Mitral Stenosis

• Increased Left Atrial Pressure and Pulmonary Venous Congestion: As the mitral valve area decreases below the normal 4-6 cm², LA pressure rises progressively to maintain forward flow across the stenotic valve. This elevation in LA pressure is transmitted retrograde to the pulmonary veins and capillaries, causing pulmonary venous hypertension. The pressure gradient across the mitral valve (mean gradient ≥5 mmHg at rest) directly correlates with disease severity. The chronically elevated LA pressure triggers neurohormonal activation (increased sympathetic tone, renin-angiotensin-aldosterone system activation) and fluid retention, further elevating intravascular volume and worsening pulmonary congestion. At the cellular level, endothelial dysfunction in pulmonary capillaries leads to increased capillary permeability; when pulmonary capillary wedge pressure exceeds plasma oncotic pressure (approximately 25 mmHg), pulmonary edema ensues. This explains the orthopnea, paroxysmal nocturnal dyspnea, and exercise intolerance characteristic of MS.

• Pulmonary Hypertension and Right Ventricular Dysfunction: Chronic pulmonary venous hypertension triggers pulmonary vascular remodeling with medial hypertrophy of pulmonary arterioles, increased smooth muscle proliferation, and deposition of collagen and elastin. This morphologic remodeling increases pulmonary vascular resistance (PVR), which initially develops as a reversible, vasoreactive component but progressively becomes fixed. The mechanism involves hypoxia-induced endothelial dysfunction, with decreased nitric oxide and increased endothelin-1 production driving vasoconstriction and vascular remodeling. Secondary (reactive) pulmonary hypertension that develops in MS can reach severe levels (pulmonary systolic pressures >60-80 mmHg), exceeding what would be expected from passive transmitted LA pressure alone. Elevated RV afterload leads to RV hypertrophy and eventual RV dilatation with functional tricuspid regurgitation, leading to right heart failure with peripheral edema, hepatic congestion, and ascites. This paradoxically may reduce symptoms from pulmonary edema as RV dysfunction limits forward flow across the stenotic mitral valve.

• Altered Left Ventricular Function and Hemodynamics: Despite LV hypertrophy being absent in pure mitral stenosis (unlike mitral regurgitation), the stenosed mitral valve prevents normal LV filling. LV end-diastolic volume and stroke volume decrease, maintaining a relatively small LV chamber. Consequently, LV systolic function (ejection fraction) remains normal or supernormal in uncomplicated MS. However, diastolic dysfunction is severe: the LV becomes stiff and resistant to filling, requiring elevated filling pressures to achieve adequate preload. The decreased LV preload (reduced stroke volume) activates baroreceptor reflex mechanisms increasing sympathetic tone, which maintains cardiac output through increased heart rate but at the cost of reducing diastolic filling time—further worsening diastolic function. Exercise magnifies these effects; increased heart rate during exertion shortens diastole disproportionately, causing the LA-LV gradient to increase dramatically and precipitating pulmonary edema. This hemodynamic liability explains why MS patients develop symptoms with minimal exertion despite normal ejection fractions.

• Atrial Arrhythmia and Thromboembolism: The chronically dilated left atrium with elevated pressure and stasis of blood creates an electrophysiological substrate for atrial fibrillation (AF). Atrial stretch activates atrial fibroblasts, promoting fibrosis and conduction abnormalities; the arrhythmogenic remodeling involves upregulation of inflammatory cytokines (TNF-α, IL-6) and altered calcium handling. AF develops in 40-50% of MS patients and carries tremendous clinical significance: loss of the atrial "kick" reduces LV filling by 20-30%, abruptly worsening hemodynamics and often precipitating acute pulmonary edema or cardiogenic shock. Additionally, AF-related blood stasis in the enlarged LA promotes thrombus formation; combined with endothelial injury from chronic pressure elevation and altered hemostasis, this creates a prothrombotic state. Transthoracic echocardiography studies demonstrate LA thrombus in 15-25% of MS patients in sinus rhythm and up to 50% with AF, explaining the requirement for anticoagulation in virtually all MS patients with AF and even in selected sinus rhythm patients.

