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Research Papers

Sequential Structural and Fluid Dynamic Numerical Simulations of a Stented Bifurcated Coronary Artery

[+] Author and Article Information
Stefano Morlacchi, Claudio Chiastra

Laboratory of Biological Structure Mechanics, Structural Engineering Department, Politecnico di Milano, 20133 Milan, Italy; Department of Bioengineering,  Politecnico di Milano, 20133 Milan, Italy

Dario Gastaldi, Giancarlo Pennati, Gabriele Dubini

Laboratory of Biological Structure Mechanics, Structural Engineering Department,  Politecnico di Milano, 20133 Milan, Italy

Francesco Migliavacca1

Laboratory of Biological Structure Mechanics, Structural Engineering Department,  Politecnico di Milano, 20133 Milan, Italyfrancesco.migliavacca@polimi.it

1

Corresponding author.

J Biomech Eng 133(12), 121010 (Dec 29, 2011) (11 pages) doi:10.1115/1.4005476 History: Received February 23, 2011; Revised November 21, 2011; Published December 29, 2011; Online December 29, 2011

Despite their success, stenting procedures are still associated to some clinical problems like sub-acute thrombosis and in-stent restenosis. Several clinical studies associate these phenomena to a combination of both structural and hemodynamic alterations caused by stent implantation. Recently, numerical models have been widely used in the literature to investigate stenting procedures but always from either a purely structural or fluid dynamic point of view. The aim of this work is the implementation of sequential structural and fluid dynamic numerical models to provide a better understanding of stenting procedures in coronary bifurcations. In particular, the realistic geometrical configurations obtained with structural simulations were used to create the fluid domains employed within transient fluid dynamic analyses. This sequential approach was applied to investigate the final kissing balloon (FKB) inflation during the provisional side branch technique. Mechanical stresses in the arterial wall and the stent as well as wall shear stresses along the arterial wall were examined before and after the FKB deployment. FKB provoked average mechanical stresses in the arterial wall almost 2.5 times higher with respect to those induced by inflation of the stent in the main branch only. Results also enlightened FKB benefits in terms of improved local blood flow pattern for the side branch access. As a drawback, the FKB generates a larger region of low wall shear stress. In particular, after FKB the percentage of area characterized by wall shear stresses lower than 0.5 Pa was 79.0%, while before the FKB it was 62.3%. For these reasons, a new tapered balloon dedicated to bifurcations was proposed. The inclusion of the modified balloon has reduced the mechanical stresses in the proximal arterial vessel to 40% and the low wall shear stress coverage area to 71.3%. In conclusion, these results show the relevance of the adopted sequential approach to study the wall mechanics and the hemodynamics created by stent deployment.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Geometric model of the atherosclerotic bifurcation. In the magnification area on the left, the stratification of arterial wall in the three layers (intima, media, and adventitia) is depicted. On the right, the illustration of the section corresponding to the maximal stenosis (45% of stenosis area) provoked by the presence of the two atherosclerotic plaques. (b) Example of the two different models of polymeric balloons: a standard cylindrical balloon (top) and a tapered balloon characterized by a conical proximal part and a cylindrical distal part (bottom). (c) CAD model of the Multilink Vision stent. On the left, the cross section of the device is depicted. Dimensions reported are in mm.

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Figure 2

Provisional side branch simulation steps. (a) Positioning of the crimped stent followed by the implantation in the main branch and the elastic recoil. (b) Final step called “standard FKB” inflation was performed with two cylindrical balloons in both branches. (c) “Simulation of the modified FKB” carried out by deploying a cylindrical balloon in the MB and a tapered one in the SB. (d) Deformed configurations of the stent struts in proximity of the bifurcation before (top) and after (bottom) the standard FKB, view from the access to the SB.

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Figure 3

(a) Creation of the fluid domain from the geometrical configuration obtained through structural simulations. (b) Example of a fully tetrahedral mesh (left) and a hybrid mesh (right) of the same cross section. It is possible to notice the internal cylinder meshed with only hexahedral elements and connected through pyramid elements to the region of tetrahedrons necessary due to the complexity of the external surface. Tissue prolapse among stent struts is also observable.

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Figure 4

Multi-domain model of the left anterior descending coronary artery. Below on the left, the 3D model of the coronary bifurcation with the lumped parameter model of part of the coronary tree connected to the outlets. (a) Flow tracing used as inlet condition (solid line) proposed by Charonko in 2009 [37] and the flow tracings obtained at the MB (line-dotted model) and at the SB (dotted line). (c) Example of the lumped parameter scheme used to model a segment of a coronary vessel characterized by two resistances, a capacitance and an inductance.

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Figure 5

Maximum principal stress contours in the artery during (a) the MB stenting implantation, (b) the standard FKB, and (c) the modified FKB inflation at the maximum balloon expansion (on the left) and after the elastic recoil (on the right)

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Figure 6

Averaged values of the maximum principal stresses in the intimal layer of the stented region of the MB in the three cases analyzed

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Figure 7

von Mises stresses contours on the stent before (a) and after (b) the standard FKB inflation at the maximum balloon expansion. In the magnification, example of the different stress state of an expanded strut in the proximal region of the main branch.

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Figure 8

Hemodynamic forces acting on the endothelial layer, contours of time-averaged wall shear stress (on the left) and OSI (on the right) for the analyzed cases: (a) stenting of the MB, (b) standard FKB inflation performed with two cylindrical balloons (3.00 mm in the MB and 2.00 mm in the SB), and (c) modified FKB inflation performed with a cylindrical 3.00 mm balloon in the MB and a dedicated conical balloon in the SB

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Figure 9

Velocity magnitude, streamlines and helicity at the average flow rate in the transversal plane after the MB stenting (a) and the modified FKB (b), respectively

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