Fetal Ebstein Anomaly

See more on Ebstein's Anomy in the CHD section.

Ebstein anomaly is an anomaly in which the tricuspid valve is displaced downward into the right ventricle. This may be associated with significant atrealisation of the right ventricle, leading to significant reduction in the right ventricular capacitance, potentially resulting in functional RV hypoplasia. These infants have typically an enlarge right atrium, and a potential right to left shunting at the atrial level (postnatally) with significant tricuspid insufficiency. They are at risk of arrhytmia (such as re-entry tachycardia). 

Severe Ebstein can be associated with circular shunt physiology, in which the blood flow enter the Pulmonary Artery via the ductus arteriosus, following which it returns to the RV by significant pulmonary insufficiency. The blood flow then enters the right atrium secondary to tricuspid valve insufficiency and to the left atrium via the patent foramen ovale. Following which, it enters the left ventricle (LV) and is pumped into the aorta, to eventually re-enter the ductus arteriosus. This physiology leads to a low cardiac output state and may compromise organ oxygenation.

Circular shunt physiology in Ebstein: Aorta → Ductus → Pulmonary artery → Pulmonary Insufficiency → Right Ventricle → Tricuspid insufficiency → Right atrium → Foramen Ovale → Left atrium → Mitral valve → Left ventricle → Aortic valve → Aorta → Ductus arteriosus (Learn more here, and here). Some have described the use of maternal NSAIDs as a way to constrict the fetal duct in an attempt to address this fatal physiology for the fetus / newborn. Article here on "Surgical Management of Neonatal Ebstein’s Anomaly Associated With Circular Shunt".

The SAS score (0 to 10) is a prognostication score developed based on fetal echocardiography for evaluating Ebstein's anomaly. It combines five echocardiographic measurements (cardiothoracic ratio, Celermajer index, RV-to-LV ratio, pulmonary flow, and ductal flow) into a single score to predict the likelihood of fetal and neonatal mortality. Higher scores indicate a greater risk of adverse outcomes. SAS for Simpson Andrews Sharland (authors’ initials).

Key Components of the SAS Score: 

• Cardiothoracic Ratio (CTR): Compares the heart's size to the chest cavity. 

  • <0.65 = 0 

  • 0.65 to 0.75 = 1

  • >0.75 = 2 

• Celermajer Index: Measures the ratio of the right atrium and atrialized right ventricle to the combined area of the functional right ventricle, left atrium, and left ventricle. 

  • <1.0 = 0

  • 1.0-1.5 = 1

  • >1.5 = 2

• Right Ventricle to Left Ventricle (RV/LV) Ratio: Compares the size of the right and left ventricles. Ratio of RV/LV size (measured in 2 dimensions just below the mitral valve annulus at end-diastole in a 4-chamber view). In the study - expressing the latter as a z score did not improve prediction.

  • <1.5 = 0

  • 1.5-2.0 = 1

  • >2.0 = 2

• Pulmonary Blood Flow: Assesses the flow of blood through the pulmonary artery, with reduced or absent flow indicating a more severe defect. 

  • Normal =0

  • Reduced = 1

  • Absent = 2

• Ductal Flow: Examines the flow through the ductus arteriosus, looking for retrograde flow, which can be associated with worse outcomes. 

  • Anterograde = 0

  • Both = 1

  • Retrograde = 2

• Scoring and Interpretation: Each of the five parameters is assigned a score of 0, 1, or 2 based on its severity, with 0 indicating normal or mild abnormality and 2 indicating a severe abnormality. The scores for each parameter are then added together to create a total SAS score, ranging from 0 to 10. A higher score is associated with a higher risk of fetal or neonatal death. 

Reference: Andrews RE, Tibby SM, Sharland GK, Simpson JM. Prediction of outcome of tricuspid valve malformations diagnosed during fetal life. Am J Cardiol. 2008 Apr 1;101(7):1046-50. doi: 10.1016/j.amjcard.2007.11.049. Epub 2008 Feb 6. PMID: 18359329.

Fetal Echocardiography Example

Moderate Ebstein's malformation of tricuspid valve with moderate to severe regurgitation. Severe right atrial dilation. Moderate RV dilatation. 

Case by Dr Wadi Mawad - Pediatric Cardiology at the Montreal Children's Hospital