In Vitro Performance Assessment of Distal Protection Devices for Carotid Artery Stenting:Effect of Physiological Anatomy on Vascular Resistance

Safety and efficacy of an open-cell stent and double-balloon protection for unstable plaques: analysis of 184 consecutive carotid artery stentings

INTRODUCTION

In our institute, most cases of carotid artery stenosis are treated by carotid artery stenting (CAS) with an open-cell stent and double-balloon protection, even if plaques are unstable. This study was performed to examine the outcome of CAS with an open-cell stent and double-balloon protection for unstable plaques.

METHODS

A total of 184 CAS procedures in our institute between October 2010 and February 2018 were assessed. Ultrasonography findings of low-echo plaques, plaque ulceration, or both were defined as unstable plaques. A plaque-to-muscle ratio (PMR) of >1.8 on T1-weighted black blood imaging using spin-echo was also defined as an unstable plaque. Seventy-four unstable plaques on ultrasonography and 86 unstable plaques evaluated by PMR were included. Open-cell stents and double-balloon protection (proximal balloon protection during lesion crossing and distal balloon protection after lesion crossing) were used in all cases.

RESULTS

On ultrasonography, perioperative asymptomatic thromboembolization was significantly more frequent in the unstable plaque group (39/74, 52.7%) than in the stable plaque group (41/110, 37.3%, p=0.0384). Asymptomatic thromboembolization was also significantly more frequent in the PMR >1.8 group (44/86, 51.2%) than in the PMR <1.8 group (36/98, 36.7%, p=0.0489). However, symptomatic thromboembolization was rare (n=5, 2.7%), and all of these patients had minor stroke. During the 4-year follow-up, the risk of ipsilateral stroke was 0.28% and 0.27% per year in patients with symptomatic and asymptomatic lesions, respectively.

CONCLUSIONS

The outcomes of CAS with an open-cell stent and double-balloon protection are acceptable. This method is effective and safe, even if carotid artery stenosis comprises unstable plaques.

Combination of flow reversal and distal filter for cerebral protection during carotid artery stenting

BACKGROUND

Carotid artery stenting (CAS) with distal filter protection allows continuous cerebral perfusion, although it is associated with a greater risk of cerebral ischemic complications than other protection systems. To reduce cerebral ischemic complications, CAS was performed under combined cerebral protection using both flow reversal (FR) and a distal filter.

METHODS

Fifty-six stenoses of 52 patients were treated with CAS using the combined protection of FR and a distal filter, with intermittent occlusion of both the common carotid artery (CCA) and the external carotid artery. The blood flow was reversed into the guiding catheter to the central venous system via an external filter, which collected the debris. Clinical outcomes, the rates of capturing visible debris, and new ischemic signals on diffusion-weighted magnetic resonance imaging (DWI-MRI) were evaluated.

RESULTS

The overall technical success rate was 92.9% (52/56). Successful stent deployment was achieved in 100% (56/56) of the cases. No procedural-related emboli causing a neurologic deficit were observed. In 38.5% (20/52) of the cases, visible debris were captured by only the external filter, and in 17.3% (9/52), visible debris were captured by both external and distal filters. In no case was visible debris noted in only the distal filter. New ischemic signals on DWI-MRI were detected in 9.6% (5/52). The 30-day myocardial infarction, stroke, and death rates were 0%.

CONCLUSIONS

The additional use of a distal filter captures emboli in 17.3% of cases, and because the occlusion is only intermittent, the procedure is potentially applicable even in those who cannot tolerate prolonged balloon occlusion of the CCA.

Historical perspective of carotid artery stenting in Japan: analysis of 8,092 cases in The Japanese CAS survey

BACKGROUND AND PURPOSE

We conducted a large retrospective survey of the clinical results of carotid artery stenting (CAS) for about 10 years performed by neurointerventionists at 43 Japanese institutions. Hence, the historical perspective of CAS in Japan was demonstrated.

METHODS

Cases were stratified into three separate periods based on the approval status of devices: the first period, in which off-label CAS was performed using balloon protection; the second period, using a limited number of approved devices under filter protection; the third period, using appropriate protection selected from several different options based on the preoperative evaluation (tailored CAS). Clinical results were retrospectively evaluated. Then 30-day results of each period were examined. The major adverse event (MAE) was defined as stroke, myocardial infarction or death.

RESULTS

Between January 2001 and December 2010, a total of 8,092 cases were registered, including 4,072, 1,526 and 2,494 in the first, second and third period, respectively. In the first period, 92 % of CAS was performed under balloon protection. In contrast, 91 % was done under filter protection in the second period. In the third period, various protection methods were used, including balloon (31 %), filter (50 %) and proximal protection (18 %). The rate of MAE at 30 days was 6.1 %, 10.2 % and 3.5 % in the first, second and third periods, respectively, and 6.3 % in all periods combined. The rate of MAE in the third period was significantly lower than that in the first and second periods.

