Classification of Cyanotic Congenital Heart Disease

Q1. Which of the following is a right heart obstructive lesion?

Pulmonary atresia

Hypoplastic left heart syndrome

Transposition of great arteries

Truncus arteriosus

Pulmonary atresia is a classic right heart obstructive lesion with decreased pulmonary blood flow.

Q2. In tricuspid atresia, the ECG axis is typically:

Right axis deviation (90° to 180°)

Left superior axis (0° to –90°)

Normal newborn axis (90° to 180°)

Extreme right axis (>180°)

Tricuspid atresia shows a left superior axis deviation (0° to –90°), which helps in diagnosis.

Q3. A newborn with oxygen saturation <90% without a difference between upper and lower limbs most likely has:

Right heart obstructive lesion

Left heart obstructive lesion

Mixing lesion

Normal physiology

Right heart obstructive lesions present with saturations <90% and no pre/post-ductal difference.

Q4. Which lesion typically shows increased pulmonary blood flow on chest X-ray?

Pulmonary atresia

Tricuspid atresia

Hypoplastic left heart syndrome

Tetralogy of Fallot

Left heart obstructive lesions such as HLHS often cause pulmonary over-circulation, seen as increased pulmonary markings on CXR.

Q5. Which of the following is a ductal-independent lesion?

Hypoplastic left heart syndrome

Pulmonary atresia

Transposition of great arteries

Critical pulmonary stenosis

TGA and other mixing lesions are ductal-independent since mixing occurs at atrial/ventricular levels.

Q6. Which finding suggests a left heart obstructive lesion on CCHD screening?

O₂ saturation <90% without gradient

Positive hyperoxia test

Greater than 3% upper vs lower O₂ saturation difference

Normal chest X-ray

A difference of >3% between pre- and post-ductal O₂ saturation suggests left heart obstructive lesions.

Q7. Critical aortic stenosis in a newborn is usually associated with:

Left axis deviation (0° to +90°)

Right axis deviation (90° to 180°)

Left superior axis (0° to –90°)

Extreme right axis (>180°)

Critical aortic stenosis is the exception among left heart lesions, showing left axis deviation.

Q8. In tetralogy of Fallot, the typical axis on ECG is:

Left superior axis

Normal newborn axis

Right axis deviation (90° to 180°)

Left axis (0° to 90°)

TOF is associated with right axis deviation.

Q9. Hyperoxia test is typically positive in which lesions?

Right heart obstructive lesions

Left heart obstructive lesions

Mixing lesions

All CCHDs

Right heart obstructive lesions show a positive hyperoxia test, whereas others usually show negative.

Q10. A newborn has O₂ saturation <95%, no gradient, and normal axis ECG. Most likely diagnosis?

Critical pulmonary stenosis

Coarctation of aorta

Transposition of great arteries

Hypoplastic left heart syndrome

TGA presents with cyanosis (O₂ sat <95%), no gradient, and usually normal axis for newborn.

Q11. Which of the following is most characteristic of Hypoplastic Left Heart Syndrome on screening?

O₂ saturation <90% without gradient

Positive hyperoxia test

Upper-lower extremity O₂ difference >3%

Right axis deviation on ECG

HLHS typically shows O₂ sat <95% with significant pre/post-ductal difference; PDA is required for systemic flow.

Q12. Which lesion often shows a left axis (0° to +90°) on ECG in a newborn?

TOF

Pulmonary atresia

TAPVR

Truncus arteriosus

Pulmonary atresia typically shows a left axis deviation (0° to +90°) on ECG.

Q13. In coarctation of aorta, which of the following is true?

No BP difference between upper and lower limbs

Positive BP gradient between upper and lower extremities

Right-to-left intracardiac shunt

Normal pulmonary blood flow

CoA causes reduced systemic flow with a characteristic BP gradient between upper and lower extremities.

Q14. Which condition is most likely to present with decreased pulmonary blood flow on CXR?

HLHS

Tricuspid atresia

TAPVR

Truncus arteriosus

Right heart obstructive lesions (e.g., tricuspid atresia) show decreased pulmonary vascular markings on CXR.

Q15. In d-TGA with associated pulmonary hypertension or CoA, which unique screening finding may be observed?

Lower O₂ saturation in the foot

Higher O₂ saturation in the foot compared to the right arm

Equal O₂ saturation in all extremities

Positive hyperoxia test

In d-TGA with PHTN or CoA, reversed differential cyanosis is observed (higher O₂ in foot than right arm).

