A novel intracranial exchange guidewire improves the navigation of various endovascular devices: An in vitro study of challenging situations

Abstract

Objective

Neuroendovascular procedures rely on successful navigation and stable access to the target vessel. The Stabilizer is a 300 cm long exchange wire with a 0.014 diameter and a soft, flexible stent at the distal end designed to assist with navigation and device delivery. This study aims to assess the efficacy of the Stabilizer for navigation in a variety of challenging environments.

Methods

The efficacy of the Stabilizer was evaluated using three challenging vascular models: a giant aneurysm model, a severe tortuosity model, and an M1 stenosis model. The Stabilizer was compared with a conventional wire during navigation in each model.

Results

In the giant aneurysm model, there was no significant difference of success during straightening of a looped wire and significantly higher success rates when advancing an intermediate catheter with the Stabilizer beyond the aneurysm neck compared to a conventional guidewire. The Stabilizer also significantly increased success rates when advancing an intermediate catheter through a model with severe tortuosity compared to a conventional guidewire, as well as exchange maneuver for intracranial stenting in a stenosis model compared to an exchange wire.

Conclusions

In our experimental model, the Stabilizer significantly improved navigation and device delivery in a variety of challenging settings compared to conventional wires.

Introduction

Neuroendovascular technology has evolved rapidly, with major advancements in the treatment of intracranial vascular diseases. The development of flexible and compliant catheters has greatly improved the ability to deliver devices by providing stabile access. ¹ Despite continued neuroendovascular technological advancements, unfavorable anatomy remains a significant challenge when navigating catheters and devices to target vessels. Moreover, the prolonged neuroendovascular procedure time is undeviatingly associated with higher radiation exposure to the patient and proceduralist

Giant aneurysms can be treated by reconstructing the parent vessel using flow diversion devices, but some challenges may exist in case of large diameter and acute angles between the inflow and outflow tracts of the aneurysm.^2,3 Loops are often made within the lumen of the giant aneurysm with the microcatheter, which needs to be straightened prior to stent deployment. Additionally, an intermediate catheter may be necessary to be advanced distal to the aneurysm neck in order to provide stability during stent delivery. Distal access can be lost during loop straightening and when advancing an intermediate navigation catheter over the microcatheter. As low-profile flow diversion stents continue to be developed and improved, distally located aneurysms are being treated more frequently, ⁴ and the ability to place devices distally continues to increase in importance.

In addition, tortuous anatomy can be challenging when advancing stiff devices such as the Wingspan stent system and attempts to advance or exchange devices can be complicated by the loss of access, vessel perforation, dissection, and vasospasm.^1,5 Hence, there is still an unmet need for stable navigation of neuroendovascular devices in challenging situations for efficient and safe treatments.

The stent anchor technique has been used for navigation during the treatment of aneurysms and ischemic stroke.^5,6 A resheathable stent is anchored in the distal vessel, which allows the catheter or device to be advanced through the tortuous anatomy or giant aneurysm without losing distal access.^5–7 However, the wire length of the stents is about 200 cm and cannot be used for exchange maneuvers. Furthermore, the cost of current stents used for this maneuver may pose limitations in widespread use of this technique.

The Stabilizer (Bolt Medical, Chuo-ku, Tokyo, Japan) is an exchange wire with a retrievable stent at the distal end (Figure 1). The Stabilizer has the potential to be used in a similar method when navigating challenging anatomy but has the added advantage of sufficient length to perform a microcatheter exchange (300 cm). Additionally, the Stabilizer is a soft, flexible device with a smaller diameter (0.014 inch) which allows it to be advanced through a small microcatheter.

Figure 1.

The stabilizer is a 300 cm long, 0.014 inch diameter wire with a retrievable stent at the distal end. The size of Stabilizer stent is 4 mm by 20 mm.

To examine the feasibility and efficacy of the Stabilizer in comparison with conventional technique, we created three artificial vascular models to investigate the efficacy of the Stabilizer for navigation of microcatheters, intermediate catheters, and stiff devices through challenging anatomy.

Materials and methods

Model preparation

To assess the efficacy of the Stabilizer for navigation, three human anterior circulation models were used to assess a variety of challenging test environments. Angulation, degree of curvature, and vessel radii were modified to represent different anatomical configurations of the cervical segment of the internal carotid artery (ICA), the carotid siphon, and the middle cerebral artery (MCA). The models also have the anterior cerebral artery and the external carotid artery (ECA).

