Comparison and modification of two cerebral protection devices used for carotid angioplasty: in vitro experiment

Meta-analysis of the Effect of Stent Design on 30-Day Outcome After Carotid Artery Stenting

Purpose: To review the contemporary literature and analyze whether stent cell design plays a role in 30-day outcomes after carotid artery stenting (CAS). Methods: A systematic review of the literature was undertaken that identified 9 studies comparing the effect of different cell design on 30-day outcome in patients undergoing CAS. Random-effects models were applied to calculate pooled outcome data for mortality and cerebrovascular morbidity. Results are reported as the odds ratio (OR) and 95% confidence interval (CI). Results: The 9 studies included 8018 patients who underwent 8028 CAS procedures (4018 open-cell stents, 4010 closed-cell stents). Six studies were retrospective in design, one was a registry, and only two studies prospectively compared the effect of different cell designs. Nearly half of the patients (3452, 43.1%) were symptomatic, with no significant difference between the closed- and open-cell stent groups (p=0.93). During the first month after the procedure, there were no significant differences in mortality (OR 0.69, 95% CI 0.39 to 1.24, p=0.21), transient ischemic attacks (OR 0.95, 95% CI 0.69 to 1.30, p=0.74), or strokes (OR 1.17, 95% CI 0.83 to 1.66, p=0.37). Conclusion: This meta-analysis showed that 30-day cerebrovascular complications after CAS were not significantly different for the open-cell group in comparison to the closed-cell group. Future prospective clinical trials comparing different free cell areas and other stent design properties are still needed to further investigate whether stent design plays a significant role in the results of carotid stenting.

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.

The Angioguard embolic protection device

Endovascular management of cardiovascular disease is quickly becoming a more popular treatment. The effectiveness in using embolic protection devices (EPDs), such as the Angioguard XP filter, during carotid artery stenting (CAS) is a topic of ongoing controversy and scrutiny. Early clinical results indicate that EPDs can reduce complications associated with CAS. However, the incidence of stroke and postprocedural embolic events are statistically similar when comparing CAS with the gold standard in carotid stenosis repair, carotid endarterectomy (CEA). The focus of this manuscript is the critical evaluation of Angioguard XP with respect to numerous in vitro and ex vivo experiments, and clinical trials that have been conducted by the authors and other researchers to investigate the efficacy of EPDs with the objective of suggesting engineering design considerations for future generations of these devices. Angioguard XP has had mixed performance outcomes in in vitro testing reported in the literature. In our laboratory, this device had undesirable measures of performance in bench-top testing protocols using in vitro flow models. Technical considerations relevant to design of EPDs, such as ideal pore size, effective wall apposition in tortuous geometry and maximization of capture efficiency have not been addressed adequately in the literature. It is likely that in the future both CAS and CEA will coexist as potential forms of treatment in the clinical management of cerebrovascular disease.

In vitro performance assessment of distal protection devices for carotid artery stenting: effect of physiological anatomy on vascular resistance

PURPOSE

To assess in vitro the performance of 5 distal protection devices (DPDs) by evaluating the capture efficiency, pressure gradient, volume flow rate, and vascular resistance in the internal carotid artery (ICA).

METHODS

The time-averaged mean peak velocity in the common carotid artery and a blood-mimicking solution were used to simulate physiologICAl conditions in a silicone carotid phantom representing average human carotid artery geometry with a 70% symmetrICAl ICA stenosis. Five milligrams of dyed 200-microm nominal diameter polymer microspheres (larger than the pore size of the devices, except Spider RX, which was tested with 300-microm-diameter particles) were injected into the ICA. The percentages of particles missed after injection and lost during device retrieval were measured for the 5 devices (Spider RX, FilterWire EZ, RX Accunet, Angioguard XP, and Emboshield). The normalized pressure gradient, fraction of the volume flow rate, and vascular resistance in the ICA were calculated.

RESULTS

Spider RX captured the most particles (missing 0.06%, p<0.05) and yielded the smallest normalized pressure gradient increase (4.2%), the largest volume flow rate fraction (0.40), and the smallest vascular resistance in the ICA (272 mmHg/L x min(-1), a 5.4% increase with respect to initial conditions). Angioguard XP captured the fewest particles (missing 36.3%, p<0.05 except Emboshield) and resulted in the largest normalized pressure gradient increase (37%) in the ICA. RX Accunet produced the smallest volume flow rate fraction in the ICA (0.30) and the largest vascular resistance in the ICA (470 mmHg/ L x min(-1), an 82.2% increase). Emboshield migrated approximately 6 cm distal to the original position after particle injection. FilterWire EZ lost the fewest particles during retrieval (0.45%, p<0.05 except Accunet RX and Spider RX) and had the best overall performance with 200-microm emboli (p<0.05 except Accunet RX).

