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Summary Table

Category	Details
Risk Factors	Maternal lithium use during first trimester; maternal benzodiazepine use; family history of congenital heart disease
Etiology	Congenital malformation: apical displacement of the septal and posterior leaflets of the tricuspid valve into the right ventricle
Patient Presentation	Cyanosis in neonates (severe forms); progressive dyspnea and exercise intolerance in adolescents/adults; palpitations from arrhythmias
Classic Physical Exam	Widely split S1 and S2; holosystolic murmur of tricuspid regurgitation at the left lower sternal border; right-sided S3 or S4; cyanosis and clubbing in advanced cases
Key Diagnostic Results	CXR: "box-shaped" or "wall-to-wall" heart (massive cardiomegaly from right atrial enlargement); ECG: right atrial enlargement, right bundle branch block, Wolff-Parkinson-White (WPW) pattern; Echocardiography: apical displacement of tricuspid valve leaflets $\geq 8\ mm/m^2$ from the annulus
Management	Mild/asymptomatic: observation and monitoring; symptomatic: surgical tricuspid valve repair (cone reconstruction); arrhythmias: catheter ablation for accessory pathways; neonates with severe cyanosis: prostaglandin E1 to maintain ductal patency
Keywords	"Apical displacement of tricuspid valve"; "atrialized right ventricle"; "box-shaped heart"; "maternal lithium exposure"; "WPW pattern on ECG"; "tricuspid regurgitation in a neonate"

1. Pathophysiology

Ebstein anomaly is a congenital cardiac defect defined by failure of delamination of the septal and posterior leaflets of the tricuspid valve from the underlying right ventricular myocardium during embryologic development. Instead of attaching at the true tricuspid annulus, these leaflets are displaced downward (apically) into the right ventricle. The anterior leaflet, while attached at the correct annular position, is typically elongated, redundant, and tethered by abnormal chordal attachments, giving it a "sail-like" appearance.

This downward displacement creates a critical anatomic consequence: the portion of the right ventricle between the true annulus and the displaced leaflets becomes functionally incorporated into the right atrium. This segment is called the atrialized right ventricle. It has a thin, dilated wall that contracts poorly because it retains ventricular myocardium receiving atrial-level pressures. The result is a functionally smaller right ventricle with reduced capacity to eject blood into the pulmonary artery.

Because the malformed tricuspid valve cannot coapt properly, tricuspid regurgitation develops. Blood regurgitates backward from the right ventricle into the enormously dilated right atrium during systole. This volume overload further enlarges the right atrium, which explains the characteristic "box-shaped" cardiomegaly seen on chest radiography. The combination of a small functional right ventricle and ongoing regurgitation reduces effective pulmonary blood flow. When this reduction is severe, desaturated blood shunts right-to-left through a patent foramen ovale or atrial septal defect (present in the majority of patients), producing cyanosis.

The abnormal tricuspid annular geometry also explains the strong association with accessory conduction pathways, particularly right-sided pathways responsible for the Wolff-Parkinson-White (WPW) pattern. The displaced and abnormal valve tissue disrupts the normal fibrous insulation between the atria and ventricles, allowing anomalous electrical connections. These pathways predispose patients to supraventricular tachycardia, atrial flutter, and atrial fibrillation, which are often the presenting complaint in adolescents and adults with milder anatomic forms.

2. Classification and Clinical Manifestation

The clinical severity of Ebstein anomaly varies enormously depending on the degree of leaflet displacement and right ventricular dysfunction. The Carpentier classification is the most tested framework:

Type	Anatomic Description	Clinical Manifestation
Type A	Adequate volume of the true right ventricle; mobile anterior leaflet; mild apical displacement	Often asymptomatic or mildly symptomatic; diagnosed incidentally or in adulthood; mild tricuspid regurgitation; exercise tolerance may be near-normal
Type B	Large atrialized component of right ventricle; mobile anterior leaflet but the body of the ventricle contracts poorly; significant displacement	Exercise intolerance, dyspnea on exertion, fatigue; intermittent cyanosis with exertion; palpitations from arrhythmias; right heart failure symptoms may develop in early adulthood
Type C	Anterior leaflet severely restricted by shortened chordae and fibrous bands; limited mobility; contracted true RV	Cyanosis at rest; signs of right heart failure (hepatomegaly, peripheral edema, jugular venous distension); poor exercise capacity; arrhythmias frequent
Type D	Near-complete atrialization of the right ventricle; tricuspid valve tissue forms a continuous sac adherent to the ventricular wall ("Uhl-like" morphology)	Severe neonatal cyanosis; functional pulmonary atresia because the tiny right ventricle cannot generate forward flow; prostaglandin-dependent circulation; high mortality without intervention

Age-based presentation patterns:

