Mechanical Properties of Five Long Stents Compared

BACKGROUND: At Green Lane Hospital, 36% of interventional patients received one or more long stents. Long stents are cost-effective, increase procedural speed and increase the range of patients that can be treated percutaneously. With the increasing array of long stent designs available, the interventionalist needs objective comparative data for rational stent selection. AIM: To compare the mechanical and physical characteristics of five long stent designs. METHODS AND MATERIALS: Characteristics investigated were radiographic appearance, stent stiffness, radial strength, force to dislodge the stent from its balloon and simulated side branch dilatation. Long stents studied were the AVEGFX 30 mm, beStent 25 mm, Crown 30 mm, Multi-Link 35 mm and NIR 32 mm. Radiographic appearance was assessed on plain non-cine film without magnification. Stiffness was tested in the unexpanded and in the expanded states using an instron to measure the force required to bend the stent 1.5 mm within its elastic range. Radial strength of the stents expanded within a tecoflex tube was assessed by subjecting each stent to pressure increments within a pressure chamber and measuring diameter reduction. The force to dislodge a stent from its balloon was measured with an instron attached to the stent with adhesive tape. Dilatation through the side of each stent (expanded to 3.5 mm) was carried out in a plexiglass phantom with 2.5, 3.0, 3.5 and 4.0 balloons. The side lumen created and the distal stenosis produced were measured. RESULTS: Radiographic appearance and radiodensity vary between stents. All stents become stiffer upon expansion. Stent flexibility varies markedly between stent designs. Flexibility and radial strength are independent characteristics. Hand crimped stents tested were less resistant to dislodgement than the manufacturer mounted stents. Side branch dilatation produced varying downstream stenosis in stents studied. Side lumen size varied with stent design, and in some cases ballon size. CONCLUSION: Objective data assist the interventionalist in choosing rationally between stents. These data assist in tailoring stent selection for particular lesions.