A 52-year-old man with a history of rheumatic fever presents with dyspnea and palpitations. On examination, he has an opening snap and a low-pitched diastolic murmur at the apex. Echocardiography confirms mitral stenosis. Which single clinical or echocardiographic feature best distinguishes mitral stenosis from mitral regurgitation?

## Discriminating Features Between Mitral Stenosis and Mitral Regurgitation **Key Point:** The opening snap is pathognomonic for mitral stenosis and is absent in mitral regurgitation. This single finding reliably distinguishes the two lesions at the bedside. ### Mechanism of the Opening Snap The opening snap occurs when the stenotic mitral valve leaflets abruptly halt their opening during early diastole, creating a sharp sound. It reflects: - Restricted leaflet mobility due to commissural fusion - Increased stiffness and reduced compliance of the valve apparatus - The snap occurs earlier in diastole when the valve is more mobile; as stenosis worsens, the snap moves closer to S~2~ ### Comparison Table: Mitral Stenosis vs. Mitral Regurgitation | Feature | Mitral Stenosis | Mitral Regurgitation | | --- | --- | --- | | **Opening snap** | Present (pathognomonic) | Absent | | **Diastolic murmur** | Low-pitched, rumbling | None (holosystolic murmur instead) | | **LA enlargement** | Present in both | Present in both | | **LV hypertrophy** | Absent (LV is small) | Present (LV dilates) | | **Pulmonary HTN** | Common in both | Can occur in both | | **Valve pathology** | Commissural fusion, thickening | Leaflet prolapse, rupture, or annular dilation | **High-Yield:** The opening snap is heard best at the left lower sternal border or apex and occurs 0.06–0.12 seconds after S~2~. It is absent in pure mitral regurgitation because the regurgitant valve does not have the restricted mobility that produces the snap. **Clinical Pearl:** A patient with mitral stenosis may have both an opening snap AND a diastolic murmur; a patient with pure mitral regurgitation has neither—only a holosystolic (pansystolic) murmur at the apex radiating to the axilla. ### Why the Other Features Are Not Discriminating - **LA enlargement & pulmonary HTN:** Both occur in mitral stenosis AND mitral regurgitation because both lesions increase LA pressure over time. - **LV hypertrophy:** Absent in mitral stenosis (LV is underfilled and small); present in mitral regurgitation (LV volume overload). However, this is an ECG finding and less reliably detected at the bedside than an opening snap.