Introduction
The most common congenital malformations afflicting the tricuspid valve are Ebstein malformation and tricuspid valvar dysplasia. These lesions are considered in this chapter, together with a brief look at acquired malformations. Tricuspid valvar abnormalities, or abnormalities of the morphologically right atrioventricular valve, are also often associated with atrioventricular septal defects with common atrioventricular junction (see Chapter 31 ), ventricular septal defect with straddling valve (see Chapter 32 ), atrioventricular discordance (see Chapter 38 ), or pulmonary atresia with intact septum (see Chapter 43 ). These lesions are described in detail in other chapters of this book. However, Uhl anomaly and fatty replacement of the wall of the right ventricle, the latter now described as arrhythmogenic right ventricular cardiomyopathy, are so frequently discussed in the setting of Ebstein malformation that brief consideration is given to these two entities even though they are not malformations of the tricuspid valve.
Ebstein Malformation
Ebstein malformation has a variable natural history depending on the degree of abnormality of the tricuspid valvar apparatus and right ventricle, both of which may range from mild to severe. If the deformity of the tricuspid valve is severe and the ventricle significantly dysfunctional, profound congestive heart failure may occur in the neonatal period or even result in intrauterine death. At the other end of the spectrum, patients with a mild degree of displacement of the septal hinge away from the atrioventricular junction may never develop symptoms or may remain asymptomatic until late adult life.
Ebstein’s own description of the malformation, with illustrations by Dr. Weiss ( Fig. 33.1 ) was based on the anatomic findings relating to the heart of Joseph Prescher, a 19-year-old laborer with cyanosis. Prescher had been troubled with dyspnea and palpitations since childhood. The first case described in the English literature was published in 1900, but it was not until 1951 that the diagnosis was made during life, using angiocardiography. By the 1950s, successful surgical palliation had been achieved, and the association with Wolff-Parkinson-White syndrome had been recognized. The 1960s heralded the first attempts at corrective surgery, including valvar replacement and repair. Throughout the 1960s and 1970s, the disease was thought to be extremely rare, accounting for no more than 0.3% of congenital heart disease, giving an estimated incidence at that time of approximately 24 per 1 million live births.
Echocardiography provides a convenient and readily available method for diagnosis, even in fetal life. The malformation is currently known to be more common and to have a broader spectrum than previously appreciated. In fact, a series of more than 200 cases collected from hospitals in southeast England revealed a nearly fivefold increase in the number of diagnosed cases per decade, with more than half of the patients younger than 1 year at diagnosis. By the 1990s it was estimated that the incidence of Ebstein malformation, including asymptomatic cases, was approximately 1 in 200,000 live births.
Anatomy
The essence of Ebstein malformation is adherence of variable segments of tricuspid valve leaflet tissue to the underlying myocardium. These leaflet segments have failed to “delaminate” during embryonic development, and the hinge point of the septal and inferior leaflets of the tricuspid valve are displaced from their expected position at the atrioventricular junction. In hearts studied at autopsy, cases can be encountered in which only the hinge of the septal leaflet is attached away from the atrioventricular junction ( Fig. 33.2 , left ). This variant is found most frequently in the setting of pulmonary atresia with an intact ventricular septum, when it is an associated malformation rather than representing the primary lesion (see Fig. 33.2 , right ).
When found in the absence of pulmonary atresia, it is unlikely that such minimal changes would produce the typical symptomatology. It can also be difficult to distinguish such minimal displacement of the septal leaflet in an otherwise normal heart from the anticipated valvar off-setting. In the cases coming to clinical attention, the entirety of the tricuspid valvar apparatus is usually malformed. Even in these cases, only the septal and inferior leaflets that have their annular attachment displaced from the atrioventricular junction, with sparing of the annular hinge of the anterosuperior leaflet.
A major problem in the analysis of the cases coming to clinical attention is precisely to distinguish, in the abnormal valve, the boundaries between the inferior and anterosuperior leaflets. In fact, the essence of the malformation is that the leaflets adopt a bifoliate configuration, with a plane of closure at the junction of the inlet and the remaining components of the right ventricle, as was shown in the initial illustration of the heart of Joseph Prescher (see Fig. 33.1 ). Such rotational changes are also the usual findings in symptomatic patients ( Fig. 33.3 ). Appreciation of this abnormal position and structure of the valve is key to subsequent analysis and arguably to selection of appropriate treatment.
