What are the characteristics and treatment options for mitral stenosis?

Mitral Stenosis: Anatomy and Physiology

Anatomic Components

The mitral valve apparatus consists of four interconnected structures: the mitral annulus, the anterior and posterior leaflets, the chordae tendineae, and the papillary muscles—abnormalities in any component can result in stenosis. 1

• The anterior leaflet is larger and sail-shaped, while the posterior leaflet is smaller and crescent-shaped, with variable commissural scallops 1
• The ventricular surface of leaflets attaches to primary and secondary chordae tendineae, which insert on two main papillary muscles (lateral and medial) 1
• The mitral annulus is a fibrous ring that normally maintains a saddle-shape configuration and undergoes dynamic changes during the cardiac cycle 1

Pathophysiology by Etiology

Rheumatic Mitral Stenosis (RMS)

Rheumatic MS accounts for 85% of all mitral stenosis cases worldwide and involves commissural fusion with thickening at the leaflet tips. 1

• The pathologic process causes commissural fusion as the primary mechanism of obstruction 1
• Progressive leaflet thickening and restriction of leaflet mobility develop over time 1
• RMS tends to present in younger patients, including during pregnancy 1
• The valve morphology typically shows preserved commissural anatomy that responds well to mechanical separation 2

Degenerative Mitral Stenosis (DMS)

Degenerative MS results from mitral annular calcification (MAC) with progressive calcium deposition, valve thickening, and chordal shortening—notably without commissural fusion. 1

• DMS is increasingly prevalent in elderly patients in developed countries as rheumatic fever incidence declines 1
• The posterior mitral leaflet is affected first, with relative preservation of anterior leaflet mobility 1
• Obstruction occurs through reduction of annular area and restriction of leaflet mobility rather than commissural fusion 1
• DMS accounts for approximately 12% of mitral stenosis cases presenting to hospitals 1

Hemodynamic Consequences

Reduced mitral valve orifice area causes elevation of left atrial pressure and pulmonary artery systolic pressure, with severity determined by the valve area and transvalvular gradient. 1

Severity Classification

• Severe MS: Mitral valve area (MVA) ≤1.0 cm² (normal >4 cm²) 1, 3
• Mean transmitral gradient ≥10 mmHg indicates severe obstruction 1, 3
• Diastolic pressure half-time ≥150 ms reflects prolonged pressure equalization 3
• Pulmonary artery systolic pressure >50 mmHg indicates severe hemodynamic consequences 1, 3

Progressive Hemodynamic Changes

• The narrowed orifice creates obstruction to left ventricular inflow during diastole 4, 2
• Elevated left atrial pressure leads to left atrial enlargement and predisposes to atrial fibrillation 3
• Chronic elevation of pulmonary venous pressure causes pulmonary hypertension and eventual right ventricular dysfunction 2
• Flow acceleration across the stenotic valve creates characteristic pressure gradients that worsen with increased cardiac output or heart rate 3

Clinical Auscultation Findings

The classic auscultatory finding is a low-pitched, rumbling diastolic murmur best heard at the apex with the bell of the stethoscope with the patient in the left lateral decubitus position. 3

• An opening snap (OS) follows S2 and precedes the diastolic murmur, representing sudden tensing of valve leaflets 3
• The S2-OS interval shortens as stenosis severity increases, reflecting higher left atrial pressure 3
• First heart sound (S1) is accentuated due to prolonged closure of the mitral valve from high left atrial pressure 3
• In severe stenosis, the diastolic murmur extends throughout diastole and increases with maneuvers that increase cardiac output (exercise, squatting) or heart rate 3

Diagnostic Assessment

Echocardiography is the preferred method for diagnosing mitral stenosis and assessing severity, with valve area by planimetry serving as the reference measurement. 1

• Transthoracic echocardiography (TTE) usually provides sufficient information for routine management 1
• Valve area using planimetry is the reference measurement of severity 1
• Mean transvalvular gradient and pulmonary pressures reflect hemodynamic consequences and have prognostic value 1
• Transesophageal echocardiography (TOE) should be performed to exclude left atrial thrombus before percutaneous mitral commissurotomy (PMC) or after embolic episodes 1
• Stress testing is indicated when symptoms are absent, equivocal, or discordant with stenosis severity 1
• Exercise echocardiography provides objective information by assessing changes in mitral gradient and pulmonary artery pressure 1

Treatment Approach by Etiology

Rheumatic Mitral Stenosis

Percutaneous mitral balloon commissurotomy (PMBC/PMC) is the first-line intervention for symptomatic severe rheumatic MS with favorable valve morphology. 1

• PMC achieves separation of fused commissures, similar to surgical commissurotomy 2
• The procedure is suitable when there is minimal calcification, no significant mitral regurgitation, and no left atrial thrombus 1
• Scoring systems help assess suitability for PMC based on valve morphology 1
• Results are comparable to surgical commissurotomy in appropriately selected patients 2

Degenerative Mitral Stenosis

PMBC is unsuitable for degenerative MS because of the absence of commissural fusion, and mitral valve replacement should be considered as the primary surgical option. 1

• The extensive annular calcification and leaflet base involvement without commissural fusion makes balloon valvuloplasty ineffective 1, 4
• Transcatheter mitral valve replacement is emerging as a potential treatment option for these patients 4
• Surgical valve replacement remains the standard approach for symptomatic severe DMS 1

Medical Management

Diuretics provide symptom relief when edema or pulmonary congestion is present, while heart rate control is essential in patients with atrial fibrillation. 1, 3

• Beta-blockers or calcium channel blockers control heart rate to prolong diastolic filling time 3
• Digoxin may be used specifically for heart rate control in atrial fibrillation 1, 3
• Anticoagulation is indicated with atrial fibrillation, history of systemic embolism, dense spontaneous contrast in the left atrium, or enlarged left atrium (diameter >60 mL/m²) 1, 3
• Vitamin K antagonists are preferred over NOACs in patients with mitral stenosis and atrial fibrillation 3

Indications for Intervention

Intervention should be limited to patients with clinically significant (moderate to severe) mitral stenosis with valve area <1.5 cm². 1

Symptomatic Patients

• NYHA class II-IV symptoms with severe MS (MVA ≤1.5 cm²) warrant intervention 1, 3
• PMC is first-line for rheumatic MS with favorable morphology 1
• Surgical options include open commissurotomy for favorable anatomy unsuitable for PMC, or valve replacement for unfavorable anatomy 1, 3

Asymptomatic Patients

• Pulmonary artery systolic pressure >50 mmHg at rest indicates need for intervention 1, 3
• New-onset atrial fibrillation or high thromboembolic risk (history of embolism, dense spontaneous contrast) warrants consideration 1, 3
• High-risk of hemodynamic decompensation (need for major non-cardiac surgery, desire for pregnancy) may prompt intervention 1

Surveillance

Asymptomatic severe mitral stenosis requires echocardiographic assessment every 2-3 years, with more frequent monitoring for very severe stenosis or borderline hemodynamics. 1, 3

• Yearly monitoring is appropriate for patients with very severe stenosis 3
• Clinical evaluation should assess for development of symptoms, atrial fibrillation, or pulmonary hypertension 3