Category: OB Ultrasound

Why It Matters in the 4-Chamber View

One of the most important structural clues in the fetal 4-chamber view is the atrioventricular (AV) valve offset.

Understanding this single feature helps differentiate:

• Normal heart anatomy

• Inlet VSD

• Atrioventricular septal defect (AVSD)

⸻

1️⃣ What Is AV Valve Offset?

In a normal heart:

• The tricuspid valve inserts slightly more apically

• Compared to the mitral valve

In other words:

The tricuspid valve sits slightly lower (closer to the apex) than the mitral valve.

This vertical difference in insertion level is called the AV valve offset.

⸻

2️⃣ Why Does This Offset Exist?

During cardiac development:

• The right ventricle forms slightly more apically than the left ventricle.

• Proper separation of the endocardial cushions allows the AV valves to insert at different levels.

If endocardial cushion development is normal,

the offset is preserved.

⸻

3️⃣ How Does It Look on Ultrasound?

On a standard 4-chamber view:

• Identify the interventricular septum.

• Look at where each AV valve leaflet attaches.

In a normal heart:

• The tricuspid valve insertion is visibly lower than the mitral valve insertion.

If this step is skipped,

important diagnoses can be missed.

⸻

4️⃣ What Happens When the Offset Is Lost?

Loss of AV valve offset strongly suggests an endocardial cushion defect, most commonly:

• Atrioventricular septal defect (AVSD)

In AVSD:

• Mitral and tricuspid valves insert at the same level.

• The central cardiac structure appears “flat.”

• A common AV valve may be present.

This is not just a septal hole —

it reflects abnormal septation of the atrioventricular junction.

⸻

5️⃣ Inlet VSD vs AVSD: The Critical Difference

Both may show a defect near the inlet septum.

But:

• Inlet VSD → Offset preserved

• AVSD → Offset lost

If the offset remains intact,

it is unlikely to be a true AVSD.

⸻

6️⃣ Practical Scanning Tips

When evaluating a possible septal defect:

1. Zoom in on the AV junction.

2. Compare the insertion levels carefully.

3. Assess valve morphology.

4. Look for a primum ASD.

5. Evaluate ventricular symmetry.

Always ask:

Are the AV valves inserting at different levels?

🔎 Quick Comparison

Feature	Normal	Inlet VSD	AVSD
AV valve offset	Present	Present	Absent
AV valves	Separate	Separate	Common/abnormal
Primum ASD	No	No	Yes
Down syndrome association	Low	Low	High

🔑 Key Takeaway

AV valve offset is a structural marker of proper endocardial cushion development.

If the offset is preserved → think simple septal defect.

If the offset is lost → suspect AVSD.

One small detail in the 4-chamber view can completely change the diagnosis.

초음파에서 어떻게 구분할까?

VSD와 AVSD는 모두 “중격 결손”이지만,

완전히 다른 질환입니다.

구분이 중요한 이유는:

• 염색체 이상 연관성
• 예후
• 수술 범위
• 산모 상담 방향

이 모두가 달라지기 때문입니다.

1️⃣ VSD란?

Ventricular Septal Defect (심실중격결손)

👉 심실 중격에만 결손이 있는 경우

초음파 소견

• 심실중격에 결손 보임
• 승모판(mitral)과 삼첨판(tricuspid) 분리되어 있음
• 정상적인 AV valve offset 유지
• 4 chamber 구조는 대체로 유지

가장 흔한 형태:

• Perimembranous VSD

작은 VSD는 출생 전 또는 출생 후 자연 폐쇄되는 경우도 많습니다.

2️⃣ AVSD란?

Atrioventricular Septal Defect (방실중격결손)

👉 단순한 “구멍”이 아니라

👉 심방 + 심실 + 판막 구조까지 함께 이상

원인:

• Endocardial cushion 발달 이상

AVSD 초음파 특징

• AV valve offset 소실
• 단일 공통 방실판막 (complete AVSD)
• Primum ASD 동반
• Inlet VSD 동반
• 좌우 심실이 비교적 대칭

가장 중요한 포인트:

승모판과 삼첨판의 높이 차이가 사라짐 (no offset sign)

🔎 4-Chamber View에서 구분 핵심

항목	VSD	AVSD
AV valve offset	유지됨	소실
판막	두개	하나(공통판막)
심방중격	정상	primum 결손
염색체 연관	낮음(단독일 경우)	다운증후군과 강한연관

🧬 염색체 이상과의 연관

AVSD는 특히:

• Trisomy 21 (다운증후군)
• Heterotaxy

와 밀접하게 관련됩니다.

