A 58-year-old man from rural India presents with progressive dyspnea on exertion for 6 months and orthopnea. He has a history of acute rheumatic fever at age 12. On examination, blood pressure is 140/90 mmHg, pulse is 88/min and regular. Auscultation reveals a loud S1, an opening snap at 80 ms after A2, and a low-pitched diastolic murmur best heard at the apex in the left lateral decubitus position. Chest X-ray shows pulmonary congestion and straightening of the left heart border. Echocardiography reveals a mitral valve area of 1.2 cm² with restricted leaflet motion and no significant regurgitation. What is the most likely diagnosis?

Explanation

## Diagnosis: Mitral Stenosis with Preserved Sinus Rhythm ### Clinical Features Supporting Mitral Stenosis **Key Point:** The constellation of findings—loud S1, opening snap at 80 ms, low-pitched diastolic murmur at apex, and echocardiographic mitral valve area of 1.2 cm²—is pathognomonic for mitral stenosis. **High-Yield:** The opening snap occurs when the stenosed mitral leaflets abruptly stop their opening excursion during diastole. Its timing (80 ms after A2) correlates with disease severity: earlier snaps indicate more severe stenosis. ### Echocardiographic Findings | Feature | Mitral Stenosis | Mitral Regurgitation | |---------|-----------------|---------------------| | Valve area | <1.5 cm² (moderate–severe) | >2 cm² (normal or enlarged) | | Leaflet motion | Restricted, doming | Excessive, flail or prolapse | | Regurgitation | Absent or trivial | Prominent color jet | | LA size | Enlarged | Enlarged | **Clinical Pearl:** A mitral valve area of 1.2 cm² defines moderate-to-severe stenosis (normal >4 cm²; mild 2.5–4 cm²; moderate 1.5–2.5 cm²). ### Why Sinus Rhythm is Preserved Here **Key Point:** Although rheumatic mitral stenosis predisposes to atrial fibrillation, this patient presents with a regular pulse (88/min) and no mention of arrhythmia on examination or ECG. Sinus rhythm can persist in chronic mitral stenosis, especially if the stenosis develops gradually and the left atrium, though enlarged, has not yet undergone sufficient electrical remodeling. **Mnemonic: SEVERE MS** — Stenosis, Elevated LA pressure, Valve area <1.5, Elevated pulmonary pressures, Restrictive leaflets, Echocardiography confirms, Murmur at apex. ### Pathophysiology 1. Rheumatic heart disease causes commissural fusion and leaflet thickening. 2. Narrowed mitral orifice increases LA-to-LV pressure gradient during diastole. 3. Pulmonary congestion results from elevated pulmonary venous pressures. 4. Straightening of the left heart border on CXR reflects left atrial enlargement pushing the left mainstem bronchus upward. **Warning:** Do not confuse the opening snap (a high-frequency sound at the moment of maximal leaflet opening) with an S3 gallop (a low-frequency sound in early diastole due to rapid ventricular filling). The opening snap in mitral stenosis is earlier and sharper. [cite:Robbins 10e Ch 12]