The silicone vascular models were prepared using the methods previously described by Kaneko et al. ⁸ The core of the model was created using a 3D fused deposition molding process with a copolymer of acrylonitrile, butadiene, and styrene, and was smoothed prior to silicone molding. Silicone was prepared and vacuum degassed prior to applying the core. The silicone was then cured at 60°C for 4 h. After 5–10 applications, the core was dissolved chemically, leaving the silicone vascular model.

In vitro experiment

The silicone models were connected to a perfusion pump with tubing to control the hydrostatic pressure to 100 mmHg, representative of mean arterial pressure. The fluid, consisting of a 60/40% water/glycerin solution with detergent, which has a similar viscosity to human blood, was heated to 37°C and perfused in the circulation at a rate of 400 mL/min. The flow rates of the ICA and ECA in the model were 240 mL/min and 160 mL/min, respectively. The flow rate of each vessel was verified before the experiments.

The efficacy of the Stabilizer compared to a conventional wire was assessed in each of the vascular models. The experiments were performed by experienced neurointerventionalists. The giant aneurysm model was used to test the utility of the Stabilizer when reducing a wire or microcatheter loop in the aneurysm. A Synchro2 standard guidewire and SL-10 microcatheter (Stryker Neurovascular) were used to access the M2 segment of the MCA, and two or three wire or microcatheter loops were formed within the giant aneurysm. Loops of wire and microcatheter were reduced while the Synchro2 or Stabilizer was used to maintain distal access. The maneuver was marked as successful if the wire was completely straightened without losing access to the M1 segment.

The efficacy of the Stabilizer when advancing an intermediate catheter through the giant aneurysm model was assessed. Each test wire was placed in the distal M2 segment of the MCA through an SL-10 microcatheter. An AXS Catalyst 5 distal access catheter (Stryker Neurovascular) was advanced over the Stabilizer or with a Synchro2 standard guidewire and the microcatheter. The navigation was recorded as a success if the Catalyst 5 catheter was advanced into the M1 segment.

In a model with severe tortuosity, each test wire was placed in the M2 segment of the MCA through a Phenom 21 microcatheter (Medtronic Neurovascular) and a 6 Fr Sofia Flow Plus catheter (MicroVention Terumo) was advanced over the Stabilizer or Synchro2 and the microcatheter. The navigation was considered a success if the Sofia intermediate catheter was advanced to the ICA terminus.

In a model with moderate tortuosity, a Wingspan stent 3 × 15 mm (Stryker Neurovascular) was advanced over the Stabilizer or CHOICE Floppy guidewire (Boston Scientific Corporation). Navigation was scored as successful if the Wingspan stent was advanced to the distal M1 segment.

Statistical analysis

Navigation with the Stabilizer versus the conventional guidewire was repeated 10 times in the vascular models. Comparisons of successful navigation between the Stabilizer and guidewire were made using the Fisher's exact test The threshold of significance for all tests was 0.05. Analyses were performed using STATA (version 13) software.

Results

Looped catheter straightening in a giant aneurysm model

The efficacy of the Stabilizer was compared to a Synchro2 guidewire when straightening redundant loops of microcatheter and wire in the giant aneurysm model. The giant aneurysm model with multiple loops of wire and microcatheter with positioning of the Synchro2 or Stabililzer in the M2 segment can be seen in Figure 2(a) and (b). Figure 2(c) shows successful reduction of the loops using the Stabilizer. The Stabilizer had a slightly higher success rate compared to the Synchro2 guidewire, but this did not reach statistical significance (Table 1, p = 0.21).

Figure 2.

Straightening a microcatheter and advancing an intermediate catheter in a giant aneurysms model. (a) Microcatheter looped within the giant aneurysm model. The tip of the Synchro2 wire positioned in the M2 segment prior to straightening a microcatheter (black arrowheads). (b) The Stabilizer is deployed in the MCA (black arrowheads). (c) Demonstration of successful microcatheter straightening. The microcatheter has been straightened (black arrow) using the Stabilizer as a distal anchor in the MCA (black arrowheads). (d) Giant aneurysm model with the Synchro2 wire positioned in the M2 segment prior to advancing the intermediate catheter (black arrowheads). (e) Stabilizer deployed prior to advancing the intermediate catheter (black arrowheads). (f) Unsuccessful advancement of the intermediate catheter using Synchro2 guidewire as an anchor. The intermediate catheter could not be advanced distal to the aneurysm (black arrow) and looped within the aneurysm (black arrowheads). (g) Successful advancement of the intermediate catheter into the MCA (black arrow) using the Stabilizer as an anchor (black arrowheads).

Table 1.

Type of in-vitro model, procedure technique, and success rate.

