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Gérard Finet MD PhD Department of Cardiology and Interven:onal Cardiology Cardiovascular Hospital -‐ Hospices Civils de Lyon INSERM Unit 1086 CARMEN Claude Bernard University Lyon 1 Lyon -‐ France
EBC 2011 – Lisbon, Portugal
LeF main atheroma: Insight into mechanical proper:es of plaque
Choy & Kassab. J Appl Physiol 2008
Scaling of myocardial mass to flow and morphometry of coronary arteries
Q0 = Q1 + Q2 Law of conserva:on of mass D0
3 = D13 + D2
3 Murray’s law
D0 = 0.678 x (D1 + D2) Linear law
Murray CD. Proc. Natl Acad. Sci. USA, 1926 Zamir M. J Theor Biology 2001
Kassab GS et al. AJP 2005 Finet G et al. EuroIntervention 2007
Distribu:ve func:on of coronary bifurca:on
Mechanical objec:ve of PCI
Reference Lumen CSA
Stenosis MLA
2D finite element analysis of stent implanta<on
Mechanism of coronary lumen enlargement
1-‐ Vessel expansion 2-‐ Axial plaque redistribu:on 3-‐ Plaque reduc:on
Lee et al. JACC 1993 Bap<sta et al. EHJ 1995
Ahmed, Mintz, et al. Circula<on 2000 Finet, Weissman, Mintz et al. Heart 2002
Mechanism of Lumen enlargement
60%
40%
Radial strain maps during stent implanta<on
Mechanical proper:es of coronary plaque
Radial displacement during sten<ng Effec<ve stress distribu<on during sten<ng
Plaque cons:tuents are:
Incompressible (Poisson’s modulus -‐ ν) Anisotropic Hyperelas=c (Young’s modulus -‐ E) Heterogeneous
Emedia = 150 kPa Ecore = 1 to 20 kPa Ehypocellular fibrosis = 500 kPa Edense fibrosis = 1000 -‐ 3000 kPa Ecalcifica=on ≥ 5000 kPa
NB : 1 bar = 100 kPa = 750 mmHg
STRAIN STRESS
Spa:al Intraplaque circumferen:al stress distribu:on
Plaque s:ffness = 1200 kPa Plaque s:ffness = 600 kPa
> 300 kPa > 300 kPa
PCS PCS PCS PCS
PCS = 550 kPa PCS = 950 kPa
STRESS (kPa) STRESS (kPa)
Lendon et al. Atherosclerosis 1991 Cheng et al. Circula<on 1993
Holzapfel et al. AJP 2005
Water displacement and arterial wall porosity
Kaltenbach et al. Cathet Cardiovasc Diagn. 1984 ; 1:213-‐219.
Summary of the mechanical impacts of stent implanta:on
Radial force exerted by the balloon on the stent and the coronary plaque Op:mal stent strain for an op:mal lumen diameter or CSA (Murray’s law) With consequently an increase in effec:ve stress distribu:on in ATS plaque The stent keeps this elevated stress state stable This stress state induces signal transduc[on in the arterial wall (mechanobiology or mechanotransduc:on)
Hoffman et al. Nature 2011;475:316-‐323.
In vivo assessment to mechanical proper:es of coronary plaque
Gray-‐scale IVUS
OCT
VH®
Ruptured plaque !cross-sections!
Adjacent non-ruptured plaque cross-sections!
IVUS imaging! IVUS imaging!Finite element meshes! Circumferential stress maps!CTH = 160 µm
CTH = 56 µm
Ohayon et al. Coronary Artery Disease 2001;12:655-‐663. Finet et al. Coronary Artery Disease 2004;15:13-‐20
Biomechanical plaque instability is a consequence of plaque excentricity, plaque composi=on, plaque heterogeneity
411 kPa
368 kPa
Fung YC. Biomechanics Springer 1997. Ohayon J et al. Am J Physiol Heart Circ Physiol 2007;293(3);H1987-‐1996.
Computerized simula:on and closing condi:ons
Artery
Fibrosis Lipid
By neglec[ng the residual stress/strain we overes[mate the peak cap strain/stress, but this peak occurs always at the same loca:on
P=14 kPa
390 kPa
Residual Von-Mises stress (kPa)
P=0 kPa
534 kPa
Quasi-‐UNIFORM distribu[ons
HETEROGENEOUS distribu[ons
Without LV mo:on
With LV mo:on
A
B
LM
LAD
LCx
LM
LAD
LCx
>300 165 30
WALL STIFFNESS
(kPa)
Influence of heart mo:on
Dynamic MRI tagging technique Torsion – Radial strain – Axial strain
Ohayon et al. Am J Physiol Heart Circ Physiol 2011
0
150
300
450
600
750
900
10 20 30 40 50
Luminal wall stretch (%)
Lum
inal
wal
l stif
fnes
s (k
Pa)
Elastic behavior of Arterial wall
300 kPa
Lesion sites
800 kPa A
Correla=on between plaque loca=on and wall s=ffness
ESS and Wall S:ffness Poten<al combina<on for predic<ng the risk of atherosclerosis
Mintz et al. Circula<on 2003;107:2660-‐2663.
Virmani et al. Circula<on 2004;109:701-‐705.
Regional remodeling as a cause of late stent malapposi:on Mechanical explana=ons
E:400 kPa!
Young’s modulus E : 400 kPa to 100 kPa
Constant pressure = 100 mmHg
(Finet G. unpublished data)
Conclusions
A biomechanical approach to atherosclero[c plaque and PCI is mandatory to improve our knowledge and our way of thinking, but does not necessarily makes things more comprehensible, but rather o_en adds novel complexi[es Computerized simula[on is a very useful tool for that These simula[ons require in vivo assessment of plaque geometry and precise elas[city maps. Grayscale IVUS or VH offer this geometrical assessment but without accuracy for detec[ng Young’s moduli. IVUS with Modulography could probably provide these data.
Le Floc’h et al. IEEE Medical Imaging 2008 -‐ Le Floc’h et al. Phys Med Biol 2010
FRANCE Jacques Ohayon, PhD Gilles Rioufol, MD, PhD USA Roderic I. Peggrew, MD, PhD Ahmed M. Gharib, MD Julie Heroux, MSc CANADA Guy Clou:er, PhD Jérémie Fromageau, PhD Roch Maurice, PhD SPAIN Manuel Doblare, PhD Miguel-‐Angel Mar:nez, PhD Mauro Malves, PhD Alberto Garcia, PhD Std