Age Group	Typical Presentation
Neonate	Severe cyanosis unresponsive to supplemental oxygen; respiratory distress; heart failure; murmur; profound cardiomegaly on CXR
Infant/Child	Failure to thrive; mild cyanosis with feeding or exertion; murmur detected during routine examination
Adolescent/Adult	Palpitations and arrhythmia (often the initial presentation); progressive exercise intolerance; dyspnea; right heart failure; paradoxical embolism causing stroke or TIA

3. Diagnostic Workup

Test	Role	Key Findings
Chest X-Ray	Best initial test (screening)	"Box-shaped" or "wall-to-wall" heart silhouette due to right atrial enlargement; decreased pulmonary vascular markings (reduced pulmonary blood flow)
ECG	Initial evaluation	Tall, broad P waves (right atrial enlargement, "Himalayan P waves"); right bundle branch block (RBBB); low-voltage QRS in right precordial leads; WPW pattern (short PR, delta wave) in 10-25% of patients; first-degree AV block
Transthoracic Echocardiography	Most accurate (confirmatory) test	Apical displacement of the septal leaflet $\geq 8\ mm/m^2$ body surface area from the mitral valve annular plane; "sail-like" anterior leaflet; atrialized portion of right ventricle; severity of tricuspid regurgitation on Doppler; presence and direction of interatrial shunting
Cardiac MRI	Adjunct for surgical planning	Precise quantification of right ventricular volumes; assessment of RV function; delineation of atrialized versus functional RV segments
Electrophysiologic Study	If arrhythmia is present	Identification and mapping of accessory pathways for catheter ablation; assessment of atrial flutter circuits
Pulse Oximetry	Screening in neonates	Resting oxygen saturation below 90% suggests right-to-left shunting

The chest X-ray is typically the first clue. In a cyanotic neonate, a dramatically enlarged cardiac silhouette with oligemic lung fields immediately raises suspicion for Ebstein anomaly. The "box-shaped" heart is one of the most recognizable radiographic patterns in pediatric cardiology and differs from the boot-shaped heart of Tetralogy of Fallot or the egg-on-a-string appearance of transposition.

The ECG provides additional supportive evidence. The combination of right atrial enlargement plus RBBB plus WPW pattern is highly suggestive of Ebstein anomaly and is a frequently tested triad. Not every patient demonstrates WPW, but when a question stem includes all three ECG findings together, it is virtually diagnostic.

Echocardiography is the gold standard. The diagnosis requires demonstration of apical displacement of the septal tricuspid leaflet by at least $8\ mm/m^2$ below the mitral annular insertion on an apical four-chamber view. Echocardiography also quantifies regurgitation severity, evaluates right ventricular function, identifies associated defects (ASD, VSD, pulmonary stenosis), and detects shunting across the atrial septum.

Cardiac MRI is not required for diagnosis but is increasingly used preoperatively. Electrophysiologic studies are reserved for patients with documented or suspected arrhythmias, particularly when catheter ablation of an accessory pathway is planned.

4. Management and Treatment

Clinical Scenario	Management	Details
Severe neonatal cyanosis	Prostaglandin E1 (alprostadil)	0.05-0.1 mcg/kg/min IV continuous infusion to maintain ductal patency and ensure pulmonary blood flow; bridge to surgery
Neonatal stabilization	Nitric oxide; mechanical ventilation	Reduce pulmonary vascular resistance to improve forward flow; optimize oxygenation
Symptomatic older child/adult with significant TR	Surgical tricuspid valve repair (cone reconstruction)	Current procedure of choice; mobilizes the anterior and posterior leaflets, rotates them to create a cone-shaped valve at the true annular level; performed with ASD closure
Tricuspid valve not repairable	Tricuspid valve replacement	Bioprosthetic valve preferred in young patients to avoid lifelong anticoagulation; mechanical valve if bioprosthetic is not feasible
Severe neonatal form (Type D / functional pulmonary atresia)	Starnes procedure (RV exclusion)	Patch closure of the tricuspid valve orifice converting the circulation to single-ventricle physiology; followed by staged Glenn and Fontan procedures
Supraventricular tachycardia / WPW	Catheter ablation of accessory pathway	Performed either as standalone procedure or at the time of surgical repair; high success rate for right-sided pathways
Atrial flutter / atrial fibrillation	Rate control or rhythm control; anticoagulation	Beta-blockers or calcium channel blockers for rate control; antiarrhythmic drugs (amiodarone, flecainide) for rhythm control; anticoagulation if atrial fibrillation is present due to stroke risk from paradoxical embolism
Asymptomatic, mild disease	Observation	Regular clinical follow-up with serial echocardiography every 1-2 years; exercise restriction counseling if significant TR or arrhythmia
Paradoxical embolism prevention	ASD/PFO closure	Performed surgically during valve repair or via transcatheter closure
Endocarditis prophylaxis	Antibiotic prophylaxis	Indicated for patients with prosthetic valves, prior endocarditis, unrepaired cyanotic defects, or repaired defects with residual shunts

In the neonatal period, the immediate priority is maintaining oxygenation. Prostaglandin E1 keeps the ductus arteriosus open, allowing left-to-right flow from the aorta into the pulmonary artery to bypass the dysfunctional right ventricle. This is the "next best step" for any cyanotic neonate with suspected ductal-dependent pulmonary circulation.

