1. VASCULAR STENTSVASCULAR STENTSOrtal LeviOrtal Levi
2. What is a Stent? A small tubular mesh usually made ofeither
stainless steel or Nitinol. Inserted into stenotic arteries to keep
thelumen patent often used after PTCA. Used at various sites
including thecoronary, renal, carotid and femoralarteries.
Non-arterial uses e.g. in bronchus,trachea, ureter, bile duct.
3. Current stent designsPalmaz, the market leader
4. Palmaz Corinthian Iliacartery stentGianturco-Roubin II
Stent
5. HistoryThe concept of vascular stents isaccredited to
Charles Dotter in 1969, whoimplanted stainless steel coils in
canineperipheral arteries.Not followed up in humans because
ofhaemodynamically significant narrowing.Not in clinical practice
until 1980s.Market leader is the Palmaz stentdesigned by Julio
Palmaz in 1985.Initially, 18 grafts placed in canine vessels,
withpatency rates approaching 80% at 35 weeks.
6. Motivation for development-Blood Thrombosis A formation of
blood clot inside a bloodvessel, obstructing the flow of blood.
Likely to lead to cardiac infraction, may resultin death.
7. Thrombus in Human Coronary Artery
8. Smoking, high BP, toxins etc cause damage to thevascular
endothelium.LDL and fibrin pass through and collect in the
sub-endothelium.Monocytes adhere to the damaged endothelium,migrate
to the sub-endothelial space and engulfLDL FOAM CELLS.SMC migration
and CT formation.Two main types of plaque:Atheromatous (athere:
gruel, oma: tumour(Fibrous (like atheroma but with connective
tissue cap(
9. CVD statisticsHeart and circulatory diseaseis the UKsbiggest
killer.In 2001, cardiovascular disease caused40% of deaths in the
UK, and killed over245,000 people.Coronary heart disease causes
over120,000 deaths a year in the UK:approximately one in four
deaths in menand one in six deaths in women.
12. PTCAMinimally invasive procedurePercutaneous access either
in the brachial orfemoral arteries.A guide wire is advanced to the
stenoticregion.A balloon is advanced along the wire
andinflated/deflated several times to fracture theplaque and open
the lumen.
13. Angioplasty and other coronary intervention procedures,
1991-2000, UKNumber of Tot al angioplast y and Rat e per Annual %
Success Mort alit yint ervent ion cent res ot her coronary million
increase (% ) (% )int ervent ion procedures1991 52 9,933 174 86
0.481992 52 11,575 203 16.5 88 0.711993 53 12,937 227 11.8 89
0.591994 54 14,624 256 13.0 90 0.601995 54 17,344 304 18.6 89
0.691996 53 20,511 359 18.1 90 0.721997 58 22,902 402 11.7 92
0.891998 61 24,899 437 8.7 92 0.801999 63 28,133 494 13.0 90
0.612000 66 33,652 590 20.0 92 0.70Source: British Cardiovascular
Intervention Society (2002) htpp://www.bcis.org.uk
14. Complications of PTCAPlaque rupture, may lead to:Thrombus
formationIntimal flapArterial ruptureAcute closureSub-optimal
resultRestenosisRequires further intervention to make
vesselpatent
15. Stenting vs. PTCAPrevents acute closureTacks back intimal
flapsLess restenosis:3050%restenosis with PTCA (coronary
arteries(.Coronary stents are associated with fewerrepeat
revascularisation proceduresRates of death and MI are low and
arenot significantly different between stentsand PTA.
16. Stent FailureRestenosis20-30%
17. Mechanism of Restenosisshear stressIntimal Hyperplasia
lumen shear stressIf baseline shear stress not restored
continuingintimal hyperplasia and RESTENOSIS
18. Factors Which Contribute to In-stent
RestenosisThrombus/platelet/fibrin adherence to
stentstruts.Metabolic disorder/smoking/atherogenicdiet.Small lumen
diameter.Stress concentration at end of stent.Flow disturbance
within stented region.
19. Thrombus in Human Coronary Artery
20. Previous flow studiesof Palmaz stentsPeacock et al. (1995)
used hotfilm probe distal to stent;found flow disturbance undermild
exercise conditions.Berry et al. (1997) performeddye injection flow
visualizationand found significant flowdisturbance within and
distal tostent; stagnation near struts.End systoleDiastoleFlow
22. Improving Vascular Stents (1(ThrombusAnticoagulantsHeparin
systemically or coated on stent.Inhibition of the GP IIb-IIIa
receptor:Prevents platelet aggregation.Available as
Abciximab.Associated with incidence of MI.PTFE coated stents.
24. Improving Vascular Stents (2(Small diameter
arteryCombination of local and systemic medicationand covered
stents.Intimal hyperplasiaBrachytherapy:Use of ionising radiation
to stop cellular proliferation.Delivery: Radioactive stents,
catheter radiation.10%restenosis but may cause
necrosis.Anti-proliferative agents e.g. rapamycin(Sirolimus(
25. Improving Vascular Stents (3(Mechanical and flow
disturbances:Compliance Matching Stent (CMS(This stent is rigid in
the middle and becomes morecompliant near its ends.This compliance
is achieved by parabolic andcantilevered struts.The middle struts
are straighter, providing someresistance to recoil and support for
theatherosclerotic plaque.
26. Compliance Matching StentCompliance Matching StentParabolic
and canti-levered struts causeends to be mostcompliant.Straighter
struts inmiddle provide stiffsupport for plaque.Transition in
between.
27. Compliance Matching StentThe gradual change from rigid to
compliantwith the CMS reduces stress concentration atthe stent
edges.The geometry of this stent also fosters morelaminar flow
through the stent.Less flow disturbance means less
intimalhyperplasia.
28. Compliance TestingString apparatusFinite Element
Analysis
34. Normal Stent vs. CMSNormal StentFlow disruptionDisturbed
shear stressIntimal hyperplasiaNo return to
baselineshearRESTENOSISCMSMore laminar flowLess disturbed
shearstressLess intimal hyperplasiaReturn to baseline shearPATENT
LUMEN
35. My PhD ProjectInvolves in vivo testing of the
CES.Comparison with SMART stent:Amount of intimal
hyperplasia.Effects on flow and pressure waves.Quantifying effect
of overstretch.In vivo sites carotid and iliac arteries.
36. Stents used in study
37. Pig femoral artery, overstretched by 25% and stented 1
month after procedure.