The impact of delivery technique on Woven EndoBridge deployment and detachment in an in vitro aneurysm model

Abstract

Background

The Woven EndoBridge (WEB) device is increasingly used for treatment of wide-neck bifurcation aneurysms. With the newer 17 system, WEB deployment has been associated with a phenomenon known as incomplete or “sticky” detachment from the delivery wire, which may lead to imprecise placement. Optimal techniques for WEB manipulation and delivery to avoid this problem are poorly defined. This study aimed to evaluate standard WEB deployment techniques and determine the impact of delivery techniques and WEB stickiness on procedural success.

Methods

An in vitro study using identical silicone middle cerebral artery aneurysm models (n = 32) assessed WEB (6 × 2 mm) deployment through a VIA 17 microcatheter via three techniques that involved: “loading,” “neutral,” and “tension” on the pusher wire. Microcatheter position was placed in varied positions from the WEB device. Woven EndoBridge stickiness was graded during detachment attempts. Primary outcomes were detachment stickiness and attempt number, compared between techniques using Fisher's exact test.

Results

The tension technique resulted in significantly fewer sticky detachments and detachment attempts compared to forward load or neutral techniques (p < 0.001). Sticky detachment was lower with tension (0% sticky) versus forward load (42% sticky, 8% very sticky) (p < 0.001). Forward load had a 50% rate of stickiness versus 0% with tension and neutral (p < 0.001). Forward load required multiple attempts in 100%, compared to 57% with neutral and 8% with tension (p < 0.001). Higher stickiness grades increased the need for multiple attempts (p < 0.001).

Conclusion

The tension technique reduces incomplete WEB detachment and enables precise single-attempt detachment, optimizing delivery precision. In vivo confirmation is needed.

Introduction

The Woven EndoBridge (WEB) device is an FDA-approved device for the treatment of wide-necked bifurcation aneurysms.^1–3 It has been shown to be extremely safe however one of the challenges in using the WEB device is its predilection for incomplete detachment also known as “sticky detachment.” While not much has been published about this issue, most WEB users report this occurrence with relatively regular frequency.^3–5 When encountering this issue, if not managed appropriately it can lead to device movement, which may impact long-term outcomes. ⁶

The manufacturer provides instructions for a load technique, involving gradual forward load of the WEB throughout delivery. ³ After full deployment, the recommendation is to take load off the device until a neutral position has been reached. While this technique worked well for most devices from the older 21–33 systems, with the development of the 17 system, incomplete detachment appears to have become more prevalent. ³ Our experience suggests a “tension” approach with gentle tension on the microcatheter-pusher wire system will dramatically reduce the incidence of “sticky” detachment. The ideal strategies for WEB manipulation during deployment have not been well-defined or researched.

Additionally, the impact of technical factors such as WEB “stickiness” on successful delivery is poorly understood. The relationship between stickiness and deployment success has not been characterized. In this in vitro study, we aimed to compare standard WEB load versus alternative traction and neutral techniques in silicone aneurysm models. We also assessed the impact of WEB stickiness on delivery outcomes, to better define the role of this variable. Our findings may optimize WEB deployment strategies, improving angiographic results and clinical success.

Methods

Technique description

This in vitro study evaluated the technique of WEB device deployment using three different techniques: forward load, neutral, and tension. All deployments were performed by a single operator with expert experience having performed more than 200 WEB deployments in humans. The WEB device was deployed in the same middle cerebral artery silicone aneurysm model (n = 32, diameter 5 mm × 3 mm) using the same size WEB device 6 × 2 SL through a Via 17 microcatheter. The specific technique used was documented for each case. Loading technique involved gradually pushing the WEB into the aneurysm while maintaining forward load throughout the deployment (Figure 1(a)). Neutral technique involved reducing load after deployment to a neutral position (Figure 1(b)). Tension technique involved having negative load on the pusher wire and microcatheter after deployment (Figure 1(c) and Figure 2). The microcatheter position was also adjusted into three various positions, distal position (close to the proximal marker in the distal quarter of the M1 segment), mid position (in the middle half of the M1 segment), and proximal position (proximal quarter of the M1 segment or distal ICA catheter position).

