8.3 Ebstein Anomaly, Tricuspid Dysplasia & Congenital Pulmonary Stenosis/Atresia

8.3 Ebstein Anomaly, Tricuspid Dysplasia & Congenital Pulmonary Stenosis/Atresia

Clinical Core: Right-sided obstructive and valvular anomalies in pediatric cardiology present across a vast clinical spectrum—ranging from benign isolated valvar pulmonary stenosis to catastrophic neonatal emergencies such as pulmonary atresia with intact ventricular septum (PA/IVS) and severe Ebstein anomaly. Pediatric sonographers must master precise apical displacement indexing for the tricuspid valve, differentiate pliable doming from myxomatous dysplastic pulmonic leaflets, localize mid-cavitary muscular gradients in double-chambered right ventricle, and rigorously interrogate ventriculocoronary connections to prevent fatal interventions in patients with right ventricular-dependent coronary circulation.

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Ebstein Anomaly of the Tricuspid Valve

Ebstein anomaly accounts for <1% of all congenital cardiac malformations. It is embryologically caused by failure of delamination of the tricuspid valve tissue from the underlying right ventricular myocardium during the 8th to 12th weeks of gestation.

1. Anatomical Hallmarks & Diagnostic 2D Criteria

• Normal vs. Pathological Apical Displacement: In the normal heart, the septal tricuspid leaflet inserts slightly more apical than the anterior mitral valve leaflet at the cardiac crux by up to 5 to 8 mm/m$^2$ BSA. In Ebstein anomaly, there is true pathological apical displacement of the hinge points of the septal and posterior tricuspid leaflets by $\ge 8\text{ mm/m}^2$ BSA (or $>15\text{ mm}$ in older children and adolescents) relative to the anterior mitral leaflet insertion.
• The "Atrialized" Right Ventricle (aRV): The portion of the anatomical right ventricle situated between the true atrioventricular fibrous annulus and the apically displaced functional tricuspid annulus becomes functionally and electrophysiologically integrated into the right atrium. This atrialized RV wall is markedly thinned, hypocontractile, or dyskinetic, paradoxically expanding during ventricular systole and acting as a compliance sink that absorbs kinetic energy.
• The Functional Right Ventricle (fRV): The remaining true right ventricle (consisting of the trabecular and infundibular components) is compressed, small in volume, and frequently dysfunctional.
• Anterior Tricuspid Leaflet Morphology: The anterior leaflet is not apically displaced; rather, it originates from the true AV annulus. It is characteristically massively enlarged, redundant, and elongated, billowing into the RV cavity like a "sail in the wind" (sail-like leaflet). However, its distal free margin is frequently tethered to the RV free wall or trabeculations by abnormal, shortened chordae, restricting effective systolic excursion.

Normal Cardiac Crux                     Ebstein Anomaly Crux
┌────────────────────────────┐          ┌────────────────────────────┐
│      LA      │     RA      │          │      LA      │     RA      │
│              │             │          │              │             │
│  Mitral ─────┼─            │          │  Mitral ─────┼─ True TV    │
│  Annulus     │             │          │  Annulus     │  Annulus    │
│              ├─ TV Annulus │          │              │             │
│              │  (Normal    │          │              │ aRV (Thin)  │
│              │   Offset    │          │              │             │
│              │  <8 mm/m²)  │          │              ├─ Displaced  │
│              │             │          │              │  TV Leaflet │
│      LV      │     RV      │          │      LV      │  (≥8 mm/m²) │
│              │             │          │              │     fRV     │
└────────────────────────────┘          └────────────────────────────┘

2. Anatomical & Echocardiographic Severity Classifications

A. Carpentier Classification (Morphological Spectrum)

• Type A: Mild apical displacement; adequate functional RV volume; mobile, unrestrictive anterior leaflet.
• Type B: Substantial apical displacement with a large atrialized RV component; anterior leaflet moves freely; functional RV is moderately reduced.
• Type C: Marked apical displacement; anterior leaflet is severely restricted and tethered to the RV free wall, causing functional RVOT obstruction.
• Type D: Near-complete failure of delamination; the entire right ventricle (except for a diminutive infundibulum) is atrialized into a thin-walled sac ("sac-like" right ventricle).

