Experimental evaluation of stent retrievers’ mechanical properties and effectiveness

Abstract

BackgroundFive randomized controlled trials recently appeared in the literature demonstrating that early mechanical thrombectomy in patients with acute ischemic stroke is significantly related to an improved outcome. Stent retrievers are accepted as the most effective devices for intracranial thrombectomy.ObjectiveTo analyze the mechanical properties of stent retrievers, their behavior during retrieval, and interaction with different clots and to identify device features that might correlate with the effectiveness of thrombus removal.Materials and methodsAll stent retrievers available in France up to June 2015 were evaluated by mechanical and functional tests aimed at investigating the variation of their radial force and their behavior during retrieval. Devices were also tested during in vitro thrombectomies using white and red experimental thrombi produced with human blood. Functional tests and in vitro thrombectomies were conducted using a rigid 3D printed vascular model.ResultsMechanical tests showed a variation in radial force during retrieval for each stent. A constant radial force during retrieval was related to continuous cohesion over the vessel wall and a higher rate of clot removal efficacy. All stent retrievers failed when interacting with white large thrombi (diameter ≥6 mm).ConclusionsNone of the tested devices were effective in removing white clots of large diameter (≥6 mm). Constant radial force during retrieval allows constant cohesion to the vessel wall and pressure over the clot; such features allow for a higher rate of clot removal.

Treatment of cerebral vasospasm with self-expandable retrievable stents: proof of concept

“…Machi et al 23 recently reviewed the mechanical properties of the commercially available stent retrievers. The radial force of the available stents is highly variable and, with the additional changes on radial force dependent on undersizing or oversizing, the picture becomes more complicated.…”

Preclinical Evaluation of the NeVaTM Stent Retriever: Safety and Efficacy in the Swine Thrombectomy Model

“…Recent reports have demonstrated a reduced efficacy of stent retrievers in simulated use when using platelet-enriched clots which mimic organized thrombi [9]. Five occlusions with large plasma-enriched “white” clots were performed (Fig.…”

“…For stent retrievers, efficacy of clot removal has been postulated to be dependent on the degree of migration of clot into the stent struts and it has been postulated that most failures are related to the presence of a large organized clot [9, 19, 23, 24]. A mechanism of failure regarding organized thrombus has been described as the stent retriever remaining compressed against the vessel wall and sliding between the stent and the wall without retrieving [9]. Multiple retrieval attempts lead to increased time to reperfusion, which would be expected to reduce the chance for meaningful clinical outcomes.…”

“…Plasma rich thrombi were prepared according to a previously published protocol [9]. Whole blood was collected into Vacutainer TM blood tubes containing 3.2% sodium citrate (1: 9 volume) which were then placed into a centrifuge at 350 g for 10 min at 22°C.…”

Histological Composition and the Origin of the Thrombus

“…Other applications of clot analysis include mechanical measurements of thromboemboli extracted from patients, which has informed the manufacture of clot analogs made on the bench to develop in the preclinical phase the next-generation medical devices for thrombectomy. [10][11][12][13] Finally, improved pathological analysis of retrieved clot to serve as a diagnostic assay for stroke cause has been proposed. Traditionally, the standard pathology report of the extracted embolus reveals "clot."…”