반면,

VSD는 단독으로 발견되는 경우가 많고

염색체 이상 위험은 상대적으로 낮습니다.

(단, 다른 소견 동반 시 재평가 필요)

🧠 임상적 사고 흐름

심실 중격에 결손이 보이면:

1️⃣ AV valve offset 확인

2️⃣ 심방중격 primum 부위 확인

3️⃣ 판막 구조 관찰

4️⃣ 좌우 심실 대칭 여부 확인

5️⃣ AVSD 의심되면 유전자 상담 고려

🔥 핵심 한 줄

VSD는 “중격의 구멍”입니다.

AVSD는 “중격과 판막 형성의 실패”입니다.

겉보기엔 비슷해 보여도

임상적 의미는 완전히 다릅니다.

Abdominal Parallel Vessels on Fetal Ultrasound

Why It Matters

In a normal fetus, the abdominal aorta and inferior vena cava (IVC) are positioned asymmetrically.

The aorta lies slightly to the left of the spine, while the IVC is located anterior and to the right.

When these vessels appear parallel and symmetric, it should raise suspicion for abnormal laterality.

Key Association: Left Atrial Isomerism

Left atrial isomerism (also known as polysplenia syndrome) is often associated with:

• Interrupted IVC with azygos continuation
• Parallel abdominal vessels
• Cardiac conduction abnormalities
• Complex congenital heart disease

The “parallel vessel sign” can be one of the earliest clues.

Clinical Insight

If parallel vessels are identified:

✔ Evaluate the three-vessel trachea (3VT) view

✔ Assess pulmonary venous drainage

✔ Check cardiac position and axis

✔ Examine abdominal situs carefully

Fetal heterotaxy is not just a heart problem —

it is a systemic laterality disorder.

초음파에서 어떻게 구분할까?

Pulmonary venous return 이상은

겉보기 심장 구조가 비교적 정상처럼 보일 수 있어서

놓치기 쉬운 질환입니다.

핵심은:

폐정맥이 좌심방(LA)으로 제대로 들어오는가?

1️⃣ Total Anomalous Pulmonary Venous Return (TAPVR)

구조

• 모든 폐정맥이 LA로 연결되지 않음
• 우심방(RA) 또는 전신 정맥계로 연결

즉,

❗ LA로 들어오는 폐정맥이 “0개”

초음파 소견

✔ LA가 작게 보일 수 있음

✔ LA posterior wall에 유입이 안 보임

✔ Posterior confluence structure

✔ Vertical vein 보일 수 있음

✔ RA dilation 가능

Color Doppler로 LA 쪽 흐름이 없으면 의심

임상

• 출생 직후 cyanosis
• 응급 수술 필요
• 특히 obstructed TAPVR는 위급

2️⃣ Partial Anomalous Pulmonary Venous Return (PAPVR)

구조

• 일부 폐정맥은 정상적으로 LA로 연결
• 일부만 비정상 연결

즉,

✔ LA로 최소 1개 이상 정상 유입 존재

초음파 소견

✔ LA로 유입 보임 (2개 중 일부)

✔ RA enlargement 있을 수 있음

✔ Confluence 구조 불완전

진단이 더 어렵고

놓치기 쉽습니다.

🔥 가장 중요한 감별 포인트

항목	TAPVR	PAPVR
LA로 유입	없음	일부있음
LA 크기	작을 수 있음	비교적 정상
RA dilation	흔함	가능
예후	수술 필수	경우에 따라

🧠 실전 접근

1️⃣ LA posterior wall 집중 관찰

2️⃣ 최소 2개 이상 폐정맥 유입 확인

3️⃣ Confluence 의심 구조 찾기

4️⃣ Vertical vein 유무 확인

🔥 놓치지 말아야 할 것

TAPVR는

4 chamber view가 거의 정상처럼 보일 수 있습니다.

