An investigation into the influence of stent strut thickness on in-stent restenosis using the finite element method

In-stent restenosis represents the major limitation for stenting procedures. In-stent restenosis is the renarrowing o f the artery lumen within a stent predominantly due to excessive growth of neointimal hyperplasia. Clinical studies have found that stent design is a key determinant in the propensity o f stents to cause restenosis, indicating a vital link between the biomechanics o f stents and the development of the disease. The ISAR-STEREO Trial specifically assessed the effect o f strut thickness on restenosis outcome and found that for the same stent design, a thinner strut stent was associated with a significant reduction o f angiographic and clinical restenosis compared to the same stent with a thicker strut. The main objective o f this study is to use the finite element method to simulate these stenting procedures, and to examine the stresses induced within the stented arterial vessel walls by the stents, thus enabling the mechanical stimuli for in-stent restenosis to be identified. \n \nFinite element models o f thin and thick strut stents were developed and the stents were deployed in various stenosed vessel geometries such that the stresses induced within the stented vessels by the two stents could be compared. The stresses were examined at the end o f stent deployment, to determine the mechanical stimuli for acute damage, and again at stent unloading, to determine the long term stimuli for in-stent restenosis. The stress analyses were used to determine the level of vascular injury caused to the artery by different strut thickness stents. \n \nThe finite element studies successfully identified differences between the mechanical loading of the arterial tissue in the vessels stented with the two different stents. The higher restenosis rate of the thicker strut stent, reported in the ISAR-STEREO clinical study, was found to be the result of the higher luminal gain achieved by the thicker strut stent, due to the lower recoil of the stent structure when both stents were expanded to the same initial lumen diameter. Further stenting analyses, however, found that the thicker strut stent resulted in a lower percentage of volume stressed at high levels compared with the thinner strut stent when it was expanded to the same final lumen diameter. This suggests that a thicker strut stent may in fact have the potential to be expanded to an optimal diameter whereby the in-stent restenosis is minimised. Therefore, it is proposed that the use of preclinical testing tools, such as finite element modelling, could be used to predetermine the deployment protocol and optimum luminal gain of a particular stent design in order to minimise the mechanical stimuli for in-stent restenosis.