❤️ VSD vs AVSD

What’s the Difference on Fetal Ultrasound?

Both involve septal defects.

But they are not the same disease.

Understanding the difference changes:

• Genetic risk
• Prognosis
• Surgical planning
• Counseling approach

1️⃣ What is VSD?

Ventricular Septal Defect

👉 A defect in the interventricular septum only.

Ultrasound findings:

• Defect in ventricular septum
• Separate mitral and tricuspid valves
• Normal AV valve offset preserved
• 4-chamber view mostly preserved

Most common type:

• Perimembranous VSD

Many small VSDs may close spontaneously.

2️⃣ What is AVSD?

Atrioventricular Septal Defect

👉 A defect involving both:

• Atrial septum
• Ventricular septum
• Atrioventricular valves

This is not just a hole.

It is a failure of endocardial cushion development.

Ultrasound findings of AVSD:

• Loss of AV valve offset
• Single AV valve (in complete AVSD)
• Common AV valve bridging both ventricles
• Primum ASD
• Inlet VSD
• Often symmetric ventricles

The classic sign:

“No offset” between mitral and tricuspid valves.

🔎 Key Differentiation on 4-Chamber View

Feature	VSD	AVSD
AV valve offset	Present	Absent
AV valves	Two separate	Single or common
Atrial septum	Usually intact	Primum defect
Genetic association	Sometimes	Strongly associated with Trisomy 21

🧬 Genetic Risk

AVSD has strong association with:

• Down syndrome (Trisomy 21)
• Heterotaxy

VSD:

• Often isolated
• Lower chromosomal association unless other markers present

🧠 Clinical Thinking Pattern

If you see a ventricular defect:

1. Check AV valve offset.
2. Look at atrial septum (primum area).
3. Evaluate valve morphology.
4. Assess for symmetry.
5. Consider genetic testing if AVSD suspected.

🔥 The Core Message

A VSD is a hole in the septum.

An AVSD is a failure of septation involving:

• Septum
• AV valves
• Endocardial cushions

They may look similar at first glance,

but the implications are very different.