As shown in Fig. 33.3 , the abnormal location of the valvar orifice represents a rotational deformity, rather than the linear, downward or apical displacement. There is, nonetheless, marked variation in the degree of failed delamination from patient to patient ( Fig. 33.4 ).
In the typical diseased valve as seen postmortem, the septal leaflet is either represented by an array of verrucous remnants adherent to the septum toward the ventricular apex ( Fig. 33.5 , left ), part of a tongue that becomes continuous with the conjoined inferior and anterosuperior leaflets (see Fig. 33.5 , middle ), or a remnant on the septum (see Fig. 33.5 , right ).
A key feature of the rotational displacement of the septal leaflet is that it can seem to be absent if attention is directed exclusively to the ventricular inlet component as seen in so-called four-chamber orientation ( Fig. 33.6 , left ).
When assessment is redirected at the junction between the atrialized right ventricular inlet component and the functional right ventricle, valvar leaflets are seen, typically forming a bifoliate valvar mechanism (see Fig. 33.6 , right ). Therefore the functional part of the right ventricle is made up of the apical and outlet components, distal to the functional valvar orifice. The inferior and anterosuperior leaflets themselves tend to be combined as an abnormal curtain, which then forms the parietal part of the abnormal valve. The part of the valvar curtain formed by the anterosuperior leaflet retains its normal hinge from the atrioventricular junction along the supraventricular crest. The hinges of the abnormal leaflets then move increasingly away from the junction as attention is directed to the attachments along the diaphragmatic surface of the ventricular mass. In most cases the valvar mechanism has clearly been incompetent, as revealed by the dysplastic nature of the abnormal leaflets. Relative to the mass of the atrialized right ventricle, the valvar orifice is also frequently judged to be stenotic. In this setting the proximal components of the right side of the heart, both the atrium and the right ventricular inlet, are dilated and thin walled. This produces “anatomic” atrialization of the walls of the ventricular inlet (see Fig. 33.3 , left ). Irrespective of the thickness of its wall, the inlet component of the ventricle is always at atrial pressures in hemodynamic terms, simply because of the abnormal location of the valvar hinge points. Electrically, because the junction remains at its normal site, ventricular potentials will be recorded from the atrialized myocardium.
Further significant clinical variation is then seen in the nature of the distal attachments of the inferior and anterosuperior components of the valvar curtain, which are almost always additionally dysplastic. In some cases the anterosuperior leaflet retains its focal attachment to the medial and anterior papillary muscles (see Fig. 33.5 , right ). In more advanced cases, the entire leading edge of the anterosuperior leaflet is attached “linearly” (with no intervening chordal supports) to a muscular shelf formed between the inlet and apical trabecular components of the ventricle ( Fig. 33.7 , left ). Between these extremes are found hearts in which the edge of the leaflet is attached in hyphenated fashion (see Fig. 33.7 , right ).
In addition to the apical attachments, abnormal tetherings are usually found between the ventricular aspect of the abnormal leaflets and the parietal ventricular wall. Such tetherings serve to constrain still further the motion of the abnormal sail produced by the combined inferior and anterosuperior leaflets. When the valvar mechanism is arranged as a bifoliate structure, then its opening is adjacent to the septum and is directed toward the ventricular outlet component. This “keyhole” can become increasingly restricted and stenotic. Should the leaflets fuse along the edges of the keyhole, the result is to produce tricuspid atresia in the setting of Ebstein malformation.
Therefore the essence of symptomatic Ebstein malformation is formation of an abnormal bifoliate valvar mechanism, with septal and parietal components. The valvar orifice is at the junction between the atrialized inlet part of the right ventricle and the “functional” right ventricle, with the latter made up of the apical and outlet ventricular components. Although the annular attachments of the septal leaflet of the valve are displaced from the atrioventricular junction, the triangle of Koch continues to be the landmark for the atrial components of the atrioventricular conduction tissue axis. Right bundle branch block is commonly found and may be caused by fibrosis in the distal conduction tissue. The frequent presence of accessory muscular pathways across the atrioventricular junctions results in a high incidence of preexcitation, being found in up to 25% of patients. The accessory pathways are often multiple and are usually found to the right of the inferior paraseptal space or in the parietal part of the junction. When found laterally, they frequently arise from a remnant of atrioventricular ring tissue and produce the so-called Mahaim variant of preexcitation.
