Mitral Stenosis

Overview

Definition

Mitral stenosis (MS) is the narrowing of the mitral valve (MV) orifice, which impedes blood flow from the left atrium (LA) into the left ventricle (LV) during diastole.

Epidemiology

• Prevalence has decreased in the developed world. 
• Incidence:
  • 1 in 100,000 in the United States
  • Higher in developing countries, where rheumatic heart disease is more prevalent
• Women > men
• Onset is usually in the 3rd and 4th decade of life.

Etiology

• Rheumatic heart disease (most common)
• Congenital 
• Mitral annular calcification
• Radiation induced
• Fabry’s disease
• Whipple’s disease
• Systemic lupus erythematosus
• Rheumatoid arthritis
• Carcinoid disease
• Conditions that mimic the hemodynamic changes of MS:
  • LA myxoma
  • Large infective endocarditis
  • Degenerated bioprosthetic MV

Pathophysiology

• Rheumatic heart disease: molecular mimicry displayed by group A-hemolytic Streptococci after pharyngeal infection → acute pancarditis → chronic valvular inflammation → 
  • Fibrosis and thickening of the valve leaflets and fusion of mitral commissures
  • Mitral calcification and stenosis with narrowing of the valve orifice
• A narrowed MV orifice → restricted LV filling → ↑ LA pressure is required to propel blood →
  • LA dilation → atrial fibrillation, LA thrombosis 
  • ↑ Pulmonary capillary wedge pressure (PCWP) → pulmonary hypertension → right heart failure
  • ↓ Stroke volume → ↓ cardiac output → left heart failure

Clinical Presentation

Clinical manifestations

• Asymptomatic in the early stages
• Symptoms of heart failure:
  • Progressive exertional dyspnea
  • Fatigue
  • Orthopnea
  • Paroxysmal nocturnal dyspnea
  • Hemoptysis → from pulmonary edema and rupture of small pulmonary vessels
• Symptoms of atrial fibrillation: 
  • Palpitations
  • Sequelae from thromboembolism
• Hoarseness (Ortner’s syndrome) → compression of the left recurrent laryngeal nerve by an enlarged LA
• Cough → compression of the bronchi by an enlarged LA
• Dysphagia → compression of the esophagus by an enlarged LA

Physical exam

• Loud S1 → abrupt closure of stenotic MV leaflets (S1 may be absent if the leaflets are heavily calcified.)
• Normal S2 split with an exaggerated P2 → pulmonary hypertension
• Early diastolic opening snap after S2, followed by a low-pitched, decrescendo-crescendo rumbling murmur:
  • Heard best at the apex
  • Murmur ↑ with squatting, handgrip (↑ afterload)
  • Murmur ↓ with decreased blood flow across the valve (tachycardia, pulmonary hypertension)
  • Opening snap becomes closer to S2 as the stenosis becomes more severe.
  • Snap may be absent if the valve is heavily calcified.
• Palpable P2 and right ventricle (RV) heave (parasternal lift)
• The point of maximal impulse is normal or ↓, due to ↓ LV filling.
• Signs of heart failure (usually right sided):
  • Jugular venous distension
  • Crackles
  • Hepatomegaly 
  • Peripheral edema
• Malar flush (“mitral facies”) → cutaneous vasodilation and hypoxemia → low cardiac output and severe pulmonary hypertension

Diagnosis

Echocardiography

• Transthoracic echocardiography (TTE):
  • Diagnostic modality of choice
  • Findings:
    • Stenotic MV
    • Valve thickening and calcification
    • Commissural fusion
    • LA dilation
    • Evaluation of LV and RV function
  • Doppler is used to evaluate: 
    • Transvalvular gradient
    • Mitral valve area (MVA):
      • Moderate MS: 1.5–2.5 cm²
      • Severe MS: < 1.5 cm²
      • Very severe MS: < 1 cm²
    • Pulmonary artery (PA) pressure
    • Associated valve disease (mitral regurgitation (MR))
• Transesophageal echocardiography (TEE): 
  • Used to exclude LA thrombus before percutaneous balloon valvuloplasty
  • Can also evaluate for LA myxomas or large vegetations that may simulate MS

