Alteration of hemodynamics in aneurysm models by stenting: Influence of stent porosity

Abstract

Recent developments in minimally invasive approach to cerebrovascular diseases include the placement of stents in arteries for treatment of aneurysms. Preliminary clinical observations and experimental studies have shown that intravascular stents traversing the orifice may lead to thrombosis and subsequent occlusion of the aneurysm. The alterations in vessel local hemodynamics due to the introduction of a stent are not yet well understood. We investigated changes in local hemodynamics resulting from stent implantation. Pulsatile flow patterns in an experimental flow apparatus were visualized using laser-induced fluorescence of rhodamine dye. The test cells were constructed in a rectangular shape to facilitate an undisturbed longitudinal view of flow patterns in parent vessel and aneurysm models with and without porous stents. Woven nitinol stents of various porosities (76%, 80%, 82%, and 85%) were investigated. The selected fluid dynamic similarity parameters (Reynolds and Womersley numbers) represented conditions usually found in high-flow, larger arteries in humans (such as the carotid artery) and low-flow, smaller arteries (such as the vertebral artery). The mean Reynolds number for the larger arteries was 180, with maximum/minimum values of 490/-30 and the Womersley number was 5.3. The mean Reynolds number for the smaller arteries was 90, with maximum/minimum values of 230/2, and the Womersley number was 2.7. For the larger arteries modeled, placement of a stent of the lowest porosity across the aneurysm orifice resulted in reduction of aneurysmal vortex speed and decreased interaction with parent vessel flow. For smaller arteries, a stent of the same porosity led to a substantial reduction of parent vessel/aneurysmal flow interaction and the appearance of a nonrecirculating crescent of fluid rich in rhodamine dye in the aneurysm dome. Our results can help explain in vivo thrombus formation within an aneurysm after placement of a stent that is compatible with local hemodynamics.

Effect of Flow Diverter Porosity on Intraaneurysmal Blood Flow

“…Earlier studies have shown that endovascular flow diverters are capable of reducing intraaneurysmal flow and that porosity is a major determinant of this flow reduction [11,15]. The current study aimed in complementing and further extending those studies, by examining and comparing the effects of two versions (D1 and D2) of a novel low-porosity endovascular flow diverter with those from a commercially available device (Neuroform) that is already in use for clinical application.…”

“…Flow patterns, velocities, pressure and their derived quantities such as shear and vorticity are made accessible by direct measurements [13,14]. Alterations of these quantities due to the insertion of a stent were quantified in previous studies by Lieber et al [11], Rhee et al [15], and Barath et al [16][17][18].…”

“…Earlier studies have shown that the efficacy of a flow diverter to reduce flow within the aneurysmal sac depends on its porosity [11] and on the local hemodynamic conditions [12].…”

Flow diverter effect on cerebral aneurysm hemodynamics: an in vitro comparison of telescoping stents and the Pipeline

“…The porosity of a stent directly affects the amount of flow that enters an aneurysm or perforating vessel covered by the stent. Studies have found that lower-porosity stents lead to greater flow reductions within aneurysms [8,9]. To reduce stent porosity across the aneurysm (using high-porosity flexible stents), many clinicians use a stent-within-a-stent technique or "telescoping."…”

Methodologies to assess blood flow in cerebral aneurysms: Current state of research and perspectives

“…Various stents exhibiting four different porosities (comprised between 76 and 85%) were investigated and the results showed the difference of aneurismal vortex reduction in large and small arteries [18]. Using a photochromic dye, Rhee et al visualized the flow in sidewall and in fusiform aneurysms models, and velocity and WSS changes due to various stents could be calculated.…”