Figure 1.

Position optimization and tension creation. Tension on the detachment zone should be optimized by the operator manipulating the delivery wire: (a) Forward load should be created on the system by the operator gently pushing the delivery wire → the microcatheter's tip will move backward as a result. (b) The system should be returned to neutral by the operator gently pulling the delivery wire → the microcatheter tip will move forward to the original position. (c) Slight tension should be created on the system by the operator continuing to pull the delivery wire → The microcatheter's tip will move forward, just past the original position.

Figure 2.

Degrees and visual indicators of tension.

Outcomes

The primary outcome investigated was the grade of stickiness encountered during WEB detachment. Thus, the technical aspects of each case were graded based on the stickiness grade. Stickiness was graded as active, slightly sticky, sticky, and very sticky. Active detachment is defined as complete and obvious separation (>1 mm) between pusher wire and proximal WEB marker. Slightly sticky was defined as obvious movement of the proximal WEB marker and pusher wire with <1 mm separation between the proximal marker and pusher wire. Sticky was defined as movement of the proximal WEB marker with no movement of the pusher wire and no separation between the proximal WEB marker and the pusher wire. Very sticky was defined as no movement of the proximal WEB marker, nor the pusher wire.

Statistical analysis

Fisher's exact test was used to compare the distribution of stickiness grades and attempts count between the deployment techniques. A two-tailed p-value <0.05 was considered statistically significant.

Results

The WEB was successfully deployed in all 32 silicone models. Neutral technique was used in 7 cases, forward load in 12 cases, and tension in 13 cases. Stickiness grades were active detachment in 14 cases, slightly sticky in 12 cases, sticky in 5 cases, and very sticky in 1 case. There was a higher incidence of stickiness in forward load with half of the cases being sticky (42%) or very sticky (8%) compared to none in the other techniques (p < 0.001) (Figure 3(a) and Table 1).

Figure 3.

Stickiness grade (a) and attempt count (b) by detachment technique.

Table 1.

Stickiness grade and attempt count by detachment technique.

Detachment technique	Stickiness grade					Attempt count
	Active (%)	Slightly sticky (%)	Sticky (%)	Very sticky (%)	p-value	One attempt (%)	More than one attempt (%), median number of attempts	p-value
Forward load	0 (0)	6 (50)	5 (42)	1 (8)	<0.001	0 (0)	12 (100), 4	<0.001
Neutral	3 (43)	4 (57)	0 (0)	0 (0)		3 (43)	4 (57), 4
Tension	12 (92)	1 (8)	0 (0)	0 (0)		12 (92)	1 (8), 1
Attempt no. (median, IQR)	1 (1, 1)	4 (2.4 4)	4 (4, 4)	4 (4, 4)	<0.001	1 (1, 1)	4 (4, 4)

Multiple deployment attempts were required more frequently with forward load compared to other techniques. With forward load, 100% of cases required more than one attempt (median four attempts) versus 57% with neutral (median four attempts) and 8% with tension (median one attempt) (p < 0.001) (Figure 3(b) and Table 1).

Higher stickiness grades were associated with an increased need for multiple deployment attempts. In active cases, 7% required more than one attempt (median one attempt), compared to 25% in slightly sticky cases, 60% in sticky cases, and 100% in very sticky cases (p < 0.001) with a median of four attempts for each (Table 1). There were no complications or safety issues. There was no significant difference in stickiness grading and attempts based on the microcatheter position.

Woven EndoBridge detachment was achieved in all cases using the Tension–Lock–Controller Technique, in which, once the WEB was appropriately positioned in the aneurysm, the microcatheter was positioned 5–8 mm proximal to the WEB implant by the operator. The delivery wire and implant were adjusted to a neutral position (with neither forward load nor tension on the delivery wire) by the operator. Slight tension was created on the system by the operator continuing to pull the delivery wire, causing the microcatheter tip to creep forward, just past the original position and the WEB may have a slight “stretched” position at the proximal marker. While maintaining constant tension on the delivery wire, the RHV was firmly locked down by the operator. The operator ensured no movement of the microcatheter or WEB implant. Under continuous fluoroscopy, the operator connected the WDC and watched for any movement of the MC or WEB. The operator pressed the detachment button and watched for movement of the WEB, indicating detachment (Figure 4).