CONCLUSION

None of the devices tested completely prevented embolization. Overall, Spider RX had the best performance and is conjectured to have the best wall apposition of the devices tested. Vascular resistance should be considered a key filter design parameter for performance testing since it represents a quantitative estimation of the "slow-flow phenomenon." Our findings should be extrapolated cautiously to help interventionists choose the best device.

Techniques in cerebral protection

Carotid angioplasty and stenting is a valid alternative option to conventional carotid endarterectomy in the treatment of carotid artery stenosis. During the stenting process, however, distal embolization can occur with neurological consequences. To avoid this, cerebral protection devices have been introduced. Three principal types of protection system have been developed: distal balloon occlusion, distal filters and proximal protection with or without reversal of flow. As protection devices became the focus of interest by manufactures and physicians, several trials are going on worldwide to analyze the characteristics of each of them and to evaluate their efficacy to reduce the rate of distal embolization.

Stent-Protected Carotid Angioplasty Using a Membrane Stent: A Comparative Cadaver Study

PURPOSE

To evaluate the performance of a prototype membrane stent, MembraX, in the prevention of acute and late embolization and to quantify particle embolization during carotid stent placement in human carotid explants in a proof of concept study.

METHODS

Thirty human carotid cadaveric explants (mild stenoses 0-29%, n = 23; moderate stenoses 30-69%, n = 3; severe stenoses 70-99%, n = 2) that included the common, internal and external carotid arteries were integrated into a pulsatile-flow model. Three groups were formed according to the age of the donors (mean 58.8 years; sample SD 15.99 years) and randomized to three test groups: (I) MembraX, n = 9; (II) Xpert bare stent, n = 10; (III) Xpert bare stent with Emboshield protection device, n = 9. Emboli liberated during stent deployment (step A), post-dilatation (step B), and late embolization (step C) were measured in 100 microm effluent filters. When the Emboshield was used, embolus penetration was measured during placement (step D) and retrieval (step E). Late embolization was simulated by compressing the area of the stented vessel five times.

RESULTS

Absolute numbers of particles (median; >100 microm) caught in the effluent filter were: (I) MembraX: A = 7, B = 9, C = 3; (II) bare stent: A = 6.5, B = 6, C = 4.5; (III) bare stent and Emboshield: A = 7, B = 7, C.=.5, D = 8, E = 10. The data showed no statistical differences according to whether embolic load was analyzed by weight or mean particle size. When summing all procedural steps, the Emboshield caused the greatest load by weight (p = 0.011) and the largest number (p = 0.054) of particles.

CONCLUSIONS

On the basis of these limited data neither a membrane stent nor a protection device showed significant advantages during ex vivo carotid angioplasty. However, the membrane stent seems to have the potential for reducing the emboli responsible for supposed late embolization, whereas more emboli were observed when using a protection device. Further studies are necessary and warranted.

Embolic protection devices for carotid artery stenting: is there a difference between filter and distal occlusive devices?

OBJECTIVES

We sought to compare the efficacy of a filter embolic protection device (F-EPD) and a distal occlusive embolic protection device (DO-EPD) in patients undergoing carotid artery stenting (CAS).

BACKGROUND

The embolic protection device (EPD) may lower the periprocedural rate of cerebral ischemic events during CAS. However, it is unclear whether there is a difference in effectiveness between the different types of EPD.

METHODS

We analyzed data from the Carotid Artery Stent (CAS) Registry.

RESULTS

From July 1996 to July 2003, 1,734 patients were included in the prospective CAS Registry. Of these patients, 729 patients were treated with an EPD, 553 (75.9%) with F-EPD, and 176 (24.1%) with DO-EPD. Patients treated with DO-EPD were more likely to be treated for symptomatic stenosis (64.5% vs. 53.4%, p = 0.011). The carotid lesions in patients treated under DO-EPD seemed to be more complicated, as expressed by a higher proportion of ulcers (p = 0.035), severe calcification (p = 0.039), a longer lesion length (p = 0.025), and a higher pre-interventional grade of stenosis (p < 0.001). The median duration of the CAS intervention was 30 min in the DO-EPD group, compared with 48 min in the filter group (p < 0.001). No differences in clinical events rate between the two groups of protection devices were observed. Multivariate analysis on the occurrence of the combined end point of in-hospital death or stroke found no difference between filter- and DO-EPD (4 of 176 [2.3%] for DO-EPD vs. 10 of 551 [1.8%] for F-EPD; adjusted odds ratio = 1.04, 95% confidence interval 0.24 to 4.44; p = 0.958).