CONCLUSIONS

The historical paradigm of CAS in Japan was demonstrated. Due to the improvement of devices, increasing experience and appropriate selection of protection, CAS is continuing to evolve into a safer and more efficacious method of stroke prevention.

Computational modeling of distal protection filters

PURPOSE

To quantify the relationship between velocity and pressure gradient in a distal protection filter (DPF) and to determine the feasibility of modeling a DPF as a permeable surface using computational fluid dynamics (CFD).

METHODS

Four DPFs (Spider RX, FilterWire EZ, RX Accunet, and Emboshield) were deployed in a single tube representing the internal carotid artery (ICA) in an in vitro flow apparatus. Steady flow of a blood-like solution was circulated with a peristaltic pump and compliance chamber. The flow rate through each DPF was measured at physiological pressure gradients, and permeability was calculated using Darcy's equation. Two computational models representing the RX Accunet were created: an actual representation of the filter geometry and a circular permeable surface. The permeability of RX Accunet was assigned to the surface, and CFD simulations were conducted with both models using experimentally derived boundary conditions.

RESULTS

Spider RX had the largest permeability while RX Accunet was the least permeable filter. CFD modeling of RX Accunet and the permeable surface resulted in excellent agreement with the experimental measurements of velocity and pressure gradient. However, the permeable surface model did not accurately reproduce local flow patterns near the DPF deployment site.

CONCLUSION

CFD can be used to model DPFs, yielding global flow parameters measured with bench-top experiments. CFD models of the detailed DPF geometry could be used for "virtual testing" of device designs under simulated flow conditions, which would have potential benefits in decreasing the number of design iterations leading up to in vivo testing.

Blood flow changes caused by distal filter protection and catheter aspiration in the internal carotid artery during carotid stenting: evaluation using carotid Doppler sonography

BACKGROUND AND PURPOSE

If blood flow in the ICA is reduced by the use of a distal filter during CAS, flow stagnation proximal to the filter occurs and this increases the probability of floating debris. The floating debris that remains after filter retrieval may cause cerebral embolism. However, if blood flow is increased by aspiration of blood from the ICA through an aspiration catheter, debris could be removed while the filter is still in place. The purpose of this study was to investigate blood flow changes in the ICA induced by filter use and aspiration.

MATERIAL AND METHODS

A filter-protection device (AngioGuard XP) was used during CAS in 13 consecutive patients with carotid stenosis. Blood flow velocity in the ICA was measured by carotid Doppler sonography during filter deployment, filter retrieval, and catheter aspiration.

RESULTS

Blood flow velocity significantly decreased with filter placement and significantly increased with filter retrieval in patients with normal angiographic flow (P < .05). Aspiration of a 20-mL blood sample from the proximal ICA column significantly increased the blood flow velocity (P < .05).

CONCLUSIONS

The blood flow changes in the ICA induced by the use of a distal filter may cause cerebral embolism in filter-protected CAS. A routine aspiration method can potentially reduce the amount of migrating debris during CAS, even in cases with angiographic normal flow.

In vitro performance assessment of distal protection filters: pulsatile flow conditions

PURPOSE

To evaluate in vitro the capture efficiency of a distal protection filter (DPF) used during carotid artery stenting and examine the longitudinal vascular impedance in the presence of a DPF.

METHODS

Four approved DPFs (Spider RX, FilterWire EZ, RX Accunet, and FiberNet) were evaluated in a physiologically realistic in vitro setup. A pulsatile programmable piston pump circulated a blood analog at a time-varying flow rate representative of the human common carotid artery. A silicone carotid bifurcation having average human dimensions was used for the carotid flow model. Microspheres ranging from 40 to 900 microm were injected to simulate embolization. The longitudinal vascular impedance was calculated as the ratio of the time-varying pressure gradient across the DPF to the time-varying flow rate in the internal carotid artery.

RESULTS

RX Accunet had the highest capture efficiency (99.4%) and Spider RX the lowest (78.1%). Spider RX increased the longitudinal vascular impedance the least after deployment (+23%), while FilterWire EZ increased the longitudinal vascular impedance the least after particles were injected (+29%). FiberNet increased longitudinal vascular impedance the most (+84%).

CONCLUSION

This investigation, unique for examining the effects of physiologically realistic pulsatile flow on DPF performance, can aid in the development of future generations of novel DPFs.