Key-words:
Beanstalk method - catheter - ledge effect - neurointervention
Introduction
The ledge effect is one of the most important barriers to successful endovascular treatment. A large-caliber aspirator is often used to perform endovascular thrombectomy for the treatment of acute ischemic stroke.[[1]],[[2]] When navigating the aspirator through the carotid siphon, the ledge effect is often encountered at the origin of the ophthalmic artery. The gold standard technique for mitigating the ledge effect is reduction of the gap between the aspirator and the inner catheter; however, this approach is not effective in some challenging cases. We performed an in vitro study to find an alternative to mitigate the ledge effect. Here, we report a new technique called the “beanstalk method,” which allows for safe navigation of a large-caliber catheter through a model of challenging vasculature, and discuss the utility of this approach.
Materials and Methods
In this study, we used the 5MAX™ ACE68™ reperfusion catheter (Penumbra Inc., Alameda, CA, USA) as the large-lumen catheter. A silicon vascular model with a notch in the middle of the curvature was used [[Figure 1]]a. In the model, the ACE68 catheter never passed through the notch, even when using a coaxial 3MAX catheter (Penumbra Inc.) [[Figure 1]]b and [[Figure 1]]c.
Figure 1: (a) Photograph of a silicon vascular model with a notch in the middle of the curvature (arrow). (b and c) The red arrows indicate the tip of the 5MAX ACE68 reperfusion catheter (Penumbra Inc., Alameda, CA, USA). The yellow arrowhead indicates the coaxial 3MAX catheter (Penumbra Inc.). The ACE68 catheter never passed beyond the notch because of the ledge effect
Beanstalk method
Two 0.014” micro-guidewires (MGWs) (Chikai 14 MGW: Asahi Intecc, Aichi, Japan) are used for navigation of the ACE68 catheter. After one MGW is navigated to the distal portion, another MGW, with a modified pigtail-shaped tip [[Figure 2]]a, is advanced along with the original MGW spirally, similar to the growth of a beanstalk. A schematic drawing is shown in [[Figure 2]]b. Then, the ACE68 catheter is advanced with the coaxial double MGW. We performed an in vitro study to investigate the mechanism that allowed for the success of this beanstalk method.
Figure 2: (a) Photograph of a 0.014” microguidewire formed into a modified pigtail shape. (b) Schematic drawing of the beanstalk method. After one guidewire is navigated to the distal portion, another is advanced along the first, in a spiral fashion. (c and d) The yellow arrowheads indicate twined wire surrounding the other wire. The red arrows indicate the tip of the ACE68, which was advanced easily, without any resistance caused by the ledge effect
Results
When the two MGWs were navigated in a simple parallel fashion, the ACE68 catheter could not follow the MGWs. However, navigation of the second MGW added torque to the MGW; the tip was twisted (3–5 times) around the former wire [[Figure 2]]c. The ACE68 catheter could then be advanced easily [[Figure 2]]d.
We thought that the effect of the beanstalk method reflected increased support from the harder MGWs, compared with the parallel double MGW. Therefore, we compared hardness using a 1-g addition at each tip. There was no apparent difference in flexibility between the parallel and spiral MGWs [[Figure 3]]. The results obtained did not confirm our hypothesis.
Figure 3: (a and b) Photograph depicting the in vitro study. The white arrowheads indicate a 1-g weight. The black arrow indicates the parallel double-wires. The red arrow showing spiral double-wires. In contrast to our expectations, there was no apparent difference in flexibility between the parallel and spiral wires
Next, we investigated the shapes of the two MGWs at the tip of the ACE68 catheter. When using parallel MGWs, the outer edge of the ACE68 was independent of the MGWs [[Figure 4]]a and [[Figure 4]]b. However, when using the beanstalk method, one of the MGWs could be traced to the outer edge of the ACE68 catheter [[Figure 4]]c and [[Figure 4]]d. We concluded that the beanstalk method could reduce the ledge effect because there was less gap between the catheter and MGWs at the outer side with the use of the beanstalk method, compared with the use of the parallel double MGW.
Figure 4: Photograph of in vitro experiments. (a and b) When using parallel wires, the outer edge of the ACE68 was independent of the wires (black arrow). (c and d) When using the beanstalk method, one of the wires can be traced at the outer edge of the ACE68 catheter (red arrow)
Discussion
We found that the severe ledge effect caused by the use of a large-caliber catheter could be mitigated by the use of a spiral double MGW. The ledge effect is one of the most important barriers to successful endovascular treatment. Large-caliber aspirators are often used to perform endovascular thrombectomy as treatment for acute ischemic stroke. The aspirator may be used alone or in combination with the stent retriever.[[1]],[[2]]
The ledge effect is often encountered at the origin of the ophthalmic artery when navigating the aspirator through the carotid siphon. Reduction of the gap between the aspirator and the inner catheter is considered the first-line approach to mitigating the ledge effect. However, this approach is not effective in some challenging cases. Although the stent retrieving into an aspiration catheter with proximal balloon technique [[2]] allows for the use of a stent retriever deployed in the distal portion as a strong anchor during navigation of the aspirator, this approach may not be effective in patients with a challenging vasculature.
Some authors have reported on the effectiveness of a buddy-wire technique in reducing the ledge effect.[[3]],[[4]] Muraoka et al.[[4]] reported that the ledge effect associated with the use of a microcatheter with a lumen of 0.027” was mitigated by the use of 0.014” and 0.010” MGWs. The authors concluded that it was important to fill the inner lumen of the catheter to the extent possible using two MGWs to reduce the ledge effect. Although thick guidewires are generally required to fill the lumen of a large-caliber aspirator, the particular anatomy of the case presented here prevents the navigation of thick wires into the intracranial artery. We, therefore, elected to use thin, soft MGWs.
The use of parallel MGWs was not effective for navigation of the aspirator. We next tried to navigate the aspirator with spiral MGWs. When this “sheep technique”[[5]] failed, we had already used the spiral wires, in a fashion similar to the growth of a beanstalk, to follow the guidewire. We used an MGW with a modified pigtail shape to achieve this spiral pattern.[[6]],[[7]] The results obtained show that the beanstalk method may be effective for decreasing the ledge effect. The gap between the catheter and the MGW traveling along the exterior of a tortuous vessel decreased in size with the use of this novel technique, compared with the use of a parallel double MGW. This technique did not require the use of thick, hard guidewires in order to fill the catheter lumen. We recommend the navigation of two microwires one after another. If the two wires are advanced into the large-caliber catheter simultaneously, they might be broken due to negotiations.
This study had some limitations. First, the creation of the modified pigtail wire required a specific skill set. It is difficult to create a small-diameter tip. Second, the use of two MGWs results in high cost, which may not be covered by a medical insurance. Third, the use of MGWs in an excessively spiral fashion may damage intracranial arteries. Studies involving larger number of experiments and cases are necessary to confirm the efficacy of the beanstalk method.
In cases with a challenging vasculature, the beanstalk method is associated with smoother navigation of large-caliber catheters than the conventional coaxial method or the buddy-wire technique.
Conflicts of interest
There are no conflicts of interest.