CONCLUSIONS

Filter EPD is the currently preferred method of EPD in clinical practice. Both F-EPD and DO-EPD seem to be equally effective during CAS.

Morphometric analysis of particulate debris extracted by four different embolic protection devices from coronary arteries, aortocoronary saphenous vein conduits, and carotid arteries

Different embolic protection devices have been introduced for endovascular interventions: filters or balloon occlusion and aspiration systems. Despite widening use in a variety of vascular beds and clinical syndromes, little is known about the particulate burden liberated from different vascular beds and caught by different protection devices. We performed histologic and morphometric analyses of particulate debris captured during stenting of degenerated saphenous vein bypass grafts and native coronary arteries during acute myocardial infarction or during elective intervention and carotid arteries to assess the relative performance of different protection devices. We analyzed 232 interventions (90 saphenous vein bypass grafts, 77 native coronary arteries, and 65 carotid arteries) with 4 different devices (65 FilterWires, 99 Interceptors, 41 GuardWires, and 27 Proxis catheters) using the RapidVue particle analyzer. No difference in embolic volume retrieved was demonstrated between devices in saphenous vein bypass grafts and carotid interventions. A smaller volume of particulate debris was retrieved by the GuardWire compared with the FilterWire and the Proxis catheter in native coronary artery interventions. The Interceptor and the GuardWire captured more smaller particles than did the FilterWire or Proxis catheter. During saphenous vein bypass graft or carotid intervention, different embolic protection strategies were performed similarly. In native coronary artery stenting, however, proximal embolic protection retrieved larger amounts of debris than did distal filters or occlusion devices. These data may allow greater tailoring of embolic protection device development and application in specific anatomic locales.

Vessel Wall Damage Caused by Cerebral Protection Devices: Ex Vivo Evaluation in Porcine Carotid Arteries

PURPOSE

To determine the extent of vessel wall damage caused by cerebral protection devices designed for carotid angioplasty by using ex vivo porcine carotid arteries.

MATERIALS AND METHODS

The local animal experimentation committee did not require its approval for this study. With a benchtop vascular model (flow rate, 470 mL/min; dicrotic pulsatile flow, 76 pulses per minute; pressure, 115/67 mm Hg [mean pressure, 91 mm Hg]) into which 85 porcine internal carotid arteries (ICAs) were inserted, five different protection devices (Angioguard [Cordis/Johnson & Johnson, Miami, Fla], Filterwire EX [Boston Scientific, Natick, Mass], Trap [Microvena, White Bear Lake, Minn], Neuroshield [Abbott Laboratories, Redwood City, Calif], and Percusurge [Abbott Laboratories]) were evaluated. Adverse movement (1 cm up, 2 cm down, and 1 cm up again) of the activated devices (deployed filters or inflated balloons [Percusurge only]) was simulated, and the device was retrieved. For each of these steps (deployment, movement, retrieval) the amount of debris from the vessel wall in the effluent of the ICA was determined by using a 100-microm filter. The Mann-Whitney test was used to test for differences, and a correction for multiple comparisons was made. P < .05 was considered to indicate a significant difference. The authors attempted to determine whether there was a notable association between the total amount of debris captured and the classification of damage at microscopy. Carotid arteries were analyzed histologically with light and scanning electron microscopy.

RESULTS

All examined protection devices caused dislodged debris, which was captured in the effluent filter. There were significant differences among the devices in terms of the total amount of debris captured in the filters (lowest amounts of debris, 4.75 mg [Angioguard] and 5.02 mg [Filterwire EX]; highest amount, 7.51 mg [Trap]; P < or = .001 for all). All devices caused histologically visible wall damage, with the degree of intimal denudation correlating with the mass of the debris. The Trap device caused the most severe intimal and subintimal wall damage. Adverse movement resulted in no increased debris dislodgment as compared with the debris dislodged during deployment and retrieval of the devices.

CONCLUSION

On the basis of the data obtained, cerebral protection devices themselves have a potential influence on embolization rates by causing debris to be dislodged during carotid stent placement.

An in vitro analysis of a carotid artery stent with a protective porous membrane

PURPOSE

To prove the effectiveness of a new stent concept with integrated protection (MembraX [MX]) by comparing it with five cerebral protection devices designed for carotid angioplasty in an in vitro model.