The abnormally located line of attachment of the valvar leaflets divides the right ventricle into proximal atrialized and distal functional portions. The proximal portion lies between the anatomic atrioventricular junction and the displaced attachments of the leaflets. Although this atrialized portion has muscular walls, in symptomatic patients the area is dilated, has thin and smooth (nontrabeculated) myocardium, and contains a high content of fibrous tissue. When very thin, it moves paradoxically during ventricular systole, and it may also expand during atrial systole. Its electrical potentials are ventricular, but its pressure pulse shows an atrial waveform.
The cavity of the “functional” right ventricle is usually smaller than that of the normal right ventricle. However, this feature may be modified by dilation, which is a frequent finding. The walls of the functional ventricle, particularly when dilated, are also usually thinner than normal. They contain fewer than normal myocytes and more fibrous tissue. Left ventricular abnormalities are also frequent. They can sometimes simply be the consequence of the gross dilation of the right-sided chambers. In severe cases the left ventricular free wall also has an abnormally high content of fibrous tissue, although its thickness is usually normal. The mitral valve is frequently nodular and thickened, and prolapse of the leaflets may occur.
Associated cardiac defects are common, particularly in the patients diagnosed in fetal or neonatal life. Almost all patients have a coexisting interatrial communication, usually a patent foramen. Any type of communication, nonetheless, may be present, including atrioventricular septal defects. A large spectrum of other lesions has been described in addition to atrioventricular septal defects, including ventricular septal defects, tetralogy of Fallot, aortic coarctation, and persistent patency of the arterial duct. The most common associated defect is pulmonary stenosis or atresia, which is found in up to one-third of those who present in infancy. Obstruction of the right ventricular outflow tract is commonly associated with Ebstein malformation when diagnosed in fetal life. In this setting, it may be difficult to distinguish structural from functional pulmonary atresia using echocardiography, especially in the presence of severe tricuspid regurgitation. The pulmonary valvar abnormality is probably secondary to the malformation of the tricuspid valve, with hypoplasia of the outflow tract resulting from low anterograde flow through the right heart. When severe Ebstein malformation is associated with fetal and neonatal distress, or death, both lungs are usually hypoplastic but otherwise normal. The hypoplasia is secondary to the gross cardiomegaly, itself caused by dilation of the right heart sufficient to produce a “wall-to-wall” appearance. In the setting of such gross dilation of the heart secondary to severe tricuspid valvar incompetence, whether the consequence of Ebstein malformation or tricuspid dysplasia with normal junctional attachments ( Fig. 33.8 ), the overall ventricular myocardium can become particularly thin.
This should not be described as “Uhl malformation.” In the lesion described by Uhl, the tricuspid and pulmonary valves were both normal. The essence of the congenital malformation is absence of the parietal mural myocardium, histologic analysis showing that the epicardial and endocardial layers of the wall lie edge to edge. It is also a mistake to correlate fibrofatty replacement of the right ventricular parietal walls with either Ebstein malformation or Uhl anomaly. Fibrofatty replacement is the essence of arrhythmogenic right ventricular cardiomyopathy, currently recognized as a cardiomyopathy in its own right, with various genetic causes. Dysplasia of the valvar leaflets is itself an intergral part of Ebstein malformation, but as shown, dysplastic leaflets can also be found when the leaflets have completely delaminated, retaining their normal hinges at the atrioventricular junction (see Fig. 33.8 ). Such dysplasia of normally hinged leaflets can produce just as much valvar incompetence as Ebstein malformation. Hence isolated dysplasia can produce the same appearance of the “wall-to-wall” heart, with the same consequences for pulmonary problems in the noenatal period.
Morphogenesis
The hallmark of Ebstein malformation is attachment of the hinges of the septal and mural leaflets within the right ventricle rather than at the atrioventricular junction. This results developmentally from failure of separation or “delamination” of these leaflets from the ventricular wall. The anterosuperior leaflet, in contrast, developing within the cavity of the ventricle as opposed to adjacent to its wall, is able to retain its normal junctional hinge. The formation of the other valvar leaflets is a relatively late embryologic event. At the time of closure of the embryonic interventricular communication, the septal and mural leaflets of the tricuspid valve have not begun to develop. These are produced subsequently by delamination relative to the superficial layer of the ventricular myocardium. Ebstein malformation is a consequence of failure of this delaminatory process. An association between some cases of Ebstein malformation and use of lithium in pregnancy has been reported.
