MRCPCH Part 2 AKP: Complete Study Guide for a High Score

Recall

6-week-old with cyanosis, ejection systolic murmur on left sternal edge, single heart sound, lung field is clear, Diagnosis?

1. TOF 

2. TGA 
3. VSD 
4. ASD
5. PDA 

Ans- a

Explanation

Clinical Scenario: A 6-week-old infant presents with acute cyanosis. On examination, there is an ejection systolic murmur at the left sternal edge, a single heart sound, and clear lung fields.

Key Features to Identify:

• Age (6 weeks): A common age for cyanotic congenital heart disease to become symptomatic as the fetal pulmonary vascular resistance has fallen and the ductus arteriosus is closing.

• Acute Cyanosis: Indicates a right-to-left shunt, deoxygenated blood bypassing the lungs and entering the systemic circulation.

• Ejection Systolic Murmur: Caused by turbulent flow across the stenotic pulmonary valve.

• Single Heart Sound (S2): The pulmonary component of the second heart sound (P2) is absent or very soft due to the severe pulmonary stenosis.

• Clear Lung Fields: This is the critical clue. It signifies decreased pulmonary blood flow. This rules out lesions that cause cyanosis with increased pulmonary blood flow (e.g., Transposition of the Great Arteries).

Differential Diagnosis: The combination of cyanosis + clear lung fields (i.e., reduced pulmonary blood flow) creates a short list:

• Tetralogy of Fallot (TOF) (Most common)

• Tricuspid atresia

• Pulmonary atresia

• Critical pulmonary stenosis

Why the Other Options Are Incorrect:

• b. TGA (Transposition of the Great Arteries): Cyanotic, but has increased pulmonary vascularity on CXR (lung fields would be “hazy” or “plethoric”), not clear. A murmur is not always present.

• c. VSD (Ventricular Septal Defect): Causes a pansystolic murmur and heart failure with increased pulmonary blood flow (lung fields would be congested). It is acyanotic unless complicated by Eisenmenger syndrome, which presents much later in life.

• d. ASD (Atrial Septal Defect): An acyanotic lesion with an ejection systolic murmur and widely split S2, not a single S2. Pulmonary blood flow is increased.

Final Diagnosis: The constellation of findings is pathognomonic for Tetralogy of Fallot. The four components of TOF are:

• Ventricular Septal Defect (VSD)

• Overriding aorta

• Right ventricular outflow tract obstruction (Pulmonary stenosis) – causing the murmur and single S2

• Right ventricular hypertrophy

The cyanosis is due to the right-to-left shunt across the VSD, exacerbated by the pulmonary stenosis restricting blood flow to the lungs.

Answer

1. TOF