Mitral Valve Disease Causes
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A healthy heart and its constituent parts are essential to the function of the cardiovascular system. The heart is situated in the thorax, posterior to the sternum and costal cartilages and rests on the superior surface of the diaphragm. It acts as a muscle pump as it expands and contracts in order to pump blood into appropriate blood vessels and then to the rest of the body (Marieb, 2010). The heart has four chambers that are regulated by four valves: the mitral valve, tricuspid valve, aortic valve, and pulmonary valve. The mitral valve is often associated with disease and is the topic of this paper. It consists of annulus, both posterior and anterior leaflets, and chordate that connect the leaflets to the papillary muscles. The three most common conditions affecting the mitral valve are stenosis, regurgitation, and prolapse (Carbello, 1993; Iung, 2002).
Structure and Function
After blood is oxygenated in the lungs, blood returns via the pulmonary veins to the left atrium where the mitral valve controls the one-way blood flow from the left atrium to the left ventricle. The mitral valve is about 4-6 cm2 in area and consists of two cusps or leaflets that are arranged in a circular pattern along with a muscles and tendons as supporting structures (Ray, 2006; Chandrashekhar, 2009). These muscles (papillary) and tendons (chordae tendineae) are attached to the leaflet-like strings on a parachute which prevent prolapse into the atrium. These leaflets are typically thin with an eyelid-like shape (Marieb, 2010). The anterior cusp is the crescent moon shaped part of the valve and represents two thirds of the valve and rises higher than the posterior leaflet which has a larger surface area (Enriquz-Sarano, 2009). Papillary muscles attach the walls of the left ventricle to the inelastic chordate tendineae. The chordate tendineae from each papillary muscle are then affixed to the leaflets. During the diastole phase of the cardiac cycle, the left ventricle relaxes and the mitral valve opens allowing blood to flow into the ventricle from the atrium. However, during the systole phase, the ventricle contracts, the intraventricular force on the blood causes the valves to close and the tendons then cause the leaflets to seal together (Marieb, 2010). Furthermore, the tendons also keep the valves from opening the wrong direction thus preventing backflow of blood into the left atrium.
One of the conditions affecting the mitral valve is mitral stenosis. Mitral stenosisis is the narrowing or obstruction of the mitral valve and occurs when valve openings are smaller than normal due to stiff or fused leaflets (Chandrashekhar, 2009). This obstruction impedes the blood flow from the left atrium into the left ventricle during diastole and causes blood to collect in the atrium. Since the blood is unable to empty from the atrium, when the atrium tries to contract the atrium ends up stretching. As the atrium is being stretched, the electrical pathways that cause the heart to have a stable rhythm can become disturbed creating palpitations (Chandrashekhar, 2009). It can also cause fatigue, dizziness, chest pain, and even coughing up blood (Ray, 2006).
Mitral stenosis is usually associated with a rheumatic heart disease that was caused by an untreated streptococcal infection (strep throat). However, the wide availability of antibiotics has drastically decreased its prevalence in industrialized nations (Carbello, 1993). Other causes include infective endocarditis, rheumatoid arthritis, systemic lupus erythematosus, carcinoid hearty disease, and severe calcification of the mitral annulus (Chandrashekhar, 2009).
There are several medical treatment options. One treatment is the use of medications such as calcium channel blockers and beta blockers to slow down the heart rate, thus allowing more time for the blood to move from the left atrium to the left ventricle (Chandrashekhar, 2009). While this does allow some patients to feel better, it does not slow the progression of the disease (Iung, 2002). The second medical option involves the use of anticoagulants like warfarin to thin the blood allowing it to flow easier. This option does help prevent strokes and thromboembolism, especially in patients with irregular heartbeats (Ray, 2006).
In addition to drug treatments, there are several surgical options. One surgical treatment that works well for patients whose valves do not leak to severely and are not calcified is percutaneous mitral balloon valvotomy (PMBV). Valvotomy involves using a catheter to inflate a balloon across the stenotic valve to split commissures and increase valve area (Chandrashekhar, 2009). Another surgical option is mitral valve repair or replacement (MVR). Mitro valve repair is more difficult and in many cases does not correct mitral regurgitation (Iung, 2002). On the other hand, repair has several benefits including better preservation of LV function, lower operative and long-term mortality, no long term dependency on anticoagulation medicine, and a reduced risk of infective endocarditis (Iung, 2002).
Mitral regurgitation is a condition in which the mitral valve does not properly close and therefore blood leaks backwards from the left ventricle into the left atrium (Carbello, 1993). It can be caused by a variety of factors such as myxmatous degeneration, rheumatic heart disease, coronary artery disease, ineffective endocarditis, cardiomyopathy, and by damage from mitral valve prolapsing or damage from heart attacks (Enriquz-Sarano, 2009). A common form of regurgitation occurs when the left ventricle broadens causing the valves to close improperly. This can be caused by prolonged high blood pressure, alcohol abuse or chronic mitral valve leakage (Ray, 2006).
