatting increases systemic vascular resistance (by kinking the femoral arteries) → reduces R-to-L shunting → increases pulmonary blood flow → temporary improvement in oxygenation.
- Less commonly described in tricuspid atresia than in TOF, but the same mechanism applies.

Signs (with Pathophysiological Basis)

Central cyanosis: Bluish discolouration of lips, tongue, mucous membranes, nail beds. Degree depends on Qp:Qs.
Clubbing: Digital clubbing develops over months in chronic cyanosis (due to chronic hypoxaemia → proliferation of connective tissue in the distal phalanges; exact mechanism debated but relates to megakaryocytes and platelet-derived growth factor bypassing the pulmonary capillary filter).
Tachypnoea: In HF subtypes (Type Ic, IIc) due to pulmonary congestion; or in all subtypes as a compensatory response to hypoxaemia.
Failure to thrive / poor weight gain: Plotting below the growth centiles.

B. Cardiovascular Examination

Left ventricular (LV) impulse at the apex — prominent and hyperdynamic ^[1]^[2].
- Why? The LV is the dominant (sole effective) ventricle, handling both systemic and pulmonary output → volume-overloaded → apical impulse is displaced and forceful.
Absent or diminished right ventricular (RV) impulse at the left parasternal area ^[1]^[2].
- Why? The RV is hypoplastic and receives minimal blood flow (only what passes through the VSD). There is insufficient RV mass to generate a palpable parasternal heave.
- This is a key distinguishing feature from other cyanotic CHDs (e.g., TOF has RV hypertrophy → parasternal heave; TGA has RV dominance).

Clinical Pearl — LV Dominance in Cyanotic CHD

If you see a cyanotic neonate with LV dominance (prominent apical impulse, no RV heave) and left axis deviation on ECG, think TRICUSPID ATRESIA. Most other cyanotic lesions (TOF, TGA, pulmonary atresia with IVS, total anomalous pulmonary venous return) have RV dominance or biventricular forces. Tricuspid atresia is the classic exception ^[1]^[2].

Single S2 (single second heart sound) ^[1]^[2]:
- Why? In most subtypes (especially Type I with decreased pulmonary blood flow), the pulmonary valve is stenotic or atretic → the pulmonary component (P2) is either very soft or absent → only the aortic component (A2) is heard → single S2.
- In subtypes with increased pulmonary blood flow (Type Ic, IIc), P2 may be audible and even loud (if pulmonary hypertension develops).

The murmur pattern depends on the subtype:

Subtype	Murmur	Mechanism
Type Ib (small VSD, ↓PBF)	Soft systolic murmur at left lower sternal border (LLSB)	Flow through the restrictive VSD → turbulence (like a small VSD murmur). Louder VSD murmurs paradoxically suggest smaller VSDs due to higher pressure gradients.
Type Ia (pulmonary atresia)	Continuous murmur or soft systolic murmur	PDA flow → continuous murmur (like any PDA); may be very soft if PDA is closing.
Type Ic (large VSD, ↑PBF)	Pansystolic murmur at LLSB + mid-diastolic rumble at apex	Large VSD (PSM); increased flow across the mitral valve (MDM) due to increased pulmonary venous return to LA → LV.
With PS	Ejection systolic murmur (ESM) at LUSB	Turbulent flow across the stenotic pulmonary valve.

No tricuspid murmur is heard (because the tricuspid valve does not exist → there is no flow across it, unlike tricuspid regurgitation or stenosis).

Hepatomegaly (due to systemic venous congestion from elevated RA pressure).
Tachycardia, gallop rhythm (S3).
Respiratory distress: subcostal and intercostal recession, nasal flaring, grunting.
Oedema: periorbital in infants (they are supine most of the time, so gravitational oedema distributes to the face rather than ankles).
Precordial bulge: in chronic cases, the hyperactive LV causes a visible and palpable bulge of the anterior chest wall.

Hepatomegaly — in all subtypes if the ASD is restrictive (elevated RA pressure → hepatic congestion), or in HF subtypes.
Polycythaemia (secondary): Chronic hypoxaemia → renal EPO production → increased red cell mass → increased haematocrit. This is a compensatory mechanism but increases viscosity and risk of thrombotic complications.
Hypoxic spells — acute desaturation episodes (see Symptoms above).

The ECG in tricuspid atresia has a very characteristic pattern that is almost pathognomonic:

ECG Feature	Explanation
Left axis deviation (LAD), superior axis (−30° to −90°)	The LV is the dominant ventricle; the hypoplastic RV contributes minimal electrical forces. The conduction system is also abnormal — the AV node and His bundle are displaced, resulting in a superior and leftward axis. This is a classic finding and a major exam favourite ^[1]^[2].
RA enlargement / Right atrial hypertrophy (RAH) — tall, peaked P waves (P pulmonale) in lead II, > 2.5mm	The RA has no direct outlet (atretic TV) → chronic pressure overload → RA dilatation and hypertrophy ^[1]^[2].
LV hypertrophy (LVH) — tall R waves in V5–V6, deep S in V1	The LV is the sole effective ventricle → volume overload → LVH ^[1]^[2].
Paucity of RV forces — absent or diminished R wave in V1, small or absent R in right precordial leads	The RV is hypoplastic → minimal electrical activity ^[1]^[2].
Left anterior hemiblock pattern may be present	Due to abnormal conduction system anatomy.

The combination of cyanosis + left axis deviation (superior axis) + RA enlargement + LV dominance on ECG is virtually diagnostic of tricuspid atresia ^[1]^[2]. This is a must-know exam point.

ECG Differentiation

A common exam trap: Most cyanotic CHDs show RIGHT axis deviation and RV dominance on ECG (e.g., TOF, TGA, TAPVR). Tricuspid atresia is the classic exception with LEFT axis deviation and LV dominance. If you see a cyanotic baby with left axis deviation — think tricuspid atresia first.

CXR Finding	Subtype	Explanation
Normal or mildly reduced heart size	Type Ib (most common)	Hypoplastic RV → overall cardiac silhouette not grossly enlarged
Oligaemic (reduced) pulmonary vascular markings	Types with ↓PBF (Ia, Ib)	Decreased pulmonary blood flow → fewer and thinner pulmonary vessels on CXR
RA enlargement	All subtypes	Chronic RA pressure overload → prominent right heart border
Concavity in the region of the main PA	Types with PS/PA atresia	Hypoplastic MPA → concavity in the left upper heart border (where the MPA should be)
Pulmonary plethora + cardiomegaly	Types with ↑PBF (Ic, IIc)	Excess pulmonary blood flow → engorged pulmonary vasculature; LV volume overload → cardiomegaly

An oligaemic lung field on CXR in a cyanotic newborn supports cyanotic CHD with decreased pulmonary blood flow rather than respiratory disease ^[3].

Echocardiography is the gold standard for diagnosis and provides:

Dense echogenic band replacing the tricuspid valve — the hallmark finding. No identifiable tricuspid valve orifice.
Hypoplastic RV — small cavity, may only be a slit.
Dilated RA and LA — RA due to pressure overload, LA due to obligatory R-to-L atrial shunt + pulmonary venous return.
ASD/PFO — with R-to-L flow on colour Doppler.
VSD — size and location clearly delineated; restrictive VSD will show a high-velocity jet on Doppler.
Great artery relationship — normally related vs transposed.
Pulmonary valve — presence/absence of stenosis or atresia.
PDA — size and flow direction.
LV size and function — typically dilated with preserved systolic function initially.

Feature	↓ Pulmonary Blood Flow (Type Ia, Ib)	↑ Pulmonary Blood Flow (Type Ic, IIc)
Cyanosis	Severe, from birth	Mild
HF symptoms	Uncommon	Prominent (tachypnoea, poor feeding, FTT)
Timing	Hours to days (as PDA closes)	2–6 weeks (as PVR falls)
S2	Single	May be split; loud P2 if pHT
Murmur	Soft systolic (VSD); continuous (PDA)	PSM (VSD) + MDM (↑mitral flow)
CXR	Oligaemic lungs, normal/small heart	Plethoric lungs, cardiomegaly
Precordium	LV impulse, NO RV impulse	LV impulse, NO RV impulse
ECG	LAD, RAH, LVH, ↓RV forces	LAD, RAH, LVH, ↓RV forces (may also have LV volume overload pattern)
Acute risk	Duct closure → collapse	Pulmonary overcirculation → HF

High Yield Summary

Tricuspid Atresia — Key Points for Exams:

Definition: Complete absence of the tricuspid valve → no RA-to-RV communication → hypoplastic RV → single (left) ventricle physiology.
Epidemiology: 1–3% of all CHD; third most common cyanotic CHD.
Obligatory features: ASD/PFO (for survival), hypoplastic RV.
Classification: By great artery relationship (Type I = NRGA, Type II = D-TGA) and VSD size (a = no VSD, b = small VSD, c = large VSD). Type Ib is the most common subtype.
Pathophysiology: Obligatory R-to-L shunt at atrial level → complete mixing in LA → cyanosis. Degree of cyanosis depends on pulmonary blood flow (Qp:Qs).
Classic presentation: Cyanotic neonate with LV dominance on exam and ECG — the OPPOSITE of most cyanotic CHDs.
ECG triad: Left axis deviation (superior axis) + RA enlargement + LV hypertrophy with diminished RV forces. This is virtually pathognomonic.
CXR: Oligaemic lung fields (in ↓PBF subtypes) or plethoric (in ↑PBF subtypes); RA enlargement.
Emergency: Duct-dependent subtypes (Ia, Ib with restrictive VSD) → PGE1 infusion is life-saving.
Definitive diagnosis: Echocardiography showing absent tricuspid valve orifice, hypoplastic RV, ASD, ± VSD, great artery relationship.

Active Recall - Tricuspid Atresia: Definition, Pathophysiology, and Clinical Features

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 217–226, sections on cyanotic CHD, univentricular heart, pulmonary atresia with IVS) ^[2] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf; Block C - Heart failure and cyanosis in children_ acyanotic and cyanotic congenital heart disease.pdf ^[3] AOS material: AOS - Paeds.pdf (Question 6 — oligaemic lung field supporting cyanotic CHD over respiratory disease) ^[4] Senior notes: Ryan Ho Cardiology.pdf (pages 192–193, sections on ASD and VSD for comparison of shunt lesions) ^[5] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (page 477–479, tricuspid regurgitation for comparison)

Differential Diagnosis of Tricuspid Atresia

When a neonate or young infant presents with cyanosis — the cardinal presenting feature of tricuspid atresia — the differential diagnosis is broad and must be approached systematically. The key first step is distinguishing cardiac from non-cardiac causes of cyanosis, and then narrowing down among the cardiac causes.

Cyanotic congenital heart disease can be categorised according to the underlying physiology: (1) decreased pulmonary blood flow, (2) increased pulmonary blood flow, and (3) severe heart failure ^[6]^[7].

This framework, directly from the GC lecture slides, is how you should structure your thinking. Tricuspid atresia most commonly falls into category (1) — decreased pulmonary blood flow — but certain subtypes (Ic, IIc with large VSD) fall into category (2) with increased pulmonary blood flow and heart failure.

Before diving into cardiac differentials, you must first establish that this is a cardiac cause of cyanosis rather than a respiratory, haematological, or neurological one. In a cyanotic neonate:

Feature	Favours Cardiac	Favours Respiratory
Tachypnoea	Present but relatively comfortable ("happy tachypnoea") — no significant recession	Present with marked recession, grunting, nasal flaring (increased work of breathing)
Response to supplemental O₂ (hyperoxia test)	PaO₂ remains < 150 mmHg (often < 100 mmHg) on 100% FiO₂ — because the problem is a fixed R-to-L shunt, not V/Q mismatch	PaO₂ typically rises > 150–200 mmHg on 100% FiO₂
CXR lung fields	Oligaemic (reduced pulmonary vascular markings) in ↓PBF lesions — this is a strong pointer to cyanotic CHD ^[3]	Parenchymal disease (opacification, ground-glass, air bronchograms)
CXR heart	Abnormal cardiac silhouette (specific shapes depending on lesion)	Usually normal cardiac silhouette
Pre/post-ductal SpO₂ difference	May be present (> 3% difference) in specific lesions (e.g., coarctation, interrupted arch)	Usually no significant difference
Murmur	May or may not be present	Usually absent

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

Hyperoxia Test — Key Concept

The hyperoxia (nitrogen washout) test is performed by placing the neonate on 100% O₂ for 10 minutes and measuring a right radial (pre-ductal) arterial blood gas. In cyanotic CHD with a fixed R-to-L shunt, the deoxygenated blood bypasses the lungs entirely — no amount of supplemental oxygen can oxygenate blood that never reaches the alveoli. Hence PaO₂ remains low. In respiratory disease, the alveoli are the problem but can still be recruited with high FiO₂, so PaO₂ rises.

