A 50-year-old man presents with progressive exertional dyspnea, presyncope, and a harsh systolic murmur at the left sternal border that increases with Valsalva maneuver and decreases with squatting. Echo shows asymmetric septal hypertrophy (IVS 22 mm), LVOTO gradient of 50 mmHg at rest increasing to 90 mmHg with provocation, and systolic anterior motion (SAM) of the mitral valve. What is the mechanism of hemodynamic worsening with Valsalva?

• A Increased afterload worsens the LVOT gradient
• B Sympathetic activation from straining increases cardiac output directly
• C Valsalva causes mitral valve prolapse superimposed on SAM
• D Decreased preload (reduced venous return) reduces LV cavity size, worsening LVOTO ✓

Explanation

In hypertrophic obstructive cardiomyopathy (HOCM), the dynamic LVOT obstruction worsens with any maneuver that reduces preload or decreases afterload, or increases contractility. Valsalva decreases venous return, reducing LV cavity size. A smaller LV cavity brings the hypertrophied septum and the anterior mitral leaflet (already drawn in by Venturi effects during systole — SAM) closer together, worsening LVOTO. Squatting increases preload (venous return), enlarges the LV cavity, and reduces obstruction — the murmur decreases. This dynamic behavior is pathognomonic of HOCM.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.