Artificial heart valve

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Artificial heart valve
Mechanical heart valves.jpg
Different types of artificial heart valves [1]
Specialty cardiology

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 heart valves, bioprosthetic tissue valves and engineered tissue valves.

Contents

The human heart contains four valves: tricuspid valve, pulmonary valve, mitral valve and aortic valve. Their main purpose is to keep blood flowing in the proper direction through the heart, and from the heart into the major blood vessels connected to it (the pulmonary artery and the aorta). Heart valves can malfunction for a variety of reasons, which can impede the flow of blood through the valve (stenosis) and/or let blood flow backwards through the valve (regurgitation). Both processes put strain on the heart and may lead to serious problems, including heart failure. While some dysfunctional valves can be treated with drugs or repaired, others need to be replaced with an artificial valve. [2]

Background

3D Medical Animation still shot of Artificial Heart Valve 3D Medical Animation still shot Artificial Heart Valve.jpg
3D Medical Animation still shot of Artificial Heart Valve

A heart contains four valves (tricuspid, pulmonary, mitral and aortic valves) which open and close as blood passes through the heart. [3] Blood enters the heart in the right atrium and passes through the tricuspid valve to the right ventricle. From there, blood is pumped through the pulmonary valve to enter the lungs. After being oxygenated, blood passes to the left atrium, where is it pumped through the mitral valve to the left ventricle. The left ventricle pumps blood to the aorta through the aortic valve.

There are many potential causes of heart valve damage, such as birth defects, age related changes, and effects from other disorders, such as rheumatic fever and infections causing endocarditis. High blood pressure and heart failure which can enlarge the heart and arteries, and scar tissue can form after a heart attack or injury. [4]

The three main types of artificial heart valves are mechanical, biological (bioprosthetic/tissue), and tissue-engineered valves. In the US, UK and the European Union, the most common type of artificial heart valve is the bioprosthetic valve. Mechanical valves are more commonly used in Asia and Latin America.[ citation needed ] Companies that manufacture heart valves include Edwards Lifesciences, [5] Medtronic, [6] Abbott (St. Jude Medical), [7] CryoLife, [8] and LifeNet Health. [9]

Mechanical valves

Mechanical valves come in three main types – caged ball, tilting-disc and bileaflet – with various modifications on these designs. [10] Caged ball valves are no longer implanted. [11] Bileaflet valves are the most common type of mechanical valve implanted in patients today. [12]

Caged ball valves

Caged ball valve Starr-Edwards-Mitral-Valve.jpg
Caged ball valve

The first artificial heart valve was the caged ball valve, a type of ball check valve, in which a ball is housed inside a cage. When the heart contracts and the blood pressure in the chamber of the heart exceeds the pressure on the outside of the chamber, the ball is pushed against the cage and allows blood to flow. When the heart finishes contracting, the pressure inside the chamber drops and the ball moves back against the base of the valve forming a seal.

In 1952, Charles A. Hufnagel implanted caged ball heart valves into ten patients (six of whom survived the operation), marking the first success in prosthetic heart valves.[ citation needed ] A similar valve was invented by Miles 'Lowell' Edwards and Albert Starr in 1960, commonly referred to as the Starr-Edwards silastic ball valve. [13] This consisted of a silicone ball enclosed in a methyl metacrylate cage welded to a ring. The Starr-Edwards valve was first implanted in a human on August 25, 1960, and was discontinued by Edwards Lifesciences in 2007. [13]

Caged ball valves are strongly associated with blood clot formation, so people who have one required a high degree of anticoagulation, usually with a target INR of 3.0–4.5. [14]

Tilting-disc valves

tilting-disc valve Chitra Valve.jpg
tilting-disc valve

Introduced in 1969, the first clinically available tilting-disc valve was the Bjork-Shiley valve. [15] Tilting‑disc valves, a type of swing check valve, are made of a metal ring covered by an ePTFE fabric. The metal ring holds, by means of two metal supports, a disc that opens when the heart beats to let blood flow through, then closes again to prevent blood flowing backwards. The disc is usually made of an extremely hard carbon material (pyrolytic carbon), enabling the valve to function for years without wearing out.[ citation needed ]

