Critical Care Medicine

Mitral stenosis

Mitral stenosis

Related condition

Predominantly caused by rheumatic heart disease (RHD), though up to 50% of patients will have no knowledge of previous RHD.

1. Description of the problem

Mitral stenosis rates are declining in the Western world, though it remains a significant problem in the developing world because of RHD. The stenotic valves cause an obstruction to flow from the left atrium to the ventricle.

Clinical features

Symptoms

Dyspnea

Shortness of breath (SOB) is the most common presenting complaint. SOB is initially on exertion, and then progresses to paroxysmal nocturnal dyspnea and orthopnea. The dyspnea is related to decreased cardiac output, increased pulmonary pressures or development of atrial fibrillation.

Palpitations

Atrial fibrillation often develops secondary to left atrial dilatation.

Hemoptysis

A rare presentation related to rupture of bronchial veins secondary to raised left atrial pressure.

Hoarseness

Ortner's syndrome is the development of hoarseness because of compression of the recurrent laryngeal nerve by the dilating left atrium.

Chest pain

Angina-like discomfort may develop either due to RV hypertension or concomitant coronary disease.

Physical Signs

Auscultation

A low-pitched diastolic murmur is the classic physical sign of mitral stenosis. The murmur is often difficult to appreciate, but may be accentuated with brief exercise (eg, sit-ups). Patient should be in left lateral decubitus position to make auscultation easier. If the patient is in sinus rhythm a late diastolic accentuation of the murmur occurs. An opening snap (OS) is characteristic. The distance of the OS from S2 is inversely proportional to the severity of the mitral stenosis. S1 is soft or absent. S2 is louder as pulmonary hypertension develops.

Other Physical Signs

An irregularly irregular pulse of AF often occurs. Mitral facies can be seen, which refers to the rosy-blue tinge to the cheeks, seen due to dilatation of the malar capillaries in mitral stenosis.

Key management points

The priorities for management are:

  1. Decrease the risk of worsening mitral stenosis secondary to recurrent RHD.

  2. Monitor disease progression with a focus on timely intervention when it is required.

  3. Diagnosis and treatment of complications such as atrial fibrillation, if or when they arise.

2. Emergency Management

Mitral stenosis is a chronic condition.It may be intially diagnosed in patients presenting acutely with pulmonary edema or atrial fibrillation with fast ventricular response. These cases should be managed along usual pulmonary edema or AF management guidelines.

3. Diagnosis

Echocardiography

Transthoracic echocardiography is of vital importance for diagnosis, assessment of severity and monitoring progression of MS. It reveals thickening of leaflets and chordae as well as restricted motion and classic "hockey-stick" deformity or diastolic doming of leaflets. Mitral valve area (usually 4 - 6 cm2) is calculated by direct planimetry or by Doppler pressure half-time. Prior to any intervention, echo is used to assess appropriateness for balloon mitral valvuloplasty (BMV, see later). Transthoracic echo will also allow assessment of LV and RV size and function, LA dilatation, and pulmonary artery pressures and clarify involvement of any other valves in RHD.

Transesophageal echocardiography (TEE) is not routinely used if the transthoracic views are adequate. It may be necessary to examine the presence of any thrombus in the LAA, or assess severity of mitral regurgitation prior to BMV.

Cardiac Catheterization

Simultaneous measurement of LV end-diastolic pressure, LA pressure, and cardiac output allows for calculation of mitral valve area via the Gorlin formula. LA pressure is estimated via pulmonary capillary wedge pressure or measured directly following transseptal puncture. However, in the presence of reliable echocardiographic data, catheterization is not required for the diagnosis.

Other diagnostic clues

ECGs may reveal P-mitrale of LA enlargement, RVH from pulmonary hypertension or AF. LA enlargement may also be noticed, particularly in lateral views as a double density at the right-heart border of chest radiographs. With LA enlargement the left main bronchus may be elevated.

Differential of a MS murmur

Aortic regurgitation causes a murmur throughout diastole, which is best heard at the lower left sternal edge, with the patient sitting forward

An atrial myxoma may have a "tumor plop" that can be mistaken for an OS. A myxoma may obstruct the valve, leading to a diastolic murmur.

4. Specific Treatment

Medical Therapy

Guidelines advocate oral penicillins in patients with RHD to prevent recurrent rheumatic fever. Oral diuretics can improve mild dyspnea. Beta-blockers may improve exercise tolerance. Atrial fibrillation should be treated as per ACC/AHA guidelines, though rhythm control can be more challenging. Oral anticoagulation should also be considered with LA diameter > 55 mm or spontaneous contrast seen in LA on echocardiography.

Percutaneous Mitral Balloon Valvuloplasty (PMV)

Treatment of choice when intervention is required. Involves transseptal puncture and inflation of balloon to split the fused commissures. An echocardiographic (Wilkins) score has been developed to predict those most likely to benefit from PMV (see below). Those with a Wilkins score of less than 8 have the best results post PMV. PMV is contraindicated in moderate or severe MR or with LA appendage thrombus.

