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Prosthetic Heart Valves Presentation by Brian Meyer.

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1 Prosthetic Heart Valves Presentation by Brian Meyer

2 Topics to Be Discussed: Introduction: How the Heart/Heart Valves Work Brief History of Artificial Heart Valves Types of Artificial Valves (Examples,Materials Used) In-Depth Look Bjork-Shiley Valves (Why Failed? And Lessons to be learned)

3 Heart/Heart Valves Heart consists of: Right Atrium and Ventricle Atrium Left Atrium and Ventricle Two Types of Valves: Atrioventricular Valve: separates the atrium from the ventricle Semi-Lunar Valve: separates the ventricles from the outgoing blood vessels

4 Heart/Heart Valves Right Atrioventricular Valve: Tricuspid Valve Left Atrioventricular Valve: Bicuspid Valve Right Semi-Lunar Valve: Pulmonary Valve Left Semi-Lunar Valve: Aortic Valve Purpose of Valves: Prevent backflow, or flow of blood back into chamber from which it came

5 Heart/Heart Valves When Ventricle expands: atrioventricular valve allows blood to flow forward to the atrium into the ventricle while the semilunar valve prevents blood from flowing back in heart When Ventricle contracts: atrioventricular valve closes to prevent backflow while semilunar valve allows blood to body or lungs Prevention of backflow: ensures the proper direction of flow and reduces amount of work heart must do to pump blood

6 When Heart Valves Stop Working Heart Valve diseases fall into two categories: stenosis- hardening of the valve incompetence- permittence of backflow 3 causes of Heart Disease: Rheumatic Fever: stiffens valve tissue, causing stenosis Congenitally defective valves: do not form properly as the heart develops, but often go unnoticed until childhood Bacterial infection: causes inflammation of valves, tissue scarring, and permanent degradation

7 Evolution of Prosthetic Heart Valves The development of the original ball-and-cage valve design can be attributed to the bottle stopper in 1858 In the early 1950’s, it led to the idea of a prosthetic heart valve consisting of a cage with a mobile spherical poppet

8 Evolution of Prosthetic Heart Valves This first heart valve was made of a Plexiglass(methyl methacylate)cage surrounding a silicone- coated nylon poppet First implanted in a human in a closed procedure in September of 1952 (descending thoracic aorta)

9 Evolution of Prosthetic Heart Valve Significant advances were made soon after to help the development of the heart valve: In 1953, marked successful use of the heart and lung machine, paving the way for the 1 st open heart operations The idea of using blood from another patient to oxygenate the blood of the patient was developed New methods were came for evacuating air from the heart New materials (Plexiglass, Teflon, and Dacron)

10 Evolution of the Prosthetic Heart Valve  On July 22, 1955, at the City General Hospital in Sheffield, England, Judson Chesterman implanted the first successful heart valve  The patient lived 14 hours after the valve was placed, but died when the poppet twisted out of position  Valve was made of Perspex, an outer cage, a poppet, and 2 buttons to fasten the valve to the outside of the heart

11 Evolution of the Prosthetic Heart Valve Starr-Edwards valve was first successful long-term valve created It was implanted in its first 8 patients in 1961 (6 of 8 survived Ball-and-Cage design Devised important “Nine Commandments” in developing a prosthetic heart valve

12 Evolution of Prosthetic Heart Valves “Nine Commandments”: Embolism Prevention Durability Ease and Security of Attachment Preservation of Surrounding Tissue Function Reduction of Turbulance Reduction of Blood Trauma Reduction of Noise Use of Materials Compatible with Blood Development of Methods of Storage and Sterilization

13 Evolution of the Prosthetic Heart Valve Since this time, over 30 mechanical heart designs have been marketed in the U.S. and abroad These valves have progressed from the simple caged ball valves, to strut- and-leaflet valves and the modern bileaflet valves, to human and animal tissue

14 Artificial Heart Valve Types

15 Mechanical Valves: Ball Valves This design uses a spherical occluder, or blocking device, held in place by a welded metal cage Problem and Why failed: Natural heart valves allow blood to flow straight through the center of the valve (central flow) Caged-ball valves completely blocked central flow and collisions with the occluder ball caused damage to blood cells Finally, these valves stimulated thrombosis, or formation of blood clots

16 Starr-Edwards Ball Valve Model: Starr-Edwards Type: Aortic Caged Ball Materials: Silicone Rubber ball with 2% barium sulfate, cage-Stellite alloy No. 21, sewing ring- knitted Teflon and polypropelene cloth 1 of 4 Starr-Edwards models developed are still used today, and is the only ball valve currently used in U.S.

