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
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Withdrawn early.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
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