Flow Impairment During Filter-Protected Carotid Artery Stent Placement: Frame-by-Frame Evaluation of Digital Subtraction Angiography Images

Objective To evaluate quantitatively flow impairment of contrast medium on digital subtraction angiography (DSA) performed before and after filter retrieval following carotid artery stent (CAS) placement with distal filter protection. Methods Retrospective analysis was performed of 55 CAS placement procedures with distal filter protection in 51 patients. From a qualitative analysis, the operators determined if there was flow reduction of contrast medium on digital subtraction angiography (DSA) before filter retrieval. A quantitative analysis was performed of frame-by-frame images before and after filter retrieval to compare the flow state of contrast medium. Results Stop-flow or slow-flow classified by the operators during CAS placement was found in 10 (18%) of 55 procedures. However, the frame-by-frame analysis of DSA images showed flow reduction of contrast medium in 46 (84%) of 55 procedures. Among 45 procedures with normal-flow as classified by the operators, 36 (80%) procedures showed ≥1 frames with delay of contrast medium based on quantitative analysis. Conclusions The frame-by-frame comparison of angiographic images revealed a much higher incidence of blood flow impairment on DSA before filter retrieval compared with the operators' classification during CAS placement procedures. Considering the high incidence of blood flow impairment, the possibility of stagnation of blood flow in the internal carotid artery (ICA) column should be expected during every CAS placement procedure.