The tricuspid valve has three leaflets: anterior, septal, and posterior. During normal embryonic development (weeks 8–12 of gestation), the inner layers of the RV myocardium undergo a process called delamination — the valve leaflets literally "peel off" from the ventricular wall and migrate upward to attach at the true atrioventricular (AV) junction (the tricuspid annulus).

In Ebstein anomaly, delamination fails ^[1]. The septal and posterior leaflets (and sometimes the anterior leaflet) fail to separate from the RV wall and remain adherent to the endocardial surface at a lower (more apical) position. The result:

1. The septal and posterior leaflets are displaced downward into the RV — they are often dysplastic, redundant, or even plastered onto the RV wall
2. The anterior leaflet is usually the least affected — it may be large and "sail-like," sometimes redundant, and may be the only mobile leaflet. However, it is often fenestrated or tethered
3. The functional tricuspid annulus is displaced apically → the "true" annulus remains in its normal position, but the effective orifice of the valve is lower

• The atrialized portion is usually thin-walled and dilated, but contracts with the RV ^[1] — this is an important detail: it still has ventricular myocardium and contracts in systole, but because it is above the functional valve, its contraction actually works against RV filling (it contracts when the RV contracts, pushing blood backward toward the RA)
• This leads to markedly elevated RA pressure ^[1]
• The functional RV is small and may have reduced contractility

Almost all patients with Ebstein anomaly have an interatrial communication — usually a patent foramen ovale (PFO) or a secundum ASD ^[1][2]. This is critical because:

• Elevated RA pressure → right-to-left shunting across the interatrial communication → cyanosis
• The degree of cyanosis depends on the RA pressure (which depends on severity of TV dysfunction and RVOT obstruction)

Other associations include:

• RVOT obstruction — can be pulmonary stenosis (PS) or pulmonary atresia ^[1] → worsens cyanosis
• VSD ^[1]
• Right bundle branch block (RBBB) ^[1] — due to abnormal conduction through the atrialized RV
• Wolff-Parkinson-White syndrome (WPWS) ^[1] — accessory pathways (usually right-sided) are present in 10–25% of patients; these predispose to supraventricular tachycardia (SVT)

• The displaced, dysplastic TV is usually incompetent (regurgitant) ^[1]
• In some patients, the valve may be stenotic (leaflets are fused or restricted) ^[1]
• Tricuspid regurgitation (TR) is the dominant lesion in most cases

• TR (and/or TS) → gross RA dilatation and hypertrophy ^[1]
• The atrialized portion of the RV also dilates
• The RA can become massively enlarged — sometimes occupying most of the left hemithorax on CXR

• Elevated RA pressure pushes blood through the interatrial communication (PFO/ASD)
• In severe cases: significant R-to-L shunt → cyanosis ^[1]
• In mild cases: bidirectional shunting ^[1] → minimal or no cyanosis at rest

• The functional RV is small
• The atrialized RV contracts paradoxically (contracts in systole but is above the valve → pushes blood backward into RA rather than forward into PA)
• Reduced effective RV output → reduced pulmonary blood flow

This is crucial in neonates:

• At birth, PVR is high → minimal flow through the pulmonary circuit regardless → severe cyanosis
• As PVR drops in the first few days/weeks of life → pulmonary blood flow increases → cyanosis may improve ^[1]
• This is why some neonates with severe Ebstein anomaly may initially appear very cyanotic but improve over the first week of life
• Conversely, in mild Ebstein anomaly: mild cyanosis at birth → disappears as PVR drops ^[1]

• In mild disease: patients may remain asymptomatic throughout childhood ^[1] → but may develop progressive RV failure and TR in adulthood with reappearance of cyanosis ^[1]
• SVT in adulthood: due to RA dilation (atrial stretch → atrial arrhythmias) and WPW syndrome (accessory pathways) ^[1]

The pathophysiology depends on: ^[1]

