Conformity of carotid stents with vascular anatomy: evaluation in carotid models

Abstract

Background and purpose: Conformity between self-expanding Wallstents and vascular anatomy is limited. Because of a lack of longitudinal flexibility, straightening effects on vascular curves occur and may result in stent-induced kinking. Our purpose was to evaluate the conformity of self-expanding stents with the course and endoluminal surface of silicone models of the normal human carotid artery.

Methods: Five different types of self-expanding carotid stents were implanted into simplified pulsatile perfused silicone models of the carotid bifurcation. The models embody elastic properties of the vessel wall similar to those of normal human arteries. All stents had the same nominal diameter and length and bridged the external carotid artery origin as well as a consecutive curve at the initial segment of the internal carotid artery. Conventional radiographs of the model were compared before and after stent placement to record changes of shape and course of the silicone artery. Dehiscences between stent filaments and arterial wall were measured on digital subtraction angiograms of the model.

Results: Implantation of braided Wallstents or the Expander with continuous filaments induced considerable straightening effects on the bifurcation angle, as well as on the curves of the internal carotid artery. Segmented designs of modular nitinol stents complied better with vascular tortuosity and showed improved adaption between stent and the endoluminal surface of the model.

Conclusion: Model experiments show that segmented nitinol stents improve the conformity between the prosthesis and vascular anatomy, and confirm new carotid stent concepts as an alternative to the Wallstent.

Fig 1.

Simplified silicone model of the human carotid artery bifurcation with a nominal angulation between the CCA and initial ICA segment of 30° counterbalanced by a curve.

Fig 2.

Digital images of the model after implantation of a self-expanding carotid stent covering the ICA curve and the bifurcation as a basis for the measurement of parameters for quantification of stent conformity. A and B, The dehiscence factor is calculated by dividing the areas of dehiscence (highlighted in B) by the area covered by the stent. C, Measurement of the ICA offset as the maximal deviation of ICA tortuosity perpendicular to the CCA midaxis (upper arrows). Definition of the CCA-ICA angle as the angulation (asterisk) between the CCA midaxis and the midaxis of the initial ICA segment up to a level of 1.5 cm above a bifurcational 0-level is indicated by a line through the midpoint of the external carotid artery origin. D, Measurement of the ICA angle (asterisk) between the tangents through the midaxes of both limbs of the ICA curve.

Fig 3.

Digital radiographs of the model without stent and after implantation of five types of self-expanding carotid stents. Note the differences of stent conformity between stents braided from continuous filaments (Wallstent and Expander) and segmented nitinol stents with an open cell design (Jostent, SMART and Zilver). See text for further explanations.