Mitral Kapak Darlığı

The mitral valve is a bicuspid valve, composed of two leaflets, situated between the left atrium and the left ventricle. Deoxygenated blood returning from the body reaches the right atrium, passes into the right ventricle, and is pumped by the right ventricle through the pulmonary artery to the lungs for oxygenation. The oxygenated blood then returns to the left atrium through the four pulmonary veins. During diastole the mitral valve opens and the oxygenated blood passes from the left atrium into the left ventricle. During systole the mitral valve closes and the oxygenated blood is ejected from the left ventricle into the aorta. The valve closes during systole in order to prevent regurgitation of blood back into the left atrium.

The normal mitral valve area is 4-6 cm². When stenosis develops, the valve area decreases, emptying of oxygenated blood from the left atrium into the left ventricle becomes impaired, and left atrial pressure rises. This rise in left atrial pressure is transmitted to the pulmonary veins and to the pulmonary capillaries, where blood is oxygenated. As the valve becomes progressively narrower, the pressure elevation and the related signs and symptoms become more pronounced. When blood and serum leak into the alveolar spaces and the lungs become congested, pulmonary oedema and death may follow.

What causes mitral valve stenosis?

In Türkiye, as in other developing countries, the most important cause of mitral stenosis is rheumatic heart disease resulting from acute rheumatic fever acquired in childhood. Acute rheumatic fever is caused by particular types of a bacterium known as group A beta-haemolytic streptococcus. Approximately 2 to 3 weeks after a streptococcal throat infection, findings appear principally in the joints, and also in the heart, the skin and the brain. The mitral valve is the cardiac valve most frequently affected by acute rheumatic fever, and rheumatic involvement is the most common cause of mitral stenosis in adults.

Other, rarer causes of mitral stenosis include:

• Congenital mitral stenosis: parachute mitral valve, accessory mitral valve, fused papillary muscles, an abnormal ring arising from atrial tissue within the left atrium
• Connective tissue and rheumatological diseases seen in adults: systemic lupus erythematosus (Libman-Sacks endocarditis), the erosive polyarticular subtype of rheumatoid arthritis
• Certain storage diseases: mucopolysaccharidoses, Fabry disease, Whipple disease
• Infective disease: fungal endocarditis
• Cardiac tumours: myxoma
• Functional mitral stenosis caused by heavy mitral annular calcification related to ageing and degeneration, or by severe aortic regurgitation

What are the symptoms?

Symptoms usually do not appear until the mitral valve area has fallen from its normal value of 4-6 cm² to 2.5 cm². Once the valve area is below 2.5 cm², symptoms develop gradually. The earliest symptoms are fatigue and reduced exercise tolerance. These symptoms arise because the blood arriving in the left atrium cannot empty adequately into the left ventricle through the narrowed mitral valve, so that left ventricular filling and, consequently, the volume of blood pumped forward into the aorta and to the body are reduced.

Because of the stenosis, blood that cannot empty completely from the left atrium into the left ventricle gradually pools backwards in the lungs. This impairs gas exchange and causes dyspnoea. In mild stenosis, breathlessness appears only with marked exertion; as the stenosis progresses, symptoms begin to appear with minimal exertion.

A valve area between 1 and 1.5 cm² is regarded as moderate mitral stenosis. When the valve area falls below 1 cm², severe mitral stenosis is present. At this stage the patient may be breathless even at rest and physical activity becomes progressively restricted. As the stenosis advances, the patient wakes from sleep with air hunger (paroxysmal nocturnal dyspnoea), gets up, walks about and tries to open a window, and feels relieved; the true mechanism of this relief is that in the upright position blood is redirected from the lungs towards the legs, so that venous return to the heart is somewhat reduced. At a more advanced stage, dyspnoea is present even while sitting and the inability to lie flat (orthopnoea) becomes prominent. The final stage is pulmonary oedema. In pulmonary oedema, markedly increased pressure in the pulmonary capillaries allows blood and serum to leak into the alveolar spaces where gas exchange takes place; the patient develops a cough producing pink, frothy sputum together with bubbling, wheezy breathing, and such patients are frequently brought to the emergency department with these symptoms. Without timely treatment, pulmonary oedema is fatal.

What complications may develop?

The rising pressure within the left atrium in mitral stenosis leads to left atrial enlargement. As the left atrium enlarges, the duration of electrical conduction is prolonged and the normal conduction cycle is disturbed, giving rise to atrial fibrillation, a serious rhythm disorder. Atrial fibrillation in turn causes further enlargement of the left atrium. As a result of this vicious cycle, blood pools in the left atrium and, where it pools, the flow characteristics of the blood are disturbed and thrombus may form in the left atrium and in the left atrial appendage. Detachment of such thrombus into the systemic circulation may result in embolism and stroke.