1. Size of the functional RV
2. Severity of TV malformation
3. Presence and degree of RVOT obstruction

This classification is based on the degree of TV displacement and RV functional anatomy, and guides surgical decision-making:

Used specifically in neonates to predict outcome. It is a ratio calculated from echocardiography:

$\text{Celermajer Ratio} = \frac{\text{Area of RA + Atrialized RV}}{\text{Area of Functional RV + LA + LV}}$

High Yield: A Celermajer ratio ≥ 1.5 in a neonate with Ebstein anomaly carries a very high mortality and may prompt consideration of early surgical intervention or even single-ventricle palliation.

From a clinical perspective, Ebstein anomaly can also be classified by presentation:

• Neonatal presentation (severe) — cyanosis, heart failure, "wall-to-wall heart" on CXR
• Childhood/adolescent presentation (moderate) — exercise intolerance, murmur found incidentally
• Adult presentation (mild) — arrhythmias (SVT from WPW), progressive RV failure, paradoxical embolism/stroke

The clinical features of Ebstein anomaly are best understood when separated into severe and mild forms, as the presentations are dramatically different ^[1]:

High Yield: The "wall-to-wall heart" on CXR in a cyanotic neonate is a classic exam image for Ebstein anomaly ^[1].

Echocardiography confirms the diagnosis and provides:

• Apical displacement of the septal TV leaflet ≥ 8 mm/m² (indexed to body surface area) below the mitral valve annulus in the apical four-chamber view — this is the diagnostic criterion
• Assessment of TV morphology (leaflet mobility, tethering, fenestrations)
• Degree of TR (and TS if present)
• Size of atrialized RV and functional RV
• Interatrial communication (PFO/ASD) and direction of shunt
• RVOT obstruction (PS or pulmonary atresia)
• LV function (may be impaired due to ventricular interdependence or compression by dilated RV)

• Fetal echocardiography: Can diagnose Ebstein anomaly prenatally (typically at 18–22 weeks gestation); cardiomegaly and TR may be detected
• Cardiac MRI: Gold standard for assessing RV volumes, function, and morphology in older children/adults; useful for surgical planning
• Cardiac catheterisation: Rarely needed for diagnosis in the echo era; may be used for electrophysiology study (if WPW/SVT) or haemodynamic assessment pre-operatively
• Pulse oximetry: Screening tool — will show desaturation in cyanotic cases

These lesions have obstruction to pulmonary blood flow → reduced pulmonary venous return → deoxygenated blood enters systemic circulation via intracardiac shunting.

Why is ductal dependence conditional in Ebstein anomaly? Because if the RVOT is patent (even if small), some antegrade pulmonary blood flow exists and the neonate is not completely dependent on the PDA. If there is pulmonary atresia or critical PS in association with Ebstein anomaly, the PDA becomes the only source of pulmonary blood flow → ductal dependent → will deteriorate catastrophically when the PDA closes (typically day 1–3 of life).

These conditions cause cyanosis through parallel circulations or obligatory mixing — pulmonary blood flow is actually increased, but the oxygenated and deoxygenated blood mix inadequately.

These are generally distinguishable from Ebstein by CXR appearance, ECG, and echo findings.

Severe Ebstein anomaly can present with neonatal heart failure (biventricular), but the CXR with massive cardiomegaly and the auscultatory findings (quadruple gallop, TR murmur) are distinctive.

The definitive diagnostic criterion for Ebstein anomaly is echocardiographic demonstration of apical displacement of the septal tricuspid valve leaflet ≥ 8 mm/m² (indexed to body surface area) below the mitral valve annulus in the apical four-chamber view.

Why this specific measurement? In a normal heart, the tricuspid valve inserts slightly more apically (toward the RV apex) than the mitral valve — this normal offset is approximately 3–5 mm in adults. In Ebstein anomaly, this offset is pathologically exaggerated. The 8 mm/m² threshold (indexed to BSA to account for body size — critical in paediatrics where the heart size varies dramatically from a 2 kg neonate to a 70 kg adolescent) has been validated as the cut-off that reliably distinguishes Ebstein anomaly from normal anatomy and from other TV abnormalities.