B. The Great Ormond Street Echocardiography (GOSE) Score / Celermajer Index

Measured in the apical four-chamber view at end-diastole, the Celermajer index quantifies the ratio of right-sided non-functional chamber area to functional pump chamber area:

$\text{GOSE Index} = \frac{\text{Area of Right Atrium (RA)} + \text{Area of Atrialized RV (aRV)}}{\text{Area of Functional RV (fRV)} + \text{Area of Left Atrium (LA)} + \text{Area of Left Ventricle (LV)}}$

• Grade 1 (Mild): Ratio $< 0.50$ (neonatal mortality <10%)
• Grade 2 (Moderate): Ratio $0.50\text{ to }0.99$ (neonatal mortality ~10% to 20%)
• Grade 3 (Severe): Ratio $1.00\text{ to }1.49$ (neonatal mortality ~40% to 50%)
• Grade 4 (Extreme): Ratio $\ge 1.50$ (neonatal mortality >80% to 100% without emergent transplantation or complex univentricular palliation)

3. Hemodynamics, Shunts & Electrophysiology

• Severe Tricuspid Regurgitation: Generates a low-velocity, broad, eccentric regurgitant jet originating deep within the RV cavity from the displaced functional orifice.
• Interatrial Shunting: An interatrial communication (PFO or secundum ASD) is present in 80% to 90% of patients. Elevated right atrial pressure forces right-to-left shunting, producing systemic cyanosis.
• Functional Pulmonary Atresia: In severe neonatal Ebstein anomaly, the combination of extreme tricuspid regurgitation and a tiny, dyskinetic functional RV prevents the RV from generating enough pressure to overcome pulmonary arterial resistance. The pulmonary valve fails to open in systole (functional pulmonary atresia), with pulmonary flow supplied entirely by retrograde flow through a patent ductus arteriosus.
• Wolff-Parkinson-White (WPW) Syndrome: Observed in 15% to 25% of Ebstein patients. Pre-excitation arises from accessory atrioventricular pathways (frequently multiple and localized along the right posteroseptal and posterolateral malformed tricuspid annulus).

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Congenital Valvar Pulmonary Stenosis

Valvar pulmonary stenosis accounts for 8% to 10% of all congenital cardiac defects.

1. Classic Dome-Shaped Valvar PS

• Morphology: Leaflets are thin, pliable, and mobile, but exhibit commissural fusion. During systole, the leaflets cannot separate fully, bulging forward into the main pulmonary artery as a mobile, conical "dome" with a narrowed central orifice.
• Post-Stenotic MPA Dilatation: High-velocity jet turbulence produces marked aneurysmal dilation of the main pulmonary artery (MPA) and frequently the left pulmonary artery (LPA). The presence or degree of post-stenotic dilatation does not correlate with hemodynamic severity.
• Percutaneous Balloon Pulmonary Valvuloplasty (BPV): First-line treatment of choice, achieving excellent long-term results (>90% success) by tearing the fused commissures.

2. Dysplastic Pulmonic Valve & Noonan Syndrome

• Morphology: The leaflets are markedly thickened, rubbery, nodular, and myxomatous with excessive disorganized spongiosa. There is NO commissural fusion; obstruction is caused by severe leaflet rigidity, bulkiness, and a narrowed, hypoplastic pulmonary annulus.
• Absence of Post-Stenotic Dilation: Because the leaflets do not dome and flow is not focused into a central jet, the post-stenotic MPA is rarely dilated and is often hypoplastic.
• Noonan Syndrome: Dysplastic pulmonary valves occur in 50% to 60% of individuals with Noonan syndrome (most frequently caused by heterozygous gain-of-function mutations in the PTPN11 gene on chromosome 12q24, followed by SOS1, RAF1, and KRAS in the RAS-MAPK pathway). Associated features include short stature, webbed neck, pectus excavatum/carinatum, hypertelorism, and coexisting hypertrophic cardiomyopathy.
• Resistance to Balloon Valvuloplasty: Because there are no fused commissures to split and the thick, myxomatous leaflets recoil elastically, BPV is typically ineffective. Surgical intervention (pulmonary valvulectomy, transannular patch, or RVOT reconstruction) is usually required.

3. Doppler Severity Stratification

$\Delta P_{\text{peak}} = 4 \times (v_{\text{max}})^2$

• Mild PS: Peak gradient $< 36\text{ mmHg}$ ($v_{\text{max}} < 3.0\text{ m/s}$)
• Moderate PS: Peak gradient $36\text{ to }64\text{ mmHg}$ ($v_{\text{max}} = 3.0\text{ to }4.0\text{ m/s}$)
• Severe PS: Peak gradient $> 64\text{ mmHg}$ ($v_{\text{max}} > 4.0\text{ m/s}$)
• Critical PS (Neonate): Cyanosis and ductal-dependent pulmonary blood flow with right-to-left interatrial shunting, regardless of the numerical Doppler gradient.

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Subpulmonic & Cavitary RV Obstructions

1. Double-Chambered Right Ventricle (DCRV)

• Pathoanatomy: Anomalous, severely hypertrophied muscular bands (aberrant moderator band, hypertrophied septoparietal trabeculations, or displaced crista supraventricularis) divide the right ventricular cavity into two distinct pressure chambers:
  1. High-Pressure Proximal Chamber: Consisting of the RV inlet and apex, exposed to systemic or suprasystemic systolic pressure.
  2. Low-Pressure Distal Chamber: Consisting of the infundibulum and RVOT, exposed to normal pulmonary arterial pressures.
• Associated VSD: A ventricular septal defect (most commonly perimembranous) is present in 80% to 90% of DCRV cases, almost invariably opening into the high-pressure proximal chamber.
• Doppler Profile: Continuous-wave Doppler displays a high-velocity, late-peaking systolic jet originating deep within the body of the right ventricle, distinctly separated from the pulmonary valve annulus.

