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Mitral valve replacement is a procedure whereby the diseased
mitral valve The mitral valve (), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all one-w ...
of a patient's heart is replaced by either a mechanical or tissue (bioprosthetic) valve. The mitral valve may need to be replaced because: * The valve is leaky (
mitral valve regurgitation Mitral regurgitation (MR), also known as mitral insufficiency or mitral incompetence, is a form of valvular heart disease in which the mitral valve is insufficient and does not close properly when the heart pumps out blood. Section: Valvular Hea ...
) * The valve is narrowed and doesn't open properly (
mitral valve stenosis Mitral stenosis is a valvular heart disease characterized by the narrowing of the opening 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 d ...
) Causes of mitral valve disease include
infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
,
calcification Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...
and inherited
collagen disease Collagen disease is a term previously used to describe systemic autoimmune diseases (e.g., rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis), but now is thought to be more appropriate for diseases associated with defects ...
. Current mitral valve replacement approaches include
open heart surgery Cardiac surgery, or cardiovascular surgery, is surgery on the heart or great vessels performed by cardiac surgeons. It is often used to treat complications of ischemic heart disease (for example, with coronary artery bypass grafting); to corr ...
and
minimally invasive cardiac surgery Minimally invasive cardiac surgery, also known as MICS CABG (Minimally Invasive Cardiac Surgery/Coronary Artery Bypass Grafting) or the McGinn technique is heart surgery performed through several small incisions instead of the traditional open-hear ...
(MICS).


Normal mitral valve anatomy and physiology

The mitral valve is a bileaflet valve sited between the left
atrium Atrium may refer to: Anatomy * Atrium (heart), an anatomical structure of the heart * Atrium, the genital structure next to the genital aperture in the reproductive system of gastropods * Atrium of the ventricular system of the brain * Pulmona ...
and left ventricle, responsible for preventing blood flowing from the ventricle to the atrium when the heart contracts. It is elliptical, and its area varies from 5.0 to 11.4 cm2. The valve leaflets are separated by two
commissure A commissure () is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology. * The most common usage of the term refers to the brain's commissures, of which there are five. Such a commi ...
s, and each leaflet of the valve (anterior leaflet, the large one, and posterior leaflet, the small one) has three sections (p1, p2, p3). Histologically, each leaflet is composed of the solid fibrosa, the spongiosa at the atrial surface and another fibroelastic layer covering the leaflets. Two
papillary muscle The papillary muscles are muscles located in the ventricles of the heart. They attach to the cusps of the atrioventricular valves (also known as the mitral and tricuspid valves) via the chordae tendineae and contract to prevent inversion or prol ...
s originating from the base of the left ventricle hold the mitral leaflets in place through
chordae tendinae The chordae tendineae (tendinous cords), colloquially known as the heart strings, are inelastic cords of fibrous connective tissue that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart. Structure The chorda ...
, which insert the edge of the leaflets, preventing them from leaking during left ventricle
systole Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. The term originates, via New Latin, from Ancient Greek (''sustolē''), from (''sustéllein'' 'to contract'; from ''sun ...
.


Vortex Formation

During normal mitral valve function fluid jets from the
left atrium The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves. There are two atr ...
through the mitral valve into the
left ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the upper ...
. The
vortex In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...
created from this jetting travels towards the apex of the left ventricle because of the asymmetric shape of the mitral valve leaflets. This vortex rotates clockwise until the isovolumetric contraction of the left ventricle opens the aortic valve and redirects the fluid flow from the apex of the left ventricle to the
systemic circulation The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
and the rest of the body. It is important to emphasize that the asymmetry of the mitral valve is very important in the diastolic flow patterns of transmitral flow. Additionally the entire systems; the mitral annulus, papillary muscles and the chordae tendinea all play a vital role in forming a sophisticated vortex that optimizes the fluid flow in the left heart. Simulations have been performed showing how all of these aspects of the mitral valve contribute to the normal vortex formation in the left heart.


