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BIOLOGICAL HEART VALVES

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BIOLOGICAL HEART VALVES Mr. S. V. GHOTKAR HISTORICAL ASPECT 1952- The first artificial heart valve to be implanted in humans was a mechanical one implanted by ... – PowerPoint PPT presentation

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Title: BIOLOGICAL HEART VALVES


1
BIOLOGICAL HEART VALVES
  • Mr. S. V. GHOTKAR

2
HISTORICAL ASPECT
  • 1952- The first artificial heart valve to be
    implanted in humans was a mechanical one
    implanted by Hufnagel his attempts heralded the
    era of cardiac valve prostheses.
  • 1955- While most workers were working on
    mechanical devices, it was Murray, who considered
    replacing a diseased valve with a valve taken
    from a donor animal. Encouraged by results of his
    experiments with dogs he implanted a valve
    harvested from a human cadaver into descending
    thoracic aorta of a 22 Yr. man who had severe AR.
    This man was a manual worker was asymptomatic
    when seen 6 Yrs later

3
1956- By this time pump oxygenater became
available Lillehei performed the first aortic
valvotomy repair using retrograde coronary
sinus perfusion.These early operations by
Hufnagel, Murray Lillehei had a great
significance as they showed that body can
tolerate natural mechanical prostheses as well
as native valves were amenable to repair. Here
began the competition between these three
modalities of treatment.
4
DEVELOPMENT OF AORTIC HOMOGRAFTS
  • Subsequently as most researchers were working on
    mechanical prostheses Murrays group in Toronto
    persisted with notion of aortic homograft
    substitution in orthotopic position.

5
  • In 1962 Alfred Gunning co-workers in Oxford
    worked out a reliable method for aortic homograft
    harvest preparation.

6
Knowledge of Gunnings work allowed Ross to
perform the first landmark sub-coronary homograft
implantation in 1962.This success was soon
followed by Barrat-Boyce in New Zealand, Mattias
Paneth Mark OBrien at Brompton
hospital.These were the people who adopted
pioneered homograft aortic replacement at a time
when most surgeons preferred the durability
simplicity of Starr Edward valve insertion with a
single row of sutures.The homograft insertion
was technically more demanding in an era when
myocardial preservation was primitive.
7
To simplify homograft implantation Weldon from
John Hopkins hospital published results of
laboratory experiments with aortic homograft
mounted on a frame.Angell adopted stent mounted
homografts for aortic, mitral tricuspid
replacement. Stent mounting increased easiness of
implantation significantly decreased incidence
of early post operative regurgitation in
comparison to free hand sewn homografts. However,
medium term results showed limited durability of
stent mounted homograft tissue. The stent thus
caused accelerated tissue failure.
8
  • Ross flexible homograft support

9
  • Shumway- Angell Cutter graft support

10
DEVELOPMENT OF PERICARDIAL PROSTHESES
  • Availability of human cadaveric material was
    always limited led to search for alternative
    materials.
  • In Zurich Senning used autologus fascia lata to
    construct a trileaflet valve, but this turned out
    to be disappointing.

11
  • Marion Ionescu in Leeds mounted heteregounus
    pericardium on a frame with a sewing ring

12
DEVELOPMENT OF PORCINE BIOPROSTHESIS
  • In 1964 after their succes with homografts,
    Gunning Duran diverted their attention to
    preservation of heteregenous valves.
  • In the same year they performed first human
    stent mounted porcine valve implantation.

13
In 1965 Duran Carpentier presented their
experience of mercurochrome preserved frame
mounted heterografts. This was soon followed by
reports by Mark OBrien about his experience with
formalin preserved pig calf aortic
heterografts. However, long term results were
poor because of primitive preservation methods.
14
  • In 1966 Ionescu developed a stent for mounting
    aortic heterograts.
  • It had Titanium support, 3 legs covered with
    dacron velour dacron felt ring was used as a
    sewing ring. The porcine aortic valve was sutured
    within the frame.

