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Prosthetic Heart Valves
Presentation by Brian Meyer
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)
Heart/Heart Valves
Heart consists of:Right Atrium and Ventricle
AtriumLeft 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 ValvePurpose 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 stenosisCongenitally defective valves: do not form properly as the
heart develops, but often go unnoticed until childhoodBacterial infection: causes inflammation of valves, tissue
scarring, and permanent degradation
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
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 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 1st 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)
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
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 Prosthetic Heart Valves
“Nine Commandments”:Embolism PreventionDurabilityEase and Security of AttachmentPreservation of Surrounding Tissue FunctionReduction of TurbulanceReduction of Blood Trauma Reduction of Noise Use of Materials Compatible with BloodDevelopment of Methods of Storage and Sterilization
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
Artificial Heart Valve Types
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-EdwardsType: Aortic Caged BallMaterials: 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 valveType: Aortic, Mitral, Tricuspid
caged ball
Materials: Ball-Silicone rubber, cage-titanium,
sewing ring-TeflonProblems: 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
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 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(19mm to 21mm)and has gained a large market share (about 40% of US tissue valves) in this group of patients
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
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)
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
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
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”
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
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