Mitral stenosis and regurgitation

The most common cause of mitral stenosis is rheumatic fever, seen mostly in the developing world. Other causes are mitral degenerative disease, severe calcification (elderly), congenital deformities, malignant carcinoid syndrome,
neoplasm A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
, left atrial appendage
thrombus A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of c ...
, endocarditic vegetations, certain inherited metabolic diseases, or complications of previous procedures at the aortic valve. Mitral stenosis causes left atrial pressure to increase, which, if left untreated, can lead to ventricular dilation,
hypertrophy Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J ...
, atrial fibrillation, and
thrombus A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of c ...
creation. Symptoms include shortness of breath (
dyspnea Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathing, breathe well enough. The American Thoracic Society defines it as "a subjective experience of brea ...
) on exertion, when lying flat (
orthopnea Orthopnea or orthopnoea is shortness of breath (dyspnea) that occurs when lying flat, causing the person to have to sleep propped up in bed or sitting in a chair. It is commonly seen as a late manifestation of heart failure, resulting from fluid ...
) or during the night (
paroxysmal nocturnal dyspnea Paroxysmal nocturnal dyspnea or paroxysmal nocturnal dyspnoea (PND) is an attack of severe shortness of breath and coughing that generally occurs at night. It usually awakens the person from sleep, and may be quite frightening. PND, as well as simp ...
), and fatigue. If mitral leaflets don't coapt (close) effectively, blood flows backwards (regurgitation) from the left ventricle towards the left atrium during systole. The most common causes are myxomatous degeneration (Barlow disease), ischemic heart disease, dilated cardiomyopathy, rheumatic valve disease, mitral annular calcification, infective endocarditis, congenital anomalies, endocardial fibrosis, myocarditis, and collagen-vascular disorders. The most used system to classify mitral valve regurgitation is Carpentier's classification, which separates mitral regurgitation into three types, depending on the leaflet motion in relation to the mitral annular plane: * Type I: the leaflets are moving normally * Type II: leaflet motion is excessive * Type III: leaflet movement is restricted.


Artificial valve types

There are two main types of artificial mitral valve: mechanical valves and tissue (bioprosthetic) valves. They come in various sizes (commonly starting from an external diameter of 19 mm and increasing by 2 mm per model).


Mechanical valves

Mechanical valves are made from metal and/or pyrolitic carbon, and can last 20–30 years. The risk of blood clots forming is higher with mechanical valves than with bioprosthetic valves. As a result, patients with mechanical valves must take blood-thinning medication (anticoagulants) for the rest of their lives, making them more prone to bleeding. There are three types of mechanical valves: # Caged ball valve (not in use any more) # Tilting disc # Bileaflet disc Bileaflet valves are the most common type of mechanical valve, offering desirable haemodynamics. The two leaflets of a bileaflet disc valve open during
diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventric ...
and close during
systole Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. The term originates, via New Latin, from Ancient Greek (''sustolē''), from (''sustéllein'' 'to contract'; from ''sun ...
.


Bioprosthetic valves

Bioprosthetic valves are made from animal tissues. Most people with bioprosthetic valves don’t need to take anticoagulants long term. However, bioprosthetic valves may only last 10–15 years. They tend to deteriorate more quickly in younger patients. Valve failure prevalence at 10 years is 30%, increasing to 35–65% at 15 years. New tissue preservation technologies are being studied to try to increase the durability of bioprosthetic valves.


Valve selection

The choice of valve depends upon the patient's age, medical condition, preferences, and lifestyle. Typically, patients younger than 65 years old will receive a mechanical valve unless they are unable to take long-term anticoagulation, and patients older than 70 years will receive a bioprosthetic valve.


