Mechanical Prosthesis - PowerPoint PPT Presentation

1 / 54
About This Presentation
Title:

Mechanical Prosthesis

Description:

Mechanical Prosthesis By Michael Shackcloth History Hufnagel began experiments on ball valves in 1946 1952 valve inserted into descending aorta Hufgnal s ... – PowerPoint PPT presentation

Number of Views:205
Avg rating:3.0/5.0
Slides: 55
Provided by: mpoullisN4
Category:

less

Transcript and Presenter's Notes

Title: Mechanical Prosthesis


1
Mechanical Prosthesis
  • By Michael Shackcloth

2
History
  • Hufnagel began experiments on ball valves in
    1946
  • 1952 valve inserted into descending aorta

3
Hufgnals Results
  • 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

4
History
  • 1952 Bailey experimented with plastic flaps and
    balls
  • 1950s 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

5
Valves Developed at the National Heart Institute
of Japan in the 1950s
6
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

7
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

8
Albert Starr and M Lowell Edwards
9
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

10
Aortic Model 1260
  • Various changes in design and manufacturing
    technique led to this model becoming commercially
    available in 1966

11
Starr Edwards Valve
  • Since mid 1970s sewing ring made of teflon and
    polypropylene
  • Mid 1980s silicone ball was used
  • Time has showed that this is an excellent valve
    withvery good long-term results

12
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

13
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

14
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

15
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

16
Lillehei Valves
  • 1966 Lillehei-Nakib - free floating titanium
    disc
  • 1967 Lillehei-Kaster - pivoting disc valve
  • 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

17
(No Transcript)
18
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 1970s.
    however there was room for haemodynamic
    improvement

19
Second Generation Mechanical Valves
  • 1960s Jura Wada developed concept of the
    pivoting disc
  • Manufactured by Cutter laboratories, USA
  • Titanium housing
  • Teflon cloth sewing ring
  • Hard teflon disc

20
  • 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

21
This episode led to much tighter regulatory rules
with regards valve development
22
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

23
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

24
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

25
Three Types Commercially Available
  • Caged Ball

26
(No Transcript)
27
Three Types Commercially Available
  • Caged Ball
  • Bileaflet

28
(No Transcript)
29
Three Types Commercially Available
  • Caged Ball
  • Bileaflet
  • Monoleaflet

30
(No Transcript)
31
Valve Constituents
  • Sewing ring
  • Occluder mechanism
  • Occluder

32
Haemodynamics
33
Ball Valve
  • 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

34
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

35
Bileaflet Prosthesis
  • Lowest gradient due to wide opening angle
  • Minimal turbulence due to
  • Wide opening angle
  • Thin leaflets
  • Large cross-sectional area

36
Advances in materials
  • Pyrolite carbon leaflets
  • Titanium or pyrolite housings
  • Tungsten to radiopacify leaflets

37
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

38
Problems With Mechanical Valves
  • Thromboembolism
  • Haemorrhage
  • Endocarditis
  • Periprosthetic leak
  • Structural valve degeneration
  • Nonstructural valve dysfunction

39
Thromboembolism
  • 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
  • Valve design
  • Surface area and texture
  • Turbulence
  • Stagnent areas

40
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

41
Endocarditis
  • 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

42
Periprosthetic Leak
  • Leakage of blood between sewing ring and host
    tissue
  • Incidence 1
  • Aetiological factors
  • Annular calcification
  • Infection
  • Annuloprosthetic mismatch
  • Excessive tension on sutures, annulus or both
  • Suture misplacement
  • Inadequate fibrous ingrowth
  • Abnormal annular tissue

43
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

44
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
  • Sterile or infected thrombus
  • Pannus formation
  • Retained strands of chordal tissue
  • Excessively long sutures
  • Annular calcification nodules

45
Mechanical Prostheses in the Aortic Position
46
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

47
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

48
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

49
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

50
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

51
Bjork-Shiley Monostrut
  • Monoleaflet prosthesis
  • Orifice ring and integral struts are constructed
    from a single piece of cobalt-chromium alloy
  • Opening angle of 70o
  • Relatively low velocity retrograde washing
    between leaflet and orifice
  • Leaflet motion is by rotation and translation

52
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

53
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

54
Omnicarbon Prosthesis
  • Monoleaflet prosthesis
  • Titanium orifice ring
  • Pyrolite carbon disc
  • Disc motion controlled by short struts
  • Opening angle 80o
Write a Comment
User Comments (0)
About PowerShow.com