Bileaflet valves

Bileaflet valve Aortic Karboniks-1 bileafter prosthetic heart valve.jpg
Bileaflet valve

Introduced in 1979, bileaflet valves are made of two semicircular leaflets that revolve around struts attached to the valve housing. With a larger opening than caged ball or tilting-disc valves, they carry a lower risk of blood clots. They are, however, vulnerable to blood backflow.[ citation needed ]

Advantages of mechanical valves

The major advantage of mechanical valves over bioprosthetic valves is their greater durability. [16] Made from metal and/or pyrolytic carbon, [10] they can last 20–30 years. [16]

Disadvantages of mechanical valves

One of the major drawbacks of mechanical heart valves is that they are associated with an increased risk of blood clots. Clots formed by red blood cell and platelet damage can block blood vessels leading to stroke. People with mechanical valves need to take anticoagulants (blood thinners), such as warfarin, for the rest of their life. [16] Mechanical heart valves can also cause mechanical hemolytic anemia, a condition where the red blood cells are damaged as they pass through the valve.[ citation needed ] Cavitation, the rapid formation of microbubbles in a fluid such as blood due to a localized drop of pressure, can lead to mechanical heart valve failure, [17] so cavitation testing is an essential part of the valve design verification process.

Many of the complications associated with mechanical heart valves can be explained through fluid mechanics. For example, blood clot formation is a side effect of high shear stresses created by the design of the valves. From an engineering perspective, an ideal heart valve would produce minimal pressure drops, have small regurgitation volumes, minimize turbulence, reduce prevalence of high stresses, and not create flow separations in the vicinity of the valve.[ citation needed ]

Implanted mechanical valves can cause foreign body rejection. The blood may coagulate and eventually result in a hemostasis. The usage of anticoagulation drugs will be interminable to prevent thrombosis. [18] [ non-primary source needed ]

Bioprosthetic tissue valves

Bioprosthetic valves are usually made from animal tissue (heterograft/xenograft) attached to a metal or polymer support. [11] Bovine (cow) tissue is most commonly used, but some are made from porcine (pig) tissue. [19] [ non-primary source needed ] The tissue is treated to prevent rejection and calcification.[ citation needed ]

Alternatives to animal tissue valves are sometimes used, where valves are used from human donors, as in aortic homografts and pulmonary autografts. An aortic homograft is an aortic valve from a human donor, retrieved either after their death or from a heart that is removed to be replaced during a heart transplant. [12] A pulmonary autograft, also known as the Ross procedure, is where the aortic valve is removed and replaced with the patient's own pulmonary valve (the valve between the right ventricle and the pulmonary artery). A pulmonary homograft (a pulmonary valve taken from a cadaver) is then used to replace the patient's own pulmonary valve. This procedure was first performed in 1967 and is used primarily in children, as it allows the patient's own pulmonary valve (now in the aortic position) to grow with the child. [12]

Advantages of bioprosthetic heart valves

Bioprosthetic valves are less likely than mechanical valves to cause blood clots, so do not require lifelong anticoagulation. As a result, people with bioprosthetic valves have a lower risk of bleeding than those with mechanical valves. [16]

Disadvantages of bioprosthetic heart valves

Tissue valves are less durable than mechanical valves, typically lasting 10–20 years. [20] This means that people with bioprosthetic valves have a higher incidence of requiring another aortic valve replacement in their lifetime. [16] Bioprosthetic valves tend to deteriorate more quickly in younger patients. [21]

In recent years, scientists have developed a new tissue preservation technology, with the aim of improving the durability of bioprosthetic valves. In sheep and rabbit studies, tissue preserved using this new technology had less calcification than control tissue. [22] A valve containing this tissue is now marketed, but long-term durability data in patients are not yet available. [23] [ non-primary source needed ]

