A 28-year-old woman presents to the cardiology clinic with a 6-month history of progressive dyspnea on exertion and palpitations. On examination, her pulse is 88 bpm, regular, and blood pressure is 118/76 mmHg. Auscultation reveals a high-pitched, holosystolic murmur best heard at the apex, radiating to the axilla. The murmur increases with hand grip and decreases with Valsalva maneuver. Echocardiography confirms mitral regurgitation with a flail leaflet. Which physiological mechanism best explains the decrease in murmur intensity during Valsalva maneuver?

Explanation

## Physiological Basis of Murmur Changes with Valsalva ### Valsalva Maneuver Effect on Preload **Key Point:** Valsalva maneuver (straining phase) decreases venous return to the heart, reducing left ventricular preload and end-diastolic volume. ### Mitral Regurgitation Murmur Physiology In mitral regurgitation (MR), the intensity and duration of the murmur depend directly on: - **Regurgitant volume** — determined by the size of the defect and the pressure gradient between LV and LA - **Left ventricular preload** — increased preload → increased LV volume → increased regurgitant flow ### Why Valsalva Decreases MR Murmur 1. **Decreased venous return** → ↓ LV preload → ↓ LV end-diastolic volume 2. **Reduced regurgitant volume** across the incompetent mitral valve 3. **Murmur intensity decreases** proportionally ### Contrast with Other Maneuvers | Maneuver | LV Preload | LV Afterload | MR Murmur | Mechanism | |----------|-----------|-------------|----------|----------| | **Valsalva** | ↓ | ↓ | **↓** | ↓ regurgitant volume | | **Hand grip** | ↔ | ↑ | **↑** | ↑ afterload → ↑ regurgitant jet | | **Squatting** | ↑ | ↑ | **↑** | ↑ preload + afterload | | **Standing** | ↓ | ↓ | **↓** | ↓ preload | **Clinical Pearl:** Hand grip increases afterload, which paradoxically increases the MR murmur because higher LV pressure drives more blood retrograde into the LA. This is a key bedside maneuver for confirming MR. **High-Yield:** The murmur of MR is **holosystolic** (pansystolic) because regurgitation occurs throughout systole whenever LV pressure exceeds LA pressure. It radiates to the axilla because the regurgitant jet is directed posteriorly toward the pulmonary veins. ### Why the Correct Answer Valsalva reduces preload → ↓ LV volume → ↓ regurgitant volume → ↓ murmur intensity. This is the primary mechanism.