Step 2: Differential Diagnosis Among Cyanotic Congenital Heart Diseases

Once cyanotic CHD is established, the next step is to determine the subtype. The GC lecture slides provide an excellent high-yield framework ^[6]^[7]:

This is the category where most subtypes of tricuspid atresia (Type Ia, Ib) fall. The common feature is obstruction to pulmonary blood flow at some level (tricuspid valve, RV, pulmonary valve, or infundibulum), leading to reduced blood reaching the lungs → reduced oxygenation → cyanosis.

Condition	Key Distinguishing Features from Tricuspid Atresia	Ductal Dependence
Tetralogy of Fallot (TOF)	RV hypertrophy → prominent RV impulse (parasternal heave); RAD on ECG; boot-shaped heart on CXR (coeur en sabot); ESM at LUSB from RVOT obstruction; hypercyanotic "Tet spells" classic. Contrast with TA: TOF has RAD and RVH, TA has LAD and LVH.	√/X — only if severe RVOT obstruction ^[6]^[7]
TOF with Pulmonary Atresia (TOF/PA)	Similar to severe TOF but no antegrade pulmonary flow; dependent on PDA or MAPCAs; RV hypertrophy present (unlike TA where RV is hypoplastic).	√ ^[6]^[7]
Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)	The closest mimic of tricuspid atresia. Both have: obligatory R-to-L atrial shunt, duct-dependent pulmonary circulation, LV dominance on ECG, absent RV impulse. Key differences: In PA/IVS, the tricuspid valve EXISTS (though often small/incompetent) → there IS a TR murmur (PSM at LLSB); RV is hypertrophied (high-pressure cavity) though hypoplastic; ± RV-coronary sinusoidal connections (RVDCC in ~1/3). In TA, no tricuspid valve at all → no TR murmur; RV is purely hypoplastic without hypertrophy. Echo is definitive. ^[1]^[6]^[7]	√ ^[6]^[7]
Critical Pulmonary Stenosis (PS)	Severe valvular PS with near-complete obstruction; RV hypertrophy present (unlike TA); prominent RV impulse; ejection click + ESM at LUSB; amenable to balloon valvuloplasty.	√ — only in critical PS ^[6]^[7]
Tricuspid Stenosis (TS)	Rare in isolation; the tricuspid valve is present but narrowed (unlike TA where it is completely absent); some antegrade flow through the TV exists; RV is small but not as hypoplastic as in TA.	X ^[6]^[7]
Ebstein's Anomaly	Malformed and downward displacement of tricuspid valve leaflets → TV exists but is displaced into the RV, creating an "atrialised" portion of RV → severe TR → RA enlargement → R-to-L shunt via PFO. Key differences from TA: TV is present (though abnormal); massive RA enlargement ("wall-to-wall heart" on CXR); quadruple gallop rhythm; widely split S1 and S2; associated with WPWS and SVT; ECG shows RBBB (not LAD). TA has LAD with LVH; Ebstein's has RBBB with RA enlargement. ^[1]^[6]^[7]	√/X — only if severe RVOT obstruction ^[6]^[7]

PA/IVS vs Tricuspid Atresia — The Closest Mimic

This is a frequent exam trap. Both PA/IVS and TA present as cyanotic neonates with duct-dependent pulmonary circulation, obligatory R-to-L atrial shunting, and LV dominance on ECG. The critical differences are:

PA/IVS: Tricuspid valve is PRESENT (though small); RV is high-pressure and hypertrophied; PSM of TR heard; ± RV-coronary fistulae (important surgical consideration); ECG may show some RV forces.
TA: Tricuspid valve is ABSENT; RV is low-pressure and purely hypoplastic; NO TR murmur; classic LAD/superior axis on ECG is the key distinguishing ECG feature. Echocardiography is definitive ^[1]^[6].

Some subtypes of tricuspid atresia (Type Ic, IIc — large VSD with unrestricted pulmonary flow) present with mild cyanosis and heart failure rather than severe cyanosis. These overlap with the "3 Ts":

Condition	Key Distinguishing Features from Tricuspid Atresia (↑PBF subtypes)	Ductal Dependence
D-Transposition of Great Arteries (D-TGA)	Most common cyanotic CHD presenting in the first day of life. Parallel circulations (deoxygenated blood recirculates systemically, oxygenated blood recirculates to lungs) → severe cyanosis despite plethoric lung fields (the CXR paradox — lots of blood in the lungs but still very cyanotic because no mixing). "Egg-on-a-string" cardiac silhouette. ECG: RAD and RVH (not LAD). Needs atrial septostomy for mixing.	√ ^[6]^[7]
Truncus Arteriosus	Single arterial trunk overriding a large VSD → both circulations supplied from one vessel → complete mixing → mild cyanosis with HF (pulmonary overcirculation). Loud single S2, ejection click, ESM at LSB, bounding pulses. Biventricular overload on ECG (contrast with TA which has pure LV dominance). CXR: cardiomegaly + pulmonary plethora. Often associated with 22q11.2 deletion. ^[1]	X — no mixing required ^[6]^[7]
Total Anomalous Pulmonary Venous Return (TAPVR)	All pulmonary veins drain anomalously into systemic venous system (RA, SVC, IVC, coronary sinus) → complete mixing in RA → obligatory R-to-L shunt via ASD. If obstructed TAPVR: severe cyanosis + pulmonary oedema (a unique combination — cyanosis with PLETHORIC, oedematous lungs). ECG: RAD, RVH (not LAD). Snowman (figure-of-8) silhouette on CXR in supracardiac type.	X — no mixing required ^[6]^[7]

Tricuspid atresia Type IIb (D-TGA with restrictive VSD) can present with systemic outflow obstruction and shock, mimicking left-sided obstructive lesions:

Condition	Key Distinguishing Features	Ductal Dependence
Coarctation of the Aorta (critical/neonatal)	Presents at 1–2 weeks when PDA closes → acute LV failure, shock, differential cyanosis (lower limbs more cyanotic than upper), absent/weak femoral pulses, BP discrepancy between arms and legs. CXR: cardiomegaly + pulmonary oedema. ECG: RVH in neonatal period.	√ — in critical coarctation ^[6]^[7]
Interrupted Aortic Arch	Complete discontinuity of the aortic arch → lower body perfusion entirely PDA-dependent → catastrophic collapse when PDA closes. Very similar presentation to critical coarctation but more severe. Associated with 22q11.2 deletion.	√ ^[6]^[7]
Critical Aortic Stenosis (AS)	Severe LV outflow obstruction → LV failure, shock, weak pulses globally. ESM at RUSB ± ejection click. ECG: LVH with strain.	√ — in critical AS ^[6]^[7]
Hypoplastic Left Heart Syndrome (HLHS)	Underdeveloped LV, aortic atresia/stenosis, mitral atresia/stenosis → systemic circulation entirely PDA-dependent → presents with grey, shocked neonate when PDA closes. Single S2 (only pulmonary valve), RV impulse dominant. ECG: RAD and RVH (not LAD — contrast with TA).	√ ^[6]^[7]

HLHS vs Tricuspid Atresia — Mirror-Image Single Ventricle Lesions

HLHS and TA are conceptual mirror images:

HLHS: LEFT-sided atresia (mitral/aortic) → hypoplastic LV → RV is the sole effective ventricle → RAD, RVH on ECG, duct-dependent SYSTEMIC circulation.
TA: RIGHT-sided atresia (tricuspid) → hypoplastic RV → LV is the sole effective ventricle → LAD, LVH on ECG, duct-dependent PULMONARY circulation (in most subtypes). Both ultimately follow the single-ventricle palliation pathway (staged Fontan), but from opposite sides.

While the focus of this section is cardiac differential diagnosis, for completeness in the cyanotic neonate workup:

Category	Examples	Distinguishing Features
Respiratory	RDS (preterm), MAS, pneumothorax, CDH, persistent pulmonary hypertension of the newborn (PPHN)	Significant work of breathing (recession, grunting); CXR shows parenchymal disease or air leak; responds to supplemental O₂ (except PPHN which may mimic cardiac)
Haematological	Polycythaemia, methaemoglobinaemia	Polycythaemia: plethoric appearance, Hct > 65%; MetHb: chocolate-brown blood, does not respond to O₂, confirmed by co-oximetry
CNS	Birth asphyxia, CNS depression, apnoea of prematurity	Abnormal tone, seizures, irregular breathing; no cardiac murmur; normal hyperoxia test if lungs are normal
Sepsis	Neonatal sepsis (GBS, E. coli)	Fever or hypothermia, poor perfusion, tachycardia; may have pulmonary infiltrates mimicking cardiac disease; blood cultures diagnostic
PPHN	Persistent pulmonary hypertension of the newborn	Can closely mimic cyanotic CHD — fails hyperoxia test, pre-/post-ductal SpO₂ difference > 10%. Echo shows R-to-L shunting at ductal/atrial level but STRUCTURALLY NORMAL HEART. This is the key distinction.

PPHN — The Great Mimicker

PPHN can fail the hyperoxia test (PaO₂ stays low) and show R-to-L shunting on echo, closely mimicking cyanotic CHD. The critical distinction is that the heart is structurally normal on echocardiography. Always get an echo in any cyanotic neonate who fails the hyperoxia test.

Feature	Tricuspid Atresia	PA/IVS	TOF	Ebstein's Anomaly	D-TGA
Tricuspid Valve	Absent	Present (small, incompetent)	Present (normal)	Present (displaced)	Present (normal)
RV	Hypoplastic (low pressure)	Hypoplastic + hypertrophied (high pressure)	Hypertrophied	Atrialised + functional	Normal or hypertrophied
ECG Axis	LAD (superior axis)	LV dominance but may have some RV forces	RAD	RBBB, ± WPWS	RAD
ECG Ventricular	LVH, paucity of RV forces	LV dominance, ↓RV forces	RVH	RA enlargement, RBBB	RVH
CXR Heart	Normal/mildly enlarged, RA prominent	Normal or enlarged (RA huge if severe TR)	Boot-shaped (coeur en sabot)	Wall-to-wall heart	Egg-on-string
CXR Lungs	Oligaemic (most subtypes)	Oligaemic	Oligaemic	Oligaemic	Plethoric (paradox)
Murmur	Soft systolic (VSD) ± continuous (PDA); NO TR murmur	PSM of TR at LLSB	ESM at LUSB (RVOT)	PSM/MDM of TR/TS, widely split S1/S2	Usually no loud murmur initially
S2	Single	Single	Single (if pulmonary atresia) or soft P2	Widely split	Single (loud)
Duct-dependent	Yes (most subtypes)	Yes	Variable	Variable	Yes

The combination of cyanosis + LAD (superior axis) + LV dominance + diminished RV forces on ECG is virtually pathognomonic for tricuspid atresia and distinguishes it from essentially all other cyanotic CHDs ^[1]^[2]^[6].

Early recognition and emergent stabilization is critical to ensure optimal outcome in patients with cyanotic congenital heart disease ^[6]^[7].

The approach to the cyanotic neonate is:

Is it cardiac? → Hyperoxia test, CXR, echo.
If cardiac — what is the pulmonary blood flow pattern? → Oligaemic vs plethoric lung fields on CXR.
What is the ECG pattern? → LAD + LVH = tricuspid atresia (the classic exception to the rule that cyanotic CHD = RAD + RVH).
Confirm with echocardiography → absent tricuspid valve, hypoplastic RV, obligatory atrial R-to-L shunt.

High Yield Summary — Differential Diagnosis of Tricuspid Atresia

Tricuspid atresia is a cyanotic CHD most commonly presenting with decreased pulmonary blood flow (Type Ia, Ib), but some subtypes present with increased PBF and HF (Type Ic, IIc).
Closest mimic: PA/IVS — both have duct-dependent pulmonary circulation, LV dominance, and absent RV impulse. Distinguished by: presence of TR murmur in PA/IVS (TV exists), high-pressure hypertrophied RV in PA/IVS, and echo showing absent vs present TV.
ECG is the key bedside differentiator: LAD + LVH + diminished RV forces = tricuspid atresia. Almost all other cyanotic CHDs show RAD + RVH.
CXR: Oligaemic lung fields + RA enlargement + concavity at PA segment → tricuspid atresia with ↓PBF.
Non-cardiac mimics: PPHN can fail the hyperoxia test → echo showing structurally normal heart distinguishes it.
Use the GC lecture framework: Classify cyanotic CHD by ↓PBF, ↑PBF, or severe HF, then assess ductal dependence — this determines urgency of PGE1 therapy.

