In vivo evaluation of safety and performance of a nitinol venous stent in an ovine iliac venous model.

BACKGROUND

Obstruction of the iliocaval venous outflow tract is a common cause of acute and chronic venous symptoms. Percutaneous stenting is now frequently performed to alleviate obstruction in the central venous system. However, currently used stents were primarily designed for biliary or arterial indications and may not be optimal for use in the venous system. This study evaluated the safety and performance of a novel venous stent (NVS) designed specifically for venous applications in an in vivo venous animal model.

METHODS

The study evaluated vascular response and safety of the NVS compared with the Wallstent Stent (WS; Boston Scientific, Marlborough, Mass) at baseline, 56, and 180 days in adult sheep. Four sheep received a single NVS in the iliac vein for acute evaluation, and eight underwent bilateral iliac vein stenting using a single NVS on one side and a single WS on the other for longer-term follow-up. Fluoroscopy and intravascular ultrasound imaging were performed at implantation to identify iliac vein diameters at baseline and again at 56 and 180 days. Both iliac veins from all 56-day and 180-day animals (n = 16) underwent histologic examination. Three sections from each vessel were reviewed for intimal strut coverage, luminal thickening, thrombus, and evidence of venous injury. Student t-tests were used to compare mean iliac vein diameters for the WS and the NVS.

RESULTS

Stent placement of the NVS and WS was successful to within 5 mm of the preselected location in all animals. During follow-up, no clinical evidence of stent thrombosis or obstruction >50% occurred in any limb. Sections of the stented vein at 56 and 180 days exhibited complete or nearly complete endothelial cell coverage, no or minimal luminal thrombus, and virtually complete neointimal coverage of every strut. The WS and NVS both caused an increase in iliac vein diameters immediately after stenting. At 180 days, there was no difference in iliac vein diameter or the percentage change in diameter compared with diameters immediately after stenting as measured by venography and intravascular ultrasound.

CONCLUSIONS

In an ovine iliac vein model, a new NVS studied to 180 days was free of thrombotic complications and significant luminal stenosis. These data support clinical evaluation of this NVS in appropriately designed human clinical trials.