Mitral valve

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Mitral valve
Diagram of the human heart (cropped).svg
Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow. (Mitral valve labeled at center right.)
Gray495.png
Base of ventricles exposed by removal of the atria. (Bicuspid (mitral) valve visible at bottom left.)
Details
Identifiers
Latin Valva atrioventricularis sinistra,
valva mitralis,
valvula bicuspidalis
MeSH D008943
TA98 A12.1.04.003
TA2 3987
FMA 7235
Anatomical terminology

The mitral valve ( /ˈmtrəl/ ), also known as the bicuspid valve or left atrioventricular valve, is a valve with two flaps in the heart that lies between the left atrium and the left ventricle. The mitral valve and the tricuspid valve are known collectively as the atrioventricular valves because they lie between the atria and the ventricles of the heart. [1]

Contents

In normal conditions, blood flows through an open mitral valve during diastole with contraction of the left atrium, and the mitral valve closes during systole with contraction of the left ventricle. The valve opens and closes because of pressure differences, opening when there is greater pressure in the left atrium than ventricle and closing when there is greater pressure in the left ventricle than atrium. [2]

In abnormal conditions, blood may flow backward through the valve (mitral regurgitation) or the mitral valve may be narrowed (mitral stenosis). Rheumatic heart disease often affects the mitral valve; the valve may also prolapse with age and be affected by infective endocarditis. The mitral valve is named after the mitre of a bishop, which resembles its flaps. [3] [4]

Structure

Operative view of the mitral valve with a chordal rupture "fail" of the anterior leaflet Preop view Mitral valve Dr Saez de Ibarra.jpg
Operative view of the mitral valve with a chordal rupture "fail" of the anterior leaflet
3D Medical Animation still shot of Mitral Valve Prolapse 3D Medical Animation Mitral Valve Prolapse.jpg
3D Medical Animation still shot of Mitral Valve Prolapse

The mitral valve is typically 4 to 6 square centimetres (0.62 to 0.93 sq in) in area and sits in the left heart between the left atrium and the left ventricle. It has two leaflets (or "cusps"), an anteromedial leaflet and a posterolateral leaflet. The opening of the mitral valve is surrounded by a fibrous ring known as the mitral annulus. The anterior cusp covers approximately two-thirds of the valve (imagine a crescent moon within the circle, where the crescent represents the posterior cusp). Although the anterior leaflet takes up a larger part of the ring and rises higher, the posterior leaflet has a larger surface area.

Chordae tendineae

The left side of the heart. The mitral valve, as well as the chordae tendinae are visible as white strings. These connect to the papillary muscles visible attaching to the muscular ventricle. Heart left atrial appendage tee view.jpg
The left side of the heart. The mitral valve, as well as the chordae tendinae are visible as white strings. These connect to the papillary muscles visible attaching to the muscular ventricle.

The valve leaflets are prevented from prolapsing into the left atrium by the action of chordae tendineae. The chordae tendineae are inelastic tendons attached at one end to papillary muscles in the left ventricle, and at the other to the valve cusps. Papillary muscles are finger-like projections from the wall of the left ventricle.

When the left ventricle contracts, the pressure in the ventricle forces the valve to close, while the tendons keep the leaflets coapting together and prevent the valve from opening in the wrong direction (thus preventing blood flowing back to the left atrium). Each chord has a different thickness. The thinnest ones are attached to the free leaflet margin, whereas the thickest ones (strut chords) are attached further from the free margin. This disposition has important effects on systolic stress distribution physiology. [5]

Annulus

Mitral annulus Mitral Valve RK.png
Mitral annulus

The mitral annulus is a fibrous ring that is attached to the mitral valve leaflets. Unlike prosthetic valves, it is not continuous. The mitral annulus is saddle shaped and changes in shape throughout the cardiac cycle. [6] The annulus contracts and reduces its surface area during systole to help provide complete closure of the leaflets. Expansion of the annulus can result in leaflets that do not join soundly together, leading to functional mitral regurgitation. [7]

The normal diameter of the mitral annulus is 2.7 to 3.5 centimetres (1.1 to 1.4 in), and the circumference is 8 to 9 centimetres (3.1 to 3.5 in). Microscopically, there is no evidence of an annular structure anteriorly, where the mitral valve leaflet is contiguous with the posterior aortic root. [8]

Function

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 to 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 left ventricle contributes about 20% to the volume in the left ventricle prior to ventricular systole and is known as the atrial kick.