Current bioprosthetic valves lack longevity, and will calcify over time. [24] When a valve calcifies, the valve cusps become stiff and thick and cannot close completely. [24] Moreover, bioprosthetic valves can't grow with or adapt to the patient: if a child has bioprosthetic valves they will need to get the valves replaced several times to fit their physical growth. [24]

Tissue-engineered valves

For over 30 years researchers have been trying to grow heart valves in vitro. [25] These tissue‑engineered valves involve seeding human cells on to a scaffold. [25] The two main types of scaffold are natural scaffolds, such as decellularized tissue, or scaffolds made from degradable polymers. [26] The scaffold acts as an extracellular matrix, guiding tissue growth into the correct 3D structure of the heart valve. [26] [25] Some tissue-engineered heart valves have been tested in clinical trials, [26] but none are commercially available.

Tissue engineered heart valves can be person-specific and 3D modeled to fit an individual recipient [27] 3D printing is used because of its high accuracy and precision of dealing with different biomaterials. [27] Cells that are used for tissue engineered heart valves are expected to secrete the extracellular matrix (ECM). [24] Extracellular matrix provides support to maintain the shape of the valves and determines the cell activities. [28]

Scientists can follow the structure of heart valves to produce something that looks similar to them, but since tissue engineered valves lack the natural cellular basis, they either fail to perform their functions like natural heart valves, or function when they are implanted but gradually degrade over time.[ citation needed ] An ideal tissue engineered heart valve would be non‐thrombogenic, biocompatible, durable, resistant to calcification, grow with the surrounding heart, and exhibit a physiological hemodynamic profile. [29] To achieve these goals, the scaffold should be carefully chosen—there are three main candidates: decellularized ECM (xenografts or homografts), natural polymers, and synthetic polymers. [29]

Differences between mechanical and tissue valves

Mechanical and tissue valves are made of different materials. Mechanical valves are generally made of titanium and carbon. [30] Tissue valves are made up of human or animal tissue. The valves composed of human tissue, known as allografts or homografts, are from donors' human hearts. [30]

Mechanical valves can be a better choice for younger people and people at risk of valve deterioration due to its durability. It is also preferable for people who are already taking blood thinners and people who would be unlikely to tolerate another valve replacement operation.[ citation needed ]

Tissue valves are better for older age groups as another valve replacement operation may not be needed in their lifetime. Due to the risk of forming blood clots for mechanical valves and severe bleeding as a major side effect of taking blood-thinning medications, people who have a risk of blood bleeding and are not willing to take warfarin may also consider tissue valves. Other patients who may be more suitable for tissue valves are people who have other planned surgeries and unable to take blood-thinning medications. People who plan to become pregnant may also consider tissue valves as warfarin causes risks in pregnancy.[ citation needed ]

Functional requirements of artificial heart valves

An artificial heart valve should ideally function like a natural heart valve. [11] The functioning of natural heart valves is characterized by many advantages:

Artificial heart valve repair

Artificial heart valves are expected to last from 10 to 30 years. [16]

The most common problems with artificial heart valves are various forms of degeneration, including gross billowing of leaflets, ischemic mitral valve pathology, and minor chordal lengthening. [24] The repairing process of the artificial heart valve regurgitation and stenosis usually requires an open-heart surgery, and a repair or partial replacement of regurgitant valves is usually preferred. [24]

Researchers are investigating catheter-based surgery that allows repair of an artificial heart valve without large incisions. [32]

Researchers are investigating Interchangeable Prosthetic Heart Valve that allows redo and fast-track repair of an artificial heart valve. [33]

Additional images

See also

Related Research Articles

<span class="mw-page-title-main">Embolism</span> Disease of arteries, arterioles and capillaries

An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule, a bubble of air or other gas, amniotic fluid, or foreign material. An embolism can cause partial or total blockage of blood flow in the affected vessel. Such a blockage may affect a part of the body distant from the origin of the embolus. An embolism in which the embolus is a piece of thrombus is called a thromboembolism.

