Atrioventricular Septal Defect

KEY FACTS

Terminology

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Central cardiac defect involving atrial (ASD) and ventricular (VSD) septal defects, atrioventricular (AV) valves, and conducting system
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  Balanced : Right and left ventricles are equal in size
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  Unbalanced : Majority of flow to 1 ventricle so unequal size

Imaging

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Missing crux (central portion) of heart on 4-chamber view
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  Normally atrial and ventricular septa meet at crux of heart and AV valves are separate and distinct
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  Tricuspid insertion normally 1-2 mm offset (toward apex) from mitral insertion
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  In atrioventricular septal defect (AVSD), usual offset of AV valves is absent
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Single AV valve makes straight line across heart in systole
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Appears as large central defect in diastole

Scanning Tips

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Use cine/video clips and color Doppler in all fetal heart evaluation
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  Look for flow through VSD, AV valve regurgitation
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Check ventricular size: Asymmetry suggests unbalanced defect
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Slow heart rate suggests heart block, so check situs, look for additional features of heterotaxy syndromes
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  Look at vessels behind heart on 4-chamber view
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    Azygos continuation of inferior vena cava (2 vessels present; aorta and dilated azygos vein)
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    Anomalous pulmonary venous return (tubular vascular confluence posterior to atria, anterior to descending aorta)
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Look for features of trisomy 21
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  ~ 50% of fetal AVSD cases have trisomy 21
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  Thick nuchal fold, rhizomelic limb shortening, duodenal atresia, echogenic bowel, pelviectasis, clinodactyly

AVSD graphic shows both ASD & VSD creating a defect in the crux of the heart

. Instead of the normally separate tricuspid & mitral valves, a single AV valve

straddles the central defect.

Four-chamber view shows a large VSD

, no atrial septum

, & a single AV valve (dots) spanning both ventricles that are similar in size, indicating a balanced AVSD. The aorta should be the only structure behind the heart on this view. Look for azygos continuation of the IVC

or anomalous pulmonary veins in heterotaxy.