MATERIALS AND METHODS

Two simulation series of embolization from carotid angioplasty have been performed. In the first series, polyvinyl-alcohol particles (150-250 microm [small], 355-500 microm [medium], 710-1000 microm [large]; 5 mg each) were injected into a silicone flow model simulating the aortic arch with a carotid bifurcation. The particles were injected proximally to the partially deployed MX stent or one of the following protection devices: Angioguard (AG), FilterWire EX (EX), Trap, Neuroshield (NS), or GuardWire Plus (GW). Particles evading the protection device were caught in a filter at the end of the flow model and weighed. In the second series, human plaque material (8-12 particles; total weight 6.09 +/- 0.01 mg; 500-1500 microm) was injected into the model with the respective devices. MX was compared with the AG, EX, Trap, and NS devices.

RESULTS

MX had the most effective overall filtration performance for polyvinyl alcohol particles in the effluent of the internal carotid artery (ICA; 0.43 mg, 2.9%), compared with NS (0.53 mg, 3.5%), GW (1.10 mg, 7.0%), EX and AG (1.18 and 1.21 mg, respectively; 7.8% and 8.0%), and Trap (1.24 mg, 8.2%). MX performed best for the small particles (2.0% passed particles into ICA; P < .05 compared with all). Human plaque material was retained best in the in vitro model by MX (0.0%), followed by NS (0.8%), EX (1.3%), Trap (2.6%), and AG (4.4%).

CONCLUSIONS

In vitro, none of the tested devices had the ability to prevent embolization completely. Comparing current designs, the MX device captured the highest percentage of the three different particle groups. Tested with human plaque emboli, MX performed effectively in filtering the particles in the ICA.

Comparison of 4 Cerebral Protection Filters for Carotid Angioplasty:An In Vitro Experiment Focusing on Carotid Anatomy

PURPOSE

To assess the influence of internal carotid artery (ICA) tortuosity on the effectiveness of 4 cerebral protection filters in an in vitro bench-top model.

METHODS

To simulate the anatomical arterial variants, 3 open flow models were constructed: one with normal carotid anatomy, 1 representing a mildly tortuous ICA, and a third imitating a severely tortuous ICA. Polyvinyl alcohol particles (150-1000 microm) served as the embolic material; the emboli were divided into 3 groups according to size: small (150-250 microm), medium (355-500 microm), and large (710-1000 microm). Five milligrams of each size group were injected separately into the ICA proximal to each of 4 protection filters: AngioGuard, FilterWire EX, TRAP, and NeuroShield. Emboli that were not caught by the protection system or were washed into the external carotid artery (ECA) ran into an effluent filter and were weighed and classified according to size.

RESULTS

In 240 test runs, the FilterWire EX presented the lowest weight of emboli in the ICA effluent under all anatomical conditions: normal anatomy 0.39 mg (2.58%), mild tortuosity 0.45 mg (2.99%), and severe tortuosity 0.50 mg (3.33%) (p>0.05). The Angioguard system showed the worst results: normal 1.21 mg (98.03%), mild tortuosity 2.54 mg (16.84%), and severe tortuosity 3.14 mg (20.91%) (p<0.001) compared to the FilterWire EX and the NeuroShield systems. The only protection device displaying no significant differences in all of the 3 emboli sizes was the FilterWire EX (p>0.05). Relevant differences in effectiveness in mildly and severely tortuous ICAs were apparent among the other devices. For all emboli sizes, the differences of the AngioGuard and TRAP systems were highly significant (p<0.001). There was no significant difference between the FilterWire EX and the NeuroShield.

CONCLUSIONS

The only protection device showing no significant decrease in efficacy in the tortuous ICA models was the FilterWire EX. In both tested anatomical variants, the protection systems ranked in the same order of effectiveness. None of the tested devices prevented embolization completely.

Comparison of various cerebral protection devices used for carotid artery stent placement: an in vitro experiment

PURPOSE

To compare the effectiveness of five basic cerebral protection devices designed for carotid angioplasty in an in-vitro bench-top model.

MATERIALS AND METHODS

Simulation of embolization from carotid angioplasty (n = 180) was performed with polyvinyl alcohol (PVA) particles (Contour; 150-1,000- micro m) in an open flow model simulating the aortic arch with a carotid bifurcation made from elastic silicone tubes. Particles (150-250 micro m [small], 355-500 micro m [medium], 710-1,000 micro m [large]; 5 mg each) were injected separately into the internal carotid artery (ICA) proximal to the placed protection device. Five devices were tested: the Angioguard (AG), Filter Wire EX (EX(A), EX(B)), Trap, Neuroshield (NS), and GuardWire Plus (GW). Particles getting past the protection device or flowing into the external carotid artery (ECA) were caught in a filter at the end of both arteries and their weight was determined.