Q16. Which lesion is NOT dependent on PDA for survival?

Truncus arteriosus

Hypoplastic left heart syndrome

Pulmonary atresia

Critical aortic stenosis

Mixing lesions like truncus arteriosus are ductal-independent, unlike HLHS or PA which require PDA.

Q17. A positive hyperoxia test in a cyanotic newborn points towards:

Right heart obstructive lesion

Left heart obstructive lesion

Mixing lesion

Sepsis

Right heart obstructive lesions improve with oxygen administration, leading to a positive hyperoxia test.

Q18. Total anomalous pulmonary venous return (TAPVR) is classified under:

Right heart obstructive lesions

Left heart obstructive lesions

Mixing lesions

Ductal-dependent lesions

TAPVR is a mixing lesion where systemic and pulmonary venous return mix before entering systemic circulation.

Q19. Which statement about PDA in left heart obstructive lesions is correct?

It supplies systemic blood flow (PA → Ao)

It supplies pulmonary blood flow (Ao → PA)

It is not required for survival

It only functions if VSD is present

In left heart obstructive lesions, PDA supplies systemic circulation by shunting from PA to Ao.

Q20. Which ECG finding is normal in newborns and seen in many mixing lesions?

Left superior axis (0° to –90°)

Left axis deviation (0° to +90°)

Extreme axis deviation (>180°)

Normal newborn axis (90° to 180°)

Mixing lesions such as TGA and truncus arteriosus usually present with normal newborn axis (90°–180°).

CCHDs are commonly classified based on the underlying physiological mechanism:

1. The “5 Ts” of Classic Cyanotic Heart Disease

A simple mnemonic often used:

Tetralogy of Fallot (TOF)
Transposition of the Great Arteries (TGA)
Tricuspid Atresia
Truncus Arteriosus
Total Anomalous Pulmonary Venous Connection (TAPVC)

(Other important cyanotic lesions may also be included, e.g., Hypoplastic Left Heart Syndrome, Ebstein’s anomaly.)

2. Physiological Classification

A. Decreased Pulmonary Blood Flow

Caused by obstruction to right ventricular outflow.
Right-to-left shunt at atrial or ventricular level provides systemic output.
Examples:
Tetralogy of Fallot
Pulmonary atresia (with or without VSD)
Tricuspid atresia
Ebstein’s anomaly

B. Increased Pulmonary Blood Flow

Mixing of systemic and pulmonary venous blood, but pulmonary over-circulation occurs.
Examples:
Transposition of Great Arteries (TGA)
Total Anomalous Pulmonary Venous Connection (TAPVC)
Truncus arteriosus
Hypoplastic Left Heart Syndrome (HLHS) (mixing lesion with duct-dependent systemic flow)
Double outlet right ventricle (some variants)

3. Embryological/Anatomical Classification

Conotruncal abnormalities → TOF, Truncus arteriosus, TGA, Double outlet RV
Septal defects with outflow obstruction → Tricuspid atresia, Pulmonary atresia with VSD
Anomalous pulmonary venous return → TAPVC
Hypoplastic structures → HLHS

4. Clinical/Echocardiographic Classification

Cyanotic lesions with decreased pulmonary blood flow → TOF, Tricuspid atresia, Pulmonary atresia
Cyanotic lesions with increased pulmonary blood flow → TGA, TAPVC, Truncus arteriosus
Single-ventricle physiology → HLHS, Univentricular heart

✅ Summary Table:

Group	Examples
Decreased pulmonary blood flow	TOF, Pulmonary atresia, Tricuspid atresia, Ebstein’s anomaly
Increased pulmonary blood flow	TGA, TAPVC, Truncus arteriosus, HLHS
Conotruncal anomalies	TOF, TGA, Truncus arteriosus, DORV
Abnormal venous return	TAPVC
Hypoplastic structures	HLHS

