Balloon/Stent Expansion Dynamics in Stenotic Arteries

Inflation balloons for stents are typically sized 1–2mm longer than endovascular stents, yet the effects of the degree of balloon overhang are unknown. In this study, a computational model capable of predicting balloon/stent/artery/plaque interactions and their effects on arterial and plaque stresses was developed to assess the effects of length mismatch and plaque classification on stent expansion characteristics and arterial stresses in diseased arteries. A 16-mm long, 1-mm unexpanded diameter, slotted tube stent was modeled and expanded using contact frictional elements by symmetrically-placed, tapered 17-mm and 18-mm balloons within an artery which contained no plaque to evaluate the effects of stent/balloon size mismatch on arterial stresses. The 18-mm balloon was then also used to expand inside an artery lined with plaque. The plaque was crescent shaped and axisymmetric with a maximum stenosis of 40%. In one model the plaque was primarily cellular, while in another model the plaque was calcified. ANSYS was used to perform the FEA. This model takes into account the multilinear elastic balloon expansion, non-linear plastic stent expansion, and the hyper-elastic arterial and plaque deformations. In this study, endflare was defined by stent diameter at proximal end with respect to stent diameter at the midpoint. Results from this study indicate that without plaque repsent, the maximum arterial stress at balloon contact is approximately proportional to the degree of balloon overhang. A 100% increase in balloon overhang results in a 4% increase in maximum endflare and a 39% change in a peak arterial stress. However, at the end of expansion, which is of the most clinical importance, the increase in max endflare is 2% and the increase in maximum arterial stress is 93% at the balloon point of contact and 45% at the point of contact with the far proximal and distal ends of the stent. When comparing the results of calcified and cellular plaque, a maximum endflare of about 55% was observed for both the calcified and cellular plaque cases during expansion. At the end of expansion the increase in max endflare is 10% for the cellular plaque and 40% of the calcified plaque. The peak equivalent stress seen by the artery was about 100% larger in the cellular case than in the calcified plaque case. This was due to much of the stress being contained within the calcified plaque. The peak stress seen by the plaque was 100% larger in the calcified than in the cellular plaque.