• Valve Apparatus Remodeling: The primary pathological process in rheumatic MS involves immune-mediated damage to valve leaflets. Acute rheumatic fever causes valve inflammation with Aschoff body formation; repeated streptococcal infections lead to progressive fibrosis, calcification, and commissural fusion of the anterior and posterior mitral leaflets. This fusion of the commissures (the lateral edges where leaflets meet) mechanically restricts leaflet motion, creating the characteristic "hockey stick" appearance on echocardiography. With disease progression, leaflet thickening increases (>4 mm is abnormal; >8 mm indicates severe changes), and subvalvular apparatus involvement develops with chordae tendinae shortening and papillary muscle fibrosis. The calcification process involves dystrophic calcification (deposition of calcium in damaged tissue) and may be promoted by oxidative stress, inflammation, and altered mineral metabolism. Degenerative calcification can eventually lead to mitral annular calcification in elderly patients with longstanding disease.

• Acute Rheumatic Fever (ARF) and Rheumatic Heart Disease (RHD): ARF remains the predominant etiology of mitral stenosis globally, accounting for >90% of MS cases in endemic areas and 50-60% in developed nations. Poststreptococcal autoimmunity occurs following untreated or inadequately treated Group A Streptococcal (GAS) pharyngitis (but NOT streptococcal skin infections); the incidence of ARF following acute GAS pharyngitis is 0.3-3% if untreated. Molecular mimicry between streptococcal M protein epitopes and myocardial/valve proteins triggers autoimmune-mediated inflammation. Initial ARF typically occurs in children and adolescents (peak age 5-15 years in developing countries), with initial carditis affecting 40-50% of ARF cases. Importantly, only 30-40% of initial carditis cases progress to chronic RHD, but recurrent ARF episodes dramatically increase this risk; the cumulative risk of RHD progression reaches 40% after multiple ARF recurrences. ARF itself may not cause significant MS acutely, but progressive fibrosis and calcification over 10-20 years leads to hemodynamically significant stenosis. Secondary prophylaxis with penicillin significantly reduces recurrence risk (benzathine penicillin G 1.2 million units IM monthly, or penicillin V 250 mg PO twice daily) and is a cornerstone of prevention in endemic regions.

• Degenerative/Calcific Mitral Stenosis: This increasingly recognized etiology develops in elderly patients (typically age >60-70 years) with chronic degenerative changes of the mitral apparatus. Unlike rheumatic MS, degenerative stenosis involves mitral annular calcification (MAC) and leaflet calcification without a history of ARF. Mitral annular calcification represents a chronic process involving dystrophic calcium deposition in the fibrous mitral annulus, particularly affecting the posterior annulus. Risk factors for MAC include chronic kidney disease (especially with hyperparathyroidism), age >70 years, hypertension, diabetes mellitus, and elevated lipoprotein(a). The calcification extends into the leaflet commissures, restricting motion and creating a functional stenosis. Hemodynamically significant degenerative MS is less common than MAC alone; approximately 5% of patients with extensive MAC develop hemodynamically significant stenosis. Degenerative MS characteristically presents in older patients without prior cardiac history, has a more indolent course than rheumatic MS, and may progress slowly or remain stable for years. Echocardiographic features include a calcified, thickened mitral valve with restricted leaflet motion but less commissural fusion than rheumatic disease.

• Congenital Mitral Stenosis: Rare congenital variants include parachute mitral valve (all chordae insert into a single papillary muscle, creating subvalvular obstruction), supramitral membrane (fibrous tissue above the mitral valve), and abnormal mitral leaflet tissue. These conditions typically present in childhood with MS or with a combination of MS and mitral regurgitation. Genetic syndromes including Marfan syndrome, Ehlers-Danlos syndrome, and others may involve valvular abnormalities. Congenital MS accounts for <1% of all MS cases but is an important consideration in young children presenting with unexplained MS.

• Other Etiologies: Left atrial myxoma or thrombus can mechanically obstruct mitral inflow, mimicking MS hemodynamically; echocardiography distinguishes these from true valve stenosis. Systemic lupus erythematosus (SLE) and antiphospholipid syndrome may cause Libman-Sacks endocarditis with valve thickening and functional stenosis (though regurgitation is more common). Carcinoid syndrome, if extensive pulmonary involvement occurs, may have RV-predominant effects but can affect left-sided valves; left-sided carcinoid involvement is rare. Radiation therapy to the mediastinum can cause fibrosis of cardiac structures including the mitral valve, leading to both stenosis and regurgitation years after treatment. Prior balloon mitral valvulotomy (BMV) or surgical commissurotomy may have incomplete initial success or restenosis in 10-20% of patients within 5-10 years, particularly with less favorable morphology at baseline.

