Mitral valve
Encyclopedia
The mitral valve is a dual-flap (bi- from the Latin, meaning double, and mitral- from the Latin, meaning shaped like a mitre
) valve
in the heart
that lies between the left atrium
(LA) and the left ventricle
(LV). The mitral valve (not to be confused with the congenital bicuspid aortic valve
) and the tricuspid valve
are known collectively as the atrioventricular
valves because they lie between the atria and the ventricles of the heart and control the flow of blood.
During diastole
, a normally-functioning mitral valve opens as a result of increased pressure from the left atrium as it fills with blood (preloading). As atrial pressure increases above that of the left ventricle, the mitral valve opens. Opening facilitates the passive flow of blood into the left ventricle. Diastole ends with atrial contraction, which ejects the final 20% of blood that is transferred from the left atrium to the left ventricle. This amount of blood is known as end diastolic volume (EDV), and the mitral valve closes at the end of atrial contraction to prevent a reversal of blood flow.
's mitre
, whence the valve receives its name.) The anterior cusp protects approximately two-thirds of the valve (imagine a crescent moon within the circle, where the crescent represents the posterior cusp). Note that although the anterior leaflet takes up a larger part of the ring and rises higher, the posterior leaflet has a larger surface area. These valve leaflets are prevented from prolapsing
into the left atrium by the action of tendons attached to the posterior surface of the valve, chordae tendineae
.
The inelastic chordae tendineae are attached at one end to the papillary muscle
s and the other to the valve cusps. Papillary muscles are fingerlike projections from the wall of the left ventricle. Chordae tendineae from each muscle are attached to both leaflets of the mitral valve. Thus, when the left ventricle contracts, the intraventricular pressure 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 to flow back to the left atrium).
Each chord has a different thickness. The thinnest ones are attached to the free leaflet margin,
whereas thickest ones (strut chords) are attached quite away from the free margin. This disposition has important effects on systolic stress distribution physiology (video).
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.
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. Leaking valves can be corrected by mitral valve annuloplasty
, a common surgical procedure that aims at restoring proper leaflet coaptation.
Mitre
The mitre , also spelled miter, is a type of headwear now known as the traditional, ceremonial head-dress of bishops and certain abbots in the Roman Catholic Church, as well as in the Anglican Communion, some Lutheran churches, and also bishops and certain other clergy in the Eastern Orthodox...
) valve
Heart valve
A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...
in the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
that lies between the left atrium
Left atrium
The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...
(LA) and the left ventricle
Left ventricle
The left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...
(LV). The mitral valve (not to be confused with the congenital bicuspid aortic valve
Bicuspid aortic valve
A bicuspid aortic valve is most commonly a congenital condition of the aortic valve where two of the aortic valvular leaflets fuse during development resulting in a valve that is bicuspid instead of the normal tricuspid configuration. Normally the only cardiac valve that is bicuspid is the mitral...
) and the tricuspid valve
Tricuspid valve
The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, between the right atrium and the right ventricle. The normal tricuspid valve usually has three leaflets and three papillary muscles. They are connected to the papillary muscles by the chordae...
are known collectively as the atrioventricular
Atrioventricular
Atrioventricular can refer to:*Left atrioventricular opening*Atrioventricular fistula*Atrioventricular node*The term "Atrioventricular valves" is used to describe the mitral valve and tricuspid valve....
valves because they lie between the atria and the ventricles of the heart and control the flow of blood.
During diastole
Diastole
Diastole is the period of time when the heart fills with blood after systole . Ventricular diastole is the period during which the ventricles are relaxing, while atrial diastole is the period during which the atria are relaxing...
, a normally-functioning mitral valve opens as a result of increased pressure from the left atrium as it fills with blood (preloading). As atrial pressure increases above that of the left ventricle, the mitral valve opens. Opening facilitates the passive flow of blood into the left ventricle. Diastole ends with atrial contraction, which ejects the final 20% of blood that is transferred from the left atrium to the left ventricle. This amount of blood is known as end diastolic volume (EDV), and the mitral valve closes at the end of atrial contraction to prevent a reversal of blood flow.
Anatomy
The mitral valve is typically 4–6 cm² in area. It has two cusps, or leaflets, (the anteromedial leaflet and the posterolateral leaflet) that guard the opening. The opening is surrounded by a fibrous ring known as the mitral valve annulus. (The orientation of the two leaflets resemble a bishopBishop
A bishop is an ordained or consecrated member of the Christian clergy who is generally entrusted with a position of authority and oversight. Within the Catholic Church, Eastern Orthodox, Oriental Orthodox Churches, in the Assyrian Church of the East, in the Independent Catholic Churches, and in the...
's mitre
Mitre
The mitre , also spelled miter, is a type of headwear now known as the traditional, ceremonial head-dress of bishops and certain abbots in the Roman Catholic Church, as well as in the Anglican Communion, some Lutheran churches, and also bishops and certain other clergy in the Eastern Orthodox...
, whence the valve receives its name.) The anterior cusp protects approximately two-thirds of the valve (imagine a crescent moon within the circle, where the crescent represents the posterior cusp). Note that although the anterior leaflet takes up a larger part of the ring and rises higher, the posterior leaflet has a larger surface area. These valve leaflets are prevented from prolapsing
Mitral valve prolapse
Mitral valve prolapse is a valvular heart disease characterized by the displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole. There are various types of MVP, broadly classified as classic and nonclassic. In its nonclassic form, MVP carries a low risk of...
into the left atrium by the action of tendons attached to the posterior surface of the valve, chordae tendineae
Chordae tendineae
The chordae tendineae, or heart strings, are cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart....
