Ebstein malformation is a rare congenital cardiac defect. The primary pathologic finding is abnormal development of the tricuspid valve marked by a downward displacement of the septal and posterior leaflets into the cavity of the right ventricle. This defect is characterized by remarkable morphologic variability and a broad spectrum of clinical presentations. Consequently, diagnosis may be made in symptomatic newborn infants, young adults, or middle-aged adults, depending on the severity of the defect and clinical manifestations.
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History of the Procedure
In 1866, Wilhelm Ebstein, a young physician in Breslau, Poland, reported findings from a postmortem examination performed 2 years earlier.  The patient was a 19-year-old laborer who presented with dyspnea and palpitations and was noted to be profoundly cyanotic. In his report, Ebstein described in great detail the morphology and clinical correlations of the congenital cardiac malformation that bears his name. His report provided a strong basis for the subsequent development of surgical techniques for the treatment of this anomaly 100 years later. 
Early surgical attempts to treat Ebstein malformation using palliative shunts resulted in extremely high mortality rates.  In 1958, Hunter and Lillihei described a technique of surgical repair that involved plication of the atrialized right ventricle, closure of the atrial septal defect, and tricuspid valve annuloplasty.  In 1964, Hardy reported the first successful repair of Ebstein malformation using this technique. 
During the 1960s, most attempts to repair the tricuspid valve were unsuccessful, and prosthetic valve replacement became the preferred approach. In 1962, Christian Barnard described the first successful tricuspid valve replacement in a patient with Ebstein malformation using a mechanical valve.  In the early 1970s, interest once again focused on tricuspid valve repair with a successful technique described by Danielson and colleagues at the Mayo Clinic.  Several modifications of tricuspid valve repair have been described recently, and early results have been successful. [8, 9, 10, 11]
Ebstein malformation is defined by a downward displacement of the annular attachments of the septal and posterior leaflets of the tricuspid valve into the inlet portion of the right ventricle. This downward displacement of the leaflets reduces the distal chamber of the right ventricle, leaving part of the ventricle above the valve as an extension of the right atrium. The entire wall of the right ventricle, both above and below the tricuspid valve, is often thin, dilated, and dysfunctional. In most patients, annular dilatation and malformation of the leaflets result in moderate-to-severe insufficiency of the tricuspid valve. Most patients have an atrial septal defect or a patent foramen ovale, which allows predominant right-to-left shunting at the atrial level. A high incidence of atrial and ventricular arrhythmia, including an association with Wolff-Parkinson-White Syndrome, occurs in these patients.
Ebstein malformation accounts for less than 1% of all congenital heart disease.  Geographical variation in the prevalence of this defect, inside or outside the United States, has not been documented. Although no increase in prevalence has been documented, an improvement in diagnostic techniques has led to earlier diagnosis. The malformation occurs in both sexes with equal frequency.
The exact embryologic cause of Ebstein malformation is unknown. The tricuspid valve leaflets form by a process of delamination of the inner layers of the inlet portion of the right ventricle.  Evidence suggests that the anterior leaflet forms earlier in development than the septal and posterior leaflets. In Ebstein malformation, the insertions of the septal and posterior leaflets are displaced to the junction of the inlet and trabecular portions of the right ventricle, indicating abnormal delamination.  The insertion of the anterior leaflet is at the level of the true annulus. The right ventricle endocardium is often thickened and fibrotic, suggesting that formation of the valve leaflets was interrupted prior to completion of the delamination process. The tricuspid valve is usually incompetent, but it may also be stenotic or even imperforate. In addition, both the atrialized right ventricular wall and the functional right ventricular wall may be abnormally thin and fibrotic.
The observed morphologic variability indicates the complexity of this defect's origin during embryologic development. Interestingly, exposure of the fetus to lithium carbonate during the first trimester has been linked to the development of Ebstein malformation.  Although no specific genetic inheritance pattern has been documented, a familial association has been reported. 
In most patients, the tricuspid valve is incompetent with some degree of functional impairment of the right ventricle. The atrialized right ventricle paradoxically moves with right atrial and right ventricular contractions. The net effect is reduced forward blood flow through the right ventricle and pulmonary arteries. The impaired filling of the functional right ventricle and the incompetence of the tricuspid valve both result in systemic venous hypertension.
The right atrium and the atrialized right ventricle become dilated, often to extreme proportions. In most patients, right-to-left shunting occurs across a defect in the atrial septum and results in cyanosis. The presence of pulmonary hypertension in neonates increases this atrial shunting and can lead to profound cyanosis in newborn infants. In some neonates, right ventricular outflow tract obstruction and pulmonary stenosis or atresia may result in a completely ductal-dependent pulmonary circulation. Both atrial arrhythmias and ventricular arrhythmias may contribute to impaired right ventricular function.
Although the primary pathology involves the right ventricle, patients with Ebstein malformation may also demonstrate abnormal left ventricular geometry and function.  The severity of left ventricular dysfunction is associated with the degree of displacement of the tricuspid valve, the size and dysfunction of the right ventricle, and the severity of paradoxical motion of the interventricular septum.
Clinical presentation widely varies. Patients presenting with Ebstein malformation range from neonates who are severely ill to adults who are mildly symptomatic. Initial presentation by older patients is rare, as only 5% will survive beyond the fifth decade.  Some patients may be completely asymptomatic with a murmur detected during a physical examination, or they may have abnormal findings on an electrocardiogram (ECG) or a chest radiograph.  Presenting symptoms are directly related to the severity of tricuspid valve incompetence, the presence or absence of an atrial septal defect, the degree of right and left ventricular dysfunction, and the presence of arrhythmia and associated cardiac defects.
