Mitral Valve Disease

The mitral valve separates the left atrium and the left ventricle of the heart and is a fibrous structure lined by endocardium. It consists of the mitral annulus, the leaflets of which comprise a large anterior or aortic leaflet and a small posterior or mural leaflet, the chordae tendineae and the papillary muscles. Abnormalities in any of these structures can cause mitral valve dysfunction. The leaflets are tethered to the left ventricle by the chordae tendinae. Chordae tendineae are attached to papillary muscles and prevent prolapse of the mitral valve leaflet to prevent reflux of blood into the left atrium.

Obstruction to flow through the valve is mitral stenosis. Regurgitation when the valve should be preventing reflux is variously called mitral insufficiency, incompetence and regurgitation. It may be argued that a stenotic valve is also insufficient or incompetent and so perhaps regurgitation is to be preferred. In addition, the chordae tendinae may fail to hold the valves shut, allowing mitral prolapse. Any of these three conditions can occur alone or in combination. Mitral valve prolapse is described in its own article.

• Disease of the valve may be congenital or acquired. Historically, much mitral valve disease has been post-rheumatic but with the decline of rheumatic fever this has waned considerably. Other causes of mitral valve disease include systemic lupus erythematosis, rheumatoid arthritis, atrial myxoma, and bacterial endocarditis. The last usually occurs on pre-existing pathology. The usual aetiologies of regurgitation are myxomatous degeneration, ruptured chordae tendineae, connective tissue disease, dilatation of the left ventricle including from dilated cardiomyopathy and rheumatic fever.
• Only about 50% of cases of classical rheumatic heart disease are associated with a history of rheumatic fever and often rheumatic fever is not followed by heart lesions. Pure mitral stenosis is highly suggestive of rheumatic heart disease.
• Acute mitral regurgitation may be caused by rupture of the chordae tendinae following myocardial infarction or trauma.

• Mitral stenosis has a female preponderance of 2:1. The incidence of mitral regurgitation increases with age.
• Mitral valve disease affects approximately 5 in 10,000 people. Myxomatous degeneration has replaced rheumatic heart disease as the leading cause of mitral valve abnormalities.

Symptoms

Stenosis tends to produce more symptoms than regurgitation but the picture is often mixed. There may be a mixture of pathologies including aortic valve disease.

• The commonest presentation of mitral valve disease is shortness of breath on exertion. This may be precipitated by atrial fibrillation.
• Orthopnoea may progresses to paroxysmal nocturnal dyspnoea.
• Effort-induced fatigue is common.
• Haemoptysis with pulmonary congestion is a late feature.
• Chest pain due to right ventricular ischaemia, coronary artery disease or a coronary embolism are uncommon presentations.
• Thromboembolism may be the first symptom of mitral valve disease.
• Palpitations may be the presenting feature.

Signs

Techniques of examination are described elsewhere and will not be repeated here. Articles include history and examination, examining the pulse and jugular venous pressure. Remember to look and feel before auscultation. Murmurs and heart sounds in children is complex and is discussed elsewhere.

Physical signs depend upon the severity of the disease and how advanced other pathologies may be, such as pulmonary congestion. Many of the following will be found only in severe and advanced disease.

As always, start with inspection before ausculatation.

• Malar flush
• Elevated jugular venous pressure
• Respiratory distress and even evidence of pulmonary oedema
• Examination of the cardiovascular system will show a diastolic thrill that is palpable over the apex
• There may be signs of right heart failure in severe disease including elevated jugular venous pressure, hepatomegaly, and peripheral oedema.

Auscultation of the heart is described elsewhere. The loudness of murmurs gives no indication of the severity of pathology.

• In mitral stenosis there is a loud S1 followed by an S2. These and the opening snap are best heard at the left sternal border. An opening snap will not occur in atrial fibrillation as there is no atrial contraction to "snap" open the valve.
• If pulmonary hypertension is present, there may be a right ventricular heave, a loud P2 and a high-pitched, decrescendo, diastolic murmur of pulmonary regurgitation called the Graham Steell murmur.
• This is followed by a low-pitched, rumbling, diastolic murmur which is heard best over the apex with the patient on the left side.
• The murmur may get softer as the stenosis increases.
• The duration, but not the intensity, of the diastolic murmur correlates with the severity of the mitral narrowing.
• Mitral regurgitation produces a pansystolic murmur, best heard at the apex and transmitted to the axilla. It is best hear with the patient on the left side.

Pathology of the mitral valve includes:

• Mitral stenosis
• Mitral regurgitation
• Mitral valve prolapse
• Subacute bacterial endocarditis can occur on an abnormal valve
• Atrial myxoma may present as mitral valve disease.

Chest x-ray may show a number of abnormalities depending upon the progression of the disease.

• Enlargement of the right ventricle.
• Left atrial enlargement with straightening of the left heart border
• Double density
• Pulmonary venous pattern shows redistribution of the flow toward the apices
• Prominent pulmonary arteries at the hilum that rapidly taper
• Kerley B lines
• Pulmonary oedema is a late feature.

Echocardiography is the most sensitive and specific non-invasive method for diagnosing mitral valve disease.

• With two-dimensional echocardiography, the size of the mitral orifice can be measured along with the cardiac chamber sizes.
• Colour Doppler can evaluate the gradient across the valve, pulmonary artery pressure, and mitral regurgitation.
• Transoesophageal echocardiography is useful for detecting vegetations that are smaller than 5 mm or thrombi in the left atrium which are not seen with transthoracic echocardiography.