• Dyspnea on Exertion (DOE): Progressive exertional dyspnea is the most common presenting symptom and reflects pulmonary venous congestion. The mechanism involves exercise-induced increases in heart rate that shorten diastolic filling time; simultaneously, increased cardiac output requirements increase the LA-LV pressure gradient. Patients describe breathlessness with climbing stairs, walking uphill, or other exertion that previously caused no symptoms. In severe MS, dyspnea occurs with minimal activity (New York Heart Association class III-IV). The dyspnea of MS is particularly pronounced with sudden increases in heart rate (e.g., emotional stress, tachyarrhythmias) because the abbreviated diastolic period allows inadequate LV filling, abruptly raising LA pressure and precipitating pulmonary edema. This contrasts with mitral regurgitation, where dyspnea develops more gradually with progressive LV dysfunction.

• Orthopnea and Paroxysmal Nocturnal Dyspnea (PND): These represent more severe pulmonary edema and occur when supine positioning increases pulmonary blood volume and LA pressure sufficiently to cause acute pulmonary edema. Patients awaken at night gasping for breath, often needing to sit upright or stand. The number of pillows required to sleep comfortably (orthopnea) correlates with disease severity. PND typically develops 2-4 hours after falling asleep when the lying position has maximally redistributed fluid to the pulmonary circulation.

• Palpitations: Patients frequently report a sensation of forceful or irregular heartbeats. In sinus rhythm, palpitations result from compensatory increases in stroke volume and sympathetic activation. Notably, development of new-onset atrial fibrillation often precipitates acute symptom worsening with palpitations, dyspnea, and sometimes chest discomfort. Rapid ventricular response in AF significantly shortens diastolic filling time, potentially causing acute hemodynamic deterioration and cardiogenic shock.

• Hemoptysis: This alarming symptom represents rupture of pulmonary capillaries secondary to severely elevated pulmonary venous pressure, particularly following acute pulmonary edema. Hemoptysis indicates advanced disease with severe elevation of LA pressure (usually >25-30 mmHg) and suggests urgent need for intervention. Pink, frothy sputum (pulmonary edema) may accompany hemoptysis in acute decompensation.

• Chest Pain: Atypical chest discomfort occurs in 15-20% of MS patients and usually reflects pulmonary hypertension with RV strain or acute pulmonary infarction from in situ thrombosis. The pain is typically pleuritic, worsened by deep breathing, and lateralized. Acute pulmonary infarction with infarction pneumonitis (Hampton's hump on chest X-ray: wedge-shaped infiltrate) can occur when pulmonary emboli lodge in the stenotic MS patient's prothrombotic milieu.

• Constitutional Symptoms: Severe chronic pulmonary hypertension and RV failure may produce fatigue, general malaise, and exercise intolerance beyond what dyspnea alone explains. Weight loss can occur in advanced disease with hepatic congestion.

• Loud First Heart Sound (S1): The mitral component of S1 (M1) is characteristically loud and accentuated in MS due to the increased force required to abruptly close a thickened, stenotic mitral valve leaflet with substantial motion remaining (in contrast to markedly calcified, immobile valves where S1 may be soft). An accentuated M1 is one of the most important bedside clues to MS. This is best appreciated with the diaphragm of the stethoscope at the apex in the supine position.

• Opening Snap (OS): The opening snap is a high-pitched, early diastolic sound occurring 60-150 ms after A2 (aortic component of S2), best heard with the diaphragm at the apex and left lateral decubitus position. The OS reflects abrupt halting of the anterior mitral leaflet motion as it reaches its maximal opening excursion against the fused, stenotic commissures. An OS is present in 60-70% of MS patients with pliable valves; its absence suggests either severe calcification (immobile valve) or trivial stenosis. Critically, the A2-OS interval (measured from aortic valve closure to opening snap) inversely correlates with MS severity: shorter intervals (<60 ms) indicate higher LA pressures and more severe stenosis, as the steeply rising LA pressure pushes the leaflet open earlier after aortic closure. This interval narrows with exercise, reflecting increased LA pressure.

