A 28-year-old woman from Delhi presents to the cardiology clinic with a complaint of exertional dyspnea and palpitations for 6 months. On examination, her blood pressure is 110/70 mmHg, heart rate 88 bpm, and she is afebrile. Cardiac auscultation reveals a mid-diastolic murmur best heard at the apex with the patient in the left lateral decubitus position. The murmur increases in intensity with exercise. There is an opening snap heard just after S2. Echocardiography confirms mitral stenosis with a valve area of 1.2 cm². Which physiological mechanism best explains the timing and character of this murmur?

Explanation

## Physiology of Mitral Stenosis Murmur ### Timing and Mechanism **Key Point:** The mid-diastolic murmur in mitral stenosis occurs during ventricular filling (diastole) when blood flows across the narrowed mitral valve from the left atrium to the left ventricle. The murmur is generated by: 1. Narrowing of the mitral valve orifice (area <2.5 cm²) 2. Turbulent flow across the stenotic valve 3. Maximum intensity when the pressure gradient between LA and LV is greatest — typically in mid-to-late diastole ### Clinical Features Explained | Feature | Physiological Basis | |---------|--------------------| | **Opening snap** | Abrupt halt of leaflet motion at maximal opening; occurs earlier with more severe stenosis | | **Increases with exercise** | Increased cardiac output → increased flow across stenotic valve → louder murmur | | **Left lateral decubitus position** | Brings apex closer to chest wall; increases audibility | | **Diastolic timing** | Occurs when AV valve is open and blood crosses from atrium to ventricle | **High-Yield:** The opening snap–murmur interval shortens with increasing severity of stenosis because the LA pressure rises more steeply, causing earlier and more forceful opening. ### Pathophysiology Timeline ```mermaid flowchart LR A["Narrowed mitral valve<br/>(area < 2.5 cm²)"]:::outcome --> B["↑ LA pressure<br/>during diastole"]:::outcome B --> C["Turbulent flow<br/>across valve"]:::outcome C --> D["Mid-diastolic<br/>murmur"]:::outcome B --> E["Opening snap<br/>at valve opening"]:::outcome ``` [cite:Harrison 21e Ch 237]