ECG may show various changes:

• In sinus rhythm an enlarged left atrium produces a broad notched P wave, most prominent in lead II, with a negative direction in V1.
• With severe pulmonary hypertension, right axis deviation and right ventricular hypertrophy can be seen.
• Atrial fibrillation is common, especially in stenosis but it is not specific.
• Cardiac catheterisation may be required to assess pressures and gradients and to check for coronary artery disease.

Non-Drug

If there is left ventricular failure, oxygen and an upright position are required.

Drugs

• If there is fast atrial fibrillation, digoxin is valuable to control the rate. It has no significant benefit otherwise.
• Diuretics and other treatment for heart failure may be required.
• Acute valve disease can be life-threatening. Emergency treatment consists of vasodilator and possibly inotropic therapy but definitive therapy generally requires surgical intervention.¹
• If the left ventricle is markedly dilated there is significant risk of mural thrombus and systemic emboli. This requires anticoagulation.
• In patients with mitral regurgitation caused by dilated cardiomyopathy, vasodilators reduce symptoms, and improve function. However, in mitral valve prolapse or hypertrophic cardiomyopathy, vasodilators may worsen the regurgitation and should be avoided. With other causes, vasodilators could potentially mask the development of left ventricular dysfunction and lead to unnecessary and harmful delays in surgery.²

Surgical

• Balloon valvulotomy can increase the lumen of a stenosed valve with subsequent reduction in left atrial pressure.³ It is most commonly used in young patients without extensive valvular calcification, in pregnant women, and in patients who are poor risk for operation. It can cause leaking of the valve too.
• Mitral valve replacement is performed if leaflets are immobile or heavily calcified. Bioprosthetic or artificial mechanical valves can be used as replacements. They usually require long-term anticoagulation.
• The operative mortality rate is between 1 and 2% for mitral commissurotomy and 2 to 5% for mitral valve replacement. Commissurotomy is an operation to cut through the flaps of the mitral valve to relieve stenosis.
• The optimum timing of surgery requires judgement. It is a major operation but it is better to undertake surgical correction before left ventricular dysfunction is well established.⁴ Improvement in surgical techniques and management now lead to a more liberal approach to valve replacement.⁵

• Dilation of the left atrium predisposes to atrial fibrillation and mural thrombi. Emboli result in 20% of patients. High risk for systemic emboli is associated with age over 35 years, atrial fibrillation with a low cardiac output and with a large left atrial appendage. Atrial fibrillation occurs in up to 40% of patients and is more common with mitral stenosis. Loss of atrial contraction decreases cardiac output by 20%.

Prevention of Subacute Bacterial Endocarditis

Bacteraemia can result in vegetations forming on damaged or abnormal valves. Anything that can cause a transient bacteraemia, including dental surgery, requires antibiotic cover. If in doubt, give cover, as SBE is very difficult to treat and has serious consequences. It makes sense to base the antibiotic on the likely organisms to enter the blood. For dentistry a single 3g of amoxicillin is usually given an hour before surgery. Clindamycin and azithromycin are used in those allergic to penicillin.

Whilst most doctors and dentists are aware of the need for antibiotic cover, body piercing and tattooing are also a risk⁶ and their practitioners are unlikely to be so aware. Patients need to be educated about the need for cover for both medical and other procedures.⁷ The matter of prophylaxis has been addressed by a consensus paper⁸ in the European Heart Journal.

In view of this, a paper in 2006 from the Working Party of the British Society for Antimicrobial Chemotherapy may seem rather controversial.⁹ They reviewed the evidence from the American Heart Association, European Cardiac Society and British Cardiac Society as well as other sources. They also noted a Cochrane review¹⁰ which failed to find any benefit from prophylactic antibiotics before dental surgery in at-risk patients. General dental hygiene appears to be important in those at risk and general background bacteraemia from activites such as cleaning teeth appears to be a greater risk than dental surgery. The working party recomended that the indication for antibiotic prophylaxis for dental treatment should be restricted to patients who have a history of previous endocarditis, or who have had cardiac valve replacement surgery, or those with a surgically constructed systemic or pulmonary shunt or conduit.⁹

Enterococci, streptococci and staphylococci can cause endocarditis in procedures other than dentistry. Thee may include endoscopy of the gastrointestinal or respiratory tract, ENT, urology and gynaecology procedures. The article suggests appropriate antibiotics for the various procedures, based on likely relevant flora. They recommend that adequate skin cleaning should be undertaken but antibiotic prophylaxis is unnecessary for cardiac catheterisation and "cosmetic" piercing of ears or nipples.⁹

As this is at variance with traditional teaching, it needs to be discussed with the patient before implementation and it is probably best to assume that, if in doubt, give antibiotic. Even "correct use of the appropriate antibiotic" does not have 100% effectiveness.

• The natural history of rheumatic heart disease is that after infection it takes 10 years for a murmur to develop, another 10 years for symptoms to start and another 10 years for symptoms to progress. Rheumatic fever does not affect just the valves but it causes long term damage to the myocardium too.
• Without surgical intervention, mitral stenosis has an 85% mortality rate 20 years after the onset of symptoms. 10 years after diagnosis of mitral regurgitation, 90% die or have a surgical procedure.