A 6-month-old infant from Mumbai is referred for evaluation of a systolic ejection murmur heard best at the left upper sternal border, radiating to the back. The infant is asymptomatic with normal growth. A chest X-ray is normal. Which investigation would be most appropriate to confirm the diagnosis of aortic stenosis and assess the severity of obstruction?

Explanation

## Clinical Presentation of Aortic Stenosis The systolic ejection murmur at the left upper sternal border radiating to the back, in an asymptomatic infant with normal chest X-ray, is consistent with **congenital aortic stenosis** — an acyanotic left-sided obstructive lesion. ## Investigation of Choice **Key Point:** Transthoracic echocardiography with continuous-wave (CW) Doppler is the gold standard, non-invasive investigation for diagnosis and severity assessment of aortic stenosis. ### Why Transthoracic Echo with CW Doppler? 1. **Direct visualization** of aortic valve morphology (bicuspid vs. tricuspid) 2. **Continuous-wave Doppler** measures peak systolic velocity across the aortic valve 3. **Calculates peak systolic pressure gradient** using the modified Bernoulli equation: $$\Delta P = 4(V_{peak})^2$$ 4. **Stratifies severity** based on gradient: - Mild: peak gradient < 25 mmHg - Moderate: peak gradient 25–50 mmHg - Severe: peak gradient > 50 mmHg 5. **Assesses left ventricular function** and wall thickness (LVH) 6. **Non-invasive, no radiation**, ideal for serial follow-up in children 7. **Guides management** — determines need for balloon valvuloplasty vs. surgical aortic valve replacement ## Comparison of Investigations | Investigation | Role | Limitation | | --- | --- | --- | | Transthoracic echo + CW Doppler | Gold standard; diagnoses, grades severity, assesses LV function | Operator-dependent; may be limited in older children with poor acoustic windows | | Transesophageal echo | Better image quality in poor acoustic windows | Invasive; not first-line in asymptomatic infants | | Cardiac MRI | Excellent for anatomy; assesses LV mass and fibrosis | Expensive; requires sedation in infants; not first-line for hemodynamic assessment | | Invasive catheterization | Direct pressure gradient measurement; therapeutic intervention | Invasive; reserved for cases where echo is inconclusive or intervention planned | **Clinical Pearl:** The modified Bernoulli equation (ΔP = 4V²) derived from continuous-wave Doppler is the cornerstone of non-invasive hemodynamic assessment in valvular heart disease. Peak gradient correlates with severity and guides timing of intervention. **High-Yield:** In an asymptomatic infant with a systolic ejection murmur and normal chest X-ray, transthoracic echocardiography with CW Doppler is both diagnostic and prognostic — it is the single most important test and should be performed before any invasive procedure.