Pathophysiology and Clinical Aspects of Ebstein Malformation
The anatomic hallmarks of Ebstein malformation, failed leaflet delamination and displacement of the valvar hinge points, combine with the variable myopathy, to produce a wide spectrum of clinical and hemodynamic manifestations. Severity is related to multiple factors, including the functional state of the tricuspid valve (degree of regurgitation or more rarely, stenosis), the status of the atrial septum, presence (or absence) of other congenital cardiovascular malformations, the degree of right ventricular dysfunction, and the amount of left ventricular dysfunction. To a lesser degree, the pathologic substrates predisposing to tachyarrhythmias produce an additional dimension contributing to the pathophysiology.
The dysfunctional nature of the right ventricular myocardium and coexisting abnormalities of the tricuspid valve impair flow through the right heart and the pulmonary circulation, contributing to (usually significant) right-sided cardiac enlargement. The absence of a “valve” between the anatomic right atrium and the atrialized segment of the right ventricle produces further atrial distension. During ventricular systole, the atrialized right ventricular myocardium may contract, adding another stimulus for atrial enlargement and an impediment to forward flow. This increase in “resistance” to outflow from the atrium will also augment the amount of right-to-left shunting through any coexisting interatrial communication.
The degree of functional impairment experienced by patients with Ebstein malformation has been directly related to these anatomic and physiologic abnormalities. Shiina and colleagues found that a small functional right ventricle and large atrialized right ventricle, extreme displacement or absence of the septal leaflet, the degree of tethering of the anterosuperior leaflet, and aneurysmal dilation of the right ventricular outflow tract were all associated with reduced functional status as measured by the New York Heart Association heart failure classification system.
Although the primary focus in Ebstein malformation has been on right-sided structures, there have been an increasing number of reports of left-sided abnormalities, specifically in left ventricular size, shape, and function. These have been attributed to right ventricle (RV) enlargement and leftward diastolic bowing of the interventricular septum compromising the left ventricle. Despite this, most unoperated patients show an appropriate increase in left ventricular ejection fraction with a reduced end-systolic volume and unchanged end-diastolic volume during formal exercise testing. In addition, Attenhofer and colleagues reported that one-fifth of their cohort with Ebstein malformation had an abnormal echocardiographic appearance of the left ventricular myocardium. These patients displayed segments with multiple layers and deep intratrabecular recesses, consistent with myocardial noncompaction. Although most patients had satisfactory left ventricular function, a small percentage showed severe systolic and diastolic dysfunction, even contributing to the need for transplantation in one young patient. These left-sided myocardial abnormalities, although seen in only a fraction of patients, support the concept that Ebstein malformation is actually a global myocardial disorder that primarily manifests itself within the right ventricle and its derivative, the tricuspid valve.
The infant with Ebstein malformation poses an especially difficult clinical problem. Pulmonary vascular resistance is always high immediately after birth and usually decreases in the first days of life. The infant with severe Ebstein malformation is poorly prepared to deal with the transition to the neonatal circulation. The combination of right ventricular myopathy, tricuspid regurgitation, and elevated pulmonary resistance can lead to poor pulmonary perfusion when the arterial duct constricts or closes. Venous pressures rise, leading to right-heart failure and cyanosis due to right-to-left shunting across the oval foramen. Until the pulmonary resistance decreases and the pulmonary flow increases, these infants present a diagnostic and therapeutic dilemma. Patency of the pulmonary outflow tract and valve must be confirmed. This can be done by demonstrating opening of the pulmonary valvar leaflets by cross-sectional echocardiographic scans or by documenting forward, or more commonly regurgitant, flow across the valve using Doppler techniques.
In the rare case where echocardiographic findings are inconclusive, an angiogram demonstrating pulmonary regurgitation following injection of contrast into the arterial duct, or the ability to advance a catheter across the valvar orifice, can confirm patency of the right ventricular outflow tract. When the outflow tract is open and the pulmonary valve competent, infusions of prostaglandin to maintain ductal patency, with or without mechanical ventilation, will often allow the baby to transition to the postnatal circulation without the need for palliative surgery.
Clinical Presentation
Patients with Ebstein malformation may present at any age. The most severe cases present prenatally or as newborns. Prenatal diagnosis is dependent on ultrasonic screening examinations. Fetal presentation is accompanied by increased heart size, a significant incidence of fetal hydrops, and, in the most severe cases, pulmonary parenchymal hypoplasia secondary to marked cardiac enlargement. Prenatal arrhythmia is not common.
