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Stem
A candidate is asked to manage a classic presentation of Mitral Stenosis in an exam setting. Use precise definitions, scores, doses, and decision thresholds.
Core knowledge (model answer backbone)
Mitral stenosis (MS) is a narrowing of the mitral valve orifice that obstructs flow from the left atrium to the left ventricle during diastole. The normal mitral valve area (MVA) is 4 to 6 cm squared; the guidelines call MVA at or below 1.5 cm squared severe (clinically significant) and at or below 1.0 cm squared very severe, with pressure half-time 150 ms or more supporting severe disease (MVA equals 220 divided by the pressure half-time). The leading cause worldwide is rheumatic heart disease (RHD), which accounts for over 90 percent of cases in developing countries — commissural fusion, leaflet thickening, subvalvular chordal shortening producing the fish-mouth valve. The classic triad of auscultation is a loud (tapping) S1, an opening snap after S2, and a low-pitched mid-diastolic rumble at the apex with presystolic accentuation in sinus rhythm. Pathophysiology is a rising transmitral gradient cascade: raised LA pressure transmits back through the pulmonary veins, causing pulmonary venous hypertension, reactive pulmonary arterial hypertension, right ventricular pressure overload and right-heart failure. Atrial fibrillation develops in about 30 percent of patients with isolated rheumatic MS and is dangerous because loss of atrial contraction and an irregular rapid rate both shorten diastolic filling and precipitate acute pulmonary oedema. Severity is graded by valve area, mean transmitral gradient, pressure half-time and pulmonary artery systolic pressure (PASP), not by murmur loudness. Management is rate control plus careful diuresis (never first-line vasodilators), a vitamin K antagonist with INR 2 to 3 for atrial fibrillation, prior embolism or left atrial thrombus, secondary prophylaxis with benzathine penicillin G, and mechanical relief by percutaneous mitral commissurotomy when the anatomy is favourable (Wilkins score at or below 8, no left atrial thrombus, less than moderate mitral regurgitation) or mitral valve replacement when it is not.
Red flags
- Acute pulmonary oedema with new fast atrial fibrillation in a young pregnant woman — suspect previously silent rheumatic MS; rate-control, diuresis, urgent echo
- Loud tapping S1 plus opening snap plus mid-diastolic rumble at the apex in sinus rhythm with AF — rheumatic MS until proven otherwise
- Embolic stroke in a young patient under 40 — consider silent rheumatic MS with AF or LA thrombus; anticoagulate, TTE/TOE for valve and LAA thrombus
- Severe MS with sudden hypotension or pulmonary oedema on initiation of any afterload-reducing agent — preload-dependent physiology; stop, restore rate control and intravascular volume
High-yield structure examiners expect
Cover: Overview & Definition, Classification, Epidemiology & Risk Factors, Pathophysiology, Clinical Presentation, Differential Diagnosis.
Key doses / thresholds (from topic teaching)
- Acute rate control: metoprolol tartrate 5 mg IV by slow injection, repeated at about 2-minute intervals for up to three doses (15 mg total), then oral metoprolol 25 to 50 mg twice daily (50 to 100 mg daily blunted the rise in resting and exercise wedge pressure in randomised MS patients in sinus rhythm).
- Diltiazem 0.25 mg/kg IV over 2 min (about 20 mg for an average adult; a second dose of 0.35 mg/kg after 15 min if needed), then an infusion of 5 to 15 mg/hr for up to 24 hours — only if beta-blockers are contraindicated.
- Digoxin IV loading 8 to 12 mcg/kg in total (half initially, then a quarter every 6 to 8 hours for two further doses), with maintenance titrated to lean body weight and renal function (typically 125 to 250 mcg daily) — for AF when rate control is incomplete or LV dysfunction coexists.
- Furosemide 20 to 40 mg IV slowly over 1 to 2 minutes for congestion (40 mg, then 80 mg if needed, in frank acute pulmonary oedema).
- Heparin 80 units/kg IV bolus then 18 units/kg/hr (weight-based nomogram) while converting to a vitamin K antagonist; INR target 2.0 to 3.0 for MS with AF, prior embolism or LA thrombus, and 3.0 (range 2.5 to 3.5) after a mechanical mitral prosthesis.
- Benzathine penicillin G 1.2 million units IM every 3 to 4 weeks (600,000 units if 25 to 27 kg or less) for at least 10 years, lifelong in high-risk patients; sulfadiazine 1 g daily if penicillin-allergic.
- Thresholds: intervene for symptomatic MS with MVA at or below 1.5 cm squared and favourable anatomy (PMC, Class 1); asymptomatic severe MS with resting PASP above 50 mmHg (Class 2a) or new-onset AF (Class 2b); mean gradient above 15 mmHg on exercise when the resting area exceeds 1.5 cm squared.
Questions
a) Define the condition and give the most important classification or severity framework used in exams. (3 marks)
- Clear one-line definition matching standard teaching.
- Named classification / stages / types with discriminating features.
- One sentence on why classification changes management.
b) Outline pathophysiology in a mechanism chain that explains the main clinical features. (3 marks)
- Initiating insult → intermediate pathway → end-organ effect.
- Link at least two symptoms/signs to mechanism.
- Mention one complication pathway (e.g. shock, perforation, herniation, arrhythmia).
c) List discriminating clinical features and bedside assessment. (3 marks)
- Classic presentation plus one atypical group (elderly, pregnancy, child, immunocompromised).
- Named signs/manoeuvres if relevant.
- What must never be missed on exam/bedside (pregnancy test, airway, glucose, etc.).
d) Investigations with thresholds and one named score if applicable. (3 marks)
- First-line tests and what positive findings mean.
- Gold-standard or definitive investigation when needed.
- Score components reproduced exactly if a named score is standard for this topic.
e) Immediate resuscitation and definitive management with doses where standard. (3 marks)
- ABC / time-critical steps first.
- First-line drug(s) with agent + dose + route (or procedure steps).
- Escalation triggers (theatre, ICU, thrombolysis window, antidote, etc.).
- Disposition and safety-netting.
Marking tips
Full marks require specificity (numbers, names, doses) not generic "give antibiotics/fluids." Regional practice (ICMR / NICE / AHA) may be cited as alternative where relevant.