Other workup

• Electrocardiography (ECG):
  • Findings are non-specific.
  • Signs of LA enlargement: 
    • “Double-peaked” P waves (P mitrale)
    • Only seen when in sinus rhythm
  • Atrial fibrillation 
  • With severe pulmonary hypertension:
    • Right axis deviation
    • “Tall” P waves 
• Chest radiograph: 
  • Straightening of the upper left border of the cardiac silhouette → LA enlargement
  • Enlarged PA → pulmonary hypertension
  • Pulmonary vascular congestion:
    • Cephalization
    • Kerley B lines 
• Cardiac magnetic resonance imaging (cMRI):
  • Used when an echocardiogram is unsatisfactory or there is a discrepancy between findings and the clinical picture
  • Can provide information on valve anatomy
  • Can assess the severity of MS
• Cardiac catheterization:
  • Part of the preoperative assessment
  • Evaluates for coronary artery disease prior to surgery
  • Can confirm ↑ LA and PA pressures, MVA

Management

• Periodic monitoring for asymptomatic patients
• Secondary prevention of rheumatic fever for patients with rheumatic MS:
  • Penicillin G 
  • Duration of therapy depends on the number of previous attacks and duration since the last episode.
• Anticoagulation for moderate-to-severe MS:
  • If atrial fibrillation is present
  • If the patient had a prior embolic event
  • If there is an LA thrombus 
  • Consider anticoagulation for severe LA enlargement.
  • Note: Warfarin is typically used because the novel anticoagulants have not been evaluated in valvular heart disease.
• Treatment of atrial fibrillation:
  • Cardioversion in unstable patients
  • Beta blockers and calcium channel blockers in stable patients
• Heart failure management:
  • Diuretics
  • Beta blockers are used cautiously (↓ heart rate can ↓ cardiac output).
  • Salt restriction
• Percutaneous mitral balloon commissurotomy (PMBC): 
  • 1st line
  • Used in severe or symptomatic MS
  • Requires favorable valve morphology with little or no MR and without LA thrombus
  • Can delay valve replacement
• Surgical MV replacement: 
  • Pursued if PMBC is contraindicated
  • Anticoagulation required:
    • 3–6 months for bioprosthetic valve
    • Lifelong for mechanical valve

Differential Diagnosis

• MR: valve disorder where blood refluxes from the LV to the LA during systole. Mitral valve prolapse (MVP) is the most common etiology. Signs and symptoms are based on severity and can include exertional dyspnea, fatigue, or edema. The exam will be notable for a systolic murmur at the cardiac apex, and an echocardiogram can establish the diagnosis and differentiate MR from MS. Treatment includes sodium restriction, diuretics, and surgery for severe cases.
• MVP: the most common cardiac valvular defect, characterized by bulging of the MV leaflets into the LA during systole. Auscultation characteristically reveals a mid-systolic click followed by a possible regurgitant murmur. Patients are generally asymptomatic. However, MVP can progress to MR in some patients. Echocardiography will establish the diagnosis and differentiate MVP from MS. Most patients do not require treatment.
• Severe aortic regurgitation: valve disorder allowing blood to reflux back into the ventricle from the aorta during diastole. Patients may present with exertional dyspnea, orthopnea, palpitations, and chest pain. An exam will show a blowing, early diastolic decrescendo murmur at the 3rd left intercostal space. Echocardiography will establish the diagnosis and differentiate severe aortic regurgitation from MS. Treatment involves surgical repair or replacement.
• Tricuspid stenosis: narrowing of the tricuspid valve, which prevents normal blood flow from the RA to the RV. Patients may be asymptomatic or may present with signs and symptoms of systemic venous congestion. A mid-diastolic murmur at the left lower sternal border distinguishes tricuspid stenosis from MS. An echocardiogram will establish the diagnosis. Management includes sodium restriction, diuretics, and surgery for severe cases.
• Tricuspid regurgitation: valve disorder allowing blood to reflux into the RA from the RV during systole. Patients may be asymptomatic or may present with signs and symptoms of systemic venous congestion. A holosystolic murmur at the left lower sternal border distinguishes tricuspid regurgitation from MS. An echocardiogram will establish the diagnosis. Management involves treating the underlying cause, sodium restriction, diuretics, and surgery for severe cases.
• ASD: an opening in the interatrial septum that allows left-to-right shunting of blood. Complications include pulmonary hypertension, heart failure, and atrial fibrillation. Adults may present with dyspnea, fatigue, and palpitations. A mid-systolic murmur with a fixed and widely split S2 at the left sternal boarder may be heard, which differs from MS. Diagnosis is made with an echocardiogram. Surgical or transcatheter closure is used as treatment.
• LA myxoma: a benign, primary cardiac tumor that can can cause MV outflow tract obstruction during diastole if located in the LA. Patients present with signs and symptoms of heart failure. The murmur can mimic MS, and a “tumor plop” is also heard as the myxoma drops into the mitral orifice. Diagnosis is made with an echocardiogram and a cMRI, which will differentiate LA myxoma from MS. Treatment includes surgical excision.