ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

considered. It has been proposed on the market to overcome the drawbacks of culotte
technique, which is one of the most commonly applied double-stenting procedures [2].
This technique consists of the implantation of a device in the SB of the bifurcation, the
re-wiring, the treatment of the main branch (MB) through the struts of the previously
implanted stent and, finally, the final kissing balloon inflation (FKB, simultaneous
expansion of two balloons in both branches of the bifurcation). Main advantages of the
culotte technique are the good coverage of the whole bifurcation and the suitability for
all the bifurcation angles. However, this method provokes a high concentration of metal
in the proximal part of the MB due to the overlap of the devices that could lead to instent
restenosis and thrombosis. The particular design of the Tryton stent, characterized
by few struts in its proximal part, should allow a decrease of the overlap region and also
an easy access to the implantation site for the second device.
The aim of this work is the numerical analysis of the culotte technique both from a
structural and fluid dynamic point of view, in order to compare the behavior of the
Tryton stent with a standard one. In particular, the performance of the dedicated stent is
evaluated in terms of ease of use during the treatment and biomechanical influence after
stents implantation. From the structural point of view, stress fields obtained in the
device and in the arterial wall and the metal-to-artery ratio are analyzed. From the fluid
dynamic point of view near-wall quantities like wall shear stress (WSS) are evaluated.
3. MATERIALS AND METHODS
3.1 Structural model
An ideal coronary bifurcation model (Fig. 1b) is created with realistic geometrical
dimensions and a bifurcation angle of 45° using Rhinoceros 4.0 Evaluation CAD
program (McNeel & Associates, Indianapolis, IN, USA). An isotropic hyperelastic
behavior is assigned to the three different layers composing the arterial wall,
considering the experimental data obtained by Holzapfel [3].
Stent geometries (Fig. 1a) are obtained using the previously mentioned CAD software
and resemble the Tryton and the Multilink Vision (Abbott Laboratories. Abbott Park,
Illinois, U.S.A) stents. The material, a cobalt-chromium alloy, is described through a
Von Mises-Hill plasticity model with isotropic hardening.
In order to simulate the stenting procedures, cylindrical polymeric balloons are created
in the expanded shape and then deflated by applying a negative pressure to the internal
surface, obtaining a multi-folded geometry (Fig. 1c). The balloons are modeled as an
elastic membrane. Bended configurations of the balloons are needed to reproduce some
steps of the procedure like the FKB. To achieve these configurations, preliminary
simulations are carried out where a deflated balloon slides along a specifically drawn
guide (Fig. 1c).
Numerical simulations of stents deployment are performed using the ABAQUS/Explicit
commercial code (Dassault Systemes Simulia Corp., RI, USA) assuming the condition
of quasi-staticity of the phenomenon [4]. Contacts between parts of the model are
defined according to general contact algorithm.
Two different simulations of the culotte technique are carried out. In the first analysis
(Fig. 2A) a Tryton stent is expanded as a SB device with a Multilink Vision stent
implanted in the MB as a workhorse stent. In the second analysis, the bifurcation is
treated with two standard Multilink Vision devices in either the SB and the MB (Fig.
2B). The whole technique can be summarized through the following steps: i) stenting of