Evaluation of stent retriever behavior at deployment and retrieval during mechanical thrombectomy

The impact of stent retriever (SR)-clot integration for mechanical thrombectomy has been highlighted by several studies. However, it has also been shown that SRs can stretch or collapse during thrombectomies in tortuous anatomies. Therefore, this study focused on the behavior of commercial SRs (Solitaire and EmboTrap) during deployment and retrieval. Benchtop experiments were performed to measure the degree of SR collapse in an arterial model of varying tortuosity, and a custom testing structure was developed to measure SR outward forces at deployment and changes in radial force density (RFD). The degree of collapse was significantly influenced by the model's tortuosity index (TI) and the number of curves the SR pushwire interacted with (p < 0.05); a slight collapse was present at deployment, while more pronounced collapse occurred during retrieval. Solitaire SRs experienced more significant collapse than EmboTrap SRs, which was most pronounced in the highest tortuosity segment (TI = 1.74) where the Solitaire and EmboTrap degrees of collapse were 67.8 % and 32.5 %, respectively. While longer SRs were shown to have greater collapse overall, their distal segments remained expanded. We hypothesize this behavior supports prior clinical studies highlighting the benefits of longer SRs; during retrieval the distal SR region applies force to the clot to assist in dislodgment. SR behavior was also reflected in RFD trends. SRs with the least collapse generated the greatest RFDs and decreased with higher tortuosity. Overall, an evaluation of SR behaviors indicated that both SR design and length will influence the degree of collapse and RFD in tortuous segments.