Active Recall - Differential Diagnosis of Tricuspid Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 217–226, sections on PA/IVS, truncus arteriosus, univentricular heart, Ebstein's anomaly) ^[2] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf ^[3] AOS material: AOS - Paeds.pdf (Question 6 — oligaemic lung field supporting cyanotic CHD) ^[6] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (pages 280–285, cyanotic CHD categorisation and DDx tables) ^[7] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (pages 593–600, cyanotic CHD categorisation, PA/IVS, Ebstein's anomaly, tricuspid valve abnormalities)

Diagnostic Criteria, Algorithm, and Investigations for Tricuspid Atresia

Unlike adult-onset conditions (e.g., heart failure with the Framingham criteria, or infective endocarditis with the modified Duke criteria), tricuspid atresia does not have a formal "diagnostic criteria" checklist. It is a structural congenital heart defect diagnosed by demonstrating the anatomical absence of the tricuspid valve. The diagnosis rests on a combination of clinical suspicion (from history, examination, ECG, and CXR) followed by definitive confirmation with echocardiography.

That said, there is a highly recognisable clinical-diagnostic pattern that functions as a practical "bedside diagnostic triad":

Clinical Diagnostic Triad of Tricuspid Atresia:

Cyanosis (from obligatory R-to-L atrial shunt)

Left axis deviation (superior axis) on ECG with LV dominance and diminished RV forces

Oligaemic lung fields on CXR (in the common ↓PBF subtypes)

This triad is virtually pathognomonic and should prompt immediate echocardiography for definitive diagnosis ^[1]^[2].

Requirements for Definitive Diagnosis (Echocardiographic)

The definitive diagnosis of tricuspid atresia requires echocardiographic demonstration of:

Criterion	Detail	Why It Matters
Absent tricuspid valve orifice	Dense echogenic band (fibrous/muscular plate) replacing the normal TV annulus; no identifiable valve leaflets opening between RA and RV on 2D imaging	This is THE defining feature — "atresia" literally means no opening
Absent RA-to-RV flow on colour Doppler	No forward flow signal across the atrioventricular groove on the right side	Confirms functional absence of the valve, not just morphological abnormality
Hypoplastic RV	Small RV cavity, often slit-like; size depends on VSD and great artery arrangement	Consequence of absent inflow; important for surgical planning
Interatrial communication with R-to-L shunt	ASD/PFO demonstrated with R-to-L colour Doppler flow	Obligatory for survival; size determines adequacy of cardiac output

Additional echocardiographic features to delineate for full classification:

VSD: presence, size, location (determines route of pulmonary blood flow in Type I)
Great artery relationship: normally related vs D-transposed vs other
Pulmonary valve: patent, stenotic, or atretic
PDA: presence, size, direction of flow
LV size and function
Aortic arch anatomy (especially in Type II — rule out coarctation/interruption)

The diagnostic pathway for tricuspid atresia follows the general approach to the cyanotic neonate, narrowing down to the specific diagnosis through a logical sequence.

Key Principles

Detection: Either antenatal (fetal echo) or postnatal (clinical cyanosis, abnormal pulse oximetry screening, abnormal murmur).
Differentiation: Cardiac vs non-cardiac cyanosis (hyperoxia test, CXR).
Characterisation: Specific cardiac lesion identification (ECG pattern recognition, echocardiography).
Classification: Subtype determination for surgical planning (echo ± cardiac catheterisation/CT/MRI).

Investigation Modalities

What: Pre-ductal (right hand) and post-ductal (either foot) SpO₂ measured at 24–48 hours of life.
Why: Universal newborn pulse oximetry screening is now standard practice in Hong Kong and many countries to detect critical congenital heart disease (CCHD) before clinical deterioration.
Abnormal result: SpO₂ < 95% in either limb, or > 3% difference between pre- and post-ductal readings → warrants further investigation.
In tricuspid atresia: SpO₂ will be low (typically 65–85% in ↓PBF subtypes) and usually triggers immediate evaluation. In ↑PBF subtypes, SpO₂ may be 85–92% — still below the 95% screening threshold.
Limitation: Not all subtypes are detected equally; balanced circulations may have borderline saturations. Screening sensitivity for all CCHD is ~75–80%.

Pulse Ox Screening — Hong Kong Context

Hong Kong public hospitals have increasingly adopted universal pulse oximetry screening for neonates. This is a simple, non-invasive bedside test that can detect duct-dependent lesions like tricuspid atresia BEFORE catastrophic ductal closure. A positive screen should trigger urgent echocardiography and consideration of PGE1.

What: Place the neonate on 100% FiO₂ for 10 minutes via a head box or tight-fitting mask. Measure right radial (pre-ductal) arterial blood gas PaO₂.
Why: Distinguishes fixed R-to-L intracardiac shunting (cyanotic CHD) from V/Q mismatch (respiratory disease).
- In cyanotic CHD: deoxygenated blood bypasses the lungs through the intracardiac shunt → supplemental O₂ cannot reach this blood → PaO₂ remains < 100–150 mmHg (often < 60–80 mmHg in TA).
- In respiratory disease: alveoli can be recruited with high FiO₂ → PaO₂ rises > 150–200 mmHg.
In tricuspid atresia: The obligatory R-to-L atrial shunt means a fixed proportion of deoxygenated blood mixes with oxygenated blood in the LA → PaO₂ will NOT significantly improve with 100% O₂.
Caveat: PPHN can also fail the hyperoxia test (because elevated PVR causes R-to-L shunting at the ductal/atrial level despite structurally normal heart) → echo is needed to distinguish.

Hyperoxia Test Result	Interpretation	Next Step
PaO₂ > 200 mmHg	Respiratory cause likely	Treat respiratory condition
PaO₂ 100–200 mmHg	Possible cardiac or PPHN	Echocardiography
PaO₂ < 100 mmHg	Strongly suggests cyanotic CHD	Start PGE1, urgent echocardiography

3. Electrocardiography (ECG) (Characterisation — The Bedside Differentiator)

The ECG is arguably the most useful bedside investigation for narrowing the differential in a cyanotic neonate because tricuspid atresia has a virtually pathognomonic ECG pattern that distinguishes it from almost all other cyanotic CHDs.

ECG Feature	Finding	Pathophysiological Explanation
P waves	Tall, peaked P waves (> 2.5 mm in lead II) — P pulmonale pattern ^[1]	The RA has no direct outlet (atretic TV) → all RA blood must exit via ASD → chronic RA pressure overload → RA dilatation and hypertrophy → increased P wave voltage. "P pulmonale" = tall, peaked P waves classically seen in right atrial enlargement.
Axis	Left axis deviation (LAD) / superior axis: typically −30° to −90° ^[1]^[2]	The LV is the sole effective ventricle → LV depolarisation dominates → axis points leftward and superiorly. Additionally, the AV node and His bundle are anatomically displaced in tricuspid atresia (conduction tissue abnormality) → abnormal initial ventricular activation vector → superior axis. This is NOT just "LVH" — it is also partly a conduction abnormality.
Precordial leads (V1–V2)	Diminished or absent R wave in right precordial leads; deep S waves in V1 ^[1]	The RV is hypoplastic → generates minimal electrical forces → right precordial leads (which normally "see" RV activity) show predominantly negative deflections.
Precordial leads (V5–V6)	Tall R waves in left precordial leads ^[1]	LV hypertrophy (volume overload — LV handles both circulations) → increased electrical forces directed towards the left → dominant R waves in V5–V6.
Overall pattern	LV dominance with paucity of RV forces ^[1]	Combines the above: the electrical activity of the heart is dominated by the LV because the RV is vestigial.
PR interval	May be prolonged (first-degree AV block in some)	Abnormal conduction system anatomy.

The ECG combination of LAD (superior axis) + RA enlargement (P pulmonale) + LV hypertrophy + diminished RV forces is virtually diagnostic of tricuspid atresia and is the key bedside differentiator from other cyanotic CHDs, which almost all show RAD + RVH ^[1]^[2].

ECG Age-Specific Interpretation

Remember that in neonates, right axis deviation and RV dominance are normal (because the RV is the dominant ventricle in utero due to high PVR). So finding left axis deviation in a neonate is already abnormal and should immediately raise suspicion for tricuspid atresia, an AV septal defect (AVSD), or other conditions with superior axis. The presence of cyanosis + LAD in a neonate is practically TA until proven otherwise.

Subtype	Additional ECG Features
Type I (NRGA)	Classic pattern as above; LVH with volume overload pattern (↑PBF subtypes may show LV volume overload — tall R + upright T in V5–V6)
Type II (D-TGA)	May show less pronounced LAD or even normal axis in some cases because the D-TGA alters ventricular loading patterns; however, LV dominance and RA enlargement still present
With large VSD and ↑PBF	LV volume overload pattern more prominent; may develop biventricular hypertrophy if pulmonary hypertension develops

4. Chest X-Ray (CXR) (Characterisation)

The CXR provides important clues about the pulmonary blood flow pattern and cardiac silhouette, both of which help narrow the differential and classify the subtype.

CXR Feature	Finding in TA	Pathophysiological Explanation
Heart size	Normal or mildly enlarged (in ↓PBF subtypes); cardiomegaly in ↑PBF subtypes	↓PBF subtypes: LV handles a modest total cardiac output → heart not grossly enlarged. ↑PBF subtypes: LV volume overload from excessive pulmonary venous return → cardiomegaly.
RA enlargement	Prominent right heart border	RA pressure overload (no outlet via TV) → RA dilatation → right atrial silhouette bulges on CXR.
Main PA segment	Concavity at the left upper heart border (in ↓PBF subtypes)	The main pulmonary artery is either hypoplastic (due to PS/atresia) or receives reduced flow → appears as a concavity where the MPA segment normally forms a gentle convexity.
Pulmonary vascular markings	Oligaemic (decreased/reduced) in Types Ia, Ib ^[1]^[3]	Decreased pulmonary blood flow → fewer and thinner pulmonary vessels visible on CXR.
	Plethoric (increased) in Types Ic, IIc	Excessive pulmonary blood flow → engorged, prominent pulmonary vessels.
LV apex	May show a rounded, upturned apex	LV is the dominant, volume-loaded ventricle → the apex is formed by the LV and appears rounded.
Aortic arch	Usually left-sided and normal; check for right arch or coarctation in Type II	Right aortic arch may be present in some complex variants.

An oligaemic lung field on CXR in a cyanotic neonate supports cyanotic CHD with decreased pulmonary blood flow — this is a high-yield AOS and exam point ^[3].

Different cyanotic CHDs have characteristic cardiac silhouettes on CXR. This is a classic exam question:

Condition	CXR Cardiac Silhouette	Why
Tricuspid Atresia	Normal/mildly enlarged, RA prominent, concave PA segment, oligaemic lungs	Hypoplastic RV + ↓PBF
TOF	Boot-shaped heart (coeur en sabot)	RV hypertrophy + upturned apex + concave PA segment
D-TGA	Egg-on-a-string	Narrow superior mediastinum (parallel great arteries)
Ebstein's Anomaly	Wall-to-wall heart	Massive RA enlargement
TAPVR (supracardiac)	Snowman / figure-of-8	Dilated vertical vein + SVC above, enlarged heart below
Truncus Arteriosus	Cardiomegaly + plethoric lungs	Single trunk, large VSD, ↑PBF

Echocardiography is the gold standard investigation for the definitive diagnosis of tricuspid atresia ^[1]^[2]. It provides complete anatomical and haemodynamic characterisation non-invasively.