Figure 4.

Summary of Tension–Lock–Controller (TLC) technique: once the Woven EndoBridge (WEB) is appropriately positioned in the aneurysm, the microcatheter should be positioned 5–8 mm proximal to the WEB implant by the operator. The delivery wire and implant should be adjusted to a neutral position (with neither forward load nor tension on the delivery wire) by the operator: (a) Tension (T)—Step 1: Slight tension should be created on the system by the operator continuing to pull the delivery wire, causing the microcatheter tip to creep forward, just past the original position and the WEB may “stretch” at the proximal marker, (b) Lock (L)—Step 2: While maintaining constant tension on the delivery wire, the RHV should be firmly locked down by the operator. The operator should ensure no movement of the microcatheter or WEB implant. (c) Controller ©—Step 3: Under fluoro, the operator should connect the WDC and watch for any movement of the MC or WEB. The operator should press the detachment button and watch for movement of the WEB, indicating detachment.

Discussion

The WEB device uses an electro-thermal detachment mechanism, similar to their company's neurovascular coils. The WEB device is attached to the delivery system using a polymer filament, or tether (Figure 5). The tether is located concentrically within a tightly wound heater coil and a larger diameter spring-shaped overcoil (Figure 5(c)). Electrical energy is delivered through the heater coil when the user activates the detachment mechanism on the WEB detachment controller. This electrical energy causes the heater coil to heat up and severs the tether. As the tether severs, the spring force of the overcoil gently pushes the WEB implant off the delivery system and causes it to detach. Our hypothesis is that sticky detachment occurs more likely when there is forward load on the pusher wire. Under this condition, the spring force of the overcoil cannot overcome the load placed on the pusher wire.

Figure 5.

(a) Image of the Woven EndoBridge (WEB), proximal marker and overcoil. (b) Overcoil purposely pulled back to expose the heater coil and tether. (c) Magnified view of the implant, heater coil, tether and overcoil.

This in vitro study demonstrates that the technique used for WEB device deployment can significantly impact the incidence of incomplete detachment. Specifically, applying tension on the delivery system during detachment dramatically reduced incomplete detachment compared to standard forward load or neutral techniques.

When deploying the WEB device with forward load, 50% of cases encountered moderate to high levels of stickiness and required multiple detachment attempts. This highlights the high rate of incomplete detachment that can occur with the standard technique recommended by the manufacturer. In contrast, utilizing tension during detachment yielded a very low 8% rate of incomplete detachment. This substantial difference confirms that the tension technique is far superior for avoiding this complication.

The reason tension facilitates detachment is likely that it gives the overcoil the best chance to spring away once the heater coil is energized and the tether melts. It is important to recognize that in actual clinical situations, using the tension technique may not be ideal in terms of WEB orientation and positioning. This may not be the optimal approach in all WEB cases, however, at minimum, getting the WEB into a neutral or non-forward load position also seems to reduce the risk of incomplete detachment.

The clinical implications of these findings are significant given the frequency of sticky detachment encountered.^3–5 Incomplete detachment can lead to movement of the WEB on final separation, and disrupting optimal device placement. ⁷ By utilizing the tension technique described, physicians can likely achieve much higher rates of first-pass success and precise positioning. This may in turn improve long-term occlusion rates and avoid complications related to suboptimal implant location.

Several limitations of the study deserve mention. As an in vitro investigation, the silicone models used may not fully recreate the complexity of in vivo deployments. However, the simplicity of the models strengthens the observed relationship between tension and successful detachment. Testing in vivo is still needed to confirm the translation of these results clinically. Additionally, only expert users were assessed given the technical nature of the study. Further evaluation across various operators would better define the generalizability of the findings.

Conclusion

This study demonstrates that applying tension on the WEB delivery system during deployment significantly reduces the incidence of incomplete detachment. This technique allows precise, first-pass delivery and should be adopted clinically to optimize procedural and angiographic outcomes. Further research is warranted to evaluate the efficacy of the tension technique for WEB deployment in vivo.