Lesion Type	Examples	Hemodynamics & Shunt Physiology	Role of PDA / PFO / VSD	Screening Findings	CXR Findings	ECG Axis Findings
Right Heart Obstructive Lesions	– Pulmonary atresia (PA)- Tricuspid atresia- TOF- Critical pulmonary stenosis	↓ Pulmonary blood flow; Right-to-left intracardiac shunt	– PDA: supplies pulmonary blood flow (Ao → PA)- PFO: RA → LA (deoxygenated)- VSD: RV → LV (deoxygenated)	– O₂ sat <90%- No upper/lower extremity gradient- Positive hyperoxia test	↓ or normal pulmonary blood flow	– PA: Left axis (0° to +90°)- Tricuspid atresia: Left superior axis (0° to –90°)- TOF & Critical PS: Right axis (+90° to +180°)
Left Heart Obstructive Lesions	– Hypoplastic Left Heart Syndrome (HLHS)- Interrupted Aortic Arch (IAA)- Coarctation of Aorta (CoA)- Critical Aortic Stenosis	↓ Systemic flow; Left-to-right intracardiac shunt → pulmonary overcirculation	– PDA: supplies systemic blood flow (PA → Ao)- PFO: LA → RA (oxygenated)- VSD: LV → RV (oxygenated)	– O₂ sat <95%- >3% upper vs. lower sat difference- Negative hyperoxia test- Positive BP gradient (except HLHS)	↑ Pulmonary blood flow	– Normal newborn axis (+90° to +180°)- Critical AS: Left axis (0° to +90°)
Mixing Lesions	– Transposition of Great Arteries (TGA)- Total Anomalous Pulmonary Venous Return (TAPVR)- Truncus Arteriosus	Complete mixing of systemic & pulmonary circulations; Ductal-independent	– PDA: Not required but may coexist- PFO: May or may not be present	– O₂ sat <95%- No upper/lower sat difference- Exception: d-TGA + PHTN/CoA → higher foot O₂ sat vs. arm- Negative hyperoxia test	Normal or ↑ pulmonary blood flow	Normal newborn axis (+90° to +180°)

🔹 20 Short Questions & Answers – CCHD Evaluation

Q1. What is the hallmark of right heart obstructive lesions on CCHD screening?
A1. Oxygen saturation <90% with no pre/post-ductal gradient; hyperoxia test positive.

Q2. Which lesions are classified as right heart obstructive?
A2. Pulmonary atresia, tricuspid atresia, tetralogy of Fallot, and critical pulmonary stenosis.

Q3. What is the primary role of PDA in right heart obstructive lesions?
A3. PDA supplies pulmonary blood flow by shunting blood from aorta to pulmonary artery.

Q4. What axis deviation is typical for tricuspid atresia?
A4. Left superior axis deviation (0° to –90°).

Q5. Which CXR finding is seen in right heart obstructive lesions?
A5. Decreased or normal pulmonary vascular markings (↓ pulmonary blood flow).

Q6. Which lesions are classified as left heart obstructive?
A6. Hypoplastic left heart syndrome, interrupted aortic arch, coarctation of aorta, and critical aortic stenosis.

Q7. What is the hallmark of left heart obstructive lesions on screening?
A7. O₂ saturation <95% with >3% difference between upper and lower extremities.

Q8. What role does PDA play in left heart obstructive lesions?
A8. PDA supplies systemic blood flow by shunting blood from pulmonary artery to aorta.

Q9. What is the typical chest X-ray finding in left heart obstructive lesions?
A9. Increased pulmonary blood flow due to left-to-right shunting and pulmonary overcirculation.

Q10. Which ECG finding is characteristic of critical aortic stenosis in newborns?
A10. Left axis deviation (0° to +90°).

Q11. Which condition among left heart obstructive lesions does NOT show BP gradient?
A11. Hypoplastic left heart syndrome (HLHS).

Q12. Which lesions are mixing type CCHDs?
A12. Transposition of great arteries, TAPVR, and truncus arteriosus.

Q13. Are mixing lesions ductal-dependent?
A13. No, mixing lesions are ductal-independent but may coexist with PDA/PFO.

Q14. What is the hallmark O₂ saturation finding in mixing lesions?
A14. O₂ saturation <95% without a pre/post-ductal gradient.

Q15. What unique feature is seen in d-TGA with pulmonary hypertension or CoA?
A15. Reversed differential cyanosis (higher O₂ in foot than right arm).

Q16. What is the hyperoxia test result in mixing lesions?
A16. Negative hyperoxia test.

Q17. What axis deviation is commonly seen in mixing lesions?
A17. Normal newborn axis (90° to 180°).

Q18. What is the ECG axis in tetralogy of Fallot?
A18. Right axis deviation (90° to 180°).

Q19. Which lesion shows left axis (0° to +90°) on ECG among right-sided lesions?
A19. Pulmonary atresia.

Q20. Summarize the CXR findings across the three groups of lesions.
A20. Right heart obstructive → decreased flow; Left heart obstructive → increased flow; Mixing lesions → normal to increased flow.

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Classification of Cyanotic Congenital Heart Disease