그래서

“폐정맥을 확인하지 않으면, 진단은 반쪽이다.”

폐정맥은

“산소가 돌아오는 길”입니다.

즉,

• 폐동맥은 나가는 길
• 폐정맥은 돌아오는 길

둘 다 봐야 circulation이 완성됩니다.

🔥 1️⃣ 폐정맥을 확인하는 가장 큰 이유

👉 Total Anomalous Pulmonary Venous Return (TAPVR)

이 질환은

• 4 chamber view가 정상처럼 보일 수 있음
• Outflow tract도 정상처럼 보일 수 있음

하지만

❗ 폐정맥이 좌심방(LA)으로 연결되지 않음

이걸 놓치면

출생 직후 심각한 청색증이 생길 수 있습니다.

🔎 2️⃣ 정상 폐정맥 확인 포인트

정상에서는:

✔ 좌심방 posterior wall로 2개 이상 유입 확인

✔ Color Doppler에서 LA로 향하는 flow

✔ Confluence 보이지 않음 (개별 유입)

🚨 3️⃣ TAPVR 의심 소견

• LA가 작게 보임
• Posterior LA wall 뒤에 confluence 구조
• Vertical vein 의심 구조
• 4 chamber view에서 폐정맥 유입 안 보임

3VT에서는

• 추가 혈관이 보일 수도 있음

🧠 4️⃣ 왜 PA만 보고 끝내면 안 될까?

많은 conotruncal anomaly에서는

outflow tract에 집중하지만

👉 Inflow도 equally 중요합니다.

특히:

• Heterotaxy
• Right atrial isomerism
• Complex CHD

에서는 pulmonary venous return 이상 동반 가능

🔥 5️⃣ 임상적으로 중요한 이유

TAPVR는

• duct-dependent lesion일 수 있음
• 응급 수술 대상
• 산전 진단 여부가 예후에 영향

💡 실전 체크리스트

폐정맥 확인할 때:

1️⃣ LA posterior wall에 유입 보이는가?

2️⃣ 최소 2개 이상 확인했는가?

3️⃣ Color Doppler 방향 정상인가?

4️⃣ 이상 confluence 보이는가?

🔥 한 줄 정리

Outflow가 정상이라고 해서 심장이 정상은 아니다.

폐정맥이 좌심방으로 들어오는지 반드시 확인해야 한다.

The Three Vessel Trachea (3VT) view is a crucial plane in fetal cardiac assessment.

When Tetralogy of Fallot (TOF) or Double Outlet Right Ventricle (DORV) is suspected,

3VT can provide important clues — but it does not always give a complete answer.

So what should we look for?

1️⃣ Normal 3VT Pattern

In a normal heart:

• Pulmonary artery (largest, most anterior)
• Aorta (slightly smaller)
• Superior vena cava (smallest)

They form a characteristic V-shape, converging toward the descending aorta.

Loss of this pattern raises suspicion.

2️⃣ 3VT in TOF

In Tetralogy of Fallot:

✔ Pulmonary artery is small (due to pulmonary stenosis)

✔ Aorta appears relatively larger

✔ The V-shape becomes asymmetric

✔ Sometimes the pulmonary artery is barely visible

However:

👉 The aorta still follows its normal anatomical course

👉 It connects to the left ventricle (despite override)

Key clue:

Pulmonary artery hypoplasia is the dominant feature.

3️⃣ 3VT in DORV

In Double Outlet Right Ventricle:

✔ Great vessel relationship may appear parallel or abnormal

✔ Both great arteries arise predominantly from RV

✔ V-shape may be distorted or absent

Unlike TOF:

👉 The problem is not just pulmonary narrowing

👉 The origin of both vessels is abnormal

The aorta may not show the expected leftward course from LV.

4️⃣ Practical Differentiation Strategy

On 3VT alone, differentiation can be difficult.

So combine with:

✔ LVOT view — Does LV connect directly to the aorta?

✔ RVOT view — Degree of pulmonary stenosis?

✔ 4-chamber + septal alignment

If pulmonary artery is small but LV–aorta connection exists → think TOF.

If both great vessels seem to arise from RV and LV lacks direct aortic connection → think DORV.

