Transcript Mechanical Prosthesis - Mike Poullis

Mechanical Prosthesis
By Michael Shackcloth
History
• Hufnagel – began experiments on ball valves in
1946
• 1952 valve inserted into descending aorta
Hufgnal’s Results
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Operated on 80 patients
Hospital mortality – 20%
10% of survivors suffered thrombosis or embolism
Many survivors dramatically improved
– Regurgitation reduced by 70%
• Above all demonstrated foreign material could be
placed in the bloodstream
• Metal ball replaced by a silicone covered ball to
reduce loud click
History
• 1952 – Bailey experimented with plastic flaps and
balls
• 1950’s Murray experimented by bypassing the
valve with a homograft
• 1955 Murray inserted a homograft successfully
into the descending aorta of a 22 yr old man
• 1959 Hufgnal developed a single cusp valve
– Cusp made of dacron cloth impregnated with silicone
rubber
– Reported use in 150 patients in 1961
– Experience showed him patients did better when 3
cusps sewn together
Valves Developed at the National Heart
Institute of Japan in the 1950’s
Mitral Valve Replacement
• Braunwald & Morrow developed a prosthesis made of
polyurethane reinforced with dacron fabric. Besides to
leaflets it had tails which passed through the ventricular
wall and were secured to imitate chordae
• 1st clinical placement 10th March 1960
Aortic Valve Replacement
• March 1960 Harken inserted ball and cage valve
in aortic annulus. Prosthesis consisted of a
stainless steel cage containing a lucite ball and a
sewing ring backed with teflon
Albert Starr and M Lowell Edwards
Aortic Valve Prosthesis
• August 1960 inserted aortic valve
• One piece stainless steel cage, silastic ball and teflon
sewing ring
• Edwards conceived idea from an 1858 wine bottle stopper
Aortic Model 1260
• Various changes in design and manufacturing
technique led to this model becoming commercially
available in 1966
Starr Edwards Valve
• Since mid 1970’s sewing ring made of teflon and
polypropylene
• Mid 1980’s silicone ball was used
• Time has showed that this is an excellent valve
withvery good long-term results
Developments in Mechanical Valve
Technology
• 1962 Barnard and Goosens developed the lenticular mitral
valve and biconical aortic valve
• Made of stainless steel and silicone rubber (replaced later
with polypropylene
• Successfully implanted but soon replaced by valve with
better flow characteristics
Gott and Daggart 1963
• Polyvinyl fluoride with lexan
ring coated with colloid
graphite
• Withdrawn early. Stasis distal
to and between leaflets led to
embolic problems
• Structural failure
Other Mechanical Valves Of This Era
• 1964 Harry Cromie – impregnated Barium
sulphate to make the valve radiopaque
• 1964 Smeloff-Cutter ball valve allowed some
regurgitation theoretically to wash the ball and
prevent thrombosis
Origin of Disc Valves
• 1965 Cross and Jones developed a valve with a lens
shaped disc of silicone rubber in a low profile cage with a
woven teflon fixation flange. The disc was reinforced
with a titanium ring
• First human implant January 1965
Lillehei Valves
• 1966 Lillehei-Nakib - free floating titanium disc
• 1967 Lillehei-Kaster - pivoting disc valve
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Opened to 80 degrees
Machined from a single block of titanium
Greatly improved central flow
Rotatable sewing cuff
6500 inserted between 1971 and 1990
Event free survival at 13 years was70% for aortic
• 1968 Kalke-Lillehei - bileaflet valve
– Good haemodynamics
– Leaflets opened to 60 degrees
– Forerunner to St Jude prosthesis
Further Developments
• 1967 DeBakey used pyrolytic carbon
making the valve relatively thrombogenic
• Due to advances in manufacturing
techniques valves were fairly durable by the
mid 1970’s. however there was room for
haemodynamic improvement
Second Generation Mechanical Valves
• 1960’s Jura Wada developed concept of the pivoting disc
– Manufactured by Cutter laboratories, USA
– Titanium housing
– Teflon cloth sewing ring
– Hard teflon disc
• Bjork found that fibrin deposition occurred in the hinge
mechanism leading to failure
• Developed a new valve withShiley
• Inlet strut was part of the orifice ring but the outlet strut
was welded in place
• Problems with outlet strut fractures led to the
development of the monostrut valve
This episode led to much tighter regulatory rules with
regards valve development
The St Jude Valve
• Nicoloff and the engineer Possis had
developed a crude bileaflet valve
• Approached Villafana, a founder of Cardiac
Pacemakers Incorporated
• Rejected by board of directors so he set up
St Jude Medical Incorporated
Bileaflet Design
• Proposed independantly by Gott, Lillehei and Wada
• Pyrolytic hydrocarbon introduced by Jack Bokros
• This resolved the question of thrombogeicity and durability
of the pivots
• Valve first implanted in 1977
Ideal valve
• Function free of mechanical failure for the
life span of the patient
• Should not increase the work of the heart
• Should not cause cellular damage to the
constituents of the blood
• Should not activate the clotting cascade
Three Types Commercially Available;
1. Caged Ball
Three Types Commercially Available;
1. Caged Ball
2. Bileaflet
Three Types Commercially Available;
1. Caged Ball
2. Bileaflet
3. Monoleaflet
Valve Constituents
• Sewing ring
• Occluder mechanism
