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Mitral Stenosis
General Considerations
The normal mitral apparatus is a complex structure whose components must permit a large volume of blood to pass from the left atrium to the left ventricle. The cross-sectional area of a normal mitral valve ranges from 4 to 6 cm2 in an adult and a transmitral pressure gradient develops when the valve is narrowed to <2.5 cm2. Left atrial pressures begin to rise and are transmitted to the pulmonary vasculature and right side of the heart. Several congenital and acquired conditions result in impaired filling of the left ventricle and may be confused with mitral stenosis.
Clinical Findings
A. SYMPTOMS AND SIGNS
Early in the disease, patients may be asymptomatic. However, conditions that increase cardiac output or heart rate will increase the mitral valvular gradient and left atrial pressure as described earlier. The elevated left atrial pressure is subsequently transmitted into the pulmonary circulation, leading to dyspnea, and may facilitate the early diagnosis of mitral stenosis. Common conditions that increase cardiac output or heart rate are exercise, hyperthyroidism, pregnancy, atrial fibrillation, and fever. In addition, venous return is augmented in the supine position and may produce orthopnea and paroxysmal nocturnal dyspnea in patients with moderate disease.
Mitral Stenosis Treatment
Primary prophylaxis consists of an early diagnosis of Group A streptococcal pharyngitis. Treatment started within 7–9 days after onset of illness may prevent rheumatic fever. Secondary prophylaxis may be individually tailored, but there are no firm guidelines. Recurrence of rheumatic fever is more common in young patients and patients who developed carditis during their initial episode. Therefore, with carditis, secondary prevention continues for 10 years or until age 25. Without carditis, secondary prevention continues for 5 years or until age 18. The prevention of repeated attacks may delay the progression of mitral stenosis.
Patients with mitral stenosis are considered to be at moderate risk for bacterial endocarditis, endocarditis prophylaxis is therefore recommended for certain procedures specified by the AHA guidelines. However, there is a recent debate concerning whether dental procedures predispose to endocarditis and whether antibiotic prophylaxis is of any value. The choice of antibiotics to treat endocarditis may be further complicated if the patient is receiving penicillin for prophylaxis against rheumatic fever. Resistance to penicillin and cephalosporins may develop in this scenario, and an alternative antibiotic should be provided for prophylaxis against endocarditis.
Medical management of mitral stenosis with normal sinus rhythm is limited. A benefit is derived from salt restriction and diuretics when there is evidence of pulmonary vascular congestion. Digitalis does not benefit patients in sinus rhythm unless an associated left ventricular dysfunction is present. Beta-blockers can significantly decrease heart rate and cardiac output. The decreased heart rate and cardiac output subsequently lead to a decrease in the transmitral gradient. Although there appears to be a physiologic advantage with the use of beta-blockers, the data are conflicting. Beta-blockers may be reserved for patients who have exertional symptoms if the symptoms occur at high heart rates. Anticoagulation is beneficial for cases with normal sinus rhythm with a prior embolic event or a left atrial dimension >55 mm Hg by echocardiography.
Medical management of mitral stenosis and atrial fibrillation can alleviate a variety of complications. Atrial fibrillation in patients with mitral stenosis is poorly tolerated due to a loss of atrial contraction and an associated rapid ventricular rate. The rate control is achieved by using a beta-blocker, calcium channel blocker, or digitalis. Electrical or chemical cardioversion should be performed with appropriate anticoagulation. Class 1A, 1C, and III agents can be used to terminate acute-onset atrial fibrillation and prevent recurrences of atrial fibrillation. Most antiarrhythmics increase the likelihood of maintaining normal sinus rhythm to approximately 50–70% of patients per year after cardioversion. Amiodarone appears to be more effective than sotalol or propafenone, although the antiarrhythmic should be tailored to the patient. In addition, a large number of patients take both digitalis and warfarin (Coumadin). The digitalis and Coumadin need to be decreased by approximately 50% due to significant drug interactions with amiodarone. Anticoagulation is necessary in patients who are unable to maintain normal sinus rhythm.
In pregnancy, the heart rate and cardiac output are increased substantially along with an increase in maternal blood volume. Nevertheless, most healthy pregnant women with mild to moderate mitral stenosis can be treated medically. Diuretics and beta-blockers appear to be safe for use in pregnancy. Quinidine or procainamide are the drugs of choice if an antiarrhythmic drug is needed to maintain normal sinus rhythm. If anticoagulation is necessary, Coumadin should be avoided and the patient should be treated appropriately with heparin. |
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