The mitral annulus changes in shape and size during the cardiac cycle. It is smaller at the end of atrial systole due to the contraction of the left atrium around it, like a sphincter. This reduction in annulus size at the end of atrial systole may be important for the proper coapting of the leaflets of the mitral valve when the left ventricle contracts and pumps blood. [9] Leaking valves can be corrected by mitral valve annuloplasty, a common surgical procedure that aims at restoring proper leaflet adjustment.

Clinical significance

Disease

There are some valvular heart diseases that affect the mitral valve. Mitral stenosis is a narrowing of the valve. This can be heard as an opening snap; a heart sound which is not normally present.

Classic mitral valve prolapse is caused by an excess of connective tissue that thickens the spongiosa layer of the cusp and separates collagen bundles in the fibrosa. This weakens the cusps and adjacent tissue, resulting in an increased cuspal area and lengthening of the chordae tendineae. Elongation of the chordae tendineae often causes rupture, commonly to the chordae attached to the posterior cusp. Advanced lesions—also commonly involving the posterior leaflet—lead to leaflet folding, inversion, and displacement toward the left atrium. [10]

A valve prolapse can result in mitral insufficiency, which is the regurgitation or backflow of blood due to the incomplete closure of the valve.

Rheumatic heart disease often affects the mitral valve. The valve may also be affected by infective endocarditis

Surgery can be performed to replace or repair a damaged valve. A less invasive method is that of mitral valvuloplasty which uses a balloon catheter to open up a stenotic valve.

Rarely there can be a severe form known as caseous calcification of the mitral valve that can be mistaken for intracardiac mass or thrombus. [11]

Investigation

The closing of the mitral valve and the tricuspid valve constitutes the first heart sound (S1), which can be heard with a stethoscope. It is not the valve closure itself which produces the sound but the sudden cessation of blood flow, when the mitral and tricuspid valves close.[ citation needed ]. Abnormalities associated with the mitral valve can often be heard when listening with a stethoscope.

The mitral valve is often also investigated using an ultrasound scan, which can reveal the size and flow of blood through the valve.

Etymology

The word mitral comes from Latin, meaning "shaped like a mitre" (bishop's hat). The word bicuspid uses combining forms of bi- , from Latin, meaning "double", and cusp , meaning "point", reflecting the dual-flap shape of the valve.

Related Research Articles

Heart valve A flap of tissue that prevent backflow of blood around the heart

A heart valve is a one-way valve that normally allows blood to flow in only one direction through the heart. The four valves are commonly represented in a mammalian heart that determines the pathway of blood flow through the heart. A heart valve opens or closes incumbent on differential blood pressure on each side.

Heart sounds Noise generated by the beating heart

Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart.

Aortic valve

The aortic valve is a valve in the human heart between the left ventricle and the aorta. It is one of the two semilunar valves of the heart, the other being the pulmonary valve. The heart has four valves; the other two are the mitral and the tricuspid valves. The aortic valve normally has three cusps or leaflets, although in 1–2% of the population it is found to congenitally have two leaflets. The aortic valve is the last structure in the heart the blood travels through before stopping the flow through the systemic circulation.

Tricuspid valve One-way valve present between right auricle and right ventricle

The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to prevent back flow (regurgitation) of blood from the right ventricle into the right atrium during right ventricular contraction: systole.

Systole

The systole is the part of the cardiac cycle during which some chambers of the heart muscle contract after refilling with blood. The term originates, via New Latin, from Ancient Greek συστολή (sustolē), from συστέλλειν, and is similar to the use of the English term to squeeze.

Papillary muscle

The papillary muscles are muscles located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves via the chordae tendineae and contract to prevent inversion or prolapse of these valves on systole. The papillary muscles constitute about 10% of the total heart mass.

Mitral valve prolapse Medical condition

Mitral valve prolapse (MVP) is a valvular heart disease characterized by the displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole. It is the primary form of myxomatous degeneration of the valve. There are various types of MVP, broadly classified as classic and nonclassic. In severe cases of classic MVP, complications include mitral regurgitation, infective endocarditis, congestive heart failure, and, in rare circumstances, cardiac arrest.

