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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Almost always caused by rheumatic heart disease (history of rheumatic fever in childhood)
- Murmur: low-pitched diastolic rumble at apex (best heard in left lateral decubitus with bell), preceded by opening snap. Closer the snap to S2, the more severe the stenosis
- Complications: AF (most common, ~40%), pulmonary HTN, hemoptysis, LA thrombus/embolism
- Anticoagulation: warfarin (NOT DOACs) for MS + AF — DOACs are contraindicated in moderate-severe MS
- Intervention: percutaneous balloon mitral commissurotomy (PBMC) if pliable valve without significant MR or LA thrombus; otherwise surgical MVR
Overview
Mitral stenosis is progressive narrowing of the mitral valve orifice, almost exclusively caused by rheumatic heart disease. Normal MV area is 4-6 cm2; symptoms typically begin when area falls below 2 cm2. The resulting LA pressure elevation transmits retrograde to the pulmonary vasculature, causing pulmonary congestion and ultimately pulmonary hypertension and right heart failure. MS is becoming rare in developed countries but remains prevalent in the developing world where rheumatic fever is still common.
Clinical Features
Symptoms
Exertional dyspnea (earliest, from pulmonary congestion)
Symptoms precipitated by increased flow states: exercise, pregnancy, AF with rapid rate, infection/fever
Hemoptysis (bronchial vein rupture from pulmonary HTN)
Embolic stroke (LA thrombus, especially if AF)
Ortner syndrome: hoarseness from LA compression of recurrent laryngeal nerve (rare, massive LA)
Signs
Low-pitched diastolic rumble at apex with presystolic accentuation (if in sinus rhythm) — best heard with bell in left lateral decubitus
Opening snap after S2: shorter S2-OS interval = more severe stenosis (higher LA pressure opens valve sooner)
Loud S1 (calcified valve snaps shut forcefully; becomes soft when immobile/calcified)
Malar flush (mitral facies — pink-purple cheeks from chronic low CO and venous congestion)
Signs of pulmonary HTN and right HF: loud P2, RV heave, JVD, peripheral edema, ascites
Investigations
First-line
EchocardiogramDiagnostic: thickened/calcified mitral leaflets ("hockey stick" anterior leaflet), reduced valve area (severe <1.0 cm2, moderate 1.0-1.5 cm2), elevated mean gradient (severe >=10 mmHg), LA enlargement, estimated PASP. Wilkins score assesses suitability for PBMC (leaflet mobility/thickening, calcification, subvalvular disease — score <=8 favorable)
ECGLAE (P mitrale = broad bifid P wave in lead II), AF (often first detected here), RVH (if pulmonary HTN)
Second-line
CXRStraightening of left heart border (LA appendage), double density (LA behind RV), splayed carina, Kerley B lines, pulmonary congestion
TEEPre-PBMC: rule out LA appendage thrombus (absolute contraindication to PBMC)
1
Medical
- Rate control for AF: beta-blocker or non-DHP CCB (slow HR, prolong diastolic filling time)
- Anticoagulation: WARFARIN for MS + AF. DOACs are CONTRAINDICATED in moderate-severe MS (INVICTUS trial showed worse outcomes with rivaroxaban vs warfarin)
- Diuretics for pulmonary congestion
- Secondary prophylaxis for rheumatic fever: penicillin V or benzathine penicillin monthly (duration depends on age and severity)
2
Intervention for symptomatic severe MS
- PBMC (percutaneous balloon mitral commissurotomy): preferred if pliable non-calcified valve (Wilkins score <=8), no significant MR, no LA thrombus
- Surgical: MVR (mechanical or bioprosthetic) if valve anatomy unfavorable for PBMC, or significant concomitant MR, or failed PBMC
- Open surgical commissurotomy: alternative if expertise available and valve anatomy suitable
USMLE Step 2 CK Exam Tips
- 1Low-pitched diastolic rumble at apex + opening snap = MS. Opening snap closer to S2 = more severe
- 2MS + AF = warfarin. DOACs are CONTRAINDICATED in moderate-severe MS — this is a classic Step 2 CK question
- 3Rheumatic MS is the only valvular disease where DOACs must not be used — know this distinction
- 4Pregnancy + MS: high risk because increased blood volume and HR worsen symptoms. Rate control with beta-blocker is key
- 5Hemoptysis in a young immigrant from a developing country + diastolic murmur = rheumatic MS
practicetest your knowledge on mitral stenosisApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — cardiovascular and beyond.
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