6.6: Mitral Stenosis

Etiology and Pathology

The leading cause of mitral stenosis is rheumatic fever, causing postrheumatic deformities. Other rare etiologies of left atrial outflow obstruction include congenital and degenerative mitral valve stenosis, severe mitral annular and/or leaflet calcification carcinoid disease, neoplasm, left atrial thrombus, infective endocarditis with large vegetations, certain inherited metabolic disorders such as Fabry’s disease, mucopolysaccharidosis, Whipple’s disease, gout, rheumatic arthritis, lupus erythematosus, methysergide therapy, and cases related to previous implanted prosthesis or commisurotomy.

Rheumatic valvular disease causes diffuse thickening of the valve leaflets by fibrous, or fibrocalcific distortion, with fusion of one or more commissures valve commissures, and fusion and shortening of the subvalvular apparatus. This combined with increasingly rigid cusps results in narrowing of the valve.

The area of the normal mitral valve orifice is 4-6 cm2. In patients with mitral stenosis, when the valve area approaches 2 cm2 or less, an early, mid and late diastolic transvalvular gradient is present between the left atrium and ventricle. With progressive mitral stenosis, transvalvular pressure gradient increases. Mitral transvalvular flow depends on cardiac output and heart rate. Shortening of diastolic phase in increased heart rate causes symptoms by reducing forward cardiac output. Mitral stenosis develops gradually, and may be asymptomatic for years.

Clinical Presentation

Patients with mitral stenosis may be asymptomatic for years. Mean age of presentation of symptoms is fifty to sixty years old. The presenting symptom in patients with mild mitral stenosis is typically dyspnea precipitated by stress or atrial fibrillation. Progression of disease with increasing left atrial and pulmonary venous pressures will cause progressive dyspnea. At advanced stage, patients are often thin and frail and complain of weakness and fatigue due to low cardiac output. When pulmonary hypertension and right ventricular failure develop, signs of tricuspid regurgitation, abdominal discomfort due to hepatomegaly and ascites can be present.

On physical examination, heart size is usually normal. An apical diastolic thrill can be palpated. A holodiastolic murmur can be auscultated at the apex with a presystolic accentuation in sinus rhythm. The intensity of this murmur is determined by the transmitral gradient. In patients with severe stenosis, calcified leaflets, or low cardiac output no diastolic murmur may be audible. An opining snap may be present due to sudden tensing of the pliable leaflets during opening. S1 may be loud when the mitral leaflets are pliable. Thickening and calcification will diminish S1 in more advanced stages. With pulmonary hypertension, S2 becomes prominent and a murmur of tricuspid regurgitation located at the xyphoid can be present. In severe mitral valve stenosis with pulmonary hypertension, pulmonary rales are audible. Intermittent malar flushes, jugular distension, and peripheral cyanosis may be present

Diagnostics

Chest Radiography

Signs of left atrial enlargement are often the earliest changes on chest radiography.

Straightening of the left heart border by prominent pulmonary arteries coupled with left atrial enlargement can be observed as well as a double contour of the left atrium and elevation of the left main stem bronchus. Distension of the pulmonary arteries and veins in the upper lung fields and pleural effusions indicate elevated pulmonary pressures. Kerley B lines may be observed in severe mitral stenosis.

Electrocardiography

Electrocardiography is in many cases normal and cannot asses the severity of mitral stenosis accurately. Atrial arrhythmias are more common in patients with advanced mitral stenosis. In sinus rhythm signs of left atrial enlargement may be present with a prolonged P wave and a negative deflection in lead V1 and left axial deviation of P wave. Signs of right ventricular hypertrophy with right-axis deviation, a tall R wave in V₁, and secondary ST-T-wave changes may be present in cases of severe pulmonary hypertension

Echocardiography

The primary diagnostic method for assessing mitral valve pathology and pathophysiology is echocardiography. The severity and consequences of the mitral stenosis can be evaluated. The valvular anatomy and morphology including valve thickening, mobility, calcification, subvalvular deformity and anatomic lesions can be assessed

Rheumatic mitral stenosis can cause reduced diastolic excursion of the leaflets and thickening or calcification of the valvular and subvalvular apparatus. Doppler is used to determine the peak and mean transvalvular pressure gradients. The valve area can be measured accurately by three-dimensional echocardiogram. Transesophageal echocardiography is able to provide more detailed information of the mitral valvular pathology than transthoracic echocardiography.

Cardiac Catheterization

Cardiac catheterization can provide information regarding coronary artery status. This diagnostic tool is not necessary to establish the diagnosis of mitral stenosis.

Prognosis

The progression of mitral stenosis ranges from 0.1–0.3cm2/year.[39] Survival rates of 80% at 10 years have been reported with asymptomatic mitral valve stenosis. Once symptoms develop related to pulmonary hypertension 10-year survival is 0–15%. Progressive heart failure is the most common cause death in the untreated patients with mitral stenosis.

Treatment

Medical treatment

No medical treatments will relief mitral stenosis. Dyspnea may be transiently relieved by diuretics or long acting nitrates. In order to slow the heart rate, Beta-blockers or calcium-channel blockers can be prescribed. Patients with atrial fibrillation should be on anticoagulants with a target INR of 2-3. In patients with severe mitral stenosis, cardioversion should not be performed prior to intervention since it does not durably restore sinus rhythm. After successful intervention cardioversion is indicated if atrial fibrillation is of recent onset and the left atrium only moderately enlarged.

Percutaneous mitral commissurotomy

Mitral stenosis can be relieved by percutaneous mitral commisurotomy. This procedure was introduced in 1980 and used worldwide ever since [40][41]. The results of balloon valvotomy are comparable to open commissurotomy.[42]

The commissural splitting of percutaneous mitral commissurotomy substantially increases the valvular area. Pulmonary pressures decrease immediately. Procedural mortality has been reported 0–3%. In 2-10% leaflet tearing results in severe mitral regurgitation. Preprocedural condition of the patients and the experience of the operator and operating team are of major influence on the complication rate of percutaneous mitral commissurotomy. Long-term results of a successful procedure have been reported with event-free survival ranges from 35–70% after 10–15 years.

Surgical intervention

Open commissurotomy or valve replacement is indicated if balloon valvotomy is unfeasible.

The concept of surgical repair of the mitral valve was first introduced in 1902 by Sir Thomas Lauder Brunton, a Scottish physician.( Brunton L, Edin MD: Preliminary note on the possibility of treating mitral stenosis by surgical methods. Lancet 1902; 1:352 [43]). The first successful mitral valve operation was a transventricular commissurotomy by Elliot Cutler in 1923. The following transventricular valvultomies performed with the cardiovalvulotome resulted in regurgitation and Cutler abandoned the procedure.

In 1948, Dwight Harken reported his series of patients with mitral stenosis successfully treated with a valvuloplasty procedure.[44]

After development of cardiopulmonary bypass, the closed commissurotomy has been replaced by an open mitral commissurotomy. This allows not only correction of commissural fusion, but also chordal and papillary fusion.

Surgical intervention can improve the functional capacity and long-term survival of patients with mitral stenosis substantially. Survival rates of 96% and freedom from valve-related complications of 92% at 15 years have been reported.[45] Surgery should be performed before New York Heart Association (NYHA) class III symptoms are present.