Mitral valve diseases
The mitral valve is a valve in the heart that lies between the left atrium (LA) and the left ventricle (LV). The mitral valve and the tricuspid valve are known as the atrioventricular valves, because they lie between the atria and the ventricles of the heart. A normally functioning mitral valve allows blood to flow into the left ventricle during ventricular diastole, and prevent blood from going retrograde from the ventricle to the left atrium during systole.
The mitral valve is made up of two valve leaflets (the anteromedial leaflet and the posterolateral leaflet) and a ring around the valve, known as the mitral valve annulus. (The orientation of the two leaflets resembles a bishop's miter, which is where the valve receives its name.) These valve leaflets are prevented from prolapsing into the left atrium by the subvalvular aparatus. The subvalvular aparatus, which lies completely in the LV, is made up of the papillary muscles and the chordae tendineae. The anteromedial papillary muscle and the posteromedial papillary muscle each attach to the walls of the LV. They are attached to their respective leaflets of the mitral valve by the chordae tendineae.
During left ventricular diastole, after the pressure drops in the left ventricle due to relaxation of the ventricular myocardium, the mitral valve opens, and blood travels from the left atrium to the left ventricle. About 70-80% of the blood that travels across the mitral valve occurs during the early filling phase of the left ventricle. This early filling phase is due to active relaxation of the ventricular myocardium, causing a pressure gradient that allows a rapid flow of blood from the left atrium, across the mitral valve. This early filling across the mitral valve is seen on doppler echocardiography of the mitral valve as the E wave. After the E wave, there is a period of slow filling of the ventricle. Left atrial contraction (left atrial systole) (during left ventricular diastole) causes added blood to flow across the mitral valve immediately before left ventricular systole. This late flow across the open mitral valve is seen on doppler echocardiography of the mitral valve as the A wave. The late filling of the LV contributes about 20% to the volume in the left ventricle prior to ventricular systole, and is known as the atrial kick.
There are many diseases which affect the mitral valve and its supporting structures. The most common disorder of the mitral valve is the partial backflow (regurgitation) of blood through the valve. Regurgitation is usually the result of valvular degeneration, which occurs most often in older members of the smaller dog breeds. In valvular degeneration, the leaflets or cusps which make up the valve, may have contracted and curled back on themselves. This allows the valve to leak. Valvular degeneration can also be a secondary result of an infection of the valve (endocarditis), or as a congenital (present at birth) malformation of the valve. With mitral regurgitation the blood backflows (leaks) from the left ventricle into the left atrium of the heart. This regurgitation frequently occurs which such velocity that it produces a turbulence. This turbulence can usually be detected as a systolic murmur, heard between the first and second heart sounds. As a result of mitral regurgitation the excess blood accumulates in the left atrium causing it to enlarge. The enlargement of the left atrium can lead to enlargement of the left ventricle. The amount of regurgitation is directly correlated with the size of the left atrium and ventricle. Severe mitral regurgitation, not only produces significant increases in the left side of the heart, it is frequently accompanied by varying degrees of congestive heart failure.
There are two ways that the mitral valve can malfunction. The most common is a leaky (or "regurgitant") mitral valve. In this case, the valve does not close properly, and blood flows backwards into the lungs when the heart muscle squeezes. Blood flowing backwards into the lungs can cause shortness of breath (first with exertion but later at rest). With time, the heart muscle will grow weaker, leading to congestive heart failure and death.
The most common cause of a leaky mitral valve is degenerative mitral valve disease. The hallmarks of degenerative mitral valve disease (also known as "floppy valve syndrome") include weakness and redundancy of the leaflets and their supporting structures. Other causes of a leaky valve include infection (endocarditis) of the mitral valve, congenital abnormalities of the mitral valve, and a weakened and dilated heart muscle (usually from previous heart attacks) that causes the two mitral leaflets to be pulled apart. Less commonly the mitral valve will not open properly (mitral valve stenosis) and the tight valve will prevent blood from flowing from the lungs into the ventricle. Mitral valve stenosis (narrowing of the mitral valve) is always caused by rheumatic fever, an attack on the valve leaflets by the immune system after certain infections. As a result of the immune attack, the leaflets become thickened, stiff, and do not open properly.
Surgery is generally recommended when a malfunctioning mitral valve causes symptoms (usually shortness of breath), or when the abnormal valve starts to cause weakness of the heart muscle.
More information on mitral valve diseases (mitral valve prolapse, mitral valve regurgitation, mitral stenosis)
What is mitral valve disease? - There are many diseases which affect the mitral valve and its supporting structures. The most common disorder of the mitral valve is the partial backflow.
What is mitral valve prolapse? - Mitral valve prolapse (MVP) is a heart valve condition marked by the displacement of a thickened mitral valve leaflet into the left atrium during systole.
What causes mitral valve prolapse? - The cause of mitral valve prolapse is unknown. It is more common in people with low body weight and low blood pressure.
What're the symptoms of mitral valve prolapse? - Symptoms of mitral valve prolapse include fatigue, palpitations, chest pain, anxiety, migraine headaches, and even stroke.
How is mitral valve prolapse diagnosed? - Mitral valve prolapse is diagnosed in the course of a physical examination. Echocardiography is useful in diagnosing a prolapsed mitral valve.
What're the treatments for mitral valve prolapse? - Most people with mitral valve prolapse (MVP) do not have symptoms or need treatment. Mitral valve prolapse can be treated with surgical replacement of the mitral valve.
What is mitral valve regurgitation? - Mitral valve regurgitation happens when some of the blood in your heart leaks from the left ventricle into the left atrium.
What causes mitral valve regurgitation? - The causes of primary mitral regurgitation include myxomatous degeneration of the mitral valve, ischemic heart disease, coronary artery disease.
What're the symptoms of mitral regurgitation? - The symptoms associated with mitral regurgitation are dependent on which phase of the disease process the individual is in.
What're the complications of mitral regurgitation? - Complications of mitral regurgitation include congestive heart failure, atrial fibrillation, blood clot, endocarditis.
How is mitral regurgitation diagnosed? - The diagnosis of mitral regurgitation usually employs imaging studies such as echocardiography or magnetic resonance angiography of the heart.
What're the treatments for mitral regurgitation? - The treatment of mitral regurgitation depends on the acuteness of the disease and whether there are associated signs of hemodynamic compromise.
What is mitral valve stenosis? - Mitral valve stenosis is a narrowing of the opening of the mitral valve in the heart. Stenosis of the mitral valve prevents the valve from opening normally.
What causes mitral stenosis? - Mitral stenosis is often caused by having had rheumatic fever. Rheumatic fever can cause an infection in the mitral valve.
What are the symptoms of mitral stenosis? - Symptoms of mitral stenosis include shortness of breath, fainting, dizziness or tiredness, chest pains (angina), chest infections.
How is mitral valve stenosis diagnosed? - Mitral valve stenosis is usually detected by a physician listening to heart sounds. The diagnosis of mitral stenosis is most easily made by echocardiography.
What're the treatments for mitral stenosis? - The treatment options for mitral stenosis include medical management, surgical replacement of the valve, and percutaneous balloon valvuloplasty.
Mitral valve repair and replacement - Mitral valve replacement surgery is open-heart surgery that is done while the patient is under general anesthesia.