What is mitral stenosis?

Mitral Stenosis

Mitral stenosis is a pathologic narrowing of the mitral valve orifice that obstructs blood flow from the left atrium to the left ventricle, causing significant morbidity and mortality if left untreated. 1

Definition and Pathophysiology

Mitral stenosis (MS) is characterized by:

• Narrowing or stricture of the mitral valve orifice that obstructs left ventricular inflow 1
• Reduction in the effective valve area, which normally measures 4-6 cm²
• Progressive obstruction typically becomes hemodynamically significant when the valve area is reduced to less than 1.5 cm² 2

The obstruction leads to:

• Increased pressure in the left atrium
• Pulmonary hypertension
• Right ventricular dysfunction
• Decreased cardiac output

Etiology

Two primary causes of mitral stenosis:

1. Rheumatic Mitral Stenosis:

   • Most common cause worldwide, especially in developing countries 3
   • Results from rheumatic fever causing commissural fusion, leaflet thickening, and chordal fusion

2. Degenerative Mitral Stenosis:

   • Increasingly common in developed countries 4
   • Secondary to severe mitral annular calcification
   • Typically affects elderly patients with multiple comorbidities 5
   • Characterized by extensive calcification at the base of leaflets and annulus without commissural fusion

3. Congenital Mitral Stenosis:

   • Less common form
   • Can present as various subtypes 1:
     • Mitral annular hypoplasia
     • Subvalvular mitral stenosis (affecting chordae tendineae and/or papillary muscles)
     • Supravalvular or intravalvular mitral ring

Clinical Manifestations

Symptoms typically develop when valve area decreases below 1.5 cm² and may include:

• Dyspnea on exertion, progressing to dyspnea at rest
• Orthopnea and paroxysmal nocturnal dyspnea
• Hemoptysis (due to rupture of bronchial veins)
• Fatigue and weakness (from decreased cardiac output)
• Palpitations (often due to atrial fibrillation)
• Systemic embolization (from left atrial thrombus)
• Right-sided heart failure symptoms (in advanced disease)

Hemodynamic Effects

• Left ventricular function is generally preserved in isolated mitral stenosis 6
• Approximately one-third of patients may have impaired left ventricular ejection fraction due to:
  • Reduced preload from inflow obstruction
  • Inadequate Frank-Starling compensation
  • Increased afterload

Diagnosis

Diagnosis is primarily based on:

1. Physical examination:

   • Opening snap following S2
   • Diastolic rumble at the apex
   • Loud S1 (in early disease)

2. Echocardiography:

   • Gold standard for diagnosis
   • Measures valve area, gradient across valve
   • Assesses valve morphology and calcification
   • Evaluates for concomitant valvular disease
   • Assesses pulmonary pressures and right ventricular function

Treatment

Treatment depends on symptom severity, valve morphology, and patient characteristics:

1. Medical management:

   • Heart rate control (beta blockers, calcium channel blockers)
   • Diuretics for symptom relief
   • Anticoagulation for atrial fibrillation
   • Endocarditis prophylaxis in selected cases

2. Interventional options:

   • Percutaneous balloon mitral valvuloplasty:

     • Treatment of choice for symptomatic patients with favorable valve morphology 3
     • Most effective in rheumatic MS with minimal calcification
     • Less effective in degenerative MS due to extensive calcification 5

   • Surgical options:

     • Open commissurotomy: For favorable valve anatomy without significant calcification
     • Mitral valve replacement: Indicated for severe symptoms with valve area <1.5 cm² when valve morphology is unfavorable for repair 2

Special Considerations

• Degenerative MS: Presents unique challenges as traditional interventions (commissurotomy, balloon valvuloplasty) are less effective due to extensive calcification 4, 5
• Elderly patients: Often have multiple comorbidities making them high-risk surgical candidates
• Emerging therapies: Transcatheter mitral valve replacement is being developed as a potential future treatment option for degenerative MS 4, 5

Prognosis

• Without intervention, severe symptomatic mitral stenosis has poor prognosis
• Successful intervention significantly improves symptoms and survival
• Long-term outcomes depend on timing of intervention, valve morphology, and presence of complications (pulmonary hypertension, atrial fibrillation)