- Mitral stenosis (MS) is the narrowing of the valve area causing obstruction of the left ventricular (LV) inflow, resulting in increased left atrial (LA) pressures and consequent elevation of pulmonary venous pressure.
- Normal valve orifice is 4 to 5 cm2; symptoms typically seen when orifice is <2.5 cm2 (1).
- Staging of the disease is used to guide appropriate treatment regimen (1).
- Stage A: “at risk of MS”—mild valve doming with normal flow velocity and NO hemodynamic obstruction or symptoms
- Stage B: “progressive MS”—increased diastolic doming, increased flow velocity, but MVA >1.5 cm2, diastolic pressure 1/2 time <150 ms
- Stage C: “asymptomatic severe MS”—diastolic doming, MVA <1.5 cm2, diastolic pressure half time >150 ms, severe LA enlargement, PASP >30 mm Hg, but NO symptoms
- Stage D: “symptomatic severe MS”—stage C with dyspnea on exertion and decreased exercise tolerance
- The most common etiology for MS is rheumatic heart disease (RHD), and MS is the most common valvular disease secondary to RHD.
- Other etiologies are discussed below.
- Global incidence of RHD remains significant with 282,000 new cases of RHD annually and 305,000 deaths attributed to RHD annually.
- Incidence of rheumatic disease in the continental United States remains low. Annual incidence of acute rheumatic fever (ARF) in the continental United States is unknown because it is no longer nationally reportable but is higher in Hawaii and American Samoa.
- Predominant age: Symptoms primarily occur in 3rd to 4th decades.
- In North America and Europe, prevalence is 1 case per 100,000 population, and patients present with severe valve obstruction in 6th decade of life. In Africa, disease prevalence is 35 per 100,000, and severe disease can often present in teens.
- Predominant sex: female > male (3:1)
Etiology and Pathophysiology
- Narrowing of the mitral valve (MV) orifice leads to obstruction of blood flow between LA and LV. This impairs LV filling during diastole and causes increased LA pressure.
- Increased LA pressure is transmitted passively (“back pressure”) to the pulmonary circulation causing pulmonary hypertension (HTN) and pulmonary congestion over time.
- Chronic LA pressure overload results in atrial dilation and fibrosis, resulting in atrial fibrillation.
- Rheumatic fever: most common cause (see “Risk Factors”)
- Pathognomonic commissural fusion, leaflet thickening, and “fish mouth appearance” seen with RHD
- The anatomic changes of severe MS is thought to be secondary to recurrent episodes of ARF as well as a chronic autoimmune process caused by cross-reactivity between a streptococcal protein and valve tissue.
- Aging (extension of mitral annular calcification)
- Rare causes: congenital (associated with mucopolysaccharidoses); autoimmune: systemic lupus erythematosus (SLE), rheumatoid arthritis, malignant carcinoid, Whipple disease, methysergide therapy; and other acquired: LA myxoma, LA thrombus, endomyocardial fibrosis
- ARF and RHD are the greatest risk factors.
- ARF occurs 2 to 3 weeks after an episode of untreated pharyngitis caused by rheumatogenic group A streptococci (GAS) organism in a genetically susceptible host.
- RHD refers to the chronic valvular damage caused by a single severe episode of ARF, multiple recurrent episodes of ARF, and/or the chronic autoimmune process from cross-reactivity between streptococcal protein and valve tissue.
- 30–40% of rheumatic fever patients eventually develop MS, presenting 20 years after diagnosis of ARF.
- Recurrent infections can accelerate the progression of the disease.
- Low socioeconomic status (i.e., crowded conditions) favors the spread of streptococcal infection.
- Aging (increasing valvular calcification)
- Chest irradiation (increasing tissue fibrosis)
- Prompt recognition and treatment of GAS infection in at-risk populations; recognition of cardinal signs and symptoms of ARF via Jones criteria
- Echocardiographic screening has been shown to increase diagnosis of RHD in asymptomatic patients residing in areas of high prevalence.
Commonly Associated Conditions
- Atrial fibrillation (30–40% of symptomatic patients)
- Associated valve lesions due to chronic inflammation (aortic stenosis, aortic insufficiency)
- Pulmonary HTN and right heart failure
- Systemic embolism, stroke, pulmonary embolism (10%)
- Infection, including infectious endocarditis (1–5%)
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