Procedure

The most common approach for surgeons to reach the heart is a
median sternotomy Median sternotomy is a type of surgical procedure in which a vertical inline incision is made along the sternum, after which the sternum itself is divided using a sternal saw. This procedure provides access to the heart and lungs for surgical pro ...
(vertically cutting the breastbone), but other incisions can be employed, such as a left or right thoracotomy. After the heart is exposed, the patient is put on a
cardiopulmonary bypass Cardiopulmonary bypass (CPB) is a technique in which a machine temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and oxygen to the body. The CPB pump itself is often referred to as a he ...
machine, also known as a heart–lung machine. This machine breathes for the patient and pumps their blood around their body – bypassing the heart – while the surgeon replaces the heart valve. Next, an aortic clamp is placed on the aorta, and the heart is stopped ( cardioplegia). Depending on the pathology of the mitral valve and surgeon's preference, various approaches can be used to access the mitral valve. The interatrial groove approach involves incising the left atrium posterior to the interatrial groove. The transatrial oblique approach is utilized when the left atrium is small. In this approach, the right atrium is opened and another incision is made at the interatrial septum. The valve is excised 4–5 mm from the annulus, leaving intact the attached chordae unless they are calcified or otherwise diseased. The valve is replaced by a mechanical or bioprosthetic valve. The replacement valve is sewn into the annulus with interrupted or horizontal mattress sutures with the pledgets on the atrial side. The atrial walls are closed, taking care not to trap air within the chambers of the heart. The heart is restarted, and the patient is taken off the heart–lung machine.


Recovery

Following surgery, patients are typically taken to an
intensive care unit 220px, Intensive care unit An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
for monitoring. They may need a
respirator A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including fumes, vapours, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories of respi ...
to help them breathe for the first few hours or days after surgery. The patient should be able to sit up in bed within 24 hours. After two days, the patient may be moved out of the intensive care unit. Patients are usually discharged after 7–10 days. If the mitral valve replacement is successful, patients can expect their symptoms to improve significantly. Some scarring occurs after surgery. After median sternotomy, the patient will have a vertical scar on their chest above their breastbone. If the heart is accessed from under the left breast there will be a smaller scar in this location. Patients with a bioprosthetic mitral valve are prescribed anticoagulants, such as
warfarin Warfarin, sold under the brand name Coumadin among others, is a medication that is used as an anticoagulant (blood thinner). It is commonly used to prevent blood clots such as deep vein thrombosis and pulmonary embolism, and to prevent strok ...
, for 6 weeks to 3 months after their operation, while patients with mechanical valves are prescribed anticoagulants for the rest of their lives. Anticoagulants are taken to prevent blood clots, which can move to other parts of the body and cause serious medical problems, such as a
heart attack A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may tr ...
. Anticoagulants will not dissolve a blood clot but they do prevent other clots from forming or prevent clots from becoming larger. Once their wounds have healed, patients should have few, if any, restrictions from daily activities. People are advised to walk or undertake other physical activities gradually to regain strength. Patients who have physically demanding jobs will have to wait a little longer than those who don’t. Patients are also restricted from driving a car for six weeks after the surgery.


Complications

As with other cardiac procedures, mitral valve replacement is associated with risks, such as bleeding, infection, thromboembolism, renal shutdown,
cardiac tamponade Cardiac tamponade, also known as pericardial tamponade (), is the buildup of fluid in the pericardium (the sac around the heart), resulting in compression of the heart. Onset may be rapid or gradual. Symptoms typically include those of obstructi ...
,
stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
, or reaction to anesthesia. The risk of death is about 1%. Risks depend on a patient’s age, general health, specific medical conditions, and heart function.


Flipped Vortex Circulation

Pedrizetti ''et al.'' studied the fluid mechanics in the left heart in 40 randomized patients with mechanical and tissue artificial heart valves. Using
echocardiography An echocardiography, echocardiogram, cardiac echo or simply an echo, is an ultrasound of the heart. It is a type of medical imaging of the heart, using standard ultrasound or Doppler ultrasound. Echocardiography has become routinely used in t ...
they quantitatively analyzed the velocity field in the left heart and found that the patients with artificial mitral valves had a consistent counterclockwise circulation, as opposed to the normal clockwise circulation that is characteristic of normal transmitral flow. To further characterize this counterclockwise circulation a
numerical simulation Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be deter ...
was performed which backed up the data taken from the echocardiograph study. This flipped vortex circulation could lead to further complications in the patient who had mitral valve replacement surgery as it was observed to cause stagnation points, crossed flows, increased energy requirements and pressure shifts from the lateral to the septal wall in the left heart.