• Occluder
Haemodynamics
Ball Valve
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Minimal leakage
Annular area for flow creates turbulence
High profile may occlude VOT
Cage may contact ventricular
wall during contraction
• Partial obstruction by the
ball in aortic position
Tilting Disc Prosthesis
• Less obstruction to blood flow
• Gradients of 6-7 mmHg
• Opening angle
– High; low gradients, increased regurgitation
– Small; High gradients; less regurgitation
Bileaflet Prosthesis
• Lowest gradient due to wide opening angle
• Minimal turbulence due to
– Wide opening angle
– Thin leaflets
– Large cross-sectional area
Advances in materials
• Pyrolite carbon leaflets
• Titanium or pyrolite housings
• Tungsten to radiopacify leaflets
Advances in Design
• Retrograde washing reduces blood stasis
and prevents thrombus formation
• Monoleaflet prosthesis have crossing bars
or central guides to prevent leaflet travel
• Bileaflet prosthesis have pivot recesses in
the orifice to prevent leaflet travel
Problems With Mechanical Valves
• Thromboembolism
• Haemorrhage
• Endocarditis
• Periprosthetic leak
• Structural valve degeneration
• Nonstructural valve dysfunction
Thromboembolism
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Defined as valve thrombosis or embolus
Valve thrombus may be occlusive or non-occlusive
Occlusive usually catastrophic
High risk in first 14 months
Then 0.5% per patient year
Majority occurs when anti-co-aggulation is disrupted
Thrombogenicity of a valve depends on;
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Valve design
Surface area and texture
Turbulence
Stagnent areas
Haemorrhage
• Defined as any episode of bleeding that causes
death, stroke, requires operation or blood transfusion
• Related to levels of anti-coaggulation
• Incidence of anti-coaggulation related death is 0.2%
per patient year
Endocarditis
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Any infection involving a prosthetic valve
Mortality ranges from 23-69%
Most frequently occurs in first few months
Late incidence 0.17% per patient year
Most common site at annular tissue
interface
• Early aggressive surgery is usually required
Periprosthetic Leak
• Leakage of blood between sewing ring and
host tissue
• Incidence 1%
• Aetiological factors
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Annular calcification
Infection
Annuloprosthetic mismatch
Excessive tension on sutures, annulus or both
Suture misplacement
Inadequate fibrous ingrowth
Abnormal annular tissue
Structural Valve Degeneration
• Mainly due to leaflet fracture
• Cracks in pivot guard reported
• If occurs in the intraoperative or early
postoperative period then it is probably due
do mishandling of the valve
Nonstructural Valve Dysfunction
• Defined as any abnormality that lead to
stenosis or regurgitation at the valve that is
not intrinsic to the valve
• Incidence 0.3% per patient year
• Causes
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Sterile or infected thrombus
Pannus formation
Retained strands of chordal tissue
Excessively long sutures
Annular calcification nodules
Mechanical Prostheses in the
Aortic Position
St Jude Medical
• Pyrolytic carbon over
graphite substrate for
housing and leaflets
• Leaflets impregnated with
tungsten for radiopacity
• Leaflets open to 85o
resulting in near central
laminar flow
• 10% regurgitant flow
• Leaflet motion by rotation
Carbomedics Prosthesis
• Solid pyrolite housing
• Pyrolite coated leaflets
over tungsten impregnated
carbon
• Radiopaque titanium
stiffened ring
• Opening angle of 78o
• Leaflets can be rotated in
the orifice
Edwards MIRA Prosthesis
• Bileaflet prosthesis
• Pyrolite coated leaflets
over tungsten
impregnated carbon
• Curved leaflets
enhance central flow
and leaflet closure
• Retrograde washing
by relative high
frequency jets
• Closes by rotation and
translation
Biocarbon Prosthesis
• Sorin Biomedica
• Titanium housing covered by
pyrolite carbon strengthens
prosthesis
• Curved leaflets
• Two effluent passages provide
continuous washing even in the
closed position
• Orifice divided into three
sections
• Sewing ring dacron and carbon
coated teflon
• Hinge mechanism supports a
rolling motion
ATS Medical
• Pyrolyte housing and
pyrolite carbon leaflets
with graphite substrate
• Convex housing with
protrusions on the inner
aspect that support the
leaflets therefore no
protruding struts
• Convex hinge mechanism
facilitate retrograde
washing
• Opening angle of 85o
Bjork-Shiley Monostrut
• Monoleaflet prosthesis
• Orifice ring and integral
struts are constructed from
a single piece of cobaltchromium alloy
• Opening angle of 70o
• Relatively low velocity
retrograde washing
between leaflet and orifice
• Leaflet motion is by
rotation and translation
Sorin Allcarbon Monoleaflet
• Chromium alloy
housing coated with a
thin film of carbon
• Pyrolytic carbon
monoleaflet
• Strut mechanism
integral with housing
• Sewing ring carbon
coated
Medtronic Hall Prosthesis
• Monoleaflet
• Central guide for leaflet
travel
• Housing and central
guide made of titanium
• Opening angle of 70-75o
• Leaflet motion is by
translation and rotation
Omnicarbon Prosthesis
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Monoleaflet prosthesis
Titanium orifice ring
Pyrolite carbon disc
Disc motion controlled by short struts
Opening angle 80o