Newborns most often present with cyanosis, whereas slightly older infants present with a combination of desaturation and symptoms of cardiac failure. Murmurs and arrhythmias are more frequently encountered as presenting complaints in older patients. Although some patients remain asymptomatic, most will have some cardiovascular symptoms. Beyond infancy, the majority will display abnormal fatigue, dyspnea, or cyanosis with exertion or palpitations. Palpitations in a cyanotic child should raise the possibility of Ebstein malformation ( Table 33.1 ).
| Prenatal ( N = 21) | Neonate ( N = 88) | Infant ( N = 23) | Child ( N = 50) | Adolescent ( N = 15) | Adult ( N = 23) | All (%) | |
|---|---|---|---|---|---|---|---|
| Cyanosis | 0 | 65 | 8 | 7 | 2 | 1 | 83 (38) |
| Heart failure | 0 | 9 | 10 | 4 | 2 | 6 | 31 (14) |
| Murmur | 0 | 8 | 3 | 33 | 5 | 3 | 52 (24) |
| Arrhythmia | 1 | 5 | 1 | 6 | 6 | 10 | 29 (13) |
| Abnormal prenatal ultrasound | 18 | 0 | 0 | 0 | 0 | 0 | 18 (8) |
Ultrasonic technology has significantly influenced the age at which most patients with Ebstein malformation are diagnosed. In 1979 Guiliani and colleagues found that just less than one-third of patients were diagnosed younger than 4 years of age. Another 40% were diagnosed younger than age 19 years, with the remainder presenting in adulthood, some at 80 years of age. In contrast, in the experience reported by Celermajer and colleagues in 1994 (see Table 33.1 ), 60% came to clinical attention at age younger 1 year, with half diagnosed prenatally or as newborns. Ten percent presented between 1 and 12 months of age, with only 30% presenting as children or adolescents. Despite the increased availability of ultrasonic examination in this more recent cohort, 10% remained undiagnosed until adulthood.
Physical Findings
Growth and development are generally normal. Inspection reveals cyanosis and digital clubbing in patients with an associated right-to-left shunt. Many have an unusual facial coloration, described as violaceous hue, flushed, florid, red-cheeked, or malar flush. Usually these patients have an associated mild polycythemia. Prominence or asymmetry of the chest is a frequent finding secondary to the dilated nature of the right heart. Arterial and venous pulsations are usually normal, even in the presence of tricuspid insufficiency. The jugular venous pulsations are not prominent because of poor transmission of the venous pulse wave in the presence of a dilated and compliant right atrium. The precordium is usually not overactive.
Auscultation may reveal multiple sounds and murmurs, especially in those with mobile anterosuperior valvar leaflets. These multiple sounds are so characteristic as to stand out even to the untrained ear. Occasionally, the heart sounds are soft, but usually they are of normal intensity. The first heart sound can be widely split because of increased excursion of the anterosuperior leaflet and the subsequent delayed closure of the abnormal tricuspid valve. The second heart sound is also widely and persistently split owing to late closure of the pulmonary valve, believed to be due to right bundle branch block. Ventricular filling sounds are common contributors to the multiplicity of heart sounds. In the presence of multiple heart sounds, there is frequently a gallop rhythm, which is fairly easily recognized. A holosystolic murmur, typically graded at 2 to 4 out of 6, is found along the left sternal border in those with an organized jet of tricuspid regurgitation. Low-intensity diastolic murmurs can be appreciated in the same location as a result of anterograde flow across the tricuspid valve. All murmurs tend to vary with respiration, increasing during inspiration. There may be few murmurs present in patients with very little functional tricuspid valvar tissue because the flows between right atrium and the ventricle are essentially unrestricted and therefore not associated with turbulence. The first heart sound is single in these cases.
Electrocardiography, Arrhythmias, and Electrophysiology Testing/Treatment
The electrocardiogram is usually abnormal and helps to confirm the clinical diagnosis ( Fig. 33.9 ). Although sinus rhythm is usually present at the time of initial diagnosis, atrioventricular dissociation or atrial fibrillation can be found, usually in older patients. In large series, one-third to one-half of the patients have prolonged PR intervals, and one-fourth to three-fourths meet the criterions for right atrial enlargement, often showing so-called Himalayan P waves. The frontal plane QRS axis is typically rightward. Most patients have right bundle branch block, and many have low-voltage QRS complexes in the right precordial leads. Findings consistent with right ventricular hypertrophy are extremely uncommon.
