**4. Pathophysiology of the newborn**

Neonates are symptomatic as a result of ineffective RV cardiac output and severe TV regurgitation. There is usually some degree of cardiomegaly which can be quite severe compressing the lungs. Furthermore, cyanosis results from systemic venous return being shunted across the ASD to the left side of the heart. Neonatal pulmonary vascular resistance (PVR) is elevated and this is a major impediment to effective antegrade flow from the diminutive and myopathic RV. In the first week of life when pulmonary vascular resistance is high pulmonary blood flow is dependent upon the PDA. This results in a physiological state referred to as "functional" pulmonary atresia. When the PVR decreases over the first week of life, the RV may then be able to overcome the afterload to establish antegrade flow. True anatomical pulmonary atresia where there is luminal discontinuity between RV and pulmonary artery is also often seen in these symptomatic neonates. These patients will have ductal dependent pulmonary circulation until a surgical procedure is performed to establish pulmonary blood flow. Left ventricular dysfunction can also play a critical role in the development of decompensated heart failure. This is related to left ventricular displacement of the interventricular septum as a result the severely dilated dysfunctional RV. This "pancaking" of the LV cavity impedes filling and diminishes systemic cardiac output. In less severe forms of EA the RV can generate effective antegrade flow especially when the PVR decreases. Antegrade flow across the RV outflow tract is accompanied by clinical improvement in symptoms. Neonates with severe TR or gross cardiomegaly who are otherwise asymptomatic have an associated mortality of 45% within the first year of life without intervention [17, 18]. The natural history of being diagnosed with EA during infancy is sobering [19]. However those who survive early childhood can expect reasonable longevity. When the disease is mild symptoms are not noticed until later in adult life. Symptoms are often related to exercise intolerance or cyanosis from progressive tricuspid regurgitation.

chamber views allow calculation of the displacement index, which measures the distance from the true septal annulus to the level of the apically displaced septal leaflet hinge point (**Image 2**).

**Image 1.** Chest x-ray of an infant with EA. there is marked cardiomegaly with a significant cardiothoracic ratio. With

Doppler echocardiography can demonstrate the presence and location of tricuspid valve regurgitation (**Image 3**) [21]. However, severity can be difficult to quantitate due to apical displacement. RV dysfunction and functional or anatomic pulmonary atresia can be evaluated by 2-D and color echocardiography [21] **Image 4**. The Great Ormond Street Echocardiogram (G.O.S.E.) score is a mortality risk stratification score for neonates with EA.It is calculated from the apical four chamber view by adding the right atrium and atrialized right ventricular volume and dividing by the sum of the functional right ventricular volume, left atrial and ventricular volumes. (18) A G.O.S.E score of 3 (ratio of 1.1–1.4) with cyanosis or 4 (ratio > 1.5) has a mortality of nearly 100% [18] **Image 5**.

Echocardiography can define other associated abnormalities with EA such as the presence of a patent ductus arteriosus, size and direction of shunting through the atrial septal defect/patent foramen ovale, presence of a ventricular septal defect, and hypertrabeculated left ventricle

Fetal echocardiography is a useful diagnostic tool for prenatal diagnosis and monitoring progression of disease in utero. The 4-chamber view of the fetal heart will demonstrate apical displacement of the tricuspid valve annulus, enlarged right ventricular and atrial size, and large tricuspid valve annulus (**Image 6**). Color flow imaging can be used to evaluate the degree of tricuspid valve regurgitation. The pulmonary valve can be evaluated by 2-D and color flow imaging to assess for pulmonary atresia. M-mode assessment can determine any rhythm abnormalities such as supraventricular tachycardia [22]. In addition, signs of hydrops such as

Fetal echocardiogram is important for monitoring clinical status of the fetus during pregnancy. A large multicenter study performed by Freud et al. evaluated over 400 fetal echocardiograms of patients with EA. They demonstrated that larger cardiothoracic ratio, more than moderate

are consistent with EA [20]. Color

Neonatal Ebstein's Anomaly

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Distance is indexed to body surface area and values >8 mm/m<sup>2</sup>

marked cardiomegaly lung development can be impaired.

suggesting left ventricular non-compaction cardiomyopathy.

pericardial effusions can be visualized (**Image 7**).
