Description

• Mitral stenosis (MS) is narrowing of the mitral valve area causing obstruction of left ventricular (LV) inflow, resulting in increased left atrial (LA) pressures and consequent elevation of pulmonary venous pressure. The most common etiology for MS is rheumatic heart disease (RHD).
• Normal valve orifice is 4 to 6 cm²; symptoms typically seen when orifice is <2.5 cm²
• Staging of the disease is used to guide appropriate treatment regimen.
  • Stage A: “at risk of MS”—mild valve doming with normal flow velocity and NO hemodynamic obstruction or symptoms; no symptoms or echocardiographic changes
  • Stage B: “progressive MS”—increased diastolic doming, increased flow velocity, but MVA >1.5 cm², diastolic pressure 1/2 time <150 ms; no symptoms; mild to moderate LA enlargement and normal pulmonary pressures at rest on echo
  • 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; severe LA enlargement and elevated PA systolic pressures >50 mm Hg on echo
  • Stage D: “symptomatic severe MS”—stage C with dyspnea on exertion and decreased exercise tolerance; severe LA enlargement and elevated PA systolic pressures >50 mm Hg on echo

Epidemiology

Global prevalence of RHD is 40.5 million cases. There are 305,000 deaths attributed to RHD annually. Incidence of rheumatic disease in the continental United States remains low (<2 per 100,000 school-aged children).

Etiology and Pathophysiology

• Narrowing of the mitral 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, leading to right-sided failure.
• 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

Risk Factors

• 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.
  • 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)
• Use of drugs: MDMA (ecstasy), ergot alkaloids

General Prevention

• Prompt recognition and treatment of GAS infection in at-risk populations; recognition of cardinal signs and symptoms of ARF via Jones criteria
• Transthoracic echo (TTE) 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), other valvular problems (aortic stenosis and insufficiency), pulmonary HTN and right heart failure, systemic embolism, infective endocarditis