.
The inelastic chordae tendineae are attached at one end to the papillary muscle
Papillary muscle
In anatomy, the papillary muscles are muscles located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves via the chordae tendinae and contract to prevent inversion or prolapse of these valves.- Action :There are five total papillary muscles in the heart, three...
s and the other to the valve cusps. Papillary muscles are fingerlike projections from the wall of the left ventricle. Chordae tendineae from each muscle are attached to both leaflets of the mitral valve. Thus, when the left ventricle contracts, the intraventricular pressure 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 to flow back to the left atrium).
Each chord has a different thickness. The thinnest ones are attached to the free leaflet margin,
whereas thickest ones (strut chords) are attached quite away from the free margin. This disposition has important effects on systolic stress distribution physiology (video).
Normal physiology
During left ventricularLeft ventricle
The left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...
diastole
Diastole
Diastole is the period of time when the heart fills with blood after systole . Ventricular diastole is the period during which the ventricles are relaxing, while atrial diastole is the period during which the atria are relaxing...
, 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
Echocardiography
An echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is a sonogram of the heart . Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart...
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
Systole (medicine)
Systole is the contraction of the heart. Used alone, it usually means the contraction of the left ventricle.In all mammals, the heart has 4 chambers. The left and right ventricles pump together. The atria and ventricles pump in sequence...
) (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.
The mitral annulus
Mitral annulus
The mitral annulus is a fibrous ring that is attached to the mitral valve leaflets. Unlike prosthetic valves, it is neither circular nor continuous. The annulus contracts and reduces its surface area during systole to help provide complete closure of the leaflets. Annular dilatation can result in...
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
Sphincter
A sphincter is an anatomical structure, or a circular muscle, that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning...
. 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. Leaking valves can be corrected by mitral valve annuloplasty
Mitral valve annuloplasty
Mitral valve annuloplasty is a surgical technique for the repair of leaking mitral valves. Due to various factors, the two leaflets normally involved in sealing the mitral valve to retrograde flow may not coapt properly...
, a common surgical procedure that aims at restoring proper leaflet coaptation.
Surface anatomy
The closing of the mitral valve and the tricuspid valve constitutes the first heart sound (S1). It is not actually the valve closure which produces a sound but rather the sudden cessation of blood flow caused by the closure of the mitral and tricuspid valves. The mitral valve opening is normally not heard except in Mitral Stenosis (narrowing of the valve) as the Opening Snap. Flow of blood into the heart during rapid filling is not normally heard except in certain pathological states where it constitutes the third heart sound (S3).See also
- Anatomy
- HeartHeartThe heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
- Heart valveHeart valveA heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...
- Papillary musclePapillary muscleIn anatomy, the papillary muscles are muscles located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves via the chordae tendinae and contract to prevent inversion or prolapse of these valves.- Action :There are five total papillary muscles in the heart, three...
- Heart
- Pathophysiology
- Mitral valve prolapseMitral valve prolapseMitral valve prolapse is a valvular heart disease characterized by the displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole. There are various types of MVP, broadly classified as classic and nonclassic. In its nonclassic form, MVP carries a low risk of...
- Mitral regurgitationMitral regurgitationMitral regurgitation , mitral insufficiency or mitral incompetence is a disorder of the heart in which the mitral valve does not close properly when the heart pumps out blood. It is the abnormal leaking of blood from the left ventricle, through the mitral valve, and into the left atrium, when...
- Mitral stenosisMitral stenosisMitral stenosis is a valvular heart disease characterized by the narrowing of the orifice of the mitral valve of the heart.-Signs and symptoms:Symptoms of mitral stenosis include:...
- Infective endocarditisInfective endocarditisInfective endocarditis is a form of endocarditis, or inflammation, of the inner tissue of the heart, such as its valves, caused by infectious agents. The agents are usually bacterial, but other organisms can also be responsible....
- The mitral valve is the most common site of native-valve endocarditis.
- Mitral valve prolapse
- Procedures to fix the mitral valve
- Mitral valve replacementMitral valve replacementMitral valve replacement is a cardiac surgery procedure in which a patient’s mitral valve is replaced by a different valve. Mitral valve replacement is typically performed robotically or manually, when the valve becomes too tight for blood to flow into the left ventricle, or too loose in which...
- Mitral valve repairMitral valve repairMitral valve repair is a cardiac surgery procedure performed by cardiac surgeons to treat stenosis or regurgitation of the mitral valve. The mitral valve is the "inflow valve" for the left side of the heart. Blood flows from the lungs, where it picks up oxygen, through the pulmonary veins, to the...
- Mitral valvuloplasty
- Mitral valve replacement
External links
- "Valves of the heart."- Mitral Valve Repair at The Mount Sinai Hospital - "Mitral Valve Function"
- Surgical Anatomy of the Mitral Valve at echoincontext.com
- Mitral Valve Repair at Englewood Hospital and Medical Center - Mitral Valve Repair
- Cardiac Valve Animations - Perioperative Interactive Education Group - Cardiac Valve Animations