MCQ: Pediatric Cardiology

Answer: B. Cardiac MRI

Detailed Explanation: Pulmonary regurgitation after TOF repair 

This child is a post-repair Tetralogy of Fallot (TOF) patient who is now developing features suggestive of significant pulmonary regurgitation with right ventricular dilatation.

After repair of TOF, especially when the repair involved a transannular patch, chronic pulmonary regurgitation is common.

The typical sequence is:

Pulmonary regurgitation → Right ventricular volume overload → RV dilatation → RV dysfunction → Arrhythmia/exercise intolerance

This patient has several important clues:

1. Reduced exercise tolerance

This suggests declining right ventricular performance.

The right ventricle is unable to maintain adequate stroke volume during exertion due to chronic volume overload.

2. Right ventricular heave

A right ventricular heave indicates:

• Right ventricular enlargement
• Increased RV workload

This supports chronic right ventricular volume/pressure overload.

3. Early diastolic murmur at the left upper sternal border

This is the classic murmur of:

Pulmonary regurgitation

During diastole:

Pulmonary artery pressure > right ventricular pressure

→ blood flows backward from pulmonary artery into RV

→ early diastolic decrescendo murmur.

4. QRS duration 190 ms

This is an important post-TOF follow-up clue.

A prolonged QRS duration (>180 ms) indicates:

• Severe right ventricular dilatation
• Increased risk of ventricular arrhythmias
• Increased risk of sudden cardiac death

It is a marker used in deciding timing of pulmonary valve replacement.

Why Cardiac MRI is the best investigation

Cardiac MRI is the gold standard for assessment of repaired TOF.

It provides accurate measurement of:

1. Right ventricular size

Important parameters:

• RV end-diastolic volume index (RVEDVi)
• RV end-systolic volume index (RVESVi)

Progressive RV enlargement is an indication for intervention.

2. Right ventricular function

MRI measures:

• RV ejection fraction
• RV contractility

3. Severity of pulmonary regurgitation

MRI can calculate:

• Pulmonary regurgitant volume
• Pulmonary regurgitant fraction

This helps determine whether pulmonary valve replacement is needed.

4. Pulmonary artery anatomy

MRI can assess:

• Branch pulmonary arteries
• RV outflow tract
• Residual lesions

Why the other options are incorrect

A. Chest radiograph

May show:

• Cardiomegaly
• Enlarged pulmonary arteries

However, it cannot accurately measure:

• RV volume
• RV function
• Pulmonary regurgitation severity

Therefore, it cannot guide timing of pulmonary valve replacement.

C. Holter monitoring

Useful for detecting:

• Ventricular arrhythmias
• Conduction abnormalities

A prolonged QRS increases arrhythmia risk, but Holter does not determine when intervention should occur.

The primary issue here is RV dilatation due to pulmonary regurgitation.

D. Exercise ECG

May demonstrate exercise-induced arrhythmias or reduced exercise capacity.

However, it does not provide the structural information needed to decide pulmonary valve replacement.

E. CT pulmonary angiography

Useful for:

• Pulmonary artery anatomy
• Pulmonary artery stenosis
• Vascular abnormalities

However, it involves radiation and is inferior to MRI for evaluating RV volumes and pulmonary regurgitation.

CPSP Pearls ⭐

1. The most important late complication after TOF repair:

Chronic pulmonary regurgitation

↓

RV volume overload

↓

RV dilatation

↓

RV dysfunction + arrhythmia

2. Remember the classic post-TOF clues:

3. Cardiac MRI is the investigation of choice in repaired TOF follow-up because it answers the most important questions:

• How big is the RV?
• How well is the RV functioning?
• How severe is pulmonary regurgitation?

4. Timing of pulmonary valve replacement

Pulmonary valve replacement is considered when there is:

• Severe pulmonary regurgitation
• Progressive RV dilatation
• RV dysfunction
• Symptoms
• Sustained arrhythmias

The goal is to intervene before irreversible RV damage occurs.