<span class="mw-page-title-main">Aortic valve</span> Valve in the human heart between the left ventricle and the aorta

The aortic valve is a valve in the heart of humans and most other animals, located between the left ventricle and the aorta. It is one of the four valves of the heart and one of the two semilunar valves, the other being the pulmonary valve. 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.

<span class="mw-page-title-main">Aortic regurgitation</span> Medical condition

Aortic regurgitation (AR), also known as aortic insufficiency (AI), is the leaking of the aortic valve of the heart that causes blood to flow in the reverse direction during ventricular diastole, from the aorta into the left ventricle. As a consequence, the cardiac muscle is forced to work harder than normal.

<span class="mw-page-title-main">Interventional cardiology</span>

Interventional cardiology is a branch of cardiology that deals specifically with the catheter based treatment of structural heart diseases. Andreas Gruentzig is considered the father of interventional cardiology after the development of angioplasty by interventional radiologist Charles Dotter.

<span class="mw-page-title-main">Mitral regurgitation</span> 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 is insufficient and does not close properly when the heart pumps out blood. It is the abnormal leaking of blood backwards – regurgitation from the left ventricle, through the mitral valve, into the left atrium, when the left ventricle contracts. Mitral regurgitation is the most common form of valvular heart disease.

Aortic valve replacement is a procedure whereby the failing aortic valve of a patient's heart is replaced with an artificial heart valve. The aortic valve may need to be replaced because:

<span class="mw-page-title-main">Valvular heart disease</span> 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.

<span class="mw-page-title-main">Mitral valve repair</span> Cardiac surgery procedure

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 from the lungs, where it picks up oxygen, through the pulmonary veins, to the left atrium of the heart. After the left atrium fills with blood, the mitral valve allows blood to flow from the left atrium into the heart's main pumping chamber called the left ventricle. It then closes to keep blood from leaking back into the left atrium or lungs when the ventricle contracts (squeezes) to push blood out to the body. It has two flaps, or leaflets, known as cusps.

<span class="mw-page-title-main">Aortic valve repair</span> Treatment of aortic regurgitation

Aortic valve repair or aortic valve reconstruction is the reconstruction of both form and function of a dysfunctional aortic valve. Most frequently it is used for the treatment of aortic regurgitation. It can also become necessary for the treatment of aortic aneurysm, less frequently for congenital aortic stenosis.

<span class="mw-page-title-main">Valve replacement</span> Replacement of one or more of the heart valves

Valve replacement surgery is the replacement of one or more of the heart valves with either an artificial heart valve or a bioprosthesis. It is an alternative to valve repair.

<span class="mw-page-title-main">Percutaneous aortic valve replacement</span> Technique for replacement of the aortic valve in a heart

Transcatheter aortic valve replacement (TAVR) is the replacement of the aortic valve of the heart through the blood vessels. The replacement valve is delivered via one of several access methods: transfemoral, transapical, subclavian, direct aortic, and transcaval, among others.

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.

<span class="mw-page-title-main">Ross procedure</span> Type of cardiac surgical operation

The Ross procedure, also known as pulmonary autograft, is a heart valve replacement operation to treat severe aortic valve disease, such as in children and young adults with a bicuspid aortic valve. It involves removing the diseased aortic valve, situated at the exit of the left side of the heart, and replacing it with the person's own healthy pulmonary valve (autograft), removed from the exit of the heart's right side. To reconstruct the right sided exit, a pulmonary valve from a cadaver (homograft), or a stentless xenograft, is used to replace the removed pulmonary valve. Compared to a mechanical valve replacement, it avoids the requirement for thinning the blood, has favourable blood flow dynamics, allows growth of the valve with growth of the child and has less risk of endocarditis.