While echo is definitive, the diagnosis is often suspected based on a constellation of clinical and investigational findings:

When: Performed on all neonates (part of the universal neonatal screening for critical CHD in many centres, including Hong Kong).

Method: Pre-ductal (right hand) and post-ductal (either foot) SpO₂ measured simultaneously.

In Ebstein anomaly, the R-to-L shunt is at the atrial level (through PFO/ASD), so both pre- and post-ductal saturations tend to be similarly low (no significant pre-post-ductal gradient, unlike PDA-dependent lesions).

Purpose: Assess heart size, heart shape, and pulmonary vascularity — this gives crucial pattern-recognition clues.

Exam Pearl: The "wall-to-wall heart" on CXR in a cyanotic neonate has a very short DDx: Ebstein anomaly (most classic), large pericardial effusion, or severe dilated cardiomyopathy. Pericardial effusion can be quickly distinguished by echo; DCM has different ECG features.

Purpose: Provides critical pattern-recognition clues and identifies associated conduction abnormalities. The ECG in Ebstein anomaly is almost always abnormal and has a distinctive pattern.

When: Performed during routine anomaly scan at 18–22 weeks gestation, or earlier if high-risk (e.g., maternal lithium use, family history of CHD).

Key findings:

• Cardiomegaly (heart occupying > 1/3 of the thorax)
• TR with massive RA dilation
• Displaced TV visible on four-chamber view
• Hydrops fetalis (pericardial effusion, ascites, skin oedema) — indicates severe disease with very poor prognosis

Clinical importance: Prenatal diagnosis allows for:

• Counselling of the family about prognosis and expected postnatal course
• Planned delivery at a tertiary centre with paediatric cardiac surgery capability (in Hong Kong: Queen Mary Hospital, Prince of Wales Hospital, Hong Kong Children's Hospital)
• Postnatal management team ready (neonatology, paediatric cardiology, paediatric cardiac surgery, NICU)
• Discussion of options if severe disease with very poor prognosis (Celermajer grade 4 prenatally)

When: Used in older children and adolescents (generally > 5–7 years, or younger with sedation/GA) for detailed anatomical and functional assessment, particularly when surgical planning is required.

Advantages over echo:

• Superior RV volumetric assessment (echo is notoriously poor at quantifying RV volumes due to the RV's complex crescent shape)
• Accurate measurement of RV ejection fraction
• Detailed assessment of atrialized vs. functional RV volumes
• Quantification of TR (regurgitant fraction)
• Assessment of myocardial fibrosis (late gadolinium enhancement)
• Better delineation of associated lesions

Limitations: Requires sedation/general anaesthesia in young children; longer scan time; less accessible than echo.

When: Not routinely needed for diagnosis in the era of high-quality echo and MRI. Specific indications:

Note on EPS in paediatric Ebstein anomaly: The accessory pathways in Ebstein anomaly can be challenging to ablate because they are often located along the displaced, abnormal annulus — they may be multiple, broad, or in unusual locations. Success rates are lower than for WPW in structurally normal hearts.

Blood tests are non-specific but important for supportive assessment:

Short course IV PGE1 infusion for those with severe neonatal cyanosis when PVR is high ^[1]

• Drug: Prostaglandin E1 (PGE1) — alprostadil
• Paediatric dose: 0.01–0.05 mcg/kg/min IV continuous infusion (start low, titrate to effect)
• Mechanism: PGE1 maintains ductal patency by relaxing the smooth muscle of the ductus arteriosus. In Ebstein anomaly with severe RVOT obstruction (or pulmonary atresia), the PDA is the only source of pulmonary blood flow — without it, the neonate will have no pulmonary perfusion and rapidly become profoundly cyanotic and acidotic

Why "short course"? The PGE1 is a bridge — it buys time while the neonatal team stabilises the baby and the surgical team plans intervention. It is not a long-term solution because:

• Side effects increase with prolonged use (apnoea, fever, hypotension, cortical hyperostosis with chronic use)
• The definitive treatment is surgical

When is PGE1 NOT needed? If the RVOT is patent and there is adequate antegrade pulmonary blood flow (i.e., the neonate is not ductal-dependent). In mild Ebstein anomaly, the PDA can be allowed to close naturally.

