Obstruction of pores in distal protection filters and angiographically-documented flow impairment during carotid artery stenting.

Purpose: To determine any relationship between angiographically documented flow impairment associated with the Angioguard XP cerebral protection filter during carotid artery stenting (CAS) and the condition of the pores in the retrieved filter.

Methods: To obtain baseline characteristics of the Angioguard XP, an unused filter was fully expanded and examined photographically from the cephalad end of the device to determine the structure of the pores in the filter basket. Ten pores assembled in a hexagonal pattern made up a pore group, several of which were arranged in 4 concentric rings surround a central hub that did not have any pores. For each ring of pore groups, the ring diameter, number of pore groups, and the mean minimum pore diameter were measured on a plane perpendicular to the long axis of the device. From these, the area of the ring membrane, the area of the pores, and the ratio of pore area to membrane area were calculated for each ring. Filters retrieved from 56 CAS procedures were retrospectively analyzed along with the operative records and intraprocedural angiograms performed after filter placement, predilation, stent placement, postdilation, aspiration of blood, and filter retrieval. The operators classified blood flow immediately before filter retrieval as normal, slow, or stopped. After retrieval, the filter was cut, rinsed with saline, fixed in 10% neutral buffer formalin, and macroscopically and microscopically inspected. The number of the open pores without any obstruction was counted for each ring.

Results: Retrieved filters from flow-impaired cases showed a significantly lower percentage of open pores in comparison to normal-flow cases (p<0.05). In some normal-flow cases, however, the obstruction rates were higher than mean obstruction rates of the slow-flow cases. In normal-flow cases, <5% of pores from the center to the second ring of the filter were open; this constituted more than two thirds of the entire filter diameter.

Conclusion: The flow state on DSA was related to, but did not completely depend on, filter patency. The low patency rate of the filter in normal-flow cases suggested that flow impairment was occurring but could not be detected by the qualitative evaluation of flow on angiography.