5️⃣ Important Reminder

3VT is a screening plane.

Definitive differentiation requires:

• Multi-plane imaging
• Careful tracing of outflow tracts
• Assessment of override degree

Bottom Line

On 3VT:

• TOF → asymmetric V-shape with small pulmonary artery
• DORV → abnormal vessel origin and distorted pattern

The critical question remains:

👉 Is the aorta directly connected to the left ventricle?

“3VT alone suggests size and alignment abnormalities, but definitive differentiation requires LVOT assessment.”

Tetralogy of Fallot (TOF) and Double Outlet Right Ventricle (DORV) can look very similar on fetal ultrasound.

Both involve:

• VSD
• Aortic override
• Abnormal outflow tract alignment

So how do we differentiate them?

1️⃣ The Key Question

👉 Where does the aorta arise from?

That is the core difference.

TOF (Tetralogy of Fallot)

✔ Aorta overrides the VSD

✔ But still primarily connected to the left ventricle

✔ Pulmonary stenosis present

On 4-chamber view:

• VSD visible
• Overriding aorta partially over septum

On outflow tract view:

• Pulmonary artery smaller than aorta

👉 Aorta originates mainly from LV (with override)

DORV (Double Outlet Right Ventricle)

✔ Both aorta and pulmonary artery arise predominantly from the right ventricle

✔ Large VSD is required for LV output

Key point:

👉 Aorta arises entirely or mostly from RV

On imaging:

• Both great vessels aligned over RV
• VSD provides LV connection

2️⃣ Why They Look Similar

Because both show:

• Overriding aorta
• VSD
• Abnormal outflow relationship

But the degree of override matters.

TOF → partial override

DORV → near complete RV origin

3️⃣ Practical Ultrasound Clues

✔ Assess the relationship of great arteries to ventricles

✔ Trace the outflow tracts carefully

✔ Look at subaortic conus presence

✔ Evaluate pulmonary stenosis severity

If pulmonary stenosis is severe and aorta is mildly overriding → think TOF.

If both great arteries sit mostly over RV → think DORV.

4️⃣ Why It Matters

Because prognosis and surgical planning differ.

TOF:

• Well-defined surgical repair
• Often isolated

DORV:

• Multiple anatomical subtypes
• Surgical strategy depends on VSD location

Clinical Tip

When unsure:

👉 Ask: Does the LV have a direct connection to the aorta?

If yes → more likely TOF

If no → think DORV

When a ventricular septal defect (VSD) is found on prenatal ultrasound,

one of the first questions parents ask is:

“Will it close on its own?”

The answer is:

👉 Yes, sometimes it does — even before birth.

But it depends on the type and size.

1️⃣ Small Muscular VSD

This is the type most likely to close spontaneously.

• Located in the muscular part of the septum
• Often small (1–2 mm)
• May become smaller as the fetal heart grows
• Can close before birth or within the first year of life

✔ Prognosis is usually excellent

✔ No major complications if isolated

2️⃣ Perimembranous VSD

This is the most common type.

• Located near the aortic valve
• Small defects may close
• Larger ones are less likely to close spontaneously

⚠ Needs follow-up because of possible:

• Aortic valve prolapse
• Aortic regurgitation

3️⃣ Inlet or Outlet VSD

These types are less likely to close before birth.

• Often associated with other structural findings
• May require postnatal cardiology follow-up
• Sometimes surgical repair is needed

Does Closure Happen in the Womb?

Yes — but not always.

Closure can occur because:

• The septum continues to grow
• Tissue gradually covers the defect
• Hemodynamic forces change as the heart matures

However, some VSDs remain stable throughout pregnancy.

Important Perspective

A small isolated VSD:

• Does not usually affect fetal growth
• Does not cause fetal heart failure
• Does not require early delivery

Most babies with small isolated VSDs are born healthy.

When Should Parents Worry?

Concern increases when:

• The VSD is large
• There are additional heart defects
• There are extracardiac anomalies
• Chromosomal risk is elevated

In those cases, further evaluation is recommended.

Bottom Line

Yes — some VSDs close before birth.

Especially small muscular defects.

The key factors are:

👉 Location

👉 Size

👉 Associated findings

Not just the presence of a “hole.”