An important concept in neonatal Ebstein anomaly: the clinical picture may improve spontaneously as PVR drops over the first days to weeks of life ^[1]. As PVR falls:

• More blood can flow antegradely through the RVOT (even if small)
• The R-to-L shunt decreases
• Cyanosis improves

This is why some centres adopt a "watchful waiting" strategy in the neonatal period — stabilise with PGE1 and supportive care, then reassess as PVR drops. If the neonate stabilises adequately, surgery can be deferred. If the neonate remains severely compromised despite falling PVR, early surgical intervention is required.

The management of paediatric heart failure follows a staged approach similar to (but not identical to) adult guidelines ^[14]:

Specific drugs and paediatric considerations:

SVT in adulthood: due to RA dilation and WPW syndrome ^[1]

Key principle for arrhythmia management in Ebstein anomaly: Always check for WPW before choosing drugs. If WPW is present, avoid AV nodal blocking agents (digoxin, verapamil, diltiazem) during atrial fibrillation/flutter — these can precipitate VF via uncontrolled accessory pathway conduction ^[15].

Indications: Majority of patients, when there is significant cyanosis or HF ^[1] — i.e., when the functional RV is large enough to sustain biventricular physiology.

This means the RV is deemed capable of supporting the full pulmonary circulation on its own. Carpentier types A and B (and some type C) are usually suitable.

Various procedures depending on pathology, including: ^[1]

The Cone Repair — Current Gold Standard

The cone repair deserves special mention as it has transformed surgical outcomes for Ebstein anomaly:

1. All leaflet tissue (anterior, posterior, septal) is mobilised from the RV wall
2. The leaflet tissue is rotated clockwise and sutured together to create a cone-shaped valve
3. The base of the cone is sutured to the true tricuspid annulus (at its anatomically correct position)
4. The atrialized RV is plicated (folded) to reduce its volume
5. The RA is reduced
6. The ASD/PFO is closed (if appropriate)

Why "cone"? The normal tricuspid valve functions like an inverted cone — blood flows through the centre, and the leaflets coapt in a cone shape. The cone repair recreates this geometry.

Outcomes: > 90% freedom from reoperation at 10 years in experienced centres; significant improvement in functional class and exercise capacity; reduction in arrhythmias.

Indications: When not compatible with biventricular physiology ^[1]

• Neonates/infants with extremely severe TV malformation ^[1]
• Palliating older, symptomatic patients with very small functional RV ^[1]

This applies to Carpentier type D (and some type C) where the functional RV is simply too small to support the pulmonary circulation. In these patients, we abandon the RV as a pumping chamber and convert the circulation to single-ventricle physiology, where the LV drives both the systemic and (passively) the pulmonary circulations.

Step 1: Conversion into single ventricular physiology ^[1]

Step 2: Fontan procedure ^[1]

Cavopulmonary connection with extracardiac conduit ^[1]

The Fontan procedure is the culmination of the single-ventricle pathway. It is typically completed in stages in paediatric practice:

Why does this work? In the Fontan circulation, venous blood reaches the lungs by passive flow driven only by the pressure gradient between systemic venous pressure (CVP ~12–15 mmHg) and left atrial pressure (~5–8 mmHg). There is no pumping chamber for the pulmonary circulation. This only works if:

