30/04/2025
**subaortic web** (also called a **discrete subaortic membrane**) is a thin, fibrous or membranous structure that forms just below the aortic valve in the left ventricular outflow tract (LVOT). It is a type of **fixed left ventricular outflow obstruction** and can lead to significant hemodynamic consequences if left untreated.
# # **Key Features:**
1. **Location:**
- Typically located within 1–2 cm below the aortic valve.
- May be attached to the ventricular septum and extend toward the mitral valve.
2. **Pathophysiology:**
- Causes obstruction to blood flow from the left ventricle into the aorta.
- Can lead to progressive **left ventricular hypertrophy (LVH)** due to increased afterload.
- May cause **aortic regurgitation** due to turbulent flow damaging the aortic valve leaflets.
3. **Clinical Presentation:**
- Often asymptomatic in mild cases.
- Symptoms (if present) may include:
- Exertional dyspnea
- Fatigue
- Chest pain
- Syncope (rare)
- A **harsh crescendo-decrescendo systolic murmur** is heard best at the left sternal border, similar to aortic stenosis but typically without a click.
4. **Diagnosis:**
- **Echocardiography (TTE/TEE):** Primary diagnostic tool; shows a thin membrane below the aortic valve with Doppler evidence of flow acceleration.
- **Cardiac MRI/CT:** Can provide additional anatomical detail if echocardiography is inconclusive.
- **Cardiac catheterization:** May be used to assess hemodynamic significance (pressure gradient across the LVOT).
5. **Treatment:**
- **Surgical resection** is the definitive treatment if:
- Significant obstruction (peak gradient > **50 mmHg** at rest or with provocation).
- Symptoms develop.
- Progressive aortic regurgitation or LV dysfunction is present.
- **Transcatheter techniques** (less common) may be attempted in select cases.
- **Lifelong follow-up** is needed due to risk of recurrence (~10–20%).
# # # **Differential Diagnosis:**
- **Valvular aortic stenosis** (different location, involves valve leaflets).
- **Hypertrophic obstructive cardiomyopathy (HOCM)** (dynamic obstruction, no discrete membrane).
- **Supravalvular aortic stenosis** (narrowing above the aortic valve).
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