A 28-year-old woman is evaluated for a systolic murmur detected on routine cardiac examination. The murmur is best heard at the left sternal border and increases with Valsalva maneuver. Which is the most common cause of this clinical presentation?

Explanation

## Clinical Presentation Analysis The key diagnostic features in this case are: - **Systolic murmur** at left sternal border (not apex) - **Increases with Valsalva** (decreases LV cavity size → increases outflow obstruction) - Young patient with no prior cardiac history ## Hypertrophic Cardiomyopathy (HCM) **Key Point:** HCM is the most common cause of a systolic ejection murmur that increases with Valsalva maneuver. The murmur in HCM arises from **dynamic left ventricular outflow tract (LVOT) obstruction** caused by anterior displacement of the mitral valve leaflet during systole. This creates a characteristic **midsystolic ejection murmur** heard best at the left sternal border. ### Valsalva Response | Maneuver | Effect on LV Cavity | Effect on LVOT Obstruction | Murmur Change | |----------|-------------------|---------------------------|---------------| | Valsalva / Standing | ↓ Cavity size | ↑ Obstruction | **↑ Murmur** | | Squatting / Leg raise | ↑ Cavity size | ↓ Obstruction | ↓ Murmur | **Clinical Pearl:** The Valsalva response is the most reliable bedside maneuver to distinguish HCM from other causes of systolic murmurs. This finding is pathognomonic for LVOT obstruction. ## Differential Murmur Characteristics | Condition | Location | Valsalva Response | Other Features | |-----------|----------|-------------------|----------------| | **HCM** | Left sternal border | **↑ (Increases)** | Bifid carotid pulse, jerky PMI | | Mitral regurgitation | Apex | ↓ (Decreases) | Holosystolic, radiates to axilla | | Aortic stenosis | Right sternal border | ↓ (Decreases) | Ejection click, slow carotid upstroke | | Pulmonary stenosis | Left sternal border | ↓ (Decreases) | Ejection click, RV heave | **High-Yield:** HCM is the most common **genetic** cause of sudden cardiac death in young athletes and the most common cause of a Valsalva-responsive systolic murmur in the general population. **Mnemonic:** **HOCM = Handgrip decreases, Obstruction increases with Valsalva, Cavity size inversely related** — remember that anything that reduces preload (Valsalva, standing) worsens the murmur.