Ebstein’s anomaly is a rare congenital heart malformation of the right ventricle and tricuspid valve. Failure of delamination of the tricuspid valve, especially of the posterior and septal leaflets from the underlying myocardium, results in variable degree of tricuspid valve and right ventricular deformity as first described by Wilhelm Ebstein,¹ a German pathologist.

The natural history of this malformation is influenced by a high rate of intrauterine and neonatal death, especially when the anomaly is associated with severe deformity of the tricuspid valve and cyanosis. At the other end of the spectrum, patients with mild dysfunction of the tricuspid valve may remain asymptomatic until late adult life.^2,3 Management, therefore, often requires a choice between a conservative approach and operative intervention. Currently available surgical techniques have demonstrated survival and functional benefit even for those patients in whom the malformation is severe.^4–7

Ebstein’s anomaly occurs relatively late in heart development, as the inner surfaces of the right atrium and ventricle are undermined distal to the atrioventricular sulcus. The anterior leaflet is formed earlier than the posterior and septal leaflets, during the third and fourth month of gestation, which may explain the differences in maturation.

The anomaly is characterized by the following (Fig. 85-1):

1. 
   

   Tricuspid valve malformations

   
   
   
   
   1. 
      

      The septal and posterior leaflets are displaced toward the apex of the right ventricle with a variable degree of adherence to the myocardium (spiral failure of delamination).

      
      
   2. 
      

      The sail-like, redundant anterior leaflet has a normal attachment to the tricuspid valve annulus, but is frequently fenestrated, having chordal attachments to the ventricular wall and eventually also linear attachments (fibrous and muscular attachments) between the leaflet and the myocardium.

   
   
2. 
   

   The right ventricle is malformed and consists of

   
   
   
   
   1. 
      

      A thin-walled “atrialized” component, defined as a segment of the right ventricle, from the level of the “true” tricuspid annulus to the level of displacement of the septal and posterior leaflets;

      
      
   2. 
      

      A thick-walled functional component (“true right ventricle cavity”), consisting of apical and outlet portions, often obstructed by chordal attachments of the anterior leaflet of the tricuspid valve. The inlet portion is small or nonexistent. The cavity of the functional right ventricle is usually smaller and, histologically contains fewer myocytes and more fibrous tissue than a normal right ventricle.

The most commonly associated anomaly is an atrial septal defect or persistent foramen ovale (in about 90 percent of the cases). Survival in symptomatic newborns with severe obstruction to pulmonary outflow depends on the presence of a patent ductus arteriosus in addition to atrial-level communication. The Wolff–Parkinson–White syndrome is present in about 10 percent of the cases. Association with an atrioventricular septal defect, ventricular septal defect, tetralogy of Fallot, congenitally corrected transposition of the great arteries, aortic coarctation or other defects is rarely observed.

The majority of cases of Ebstein’s anomaly are sporadic, but familial cases have been reported. Gestational exposure to lithium increases the relative risk of any malformation, including cardiac anomalies, by two to three times.

Tricuspid Valve

The degree of displacement, hypoplasia, and tethering of the leaflets, as well as existing fenestrations and the dilation of the right atrioventricular junction, determine the degree of regurgitation. The large anterior leaflet with the linear attachments may divide the inlet from the muscular portion, mimicking tricuspid stenosis or even tricuspid atresia if there are no leaflet fenestrations. Attachments of the anterior leaflet to the right ventricular outflow tract can also inhibit the normal flow to the pulmonary artery, inducing the development of pulmonary atresia in about 10 percent of infants.

Right Ventricle

The two parts of the right ventricle show a specific movement pattern affecting forward flow. During atrial systole, the atrialized component balloons out, which may significantly reduce forward flow into the functional component of the right ventricle. During ventricular systole, the atrialized component of the right ventricle contracts, pushing the blood backward to the right atrium, resulting in an increase in systemic venous pressure and subsequent right atrial dilatation, even in the absence of significant tricuspid valve regurgitation.

Left Ventricle

Right ventricular dilation can induce the interventricular septum to bulge toward the left and thus significantly compromise left ventricular function (ventricular interdependence).

Postnatal Hemodynamics

Depending on the severity of Ebstein’s anomaly and the associated heart defects, postnatal hemodynamics can be extremely variable.