RESULTS

For small, medium, and large particles, the lowest weight of emboli in the effluent of the ICA was obtained with the NS (0.28 mg, 0.18 mg, and 0.07 mg, respectively; P <.001 compared to all other devices except the GW for small particles only). The GW had the highest embolization rate into the ECA for all particle sizes. When combining the particle weights for the different protection devices, the NS showed the lowest weight of emboli into the ICA filter (0.53 mg/3.5%; P <.001 compared to all [>1.1 mg/7.0%]). The GW revealed the highest weight of emboli into the ECA (1.2 mg/7.6%; P <.001 compared to all [<0.59 mg/0.09%]). Effectiveness of the EX(B) device was enhanced when circumferentially deployed under direct view (EX(B), 0.39 mg/2.58%; EX(A), 1.18 mg/7.81%; P <.001).

CONCLUSIONS

In vitro, none of the tested devices or modifications has the ability to prevent embolization completely. An occlusion balloon leads to increased embolization into the ECA. The effectiveness of the EX might be enhanced with design improvements. During this evaluation, the NS was most effective for preventing PVA particle embolization of the three different particle groups within this in-vitro model.

Controversies in carotid stenting

Endovascular therapies are now commonly used in many vascular sites. However, the role for carotid angioplasty and stenting (CAS) remains an unproven therapy with some potential benefits. Initial results of CAS were worse than the surgical standard of carotid endarterectomy (CEA) and did not meet American Heart Association guidelines. However, recent improvements have resulted in improved stroke morbidity rate that may approach that of CEA. Specifically, the embolic problem associated with CAS has been reduced with embolic protection devices, but the ultimate effect of these protection devices remains uncertain. Initial comparison studies of CAS to CEA showed an unacceptably high stroke morbidity rate in the CAS group. As a result, multiple randomized clinical trials have been initiated to compare the results of CAS with embolic protection to that of CEA. While these studies are underway, the authors advocate a careful application of CAS to be used as a complementary tool for the carotid surgeon to use in special circumstances when CEA cannot be undertaken with acceptable morbidity. Furthermore, since the reported stroke morbidity rate of CAS exceeds the AHA recommendation for treatment of asymptomatic patients, most nonsurgical patients with asymptomatic disease should be treated with medical therapy.

In vitro comparison of four cerebral protection filters for preventing human plaque embolization during carotid interventions

PURPOSE

To evaluate in an in vitro bench-top model the efficacy of 4 filtration devices designed for cerebral protection during carotid angioplasty.

METHODS

Embolization during carotid angioplasty was simulated with human plaque material (8 to 12 particles weighing 6.02 +/- 0.10 mg) in an open flow model with the aortic arch and carotid bifurcation made from elastic silicone tubes and saline used as the fluid medium. The 500 to 1500-microm particles were injected into the internal carotid artery (ICA) in front of the test protection device, which was deployed 5 cm distal to the bifurcation. Particles getting past the protection device or flowing into the external carotid artery (ECA) were caught in 100-microm filters and weighed. Ten trials were made on each of 4 devices: Angioguard, FilterWire EX, TRAP, and NeuroShield. All were deployed according to the manufacturers' directions except the FilterWire, which was manually repositioned in all tests to eliminate a gap between the filter and the tube wall.

RESULTS

The lowest weight of missed particles in the effluent was obtained with the NeuroShield (0.05 +/- 0.04 mg, 0.8% of injected particle weight) and FilterWire (0.08 +/- 0.05 mg, 1.3%; p=0.254 compared to NeuroShield, p=0.006 versus TRAP). The weight of particles missed by the TRAP device (0.16 +/- 0.06 mg, 2.6%; p<0.001 versus NeuroShield and Angioguard, p<0.05 compared to FilterWire) was higher, and the largest amount of missed particles was observed with the Angioguard filter (0.27 +/- 0.06 mg, 4.4%; p<0.001 compared to all). NeuroShield and FilterWire were significantly different (p<0.001) compared to Angioguard and TRAP in a pairwise analysis. No embolization into the ECA occurred.

CONCLUSIONS

In vitro, none of the tested devices had the ability to completely prevent embolization into the ICA. Comparing current designs, the NeuroShield filter and the FilterWire EX captured the highest percentage of human particles in this in vitro model, probably due to their larger filter volume.