User:Chalikesalsa/Artificial heart valve

Wikipedia stable document

Denny, Amber, Finacy

Lead Section

An artificial heart valve is a one-way valve implanted into the heart of a patient to replace a dysfunctional native heart valve (valvular heart disease). Artificial heart valves can generally be separated into two classes: mechanical heart valve, bioprosthetic valve and tissue heart valve.

Mechanical heart valves and tissue heart valves have different structures, advantages and disadvantages. Mechanical valves are made of titanium and carbon whereas tissue heart valves are composed of human and animal tissues. The structure of mechanical valves include two leaflets and a ring of knitted fabric encircling a metal ring. The tissue valves instead are enclosed by a ring of knitted fabric which is sewn onto the heart. The valves are also applied in different disciplines.

Mechanical heart valves and and bioprosthetic valves both are not adaptable to the physical changes of human bodies. The patients using these valves need to replace them once in a while to make them function properly. Moreover, mechanical valves tend to cause foreign body rejections and sometimes the patients can hear the clicking noise of them.

Tissue engineered heart valves require a scaffold and living cells to be produced. Common materials used for scaffold include natural polymers like collagen and synthetic polymers like nanofiber. They are usually designed specifically for individual patients. To ensure the 3D cell structural environment, 3D printing can be used to minimize the error when producing these valves. Due to the limitations of knowledge in 3D cell structural behavior, scientists are not able to produce tissue engineered valves that have comparable quality to the natural healthy human valves.

The new generation of artificial heart valves polymeric heart is claimed to have more benefits than the current artificial heart valves. The benefits include higher durability, reduced blood clots

The main problem with artificial valves today is the regurgitation caused by form degeneration, and to repair the deformed valves, in most cases, support in the ventricle is required for any surgical operation to be performed. Further methods and inventions are described in details below.

As an alternative option during an irreversible heart failure, an artificial total heart is preferred over artificial heart valves as it functions the same as a normal heart in many ways. It serves as a last resort, but not a long term option.

1 Types of artificial heart valve

1.1 Why artificial heart valves (types of heart valves and reasons for heart valves damages)

A heart contains four valves which are constantly open and closed to let blood flow into [1]. The four types of heart valves are the tricuspid, pulmonary, mitral and aortic valves. Tricuspid valve allows blood to pass through when it flows back from heart to body [1]. The pulmonary valve allows blood to flow to lungs and get oxygen [1]. The Mitral valve is where blood flows into after pickup oxygen from lungs [1]. The aortic valve is from the bottom left chamber. Blood flows into the human body from an aortic valve [1].

There are multiple causes for heart valve damages such as age related changes, side effects from other disorders, rheumatic fever, or infections etc [2]. Other disorders include: high blood pressure and heart failure which can enlarge the heart and arteries [2]; Scar tissue caused by heart attack or injury. The common infections which can cause heart valves damage is infective endocarditis or germs that enter the heart through the bloodstream [2].

1.2 Mechanical heart valves

1.2.3 Disadvantages of mechanical heart valves


 * 1.1.3.2 Noise
 * An investigation with 73 patients after valve replacement shows 65% of patients can hear their own valves; 18% have sleep disturbances; 5% feel unwell during the day; 12% prefer less noisy valves [3].

1.2.3.5 Foreign body rejection and lack of adaptation to growth

Implanting mechanical valves will cause foregin body rejection. The blood may coagulate and eventually result in a hemostasis. The usage of anticoagulation drugs will be interminable to prevent thrombosis [4]. The side effect of Heparin, the most commonly used anticoagulant, includes hardship of forming blood clots and can cause major bleeding. It may also cause Heparin induced thrombocytopenia (HIT), heparin-associated osteoporosis (HAO) and skin allergies [5].

Mechanical valves sometimes cause infections. When infections happen it would be very hard to cure unless changing the heart valves.

Mechanical valves are not able to adapt to the changes like physical growth of the body. The patient will have to get the valves replaced if the size of their heart changes [4].

1.3 Bioprosthetic heart valves

1.3.2 Disadvantages of bioprosthetic heart valves

Current bioprosthetic valves lack longevity, and will calcify as time flows [6]. The valves will make the valve cusp become stiff and thick that cannot close completely when the valves calcify [6]. 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 [6].

1.4 Tissue-engineered valves

1.4.1 Modeling and 3D printing of heart valves

Usually the tissue engineered heart valves are patient specific and will need to have a pre-design [7]. Modelling will enable the doctor to design appropriate heart valves based on the patient’s physical status. 3D printing is used because of its high accuracy and precision of dealing with different biomaterials [7]. 3D printing can help with minimizing the error that may occur when producing the valves. The structure of the valves is very important to make it functioning properly, and 3D printing is the best way to produce these structures. [7]. The most important technique of 3D printing in making a heart valve is microstamping. It allows the cells to be arranged in the predesigned 3D structure, which enables the valves to function [7].

1.4.2 Nanofiber as the scaffold of tissue engineered valves

Nanofiber is a biodegradable and synthesized material. It is able to provide a good framework for the cells to grow [4]. The surface of nanofiber provides a suitable environment for the cells to adhere. Even though most of the drugs have a long protein chain, they can still stick well on the surface of nanofiber [4]. Therefore, nanofibers are used as scaffolds for musculoskeletal tissue engineering. and as a carrier for the controlled release of drugs, DNA, and proteins. [5]

1.4.3 Types of cells used in tissue engineering

Cells that are used for tissue engineered heart valves are expected to secrete the extracellular matrix (ECM) [6]. Extracellular matrix provides support to maintain the shape of the valves and determines the cell activities [8]. There are three types of cells commonly used to produce heart valves: stem cells, progenitor cells and differentiated cells [6]. These cells can be found in the individual patients’ bodies or from their bloodstream to maximize the adaptability of the valves [6].

1.4.4  Challenges that tissue engineered valves are facing

Scientists now can follow the structure of heart valves to produce something that looks similar to them [9]. However, since the tissue engineered valves lack of living cells, they either fail to perform their functions like natural heart valves, or they are functioning when they are implanted, but gradually degrade over time [9]. It is hardly possible to fix cell degrading without replacing the heart valves. Scientists are researching on producing durable tissue engineered valves but until now only natural valves can be both functioning and adapting [9].

1.4.5 Future of tissue engineering valves

Tissue engineered heart valves are aiming to achieve these goals: anti‐thrombogenic, biocompatible, durable, resistant to calcification, and exhibits a physiological hemodynamic profile [10]. The valve should also grow with the human body [10].

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 [10]. To select the most suitable material, we should consider the following aspects: 1. The interaction of cells and scaffold. 2. Fabrication of the materials and the impact on the 3D structure. 3. The durability of the scaffold [10].

1.5 Difference between mechanical and tissue valves

Mechanical and tissue valves are made by different materials. The materials used in making mechanical valves are titanium and carbon [11]. 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 [11]. The valves made from animal tissues, such as the porcine (pig), bovine (cow) and equine (horse) models, are secured with a preserving solution [11].

The structure of both valves are different too. The mechanical valves generally include two leaflets and a ring of knitted fabric encircling a metal ring [11]. The tissue valves instead are  enclosed by a ring of knitted fabric which is sewn onto the heart [11].

Mechanical and tissue valves are also applied in different fields. Mechanical valves are used in aortic and mitral replacement surgeries [11]. However tissue valves are mainly implemented in open heart surgery or in a minimally invasive aortic operation such as transcatheter aortic valve implantation (TAVI) [11].

1.6 Choosing Artificial Hearts

Choosing artificial valves are depending on factors such as patients’ age, physical condition, other medications etc [12]. Patients should always follow doctors’ recommendations in selecting artificial valves.

Mechanical valves can be a better choice for younger people(younger than 65) and people at risk of valve deterioration due to its durability [12]. It is also preferable to patients who are already taking warfarin and people who would be at risk for another valve replacement operation [12].

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 [12]. Other patients who may be more suitable for tissue valves are the ones who have other planned surgeries and are not willing to take blood-thinning medications. People who have pregnancy plans may also consider tissue valves as there is a risk for warfarin for pregnancy [12].

3 Artificial Heart Valve Repair

Artificial heart valves are expected to last from 10 to 30 years, and by the time, the patient will often have a new heart valve installed [13].

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 [13].

The repairing process of the artificial heart valve regurgitation (mitral or tricuspid regurgitation)  and stenosis usually requires the surgeon for an open-heart surgery, and a repair or partial replacement of regurgitant valves, such as mitral valve, is usually preferred [13]. There have been numerous inventions developed in this field for proper artificial heart valve repair.

A general method of supporting an artificial heart valve according to the current invention, such as a distance adjusting device within the valve, the supporting design is first linked with and then anchored at the annulus of the valve, or it may already have an extending pillar for anchor [14]. For most cases, in the deployed state, the anchor is positioned in perpendicular to the longitudinal axis [15]. To open and close the leaflet, the pillar is then connected to one of the valve leaflets for supporting. With all kinds of repairing apparatus, the pillar may be positioned along with a flexible tensile member, for example, an natural or artificial rope. Or a type of direct connection involves extending a coil from the pillar into the two nearby leaflets to bridge with the center parts of the leaflets. Other forms of connections for supporting purpose also involve artificial chord or pillar attachments described above [14].

Although the methods of the current inventions are aimed at contracting the artificial heart valve’s annulus, particularly for the treatment of valve regurgitation, these inventions may find wider applications. Especially, the clip deployment device can be used in other circumstances, such as to transfer a plurality of sequential clips in a straight or curved manner to tighten the tissue or optionally bind the tether portion of the tissue [13].

From the current inventions, their methods and systems are generally designed for convenience in transvascular, minimally invasive and other surgical procedures by improving the efficiency of delivery of the therapeutic apparatus [15].

Researchers are developing catheter based surgery that repairs the artificial heart valve without cutting for any incision, also referred to as “percutaneous”, and also utilizing polymers to produce flexible leaflet valves, while inheriting the advantages of current commercial bioprosthetic and mechanical valves [16].

5 See also

5.1  Alternative Out: Artificial Total Heart

The total artificial heart is a dual-ventricular, pneumatic, pulsatile blood pump that will be transplanted to substitute for the ventricle and its four heart valves (see Figure 1) [17].

Figure1: the CardioWest Total Artificial Heart [17]

The total artificial heart (TAH) device, for now, can only be approved by the FDA for biventricular heart failure, and this is only to earn time for the patient for a heart transplantation [18].

In case of an irreversible biventricular failure, TAH can greatly increase the chance of survival compared to cardiac valves, and the survival rates for one-year and five-year after the successful transplantation are 86% and 64% [17].

The patient's hemodynamic status was alleviated with implantation of a total heart, and the cardiac index increased from the baseline value of 1.9 to 3.2 liters per square meter [17].

Not only promoting immediate hemodynamic recovery and clinical stability, the implantation of the total artificial heart improves the prognosis of the dying patient, leading to the restority of the end-organs, which ultimately prepares the patient for cardiac transplantation [17].

The total artificial heart has served as an emergent rescue device, and it fails in long term usage because it might cause hemolysis and thrombosis. Due to the inflexible structure of TAH that would lead to blood clot, bleeding, infection, and organ failures are the most common obstacles [18].

Experiment on continuous-flow TAH shows a patient’s pulseless circulation without affecting homeostasis or exercise[19].

The continuous-flow TAH is more durable, responsive, compatible for the human body compared to a conventional TAH [19].

7 Further reading

7.1 Current Status of Artificial Heart Valves

A new type of artificial heart valves -- polymeric heart, which is developed by UK scientists, is said to offer more benefits compared to current artificial heart valves [20]. Researchers claim that polymeric hearts can have higher durability and can potentially solve blood clots, and biocompatibility issues which are contained by current artificial heart valves [20].

References

[1] H. and V. Team, “Heart Valve Replacement: Which Type Is Best for You?,” Health Essentials from Cleveland Clinic, 26-Dec-2018. [Online]. Available: https://health.clevelandclinic.org/heart-valve-replacement-which-type-is-best-for-you/.

[2] D. Muraru, A. M. Anwar, and J.-K. Song, “Heart valve disease: tricuspid valve disease,” Oxford Medicine Online, 2016.

[3] A. Moritz, E. Wolner, U. Steinseifer, H. Wolters, H. Reul, G. Kobina, K. Neuwirth-Riedl, Closing click of St Jude Medical and Duromedics Edwards bileaflet valves: Complaints created by valve noise and their relation to sound pressure and hearing level, European Heart Journal, Volume 12, Issue 6, June 1991, Pages 673–679, https://doi.org/10.1093/eurheartj/12.6.673

[4] N. Mehrdad; E. Ali (2016, Dec 1). Nanofibrous bioengineered heart valve—Application in paediatric medicine [Online]. Available: https://www.sciencedirect.com/science/article/pii/S0753332216318522?via%3Dihub

[5] W Jeanine M. Bick, L. (1998, May 1). HEPARIN-INDUCED THROMBOCYTOPENIA, PARADOXICAL THROMBOEMBOLISM, AND OTHER SIDE EFFECTS OF HEPARIN THERAPY [Online]. Available: http://www.sciencedirect.com/science/article/pii/S0025712505700158

[6] H. Anwarul, S. John; P. Modarres, H. Bakhaty, A. Nasajpour, A. Mofrad,  R. K. Mohammad S. Amir (2016, Oct 1). Micro and nanotechnologies in heart valve tissue engineering [Online]. Available: http://www.sciencedirect.com/science/article/pii/S0142961216303325

[7] T Andrea S. Tomov, L. Martin.; Cetnar, Alex; Lima, Bryanna; Nish, Joy; McCoy, Kevin; Mahmoudi, Morteza; Serpooshan, Vahid (2019, Jun 01). Biomaterial approaches for cardiovascular tissue engineering [Online]. Available: https://doi.org/10.1007/s42247-019-00039-3

[8] E. D.Hay (2013, Nov 11). Cell Biology of Extracellular Matrix: Second Edition [Online]. Available: https://books.google.com/books?hl=en&lr=&id=uwPTBwAAQBAJ&oi=fnd&pg=PA2&dq=extracellular+matrix&ots=FIOOmsykh4&sig=3i5qxsfoejIA5utasVAktcFABNM#v=onepage&q=extracellular%20matrix&f=false

[9] Chester, Adrian H.; Grande-Allen, K. JaneMike Steere (2020, Apr, 21). Which Biological Properties of Heart Valves Are Relevant to Tissue Engineering? [Online]. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7186395/

[10] Nachlas, Aline L. Y.; Li, Siyi; Davis, Michael E. (2017). Developing a Clinically Relevant Tissue Engineered Heart Valve—A Review of Current Approaches [Online]. Available: https://onlinelibrary.wiley.com/doi/abs/10.1002/adhm.201700918

[11] J. B. Schmidt and R. T. Tranquillo, “Tissue-Engineered Heart Valves,” Heart Valves, pp. 261–280, 2013.

[12] British Heart Foundation, “How do replacement heart valves work?,” BHF. [Online]. Available: https://www.bhf.org.uk/informationsupport/heart-matters-magazine/medical/replacement-heart-valves. [Accessed: 01-Aug-2020].

[13] R. Morales, "US6986775B2 - Devices and methods for heart valve repair - Google Patents", Patents.google.com, 2006. [Online] Available: https://patents.google.com/patent/US6986775B2/en.

[14] P. Spense, "US6797002B2 - Heart valve repair apparatus and methods - Google Patents", Patents.google.com, 2004. [Online] Available: https://patents.google.com/patent/US6797002B2/en.

[15] N. Starksen, "US9226825B2 - Delivery devices and methods for heart valve repair - Google Patents", Patents.google.com, 2016. [Online] Available: https://patents.google.com/patent/US9226825B2/en.

[16] D. Bezuidenhout, D. F. Williams, and P. Zilla, “Polymeric heart valves for surgical implantation, catheter-based technologies and heart assist devices,” Biomaterials, 16-Oct-2014. [Online] Available: https://www.sciencedirect.com/science/article/pii/S0142961214010114.

[17] J. Copeland, "Cardiac Replacement with a Total Artificial Heart as a Bridge to Transplantation | NEJM", New England Journal of Medicine, 2004. [Online] Available: https://www.nejm.org/doi/full/10.1056/NEJMoa040186.

[18] J. Skroback, "SynCardia 70cc TAH-t for Destination Therapy (DT) - Full Text View - ClinicalTrials.gov", Clinicaltrials.gov, 2014. [Online]. Available: https://clinicaltrials.gov/ct2/show/NCT02232659.

[19] I. O. H. Frazier, "Continuous-Flow Total Artificial Heart Supports Long-Term Survival of a Calf", PubMed Central (PMC), 2009. [Online] Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2801939/.

[20] S. X. staff, “New heart valve could transform open heart surgery for millions of patients globally,” Medical Xpress - medical research advances and health news, 29-Jun-2020. [Online]. Available: https://medicalxpress.com/news/2020-06-heart-valve-surgery-millions-patients.html.