17 Magovern-Cromie Ball Valve Model: Magovern-Cromie valve Type:Aortic Caged Ball Materials: Ball-Silicone rubber with barium, cage-titanium, sewing ring-none, Cage open at top

18 Smeloff-Suttor Ball Valve Model: Smeloff-Suttor valve Type: Aortic, Mitral, Tricuspid caged ball Materials: Ball-Silicone rubber, cage-titanium, sewing ring-Teflon Problems: Ball Variance, swelling of ball from lipid absorbtion, can cause sticking of ball in inflow orifice

19 Mechanical Valves: Single Leaflet Disc Valves Uses a tilting occluder disk to better mimic natural flow patterns through the heart tilting pattern allow more central flow while still preventing backflow Some damage still occurs to blood cells Reduces thrombosis and infection, but does not eliminate either problem

20 Bjork-Shiley Standard Aortic Valve Model: Bjork-Shiley Standard Type: Aortic Tilting Disc Materials: Disk-Pyrolytic Carbon, cage-Haynes 25, sewing ring-Teflon

21 Medtronic-Hall Valve Model: Medtronic-Hall A7700 (aortic), M7700 (mitral) Type: Aortic and Mitral Tilting Disk Materials: Cage-titanium, Disk-Pyrolytic carbon, sewing ring-knitted teflon

22 Other Single Leaflet Disc Valves Another similar valve is the caged disc valve Examples are Starr- Edward Model 6500 and the Kay-Shiley Model

23 Mechanical Valves: Bileaflet Disc Heart Valves Consists of two semicircular leaflets that pivot on hinges integrated onto the flange Carbon leaflets and flange exhibit high strength and excellent biocompatibility Provide closest approximation to central flow Allows small amount of backflow as leaflets cannot close completely

24 St. Jude Bileaflet Valve Model: St. Jude Valve Standard Design :Mitral, Aortic, Tricuspid Bileaflet Valve Materials-Cage and disk- pyrolytic carbon, sewing ring-double velour knitted polyester

25 Animal Tissue Valves Heterograft or Xenograft Vavles Most commonly used tissues are the porcine (pig) valve tissue and Bovine (cow) pericardial tissue

26 Porcine (pig) Valves Two major brands of porcine available today, Hancock and Carpentier-Edwards Has good durability and and good hemodynamics Materials: Porcine valve tissue, stents made of wire, Elgiloy(cobalt-nickel alloy), sewing ring-knitted Teflon

27 Pericardial (cow) Valves Lasts as long as standard porcine valves at 10 years The pericardial valve has excellent hemodynamics, even in smaller sizes(19mm to 21mm)and has gained a large market share (about 40% of US tissue valves) in this group of patients

28 Stentless Porcine Valve Stentless valves are made by removing the entire aortic root and adjacent aorta as a block from the pig Drawbacks: Valve is more difficult to to implant and requires special measurements for successful implantation

29 Homografts(Human to Human) Homografts are valves transplanted from one human to another After donation, valves are preserved in liquid nitrogen(cyropreserved) until needed Since the valve must be thawed overnight, the patient’s size must be known beforehand As with heart transplants, homograft availability is limited by donor availability

30 Autografts (Ross Procedure) Autografts are valves taken from the same patient in which the valve is implanted Used for patients with diseased aortic valves Advantages: patient receives a living valve in the aortic position Better durability and hemodynamics Disadvantages: difficult procedure for the surgeon and involves considerable skill and time most common problem is leakage of the valve (aortic regurgitation)

31 Animal Tissue Valves vs. Mechanical Valves With the animal tissue, patients do not need lifelong anticoagulant therapy required with mechanical valves Animal tissue is also inexpensive and mass-produced However, animal tissue has uncertain durability (5- 15 years )that will inevitably require a risky re- operation Mechanical valves can also fail suddenly and catastrophically Have serious problem with thromboembolism

32 Bjork-Shiley Prosthetic Heart Valve In 1979, the Bjork-Shiley valve was modified to open from 60 to 70 degrees (Convexo-Concave valve) 82,000 were implanted between the time of its invention and its removal from the market in 1986 Between 1979 and 1990, 600 fractures occurred with 2 out of 3 fractures resulting in death

33 Bjork-Shiley Valve: Initial Fracture Assessment Investigators determined that the floating disc opens and slams shut at least 70 times per minute or 40 million times per year, causing fatigue failure Although changes were made, fractures continued to occur Finally, in 1984, Shiley discovered the source, known as “Bimodal Closure Phenomenon”

34 Bjork-Shiley Valve: Role of the FDA In 1979, the Bjork-Shiley valve was approved very quickly, only six months after Shiley’s first request The main criticism of the FDA was its delay in removing the valve from the market despite knowledge of the outlet struts susceptibility to fracture The Bjork-Shiley heart valve failure prompted the FDA to make substantial changes in its policies

35 Impact of Bjork-Shiley Convexo- Concavo(BSCC) Heart Valves The deaths and sicknesses have greatly effected Shiley Incorporated, the FDA, and the medical industry Overall, Shiley and its associate company, Pfizer, have faced hundreds of lawsuits and paid more in legal fees and lobbying costs than if they had simply replaced the valves According to the Federal Device Amendments, the BSCC is a justified killer

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