What to Assess on Echo — Systematic Approach

Parameter	What to Look For	Clinical Significance
Tricuspid valve	Dense echogenic band replacing the TV orifice; no identifiable valve leaflets; no RA-to-RV flow on colour Doppler	Confirms the diagnosis of tricuspid atresia (vs PA/IVS where TV is present but small, or Ebstein's where TV is present but displaced)
Right ventricle	Size of RV cavity — typically slit-like or very small; measure Z-score	Degree of RV hypoplasia determines surgical pathway (biventricular repair is NOT possible)
Interatrial septum	ASD/PFO: size, direction and velocity of shunt flow	If restrictive (high-velocity flow, small defect) → RA pressure is dangerously high → may need urgent balloon atrial septostomy (Rashkind procedure)
Ventricular septum	VSD: presence, size, location; Doppler gradient across VSD	Restrictive VSD → reduced pulmonary blood flow → worsening cyanosis; VSD may become more restrictive over time (especially muscular VSDs)
Great arteries	Relationship: normally related (aorta posterior-right, PA anterior-left) vs D-transposed	Determines Type I vs Type II — critical for surgical planning
Pulmonary valve and artery	Patent, stenotic, or atretic; size of MPA and branch PAs; Doppler gradient	Determines subtype (a, b, c) and whether PDA is the sole source of pulmonary blood flow
PDA	Presence, size, direction of flow (L-to-R from aorta to PA)	In duct-dependent subtypes, PDA is the lifeline for pulmonary blood flow; monitor its patency during PGE1 infusion
Left ventricle	Size, function (EF/FS), wall thickness	LV is the sole effective ventricle — must assess its long-term capacity; LV dysfunction is a contraindication to Fontan
Mitral valve	Morphology, presence/degree of MR	Important for long-term single-ventricle physiology; significant MR worsens prognosis
Aortic arch	Hypoplasia, coarctation, interruption (especially in Type II)	Type II with D-TGA may have associated aortic arch anomalies
Pulmonary veins	Normal drainage pattern	Rule out associated anomalous pulmonary venous return

Echo Distinguishes TA from Its Closest Mimics

The echo directly answers the key differentiating questions:

TA vs PA/IVS: In PA/IVS, the tricuspid valve EXISTS (though small and incompetent) and there IS RA-to-RV flow (with TR). In TA, the TV is completely absent with NO flow.
TA vs Ebstein's: In Ebstein's, the TV leaflets are present but displaced downward into the RV. In TA, there are no leaflets at all.
TA vs AVSD: AVSD has a common AV valve; TA has absence of the right AV valve with an intact (usually normal) left AV valve (mitral).

Parameter	Expected Finding	Explanation
PaO₂	Low (typically 25–50 mmHg in ↓PBF subtypes)	Fixed R-to-L shunt → deoxygenated blood mixed with oxygenated blood → low arterial PaO₂
PaCO₂	Normal or low	Tachypnoea (compensatory hyperventilation in response to hypoxaemia) blows off CO₂
pH	Normal or low (metabolic acidosis)	If pulmonary blood flow is critically low → tissue hypoxia → anaerobic metabolism → lactic acidosis
Lactate	Normal or elevated	Elevated lactate indicates tissue hypoperfusion — a sign of haemodynamic compromise
Base excess	Negative (base deficit) if acidotic	Metabolic acidosis from poor tissue oxygenation

Severe metabolic acidosis and hypoxemia in a cyanotic neonate with duct-dependent circulation is a medical emergency — indicates inadequate pulmonary blood flow and tissue perfusion ^[1].

Test	Purpose	Expected Findings
Full blood count (FBC/CBC)	Assess polycythaemia, anaemia, infection	Secondary polycythaemia (elevated Hb, Hct > 65%) develops over weeks–months as a compensatory response to chronic hypoxaemia (renal EPO production ↑ → increased erythropoiesis). In neonates, may be initially normal.
Coagulation profile	Baseline before procedures/surgery	Chronic cyanosis and polycythaemia can cause coagulopathy (platelet dysfunction, low-grade DIC)
Renal function (RFT)	Assess end-organ perfusion	May show elevated creatinine/BUN if cardiac output is severely compromised
Liver function (LFT)	Assess hepatic congestion	Elevated transaminases if RA pressure is high (hepatic congestion from elevated RA → hepatomegaly)
Blood glucose	Neonatal hypoglycaemia screening	Stressed neonates are at risk of hypoglycaemia which can worsen neurological outcomes
Calcium, electrolytes	Baseline; rule out DiGeorge	Hypocalcaemia may suggest 22q11.2 deletion (if associated conotruncal anomalies)
Chromosomal/genetic testing	If dysmorphic features or associated anomalies	Karyotype, FISH for 22q11.2, microarray as indicated

Cardiac catheterisation is not usually required for initial diagnosis (echo is sufficient) but plays important roles in:

Indication	What It Provides
Pre-Fontan haemodynamic assessment	Measures pulmonary artery pressure, PVR, LV end-diastolic pressure — all critical determinants of Fontan eligibility. Low PVR (< 3 Wood units·m²) and low PA pressure (mean < 15 mmHg) are prerequisites for successful Fontan circulation ^[1].
Assessment of pulmonary artery anatomy	Demonstrates size, confluency, and distortion of branch PAs (especially after prior shunt surgery which can cause PA stenosis)
Balloon atrial septostomy (Rashkind procedure)	Interventional — if the ASD/PFO is restrictive → urgent enlargement of the interatrial communication to decompress the RA and improve cardiac output
Coil embolisation of aortopulmonary collaterals	If significant MAPCAs or collateral vessels are present, they may need to be occluded before Fontan to prevent volume overload
Test occlusion of fenestration	In patients with a fenestrated Fontan, test occlusion can assess haemodynamic tolerance before definitive closure

Haemodynamic Data from Catheterisation

Measurement	Normal Range for Fontan Candidacy	Why
Mean PA pressure	< 15 mmHg	The Fontan circuit relies on passive flow of systemic venous blood into the PA without a pumping chamber — high PA pressure → Fontan failure
PVR	< 3 Wood units·m²	High PVR opposes passive pulmonary flow → Fontan failure
LV EDP	< 12 mmHg	Elevated LV filling pressure → raised LA pressure → raised pulmonary venous pressure → effectively raises PA pressure → impedes Fontan flow
Transpulmonary gradient	< 10 mmHg	Difference between mean PA pressure and LA pressure; must be low for passive flow

Role	Details
Volumetric assessment	Precise measurement of RV and LV volumes, LV ejection fraction — more accurate than echo for single-ventricle morphology
Great vessel anatomy	Delineates great artery relationships, aortic arch anatomy, branch PA anatomy with high spatial resolution
Post-surgical follow-up	Assesses shunt patency, PA distortion, Fontan pathway patency, and LV function after staged palliation
Tissue characterisation	Can detect myocardial fibrosis (late gadolinium enhancement) in the volume-loaded LV — prognostic significance
Limitations in neonates	Requires sedation/general anaesthesia; long scan times; less available than echo — usually reserved for older infants/children pre-Glenn or pre-Fontan

Role	Details
Rapid anatomical assessment	Quick scan, good for delineating pulmonary artery anatomy, aortopulmonary collaterals, aortic arch in complex cases
Pre-surgical planning	Used when MRI is contraindicated or unavailable; excellent spatial resolution
Limitations	Ionising radiation (important in children — ALARA principle); limited functional assessment compared to MRI

Aspect	Detail
Timing	Performed at 18–22 weeks gestation during the routine anomaly scan; may be earlier if high-risk (family history, abnormal screening)
What to look for	Four-chamber view will show absence of the tricuspid valve with a hypoplastic RV; absent RA-to-RV flow on colour Doppler
Advantage of antenatal diagnosis	Allows planned delivery at a tertiary centre with paediatric cardiac surgery capability; immediate postnatal PGE1 can be arranged before ductal closure; significantly improves outcomes compared to postnatal diagnosis after clinical deterioration
Hong Kong context	Fetal cardiac screening is increasingly performed at centres like QMH, PWH, and QEH; however, detection rates are still not 100% — many cases are still diagnosed postnatally

Investigation	Timing	Key Findings in TA	Primary Role
Fetal echo	Antenatal (18–22 wk)	Absent TV, hypoplastic RV	Early detection, delivery planning
Pulse oximetry	Postnatal (24–48 h)	SpO₂ < 95%	Screening for CCHD
Hyperoxia test	Postnatal (acute)	PaO₂ < 100 mmHg on 100% O₂	Cardiac vs respiratory cyanosis
ECG	Postnatal (bedside)	LAD, RAE (P pulmonale), LVH, ↓RV forces	Bedside differentiation — virtually pathognomonic ^[1]
CXR	Postnatal (bedside)	Oligaemic lungs (↓PBF) or plethoric (↑PBF); RA prominent; concave PA segment	Pulmonary blood flow assessment, cardiac silhouette
Echocardiography	Postnatal (urgent)	Absent TV orifice, hypoplastic RV, ASD with R-to-L shunt, ± VSD, great artery relationship	Gold standard — definitive diagnosis and classification ^[1]^[2]
ABG	Acute	Low PaO₂, ± metabolic acidosis	Severity assessment
FBC, coagulation, RFT, LFT	Baseline	Polycythaemia (chronic); coagulopathy; end-organ assessment	Monitoring
Cardiac catheterisation	Pre-Glenn/Fontan	PA pressure, PVR, LV EDP; PA anatomy	Haemodynamic assessment, Fontan eligibility
Cardiac MRI	Pre-Glenn/Fontan	LV volumes and EF; great vessel and PA anatomy; myocardial fibrosis	Comprehensive anatomical and functional assessment
CT angiography	As needed	PA anatomy, collaterals, aortic arch	Complementary anatomical assessment

High Yield Summary — Diagnosis and Investigations

Tricuspid atresia is diagnosed definitively by echocardiography demonstrating absent TV orifice, hypoplastic RV, and obligatory R-to-L atrial shunt.
The ECG is the most useful bedside differentiator: LAD (superior axis) + RA enlargement (P pulmonale) + LVH + diminished RV forces is virtually pathognomonic and distinguishes TA from nearly all other cyanotic CHDs (which show RAD + RVH).
CXR: Oligaemic lung fields + RA prominence + concave PA segment in ↓PBF subtypes; plethoric lungs + cardiomegaly in ↑PBF subtypes.
Pulse oximetry screening (SpO₂ < 95%) and hyperoxia test (PaO₂ < 100 mmHg on 100% O₂) are critical early steps to distinguish cardiac from respiratory cyanosis.
Cardiac catheterisation is not needed for initial diagnosis but is essential before staged Fontan surgery to assess PA pressure (< 15 mmHg), PVR (< 3 Wood units·m²), and LV EDP (< 12 mmHg) — the haemodynamic prerequisites for Fontan candidacy.
Fetal echo can detect TA antenatally, allowing planned delivery at a cardiac centre and immediate PGE1 — significantly improves outcomes.

Active Recall - Diagnosis and Investigations for Tricuspid Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 217–222, sections on PA/IVS, univentricular heart, investigations) ^[2] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf ^[3] AOS material: AOS - Paeds.pdf (Question 6 — oligaemic lung field supporting cyanotic CHD) ^[6] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (pages 280–285, cyanotic CHD categorisation, TV abnormalities) ^[7] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (pages 593–600, cyanotic CHD categorisation, PA/IVS, tricuspid atresia)

Management of Tricuspid Atresia

Tricuspid atresia is a single-ventricle lesion — the RV is hypoplastic and can never support the pulmonary circulation independently. Therefore, unlike lesions such as TOF or VSD where a biventricular repair (separating the circulations into two pumping chambers) is the goal, tricuspid atresia is managed by staged single-ventricle palliation culminating in the Fontan operation ^[1]^[8].

The fundamental concept: since you cannot create a functioning RV, you redirect systemic venous blood passively into the pulmonary arteries, bypassing the need for a subpulmonary ventricle entirely. The LV then serves as the sole systemic pump.

Think of it as three surgical stages, each building on the last:

Stage	Timing	Goal	Operation
Stage 1 (Neonatal)	Days to weeks of life	Ensure adequate but not excessive pulmonary blood flow; ensure unobstructed systemic output	PGE1 → mBTS or PA banding (depending on subtype)
Stage 2 (Infancy)	4–6 months	Volume-unload the single ventricle; provide stable source of pulmonary blood flow	Bidirectional Glenn (superior cavopulmonary anastomosis)
Stage 3 (Early childhood)	2–4 years	Complete separation of systemic and pulmonary circulations	Fontan operation (total cavopulmonary connection)

Stage 0: Emergency Neonatal Stabilisation

This is not a "surgical stage" but the critical initial resuscitation that keeps the baby alive until surgery can be performed.

Emergency IV PGE1 infusion to maintain ductal patency is the first and most critical step in duct-dependent subtypes ^[1].