2. Branch Pulmonary Artery Stenosis (Peripheral PS / PPS)

• Syndromic Associations:
  • Alagille Syndrome: Mutations in JAG1 (98%) or NOTCH2. Associated with bile duct paucity, cholestatic jaundice, butterfly vertebrae, prominent forehead, pointed chin, and peripheral pulmonary artery stenosis in >90% of cases.
  • Williams-Beuren Syndrome: Bilateral branch pulmonary artery stenosis coexists with supravalvular AS in up to 70% of cases.

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Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)

PA/IVS is a cyanotic defect characterized by complete anatomical obstruction of the pulmonary valve with an intact ventricular septum and concordant AV/VA alignments.

1. Right Ventricular Cavity Morphology & Repair Pathways

Because the ventricular septum is intact, the right ventricle is a closed muscular chamber in utero, resulting in extreme intracavitary hypertension ($>120\text{ to }180\text{ mmHg}$):

• Tripartite RV (Mild Hypoplasia): Inlet, trabecular, and outlet components are all present. Adequate volume to support two-ventricle repair.
• Bipartite RV (Moderate Hypoplasia): Inlet and outlet present; trabecular apical portion is obliterated by concentric muscular hypertrophy. Candidate for 1.5-ventricle repair (bidirectional Glenn shunt + RV decompression).
• Unipartite RV (Severe Hypoplasia): Only the inlet portion is identifiable; trabecular and infundibular portions are absent. Slit-like cavity mandating staged single-ventricle palliation (Fontan pathway).

2. Ventriculocoronary Connections & RV-Dependent Coronary Circulation (RVDCC)

• Ventriculocoronary Arterial Connections (VCACs / Myocardial Sinusoids): Chronic extreme RV systolic pressure forces blood from the RV cavity backward through persistent embryonic myocardial sinusoids directly into the epicardial coronary arterial branches.
• Right Ventricular-Dependent Coronary Circulation (RVDCC): Occurs when proximal stenosis, interruption, or ostial atresia of the native coronary arteries prevents normal antegrade perfusion from the aorta. In this setting, myocardial perfusion of that coronary territory depends entirely on high-pressure desaturated blood driven retrograde from the right ventricle during systole.
• THE FATAL TRAP OF RV DECOMPRESSION: If RVDCC is present, any procedural decompression of the right ventricle (radiofrequency perforation, balloon valvuloplasty, or surgical patch) is ABSOLUTELY CONTRAINDICATED. Decompressing the RV abruptly drops RV cavity systolic pressure below coronary perfusion pressure, immediately terminating blood flow to the dependent myocardium, inducing catastrophic transmural myocardial infarction, ventricular fibrillation, and death. Patients with RVDCC must undergo single-ventricle palliation.

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Comparison of Right Heart Obstructive & Valvar Lesions

Clinical Pearls & Sonographic Traps

[!WARNING] The Absolute Contraindication to RV Decompression in RVDCC: In neonates with PA/IVS, detecting retrograde color Doppler flow from the RV cavity into myocardial sinusoids and epicardial coronary vessels mandates exhaustive multiplane interrogation of the coronary tree. If proximal coronary stenosis or interruption is present (RV-dependent coronary circulation), never attempt radiofrequency pulmonary valve perforation or surgical RV decompression. Decompressing the RV cavity abruptly stops coronary perfusion to the dependent myocardium, causing instantaneous, fatal transmural myocardial infarction.

[!TIP] Normal vs. Pathological Tricuspid Valve Offset: Remember that the normal pediatric heart exhibits physiological apical displacement of the tricuspid septal leaflet relative to the anterior mitral leaflet of up to 5 to 8 mm/m$^2$ BSA. Only apical displacement greater than or equal to 8 mm/m$^2$ BSA establishes the diagnosis of Ebstein anomaly. In infants, calculate the displacement index by dividing the absolute distance (in mm) by the body surface area (BSA, in m$^2$).

[!NOTE] DCRV vs. Infundibular Pulmonic Stenosis: To distinguish a double-chambered right ventricle from isolated infundibular pulmonic stenosis, carefully assess the position of the high-velocity jet relative to the pulmonary valve annulus. In DCRV, the anomalous muscle bundles and the resulting turbulent acceleration originate deep within the middle of the RV body, well below the infundibular chamber, with a characteristic late-peaking systolic spectral Doppler contour.