As pulmonary vascular resistance drops naturally over the first days of life, some neonates with moderate forms improve spontaneously because the right ventricle can eject more effectively against lower resistance. These patients can be managed conservatively and monitored.

For older children and adults with progressive symptoms, the cone reconstruction (da Silva technique) is the current preferred surgical approach. It restores near-normal tricuspid valve function by reconstructing the valve into a conical shape at the anatomic annulus. Outcomes are favorable, with low operative mortality and durable long-term results.

In the most severe neonatal forms where biventricular repair is not possible, the Starnes procedure commits the patient to single-ventricle palliation. The tricuspid valve is patched closed, the atrial septum is widely opened, and a systemic-to-pulmonary artery shunt (modified Blalock-Taussig shunt) is placed. Subsequent staged operations (bidirectional Glenn at 4-6 months, Fontan at 2-4 years) complete the single-ventricle pathway.

Arrhythmia management is a parallel consideration. Accessory pathways should be ablated whenever possible, especially before surgical repair, to reduce perioperative arrhythmia risk. Avoid digoxin in patients with WPW because it shortens the refractory period of the accessory pathway and can trigger ventricular fibrillation during atrial fibrillation.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Is Similar	Key Discriminator
Tetralogy of Fallot	Cyanotic congenital heart disease in a neonate; decreased pulmonary blood flow	Boot-shaped heart (coeur en sabot) on CXR, not box-shaped; right ventricular hypertrophy on ECG rather than right atrial enlargement; tet spells (hypercyanotic episodes) relieved by squatting; echocardiography shows overriding aorta and VSD
Tricuspid Atresia	Cyanosis with decreased pulmonary blood flow; right-to-left atrial shunting	Left axis deviation and left ventricular hypertrophy on ECG (distinguishing hallmark); absent tricuspid valve rather than displaced; obligatory ASD for survival
Pulmonary Atresia with Intact Ventricular Septum	Cyanotic neonate with ductal-dependent pulmonary circulation; prostaglandin-responsive	No tricuspid valve displacement on echo; small right ventricle with thick walls (hypertrophied, not atrialized); no WPW pattern
Atrial Septal Defect (Secundum)	Fixed widely split S2; right heart enlargement on imaging	Acyanotic (left-to-right shunt); no tricuspid valve displacement; no WPW association; right ventricular volume overload but normal tricuspid valve morphology
WPW Syndrome (isolated)	Delta wave and short PR interval on ECG; supraventricular tachycardia	No structural heart disease on echocardiography; no cyanosis; no cardiomegaly; normal tricuspid valve anatomy
Uhl Anomaly	Paper-thin right ventricle; right heart failure	Extremely rare; absence of right ventricular myocardium (replaced by fibrous tissue) rather than valve displacement; no atrialized ventricle concept; tricuspid valve is anatomically normal

6. Traps and High-Yield Pearls

The most common way students miss Ebstein anomaly questions is by not connecting the ECG findings to the structural diagnosis. A question stem may present an adolescent with palpitations and a WPW pattern on ECG without immediately obvious cyanosis. Students fixate on the arrhythmia and select "WPW syndrome" or "SVT" without recognizing that the combination of WPW plus right atrial enlargement plus RBBB should trigger suspicion for an underlying structural lesion. When the echocardiogram is then described as showing an apically displaced tricuspid valve, the diagnosis becomes clear, but students who did not anticipate a structural cause will have already committed to the wrong answer.

Another trap involves the maternal exposure history. A question may describe a neonate born to a mother on lithium for bipolar disorder who presents with cyanosis and cardiomegaly. Students who do not recall the lithium-Ebstein association may default to more common cyanotic heart diseases. While the absolute risk increase from lithium exposure is modest compared to older estimates, it remains a heavily tested link.

The radiographic appearance is another discriminator that students frequently confuse. The "box-shaped heart" of Ebstein anomaly must be distinguished from the "boot-shaped heart" of Tetralogy of Fallot and the "egg-on-a-string" silhouette of transposition. Each silhouette is essentially a one-line diagnosis on the exam.

Finally, students must remember that not all Ebstein anomaly patients are cyanotic. Mild forms present in adulthood with arrhythmias alone, no shunting, and no desaturation. The core competency being tested is the ability to recognize the disease across a wide clinical spectrum, from a critically ill cyanotic neonate to an otherwise healthy young adult with recurrent palpitations, and to connect both presentations to the same underlying pathology: displacement of the tricuspid valve leaflets into the right ventricle.

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