Background Aneurysm coil packing density has been studied as a surrogate for treatment outcome, but clinical results are conflicting. Previous work applying computational fluid dynamics simulations to coil embolization of cerebral aneurysms found that embolization increases residence time (RT) and lowers cumulative shear (shear history; SH) of blood components within the aneurysm dome, suggesting that embolization promotes clot formation via a low shear stress-mediated pathway associated with stagnation of flow.¹ The goal of this investigation is to determine whether RT and SH can be used to identify optimal coil packing density for coiled cerebral aneurysm outcome prediction, using particle tracking simulations.

Method Computational fluid dynamics simulations of patient-specific aneurysms were performed before and after coil embolization treatment. Massless particles were virtually injected and individually tracked in each simulation, and blood flow was simulated with patient-specific boundary conditions. The coil mass was treated as a porous medium with a porosity corresponding to the in vivo treatment packing density. Simulations were also run with porosities corresponding to 50%, 150%, and 200% of the in vivo treatment packing density for each subject.

Results Five subjects were included. The relative decrease in the rate of particles entering an aneurysm had a strong correlation with increasing packing density (R² = 0.944, P < 0.001). A packing density of approximately 33.3% resulted in approximately a 70% reduction in particles entering the aneurysm. Above this packing density, the absolute number of particles was considered to be too low to be statistically reliable, and therefore further particle tracking analyses focused on simulations with packing densities less than 33.3%. Within these simulations, increasing packing density was associated with a linear increase in RT (R² = 0.462, P < 0.003) and a decrease in SH (R² = 0.547, P < 0.001), with SH nearing 0 as packing density approached 33.3%.

Conclusions The results show that increasing packing density has a predictable effect on biologically relevant metrics calculated via computational fluid dynamics with particle tracking. These changes are thought to reflect alterations in the biomechanical microenvironment that promote stable thrombus formation, which is critical for the success of endovascular therapies. Our results suggest that the maximal hemodynamic effects of packing density may be achieved near a 33.3% threshold.

Reference

1. Bass DI, Marsh LMM, Fillingham P, Lim D, Chivukula VK, Kim LJ, et al. Modeling the mechanical microenvironment of coiled cerebral aneurysms. J Biomech Eng. 2023;145(4):1-8.

Disclosures D. Bass: None. L. Marsh: None. M. Barbour: None. V. Chivukula: None. P. Fillingham: None. L. Kim: None. A. Aliseda: None. M. Levitt: 1; C; Medtronic: Investigator-initiated unrestricted educational grant; consultant Stryker: Investigator-initiated unrestricted educational grant, Stryker: Investigator-initiated unrestricted educational grant. 2; C; Medtronic, Stereotaxis, Metis Innovative. 4; C; Fluid Biomed. 5; C; Aeaean Advisers. 6; C; JNIS and Frontiers in Surgery Editorial Boards.