Up to 25% of patients with Ebstein malformation have the Wolff-Parkinson-White pattern on their electrocardiogram. This is due to the presence of accessory myocardial atrioventricular connections across the insulating plane of the atrioventricular junction. In some, this may be intermittent, and several resting or exercise electrocardiograms or 24-hour ambulatory electrocardiograms may have to be examined to find the characteristic pattern. In addition, concealed accessory pathways, without manifest delta waves but capable of retrograde conduction, are not uncommon. Absence of anterograde preexcitation indicates neither that the accessory connection is no longer present, nor that the patient is no longer susceptible to tachycardia. The presence of left axis deviation in a patient with Ebstein malformation suggests the presence of the Mahaim variant of preexcitation, produced by atriofascicular tracts.
Arrhythmias in the nonneonatal, unoperated patient with Ebstein malformation are common. Almost 80% of preoperative patients in this series either had documented arrhythmias or histories of palpitations, near-syncope, or syncope. In those with documented arrhythmias, 50% had paroxysmal supraventricular tachycardia, 25% had paroxysmal atrial fibrillation or flutter, another 25% had ventricular arrhythmias, either with frequent ventricular premature complexes or nonsustained ventricular tachycardia, and 10% had some form of atrioventricular block. In those with ventricular arrhythmias, 30% also had paroxysmal supraventricular tachycardia, another 30% had paroxysmal atrial fibrillation or flutter, and one patient had complete heart block. The patients with arrhythmias or symptoms compatible with arrhythmia were significantly older than those without symptoms or arrhythmias.
Given that arrhythmias are so common, additional preoperative, intraoperative, and postoperative procedures are often required to reduce/eliminate these issues. Prior to the widespread application of complex antiarrhythmic procedures, surgical intervention appeared to decrease the frequency of arrhythmias, at least in early, short-term follow-up. Supraventricular tachycardias decreased from one-half to one-quarter postoperatively in the earliest cohorts. Despite the overall reduction in arrhythmias, when arrhythmias were observed early during postoperative recovery, these patients had an increased risk of late sudden death. Introduction of more extensive antiarrhythmic surgery has improved results even further. Accessory pathways are usually ablated preoperatively in the electrophysiology suite, with early success rates approaching 80%. However, due to the width/multiplicity of pathways that can be present in Ebstein malformational, 30% to 40% may require more than one procedure. Stulak et al. reported their results using the right and biatrial maze procedure for atrial aflutter/fibrillation in 86 patients with Ebstein malformation. More than 75% of the cohort was free of arrhythmia recurrence and off of antiarrhythmia medications at a median of more than 4 years after surgery.
Chest Radiography
The cardiac size may vary from near normal to extreme cardiomegaly. When the heart is severely dilated, it takes on a globular shape ( Fig. 33.10A ). There may be a dramatic change from preoperative to postoperative radiographs (see Fig. 33.10B ). The dilated right atrium is responsible for most of the enlarged cardiac silhouette. In the frontal view, the right atrium produces a significant convexity of the right heart border, and in the lateral view, the right atrium may fill the entire retrosternal space. The convex left border is primarily due to dilation of the right ventricular outflow tract. The convexities of both left and right heart borders produce the characteristic globular cardiac silhouette. In cyanotic patients with a right-to-left shunt, the pulmonary vascular markings appear decreased. In the asymptomatic patient, the heart may have a normal size and shape.
Echocardiography
Echocardiography has become the procedure of choice for both the diagnosis and long-term assessment of patients with Ebstein malformation. In cases where echocardiographic images are poor, cardiac magnetic resonance or computed tomography scans can provide similar information. These radiographic techniques also provide the ability to quantitatively assess right ventricular size and are being used with greater frequency.
As early as 1984, echocardiography had become sufficiently validated that angiography was no longer necessary to diagnose Ebstein malformation. The anatomic shift of the tricuspid valve hinge points and effective orifice, as well as the failed delamination of the valve components proximal to the hinges, should bear the most weight in making the diagnosis because these features are specific to Ebstein malformation. The displacement of the annular hinge points is readily appreciated ( Fig. 33.11 ), as is the adherence of portions of the tricuspid apparatus to the myocardium. In cases where the diagnosis is not clear, the most sensitive and specific single diagnostic feature is the displacement of the annular hinge of the septal leaflet. This displacement is most easily demonstrated by comparison to the annular hinge of the mitral leaflet as seen in the apical four-chamber view. In patients with Ebstein malformation, the distance separating these two attachments is exaggerated and can easily be measured ( Fig. 33.12 ). This distance, when divided by the body surface area in square meters, is known as the displacement index. An index value greater than 8 mm/m 2 reliably distinguishes those with Ebstein malformation from both normal patients and from patients with other disorders associated with enlargement of the right ventricle.
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