Beyond the neonatal period, most patients present with dyspnea, fatigue, and some degree of cyanosis. In most patients, exercise tolerance is markedly compromised and maximum oxygen uptake during exercise is less than half of predicted.  Despite these findings, growth and development are usually normal. The most common clinical presentations by age are as follows: cyanosis in neonates, heart failure in infants, incidental murmurs in older children, and arrhythmia and exercise intolerance in adolescents and adults.
Paroxysmal supraventricular arrhythmia occurs in 25-40% of patients; this condition is most often found in teenagers or young adults. [3, 12] Ventricular arrhythmia is also common, and Wolff-Parkinson-White syndrome has been diagnosed in 10-18% of patients. [3, 12] Sudden death due to ventricular arrhythmia may occur in as many as 5-7% of patients.  Patients with atrial or ventricular arrhythmia may present with episodes of syncope, near syncope, or recurrent palpitation. Likewise, patients with mild manifestations present as late as the third or fourth decade of life with complaints of palpitation or mild exercise intolerance. The most common causes of death are congestive heart failure, severe hypoxia, and cardiac arrhythmia. [20, 21]
Upon physical examination, jugular venous distension and a prominent v wave in the jugular pulse may indicate severe tricuspid regurgitation. Heart sounds are usually soft, and the first and second heart sounds are widely split. A systolic murmur of tricuspid regurgitation may be heard along the left sternal border, but this may also be due to right ventricular outflow tract obstruction. The liver may be palpably enlarged, but ascites and peripheral edema are rare. Evidence of significant cyanosis may be seen in the extremities.
Indications for surgical intervention in patients with Ebstein malformation include the following:
Functional New York Heart Association (NYHA) class III or class IV symptoms
Significant or progressive cyanosis
Decline in exercise tolerance
Significant decrease in growth curve
Severe cardiomegaly (cardiothoracic ratio >0.65)
Associated cardiac anomalies, including right ventricular outflow tract obstruction
Refractory atrial or ventricular arrhythmia
History of paradoxical embolus
The characteristic finding of Ebstein malformation is a downward displacement of the attachments of the septal and posterior leaflets of the tricuspid valve below the true tricuspid annulus. These valve leaflets are often hypoplastic and adherent to the endocardial surface of the right ventricle. The commissure between these 2 leaflets is usually the point of maximal displacement. The anterior leaflet is typically larger than normal and sail-like in appearance. The anterior leaflet may be thin and fenestrated, and it may also adhere to the endocardial surface of the right ventricle. Rarely, a leaflet can divide, resulting in a double-orifice valve. 
The individual valve leaflets may be larger or smaller than expected. The chordae tendineae and papillary muscles are often abnormal in their number, development, and location. In rare instances, the anterior leaflet may attach to the apical region of the right ventricle and obstruct blood flow through the right ventricular outflow tract. Additionally, the tricuspid annulus is usually enlarged to 2-4 times the normal size.
Anatomical features of Ebstein malformation are presented in the image below.
The displacement of the septal and posterior leaflets of the tricuspid valve into the right ventricle leaves a portion of the right ventricular wall between the leaflet attachments and the true annulus in continuity with the right atria. This atrialized right ventricle is usually very thin and dilated with a decrease in the actual number of myocardial fibers. The functional right ventricle below the valve may also be thin and dilated with decreased contractile function. 
The anatomy of the conduction system is normal; the atrioventricular node is located at the apex of the triangle of Koch, and the sinoatrial node is located at the junction of the superior vena cava and the right atrium. The location of the bundle of His is normal, but abnormalities of the right bundle branch have been described. [23, 24] Accessory atrioventricular connections are present in as many as 20% of patients and are associated with Wolff-Parkinson-White syndrome. [25, 26, 27]
The right atrium is enlarged and may reach enormous size. An atrial septal defect is usually present and ranges from a patent foramen ovale to a large secundum defect. The coronary arteries are normal in distribution, and the right coronary artery is often displaced by the enlarged right atrium and atrialized right ventricle. Associated cardiac anomalies include pulmonary stenosis or atresia, ventricular septal defect, patent ductus arteriosus, tetralogy of Fallot, and coarctation of the aorta. [3, 21] In patients with Wolff-Parkinson-White syndrome, accessory pathways are typically the atrioventricular type and are localized to the right ventricular free wall or to the posterior interventricular septum (bundles of Kent). 
Ebstein malformation of the left atrioventricular valve occurs in up to 75% of patients with L-transposition of the great arteries or corrected transposition of the great arteries.  In these patients, displacement of the septal and posterior leaflets is similar to that in right-sided lesions, but the anterior leaflet is usually smaller.  In addition, the wall of the functional right ventricle is rarely thin and dilated, and the wall of the atrialized right ventricle is also less thin and dilated. Left-sided accessory pathways have been described only in those patients with Ebstein malformation of the left-sided atrioventricular valve.
Patients with Ebstein malformation and biventricular failure should not undergo attempted repair of the defect, and they should be considered candidates for orthotopic heart transplantation. Neonates with Ebstein malformation are controversial because some patients with severe defects may not be considered candidates for surgery (except possibly for heart transplantation).
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