• Diastolic Rumble: A low-pitched, mid-to-late diastolic murmur is the classic auscultatory finding, heard best with the bell of the stethoscope applied lightly at the apex in the left lateral decubitus position during expiration. The murmur results from turbulent flow across the stenotic mitral valve during the rapid filling phase of diastole. Critically, the duration of the diastolic murmur correlates with MS severity: brief murmurs (early-to-mid-diastolic) suggest mild stenosis, while murmurs extending through diastole into presystole indicate severe stenosis with prolonged high LA-LV gradient throughout diastole. A presystolic accentuation of the murmur (in sinus rhythm) occurs due to vigorous atrial contraction increasing flow rate just before ventricular systole. In atrial fibrillation, this presystolic accentuation is absent since there is no coordinated atrial contraction. The murmur increases with maneuvers that increase mitral flow (leg raise, cough, amyl nitrite inhalation increasing diastolic flow), important for bedside diagnosis.

• **Signs of Pulmonary

Initial (supportive) studies

• ECG: look for P mitrale — a broad, notched P wave in lead II with a wide negative terminal deflection in V1, reflecting left atrial enlargement. Atrial fibrillation is common; right-axis deviation and tall R in V1 signal right ventricular hypertrophy from pulmonary hypertension. The ECG never shows LVH in pure MS, because the LV is underfilled rather than pressure-loaded.
• Chest radiograph: straightening of the left heart border (LA appendage enlargement), a double density behind the right heart border, splaying of the carina with elevation of the left mainstem bronchus, and Kerley B lines with cephalization of flow from chronic pulmonary venous hypertension.

Confirmatory test — transthoracic echocardiography (TTE)

• TTE is the diagnostic standard per the ACC/AHA 2020 Valvular Heart Disease Guideline. Two-dimensional imaging shows commissural fusion, thickened leaflets, diastolic doming with the hockey-stick deformity of the anterior leaflet, and a dilated LA.
• Quantitation: mitral valve area (MVA) by planimetry and by Doppler pressure half-time (PHT); mean transmitral gradient; and pulmonary artery systolic pressure estimated from the tricuspid regurgitant jet.
• Severity staging (ACC/AHA 2020): MVA ≤1.5 cm² defines severe MS, and ≤1.0 cm² very severe; PHT ≥150 ms corresponds to severe stenosis. Mean gradient supports severity but is heart-rate and flow dependent, so it is not the defining criterion.

Adjunctive testing

• Transesophageal echocardiography: mandatory before percutaneous balloon mitral commissurotomy to exclude left atrial or appendage thrombus and to grade mitral regurgitation.
• Wilkins (Abascal) score: grades leaflet mobility, thickening, calcification, and subvalvular disease; a low score (favorable morphology) predicts success with balloon commissurotomy.
• Exercise/stress echocardiography: for discordance between symptoms and resting severity, measuring the exercise mean gradient and pulmonary pressure.
• Invasive catheterization: reserved for persistent discordance between echo and clinical findings.

Immediate stabilization of acute decompensation

• Rate control is the emergency priority: tachycardia shortens diastole and abruptly raises left atrial pressure. Use an IV beta blocker (e.g., metoprolol) or a nondihydropyridine calcium channel blocker (e.g., diltiazem); digoxin is an option in AF with hypotension or poor LV function.
• Synchronized cardioversion if new AF with rapid rate causes hemodynamic collapse.
• Loop diuretics (furosemide) and sodium restriction relieve pulmonary congestion, but over-diuresis drops the transmitral gradient and cardiac output.

Chronic medical therapy (symptom control only — no drug alters the stenosis)

• Rate-slowing agents: beta blockers or nondihydropyridine CCBs lengthen diastolic filling time and improve exertional symptoms.
• Anticoagulation: the ACC/AHA 2020 guideline recommends a vitamin K antagonist (warfarin) for rheumatic MS with atrial fibrillation, prior embolism, or left atrial thrombus. DOACs are not appropriate in rheumatic MS with AF — the INVICTUS trial found a VKA superior to rivaroxaban in rheumatic heart disease.
• Secondary rheumatic prophylaxis with penicillin per AHA recommendations in patients with rheumatic heart disease.

Definitive (mechanical) therapy

• Percutaneous balloon mitral commissurotomy (PMBC): first-line definitive treatment for symptomatic severe rheumatic MS with favorable valve morphology, no left atrial thrombus, and no more than mild mitral regurgitation (ACC/AHA 2020, at a comprehensive valve center). It splits the fused commissures.
• Surgical mitral valve repair or replacement: for severe MS with unfavorable morphology, heavy calcification, significant MR, LA thrombus, or failed/restenosed PMBC. Degenerative calcific MS generally requires surgery rather than PMBC because commissural fusion is absent.