Mild Displacement of the Tricuspid Valve

With mild displacement of the posterior and septal leaflets of the tricuspid valve and good function of the right ventricle, postnatal circulation will be normal, with only mild tricuspid regurgitation and sufficient antegrade pulmonary blood flow.

Moderate Displacement of the Tricuspid Valve

A higher degree of displacement results in a higher grade of tricuspid regurgitation, enhanced by the postnatally high pulmonary vascular resistance. Elevated right atrial pressure promotes right-to-left shunting on an atrial level with a variable degree of cyanosis, depending on the ductal flow. If the pulmonary outflow tract is patent, ductal flow increases the right ventricle afterload and has a negative impact on tricuspid valve function. Clinically tolerable closure of the duct with sufficient antegrade pulmonary blood flow is a positive prognostic factor in infants.⁸ In the case of pulmonary atresia, the duct may be the only source of pulmonary blood flow.

Severe Displacement of the Tricuspid Valve

Severe displacement of the posterior and septal leaflets results in severe tricuspid regurgitation and a large atrialized component of the right ventricle. If the duct is open, the right ventricle is usually not capable of opening the pulmonary valve, mimicking pulmonary atresia. Systemic venous return is shunted to the left ventricle across the atrial septal defect, and the resulting physiology is similar to that of tricuspid or pulmonary atresia.

Hemodynamics Beyond Infancy

Children with minor tricuspid regurgitation and a functioning right ventricle come to clinical attention because of associated lesions. Volume overload of the right ventricle, due to a left-to-right shunt at the atrial level, might accelerate the development of important tricuspid regurgitation. With more prominent tricuspid regurgitation, cyanosis may occur on exertion, unmasking the limited capability to augment right ventricular output.

Arrhythmias

Arrhythmias occur in 20 to 30 percent of all patients. Deficient fibrous development of the tricuspid valve annulus, with accessory muscular pathways across the atrioventricular junction, results in a high incidence of preexcitation (Wolf–Parkinson–White syndrome). A stretched, fibrotic and dysplastic right ventricular myocardium is a substrate for ventricular arrhythmias. Incomplete fibrous encasement of the atrioventricular node and the bundle of His can cause reentry tachycardias. Rapid conduction of atrial arrhythmias or ventricular tachycardias accounts for 3 to 10 percent of sudden death.

Patients may present at any age. Prenatally, the fetus may suffer from tachyarrhythmia, pulmonary parenchymal hypoplasia secondary to cardiomegaly, or hydrops. Newborns and young infants often present with cyanosis, tachypnea, enlarged liver, and other symptoms of cardiac failure. Neonates disclosing the most extreme forms of this anomaly will become critically ill immediately after birth, requiring intensive medical treatment and ventilatory support. Beyond infancy, the child may show limited cyanosis during exercise, but there is rarely failure to grow and development of congestive heart failure with cardiomegaly. With increasing age, cyanosis and limited exercise tolerance, with dyspnea and palpitations, will become more prominent. The dominant mode of clinical presentation in adolescents and young adults is arrhythmia and limited exercise tolerance. Mild forms of Ebstein’s anomaly may not become symptomatic until adulthood.³

Physical Examination

Prominence or asymmetry of the chest is linked to the dilated right heart. Cyanosis and digital clubbing are secondary to a chronic right-to-left shunt. Multiple abnormal sounds and murmurs are evident on cardiac auscultation. The first and the second heart sounds are widely split due to increased excursion of the anterosuperior leaflet, the delayed closure of the abnormal tricuspid valve, and the late closure of the pulmonary valve secondary to right bundle branch block. A systolic murmur usually suggests either some associated cardiac anomaly or tricuspid regurgitation.

Chest X-Ray

Variable cardiomegaly, secondary to enlargement of the right atrium, is typical. Pulmonary vascular markings are normal or diminished, according to the degree of right ventricular outflow tract obstruction (Fig. 85-2).

Electrocardiogram

Characteristically, the ECG is abnormal, presenting with a right bundle branch block and prominent P-waves that reflect the enlargement of the right atrium. The P-R interval may be prolonged up to a first degree of AV block, and the occurrence of the Wolff-Parkinson-White syndrome is not infrequent. Atrial rhythm problems such as atrial fibrillation, atrioventricular nodal reentry tachycardia, focal atrial tachycardia, and atrial flutter are common in older patients. Holter monitoring should therefore be performed repeatedly, especially in the symptomatic patient.

