Atrioventricular septal defect

Atrioventricular septal defects (AVSDs), also known as atrioventricular canal defects or endocardial cushion defects, comprise a relatively wide range of defects involving the atrial septum, ventricular septum, and one or both of the tricuspid or mitral valve. They can represent 2-7% of congenital heart defects. 

Epidemiology

The estimated prevalence is at ~3-4 in 10,000 births.

Pathology

It results from deficient development of the apical portion of the atrial septum, basal portion of the interventricular septum, as well as atrioventricular valves. All four chambers of the heart communicate therefore both left to right and right to left shunts can occur.

Classification

Many have been used but can be broadly divided into:

• complete 
• incomplete 

An AVSD may also be balanced or unbalanced ⁸.

Associations

• trisomy 21 (Down syndrome): may be present in up to 50% of cases ⁴
• trisomy 18 (Edwards syndrome): may be present in up to 25 % of cases ⁷
• heterotaxy syndromes ⁷
  • may be present in up to 10% of cases of asplenia (Ivemark) syndrome ⁴

Radiographic features

Plain radiograph

Plain chest radiographic features are often not specific but may show have cardiomegaly +/- features of pulmonary hypertension and mitral valve insufficiency.

Echocardiography

Allows direct visualization of the defect spectrum and often a large defect of the midline heart structures are seen. Color Doppler often aids in further visualization of the central opening.

Angiography

An AVSD can give a classical "Gooseneck" sign on a lateral left ventricular angiogram ³.

MRI

Allows direct visualization of defect spectrum. Can be superior in assessing cardiac chamber dimensions and to assess the presence/extent of ventricular hypoplasia which is a determinant of surgical risk.