15
Carpentier next produced a stent made of
stainless steel coated with Teflon to minimise
thromboembolism he used mercurial salt for
tissue preservation. This stent is the precursor
of stent used in modern Carpentier- Edward
valveWithin 5 yrs of use of stented valves it
was realised that stent mounting caused excessive
stress on the biological tissue which resulted in
accelerated degeneration. This setback caused
practice of stent mounting to disappear.
16
  • 1968 -Preservation of tissues with formaldehyde
    or mercurochrome was proving disappointing, this
    problem was soon resolved by Carpentier who
    employed gluteraldehyde preservation for the
    first time.
  • The chemical treatment of tissues prevents
    collagen denaturation reduces antegenicity of
    foreign tissues.

17
Carpentier considered the stent mounted,
chemically treated porcine xenograft as a hybrid
of biological mechanical structures hence
named them as Bioprostheses.Central laminar
flow was a remarkable positive aspect of these
bioprostheses but still presence of the stent was
partly obstructive.With efforts of Carpentier,
Hancock Angell gluteraldehyde preserved,
stented porcine valves became commercially
available were soon in great demand
18
DEVELOMPENT OF PULMONARY AUTOGRAFTS
  • In 1967 Ross performed the first pulmonary
    autograft operation for aortic valve replacement.
    Initially autogenous pulmonary valve was used as
    a sub- coronary implant later as a full aortic
    root replacement.
  • Ross anticipated that autologus pulmonary valve
    will remain viable maintain potential for
    growth in children. Experience have shown this to
    be true.

19
Whilst Ross persisted with his operation others
were reluctant to perform a complex double root
replacement for isolated aortic disease which
otherwise could be treated with very low
morbidity mortality with a stented valve.
20
DEVELOPMENTS IN REPLACEMENT OF MITRAL VALVE
  • Ross then attempted to replace mitral valve with
    a mitral homograft. Though early post-operative
    hemodynamics were excellent, most patients
    sustained rupture of chordae tendeniae within a
    few months of operation. In addition proper
    placement of papillary muscles inside LV required
    considerable judgment skills. Because of these
    reasons MV homografts replacement has never
    regained wide spread acceptance.

21
RESSURECTION OF STENTLESS VALVES
  • It was being increasingly realised that presence
    of stent is a disadvantage as it accelerates
    tissue degeneration. It also tends to obstruct
    the flow through the valve albeit to much lesser
    extent than mechanical valves.

22
  • In 1988 Tyrone David re-explored the use of
    stentless gluteraldehyde fixed aortic xenograft.
  • Hemodynamic evaluation showed very small
    gradients minimal regurgitation in early
    implants.

23
David then went on to develop a low pressure
fixed stentless, cloth covered porcine valve.
This device is now known as Toronto SPVmarketed
by SJM Inc. This device lacks sewing ring this
allows insertion of a larger valve in individual
annulus. This valve provided an alternative to
aortic homografts which are always in limited
supply inspite of development of cryopreservation
techniques.
24
St. Jude Toronto SPV
25
Along the same lines Medtronic Inc. introduced
their stentless Freestyle valve in the form of
porcine aortic root with Dacron covering of
inflow portion. This is a gluteraldehyde
preserved, zero pressure fixed valve treated with
alpha-amino- oleic acid which acts as a
anti-mineralising agent.
26
Medtronic Freestyle Stentless Valve
27
SPECTRUM OF BIOLOGICAL VALVES AVAILABLE FOR
CLINICAL USE TODAY
  • Stented porcine valves e.g. C. E., Hancock
  • Stentless porcine valves e.g. Toronto SPV
  • Pericardial xenografts
  • Aortic or pulmonary allografts
  • Pulmonary autografts

28
STENTED PROSTHESES
  • Stents used in modern valves are made-up of
    Elgiloy, Delrin, Acetylco-polymer resin.
  • Advantages of a stent-
  • Stent provides framework for supporting the
    leaflets, it also makes implantation easier as
    compared to valves without a stent.

29
Disadvantages of the stent
  • They increase stress on leaflets causing
    accelerated degeneration.
  • They are obstructive to flow hence increase the
    gradients across the valve.
  • In mitral position they can cause LVOT
    obstruction or even rupture of LV especially when
    a large valve is used in presence of small LV
    cavity.

30
Comparison between orifice area in stented and
stentless valves
  • Stentless Stented

31
PRESERVATION/ FIXATION OF TISSUES IN BIOLOGICAL
VALVES
  • Currently gluteraldehyde is the preferred agent.
  • It cross links the collagen increases the
    strength of tissues
  • It also acts as a sterilizing agent.
  • Preservation with gluteraldehyde can be done at
    High pressure ( 60 - 80 mm Hg) Low pressure
    ( Less than 2 mm Hg ) No pressure ( 0 mm Hg
    )

32
Modern prostheses are fixed with either low
pressure or zero pressure, this is believed to
maintain collagen crimp frame work which will in
turn maintain physical properties of biological
tissues.
33
ANTI-MINERALIZATION TRATMENT
  • Dystrophic calcification is an important factor
    which contributes to delayed failure of
    biological valves. This problem is more severe in
    patients who are young or who have chronic renal
    failure.
  • Pathogenesis of bioprosthetic calcification is
    incompletely understood.
  • Calcification occurs initially in areas of
    maximal mechanical stress e.g. commissures. But
    there are both host related bioprosthesis
    related factors.

34
Gluteraldehyde in itself is a promoter of
calcification as it can chelate calcium.There
are various agents which are currently being used
as decalcification agents v.i.z. Alpha- oleic
acid, Polysorbate 80, Sodium decadecyl sulphate,
Toludin blue etc.Cells cellular antigens are
also believed to promote calcification. They can
be removed by enzymatic detergents leaving only
acellular matrix. This process is presently used
in SJM-X-CELL investigational prosthesis.
35
CURRENT RESEARCH IN BIOPROSTHETIC PRESERVATION
  • Use of gluteraldehyde can be detrimental. There
    is extensive research going on to find an
    alternative.
  • Epoxy compound Denacol has been found to be
    useful, however high concentrations can be
    cytotoxic.
  • Diphosphonates, acyclazide, carbodimide are other
    agents are under investigation.
  • Photo-oxidation of bioprostheses promotes
    collagen cross linking is being experimented.
  • Seeding of viable endothelial cell on biological
    tissues with the aim of endothelization of
    bioprosthesis is also under investigation.

36
PROCESSING OF ALLOGRAFTS
  • Presently three types of allografts are
    available
  • Cryopreserved
  • Antibiotic preserved- with cryopreservation they
    are obsolete now.
  • Fresh allografts- They are available increasingly
    due to increased no. of heart transplants.

37
ALLOGRAFT PROCURMENT
  • Nondiseased valves are removed from hearts of
    heart transplant recipients ( Age 6month- 55
    years).
  • Sterile technique is observed during harvesting.
  • Ascending aorta with aortic valve in situ is
    removed, origin of innominate artery marks the
    distal extension LV base with AML marks the
    proximal extent of the block.

38
Harvesred Aortic Allograft Block
39
  • Harvested sterile graft is then preserved in
    culture medium ( RPMI 1640) Antibiotics e.g.
    Lincomycin Cefoxitin Vanco polymixin B
  • Stored at 4 C
  • This graft can then be used directly as a
    homovital graft or can be cryopreserved (- 40
    C) for future use.

40
  • During allograft preservation viability of
    cellular mechanical components is very
    important.
  • Fresh allografts do have clearly viable cells (
    endothelial fibroblasts ) at the time of
    implantation.
  • However, preservation of cellular viability has
    disadvantage of inducing immunological response

41
HEMODYNAMICS OF BIOPROSTHETIC VALVE
  • Bioprostheses have superior hemodynamic
    performance as compared to any mechanical
    prosthesis currently available.
  • Central laminar flow is the the biggest
    advantage, this minimizes turbulence also
    decreases gradients.However, presence of stent
    does impede flow.
  • The hemodynamic performance of free hand
    allograft is excellent is more or less similar
    to native valve.

42
MECHANICAL Vs TISSUE VALVES
  • OVER THE PAST 20 YEARS MECHANICAL TISSUE VALVES
    HAVE CONTINUED TO IMPROVE THOUGH DEBATE OVER
    THEIR RELATIVE MERITS CONTINUES.

43
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44
INDICATIONS FOR USE OF BIOLOGICAL VALVES
  • Biological valves are preferred when -
  • There is contraindication to use of
    anticoagulation
  • Women in reproductive age group who wish to
    conceive
  • Patients over 65 year of age

45
  • STS database reveals that -
  • Mechanical valves were used in 56-62,
  • Xenograft in 32-38
  • Allograft or autografts in 6

46
  • For AVR, generally
  • 65 yrs above Bioprosthesis preferred
  • 40 65yrs - Mechanical or allografts
  • 16 65yrs Mechanical, allografts or
    autografts
  • Paediatric group Mechanical or autograft

47
  • Stentless porcine bioprostheses are currently
    recommended for elderly with small annuli.
  • It is also proposed as an alternative to
    allografts.
  • Limited supply of allografts restricts its use
    to selected patients, particularly those with
    native valve or prosthetic valve endocarditis
    complicated by annular abscess or ventriculo-
    aortic discontinuity.
  • They are also preferred in young middle
    aged patients.

48
CONTRAINDICATIONS TO BIOLOGICAL PROSTHESES
  • Mechanical valves are preferred than biological
    in patients who have
  • - Hypercalcemic syndrome
  • -CRF
  • Bioprostheses are usually avoided in young
    patients as degeneration calcification occurs
    early.

49
CLINICAL PERFORMANCE OF BIOLOGICAL VALVES
  • Clinical performance of a valvular prosthesis is
    judged according to the Guidelines for
    reporting morbidity after cardiac valvular
    operations
  • ( Edmunds etal, ATS, 1988)
  • Literature provides extensive documentation of
    individual prostheses, combination of prostheses
    comparisons between mechanical biological
    prostheses. Only few randomised studies are
    available which include Veterans Administrative
    trial (VA) study on valvular heart disease
    Edinburgh heart valve trial.

50
PERFORMANCE OF STENTED XENOGRAFT PROSTHESES
  • Current C-E pericardial prosthesis- Pellerin
    co-authors in 64 yr old population report 10 yr
    freedom of structural failure of 93.5. At 12
    yrs no patient had reoperation for structural
    failure.
  • Cosgrove co-authors have come out with
    similar results.

51
CLINICAL PERFORMANCE OF ALLOGRAFTS
  • There are no randomised trials comparing
    allografts to mechanical or bioprosthetic valves.
  • Thromboembolism essentially does not occur
    with allografts.
  • The method of allograft preservation
    determines the rate of structural valve
    degeneration.
  • OBrien reports 91 freedom from structural
    at 12 yrs for patients between 20-60 yrs.

52
CLINICAL PERFORMANCE OF AUTOGRAFTS
  • Ross has reported 85 freedom from reoperation
    at 20 yrs for his procedure of pulmonary
    autograft for aortic root replacement.
  • Elkins report that pulmonary autografts in
    children grow with somatic growth.
  • The complexity of this operation related
    morbidity mortality affect the eventual place
    of this operation for aortic valve replacement
    surgery.

53
PERFORMANCE OFBIOPROSTHESES IN MITRAL POSITION
  • Jamieson etal have reported that durability of
    bioprostheses is less in mitral position than in
    aortic position.
  • This more rapid deterioration may be due to
    higher pressure sustained by cusps during
    ventricular systole than pressure sustained
    during diastole.

54
  • THANK YOU
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