Aspect	Detail
Drug	Prostaglandin E1 (PGE1 / alprostadil)
Route	Continuous IV infusion (central or peripheral — central preferred for reliability)
Dose (paediatric)	Starting dose: 0.05–0.1 mcg/kg/min; maintenance: 0.01–0.05 mcg/kg/min once ductal patency is re-established
Mechanism	PGE1 relaxes the smooth muscle of the ductus arteriosus wall, reversing the physiological ductal closure mediated by rising PaO₂ and falling circulating prostaglandins after birth. It acts on EP₂ and EP₄ receptors → increases cAMP → smooth muscle relaxation → duct reopens/stays open.
When to start	Immediately upon clinical suspicion of duct-dependent CHD — do NOT wait for echocardiographic confirmation. A cyanotic neonate who fails the hyperoxia test should be started on PGE1 empirically.
Indication in TA	Type Ia (pulmonary atresia, no VSD) — absolutely duct-dependent; Type Ib with very restrictive VSD — functionally duct-dependent; Type IIb — duct-dependent systemic circulation

Side Effects of PGE1 (Important for Exams)

Side Effect	Mechanism	Management
Apnoea (most important, ~12%)	PGE1 acts on central respiratory centres → respiratory depression	Must have intubation equipment at bedside; neonates on PGE1 should ideally be in a NICU/PICU setting with ability to intubate and ventilate
Hypotension	Vasodilatory effect of PGE1 on systemic vasculature	Volume resuscitation; rarely needs inotropes
Fever	Direct pyrogenic effect	Supportive; distinguish from sepsis
Seizure-like activity	CNS effect (rare)	Monitor; usually resolves with dose reduction
Flushing, oedema	Vasodilation, capillary leak	Usually mild and self-limiting
Long-term (> 5–7 days): cortical hyperostosis of long bones	Periosteal new bone formation (mechanism unclear)	Minimise duration by proceeding to surgery when stable

PGE1 — The Rule of Threes

Think of PGE1 side effects as "the baby becomes floppy":

Apnoea (prepare to intubate)
Hypotension (prepare for volume)
Fever (don't assume sepsis) Always have airway management equipment ready at the bedside before starting PGE1.

Aspect	Detail
What	Catheter-based procedure: a balloon-tipped catheter is advanced from the femoral vein → IVC → RA → across the PFO/ASD into the LA, then inflated and rapidly pulled back to tear open the atrial septum
Why	If the ASD/PFO is restrictive → RA pressure rises dangerously → inadequate blood crosses to the LA → poor cardiac output and profound cyanosis
Indication in TA	Restrictive interatrial communication identified on echo (small ASD with high-velocity flow, severely dilated RA, bowing of interatrial septum towards LA)
Goal	Create a large, unrestrictive interatrial communication to allow free flow of systemic venous blood from RA → LA
Timing	Urgent — can be performed at the bedside in NICU under echo guidance, or in the catheterisation laboratory

For Type Ic and IIc where pulmonary overcirculation causes HF:

Drug	Dose (Paediatric)	Mechanism	Notes
Furosemide (frusemide)	1–2 mg/kg/dose PO or IV, 1–3 times daily	Loop diuretic → inhibits Na-K-2Cl cotransporter in thick ascending limb of Henle → reduces preload and pulmonary congestion	First-line for symptomatic fluid overload
Spironolactone	1–3 mg/kg/day PO in 1–2 divided doses	Aldosterone antagonist → potassium-sparing diuretic; also has anti-fibrotic/remodelling effects	Used in combination with furosemide to reduce K⁺ losses
Captopril (ACEI)	0.1–0.5 mg/kg/dose PO TDS (neonates: start low, uptitrate)	Inhibits ACE → reduces angiotensin II → decreases afterload and neurohormonal activation → reduces LV wall stress	Caution: avoid in ↓PBF subtypes — reducing SVR can worsen R-to-L shunting and cyanosis (same principle as avoiding ACEI in TOF → triggers "Tet spells") ^[8]
Digoxin	5–10 mcg/kg/day PO in 2 divided doses (maintenance); loading dose available but rarely used in neonates	Na/K ATPase inhibitor → increases intracellular Ca²⁺ → improves contractility (positive inotrope); also slows AV conduction	Seldom used due to narrow therapeutic index; monitor digoxin levels (therapeutic: 0.5–0.9 ng/mL) ^[1]
High-calorie feeds	≥ 120–150 kcal/kg/day	Meet increased metabolic demands of HF + chronic hypoxaemia	May need NG/nasojejunal feeds if oral intake is inadequate

General supportive measures for paediatric heart failure: bed rest with head elevation, nutritional support with high caloric diet, fluid restriction, cautious O₂ supplementation ^[1].

Oxygen Caution in L-to-R Shunts

Caution with O₂ in large L-to-R shunts (↑PBF subtypes): supplemental O₂ → increases alveolar PO₂ → pulmonary vasodilation → decreases PVR → increases L-to-R shunting → worsens pulmonary overcirculation and HF. Use O₂ judiciously — target SpO₂ ~75–85% in balanced single-ventricle physiology, NOT 95–100% ^[1].

Stage 1: Initial Palliative Surgery (Neonatal Period — Days to Weeks)

The goal of Stage 1 is to establish a stable and controlled source of pulmonary blood flow while protecting the pulmonary vasculature from damage (from either too much or too little flow).

Modified Blalock-Taussig shunt: provides extra pulmonary flow for cyanotic heart disease with inadequate pulmonary flow or in frank duct-dependent pulmonary circulation ^[1].

Aspect	Detail
What	A synthetic Gore-Tex graft (3.0–4.0 mm) is placed from the innominate or subclavian artery to the ipsilateral pulmonary artery → creates a systemic-to-pulmonary artery shunt → L-to-R shunting → augments pulmonary blood flow
Indication	Type Ia (pulmonary atresia, no VSD), Type Ib (restrictive VSD with ↓PBF), PA/IVS before Fontan, univentricular heart with inadequate pulmonary flow ^[1]
Why "modified"?	The original Blalock-Taussig shunt (1944) directly anastomosed the subclavian artery end-to-side to the PA, sacrificing the subclavian. The modified version interposes a synthetic graft, preserving the subclavian.
Clinical sign to monitor	Always listen for the shunt murmur on follow-up — a continuous murmur under the clavicle. Loss of this murmur suggests shunt thrombosis/occlusion — a surgical emergency, as the child's pulmonary blood flow depends entirely on this shunt ^[8]
Complications	Shunt thrombosis (potentially fatal), shunt stenosis, PA distortion at anastomosis site, overcirculation (if shunt too large → HF), phrenic nerve injury
Anticoagulation	Low-dose aspirin (3–5 mg/kg/day) is commonly given post-shunt to reduce thrombotic risk

Alternative to mBTS: PDA Stenting

In some centres, a stent is placed percutaneously within the PDA (via cardiac catheterisation) to keep it open instead of performing surgical mBTS.
Advantages: avoids sternotomy/thoracotomy in a fragile neonate; less PA distortion.
Disadvantages: stent may be too large/small; neointimal proliferation → restenosis; not suitable for all anatomies.

Pulmonary artery banding: restricts excess pulmonary flow for univentricular heart with excessive pulmonary flow or uncontrolled HF ^[1].

Aspect	Detail
What	A constricting band (usually a strip of silicone or Dacron tape) is placed around the main pulmonary artery → narrows its lumen → restricts pulmonary blood flow
Indication	Type Ic (NRGA, large VSD, ↑PBF), Type IIc (D-TGA, large VSD, ↑PBF), or any TA subtype with uncontrolled pulmonary overcirculation and HF
Why?	Unrestricted pulmonary blood flow → pulmonary vascular disease (irreversible pHTN if unchecked) → destroys Fontan candidacy. PA banding protects the pulmonary vasculature and controls HF while the child grows towards Glenn/Fontan.
Adjustment	The band tightness is critical — too tight → inadequate PBF → cyanosis; too loose → persistent overcirculation. Aim for a balanced Qp:Qs of ~1:1.
Complications	Band migration, PA distortion, band erosion into PA wall, suboptimal banding (too tight/loose), branch PA stenosis at band site

In Type IIb (D-TGA with restrictive VSD → subaortic obstruction):

The VSD is the route from LV → RV → aorta. If restrictive, systemic output is compromised.
May require a Damus-Kaye-Stansel (DKS) procedure: the proximal MPA is transected and anastomosed end-to-side to the ascending aorta → creates a wide, unobstructed pathway from the LV → neo-aorta. Pulmonary blood flow is then provided by an mBTS.
± Aortic arch repair if associated coarctation or interruption.
Conceptually similar to the Norwood procedure used for HLHS, adapted for the specific anatomy of TA Type II.

Aspect	Detail
Timing	4–6 months of age ^[1]
What	The SVC is disconnected from the RA and anastomosed end-to-side to the right pulmonary artery (RPA). Blood from the SVC (upper body) now flows passively and directly into the pulmonary arteries, bypassing the heart.
Why this timing?	At 4–6 months, the PVR has fallen sufficiently from its neonatal highs to allow passive flow from the SVC into the PA. Earlier than this, PVR is too high for passive flow to work.
Haemodynamic effect	The SVC blood (upper body venous return, ~40–50% of total venous return in an infant) now goes directly to the lungs → the LV is partially volume-unloaded (it no longer has to pump the SVC blood through a shunt to the lungs) → reduces LV work → protects LV function long-term.
Why "bidirectional"?	Blood from the SVC can flow into BOTH the right and left pulmonary arteries (the PA confluence is maintained).
What happens to the mBTS?	The mBTS is taken down (ligated) at the time of Glenn, as the SVC now provides pulmonary blood flow from the upper body.
What about IVC flow?	IVC blood (lower body) still returns to the RA → LA → LV → aorta. It is NOT going to the lungs at this stage → child remains cyanotic (SpO₂ typically 75–85%). This is expected and tolerated.
Post-Glenn SpO₂	~75–85% — the child is still cyanotic because IVC blood (deoxygenated, lower body) is still mixing with pulmonary venous return in the LA.

The Glenn is an intermediate step that volume-unloads the single ventricle while the child grows large enough for the Fontan. The child remains cyanotic post-Glenn because IVC blood still enters the heart without passing through the lungs.

Why Not Go Straight to Fontan in the Neonatal Period?

PVR is too high in neonates → passive flow from the systemic veins to the PA would fail.
The PA bed needs to mature — neonatal pulmonary vasculature is reactive and cannot handle passive venous return.
Risk of Fontan failure is unacceptably high in small infants.
The staged approach allows assessment of haemodynamics at each step and identification of any problems (e.g., PA distortion, AV valve regurgitation, ventricular dysfunction) before committing to the Fontan.

This is the definitive palliation for all single-ventricle lesions, including tricuspid atresia.

Aspect	Detail
Timing	2–4 years of age (some centres: 3–5 years)
What	The IVC is disconnected from the RA and connected to the pulmonary arteries via either an intracardiac lateral tunnel or an extracardiac conduit. Now ALL systemic venous blood (SVC via Glenn + IVC via Fontan) flows passively to the lungs without passing through a pumping chamber.
Two main techniques	(1) Lateral tunnel Fontan: an intra-atrial baffle (Gore-Tex patch) channels IVC blood within the RA to the PA. (2) Extracardiac conduit Fontan: a Gore-Tex tube (18–22 mm) connects the transected IVC directly to the underside of the RPA, completely outside the heart. Extracardiac conduit is the preferred modern technique — fewer arrhythmias (no suture lines within the atria).
Fenestration	A small (4 mm) fenestration (hole) may be created between the Fontan conduit and the RA/LA → acts as a "pop-off valve" → allows R-to-L shunting under conditions of high PVR → maintains cardiac output at the expense of mild cyanosis. Fenestration reduces early post-operative complications (effusions, low output). Can be closed later by transcatheter device.
Post-Fontan physiology	All systemic venous blood now passes through the lungs passively → returns to the LA → LV → aorta. The child should be near-normal SpO₂ (90–95% with fenestration, > 95% without).

The Fontan circulation is fundamentally different from normal physiology — there is NO subpulmonary ventricle. Systemic venous blood reaches the lungs solely by the pressure gradient between CVP (central venous pressure, typically 12–15 mmHg) and LA pressure (typically 5–8 mmHg). This is a low-flow, high-venous-pressure circulation.

Prerequisites for Fontan (Assessed by Pre-Fontan Cardiac Catheterisation)

Parameter	Required Value	Why
Mean PA pressure	< 15 mmHg	Higher PA pressure → insufficient gradient for passive flow → Fontan failure
PVR	< 3 Wood units·m²	High PVR opposes passive venous flow → Fontan failure
LV EDP	< 12 mmHg	Elevated LV filling pressure → elevated LA pressure → elevated pulmonary venous pressure → effectively raises "downstream" pressure → impedes passive flow
PA anatomy	Confluent, adequate-sized branch PAs without significant stenosis	Distorted or hypoplastic PAs → high resistance to flow
AV valve function	No more than mild regurgitation	Significant MR → LV volume overload → elevated LA/LV pressures → Fontan failure
Ventricular function	Preserved systolic function (EF > 50%)	Poor ventricular function → elevated filling pressures → Fontan failure
Sinus rhythm	Preferred	AV dyssynchrony from arrhythmias impairs filling

Fontan Contraindications

The Fontan is contraindicated if:

Mean PA pressure ≥ 15 mmHg or PVR ≥ 3 WU·m²
Severe ventricular dysfunction (EF < 40%)
Significant AV valve regurgitation not amenable to repair
Severely distorted or hypoplastic pulmonary arteries
Uncontrolled arrhythmias

These patients may need heart transplantation instead.

