Mortier, Peter

Ghent University Academic Bibliography

Improving side branch access during bifurcationstenting - a finite element studyPeter MortierSupervisor(s): Benedict Verhegghe, Pascal VerdonckAbstract—Stents are supporting tubular mesh structures which are de-ployed in obstructed arteries in order to reopen them. This is a widelyused technique but some problems remain unsolved. Treating the narrowedarteries which occur at the location of bifurcations remains a challengeand is generally associated with an increased complication rate. Severaltechniques have been proposed to treat these lesions, but all the suggestedmethodologies have specific limitations. Therefore, further investigationsremain very meaningful and numerical simulations may provide interest-ing insights in the mechanical aspects of the different interventional tech-niques. In this study, an innovative numerical model to examine one ofthe proposed techniques (side branch balloon inflation) is presented. Theresults indicate the complexity of implanting stents at the location of bi-furcations. In future, more advanced computer models will be developedin order to account for more realistic behaviour of the arterial wall. Suchmodels can lead to improved stent designs and/or better techniques to treatbifurcation lesions.Keywords—bifurcated arteries, stent, balloon inflation, finite elementI. INTRODUCTIONSTENTS are small tube-like medical devices, used to treatclogged sections of blood vessels, a phenomenon frequentlyencountered in the coronary circulation. Stents improve the lo-cal blood flow by partially restoring the normal vessel diam-eter. This well-established intervention shows good results inmost cases. However, some problems remain unsolved. Manyof these stenoses occur in bifurcated regions and treating theselesions with stent implantations remains a challenge, becausethis is associated with a higher complication rate [1], [2]. Sev-eral stent implantation techniques have been proposed, but allof them have specific limitations [3], [4]. Computer models area suitable tool to investigate the numerous proposed techniques.One of these techniques involves the inflation of a balloon toopen the side branch after the implantation of a stent in the mainbranch. This balloon inflation is performed to reduce the distur-bance of the blood flow towards the side branch.II. MATERIALS AND METHODSIn this study ABAQUS was used for creating the geometri-cal model and for solving the finite element problems. Themodel consists of a balloon-expandable stent, resembling theCYPHERTM stent (nominal diameter 3 mm, nominal length 8mm; Cordis) in its already expanded state. The stent is made of316L stainless steel, which is described by a Young’s modulusof 196000 N/mm2, a Poisson’s ratio of 0.3, and a yield stressof 375 N/mm2. The stent is located in the main branch of theanatomical bifurcation (figure 1), which is approximated by tworigid tubes, intersecting at an angle of 45 and with a diameter of2.5 and 3 mm for the side and main branch respectively.Peter Mortier, Institute Biomedical Technology (IBiTech), Ghent University,Belgium. E-mail: P.Mortier@UGent.be .Fig. 1. Initial stent and balloon configuration and anatomical characteristicsA trifolded RAPTORTM balloon (nominal diameter 2.5 mm,Cordis) is positioned in both the main and side branch, crossingthe CYPHERTM stent as depicted in fig. 1 and the opening ofthe side branch is induced by balloon inflation up to 1.5 N/mm2.The balloon properties are based on the compliance chart pro-vided by the manufacturer. These properties were validated bythe virtual expansion of a cylindrical balloon with tapered ends.The numerically obtained pressure/diameter relation shows avery good agreement with the original compliance data (max-imum percentage difference less than 4%, i.e. at a pressure of 1N/mm2), as shown in figure 2.Fig. 2. Data provided by the manufacturer (solid diamonds) and extrapolatedvalues (empty diamonds) compared with the numerical results (line).III. RESULTS AND DISCUSSIONFigure 3 shows the impact of the inflation of the side branchballoon on the stent cell that limits the side branch accessibility.The balloon deforms and enlarges this stent cell, which probablyresults in an optimized perfusion of the side branch. In orderto examine the exact impact of this technique on the blood flowpattern, Computational Fluid Dynamics (CFD) modelling seemsappropriate and will be performed in these geometries in future.Fig. 3. View into the side branch at different inflation pressures (p) (balloon notshown), showing the gradually increasing cell opening.Despite the previously described positive consequences of theside branch balloon inflation, there is one major drawback of thisintervention. A part of the stent, scaffolding the main branch, ispushed towards the centre of the main branch lumen (figure 4,lower panel). This is of course suboptimal as such a deformationnegatively affects the scaffolding properties of the stent.Therefore, more complex strategies should be considered toimprove the side branch accessibility during bifurcation stent-ing and one promising technique (i.e. kissing balloon inflation)involves the simultaneous inflation of two balloons, one in themain branch and one in the side branch. The main branch bal-loon guarantees optimal scaffolding, while the side branch bal-loon enlarges the stent cell that is in front of the side branchopening.IV. CONCLUSIONMany stents are implanted at bifurcation lesions, in such away that they block the side branch. An optimization of theblood flow towards the side branch can be achieved by inflatinga side branch balloon. This technique results in an enlargementFig. 4. Inflation of the side branch balloon results in a inadequate scaffoldingof the main branch (indicated by the arrow).of the stent cell blocking the side branch as shown by our nu-merical results. A major limitation of this straightforward tech-nique is that the scaffolding properties of the stent are negativelyaffected, and therefore, other strategies such as kissing ballooninflation may be preferred. Future computational studies will in-clude more realistic arterial wall behaviour. More complex tech-niques used for bifurcation stenting will also be investigated.ACKNOWLEDGMENTSThe authors acknowledge Matthieu De Beule and Denis VanLoo for their valuable support. First author’s research is sup-ported by a BOF-grant (O1D22606) from Ghent University.REFERENCES[1] Lefevre et al., Stenting of Bifurcation Lesions: Classification, Treatments,and Results, Cathet. Cardiovasc. Intervent., 2000, 49:274-283.[2] Garot et al., Nine-Months Outcome of Patients Treated by PercutaneousCoronary Interventions for Bifurcation Lesions in the Recent Era, J. Am.Coll. Cardiol. , 2005, 46:606-612.[3] Seifeddin et al., Bifurcation Stenting: Unnecessary Challenge or a LastFrontier in Intervention, J. Intervent. Cardiol., 2004, 19:S27-S39.[4] Louvard et al, Percutaneous Coronary Intervention for Bifurcation Coro-nary Disease, Heart, 2004, 90:713:722.

Improving side branch access during bifurcation stenting: a finite element study

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Improving side branch access during bifurcation stenting: a finite element study

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