John Kaufman, MD, FSIR
Chair, Department of Interventional Radiology
Dotter Interventional Institute/OHSU
Disclosure(s): No relevant disclosure to display
Prior studies have reported vein narrowing adjacent to conventional iliac vein stents due to the Poisson effect. Multiple clinical studies report venous inflow as a predictor of stent outcomes. The purpose of this study was to evaluate the change in venous inflow lumen adjacent to an auxetic stent that applies both radial and longitudinal forces on the vein wall counteracting the Poisson effect.
Materials and Methods:
Two adult ovine were used with IACUC approval. An investigational 12 mm x 55 mm self-expanding, laser-cut nitinol stent with auxetic geometric properties was utilized for this study (custom made; Auxetics, Inc.). A single auxetic stent was deployed in the right iliac vein and two partially overlapping auxetic stents in the left iliac vein. Baseline and post-stent venography and intravascular ultrasound (IVUS) was performed of the iliac segment. Aspirin 81mg PO daily was given during the survival period. After a 3-month follow-up period (87d and 107 d), both animals underwent repeat venography and IVUS. Following euthanasia, the stented iliac veins were formalin fixed and sent to CV Path (Gaithersburg, MD) for histopathology analysis. Analysis of venographic and IVUS data was performed using Image J (ImageJ, NIH). Statistical analysis was performed using Microsoft Excel (Microsoft Corp, Redmond, Washington). Mean ± SD are reported.
There was a significant increase of the stented segment lumen area on IVUS immediately following stent placement and further significant increase at 3-month follow-up (pre-stent 44.6±3.2 mm2; immediate post-stent 58.1±6.0 mm2; 3-month follow-up 72.0±7.1 mm2; p< 0.01 pre- to post-stent & post-stent to 3-month). There was a significant increase of the unstented inflow vein lumen area on IVUS immediately following stent placement and further significant increase at 3-month follow-up (pre-stent 47.7±3.7 mm2; immediate post-stent 53.4±2.8 mm2; 3-month follow-up 64.8±2.2 mm2; p< 0.01 pre- to post-stent & post-stent to 3-month). Histopathology demonstrated overall minimal inflammation, mild vessel wall injury, near complete strut endothelialization, and low neointimal thickening (1.1±0.5mm).
Use of an auxetic stent which applies longitudinal force on the vein wall to counteract the Poisson effect resulted in increased inflow vein lumen area immediately following stent placement, and further increase at 3-month follow-up. Given the known association between venous stent inflow and patient outcomes, the use of stents with auxetic properties may be a strategy for preserving venous inflow during stenting to improve outcomes.