Stage	Age	Procedure	Goal	Post-Op SpO₂
0 (Emergency)	Birth	PGE1 ± septostomy	Keep baby alive	65–85%
1 (Neonatal)	Days–weeks	mBTS (↓PBF) or PAB (↑PBF)	Balanced pulmonary flow	75–85%
2 (Infancy)	4–6 months	Bidirectional Glenn	Volume-unload LV; stable PBF from SVC	75–85%
3 (Early childhood)	2–4 years	Fontan (TCPC)	Complete cavopulmonary separation	90–95%

Post-Fontan Long-Term Management

The Fontan circulation is a palliation, not a cure. These patients require lifelong specialist follow-up.

Drug	Indication	Mechanism / Notes
Aspirin (3–5 mg/kg/day) or warfarin (INR 2.0–3.0)	Thromboprophylaxis — Fontan conduit has non-endothelialised surfaces → thrombosis risk; sluggish, low-velocity flow → stasis → Virchow's triad	Practice varies between centres: some use aspirin alone, some warfarin, some both. DOAC use in Fontan is under investigation.
ACEI (enalapril/captopril)	Afterload reduction for the single ventricle; possible anti-remodelling benefit	Evidence in Fontan is mixed, but commonly used.
Diuretics (furosemide, spironolactone)	Manage fluid retention, oedema, effusions	Elevated systemic venous pressure in Fontan → oedema, hepatic congestion, effusions.
Sildenafil / bosentan	Pulmonary vasodilators — reduce PVR → improve Fontan flow	Used in selected patients with elevated PVR or "failing Fontan."
Antiarrhythmics	Manage atrial arrhythmias (common late complication)	Fontan patients are prone to atrial flutter/fibrillation due to atrial suture lines, elevated pressures, and chronic atrial dilatation.

Aspect	Detail
Exercise	Moderate activity encouraged; competitive/strenuous sport generally restricted. Exercise capacity is reduced (~60–70% of normal) due to limited ability to increase cardiac output (no subpulmonary pump).
Growth and development	Regular monitoring; many Fontan patients have mild growth restriction and delayed puberty. Nutritional optimisation essential.
Neurodevelopmental follow-up	Increased risk of neurodevelopmental delay due to chronic hypoxaemia in early life, multiple surgeries, and perioperative cerebral insults.
Reproductive counselling	Fontan women can become pregnant but are HIGH RISK — elevated CVP, fixed low cardiac output, risk of arrhythmia, thrombosis, and maternal cardiac decompensation. Requires specialist obstetric-cardiac team.
Hepatic surveillance	Fontan-associated liver disease (FALD) develops universally over time due to chronic hepatic venous congestion → fibrosis → cirrhosis → risk of hepatocellular carcinoma. Regular liver USS, elastography, and AFP screening.
Protein-losing enteropathy (PLE)	A serious late complication — enteral protein loss due to elevated mesenteric venous pressure → hypoalbuminaemia, oedema, ascites, immunodeficiency.

Indication	Detail
Failed Fontan	Progressive ventricular dysfunction, refractory arrhythmias, intractable PLE, severe FALD
Not a Fontan candidate	Unfavourable haemodynamics (high PVR, poor ventricular function, severe PA distortion)
Declining single-ventricle function	Progressive LV failure despite maximal medical therapy

Transplantation is the only definitive cure but is limited by donor availability, especially for paediatric hearts in Hong Kong. Post-transplant immunosuppression and long-term graft survival remain challenges.

Subtype	Stage 1	Stage 2	Stage 3	Special Considerations
Type Ia (no VSD, PA)	PGE1 → mBTS	Glenn at 4–6m	Fontan at 2–4y	Entirely duct-dependent; most urgent
Type Ib (small VSD, ↓PBF)	PGE1 → mBTS	Glenn	Fontan	Most common subtype; VSD may become more restrictive over time
Type Ic (large VSD, ↑PBF)	Anti-failure Rx → PAB	Glenn	Fontan	Protect pulmonary vasculature; avoid irreversible pHTN
Type IIb (D-TGA, small VSD)	PGE1 → DKS + mBTS ± arch repair	Glenn	Fontan	Systemic outflow obstruction; complex surgery
Type IIc (D-TGA, large VSD, ↑PBF)	Anti-failure Rx → PAB	Glenn	Fontan	Similar to Type Ic management

High Yield Summary — Management of Tricuspid Atresia

Tricuspid atresia = single-ventricle physiology → biventricular repair is impossible → managed by staged single-ventricle palliation culminating in the Fontan operation.
Emergency neonatal management: IV PGE1 to maintain PDA (duct-dependent subtypes); balloon atrial septostomy if ASD is restrictive; anti-failure medications if pulmonary overcirculation.
PGE1 side effects: Apnoea (most important — have intubation equipment ready), hypotension, fever.
Stage 1 (neonatal): mBTS for ↓PBF subtypes; PA banding for ↑PBF subtypes; DKS ± arch repair for systemic outflow obstruction.
Stage 2 (4–6 months): Bidirectional Glenn — SVC to RPA → volume-unloads the LV; child remains cyanotic (SpO₂ 75–85%).
Stage 3 (2–4 years): Fontan (TCPC) — IVC to PA → all venous blood passively flows to lungs → near-normal SpO₂. Requires favourable haemodynamics: PA pressure < 15, PVR < 3, LVEDP < 12.
Post-Fontan: Lifelong follow-up; thromboprophylaxis (aspirin or warfarin); monitor for Fontan-associated liver disease, PLE, arrhythmias, exercise limitation.
Heart transplantation: For failed Fontan, non-Fontan candidates, or progressive ventricular failure.

Active Recall - Management of Tricuspid Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 200, 218, 222 — management of PA/IVS, univentricular heart, staged palliation, mBTS/PAB indications, HF management in CHD) ^[2] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf ^[8] Senior notes: Ryan Ho Cardiology.pdf (page 188 — TOF management including mBTS, PGE1, complete repair principles, ACEI avoidance in ↓PBF lesions)

Complications of Tricuspid Atresia

Complications in tricuspid atresia arise at every stage of the disease — from the unrepaired natural history through each surgical palliation and into the long-term Fontan circulation. Understanding these complications requires tracing them back to the underlying abnormal physiology at each phase.

The complications can be organised into:

Complications of the unrepaired/pre-surgical state (related to chronic cyanosis, hypoxaemia, and abnormal haemodynamics)
Complications of each surgical stage (mBTS, Glenn, Fontan — each introduces its own risks)
Long-term complications of the Fontan circulation (the most important category for exams, as these patients survive into adulthood)

1. Complications of the Unrepaired/Pre-Surgical State

These complications relate to chronic cyanosis (in ↓PBF subtypes) or chronic volume overload and heart failure (in ↑PBF subtypes). In modern practice with early surgical intervention, many of these are prevented, but they remain relevant for delayed diagnoses or resource-limited settings.

Complication	Pathophysiology	Clinical Significance
Secondary polycythaemia (reactive erythrocytosis)	Chronic hypoxaemia → renal hypoxia-sensing cells detect low PaO₂ → increased erythropoietin (EPO) production → bone marrow stimulated to produce more red blood cells → elevated haematocrit and haemoglobin	Compensatory: improves oxygen-carrying capacity. Detrimental: hyperviscosity when Hct > 65% → sluggish microcirculatory flow → headache, fatigue, visual disturbance, stroke risk ^[1]^[8]
Hyperviscosity syndrome	Follows from polycythaemia — blood viscosity increases exponentially when Hct > 65% → impaired microvascular perfusion	Risk of thrombotic events (cerebral vein thrombosis, stroke); symptoms include headache, dizziness, blurred vision, paraesthesia. In severe cases, partial exchange transfusion (isovolaemic phlebotomy replacing blood with saline/albumin) to reduce Hct to ~60%
Cerebral abscess	Cyanotic CHD with R-to-L shunting → deoxygenated venous blood bypasses the pulmonary capillary filter (which normally traps bacteria and microemboli) → bacteraemia can seed the brain directly → brain abscess. Also, polycythaemia → microthrombi → microinfarcts → nidus for infection	A classic complication of cyanotic CHD in children ^[1]^[8]. Presents with headache, fever, focal neurological deficits, seizures. Most common organisms: Streptococcus, Staphylococcus, anaerobes. Requires prolonged IV antibiotics ± neurosurgical drainage.
Cerebral thromboembolism / stroke	Polycythaemia + hyperviscosity → sluggish cerebral blood flow → thrombosis. Also, paradoxical embolism: venous thrombi (e.g., from DVT) cross the obligatory R-to-L atrial shunt and embolise to the cerebral circulation, bypassing the pulmonary filter	Risk is highest during dehydration (further increases viscosity). Iron deficiency worsens risk — iron-deficient red cells are less deformable → increased viscosity even at lower Hct → maintain adequate iron stores
Infective endocarditis (IE)	Turbulent flow across abnormal cardiac structures (VSD, PDA, mBTS graft) → endothelial damage → platelet-fibrin deposition → susceptible to bacterial seeding during transient bacteraemia	All patients with tricuspid atresia (repaired or unrepaired) are at high risk for IE and require antibiotic prophylaxis for dental and certain surgical procedures per AHA/ESC guidelines. Common organisms: viridans streptococci (dental procedures), Staphylococcus aureus
Growth failure / failure to thrive	Chronic hypoxaemia → impaired cellular metabolism and oxygen delivery to tissues → reduced growth velocity. Also, increased work of breathing and cardiac work → increased caloric expenditure with often reduced intake	Stunted growth from hypoxia ^[1]^[8] is a hallmark of unrepaired cyanotic CHD. Height and weight often below the 3rd–10th centile. Nutritional optimisation with high-calorie feeds (> 120 kcal/kg/day) is essential.
Coagulopathy	Polycythaemia → dilution of clotting factors (less plasma volume per unit of blood); also, abnormal platelet function in chronic cyanosis; low-grade DIC from chronic tissue hypoxia	Increased risk of both thrombosis (from hyperviscosity) and bleeding (from coagulopathy) — a paradoxical haemostatic state. Presents as easy bruising, mucosal bleeding, or excessive surgical bleeding.
Clubbing	Chronic hypoxaemia → megakaryocytes and platelet clumps bypass the pulmonary capillary filter (which normally fragments them) → reach the systemic capillaries of the digits intact → release PDGF and VEGF → connective tissue proliferation in distal phalanges → bulbous fingertips	Develops over months; degree correlates with duration and severity of cyanosis. Reversible if cyanosis is corrected early.
Hyperuricaemia and gout	Secondary polycythaemia → increased red cell turnover → increased purine metabolism → elevated uric acid	More relevant in older children/adolescents with chronic cyanosis. Rarely symptomatic in young children.

Iron Deficiency in Cyanotic CHD

A common trap: you might think a high Hb means the child cannot be iron deficient. Wrong. Iron deficiency in cyanotic CHD is dangerous — it produces microcytic, less deformable red cells that increase blood viscosity disproportionately to the haematocrit. This paradoxically increases stroke risk even at a "lower" Hct. Always check ferritin and iron studies, and supplement iron if deficient. Do NOT phlebotomise an iron-deficient polycythaemic patient without correcting iron stores first.

Complication	Pathophysiology	Clinical Significance
Congestive heart failure	Large VSD → unrestricted pulmonary blood flow → LV volume overload → LV dilatation and failure; pulmonary congestion → respiratory distress	Presents at 2–6 weeks as PVR falls. Managed with diuretics, ACEI, and Stage 1 PA banding ^[1]
Pulmonary vascular disease / Eisenmenger syndrome	Chronic excessive pulmonary blood flow → shear stress on pulmonary arterioles → intimal proliferation, medial hypertrophy, and eventual obliterative changes → irreversible pulmonary hypertension → reversal of shunt direction ^[1]^[8]	If left unbanded/unrepaired, progressive irreversible pulmonary vascular disease develops — this destroys Fontan candidacy because the Fontan requires low PVR. This is why early PA banding is critical in ↑PBF subtypes.
Recurrent respiratory infections	Pulmonary congestion → fluid-filled, poorly ventilated alveoli → ideal environment for bacterial growth → recurrent pneumonia and lower respiratory tract infections	Common presentation in infants with unrepaired ↑PBF subtypes

Eisenmenger syndrome is an irreversible catastrophe in single-ventricle physiology — once established, the child is no longer a Fontan candidate and the only option is heart-lung transplantation ^[1]^[8].

2. Complications of Each Surgical Stage

Complication	Mechanism	Clinical Significance
Shunt thrombosis/occlusion	Synthetic graft → non-endothelialised surface → thrombogenic; small-calibre graft with relatively low flow → prone to clotting	A blocked BT shunt can kill ^[8] — the child's pulmonary blood flow is entirely shunt-dependent. Loss of the continuous shunt murmur on auscultation is an ominous sign. Emergency: heparin, thrombolysis, or urgent surgical revision.
Shunt stenosis	Neointimal proliferation within the graft → progressive narrowing → reduced PBF → worsening cyanosis	Gradual onset; may require shunt revision or early advancement to Glenn
Pulmonary artery distortion	Surgical anastomosis → fibrosis and scarring at the junction → stenosis of the ipsilateral PA	Can compromise PA anatomy for future Glenn/Fontan. This is why some centres prefer PDA stenting (less PA distortion).
Overcirculation (shunt too large)	If the graft diameter is too large relative to the child's size → excessive L-to-R shunting → pulmonary overcirculation → HF	Balance is critical — shunt must be appropriately sized
PA band complications	Band migration, band erosion into PA wall, PA distortion at band site, suboptimal banding (too tight or too loose)	Too tight → cyanosis; too loose → persistent overcirculation. Requires careful intraoperative assessment and post-operative monitoring.

Complication	Mechanism	Clinical Significance
SVC syndrome	Obstruction or stenosis at the SVC-PA anastomosis → impaired upper body venous drainage → facial oedema, plethora, headache, raised intracranial pressure	Requires urgent intervention (balloon angioplasty ± stenting)
Persistent cyanosis (lower than expected SpO₂)	Pulmonary arteriovenous malformations (PAVMs) → intrapulmonary R-to-L shunting. These develop because the hepatic venous effluent (which contains a hepatic factor that inhibits PAVM formation) no longer reaches the lungs (IVC blood goes to the heart, not the PA post-Glenn).	PAVMs are a well-recognised complication of the Glenn — they tend to resolve after Fontan completion when IVC blood (containing the hepatic factor) is re-routed to the lungs
Venous collaterals	Elevated SVC pressure → formation of veno-venous collaterals (decompressing SVC into the IVC/azygos system) → deoxygenated blood bypasses the lungs → cyanosis	May require coil embolisation before or during Fontan
Arrhythmias	Atrial suture lines → scar-mediated re-entry circuits → atrial flutter/tachycardia	May compromise haemodynamics in single-ventricle physiology; managed with antiarrhythmics or catheter ablation

Complication	Mechanism	Clinical Significance
Prolonged pleural/pericardial effusions	Elevated systemic venous pressure (CVP 12–15 mmHg) post-Fontan → increased hydrostatic pressure in the thoracic duct and pleural capillaries → transudative effusions	The most common early post-Fontan complication — can prolong ICU/hospital stay by weeks. Management: chest drains, diuretics, ± fenestration creation/revision, low-fat (MCT-based) diet to reduce chylous output if chylothorax develops.
Low cardiac output syndrome	Fontan circulation is inherently low-output (no subpulmonary pump) → CO depends on preload (venous pressure) driving blood through the lungs passively → any increase in PVR or decrease in preload → low CO	Presents with poor perfusion, cool extremities, oliguria, metabolic acidosis. Managed with volume optimisation, inotropes (milrinone as inodilator), pulmonary vasodilators (iNO, sildenafil).
Arrhythmias	Atrial suture lines (especially in lateral tunnel Fontan) → substrate for re-entrant atrial arrhythmias	Atrial flutter/tachycardia very common; may cause acute Fontan failure due to loss of AV synchrony and reduced diastolic filling time
Fontan pathway thrombosis	Non-endothelialised conduit surfaces + sluggish, low-velocity flow → thrombosis within the Fontan circuit	Risk of pulmonary embolism, Fontan obstruction. Requires thromboprophylaxis (aspirin or warfarin).

3. Long-Term Complications of the Fontan Circulation

These are the most important complications to know as they affect quality of life and long-term survival. The Fontan circulation is a palliation, not a cure — chronic elevation of systemic venous pressure and chronically reduced cardiac output cause progressive multi-organ dysfunction.

The Fontan state creates a unique pathophysiology: chronic systemic venous hypertension (CVP ~12–15 mmHg) + chronically reduced cardiac output (inability to augment CO with exercise) → multi-organ consequences.

Aspect	Detail
Mechanism	Chronically elevated hepatic venous pressure (equal to Fontan pathway pressure, 12–15 mmHg) → persistent hepatic congestion → centrilobular sinusoidal dilatation → perisinusoidal fibrosis → progressive hepatic fibrosis → cirrhosis over years to decades
Timeline	Universal to some degree after 10–20 years of Fontan physiology; virtually all Fontan patients have histological liver abnormalities by adulthood
Clinical features	Initially asymptomatic; progresses to portal hypertension (ascites, variceal bleeding), coagulopathy (synthetic liver failure), and eventually risk of hepatocellular carcinoma (HCC)
Screening	Regular liver USS + elastography (FibroScan) to assess fibrosis stage; LFTs; AFP for HCC screening; some centres advocate liver biopsy in selected patients
Management	No specific treatment can reverse the underlying cause (elevated CVP is intrinsic to Fontan physiology). Manage complications (diuretics for ascites, endoscopic variceal management). Ultimate treatment: heart transplantation (± combined heart-liver transplantation if cirrhosis is advanced).

FALD — A Universal Consequence

Fontan-associated liver disease is NOT a complication of "failed" Fontan — it develops in ALL Fontan patients to some degree because the hepatic venous pressure is chronically elevated by the nature of the Fontan circuit. It is progressive and currently irreversible without transplantation. This is one of the main drivers of long-term morbidity and mortality in the Fontan population.

Aspect	Detail
Incidence	5–15% of Fontan patients; one of the most feared complications
Mechanism	Chronically elevated mesenteric venous pressure → intestinal lymphatic congestion and rupture → loss of protein-rich lymph into the gut lumen → enteral protein loss → hypoalbuminaemia
Clinical features	Oedema (peripheral, facial, ascites), chronic diarrhoea, malnutrition, recurrent infections (loss of immunoglobulins → secondary immunodeficiency), poor wound healing
Diagnosis	Raised faecal alpha-1 antitrypsin clearance (alpha-1 antitrypsin is a protein that resists gut digestion — if elevated in stool, confirms enteral protein loss); low serum albumin (< 30 g/L); low serum immunoglobulin levels
Management	High-protein, low-fat diet (MCT-based fats to reduce lymphatic load); IV albumin infusions; diuretics (spironolactone); heparin (unfractionated or LMWH — mechanism unclear but may improve haemodynamics); subcutaneous octreotide (reduces splanchnic blood flow); oral budesonide (anti-inflammatory effect on gut mucosa). Refractory cases → Fontan revision, fenestration creation, or heart transplantation.
Prognosis	5-year survival after PLE diagnosis is ~50% — it is a marker of failing Fontan physiology

Aspect	Detail
Mechanism	Multiple factors: (1) Chronic atrial dilatation from elevated venous pressure → atrial stretch → electrical remodelling; (2) Surgical suture lines within the atria (especially lateral tunnel Fontan) → scar-mediated re-entry circuits; (3) Sinus node dysfunction from surgical damage
Types	Intra-atrial re-entrant tachycardia (IART) / atrial flutter is the most common; also atrial fibrillation, sinus node dysfunction (bradycardia-tachycardia syndrome), junctional rhythms
Clinical significance	Arrhythmias are poorly tolerated in Fontan physiology — loss of AV synchrony and rapid rates → reduced diastolic filling time → reduced preload to the PA → reduced cardiac output → acute Fontan failure
Management	Rate control (amiodarone, beta-blockers — with caution); antiarrhythmic drugs; catheter ablation for re-entrant circuits; Fontan conversion surgery (converting a lateral tunnel to an extracardiac conduit + ablation of arrhythmia substrate) in refractory cases; pacemaker for bradycardia

Aspect	Detail
Mechanism	Sluggish, low-velocity blood flow within the Fontan circuit (no pumping chamber) → stasis (Virchow's triad); non-endothelialised conduit surfaces → prothrombotic; chronic hepatic dysfunction → coagulation factor imbalance
Types	Fontan pathway thrombus, pulmonary embolism (obstructs passive flow → catastrophic haemodynamic compromise), systemic thromboembolism (if fenestration present → paradoxical embolism → stroke), intracardiac thrombus
Incidence	10–25% lifetime risk
Prevention	Lifelong thromboprophylaxis — aspirin (3–5 mg/kg/day) or warfarin (INR 2.0–3.0); practice varies between centres. DOACs are under investigation.
Acute management	Anticoagulation (heparin → warfarin transition); thrombolysis in haemodynamically significant PE; surgical or catheter thrombectomy in refractory cases

Aspect	Detail
Mechanism	Fontan circulation cannot augment cardiac output normally during exercise — there is no subpulmonary pump to increase pulmonary blood flow → limited preload augmentation → VO₂ max typically 50–70% of predicted
Clinical significance	Most Fontan patients can perform activities of daily living but have significantly reduced peak exercise capacity. Competitive sport is generally restricted but moderate recreational activity is encouraged for cardiovascular fitness and psychosocial wellbeing.
Assessment	Cardiopulmonary exercise testing (CPET) to quantify VO₂ max; performed periodically during follow-up

Aspect	Detail
Mechanism	Elevated systemic venous pressure → pulmonary lymphatic congestion → lymphatic fluid leaks into the bronchial tree → forms thick, rubbery casts that occlude the airways
Incidence	Rare (~1–4% of Fontan patients) but potentially fatal
Presentation	Chronic cough, expectoration of branching bronchial casts, dyspnoea, respiratory distress; can cause acute airway obstruction → respiratory failure
Management	Bronchoscopic cast removal (acute); inhaled tPA or hypertonic saline; dietary modification (low-fat, MCT diet); thoracic duct ligation; interventional lymphatic procedures (lymphatic embolisation/imaging-guided interventions — a growing field)

Aspect	Detail
Mechanism	Multifactorial: (1) Chronic hypoxaemia in early life (before complete palliation) → impaired brain development; (2) Multiple cardiac surgeries with cardiopulmonary bypass → cerebral microemboli, inflammatory response; (3) Periods of low cardiac output → cerebral hypoperfusion; (4) Genetic/syndromic associations
Clinical significance	30–50% of Fontan patients have some degree of neurodevelopmental impairment — including motor delays, attention difficulties, learning disabilities, executive function deficits, behavioural/emotional challenges
Management	Regular neurodevelopmental assessment; early intervention with physiotherapy, occupational therapy, speech therapy as needed; educational support; psychosocial support for the child and family

Aspect	Detail
Mechanism	Chronically reduced cardiac output → reduced renal perfusion; elevated renal venous pressure (from elevated CVP) → "cardiorenal" physiology; nephrotoxic medications (diuretics, ACEIs)
Clinical significance	Progressive mild chronic kidney disease develops in many adult Fontan patients; GFR declines more rapidly than age-matched controls. Cystatin C may be a more sensitive marker than creatinine in this population (muscle mass is often low).