• PVR is low (any increase in PVR → inadequate pulmonary blood flow → hypoxia)
• The single ventricle (LV) has good function
• There is no significant AV valve regurgitation

Important for family-centred care:

• Mild Ebstein anomaly: pregnancy is usually well-tolerated with close monitoring
• Moderate-severe: high-risk pregnancy; pre-conception counselling essential
• Fontan circulation: pregnancy carries significant risk (arrhythmias, HF, thromboembolism)
• Genetic counselling: recurrence risk for CHD in offspring is ~3–5%
• If mother is on medications: ensure teratogenicity is reviewed (e.g., warfarin if on anticoagulation for mechanical valve or Fontan)

• Balance basic physical activity vs risk from exercise → guidelines available ^[14]
• Mild Ebstein: generally no restriction; avoid competitive/high-intensity sport if WPW is present (risk of sudden death)
• Moderate: individualised based on exercise testing
• Post-Fontan: significant exercise limitation is expected; encourage moderate activity within limits
• Patients with WPW and Ebstein: restrict competitive sport until the accessory pathway has been ablated or proven to be low-risk on EPS

Congestive HF ^[1] is the immediate life-threatening complication in severe neonatal Ebstein anomaly. The management of paediatric HF follows the staged approach (ACEI/BB/MRA/diuretics) outlined in the management section ^[14].

Why does LV failure occur in a primarily right-sided lesion? Two mechanisms:

• Ventricular interdependence: the LV and RV share the interventricular septum and are enclosed in the same pericardial sac. When the RV massively dilates, it pushes the septum leftward → compresses the LV cavity → reduced LV filling → reduced LV output. This is called "septal bowing."
• Reduced LV preload: if the RV cannot pump blood through the lungs effectively, less blood returns via the pulmonary veins to the LA → the LV is underfilled → reduced cardiac output, even though LV myocardial function may be intrinsically normal.

Even in mild Ebstein anomaly where the patient is asymptomatic in childhood ^[1], the chronic volume load from TR takes its toll over decades. The RV progressively dilates, its contractile function deteriorates, and the TR worsens — creating a vicious cycle.

Cyanosis may reappear in adulthood with progressive RV failure and TR ^[1] — the rising RA pressure drives increasing R-to-L shunting through the PFO/ASD, which had been quiescent since childhood.

Severe Ebstein anomaly (Celermajer grade 4, ratio ≥ 1.5) carries very high neonatal mortality, especially if associated with pulmonary atresia, hydrops fetalis, or severe biventricular dysfunction. The mortality can exceed 50% even with intervention.

SVT in adulthood: due to RA dilation and WPW syndrome (associated) ^[1]

The risk of sudden cardiac death in Ebstein anomaly is related to:

• Pre-excited AF (as above) — the primary mechanism in patients with WPW
• Ventricular tachycardia/fibrillation — from RV myocardial fibrosis and dysfunction
• Severe bradycardia — from associated conduction disease (RBBB, AV block)

The risk is highest in patients with:

• Documented WPW with short refractory period of the accessory pathway (< 250 ms)
• Severe RV dysfunction
• History of syncope
• History of resuscitated cardiac arrest

Prevention: Electrophysiology study (EPS) for risk stratification; catheter or surgical ablation of accessory pathways; ICD implantation in select high-risk patients.

This is a critically important complication that is unique to conditions with R-to-L intracardiac shunting.

Mechanism:

1. A venous thrombus forms (e.g., from deep vein thrombosis, or in the massively dilated RA itself)
2. Instead of travelling to the lungs (where it would cause a PE), the thrombus crosses the interatrial communication (PFO/ASD) via the R-to-L shunt
3. It enters the systemic arterial circulation
4. It lodges in a cerebral artery → ischaemic stroke
5. Or in other systemic arteries → limb ischaemia, renal infarction, mesenteric ischaemia, etc.

This is called "paradoxical" because the embolus originates in the venous system but causes an arterial event — seemingly "paradoxical" under normal physiology where venous thrombi only cause PE.