Model	Technique	Successful Navigation rate		p value
		Stabilizer	Conventional wire
Giant Aneurysm	Microcatheter straightening	10/10	7/10	p = 0.21
Giant Aneurysm	Advancement of intermediate catheter	8/10	2/10	p < 0.001
Severe tortuosity model	Advancement of intermediate catheter	9/10	1/10	p = 0.001
M1 stenosis model	Exchange for Wingspan	9/10	0/10	p < 0.001

Advancing an intermediate catheter through a giant aneurysm model

The Stabilizer was compared to a Synchro2 guidewire during the advancement of an intermediate catheter through a giant aneurysm model. The model before advancing the Catalyst 5 with the Synchro2 guidewire and Stabilizer positioned in the M2 segment are shown in Figure 2(d) and (e), respectively. Unsuccessful navigation of the Catalyst 5 when using the Synchro2 guidewire and successful navigation when using the Stabilizer are shown in Figure 2(f) and (g) respectively. The Stabilizer had a significantly higher success rate (80% vs. 20%) compared to the conventional guidewire when advancing the Catalyst 5 through the giant aneurysm model (p < 0.001). Success rates are shown in Table 1. The Catalyst 5 had a tendency to become caught at the outlet of the giant aneurysm when using the conventional guidewire. When the Catalyst 5 was pushed again to advance it further, the catheter would build up significant resistance and form redundancies without advancing into the distal parent artery. In contrast, slight tension could be applied to the Stabilizer, allowing the intermediate catheter to easily glide through the outlet of the aneurysm.

Advancing an intermediate catheter through a severe tortuosity model

The efficacy of intermediate catheter navigation was compared between the Stabilizer and a Synchro2 guidewire in a model with severe tortuosity. The severe tortuosity model before navigation using the Synchro2 guidewire and before and after successful navigation while using the Stabilizer for support is shown in Figure 3(a) to (c). The Stabilizer had significantly higher success rates when advancing a 6 Fr Sofia through a model with severe tortuosity compared to a conventional guidewire (p = 0.001, (Table 1)). Like in the giant aneurysm model, the ability to apply tension to the Stabilizer facilitated navigation of the device through the curvature.

Figure 3.

Advancing an intermediate catheter in a tortuous vessel model. (a) The tip of the Synchro2 wire is positioned in the M2 segment (black arrowheads) in the severe tortuosity model prior to advancing the intermediate catheter (black arrowheads). (b) Stabilizer deployed in the M2 segment prior to advancing the intermediate catheter (black arrowheads). (c) Successful advancement of the intermediate catheter into the M1 segment (black arrow). The Stabilizer is still in place in the M2 segment (black arrowheads).

Exchange maneuver in an M1 stenosis model

The Stabilizer had significantly higher success rates when compared to the CHOICE Floppy guidewire (p < 0.001). Success rates are shown in Table 1. When the conventional exchange wire was used to perform the exchange, the Wingspan Stent could not be advanced to the MCA despite applying substantial force. The placement of the CHOICE Floppy wire in the M1 stenosis model prior to the exchange maneuver is shown in Figure 4(a). The M1 stenosis model before and after successful exchange and advancement of the Wingspan stent using the Stabilizer is shown in Figure 4(b) and (c).

Figure 4.

Intracranial stent exchange maneuver. (a) CHOICE Floppy wire deployed in the M1 stenosis model prior to exchange maneuver (black arrowheads). (b) Stabilizer deployed in the M2 segment (black arrowheads). (c) Successful exchange and advancement of the Wingspan stent into the M1 segment (black arrow).

Discussion

Our study showed that the Stabilizer significantly increases success rates in navigation and device delivery in a variety of challenging settings. In our giant aneurysm model, the Stabilizer had higher rates of success during the straightening of a looped wire as well as with advancing an intermediate catheter distal to the aneurysm. The Stabilizer also significantly increased success rates when advancing an intermediate catheter through a model with severe tortuosity and when performing an exchange maneuver with the Wingspan stent in an M1 stenosis model.

Giant aneurysms present unique challenges for achieving and maintaining access, including unfavorable angles between the inflow and outflow tracts, flow characteristics, and wide or complex necks.^2,6,7 Previously proposed techniques to maintain access while intra-aneurysmal looping are reduced or while the necessary larger catheters are advanced include balloons,^1,7,9,10 detachable coils, ² stents,^6,11–16 microwires, ¹⁷ stent retrievers,^18,19 and the rapid pull-back technique. ²⁰ In this study, the results suggested that the Stabilizer could be used for multiple techniques while treating a giant aneurysm, including straightening of intra-aneurysmal looping, exchange for a stent delivery catheter, and advancement of an intermediate catheter.