Aspect	Detail
Mechanism	Living with a chronic, complex cardiac condition from birth → repeated hospitalisations, surgeries, activity restriction, visible differences (scars, cyanosis, clubbing)
Clinical significance	Increased rates of anxiety, depression, body image concerns, social difficulties. Family-centred care is essential — support for parents/siblings as well as the patient. Transition from paediatric to adult congenital heart disease (ACHD) services is a critical period.
Management	Psychological screening at regular intervals; access to clinical psychology/psychiatry; peer support groups; structured transition programmes

Category	Complication	Key Mechanism
Chronic cyanosis	Polycythaemia, hyperviscosity, cerebral abscess, stroke, coagulopathy, growth failure, clubbing, IE	R-to-L shunt → bypass of pulmonary filter; chronic hypoxaemia → EPO ↑; turbulent flow → IE risk
↑PBF subtypes	HF, pulmonary vascular disease/Eisenmenger	Unrestricted pulmonary flow → volume overload, irreversible arteriolar changes
mBTS	Shunt thrombosis, PA distortion, overcirculation	Synthetic graft thrombogenicity; surgical anastomosis scarring
Glenn	SVC syndrome, PAVMs, venous collaterals	Anastomotic stenosis; loss of hepatic factor to lungs; venous decompression
Fontan (early)	Effusions, low output, arrhythmias, pathway thrombosis	Elevated CVP, passive flow, atrial suture lines
Fontan (late)	FALD, PLE, arrhythmias, thromboembolism, exercise intolerance, plastic bronchitis, neurodevelopmental delay, renal dysfunction	Chronic venous hypertension, low CO, hepatic/mesenteric/pulmonary lymphatic congestion, perioperative brain injury

High Yield Summary — Complications of Tricuspid Atresia

Chronic cyanosis complications: polycythaemia/hyperviscosity → stroke, cerebral abscess (bypass of pulmonary filter), coagulopathy, growth failure, clubbing, infective endocarditis.
Eisenmenger syndrome: irreversible pulmonary vascular disease from unprotected excessive PBF → destroys Fontan candidacy → only option is heart-lung transplant.
mBTS complications: shunt thrombosis is potentially fatal — always auscultate for the shunt murmur; loss of murmur = emergency.
Glenn complications: SVC syndrome; PAVMs (from absent hepatic factor in pulmonary circulation); venous collaterals causing persistent cyanosis.
Fontan long-term (most important):
- FALD — universal; chronic hepatic congestion → fibrosis → cirrhosis → HCC risk.
- PLE — 5–15%; enteral protein loss → hypoalbuminaemia, oedema, immunodeficiency; 50% 5-year survival.
- Arrhythmias — IART/atrial flutter most common; poorly tolerated in Fontan physiology.
- Thromboembolism — 10–25% lifetime risk; lifelong anticoagulation required.
- Exercise intolerance — VO₂ max 50–70% predicted; no subpulmonary pump.
- Plastic bronchitis — rare but potentially fatal; lymphatic casts occlude airways.
Neurodevelopmental delay: 30–50% of Fontan patients; multifactorial (hypoxaemia, CPB, low CO).
Lifelong specialist follow-up is mandatory — the Fontan is a palliation, not a cure.

Active Recall - Complications of Tricuspid Atresia

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (pages 193, 220 — Eisenmenger syndrome complications, ductal-dependent circulation, TGA late complications, common-mixing conditions) ^[2] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf ^[8] Senior notes: Ryan Ho Cardiology.pdf (pages 186, 188, 191 — Eisenmenger syndrome complications including stunted growth, polycythaemia, cerebral embolism/abscess, PA thrombosis; TOF mBTS complications; CoA long-term outcomes)

High Yield Summary

Tricuspid Atresia — Key Points for Exams:

Definition: Complete absence of the tricuspid valve → no RA-to-RV communication → hypoplastic RV → single (left) ventricle physiology.
Epidemiology: 1–3% of all CHD; third most common cyanotic CHD.
Obligatory features: ASD/PFO (for survival), hypoplastic RV.
Classification: By great artery relationship (Type I = NRGA, Type II = D-TGA) and VSD size (a = no VSD, b = small VSD, c = large VSD). Type Ib is the most common subtype.
Pathophysiology: Obligatory R-to-L shunt at atrial level → complete mixing in LA → cyanosis. Degree of cyanosis depends on pulmonary blood flow (Qp:Qs).
Classic presentation: Cyanotic neonate with LV dominance on exam and ECG — the OPPOSITE of most cyanotic CHDs.
ECG triad: Left axis deviation (superior axis) + RA enlargement + LV hypertrophy with diminished RV forces. This is virtually pathognomonic.
CXR: Oligaemic lung fields (in ↓PBF subtypes) or plethoric (in ↑PBF subtypes); RA enlargement.
Emergency: Duct-dependent subtypes (Ia, Ib with restrictive VSD) → PGE1 infusion is life-saving.
Definitive diagnosis: Echocardiography showing absent tricuspid valve orifice, hypoplastic RV, ASD, ± VSD, great artery relationship.

High Yield Summary — Differential Diagnosis of Tricuspid Atresia

Tricuspid atresia is a cyanotic CHD most commonly presenting with decreased pulmonary blood flow (Type Ia, Ib), but some subtypes present with increased PBF and HF (Type Ic, IIc).
Closest mimic: PA/IVS — both have duct-dependent pulmonary circulation, LV dominance, and absent RV impulse. Distinguished by: presence of TR murmur in PA/IVS (TV exists), high-pressure hypertrophied RV in PA/IVS, and echo showing absent vs present TV.
ECG is the key bedside differentiator: LAD + LVH + diminished RV forces = tricuspid atresia. Almost all other cyanotic CHDs show RAD + RVH.
CXR: Oligaemic lung fields + RA enlargement + concavity at PA segment → tricuspid atresia with ↓PBF.
Non-cardiac mimics: PPHN can fail the hyperoxia test → echo showing structurally normal heart distinguishes it.
Use the GC lecture framework: Classify cyanotic CHD by ↓PBF, ↑PBF, or severe HF, then assess ductal dependence — this determines urgency of PGE1 therapy.

High Yield Summary — Diagnosis and Investigations

Tricuspid atresia is diagnosed definitively by echocardiography demonstrating absent TV orifice, hypoplastic RV, and obligatory R-to-L atrial shunt.
The ECG is the most useful bedside differentiator: LAD (superior axis) + RA enlargement (P pulmonale) + LVH + diminished RV forces is virtually pathognomonic and distinguishes TA from nearly all other cyanotic CHDs (which show RAD + RVH).
CXR: Oligaemic lung fields + RA prominence + concave PA segment in ↓PBF subtypes; plethoric lungs + cardiomegaly in ↑PBF subtypes.
Pulse oximetry screening (SpO₂ < 95%) and hyperoxia test (PaO₂ < 100 mmHg on 100% O₂) are critical early steps to distinguish cardiac from respiratory cyanosis.
Cardiac catheterisation is not needed for initial diagnosis but is essential before staged Fontan surgery to assess PA pressure (< 15 mmHg), PVR (< 3 Wood units·m²), and LV EDP (< 12 mmHg) — the haemodynamic prerequisites for Fontan candidacy.
Fetal echo can detect TA antenatally, allowing planned delivery at a cardiac centre and immediate PGE1 — significantly improves outcomes.

High Yield Summary — Management of Tricuspid Atresia

Tricuspid atresia = single-ventricle physiology → biventricular repair is impossible → managed by staged single-ventricle palliation culminating in the Fontan operation.
Emergency neonatal management: IV PGE1 to maintain PDA (duct-dependent subtypes); balloon atrial septostomy if ASD is restrictive; anti-failure medications if pulmonary overcirculation.
PGE1 side effects: Apnoea (most important — have intubation equipment ready), hypotension, fever.
Stage 1 (neonatal): mBTS for ↓PBF subtypes; PA banding for ↑PBF subtypes; DKS ± arch repair for systemic outflow obstruction.
Stage 2 (4–6 months): Bidirectional Glenn — SVC to RPA → volume-unloads the LV; child remains cyanotic (SpO₂ 75–85%).
Stage 3 (2–4 years): Fontan (TCPC) — IVC to PA → all venous blood passively flows to lungs → near-normal SpO₂. Requires favourable haemodynamics: PA pressure < 15, PVR < 3, LVEDP < 12.
Post-Fontan: Lifelong follow-up; thromboprophylaxis (aspirin or warfarin); monitor for Fontan-associated liver disease, PLE, arrhythmias, exercise limitation.
Heart transplantation: For failed Fontan, non-Fontan candidates, or progressive ventricular failure.

High Yield Summary — Complications of Tricuspid Atresia

Chronic cyanosis complications: polycythaemia/hyperviscosity → stroke, cerebral abscess (bypass of pulmonary filter), coagulopathy, growth failure, clubbing, infective endocarditis.
Eisenmenger syndrome: irreversible pulmonary vascular disease from unprotected excessive PBF → destroys Fontan candidacy → only option is heart-lung transplant.
mBTS complications: shunt thrombosis is potentially fatal — always auscultate for the shunt murmur; loss of murmur = emergency.
Glenn complications: SVC syndrome; PAVMs (from absent hepatic factor in pulmonary circulation); venous collaterals causing persistent cyanosis.
Fontan long-term (most important):
- FALD — universal; chronic hepatic congestion → fibrosis → cirrhosis → HCC risk.
- PLE — 5–15%; enteral protein loss → hypoalbuminaemia, oedema, immunodeficiency; 50% 5-year survival.
- Arrhythmias — IART/atrial flutter most common; poorly tolerated in Fontan physiology.
- Thromboembolism — 10–25% lifetime risk; lifelong anticoagulation required.
- Exercise intolerance — VO₂ max 50–70% predicted; no subpulmonary pump.
- Plastic bronchitis — rare but potentially fatal; lymphatic casts occlude airways.
Neurodevelopmental delay: 30–50% of Fontan patients; multifactorial (hypoxaemia, CPB, low CO).
Lifelong specialist follow-up is mandatory — the Fontan is a palliation, not a cure.

Tricuspid Atresia

Definition

Epidemiology

Anatomy and Embryology

Normal Tricuspid Valve

Embryological Basis of Tricuspid Atresia

Obligatory Associated Anomalies

Relationship of the Great Arteries

Classification

Etiology (Focus on Hong Kong Context)

Pathophysiology

Step-by-Step Haemodynamics (Type Ib — Most Common)

Key Haemodynamic Concepts

Complete Mixing

Volume Overload of the LV

RA Pressure and the Interatrial Communication

Duct-Dependent Pulmonary Circulation

Duct-Dependent Systemic Circulation (Type IIb)

Pathophysiology Summary Table

Clinical Features

Symptoms (with Pathophysiological Basis)

A. Cyanosis (Most Subtypes)

B. Hypercyanotic/"Tet" Spells (in subtypes with decreased pulmonary blood flow)

C. Heart Failure Symptoms (Type Ic, IIc — increased pulmonary blood flow subtypes)

D. Poor Feeding and Failure to Thrive

E. Rapid Deterioration After Birth (Duct-Dependent Subtypes)

F. Exertional Dyspnoea and Exercise Intolerance (Older Unrepaired Children — Rare in Modern Practice)

G. Squatting (Historical/Older Children)

Signs (with Pathophysiological Basis)

A. General Inspection

B. Cardiovascular Examination

Precordium and Apex Beat

Heart Sounds

Murmurs

Signs of Heart Failure (in increased pulmonary blood flow subtypes)

C. Other Signs

ECG Findings (Key Diagnostic Clue)

Chest X-Ray Findings

Echocardiographic Findings (Definitive Diagnostic Tool)

Summary of Clinical Presentations by Subtype

Active Recall - Tricuspid Atresia: Definition, Pathophysiology, and Clinical Features

References

Framing the Clinical Problem

Step 1: Cardiac vs Non-Cardiac Cyanosis

Step 2: Differential Diagnosis Among Cyanotic Congenital Heart Diseases

Category 1: Cyanotic CHD with Decreased Pulmonary Blood Flow (↓PBF)

Category 2: Cyanotic CHD with Increased Pulmonary Blood Flow (↑PBF) — "The 3 Ts"

Category 3: Cyanotic CHD with Severe Heart Failure (Duct-Dependent Systemic Circulation)

Step 3: Non-Cardiac Causes of Neonatal Cyanosis

Diagnostic Approach Algorithm (Mermaid Diagram)

Key Distinguishing Features of Tricuspid Atresia vs Its Closest Differentials

Summary of Differential Diagnosis Framework

Active Recall - Differential Diagnosis of Tricuspid Atresia

Diagnostic Criteria

Diagnostic Algorithm

Investigation Modalities

1. Pulse Oximetry Screening (Neonatal — Detection)

2. Hyperoxia Test (Nitrogen Washout Test) (Neonatal — Differentiation)

3. Electrocardiography (ECG) (Characterisation — The Bedside Differentiator)

ECG Findings in Tricuspid Atresia — Detailed Interpretation

ECG Variations by Subtype

4. Chest X-Ray (CXR) (Characterisation)

CXR Findings — Detailed Interpretation

CXR Shape Comparison Table (Exam Favourite)

5. Echocardiography (Definitive Diagnosis + Classification)

6. Arterial Blood Gas (ABG) (Acute Assessment)

7. Blood Tests (Baseline and Monitoring)

8. Cardiac Catheterisation (Pre-Surgical Planning / Interventional)

9. Cardiac MRI (Complementary / Pre-Surgical Planning)

10. CT Angiography (Complementary)

11. Fetal Echocardiography (Antenatal Detection)

Investigation Summary Table

Active Recall - Diagnosis and Investigations for Tricuspid Atresia

Management Principles

Management Algorithm

Stage 0: Emergency Neonatal Stabilisation

A. Prostaglandin E1 (PGE1 / Alprostadil) Infusion

B. Balloon Atrial Septostomy (Rashkind Procedure)

C. Medical Management of Heart Failure (↑PBF Subtypes)

Stage 1: Initial Palliative Surgery (Neonatal Period — Days to Weeks)