Apical displacement of septal and posterior tricuspid valve leaflets

Coaptation point of tricuspid valve (i.e., where valve leaflets fit together) is lowered into right ventricle (RV)

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  Low valve coaptation point causes “atrialization” of RV

  
  
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  Right atrium (RA) is large; functional RV is small

Tricuspid valve dysplasia + leaflet malposition → tricuspid regurgitation

Tricuspid regurgitation → right atrial enlargement

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  Right atrial enlargement can be severe by 3rd trimester

  
  
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  Creates wall-to-wall heart appearance

Atrialization of ventricle → small functional RV

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  Pulmonary artery often small or atretic

In utero mortality rate is 45%

Check for offset of valves on 4-chamber view of every fetal heart scan

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  Tricuspid leaflet should be more apically inserted than mitral

  
  
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  Mean mitral valve-tricuspid valve distance in 2nd trimester is 2.8 ± 0.9 mm

  
  
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  Mean mitral valve-tricuspid valve distance in 3rd trimester is 4.6 ± 1.1 mm

Abnormal offset of tricuspid valve is key to making diagnosis of Ebstein anomaly

At 18-20 weeks, RA enlargement may not be dramatic

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  If abnormal offset, bring patient back for follow-up

Use Doppler (color ± pulsed wave) to look or tricuspid regurgitation

Use 3-vessel view to assess size of outflow tracts, as pulmonary artery is often small

Look for other abnormalities

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  Ebstein anomaly has been described in trisomy 21, 18