A 28-year-old woman presents to the cardiology clinic with a history of progressive dyspnea on exertion and palpitations for 6 months. On examination, her blood pressure is 110/70 mmHg, heart rate 88 bpm, and respiratory rate 18/min. Auscultation reveals a high-pitched, blowing pansystolic murmur best heard at the apex with radiation to the axilla. The murmur increases in intensity with handgrip maneuver. Echocardiography confirms mitral regurgitation with a dilated left atrium and left ventricle. Which physiological mechanism best explains the increase in murmur intensity with handgrip maneuver?

Explanation

## Physiology of Mitral Regurgitation Murmur and Handgrip Maneuver ### Mechanism of the Murmur **Key Point:** Mitral regurgitation (MR) produces a pansystolic (holosystolic) murmur because the incompetent mitral valve allows blood to flow backward into the left atrium throughout systole, whenever left ventricular pressure exceeds atrial pressure. ### Handgrip Maneuver Physiology The handgrip maneuver is an isometric exercise that: 1. **Increases systemic vascular resistance (SVR)** by causing vasoconstriction of peripheral arterioles 2. **Increases afterload** on the left ventricle 3. **Increases the pressure gradient** between the left ventricle and left atrium during systole 4. **Augments regurgitant flow** across the incompetent mitral valve **High-Yield:** The increased pressure difference drives more blood backward through the defective valve, making the murmur louder and longer. This is a classic bedside maneuver to confirm MR. ### Differential Response of Murmurs to Handgrip | Murmur Type | Response to Handgrip | Mechanism | |---|---|---| | **Mitral Regurgitation** | **Increases** | ↑ Afterload → ↑ LV-LA gradient → ↑ regurgitant flow | | Aortic Stenosis | Increases | ↑ Afterload → ↑ transvalvular gradient | | Mitral Stenosis | No change | Stenotic lesion; flow determined by gradient, not valve competence | | Hypertrophic Cardiomyopathy | Decreases | ↑ Afterload → ↓ LV outflow obstruction | | Aortic Regurgitation | Increases | ↑ Afterload → ↑ regurgitant flow | **Clinical Pearl:** Handgrip maneuver is particularly useful in the clinic to distinguish MR from other systolic murmurs when the diagnosis is uncertain on initial auscultation. ### Why This Patient's Findings Fit MR - **Pansystolic murmur:** Begins with S1, continues through systole, may obscure S2 - **Apex location with axillary radiation:** Regurgitant jet directed posteriorly toward left atrial appendage - **Exertional dyspnea:** Due to elevated pulmonary venous pressure from left atrial volume overload - **Dilated left atrium and ventricle:** Chronic volume overload from regurgitation [cite:Harrison 21e Ch 237]