A 28-year-old woman presents to the cardiology clinic with a history of recurrent syncope during exertion. On examination, a loud systolic murmur is heard at the left lower sternal border that increases with Valsalva maneuver and standing position. Echocardiography reveals left ventricular hypertrophy with systolic anterior motion (SAM) of the mitral valve. What is the physiological basis for the increase in murmur intensity with Valsalva maneuver?

Explanation

## Physiological Mechanism of Valsalva Effect in HOCM ### Pathophysiology of the Murmur In hypertrophic obstructive cardiomyopathy (HOCM), the systolic murmur arises from **dynamic left ventricular outflow tract (LVOT) obstruction** caused by systolic anterior motion of the mitral valve leaflet, which impinges on the hypertrophied ventricular septum. ### Effect of Valsalva Maneuver **Key Point:** Valsalva maneuver decreases venous return → reduces left ventricular preload → **decreases LV cavity size** → brings the anterior mitral leaflet closer to the septum → **increases the degree of LVOT obstruction** → increases the velocity of blood flow through the narrowed orifice → **louder murmur**. ### Contrast with Other Maneuvers | Maneuver | LV Cavity Size | LVOT Obstruction | Murmur Intensity | |----------|---|---|---| | Valsalva / Standing | ↓ | ↑ | **↑** | | Squatting / Leg raise | ↑ | ↓ | ↓ | | Handgrip | ↑ (afterload) | ↓ | ↓ | | Amyl nitrite | ↓ (afterload) | ↑ | ↑ | **Clinical Pearl:** The **increase in murmur with Valsalva is pathognomonic for HOCM** and helps distinguish it from aortic stenosis (where the murmur decreases with Valsalva due to reduced aortic flow). ### Why the Correct Answer Valsalva reduces preload → LV cavity shrinks → SAM leaflet moves closer to the septum → increased obstruction → louder murmur. This is the **direct geometric consequence** of reduced ventricular volume. **High-Yield:** Remember: **"Valsalva makes HOCM louder, aortic stenosis quieter."** This is a classic NEET PG discriminator.