Atrioventricular septal defect
A 36 year old female was referred by obstetrician for NT scan.
Ultrasound findings and discussion:
In this case we can see single AV valve instead of two separate valves (mitral & tricuspid) .
Small left heart on 4 CH view.
Large central defect in heart.
All these features are suggestive of complete AVSD.
Genetic counseling done .Patient was advised amniocentesis.
Atrioventricular Septal Defect (AVSD)
Atrioventricular Septal Defect (AVSD), also called an endocardial cushion defect, is a congenital heart defect characterized by failure of the atrioventricular septum to form properly, leading to abnormal communication between the atria and ventricles. AVSD is highly associated with chromosomal abnormalities, especially Trisomy 21 (Down Syndrome).
Fetal Ultrasound Findings:
AVSD is best diagnosed between 18–22 weeks during the fetal anomaly scan using four-chamber and outflow tract views.
Absent Atrioventricular (AV) Septum
Single common AV valve instead of separate mitral and tricuspid valves.
No distinct separation between left and right atria/ventricles.
Large, Central Defect in the Heart
Best seen in the four-chamber view.
Appears as a single, large hole in the middle of the heart.
Unbalanced AVSD (Severe Cases)
One ventricle (left or right) is significantly smaller.
May lead to hypoplastic left or right heart syndrome.
Atrioventricular Valve Abnormalities
Single AV valve instead of two separate valves (mitral & tricuspid).
May have valve regurgitation, leading to atrial enlargement.
Color Doppler Findings
Common AV Valve Regurgitation
Turbulent, bidirectional flow across the common AV valve.
Helps assess severity of AV valve insufficiency.
Abnormal Left-to-Right Shunting
Left-to-right flow at the atrial and ventricular levels.
Bidirectional shunting in some cases.
Pulmonary Overcirculation
Increased pulmonary blood flow due to left-to-right shunting.
Risk of fetal hydrops in severe cases.
Types of AVSD & Imaging Features
Type | Key Features on Ultrasound | Clinical Implications |
Complete AVSD | Large central defect, single AV valve | Highly associated with Trisomy 21 |
Partial AVSD | Separate AV valves, primum ASD, small VSD | Less severe, may be isolated |
Unbalanced AVSD | One ventricle smaller than the other | Risk of hypoplastic left/right heart |
Differential Diagnosis
Condition | Key Differentiating Features |
Isolated Ventricular Septal Defect (VSD) | No common AV valve, normal atrial septum |
Isolated Atrial Septal Defect (ASD) | No VSD component, normal AV valves |
Tetralogy of Fallot (TOF) | Overriding aorta, pulmonary stenosis, small RV |
Double Outlet Right Ventricle (DORV) | Both great vessels arise from RV |
Genetic Associations & Extra-Cardiac Anomalies
Trisomy 21 (Down Syndrome) – Most Common (~40–50% of AVSD cases)
Trisomy 18, Trisomy 13 (Less Common)
Heterotaxy Syndrome (Right or Left Isomerism)
Polysplenia or asplenia
Situs inversus or situs ambiguous
Abnormal systemic and pulmonary venous return
Prognosis & Postnatal Considerations
Surgical Repair Required
Complete AVSD → Corrective surgery at 3–6 months postnatally.
Partial AVSD → Surgical closure of ASD/VSD at 6–12 months.
Further Reading:
