echocardiography because they can contribute to the development of hydrops A ratio of the combined right atrial and atrialized ventricular area compared with the combined area of the functional right ventricle and left heart greater than 1 was shown to be associated with very poor fetal or neonatal outcome.51 Other fetal or neonatal findings that were associated with increased risk of mortality were a larger atrial septal defect, functional or anatomic pulmonary atresia, or reduced left ventricular function FIG 33.17 Images taken during a fetal echocardiogram performed at 28 weeks’ gestation The examination revealed marked cardiomegaly due to Ebstein malformation and severe tricuspid regurgitation The right atrium (RA) and right ventricle (RV) are massively dilated and occupy the majority of the thoracic cavity, reducing the space available for the developing lungs There is severe tricuspid regurgitation (arrow at right) with the jet originating deep within the RV cavity due to the displaced functional valve orifice The left ventricle (LV) is normal in size, although it appears small in comparison to the gigantic right-sided chambers A, Anterior; LA, left atrium; R, right Exercise Testing Exercise studies performed before and after surgery have revealed several interesting findings.52–54 In the largest of these series,54 unoperated patients had significantly reduced indexes of exercise tolerance for work, duration, and maximal oxygen uptake In postoperative patients, these indexes all increased and approached the lower limits of normal Arterial saturations of oxygen both at rest and during exercise were significantly lower in unoperated than in postoperative patients, undoubtedly due to closure of the atrial septal defect In the unoperated patient, progressively lower saturations at rest and at maximum exercise were associated with progressively reduced exercise tolerance Surgical intervention improved exercise tolerance Most postoperative patients had resting and exercise cardiac outputs that were similar to the normal population Patients with an atrial septal defect and right-to-left shunting demonstrated excessive ventilation at rest and during exercise In these patients, a right-to-left shunt is a strong stimulus to increased ventilation Cardiac Catheterization and Hemodynamics In the early days of intracardiac investigation, patients with Ebstein malformation were at increased risk during catheterization These concerns have now been dispelled by modern techniques of hemodynamic monitoring, more flexible catheter materials, and the availability of effective treatment for arrhythmias Even though patients with Ebstein malformation can currently be safely studied, the need to do so arises infrequently, with noninvasive imaging techniques providing nearly all necessary information However, catheterization may still be required when there are clinical questions regarding pulmonary arterial pressure or resistance Prior studies have shown that there is usually moderate elevation of the right atrial pressure, often with a dominant V wave and steep Y descent When the right atrium is massively dilated, the atrial pressure may be normal in spite of severe tricuspid regurgitation Most often, the right ventricular pressures are normal, but in some the end-diastolic pressure may be elevated In general, the pulmonary arterial pressure is normal, but it may be decreased in those with severe tricuspid regurgitation and right-to-left shunting In those with an atrial septal defect, right-to-left shunting will result in systemic arterial desaturation Historically significant is a technique of simultaneously recording the intracavitary pressure and intracardiac electrogram tracing When a catheter with an end hole and an electrode at the tip was positioned in the atrialized portion of the right ventricle, the pressure tracing recorded was atrial, but the electrogram showed ventricular activity This was one of the earliest methods used confidently to make a diagnosis of Ebstein malformation Angiocardiography Angiocardiography is rarely needed in the current era In the typical patient, injection of contrast medium in the right ventricle, viewed in the frontal projection, will demonstrate tricuspid regurgitation, the large sail-like anterosuperior leaflet, and frequently a distinct notch at the inferior cardiac border to the left of the spine The notch is created by the displaced tricuspid valve and marks the point of division between the atrialized and functional zones of the right ventricle Frequently, a trilobed appearance occurs as a result of contrast medium outlining the enlarged right atrium, atrialized ventricle, and the outflow portion of the functional ventricle Clinical Prognosis and Treatment of Patients With Ebstein Malformation The outcome of Ebstein malformation depends a great deal on the age of the patient at presentation, the severity of the lesion, and the presence of associated defects, these features being interrelated Severely affected fetuses or neonates can easily be detected with echocardiography As a result of their severe disease, they generally have a poor outcome.8 In one series, all neonates died when the combined area of the right atrium and atrialized right ventricle was greater than the combined area of the functional right ventricle, left atrium, and left ventricle.55 Although mortality is no longer guaranteed in this group, they still represent those with the greatest risk of early death Mild disease in neonates and young children has a relatively good outcome, depending primarily on the presence of associated lesions The natural history of Ebstein malformation was first reviewed by Watson in 1974.6 Only 35 patients were younger than 1 year old, 403 were between 1 and 25 years, and 67 were older than 25 years Cardiac failure was present in almost 75% of infants In contrast, 80% of the patients presenting at older ages had normal growth and development during infancy In addition, almost 75% of the patients aged from 1 to 25 years and 60% of those older than 25 years had little or no disability at the time of diagnosis and were placed in the first or second categories of the classification of the New York Heart Association In the overall cohort, 77 (15.2%) died secondary to medical complications of the disease After