Sudden rises in left atrial pressure may rarely cause bleeding from the bronchial veins that drain into the pulmonary veins, resulting in haemoptysis — the expectoration of blood. In some cases, marked enlargement of the left atrium may compress the laryngeal nerve and cause hoarseness.

In patients who are not treated at the appropriate time, the increase in left atrial pressure is also transmitted to the main pulmonary artery; the resulting pulmonary hypertension increases the afterload on the right heart and right heart failure begins to develop.

How is mitral stenosis diagnosed?

Echocardiography is an important diagnostic tool in mitral stenosis, and the highly advanced ultrasound systems available today allow the diagnosis to be established readily. Transthoracic echocardiography (TTE), performed simply by placing an ultrasound probe on the front of the chest, clearly demonstrates the stenotic mitral valve and allows the mitral valve area to be calculated. Once the diagnosis has been made by TTE, transoesophageal echocardiography (TEE) is usually performed — the patient swallows a probe that is positioned in the oesophagus — in order to clarify the degree of stenosis, to determine whether any accompanying regurgitation is present, to assess the condition of the subvalvular apparatus, and to examine for the presence or absence of thrombus in the left atrium, particularly in the left atrial appendage.

On the basis of these examinations, a dedicated echocardiographic scoring system is used to determine whether the valve is suitable for treatment without surgery. In addition to two-dimensional TEE, three-dimensional echocardiography (3D-TEE), which demonstrates the subvalvular apparatus more clearly, readily establishes whether the valve anatomy is suitable for treatment without open surgery. Echocardiography is thus a highly useful instrument for establishing both the diagnosis and the treatment of mitral stenosis. In our clinic, TTE together with two-dimensional and three-dimensional TEE is performed in every patient in whom mitral stenosis is suspected.

Opening the mitral valve without surgery: who is suitable for mitral balloon valvuloplasty?

Mitral balloon valvuloplasty, also known as percutaneous mitral commissurotomy, is dilatation of the stenotic valve with a balloon, performed through fine catheters introduced via the groin and without the need for open heart surgery.

This treatment is generally performed in patients who have:

• Advanced mitral valve stenosis
• Symptoms such as breathlessness, early fatigue or palpitations
• Valve anatomy suitable for the procedure
• No severe mitral regurgitation
• No thrombus in the left atrium

In some circumstances the treatment may also be recommended in the absence of marked symptoms, if pulmonary artery pressure has risen or a rhythm disorder has developed.

How is mitral balloon valvuloplasty performed?

The veins in the groin carry deoxygenated blood from the legs to the right atrium. In our catheterisation laboratory we make small punctures in the femoral vein with a fine needle and place a sheath into the vein. Through this sheath we advance our small catheters into the right atrium. A special needle (Brockenbrough needle) is then introduced and a transseptal puncture is made in order to cross from the right atrium into the left atrium. After crossing the atrial septum, a specific halo-shaped guidewire is positioned in the left atrium. Over this guidewire a special balloon is advanced into the left atrium. Using various manoeuvres we cross the mitral valve and inflate the distal portion of the balloon in the left ventricle. The balloon is then pulled back and, exactly across the mitral valve, all segments of the balloon are inflated to dilate the stenotic mitral valve. After the procedure the valve area is recalculated and the gradient across the valve is measured. If the valve has been adequately opened, the procedure is terminated.

Can mitral balloon valvuloplasty be used in every patient?

Mitral balloon valvuloplasty is not used in every patient with a diagnosis of mitral stenosis. The treatment is reserved for appropriate patients: those with a low echocardiographic score are the ideal candidates for balloon therapy. Open surgery is recommended, however, for patients with severe involvement of the subvalvular apparatus, for patients with severe mitral or aortic regurgitation, for patients with thrombus in the left atrium or the left atrial appendage, and for patients with severe, complex coronary artery disease. Echocardiographic assessment before the procedure is therefore essential in determining the appropriate treatment in patients with mitral stenosis.

Are there complications related to the procedure?

Compared with open heart surgery, complications of this treatment modality are very rare. The complications associated with open heart surgery, such as bleeding or trauma to the great vessels and surrounding structures, are not encountered, and because the chest is not opened the cosmetic advantage is also considerable. A hole is created in the atrial septum during the procedure, but it usually heals afterwards. The transseptal puncture also carries a risk of injury to cardiac structures and of pericardial effusion or tamponade, although this is very rare compared with open heart surgery. For these reasons, both European and American cardiology guidelines recommend mitral balloon valvuloplasty as the first-choice treatment in suitable patients with mitral valve stenosis.

In suitable patients, mitral balloon valvuloplasty is an effective method that provides successful results, shortens the hospital stay and can reduce the need for open heart surgery. It is not, however, appropriate for every patient. The decision to treat must therefore be made by cardiologists after echocardiography and any other necessary investigations.