A 3-year-old boy with cyanotic heart disease presents with a history of squatting posture during play and episodes of cyanosis. Clinical examination reveals a single S2 and a systolic ejection murmur at the left upper sternal border. Chest X-ray shows a 'boot-shaped' heart with decreased pulmonary vascular markings. Which investigation is most appropriate to confirm the diagnosis and assess the anatomical details for surgical planning?

Explanation

## Investigation of Choice for Tetralogy of Fallot Diagnosis **Key Point:** Transthoracic echocardiography with color Doppler is the gold standard non-invasive investigation for diagnosing and assessing tetralogy of Fallot (TOF) in pediatric patients. ### Why Echocardiography is Optimal **High-Yield:** Echocardiography provides: - Direct visualization of the four anatomical hallmarks: VSD, RV outflow tract obstruction (RVOTO), RV hypertrophy, and overriding aorta - Real-time assessment of shunt direction and magnitude using color Doppler - Measurement of RV pressure gradients across the pulmonary valve - Assessment of pulmonary artery size and branch anatomy - Evaluation of associated lesions (ASD, PDA, coronary artery anomalies) - No radiation exposure — critical in pediatric practice ### Clinical Pearl **Clinical Pearl:** The characteristic echocardiographic findings in TOF include: - Large perimembranous VSD with anterior deviation of the infundibular septum - Overriding aorta (>50% of aortic diameter over the VSD) - RV hypertrophy with narrowed RVOT - Increased RV/LV pressure ratio on Doppler assessment ### Role of Other Investigations | Investigation | Role in TOF | Limitation | |---|---|---| | Chest X-ray | Initial screening (boot-shaped heart, ↓ pulmonary markings) | Cannot assess hemodynamics or detailed anatomy | | ECG | Shows RV hypertrophy (right axis deviation, tall R in V1) | Non-specific; cannot diagnose TOF | | Cardiac catheterization | Reserved for pre-operative coronary mapping or when echo inconclusive | Invasive; not first-line in modern practice | | CT angiography | Useful for complex anatomy or pre-operative planning in selected cases | Higher radiation; not routine in pediatrics | **Tip:** In the modern era, transthoracic echocardiography alone is sufficient for diagnosis and initial surgical planning in most pediatric TOF cases. Cardiac catheterization is reserved for hemodynamic assessment in complex cases or when coronary artery anomalies are suspected.