B5: Cardiovascular Mechanics I

FINITE ELEMENT ANALYSIS TO PREDICT OCCURRENCE OF CORONARY STENT FRACTURE BY CYCLIC BENDING MOTION

Xiaodong Zhu, Kiyotaka Iwasaki,

Mitsuo Umezu Waseda University, Japan

Introduction
Coronary stent fracture (SF) is recognized as one of the causes of in-stent restenosis or stent thrombosis. Cyclic bending motion of coronary artery has been identified as the primal predictor of SF. The aim of this study is to investigate SF probability of current drugeluting stents and elucidate the key factor of SF using finite element analysis (FEA).
 

Methods
Three-link CoCr L605 stent (Xience V, Abbott Vascular), two-link stainless steel SUS316L stent (Nobori, Terumo) and two-link PtCr stent (Promus Element, Boston Scientific) were chosen as subjects. Three-dimensional geometries of the stents were constructed based on micro-CT measurement. Referenced data of mechanical properties such as elastic modulus, poisson’s ratio, yield stress, fatigue strength and ultimate tensile stress were used in the FEA. The processes of crimping and deploying the stent were simulated. The stent was crimped on a balloon by applying enforced displacement. Next, the stent was deployed into a hyper-elastic bended coronary artery model. Then, the coronary artery model was cyclically bended from the diastolic angle of 125° to the systolic angle of 105°. Fatigue safety factor (FSF) was calculated using stress amplitude and mean stress. The SF risk was evaluated using Goodman fatigue diagrams.
 

Results
The maximum values of 1/FSF were 1.16 and 1.53 for the CoCr and SUS316L stents, respectively, indicating that the SF risks were high. For the PtCr stent, the maximum value of 1/FSF was 0.83, indicating that the SF risk was low. The locations with higher SF risk identified by FEA were coincident with the fracture locations in the durability tests. Moreover, the FEA data indicated that stress amplitude had a greater effect on SF occurrence.

Conclusions
The FEA was useful to predict SF risk. It was elucidated that stress amplitude was the key factor of the coronary SF in cyclically-bended coronary artery.

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