Mitral Stenosis

Mitral Stenosis The normal mitral valve area is 4.0 to 5.0 cm2. Narrowing of the valve area to <2.5 cm2 must occur before development of symptoms. A mitral valve area >1.5 cm2 usually does not produce symptoms at rest. However, if there is an increase in transmitral flow or a decrease in the diastolic filling period, there will be a rise in left atrial pressure and development of symptoms. Thus, the first symptoms of dyspnea in patients with mild MS are usually precipitated by exercise, emotional stress, infection, pregnancy, or atrial fibrillation with a rapid ventricular response. However, once significant limiting symptoms occur, there is a dismal 10-year survival rate of 0% to 15%, and when there is severe pulmonary hypertension, mean survival drops to <3 years. Mortality of untreated patients with MS is caused by progressive heart failure in 60% to 70%, systemic embolism in 20% to 30%, pulmonary embolism in 10%, and infection in 1% to 5%. Evaluation and Management of the Asymptomatic Patient The diagnosis of MS should be based on the history, physical examination, chest x-ray, and ECG. The diagnostic tool of choice in the evaluation of a patient with MS is 2-D and Doppler echocardiography. The morphological appearance of the mitral valve apparatus should be assessed by 2-D echocardiography, including leaflet mobility, leaflet thickness, leaflet calcification, subvalvular fusion, and appearance of the commissures. These features may be important when considering the timing and type of intervention to be performed. Chamber size and function as well as other structural valvular, myocardial, or pericardial abnormalities should also be assessed. the mitral valve area can be noninvasively measured by either the diastolic half-time method or the continuity equation. The half-time method may be inaccurate in patients with abnormalities of left atrial or LV compliance, those with associated AR, and those with previous mitral valvotomy. Medical Therapy 1. General Principles.

Because MS is primarily caused by rheumatic fever, prophylaxis against rheumatic fever is recommended. Appropriate endocarditis prophylaxis is also recommended. Patients who have more than a mild degree of MS should be counseled to avoid unusual physical stresses. Agents with negative chronotropic properties, such as ß-blockers or calcium channel

blockers, may be of benefit in patients with sinus rhythm who have exertional symptoms if the symptoms occur with high heart rates. Salt restriction and intermittent administration of a diuretic are useful if there is evidence of pulmonary vascular congestion. Digitalis does not benefit patients with MS in sinus rhythm unless there is left and/or right ventricular dysfunction. 2. Atrial Fibrillation.

Atrial fibrillation develops in 30% to 40% of patients with symptomatic MS. Significant hemodynamic consequences may result from acute development of atrial fibrillation, with loss of atrial contribution to LV filling, and from the rapid ventricular rate. Atrial fibrillation occurs more commonly in older patients and is associated with a poorer prognosis, with a 10-year survival rate of 25% compared with 46% in patients who remain in sinus rhythm. The risk of arterial embolization, especially stroke, is significantly increased in patients with atrial fibrillation. Treatment of an acute episode of rapid atrial fibrillation consists of anticoagulation with heparin and control of the heart rate response. Intravenous digoxin, calcium channel blockers, or ß-blockers should be used to control ventricular response. If there is hemodynamic instability, electrical cardioversion should be undertaken urgently, with intravenous heparin before, during, and after the procedure. 3. Prevention of Systemic Embolization.

Systemic embolization may occur in 10% to 20% of patients with MS. The risk of embolization is related to age, the presence of atrial fibrillation, and history of previous embolic events. One third of embolic events occur 1 month after onset of atrial fibrillation, and two thirds occur within 1 year. The frequency of embolic events does not seem to be related to severity of MS, cardiac output, size of left atrium, or presence of symptoms. Recommendations for Anticoagulation in Mitral Stenosis Indication 1. Patients with atrial fibrillation, paroxysmal or chronic. 2. Patients with a prior embolic event. 3. Patients with severe MS and left atrial dimension 55 mm by echocardiography.* 4. All other patients with MS.

Class I I IIb III

Patients with NYHA functional Class II symptoms and moderate or severe stenosis (mitral valve area 1.5 cm2 or mean gradient 5 mm Hg) may be considered for mitral balloon valvotomy if they have suitable mitral valve morphology. Patients who are symptomatic with a significant elevation of pulmonary artery pressure (>60 mm Hg), mean transmitral gradient (>15 mm Hg), or pulmonary artery wedge pressure ( 25 mm Hg) on exertion have hemodynamically significant MS and should be considered for further intervention. Alternatively, patients who do not manifest elevation in pulmonary artery, pulmonary artery wedge, or transmitral pressures coincident with

development of exertional symptoms most likely would not benefit from intervention on the mitral valve.