In chronic mitral regurgitation there is a gradual increase in left atrial size, while left atrial and pulmonary venous pressures do not increase until late stages of the disease and may remain asymptomatic for years (Enriquz-Sarano, 2009). As the regurgitation becomes more pronounced, the increased volume overloads the left ventricle causing the left ventricle to dilate and become hyperdynamic creating an increase in afterload, contractile dysfunction, and heart failure (Iung, 2002). Due to the left atrial enlargement, chronic mitral regurgitation patients are more prone to atrial fibrillation and thromboembolism (Enriquz-Sarano, 2009). As the condition progresses additional blood is leaked back into the atrium, causing patients to become fatigued, breathless and can eventually become disabled. Unfortunately, medicine has limited benefit; however, diuretics that reduce the fluid in the body and drugs that can reduce blood pressure may offer limited help (Enriquz-Sarano, 2009). Surgery timing is critical. It should not be done too soon creating unnecessary patient risk, nor should it be performed after the heart muscle is too weak to withstand the surgery. Long-term patients can develop pulmonary hypertension and right-sided heart failure. However, prognosis is excellent if the surgery is performed before the heart is too weak especially if the mitral valve can be repaired (Ray, 2006).
Acute mitral regurgitation is unusual. It is typically caused by an infected heart valve or a trauma to the valve structure such as a chordal rupture or papillary muscle rupture (Iung, 2002). When acute and severe, the left atrial and pulmonary venous pressures rapidly increase causing pulmonary venous hypertension and congestion as well as pulmonary edema. It is usually symptomatic because of the sudden regurgitant volume load in the nondilated left atrium and ventricle. This leads to pulmonary venous hypertension and congestion and causes the patient to become extremely ill and typically necessitate an emergency replacement of the valve.
Mitral Valve Prolapse
Mitral valve prolapse is a condition in which one or both of the mitral valve flaps bulge back into the left atrium during systole. This can cause the valve tissues to become floppy and stretchy, thus preventing the valve from forming a tight seal and causing the valve to leak. Mitral valve prolapse is the most common type of mitral valve disease in America. Patients with myxomatous valve disease are at an increased risk and often have elongated and thickened leaflets. Mitral valve prolapse can cause mitral regurgitation; and while mild, it can be progressive often necessitating valve repair or replacement. Patients with mitral valve prolapse are usually asymptomatic; however, in the past it has been linked to arrhythmia, atypical chest pain, dyspnea, palpitations, anxiety, syncope, etc. but testing has failed to confirm these reports. Most people diagnosed with mitral valve prolapse have no long-term medical problems associated with it and have a normal life expectancy.
Mitral valve prolapse can often times be diagnosed with a simple physical examination. The diagnosis is confirmed with an electrocardiogram as well as to determine the severity of mitral regurgitation. Patients that do not have heart rhythm disturbances, mitral regurgitation, and whose heart is otherwise healthy are thought of as low risk for long-term problems. For other patients, especially those with severe regurgitation, are considered at risk for valve infections and typically require preventative antibiotics before surgery and before dental work. Medication can also be used to help alleviate some of the symptoms, drugs such as beta blockers decrease the force with which the heart contracts and block the effects of increased adrenaline levels can help..
A preliminary mitral valve disease diagnosis can often be made by an experienced physician simply by listening to the heart through a stethoscope. Chest radiology can also be utilized to show pulmonary congestion and enlargement of the left arteries and left atrium. Furthermore, an electrocardiogram (EKG) can be used to show atrial fibrillation, left atrial enlargement or in an advanced case, right ventricular hypertrophy. Also, an echocardiograph can then be utilized to diagnose mitral valve disorders as well as to determine which treatment would be best and to check the progress and effectiveness of any treatment administered. A transesophageal echocardiogram (TEE) is a type of echocardiograph that is especially effective for observing the mitral valve and its operation. It utilizes a small tube with a probe on the end that is swallowed and allows observation from the esophagus. Cardiac catheterization (angiogram), radionuclide scans, and magnetic resonance imaging (MRI) can also be utilized.
Mitral valve diseases are some of the most common forms of heart valve diseases. Mitral stenosis, although rare in industrialized countries continue to remain a severe medical problem especially in developing countries. While medical therapy can suppress some symptoms, minor surgeries such as those utilizing balloons may be an option. In other patients, heart valve surgery will be needed to either repair or replace the valves. Mitral regurgitation may accompany other heart diseases and should be surgically corrected when severe or when decreasing heart function necessitates, preferably utilizing repair over valve replacement. Mitral valve prolapse is typically not harmful but for a small minority can lead to mitral regurgitation or other problems. Patients with mitral prolapse should consider using antibiotic prophylaxis before some dental and surgical procedures.
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