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By Koen R. Deloose, MD. View PDF Reprints. Bare-metal stent BMS design and its clinical implications for treating infrainguinal peripheral artery disease have returned to the spotlight for a variety of reasons. One of the most notable is driven by the infamous Katsanos et al publication and the resulting questions surrounding paclitaxel-eluting devices. Regardless, for all interventionalistsβboth paclitaxel believers and nonbelievers alikeβthere is still a strong need for modern-generation stents to perform well in increasingly demanding clinical scenarios.
With renewed interest, the scientific community is looking to see if the clinical outcomes of these modern devices in these challenging scenarios are overruling the current gold standard. This late healing phenomenon leads to loss of patent vessel lumen and recurrence of claudication and chronic limb-threatening ischemia symptoms. Target lesion revascularization is a logical sequence in this setting. During the last decade, it became clear that ISR is associated with many self-expanding BMS design features, such as longer stent lengths, smaller stent diameters, nonadapted strut thicknesses, high metal-to-artery ratios, lack of flexibility, and suboptimal radial forces.
Mechanical engineering is a science of compromise. Therefore, altering any single characteristic of a stent inevitably affects other properties. There is a very complex interaction between every feature of stent design and how the device behaves in clinical practice. One potential predictor of good stent performance is an ideal amount and balance of the three radial forces: chronic outward force COF , the radial force that a self-expanding stent exerts at expansion on the vessel wall; radial resistive force RRF , the force the stent resists under circumferential compression; and crush resistance CR , the force the stent resists under focal compression.
Complex engineering techniques, such as programming the fully open stent diameter higher than the normal nominal diameter, can also manipulate the different radial forces of the device. Figure 1. The programming of hysteresis curves can impact the expansion and compression forces of a stent. Accomplishing the right amount of these forces is crucial. For example, on one hand, the COF needs to be high enough to restore the vessel lumen to near-normal diameter.
On the other hand, too much COF eg, from higher oversizing ratios can cause a significant chronic increase in wall shear and structural stress to the arterial wall, inflammatory response, deep vascular injury with internal elastic lamina fracture, and finally, the development of myointimal hyperplasia.