Wilkins Score

(0 - 4 points in each category, 0 is normal, total from cumulative points)

Mobility

1. Highly mobile with only leaflet tips restricted

2. Mild leaflet restriction with only bases moving normallly

3. Valve moves forward in diastole, mainly from the base

4. No or minimal diastolic movement of the base

Subvalvular Thickening

1. Minimal thickening below leaflets

2. Chordal thickening up to one third of the chordal length

3. Thickening of entire leaflet

4. Extensive thickening to the papillary muscles

Thickening of leaflets

1. Near normal (4-5 mm)

2. Marginal thickening (5-8 mm) with near-normal thickness of mid-leaflets

3. Thickening of entire leaflet (5-8 mm)

4. Extensive thickening of all leaflet tissue (>8-10 mm)

Calcification

1. Single area of echo brightness

2. Scattered areas of increased brightness along leaflet margins

3. Brightness extending to midportion of leaflets

4. Extensive brightness throughout leaflet tissue

Surgical Treatment

Closed Mitral Valvotomy

Closed valvotomy or commissurotomy was the earliest surgical approach, but it has been superseded by BMV or open valvotomy.

Carried out via a thoracotomy, without cardiopulmonary bypass using a transatrial or transventricular dilator.

Open Mitral Valvotomy

Carried out on cardiopulmonary bypass and allows direct visualization of the valve. The commissures are incised, the chordae are separated and the papillary muscles are split, if needed. Calcium from the leaflet tips is debrided. A surgical Maze and/or left atrial appendage amputation can also be carried out for patients with AF.

Mitral Valve Replacement

MVR with a metallic or bioprosthetic valve is considered if there is concomitant mitral regurgitation. Extensive fibrosis or commissural calcification may also favor MVR. Metallic MVRs are most commonly used.

Figure 1 shows management strategy for mitral stenosis in patients with NYHA Functional Class III and IV. Figure 2 shows management strategy for mitral stenosis in patients with NYHA Functional Class II.

Figure 1.

Management of Mitral Stenosis in Patients with NYHA Functional Class III and IV

Figure 2.

Management of Mitral Stenosis in Patients with NYHA Functional Class II

5. Disease monitoring, follow-up and disposition

Annual clinic follow-up is recommended for patients with mild symptoms. Annual echocardiography is not necessary unless there has been a change in symptoms. Following intervention a baseline echocardiogram should be done and the patient is usually seen with a repeat echocardiogram at least annually.

Pathophysiology

The vast majority of cases are secondary to RHD. Mitral stenosis occurs up to 20 years following an episode of rheumatic fever. There is deposition of calcium and chordal and commissural fusion. Normal mitral valve area is 4-6 cm2. In mild mitral stenosis it is 2.0-1.5 cm2. In moderate mitral stenosis it is 1.0-1.5 cm2. In severe mitral stenosis it is less than 1 cm2. Increasing severity is also diagnosed by increasing mean transvalvular gradient and PA pressures. In severe mitral stenosis the gradients are > 10 mmHg and 50 mmHg respectively. For moderate and mild stenosis, the gradients are 5 -10 mmHg and 30-50 mmHg; and <5 mmHg and <30 mmHg. For any given valve area, the transvalvular gradient is proportional to the square of the flow rate across the valve, so if this flow rate doubles (eg, in atrial fibrillation, pregnancy or exercise) the transvalvular gradient will quadruple. This explains why previously asymptomatic people can decompensate quickly if they develop AF or become tachycardic for any other reason. The increased LA pressure can lead to increasing pulmonary pressures and in turn right heart failure.

Epidemiology

There has been a steady decline in the incidence of mitral stenosis in the US, with estimates of 1 in 100,000, but this rises to 35 per 100,000 in Africa and 100-150 per 100,000 in India. Two thirds of patients with rheumatic mitral stenosis are female. Onset of symptoms is usually in the third or fourth decade of life.

Prognosis

In those with minimal or no symptoms, survival is 80% at ten years Data from the presurgical era quotes 5-year survival at 62% for patients in NYHA Class III but only 15% for those in NYHA Class IV.

If severe pulmonary hypertension develops, average survival is three years.

Special considerations for nursing and allied health professionals.

NA

What's the evidence?

Bonow, RO. "ACC/AHA 2006 Guidelines for the mananagement of patients with valvular heart disease: a report of the American College of Cardiology/ American Heart Association Task force on Practice Guidelines (writing committee to revise the 1998 Guidelines for the Management of Patients with Valvular Heart Disease): Developed with the collaboration with the Society of Cardiovascular Anesthesiologists; endorsed by the Society for Cardiovascular Angiography and Interventions and the Society for Thoracic Surgeons". Circulation. vol. 114. 2006. pp. e84-231.

The definitive guidelines from the ACC/AHA for the treatment of all valvular diseases.

Gorlin, R. "Hydraulic Formula for the calculation of area of the stenotic mitral valve, other cardiac values and central circulatory shunts". Am Heart J. vol. 41. 1951. pp. 1.

Gorlin decribes the formula that remains the gold standard for calculation of mitral stenosis severity in the catheterization laboratory.

Nishimura, RA. "ACC/AHA guideline update on Valvular Heart Disease : Focused update on Infective Endocarditis: A Report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines Endorsed by the Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Intervention, and Society of Thoracic Surgeons". Circulation. vol. 118. 2008. pp. e523-e661.

An update on the 2006 guidelines, with reference to endocarditis.

Reyes, VP. "Percutaneous balloon valvuloplasty compared with open surgical commissurotomy for mitral stenosis". N Engl J Med. vol. 331. 1994. pp. 961-967.

A randomized trial of 60 patients with severe mitral stenosis comparing PMV with open surgery. At three years 72% of the PMV group versus 57% of the surgical group were in NYHA Class I.

Wilkins, GT. "Percutaneous balloon dilatation of the mitral valve: an analysis of echocardiographic variables related to outcomes and the mechanisms of dilatation". Br Heart J. vol. 60. 1988. pp. 299-308.

A paper from 1988 from which we get the "Wilkins Score" for determining whether a patient is a candidate for a percutaneous balloon valvuloplasty.
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