Minimally invasive mitral valve replacement

Since the 1990s, surgeons have been working on less invasive approaches to mitral valve surgery, known as minimally invasive cardiac surgery (MICS). Minimally invasive mitral valve replacement involves a small incision (5–8 cm) just below the right breast. The benefits of MICS over conventional surgery include reduced hospital stay and blood transfusion requirements, and a smaller scar.


Transcatheter mitral valve replacement

Rather than removing the existing valve, transcatheter mitral valve replacement involves wedging a new valve into the site of the existing valve. The replacement valve is delivered to the site of the existing valve through a tube called a catheter. The catheter may be inserted through the femoral artery in the thigh, or through a small incision in the chest. Once the replacement valve is in place, it is expanded, pushing the old valve’s leaflets (the sections that open and close) out of the way. Transcatheter mitral valves are still being studied in clinical trials; none are commercially available.


Alternatives to mitral valve replacement


Repair

Many mitral valves can be repaired instead of replaced. In fact,
mitral valve repair Mitral valve repair is a cardiac surgery procedure performed by cardiac surgeons to treat stenosis (narrowing) or regurgitation (leakage) of the mitral valve. The mitral valve is the "inflow valve" for the left side of the heart. Blood flows fro ...
is recommended by international guidelines wherever possible. Advantages of mitral valve repair over replacement include lower surgical mortality (~1% for repair ''vs'' ~5% for replacement), lower rates of
stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
and
endocarditis Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves. Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or the ...
(an infection of the heart’s inner lining), equivalent or better long‑term durability, and improved long-term survival. Patients who have their valve repaired have a similar life expectancy to the general population. In addition, patients may not need to take anticoagulants long term following mitral valve repair.


Non-surgical options

For individuals with few symptoms, or those with contraindications to surgery, options exist for medical treatment in both
mitral insufficiency Mitral regurgitation (MR), also known as mitral insufficiency or mitral incompetence, is a form of valvular heart disease in which the mitral valve is insufficient and does not close properly when the heart pumps out blood.
and
mitral valve stenosis Mitral stenosis is a valvular heart disease characterized by the narrowing of the opening 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 d ...
, although they won't cure the conditions. Such medical treatments include
diuretics A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics in ...
,VOC=VITIUM ORGANICUM CORDIS, a compendium of the Department of Cardiology at Uppsala Academic Hospital. By Per Kvidal September 1999, with revision by Erik Björklund May 2008 Chapter 1: Diseases of the Cardiovascular system > Section: Valvular Heart Disease
vasodilator Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstriction, ...
s, and
ACE inhibitor Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a class of medication used primarily for the treatment of hypertension, high blood pressure and heart failure. They work by causing relaxation of blood vessels as well as a decrease i ...
s.


See also

*
Mitral regurgitation Mitral regurgitation (MR), also known as mitral insufficiency or mitral incompetence, is a form of valvular heart disease in which the mitral valve is insufficient and does not close properly when the heart pumps out blood.
*
Mitral stenosis Mitral stenosis is a valvular heart disease characterized by the narrowing of the opening 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 d ...
*
Artificial heart valve An artificial heart valve is a one-way valve implanted into a person's heart to replace a heart valve that is not functioning properly (valvular heart disease). Artificial heart valves can be separated into three broad classes: mechanical hear ...
*
Cardiac surgery Cardiac surgery, or cardiovascular surgery, is surgery on the heart or great vessels performed by cardiac surgeons. It is often used to treat complications of ischemic heart disease (for example, with coronary artery bypass grafting); to corr ...
*
Heart-lung machine Cardiopulmonary bypass (CPB) is a technique in which a machine temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and oxygen to the body. The CPB pump itself is often referred to as a ...


References


Sources

* * * {{cardiac surgery Valvular heart disease Cardiac surgery