The Björk-Shiley
Heart Valve
Normal cardiac function
pulmonary valve
(to lungs)
aortic valve
(to body)
mitral valve
Natural aortic valve
tricuspid valve
Heart Valve Disease

Problems
 Stenosis:
hardening of the tissue, preventing
complete opening
 Incompetence: allowing backflow

Causes
 Rheumatic
fever (stenosis)
 Congenital defects
 Bacterial infection (inflammation, scarring)

60,000 valve replacements each year in U.S.
Design Requirements
Unidirectional flow
 Durable: 40 million cycles/year
 Blood compatible: no thrombus, embolus
 Central flow: laminar, not turbulent
 Closing not damaging to blood cells

Starr-Edwards caged ball valves
The original Starr-Edwards
mitral valve, implanted
1960. Lucite cage, Silastic
rubber ball occluder.
Starr-Edwards Model 1260
introduced 1968. Teflon
and polypropylene sewing
ring, cast Stellite 21 cage.
Still in use.
Starr-Edwards 2400
introduced 1972. Hollow
Stellite ball, cloth covered
Stellite cage.
Discontinued 1980.
Materials for Artificial Heart Valves

Cage/flange






Occluder




Lucite (Plexiglas, PMMA = polymethyl methacrylate)
Stainless steel
Stellite, Haynes (Co-Cr-Mo-Ni)
Titanium
Pyrolitic carbon (LTI carbon)
Silicone
Delrin (POM = polyoxymethylene)
Pyrolitic carbon (LTI carbon)
Sewing ring


Dacron (PET = polyethylene terephthalate)
Teflon (PTFE = polytetrafluoroethylene)
Other caged occluder valves
Barnard-Goosens
Smeloff-Cutter
Harken
Kay-Shiley

Advantages of caged occluder valves
 Indestructible—caged
ball still used
 Built-in redundancy of multiple struts
 Low regurgitation (backflow)

Shortcomings of caged occluder valves
 Turbulent
flow
 Large profile
 Damage to cells
 Requires permanent anticoagulant therapy

A new design was needed
Björk-Shiley Tilting Disc Valves



Donald P. Shiley, an engineer in Santa Ana, CA with a
garage
Late 1960’s began developing heart valves
Viking O. Björk, a Swedish heart surgeon came on board
a few years later
Radial-spherical (R/S) valve introduced in
1974. Subjected to several design changes.
Flat occluder disc, originally of Delrin, later
changed to pyrolytic carbon. Stellite housing.
Opens to 50-60 degrees. Inlet and outlet
struts are welded to the flange. Early failures
of the inlet strut welds were eliminated with a
change to the welding process.
Björk-Shiley Convexo-Concave valve
Section view illustration showing open (left)
and closed (right) positions of the BjörkShiley Convexo-Concave valve. Blood flows
from left to right. The flange and inlet and
outlet struts retain the occluder disc as it
floats freely between the open and closed
positions.
Photo of the Björk-Shiley ConvexoConcave valve, a tilting-disc valve.
Inlet strut is integral with the flange;
outlet strut is welded to the flange.
Björk-Shiley Convexo-Concave valve:
The Good News
C/C disc improves hemodynamics—
decreased complications due to
thromboembolism (TE)
 Received FDA approval in 6 months
 Became the most popular valve in the
world (ultimately represented half of all
valves implanted)

Björk-Shiley Convexo-Concave valve:
The (Really) Bad News

First outlet strut fracture in 1978 during clinical
trials
Cause of failure?

Manufacturing or Design?



Failure always at outlet strut weld
Based on experience with R/S valve, changed welding
process—focused on manufacturing
Instituted 5 other manufacturing changes





increased the outlet strut angle to reduce stresses induced
during installation of the occluder disc
instituted a strut deflection test to identify valves which exhibit
high deflections under a test load
implemented a test for residual stresses
developed an inspection procedure for weld structure and
penetration
tightened tolerances for the location of the outlet strut on the
flange
“Earn as you learn”




Valve not withdrawn from
the market during the
time these changes were
made
Real cause of failure not
conclusively determined
Patients with BSCC
valves not notified of
potential fracture (failure
of honor system)
FDA guidelines for
defining acceptable
failure
The Real Culprit: Bimodal Closure


Faulty logic: the weld fails, so the weld is the problem
Bimodal Closure and Interference

contour mismatch between the disc occluder and the
adjacent surfaces of the inlet strut
 multiple equilibrium points for the occluder disc in its
closed position
 rocking of the occluder on the inlet strut during closure
could result in the occluder contacting the outlet strut at its
tip rather than at its base as designed
 contact at the tip of the outlet strut would apply excessive
bending stresses to the weld union and result in eventual
fatigue failure.
A Design Failure
Section view illustration showing a Björk-Shiley Convexo-Concave
valve in the closed position. The valve's design calls for the occluder
disc to impact the outlet strut at its base, but in bimodal closure the
disc impacts the outlet strut at its tip. This induces greater stress in
the weld between the flange and outlet strut and hence reduces the
fatigue life of the valve.
Resolution
Bimodal closure phenomenon recognized
and corrected in the spring of 1984
 None of 8000 valves produced after 1984
fractured
 Valve finally pushed off the market in
1986, just as the fracture problem was
solved

Björk-Shiley Monostrut Valve





Introduced 1982
Opening angle 80°
Flange and both struts
machined from a single piece
of titanium (no welds)
Alliance Medical Technologies
bought rights to monostrut
from Sorin Biomedical
120,000 implanted since 1982
with no fractures
Another alternative: Bileaflet valves
Photo of the St. Jude valve, the first bileaflet valve. The occluder leaflets swing open and
closed on hinges, eliminating the problems associated with strut impact. The leaflets do not
close completely, however, allowing some backflow to occur.
Other Bileaflet valves
St. Jude Medical
Sorin
EdwardsDuromedics
Carbomedics
Why did I tell you this story?

The engineering design process
 it involves iteration

Biomechanics
 Fluid mechanics
 Mechanics of materials

Materials
 Blood
compatibility
 Fatigue resistance



Creativity
FDA considerations
Ethics
Resources
http://www.me.utexas.edu/~uer/heartvalves/index.html
http://members.evansville.net/ict/prostheticvalveimagegallery.htm