The Structure and Function of Endovascular Stents: A Primer for the Interventional Nephrologist

Abstract

The use of stents has become common practice in various interventional fields. The purpose of this article is to provide the interventionalist with an understanding of the basic structure stent. We describe the etymology, the classification and describe various terms used by engineers as they strive to develop that "ideal" stent. We also describe the fabrication process briefly and finally elaborate on the characteristic "build and cut" of some commonly used stents.

Stent Migration and Bail-out Strategies

“…Self-expanding nitinol stents are now the de facto standard for use in the venous circulation as they have larger diameters with relatively low profiles, are more flexible and depending on the design, offer excellent conformability and minimal foreshortening. Because of their shape memory properties, they have an intrinsic radial expansive force and therefore a high expansibility ratio (defined as the diameter of the stent in the expanded state over that in the crimped state) (6, 7).…”

“…This is because of the direction of flow of venous blood as well as the gradual increase in the diameter of the veins as they get closer to the heart. One of the properties of self-expanding stents is their tendency to shorten as they approach their nominal diameter, the magnitude of which is dependent on stent architecture (6). The reverse, i.e., compression with resultant stent elongation, also holds true.…”

“…Whether pre-dilation of a stenotic segment, prior to self-expanding stent deployment, is a risk factor is debatable (9, 10). Covered stents by inhibiting neo-intimal growth through the stent struts prevent stent incorporation into the vessel wall, which may facilitate migration (6). Among operator errors, the most common reason for stent migration in one study was under-sizing of stents followed by dislodgement while inflating a balloon or balloon rupture when balloon expandable stents were used (3, 4).…”

“…Finally, improper removal of the delivery system after stent deployment may cause stent migration if the tip is caught within the stent struts. To prevent “jumping” and entanglement of the tip within the stent, a number of unique modifications have been made to the delivery system (6).…”

A simple indispensable maneuver to prevent stent migration during deployment

“…A delivery system designed with the proprietary EX.P.R.T. (Exact Placement Release Technology) prevents premature “jumping” of the stent during deployment (4), but covered stents currently in use for vascular access do not come with this delivery system. Nevertheless, once the stent graft is completely expanded over its entire length, the impact of this displacement force becomes negligible since blood flow runs rather freely through the open stent lumen and post-dilation can be performed with ease.…”