Distal filtration versus flow reversal: An ex vivo assessment of the choices for carotid embolic protection

Abstract

Objectives: Choices for embolic protection during carotid stent procedures include distal filtration (DF) and proximal occlusion with flow reversal (POFR). DF devices are widely used but have produced only modest improvements in clinical outcomes. There is less experience with POFR devices but single center reports suggest reduced emboli detected by transcranial Doppler (TCD). To determine if POFR offers a significant improvement in embolic protection, we tested five DF devices and two POFR devices with 8F and 10F sheath design in an ex vivo angioplasty system using human carotid plaques excised en bloc. Physiologic pressures and flows were used and the efficiency of plaque fragment removal by these devices compared. Methods: Thirty-three human carotid plaques removed en bloc were secured in tailored polytetrafluoroethylene (PTFE) grafts. The distal PTFE was either 6 mm or 5 mm inner diameter (ID). Saline was delivered through the excised carotid plaque as follows: a cleaning 50 mL flush was done prior to the angioplasty procedure and discarded; further flushes of forward flow were done with five pressurized "pulsations" of 10 mL each (50 mL), peak pressure 140 mm Hg. Balloon angioplasty was done with a 4 mm and then a 6 mm balloon. DF flushes were applied after each angioplasty and "postprocedure" after the device was removed. With POFR, 50 mL were collected through the sheath after balloon angioplasty by either back-pressure of 20 mm Hg, 40 mm Hg or 60 mm Hg, or by aspiration. Postangioplasty pressurized forward flush of 50 or 100 mL was done as described. Each flush was collected, centrifuged, and examined for plaque fragments. Fragments greater than 60 microns were sized and counted on a 100 micron grid. Results: When DF devices were used in 6 mm lumen PTFE, the percent of fragments trapped was poor (13.7% to 27.8%). There were no statistically significant differences between the devices. The capture of fragments improved (22% vs 51.4%, P < .001) when devices appropriate for a 6 mm lumen were used in a 5 mm PTFE "ICA", functionally over-sizing the devices. POFR efficiency improved with increasing back-pressures and with repeated aspirations. Postprocedure, successive flushes of pressurized forward flow yielded additional plaque fragments and when the efficiency of POFR was assessed with forward flushing volumes similar to those used for DF, the efficiencies were similar, although larger fragments were more efficiently removed with POFR. Conclusion: In our model, both protection strategies were less than ideal. For POFR, high back pressures or multiple aspirations improve the efficiency of cerebral protection but additional fragments were released by pressurized flow even after aspiration of 150 mL of saline. DF devices create a pressure gradient and fragments apparently went around the device with pressurized flow in our PTFE lumen. Over-sizing of DF devices partially corrected this problem and increased over all DF efficiency to be comparable to POFR for smaller fragments but not for larger fragments.