Risk factors for paradoxical embolism in Ebstein anomaly:

• Large interatrial communication with significant R-to-L shunt
• Severely dilated RA (promotes stasis → thrombus formation within the RA itself)
• Atrial fibrillation (further promotes stasis and thrombus formation, especially in the RA appendage)
• Cyanotic polycythaemia (see below) → hyperviscosity → increased thrombosis risk
• Immobility / dehydration / surgery → conventional DVT risk factors

Prevention: Anticoagulation (especially if AF is present or RA is severely dilated); ASD/PFO closure (when surgically appropriate); adequate hydration.

A related complication of R-to-L shunting: bacteraemia can bypass the pulmonary filter (normally the lungs filter out small bacterial emboli) and seed directly into the cerebral circulation → brain abscess. This is rare but more commonly associated with cyanotic CHD in general.

Mechanism: Chronic hypoxaemia → kidney detects low PaO₂ → increased erythropoietin (EPO) production → stimulates bone marrow → increased red blood cell production → elevated haemoglobin and haematocrit.

Why is this a problem? While the increased Hb temporarily improves oxygen-carrying capacity, excessive polycythaemia (Hct > 65–70%) causes:

• Hyperviscosity → sluggish blood flow → increased risk of thrombosis (stroke, DVT, PE)
• Headache, dizziness, visual disturbances — from hyperviscosity-related cerebral symptoms
• Iron deficiency (paradoxically) — the high rate of erythropoiesis depletes iron stores; iron-deficient red cells are microcytic and rigid → even worse rheology (blood flows less easily)
• Coagulopathy — severely polycythaemic patients can develop a consumption coagulopathy (depletion of clotting factors) → bleeding tendency despite the high Hct

Management:

• Adequate hydration (critical to prevent hyperviscosity crises)
• Iron supplementation if iron-deficient (counterintuitive but essential — iron-deficient RBCs are more rigid and worsen viscosity)
• Phlebotomy only for symptomatic hyperviscosity with Hct > 65% — NOT routine, as it can worsen iron deficiency
• Definitive treatment: correct the underlying cyanosis (surgical repair)

Chronic cyanotic CHD can produce a complex coagulopathy:

• Thrombocytopenia (mild; mechanism unclear, possibly splenic sequestration or consumption)
• Abnormal platelet function
• Reduced synthesis of clotting factors (if hepatic congestion from RV failure impairs liver function)
• Consumption coagulopathy from hyperviscosity

This is clinically relevant peri-operatively — always check a coagulation profile before surgery in cyanotic CHD patients.

The abnormal, dysplastic tricuspid valve in Ebstein anomaly creates a nidus for bacterial adherence → increased risk of infective endocarditis. The turbulent flow from TR also damages the endothelial surface, further promoting vegetation formation.

Key points:

• Right-sided IE (tricuspid valve) is more common than left-sided in Ebstein anomaly
• Right-sided IE may present with septic pulmonary emboli → multiple peripheral lung abscesses, cough, pleuritic chest pain, haemoptysis
• Common organisms: Staphylococcus aureus (most common overall in right-sided IE), viridans streptococci, enterococci
• Diagnosis: Modified Duke criteria ^[16]
• Prevention: Antibiotic prophylaxis before high-risk dental procedures (amoxicillin 50 mg/kg PO, max 2g, 30–60 min before procedure; clindamycin 20 mg/kg, max 600 mg, if penicillin-allergic). Current guidelines recommend prophylaxis for patients with prosthetic valves, prior IE, unrepaired cyanotic CHD, or repaired CHD with residual defects

Patients with reduced pulmonary blood flow may have impaired pulmonary defence mechanisms. Additionally, pulmonary congestion (if left-sided failure develops) predisposes to pneumonia.

The Fontan circulation, while life-saving, creates a fundamentally abnormal physiology with significant long-term complications: