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Mechanical Heart Valves that replace the function of heart valves in our body
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BT5011 : Biomaterials Engineering
MECHANICAL HEART VALVES
By
Yanamala Vijay Raj
Praveen Krishna V.
1
Heart/Heart Valves
A heart valve normally
allows blood to 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. A heart valve opens or
closes incumbent upon
differential blood pressure on each
side
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When Heart Valves Stop Working
ARTIFICIAL VALVES:
An artificial heart valve is
a device implanted in the
heart of a patient with
valvular heart disease.
When one of the four
heart valves malfunctions,
the medical choice may
be to replace the natural
valve with an artificial
valve. This requires open-
heart surgery.
Need and function-when does natural valveneed be replaced
Heart Valve diseases fall into two categories:
Stenosis- hardening of the valve andincompetence- permittance of backflow
3 causes of Heart Disease:
Rheumatic Fever: stiffens valve tissue, causingstenosis
Congenitally defective valves: do not formproperly as the heart develops, but often gounnoticed until childhood
Bacterial infection: causes inflammation ofvalves, tissue scarring, and permanentdegradation
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Evolution of Prosthetic Heart Valves
The development of the originalball-and-cage valve design canbe attributed to the bottlestopper in 1858
In the early 1950’s, it led to theidea of a prosthetic heart valveconsisting of a cage with amobile spherical poppet
On July 22, 1955, at the City GeneralHospital in Sheffield, England, JudsonChesterman implanted the firstsuccessful heart valve
The patient lived 14 hours after thevalve was placed, but died when thepoppet twisted out of position
Valve was made of Perspex, an outercage, a poppet, and 2 buttons to fastenthe valve to the outside of the heart
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•Starr-Edwards valve was first successful long-termvalve created•It was implanted in its first 8 patients in 1961 (6 of8 survived•Ball-and-Cage design•Devised important “Nine Commandments” indeveloping a prosthetic heart valve.
Since this time, over 30 mechanical heart designshave been marketed in the U.S. and abroadThese valves have progressed from the simple cagedball valves, to strut-and-leaflet valves and themodern bileaflet valves, to human and animal tissue
So, To Summarize
•1952 – Dr. Charles Hufnagel
designed and implanted a mechanical
heart valve into a thirty year old
female.
•1960 – The Starr-Edwards ball valve
was created. It was based off of Dr.
Charles Hufnagel’s design.
•1969- The Bjork-Shiley valve started
being used and it was based on a
tilting disc design.
•1979 – Bileaflet valves start being
used and up to this day, their designs
are still being improved upon.
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Types of valves - advantages and disadvantages
•Mechanical- There are three types. The caged ball, tilting disk, andbileaflet. Lasts for over 20 years•Tissue(biological)- valves that are used from animals to implant themback into humans. Typically lasts between 10-15 years
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Characteristics of ideal heart valve“Nine Commandments”:
oEmbolism PreventionoDurabilityoEase and Security of AttachmentoPreservation of Surrounding Tissue FunctionoReduction of TurbulenceoReduction of Blood TraumaoReduction of NoiseoUse of Materials Compatible with BloodoDevelopment of Methods of Storage and Sterilization
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Unidirectional flow Durable : 40million cycles/year Blood compatible: no thrombus, embolus Central flow: Laminar not turbulent Closing not damaging blood cells Last but not the least important – It should be quiet
“An ideal Prosthetic valve”
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Starr-Edwards Ball-in-Cage Valve
The ball valve was the first mechanical heartvalve used and designed by Charles Hufnagel.
The Starr-Edwards ball valve was first usedclinically as a mitral valve replacement in1960.
After the Starr-Edwards valve was established,several other design variations were createdsuch as Magovern–Cromie, DeBakey–Surgitool, and Smeloff–Cutter ball valves.
Ball valves operate on the simple principle thatthe ball will be forced to one side of the valve orthe other depending on which way blood isflowing.
They were modeled after ball valves used inindustrial applications to allow the flow of fluidson only one direction.
When the pressure exerted by the heart onto theblood (and the ball) exceeds the pressure in theaorta, the ball is pushed away from the heart.
This is the open position of the valve and bloodcan flow out of the heart into the aorta. After theheart ejects blood, the pressure inside the heart isgreatly reduced so blood will try to flow backinside the heart.
The negative pressure sucks the ball valvebackwards. It fits over the opening of the heartand prevents backflow of blood
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Björk–Shiley valveConstruction• The Björk–Shiley valve consists of
a single carbon-coated disc in ametal housing.
• The disc is held in place by twometal struts, an inflow and anoutflow strut.
• The housing is made from thealloy Haynes 25, which iscomposed of 51% cobalt,20% chromium, 15% tungsten,and 10% nickel.
• The Björk–Shiley valve wasconsidered very durable and waswidely used in the 1970
The Björk–Shiley valve is a mechanical prosthetic heart valve. The valve was co-invented by American engineer Donald Shiley and Swedish heart surgeon Viking Björk.
Beginning in 1971, it has been used to replace aortic valves and mitral valves. It was the first successful tilting-disc valve
Tilting disc valves can open at an angle of60° and at a rate of 70 beats per minute.
The angular opening of this valve reducesdamage to blood cells.
These are major improvements over the balldesign but the struts of the tilting disc valvestend to fatigue and fracture over longperiods of time.
The convexo concave shape of disc wasreplaced by flat discs starting 1986following lawsuits due to failure of 619valves out of 80,000 implanted.
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Medtronic-Hall Valve Tilting Disk
The Medtronic-Hall valve was developed to improve on existing tilting disc valves by
reducing the risk of valvular thrombosis.
This was to be accomplished by improving the hemodynamics and by allowing the
disc to move
downstream away from the orifice during opening.
The valve was also designed for maximal structural durability to minimize the risk of
mechanical breakage.
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Two semicircular leaflets that rotate about struts attached to the valve housing
Good hemodynamic performance - improved flow characteristics, lowertransvalvular pressure gradients, less blood flow turbulence, improvedhemodynamics at a given annular diameter, a larger orifice area and low bulkand flat profile
the least thrombogenic of the artificial valves
most commonly implanted mechanical valve
Bileaflet valves
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Hemodynamics of blood flowHowever, in spite of improved design and hemodynamics – still haunted by numerous
complications and the most dreaded one of valve thrombosis
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Biomaterials used•Many different materials are used in the creation of artificial heart valves.
• Metal alloys consisting of stainless steel or titanium are often used to give mechanical strength and for their corrosion resistance properties.
• The struts on some leaflet valves and the cage on caged-ball models are commonly made of metal alloys due to their strength and durability requirements
Pyrolytic carbon is another valuable material for its strength and its ability to prevent clotting.
This material has a similar structure to graphite and was originally developed forapplications in the nuclear fuel industry as a coating for nuclear fuel particles. However, it wassoon realized that pyrolytic carbon had biomedical applications.
It is biocompatible, thromboresistant, resistant to wear, and has high strength and durability.
It is able to stand up to the repeated opening and closing cycles it must endure when used inmechanical heart valve.
It is commonly used for the inner orifice and the leaflets of bileaflet valves. The ATS Bi-leafletvalve shown here has leaflets made of pyrolytic carbon
15
oA material often used for the suture ring (which is used to attach the valve to the body) isDacron.
o Dacron is a long chain polyester made from ethylene glycol and terephthalic acid. It is asynthetic fiber that has many uses in industry, including thermal insulation and sails forboats.
o In biomedical applications this material is also commonly used for vascular grafts. It isrelatively inert and its porosity allows tissue in growth.
oAnother material that is commonly used for the suture ring is Teflon
oTeflon is used in many medical applications because of its signature low coefficient offriction
o Teflon is relatively inert and highly biocompatible. As with Dacron it is often used forvascular grafts. 16
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Failure modes in mechanical valve
Problems that interfere with the successful performance of valves can be grouped as below.
•Degradation of valve components•Structural failure•Clinical complications associated with the valve.
Clinically, valve failure has been considered to be present if any of the followingevents require reoperation and/or cause death:
•Anticoagulant-related hemorrhage (ACH),•Prosthetic valve occlusion (thrombosis or tissue growth),•Thromboembolism•Prosthetic valve endocarditis (PVE),•Hemodynamic prosthetic dysfunction, including structural failure of prostheticcomponents (strut failure, poppet escape, ball variance),•Reoperation (valve replacement) for any other reason (e.g.; hemolysis, noise,incidental) etc
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Evaluation of Prosthetic Valves20
Patient’s height, weight, and BSA should be recorded to assess whether prosthesis-patient mismatch (PPM) is present.
Valves should be imaged from multiple views, with attention to:
Opening & closing motion of the moving parts (leaflets for bioprosthesis and occluders for mechanical ones)
Presence of leaflet calcification or abnormal echo density attached to the sewing ring, occluder, leaflets, stents, or cage
Appearance of the sewing ring, including careful inspection for regions of separation from native annulus & for abnormal rocking motion during the cardiac cycle
Echo Imaging of Prosthetic Valves
Regurgitation occurs at the disc margins The regurgitant jets converge toward the center of the valve
PARAMENTERS
CLINICAL INFORMATION Date of valve replacement
Type and size of the prosthetic valve
Height, weight and body surface area
Symptoms and related clinical findings
BP and Heart Rate
IMAGING OF THE VALVES Motion of leaflets or occluder
Presence of calcification on the leaflets or
abnormal densities on the various
components of the prosthesis
Valve sewing ring integrity and motion
PARAMENTERS
DOPPLER ECHOCARDIOGRAPHY OF
THE VALVE
Contour of jet velocity signal
Peak velocity and gradient
Mean pressure gradient
VTI of the jet
DVI
Pressure half time in MV and TV
EOA
Presence, location and severity of
regurgitation
Caged-Ball Valve
Single-Leaflet Valve
Bileaflet Valve
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Improvements that researchers will attempt to make in the future include:
•Longer lifespan of the heart valves.•Lower rejection rate.•Less risk of blood clots in mechanical heart valves.•Remove the need for blood thinning medication.•Implant the artificial heart valves through a less intrusive method (currently open-heart surgery).•Polymeric Heart Valves - Scientists are looking more into polymer materials for heartvalves because it’s easy to fabricate, has a large range of polymer properties, anddurability.•Tissue engineered heart valves- Obtaining the number of types of cells for tissuevalves, lack of scaffold material
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References
"Artificial Heart Valve." Wikipedia. Wikimedia Foundation, 16 Sept. 2012. Web. 16 Sept. 2012. <http://en.wikipedia.org/wiki/Artificial_heart_valve>.
Fisher, John. Artificial Heart Valve. University of Leeds, assignee. Patent 5500016. 19 Mar. 1996. Print.
Kidane, Asmeret G. "Current Developments and Future Prospects for Heart Valve Replacement Therapy." Wiley Online Library (n.d.): n. pag.
Http://onlinelibrary.wiley.com/doi/10.1002/jbm.b.31151/full. 9 July 2008. Web. 19 Sept. 2012.
<http://onlinelibrary.wiley.com/doi/10.1002/jbm.b.31151/full>.
"Mechanical Heart Valve Replacement Devices." Mechanical Heart Valves. N.p., n.d. Web. 19 Sept. 2012. <http://www.heart-valve-
surgery.com/mechanical-prosthetic-heart-valve.php>.
Oakley, Reida E., Peter Kleine, and David Bach. "Choice of Prosthetic Heart Valve in Today’s Practice." American Heart Association (2008): n. pag.
American Heart Association. Circulation. Web. 16 Sept. 2012. <http://circ.ahajournals.org/content/117/2/253.full>.
Peck, Peggy. "Replacement Heart Valves Built to Last, and Even Grow." WebMD. WebMD, n.d. Web. 16 Sept. 2012. <http://www.webmd.com/heart-
disease/news/20000804/replacement-heart-valves-built-to-last-even-grow?page=2>.
"Pericardial Heart Valves." Wikipedia. Wikimedia Foundation, 04 Jan. 2012. Web. 19 Sept. 2012. <http://en.wikipedia.org/wiki/Pericardial_heart_valves>.
"Pericardial Heart Valves." Wikipedia. Wikimedia Foundation, 04 Jan. 2012. Web. 19 Sept. 2012. <http://en.wikipedia.org/wiki/Pericardial_heart_valves>.
Pick, Adam. "Porcine Valves – What Is A Porcine Heart Valve Replacement?" Porcine Valves – What Is A Porcine Heart Valve Replacement? N.p.,
27 Aug. 2007. Web. 19 Sept. 2012. <http://www.heart-valve-surgery.com/heart-surgery-blog/2007/08/27/porcine-valve/>.
Pick, Adam. "Porcine Valves – What Is A Porcine Heart Valve Replacement?" Porcine Valves – What Is A Porcine Heart Valve Replacement? N.p.,
27 Aug. 2007. Web. 19 Sept. 2012. <http://www.heart-valve-surgery.com/heart-surgery-blog/2007/08/27/porcine-valve/>.
"Prosthetic Heart Valve." Prosthetic Heart Valve. AHA, 7 June 2011. Web. 16 Sept. 2012.
<http://circ.ahajournals.org/content/123/22/2602/F3.expansion.html>.
"Types of Artificial Heart Valves." Central Florida Hospitals. N.p., n.d. Web. 16 Sept. 2012. <http://www.cfhalliance.org/allianceheart/HeartValve-
Artificial.html>.