Contraindicated or avoided

• DOACs for AF in rheumatic MS; PMBC with LA thrombus or moderate-to-severe MR; aggressive vasodilators/afterload reduction, which reduce preload without improving the fixed obstruction; and routine infective endocarditis antibiotic prophylaxis, which ACC/AHA no longer recommends for native-valve MS.

Complications of the disease

• Atrial fibrillation: LA stretch and fibrosis create the substrate; loss of atrial kick plus a short diastole can precipitate abrupt decompensation. Signalled by an irregularly irregular pulse with loss of presystolic accentuation of the rumble.
• Systemic thromboembolism / cardioembolic stroke — emergency: stasis in the dilated LA and appendage. Sudden focal neurologic deficit, cold pulseless limb, or flank pain with hematuria (renal infarct). MS is a classic source of embolism in a young patient with stroke.
• Acute pulmonary edema — emergency: any tachycardic stressor (fever, pregnancy, exercise, new AF) raises the gradient; presents with orthopnea, pink frothy sputum, and diffuse crackles.
• Pulmonary hypertension with right heart failure: reactive pulmonary vascular remodeling raises RV afterload, producing a right ventricular heave, loud P2, elevated JVP with prominent v waves from functional tricuspid regurgitation, hepatomegaly, ascites, and edema.
• Hemoptysis: rupture of bronchial venous collaterals under high LA pressure; brisk bleeding can be an airway emergency.
• Ball-valve LA thrombus or coexistent myxoma physiology — emergency: syncope or sudden death from intermittent orifice occlusion, often positional.
• Ortner syndrome (cardiovocal syndrome): hoarseness from compression of the left recurrent laryngeal nerve by the massively dilated left atrium.
• Pregnancy decompensation: the physiologic rise in heart rate and plasma volume in the second and third trimesters unmasks previously silent MS.

Complications of treatment

• After balloon commissurotomy: acute severe mitral regurgitation from leaflet tearing (new holosystolic murmur with flash pulmonary edema — emergency, may need urgent surgery); cardiac tamponade from transseptal puncture (hypotension, pulsus paradoxus, JVD — emergency); iatrogenic atrial septal defect; embolic stroke; and late restenosis.
• After valve replacement: prosthetic valve thrombosis (muffled mechanical click, new gradient — emergency), thromboembolism, paravalvular leak with hemolysis, prosthetic valve endocarditis, and structural degeneration of bioprostheses.
• Anticoagulation: warfarin-related major bleeding, including intracranial hemorrhage.

• The triad that names the lesion: loud S1, an opening snap, and a low-pitched diastolic rumble at the apex, best heard with the bell in the left lateral decubitus position. In a young immigrant or a patient with a childhood sore-throat history, this is rheumatic MS until proven otherwise.
• Two severity clues from the bedside exam: a shorter A2–opening snap interval and a longer rumble both mean more severe stenosis. Examiners love reversing this — a long A2–OS interval means milder disease.
• Single best next step for any suspected MS: transthoracic echocardiography. Do not order catheterization first.
• The number to know: mitral valve area ≤1.5 cm² defines severe MS in the ACC/AHA 2020 valve guideline.
• Before balloon commissurotomy, get a TEE. Left atrial appendage thrombus and more-than-mild mitral regurgitation are the two findings that convert the patient from a PMBC candidate to a surgical candidate.
• Anticoagulate rheumatic MS with AF using warfarin, not a DOAC — the association examiners test most, supported by the INVICTUS trial. Rheumatic MS is also excluded from CHA₂DS₂-VASc–based DOAC decision-making.
• Pregnancy is the classic unmasking scenario: rising heart rate and volume in the second/third trimester precipitate pulmonary edema in a previously asymptomatic woman. First-line therapy is a beta blocker plus a loop diuretic; balloon commissurotomy is preferred over surgery if intervention is required.
• Common distractors: the Austin Flint murmur of aortic regurgitation is an apical diastolic rumble without a loud S1 or opening snap; left atrial myxoma gives a tumor plop with positional symptoms and constitutional features; and native-valve MS does not warrant routine infective endocarditis antibiotic prophylaxis under current ACC/AHA recommendations.