Artificial Heart Valves

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

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

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

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

History The first ever invented artificial heart valve was designed by Charles A. Hufnagel which was the caged-ball design Judson Chesterman implanted the first successful heart valve (at the City General Hospital in Sheffield, England) The patient lived 14 hours after the valve was placed, but died when the poppet twisted out of position the first human was implanted with the ball and cage design Binet and associates, started using porcine aortic valves for humans The Bjork-Shiley valves was the first tilting-disc design to come out 1979-the bileaflet design was introduced which was composed of two semicircular leaflets that shifted open and closed

Types of Artificial Heart Valves Mechanical- There are three types. The caged ball, tilting disk, and bileaflet Tissue(biological)- Valves that are used from animals to implant them back into humans

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)

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

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

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

Mechanical Heart Valves All the types of mechanical heart valves are still in use today. Usually made of titanium or carbon which makes them strong and very durable Three types of mechanical heart valves

Tissue Heart Valves (biological valves) Using valves from other animals. The procine valve of a pig is the most comparable valve to a human. Xenotransplantation Pericardial valves: Biological valve tissue can be taken from a cow or horses pericardial sac and be sewed to a metal frame.

Advantages Mechanical heart valves: The biggest advantage is the durability. While the tissue heart valves are estimated to last about years, a mechanical heart valve can last 30 year. Tissue heart valves: There is minimal blood regurgitation, minimal transvalvular pressure gradient, self repairing. Does not require and anti-coagulant drug.

Advantages & Disadvantages Mechanical heart valves In order to decrease the risk of blood clotting, the patient must take blood thinners, Have serious problem with thromboembolism, fail suddenly and catastrophically Some patients can hear their mechanical heart valve open and close. Tissue heart valves Patients do not need lifelong anticoagulant therapy Inexpensive and mass-produced Wear, there is a small possibility that the body will reject the valve, inability to implant them into infants and children. uncertain durability (5-15 years) that will inevitably require a risky re-operation

Artificial Heart Valve Types

Figure. Algorithm for selecting a valve procedure. El Oakley R et al. Circulation 2008;117: Copyright © American Heart Association

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

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.

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

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

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

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

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

Impact of Bjork-Shiley Convexo- Concavo(BSCC) Heart Valves 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 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

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

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

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

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

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

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

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

Stentless Porcine Valve

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

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)

Implanting Both mechanical and tissue heart valves require open heart surgery It’s more common in tissue valves for a re-operation Complete recovery from surgery could be a couple of weeks to several months Currently: 55% mechanical valves 45% tissue valves

Future of heart valve replacement Polymeric Heart Valves - Scientists are looking more into polymer materials for heart valves because it’s easy to fabricate, has a large range of polymer properties, and durability. Tissue engineered heart valves- Obtaining the number of types of cells for tissue valves, lack of scaffold material