Diastole

Diastole is the part of the cardiac cycle during which the heart refills with blood after the emptying done during systole (contraction). Ventricular diastole is the period during which the two ventricles are relaxing from the contortions/wringing of contraction, then dilating and filling; atrial diastole is the period during which the two atria likewise are relaxing under suction, dilating, and filling. The term originates from the Greek word διαστολή (diastolē), meaning "dilation", from διά + στέλλειν.

Mitral valve stenosis Mitral valve disease that is characterized by the narrowing of the orifice of the mitral valve of the heart

Mitral stenosis is a valvular heart disease characterized by the narrowing of the orifice of the mitral valve of the heart. It is almost always caused by rheumatic valvular heart disease. Normally, the mitral valve is about 5 cm2 during diastole. Any decrease in area below 2 cm2 causes mitral stenosis. Early diagnosis of mitral stenosis in pregnancy is very important as the heart cannot tolerate increased cardiac output demand as in the case of exercise and pregnancy. Atrial fibrillation is a common complication of resulting left atrial enlargement, which can lead to systemic thromboembolic complications like stroke.

Jugular venous pressure

The jugular venous pressure is the indirectly observed pressure over the venous system via visualization of the internal jugular vein. It can be useful in the differentiation of different forms of heart and lung disease. Classically three upward deflections and two downward deflections have been described.

Mitral insufficiency Form of valvular heart disease

Mitral regurgitation (MR), also known as mitral insufficiency, or mitral incompetence is a form of valvular heart disease in which the mitral valve does not close properly when the heart pumps out blood. It is the abnormal leaking of blood backwards from the left ventricle, through the mitral valve, into the left atrium, when the left ventricle contracts, i.e. there is regurgitation of blood back into the left atrium. MR is the most common form of valvular heart disease.

Chordae tendineae

The chordae tendineae , colloquially known as the heart strings, are tendon-resembling fibrous cords of connective tissue that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart.

A transthoracic echocardiogram (TTE) is the most common type of echocardiogram, which is a still or moving image of the internal parts of the heart using ultrasound. In this case, the probe is placed on the chest or abdomen of the subject to get various views of the heart. It is used as a non-invasive assessment of the overall health of the heart, including a patient's heart valves and degree of heart muscle contraction. The images are displayed on a monitor for real-time viewing and then recorded.

Cardiac cycle

The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, dubbed systole. After emptying, the heart immediately relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems. A normally performing heart must be fully expanded before it can efficiently pump again. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 seconds to complete the cycle. There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously,. At the start of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria; then, near the end of ventricular diastole–late, the two atria begin to contract, and each atrium pumps blood into the ventricle below it. During ventricular systole the ventricles are contracting and vigorously pulsing two separated blood supplies from the heart—one to the lungs and one to all other body organs and systems—while the two atria are relaxed. This precise coordination ensures that blood is efficiently collected and circulated throughout the body.

Valvular heart disease Disease in the valves of the heart

Valvular heart disease is any cardiovascular disease process involving one or more of the four valves of the heart. These conditions occur largely as a consequence of aging, but may also be the result of congenital (inborn) abnormalities or specific disease or physiologic processes including rheumatic heart disease and pregnancy.

Mitral valve replacement is a procedure whereby the diseased mitral valve of a patient's heart is replaced by either a mechanical or tissue (bioprosthetic) valve.

The following outline is provided as an overview of and topical guide to cardiology, the branch of medicine dealing with disorders of the human heart. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery disease, heart failure, valvular heart disease and electrophysiology. Physicians who specialize in cardiology are called cardiologists.

Third heart sound Medical condition

The third heart sound or S3 is a rare extra heart sound that occurs soon after the normal two "lub-dub" heart sounds (S1 and S2). S3 is associated with heart failure.

The E/A ratio is a marker of the function of the left ventricle of the heart. It represents the ratio of peak velocity blood flow from left ventricular relaxation in early diastole to peak velocity flow in late diastole caused by atrial contraction. It is calculated using Doppler echocardiography, an ultrasound-based cardiac imaging modality. Abnormalities in the E/A ratio suggest that the left ventricle, which pumps blood into the circulation, cannot fill with blood properly in the period between contractions. This phenomenon is referred to as diastolic dysfunction and can eventually lead to the symptoms of heart failure.

Cardiac physiology or heart function is the study of healthy, unimpaired function of the heart: involving blood flow; myocardium structure; the electrical conduction system of the heart; the cardiac cycle and cardiac output and how these interact and depend on one another.

References

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Further reading