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