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Abstract
Introduction/Purpose Despite improved acute ischemic stroke (AIS) outcomes with mechanical thrombectomy (MT), treatment still frequently fails to achieve recanalization on the first attempt and fails altogether 20-30% of the time. Additionally, experimental MT studies commonly report 100% recanalization, highlighting clear differences between in vivo and in vitro scenarios. To more accurately represent MT in benchtop models, and to determine the factors underlying recanalization discrepancies, stent retriever (SR) removal forces and surface frictional forces will be investigated in models of varying geometry and material and compared with bovine carotid arteries.
Materials and Methods A flow loop was developed (figure 1A) with a peristaltic pump, fluid reservoir, and various cerebral artery models (straight tubes, 90 and 180° bends, and a silicone MCA). To mimic MT, an SR and microcatheter was passed through a hemostatic valve and deployed across lodged blood clots. The SR, connected to a force gauge, was pulled at a constant speed while recording the removal forces. Three SRs were evaluated: Solitaire Platinum (4x20mm) and Solitaire2 (4x15 and 6x30mm).Frictional tests were performed between 0-40% hematocrit clots, bare nitinol, and common artery model materials (glass, silicone, PVC, and bovine carotid). Additional tests were performed with nitinol SRs and the same model materials. To evaluate frictional forces, blood clots and unfolded SRs (figure 1B) were pulled across each material surface via an Instron machine. Tests were performed on dry and wetted material surfaces and compared to bovine carotid samples.
Results SR removal forces were found to increase with model tortuosity (0.56N in straight and 1.38N in 180° models). A comparison of clot properties found that diameter correlated slightly with removal force, while clot hematocrit showed no significant correlation.In frictional testing, wetted material surfaces displayed lower forces compared to dry surfaces (0.19 vs 0.86N for silicone) but were still significantly lower than those between SRs and bovine carotids (0.47N). SR frictional forces were also significantly higher between all tested materials compared to those of blood clots (0.19 vs 0.08N for silicone).
Conclusion Clot hematocrit did not influence SR removal forces, while model tortuosity positively correlated. Testing concluded that common AIS model materials underpredict the frictional forces that likely occur in-vivo by 2-4x. Additionally, it was determined that SR-artery frictional forces are much larger than clot-artery frictional forces and are the primary driver of overall removal force. The decreased forces between clots/SRs and experimental materials could explain the higher recanalization rates observed in in-vitro models.
Disclosures D. Poulos: None. O. Elkhayyat: None. M. Froehler: 1; C; Siemens, Medtronic, Genentech, Stryker, NIH. 2; C; Cerenovus, Balt, The Jacobs Institute, Oculus. B. Good: 1; C; Medtronic.