Indications for Surgical or Percutaneous Valvotomy The immediate results of percutaneous mitral valvotomy are similar to those of mitral commissurotomy. The mean valve area usually doubles (from 1.0 cm2 to 2.0 cm2), with a 50% to 60% reduction in transmitral gradient. Overall, 80% to 95% of patients may have a successful procedure, which is defined as a mitral valve area >1.5 cm2 and a decrease in left atrial pressure to 18 mm Hg in the absence of complications. The most common acute complications reported in large series include severe MR, which occurs in 2% to 10%, and a residual atrial septal defect. A large atrial septal defect (>1.5:1 left-to-right shunt) occurs in up to 12% of patients with the double balloon technique and in <5% with the Inoue balloon technique. Less frequent complications include perforation of the left ventricle (0.5% to 4.0%), embolic events (0.5% to 3%), and myocardial infarction (0.3% to 0.5%). The mortality for patients who undergo balloon valvotomy in larger series has ranged from 1% to 2%; however, with increasing experience in the procedure, percutaneous mitral valvotomy can be done in selected patients with a mortality of <1%. However, longer-term follow-up studies at 3 to 7 years indicate more favorable hemodynamic and symptomatic results with percutaneous balloon valvotomy than with closed commissurotomy and results equivalent to those of open commissurotomy. Relative contraindications to percutaneous balloon valvotomy include the presence of a left atrial thrombus and significant (3+ to 4+) MR. In asymptomatic patients with a favorable valve morphology, percutaneous mitral valvotomy may be considered if there is evidence of a hemodynamic effect on left atrial pressure (new-onset atrial fibrillation) or pulmonary circulation (pulmonary artery pressure >50 mm Hg at rest or >60 mm Hg with exercise). The strength of evidence for this recommendation is low because there are no data comparing the results of percutaneous balloon valvotomy and medical therapy in such patients.

Indications for Mitral Valve Replacement In the young, healthy person, MVR can be performed with a risk of <5%. However, in the older patient with concomitant medical problems or pulmonary hypertension at systemic levels, the risk of MVR may be 10% to 20%. It is controversial whether asymptomatic or mildly symptomatic patients with severe MS (valve area <1 cm2) and severe pulmonary hypertension (pulmonary artery systolic pressure >60 to 80 mm Hg) should undergo MVR to prevent right ventricular failure, but surgery is generally recommended in such patients. It is recognized that patients with such severe pulmonary hypertension are rarely asymptomatic.

Recommendations for Mitral Valve Replacement for Mitral Stenosis Indication Class 2 1. Patients with moderate or severe MS (mitral valve area 1.5 cm )* and I NYHA functional Class III-IV symptoms who are not considered candidates for percutaneous balloon valvotomy or mitral valve repair. 2. Patients with severe MS (mitral valve area 1 cm2)* and severe pulmonary hypertension (pulmonary artery systolic pressure >60 to 80 mm Hg) with NYHA functional Class I-II symptoms who are not considered candidates for percutaneous balloon valvotomy or mitral valve repair.

Mitral Valve Prolapse MVP is the most common form of valvular heart disease and occurs in 2% to 6% of the population. MVP often occurs as a clinical entity with little or no MR but is also the most common cause of significant MR in the United States. Infective endocarditis is a serious complication of MVP, which is the leading predisposing cardiovascular diagnosis in most series of patients reported with endocarditis. Because the absolute incidence of endocarditis is extremely low for the entire MVP population, there has been much controversy about the risk of endocarditis in MVP. Dynamic auscultation is often useful for establishing the clinical diagnosis of the MVP syndrome. The M-mode echocardiographic definition of MVP includes 2-mm posterior displacement of 1 or both leaflets or holosystolic posterior "hammocking" >3 mm. On 2D echocardiography, systolic displacement of 1 or both mitral leaflets in the parasternal long-axis view, particularly when they coapt on the atrial side of the annular plane, indicates a high likelihood of MVP. The diagnosis of MVP is even more certain when leaflet thickness is >5 mm.