Mitral Stenosis

  • Mitral stenosis (MS) is characterized by incomplete opening of the mitral valve during diastole, which limits antegrade flow and yields a sustained diastolic pressure gradient between the left atrium (LA) and the left ventricle (LV).

Etiology

  • Rheumatic MS
    • Because of the increased use of antibiotics, the incidence of rheumatic heart disease as a cause of MS has decreased.
    • Two-thirds of patients with rheumatic MS are female; may be associated with mitral regurgitation (MR).
    • Rheumatic fever can cause fibrosis, thickening, and calcification, leading to fusion of the commissures, leaflets, chordae, and/or papillary muscles.
  • Other causes of MS: substantial mitral annular calcification (calcific MS), systemic lupus erythematosus (SLE), rheumatoid arthritis, congenital, oversewn or small mitral annuloplasty ring; “functional MS” may occur with obstruction of the LA outflow because of tumor (particularly myxoma), LA thrombus, or endocarditis with a large vegetation.

Pathophysiology

  • Increased transvalvular flow or decreased diastolic filling time may lead to worsening symptoms of MS. This occurs with pregnancy, exercise, hyperthyroidism, atrial fibrillation (AF) with rapid ventricular response, and fever.
  • MS causes increased pressure in the LA, which then dilates as a compensatory mechanism. This causes the LA to dilate and fibrose, which then leads to atrial arrhythmias and thrombus formation.
  • A sustained increase in pulmonary venous pressures is transmitted backward to cause PH and with time, increased pulmonary vascular resistance and right ventricular pressure overload and dysfunction.

Diagnosis

History

  • After a prolonged asymptomatic period, patients may report any of the following: dyspnea, decreased functional capacity, orthopnea, paroxysmal nocturnal dyspnea, fatigue, palpitations, systemic embolism, hemoptysis, chest pain.

Physical Examination

  • Opening snap (OS) caused by sudden tensing of the valve leaflets; the A2-OS interval varies inversely with the severity of stenosis (shorter interval = more severe stenosis).
  • Mid-diastolic rumble: low-pitched murmur heard best at the apex with the bell of the stethoscope; the severity of stenosis is related to the duration of the murmur, not intensity.
  • Signs of right-sided heart failure and PH.

Diagnostic Testing

  • ECG: left atrial enlargement (LAE), AF, right ventricular hypertrophy
  • CXR: enlarged chambers, calcification of the mitral valve and/or annulus
  • TTE:
    • Assess valve leaflets and subvalvular apparatus
    • Determine mitral valve area (MVA) and mean transmitral gradient
    • Estimate pulmonary artery systolic pressure and evaluate right ventricular size and function
  • Transesophageal echocardiogram (TEE): evaluate MV morphology and hemodynamics in patients with MS for whom TTE was suboptimal. Also used to rule out left atrial thrombus.
  • Exercise stress testing: indicated when symptoms are out of proportion to severity indicated by TTE. Can get assessment of exercise capacity, mean transmitral gradient with exercise, and increase in PA pressures with exercise.
  • Cardiac catheterization
    • Rarely indicated; however, it can be performed when clinical and echocardiography assessment are discordant; however, to obtain an accurate assessment, direct left atrial hemodynamics via transeptal puncture is required.
    • Reasonable in patients with MS to assess the cause of severe PH when out of proportion to the severity of MS as determined by noninvasive testing.

Treatment

Medical Management

  • Diuretics, β-blockers, and low-salt diet for heart failure symptoms.
  • AF occurs in 30%–40% of patients with severe MS.
    • Therapy is mostly aimed at rate control and prevention of thromboembolism.
    • AHA/ACC Guidelines—Class I indications for anticoagulation for prevention of 
systemic embolization in patients with MS regardless of CHADS2VASC score.1,2

Percutaneous Mitral Balloon Commissurotomy

  • Balloon inflation separates the leaflets, yielding an increased valve area.
  • Indicated only in rheumatic MS where there is thickening of the leaflets and annulus is mostly spared.
  • It compares favorably with surgical mitral commissurotomy (open or closed) and is the procedure of choice in experienced centers in patients without contraindications (such as moderate or more mitral regurgitation and left atrial appendage thrombus).
  • Recommendations for percutaneous mitral balloon commissurotomy1,2:
    • Symptomatic patients with severe MS (valve area ≤1.5 cm) (stage D) and favorable valve anatomy in the absence of contraindications (i.e., LA clot or moderate to severe MR) (Class I)
    • Asymptomatic patients with very severe MS (valve area ≤1.0 cm) (stage C) and favorable valve anatomy in the absence of contraindication (Class IIa)
    • Asymptomatic patients with severe MS (stage C) and favorable valve anatomy in the absence of a LA clot or moderate to severe MR who have new-onset AF (Class IIb)
    • Symptomatic patients with MVA <1.5 cm with hemodynamically significant MS during exercise (Class IIb)
    • Severely symptomatic patients with severe MS (MVA <1.5 cm) (stage D) who have suboptimal valve anatomy and are not surgical candidates or high-risk surgical candidates (Class IIb)

Surgical Management

Recommendations for mitral valve surgery1,2:

  • Severely symptomatic patients with severe MS (valve area <1.5 cm; stage D) who are not high risk for surgery and who are not candidates for or failed previous percutaneous mitral balloon commissurotomy (Class I).
  • Concomitant MV surgery is indicated for patients with severe MS (valve area <1.5 cm; stage C or D) undergoing other cardiac surgery (Class I).

References

  1. Nishimura RA, Otto CM, Bonow RO, et al. 2014 AHA/ACC guideline for the management of patients with valvular heart disease: executive summary: a report of the American College of Cardiology/American Heart Association task force on practice guidelines. J Am Coll Cardiol. 2014;63:2438-2488.  [PMID:24603192]
  2. Nishimura RA, Otto CM, Bonow RO, et al. 2017 AHA/ACC focused update of the 2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association task Force on clinical practice guidelines. Circulation. 2017;135:e1159-e1195.  [PMID:28298458]

Outline


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