<span class="mw-page-title-main">Marian Ionescu</span> British cardiac surgeon

Marian Ion Ionescu is a Romanian-born British cardiac surgeon. His interest in heart surgery covered several aspects of this specialty. He was an inventor of surgical devices, mostly artificial heart valves, a scientist in the broad term and a medical educator.

The pericardial heart valve was invented by Marian Ionescu, a British surgeon working at the General Infirmary in Leeds, England. He created this artificial bioprosthetic heart valve as a three-cusp structure made of chemically treated bovine pericardium attached to a Dacron cloth-covered titanium frame.

Decellularization of porcine heart valves is the removal of cells along with antigenic cellular elements by either physical or chemical decellularization of the tissue. This decellularized valve tissue provides a scaffold with the remaining extracellular matrix (ECM) that can then be used for tissue engineering and valve replacement in humans inflicted with valvular disease. Decellularized biological valves have potential benefit over conventional valves through decreased calcification which is thought to be an immuno-inflammatory response initiated by the recipient.

<span class="mw-page-title-main">Nina Starr Braunwald</span> American thoracic surgeon and medical researcher (1828-1992)

Nina Starr Braunwald (1928–1992) was an American thoracic surgeon and medical researcher who was among the first women to perform open-heart surgery. She was also the first woman to be certified by the American Board of Thoracic Surgery, and the first to be elected to the American Association for Thoracic Surgery. In 1960, at the age of 32, she led the operative team at the U.S. National Institutes of Health (NIH) that implanted the first successful artificial mitral human heart valve replacement, which she had designed and fabricated. She died in August 1992 in Weston, Massachusetts, after a career that included prominent appointments at the NIH, University of California, San Diego, Harvard Medical School, and Brigham and Women's Hospital.

<span class="mw-page-title-main">Decellularized homografts</span>

Decellularized homografts are donated human heart valves which have been modified via tissue engineering. Several techniques exist for decellularization with the majority based on detergent or enzymatic protocols which aim to eliminate all donor cells while preserving the mechanical properties of the remaining matrix.

Tissue engineered heart valves (TEHV) offer a new and advancing proposed treatment of creating a living heart valve for people who are in need of either a full or partial heart valve replacement. Currently, there are over a quarter of a million prosthetic heart valves implanted annually, and the number of patients requiring replacement surgeries is only suspected to rise and even triple over the next fifty years. While current treatments offered such as mechanical valves or biological valves are not deleterious to one's health, they both have their own limitations in that mechanical valves necessitate the lifelong use of anticoagulants while biological valves are susceptible to structural degradation and reoperation. Thus, in situ (in its original position or place) tissue engineering of heart valves serves as a novel approach that explores the use creating a living heart valve composed of the host's own cells that is capable of growing, adapting, and interacting within the human body's biological system.

Percutaneous pulmonary valve implantation (PPVI), also known as transcatheter pulmonary valve replacement (TPVR), is the replacement of the pulmonary valve via catheterization through a vein. It is a significantly less invasive procedure in comparison to open heart surgery and is commonly used to treat conditions such as pulmonary atresia.

References

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  31. ↑ Kasegawa H, Iwasaki K, Kusunose S, Tatusta R, Doi T, Yasuda H, Umezu M (January 2012). "Assessment of a novel stentless mitral valve using a pulsatile mitral valve simulator". The Journal of Heart Valve Disease. 21 (1): 71–5. PMID   22474745.
  32. ↑ Bezuidenhout D, Williams DF, Zilla P (January 2015). "Polymeric heart valves for surgical implantation, catheter-based technologies and heart assist devices". Biomaterials. 36: 6–25. doi:10.1016/j.biomaterials.2014.09.013. PMID   25443788.
  33. ↑ Roberto de Menezes Lyra | title = Eight Types of Interchangeable Prosthetic Heart Valve: A Mini Review. | journal = https://globaljournals.org | https://globaljournals.org/GJMR_Volume22/2-Eight-Types-of-Interchangeable-Prosthetic-Heart-Valve.pdf

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