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- The mitral apparatus is made up of the apparatus, anterior and posterior leaflets which are attached to the anterolateral and posteromedial papillary muscles via the chordae.
- Mitral stenosis (MS) is the narrowing of the valve area causing obstruction of the left ventricular inflow, resulting in increased left atrial pressures and consequent elevation of pulmonary venous and atrial pressures.
- Normal valve orifice 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. Stages vary from A (with risk factors), B (hemodynamically obstruction), C (severe but no symptoms), to D (symptomatic) (1).
- The most common etiology for MS is rheumatic heart disease (RHD), and MS is the most common valvular disease secondary to RHD.
- Other etiologies will be discussed below.
- Globally, the prevalence of RHD is 30 million. Approximately 470,000 new cases are reported and 233,000 deaths are attributed to RHD yearly (2).
- Predominant age: Symptoms primarily occur in 3rd to 4th decades. Predominant sex: female > male (3:1)
Incidence of rheumatic disease in the continental United States remains low. Annual incidence of acute rheumatic fever in the continental United States is unknown, because it is no longer nationally reportable, but is higher in Hawaii and American Samoa. Global burden remains significant (3).
Etiology and Pathophysiology
- Narrowing of the valve 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 (see “Risk Factors”)
- Pathognomonic commissural fusion, leaflet thickening, and “fish mouth appearance” seen with RHD
- 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
- Rheumatic fever is the greatest risk factor.
- 30–40% of rheumatic fever patients eventually develop MS, presenting 20 years after diagnosis of rheumatic fever.
- Acute rheumatic fever occurs 2 to 3 weeks after an episode of untreated pharyngitis caused by rheumatogenic group A streptococci (GAS) organism in a genetically susceptible host.
- 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 acute rheumatic fever via Jones criteria
- Ultrasound-based 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%)
- Chronic rheumatic myocarditis