When catheterizing the distal parent vessel in a giant aneurysm, the wire often must be looped in the dome prior to exiting the aneurysm. The microcatheter tip in the distal parent vessel may be pulled back into the aneurysm dome when attempting to straighten the loop for stent delivery.^2,19 In 2007, Cekirge et al. described a balloon anchoring technique in which a Hyperform balloon catheter (Medtronic) was inflated in the distal parent vessel while the wire was gently retracted and the loop straightened. ²¹ Other balloons have been used for similar techniques, including the Sceptor XC (Microvention Terumo) and the Gateway balloon catheter (Stryker Neurovascular)^1,8 While the use of a balloon may provide adequate support, drawbacks include temporary occlusion of flow, over-straightening of curved segments and potential vessel rupture. We found that the Stabilizer had higher rates of success when straightening loops in a giant aneurysm compared to a conventional guidewire. In contrast to a balloon, the stent of the Stabilizer is unlikely to cause excessive straightening of a vessel and does not occlude flow. The wire of the Stabilizer has a small diameter (0.014 inch) and is soft and flexible which allows it to be advanced even when access is tenuous.

When placing flow diversion stents in giant or complex aneurysms, an intermediate navigation catheter may be advanced beyond the neck of the aneurysm. ²² The intermediate catheter can provide sufficient support during the “push phase” of stent deployment, and can be used to “nudge” the proximal end of the stent to encourage complete opening and improved wall apposition. ²³ By advancing an intermediate catheter distally, the risk of device prolapse back into the aneurysm is decreased, less tension occurs within the guide catheter, and one-to-one torque responsiveness can be preserved.^24,25 In the present study, the ICA model had focal stenosis distal to the aneurysm, which made it difficult to navigate the intermediate catheter to the MCA. By using the Stabilizer as an anchor, the intermediate catheter could be easily advanced distal to a giant aneurysm.

In patients with severe tortuosity, the initial delivery of intermediate catheters to the target vessel during endovascular procedures can be time-consuming and may require multiple attempts. Stent retrievers and balloon catheters have been used to facilitate navigation of intermediate catheters during catheters to target vessels for mechanical thrombectomy.^1,5,26–28 Like a stent retriever, the Stabilizer can be used as an anchor when advancing an intermediate catheter through severe tortuosity, as was demonstrated in the present study.

The Stabilizer can also be used to maintain distal access during microcatheter exchange. In the Stenting versus Aggressive Medical Therapy for Intracranial Arterial Stenosis (SAMMPRIS), 4 of 224 patients (1.7%) who underwent Wingspan stent placement experienced symptomatic intracranial hemorrhage that was attributed to guidewire perforation. ²⁹ In our study, the Stabilizer improved navigation of the Wingspan stent through a moderately curved segment. In addition to improving navigation, the Stabilizer is expected to reduce the risk of vessel perforation during the exchange because of its stable position and the presence of the expanded stent at the end of the wire.

Several reports described the off-label use of traditional stent retrievers for the exchange of microcatheters in the setting of giant aneurysms.^18,19 The initial navigation through a challenging giant aneurysm is often performed using a flexible guidewire and small microcatheter such as 0.0165 inch inner diameters, but the small microcatheter must be replaced with a larger microcatheter with an 0.027 inner diameter through which a flow diversion stent can be deployed. ¹⁹ When a traditional stent retriever is used, special steps must be taken to prevent air embolism when the second microcatheter is introduced because the wire is not long enough to perform a typical exchange maneuver. ¹⁸ Additionally, when advancing the second microcatheter, the operator does not have control of the stent push wire due to its short length.^18,19 These issues are resolved by the 300 cm length of the Stabilizer as it is designed to be used for exchanges. With adequate exchange length, the second microcatheter can be introduced without an increased risk for air embolism, and the operator has control of the exchange wire at all times.

One limitation of our study is that it was performed in an in vitro setting and may not reflect the many factors that can affect navigation in a clinical setting. Complications such as vessel perforation, dissection, or aneurysm rupture cannot be reproduced in the silicone models. Future in vivo or clinical studies will be necessary to assess the safety and efficacy of the Stabilizer.

Conclusions

In this experimental model, the use of the Stabilizer resulted in higher rates of successful navigation compared to navigation with a conventional guidewire. The Stabilizer has a variety of potential uses, including straightening of redundant loops in giant aneurysms or navigation of intermediate catheters in giant aneurysms, navigation through tortuous anatomy, catheter exchanges, and navigation of stiff devices. The small diameter allows the device to be advanced smoothly through difficult anatomy without losing distal access, and the presence of a stent at the distal end of the 300 cm wire improves the ability to perform a stable exchange maneuver. The safety and efficacy of the Stabilizer should be evaluated further in future clinical studies.