Echocardiography

Echocardiography is diagnostic, not only for outlining the morphology and physiology, but also for assessing the suitability for reconstructive surgery (Fig. 85-3). The evaluation should clarify:

1. 
   

   The morphology of the tricuspid valve

   
   
   
   
   1. 
      

      Displacement of the annular hingepoint of the septal and posterior leaflets

      
      
   2. 
      

      Morphology of the anterior leaflet with elongation, tethering, chordal support, and mobility of the free leading edge

      
      
   3. 
      

      Papillary muscle location and attachments

   
   
2. 
   

   Function of the tricuspid valve

   
   
   
   
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      Degree of regurgitation based on Doppler scanning of jet velocity and not on the quantity of regurgitation

      
      
   2. 
      

      Number of regurgitant jets

      
      
   3. 
      

      Function and mobility of the anterior, septal and posterior leaflets

   
   
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   The right ventricle

   
   
   
   
   1. 
      

      Size and function

      
      
   2. 
      

      Morphology of the outflow tract

      
      
      
      
      1. 
         

         Degree of obstruction by the anterior leaflet

         
         
      2. 
         

         Function and morphology of the pulmonary valve

   
   
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   The left ventricle

   
   
   
   
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      Systolic and diastolic function

      
      
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      Presence of noncompaction

   
   
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   The size of the PDA, atrial septal defect, and shunt direction

   
   
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   Associated anomalies

Echocardiographic evaluation has several pitfalls: The severity of tricuspid regurgitation is frequently underestimated; therefore, surgical intervention might be inappropriately deferred. Proper evaluation of the right ventricular outflow tract, the proximity of the tricuspid valve tissue to the pulmonary valve (indicating severe displacement of the leaflet) and assessment of the effective capacity of the right ventricle below the point of coaptation are challenging.⁹

Magnetic Resonance Imaging

Magnetic resonance imaging complements echocardiography in delineating apical displacement, mobility and function of the tricuspid valve. This modality is accurate in evaluating the size and the function of the atria, both ventricles and ventricular outflow tracts.

Exercise Testing

Exercise testing is used routinely to evaluate the patient before and after surgery, and aids in indicating the timing of surgical intervention.

Catheterization

Diagnostic cardiac catheterization is not routinely performed, unless the pulmonary vascular resistance is to be evaluated before a planned bidirectional Glenn superior cavo-pulmonary anastomosis. A selective coronary angiogram is indicated in patients over 40 years of age or in those with a high risk of coronary artery disease. A preoperative invasive electrophysiological study with ablation is performed in patients with evidence of ventricular pre-excitation on ECG and in all patients with a history of recurrent supraventricular tachycardia, undefined wide-complex tachycardia, or syncope.¹⁰

The main goal is to support newborns through the period of transition from fetal to neonatal circulation. All measures are therefore taken to lower pulmonary vascular resistance while preserving duct-dependent pulmonary circulation. The critically ill neonate requires mechanical ventilation, sedation, paralysis, hyperventilation, correction of metabolic acidosis, appropriate inotropic/volume management, and a prostaglandin E₁ infusion. After stabilization, when pulmonary vascular resistance begins to fall, the prostaglandin is stopped to allow ductal constriction. Subsequently, the true functional capability of the right ventricle in providing antegrade flow is evaluated. At this point, pulmonary vasodilator therapy may be useful.¹¹

Older patients require either no treatment or treatment for symptoms of cardiac failure or arrhythmias. Oral anticoagulation should be considered in the case of paroxysmal or chronic atrial fibrillation or flutter.

Indication for Surgery

Neoanates and Young Infants

Typically, the indications for surgery are ventilator dependence, severe cardiac failure, prostaglandin-dependent circulation, and gross cardiomegaly.¹²

Older Children and Adults

Indications for operation include one or more of the following: poor growth, symptoms of dyspnea or decreased exercise tolerance (NYHA functional class III, IV), cyanosis (oxygen saturation <90 percent), paradoxical embolism, progressive cardiomegaly (cardiothoracic ratio >0.6), reduced left ventricle function, tachyarrhythmias that are not controllable by medication or amenable to catheter-based intervention, and significant associated lesions (atrial septal defect, ventricular septal defects, pulmonary stenosis).^5,13,14 In asymptomatic patients, the indication for surgery remains controversial. The arguments in favor of earlier operation are²: