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

geometries, such as the intersection zones between strut stent and arterial wall, where
tetrahedral elements become necessary. The discretization method consists in the
creation of internal cylinders along the MB and the SB. These cylinders are meshed
with only hexahedral elements while in the region between them and the arterial wall a
tetrahedral mesh is created. Lastly, merging of the two mesh types is performed through
pyramidal elements.
Transient simulations are carried out using ANSYS Fluent 13 (Ansys Inc., Canonsburg,
PA, USA). Artery and stent struts are assumed to be rigid and defined with a no-slip
condition. A pulsatile blood flow tracing is applied at the inlet as a paraboloid-shaped
velocity profile according to Davies et al. study [7]. The average flow rate value is 60
ml/min (mean velocity = 0.13 m/s) and the duration of the cardiac cycle is 0.903 s. The
adopted profile is representative of a typical flow tracing of a human left anterior
descending coronary artery. At the outlet cross sections, a flow split of 70% in the MB
and 30 % in the SB is imposed. Blood flow is modeled as a non-Newtonian fluid
through the Carreau’s model proposed by Seo et al. [8]. A coupled solver is used with a
second-order upwind scheme for the momentum spatial discretization and a first-order
time implicit scheme to discretize the governing equations. Under-relaxation factors of
0.3 for pressure and momentum and 1 for density are used. Convergence criterion for
continuity and velocity residuals are set to 10 −6 .
4. RESULTS AND DISCUSSION
Despite their current success, stenting procedures are still involved in several medical
complications like sub-acute thrombosis and in-stent restenosis. Clinical and biological
studies relate these drawbacks to the non-physiological biomechanical conditions
provoked by the presence of the stents in the bifurcation.
From the structural point of view, the metal-to-artery ratio and the deformation fields in
the implanted device are used to compare the culotte technique in the two simulated
procedures. Figure 3A illustrates the amount of struts in contact with the arterial wall in
the proximal part of the MB where the two devices overlap. The expansion of two
standard devices causes a higher metal-to-artery ratio leading to a major possibility of
injury during stent placement and an extremely modified hemodynamic field. Secondly,
considering the stent implanted in the SB, simulations show that lower values of plastic
equivalent deformations are found in the dedicated device if compared to the standard
(Fig. 3B). Literature studies [9] show that very high deformations in the device could
lead to structural damage and delamination of the polymer that covers the stent struts
and carries anti-proliferative drugs. The delamination could bring to an inhomogeneous
A B MULTILINK VISION TRYTON
Figure 3. A) Qualitative comparison of the metal-to-artery ratio between the simulation with dedicated
(left) or standard (right) devices. B) Plastic equivalent deformations on the SB stent implanted. As shown
in the close-up details, higher values are found in the Multilink stent (left).