Millipede⁸⁸ and Millipede⁷⁰ catheters for contact aspiration thrombectomy in acute stroke: A multicenter experience

Abstract

Background

Aspiration is rapidly becoming the first-line strategy for mechanical thrombectomy for LVOs. Superbore aspiration catheters (lumen ≥ 0.088") have been suggested to provide advantages over conventional aspiration including improved recanalization and reduced distal emboli owing to distal flow control. The objective of this study was to assess the technical feasibility and safety of contact aspiration using the novel Millipede⁸⁸ Superbore catheter and the Millipede⁷⁰ catheter.

Methods

A retrospective analysis of consecutive cases using the Millipede⁸⁸ Superbore catheter as first-line for the treatment of large vessel occlusions was conducted. Key outcome parameters assessed were navigation to target occlusion, recanalization success, procedure-related complications, NIHSS, and symptomatic intracranial hemorrhage at 24 h.

Results

26 patients were treated using Millipede catheters. The first-pass effect, defined as mTICI ≥ 2c reperfusion using contact aspiration, was achieved in 69% of cases. mTICI ≥ 2c at final angiography was obtained in 88% of cases. Contact aspiration alone was used in 92% of cases. No catheter-related complications, such as dissections or perforations, or embolization to new territory was reported. sICH did not occur in any of the cases. The median drop in NIHSS at 24 h was eight points.

Conclusions

In the majority of cases, aspiration using the Millipede⁸⁸ catheter results in excellent recanalization with one pass, with an excellent safety profile. These data suggest that aspiration thrombectomy using the Millipede⁸⁸ Superbore catheter is feasible and safe. A large prospective trial of Millipede⁸⁸ for aspiration thrombectomy is underway.

Introduction

Since the landmark trials published in 2015,^1–5 reperfusion outcomes in mechanical thrombectomy (MT) have progressively improved as interventionists combine a wide range of devices such as stent retrievers, aspiration catheters, and balloon guide catheters in a multitude of techniques. ⁶ Recently, as reperfusion outcomes have plateaued, contact aspiration first has emerged as a preferred first-line strategy due to its simplicity, speed, and effectiveness. If initially unsuccessful, the technique can be easily augmented to include a stent retriever in a combined aspiration and stent retriever technique.

Of late, the lumen of aspiration catheters has increased substantially, most recently to 0.088 in., which is also known as Superbore aspiration.^7–9 These catheters are distinct from large-bore aspiration catheters which have a lumen up to 0.074". Superbore catheters have substantially increased aspiration power and have been shown in vitro to offer local flow arrest or reduction, and flow reversal upon aspiration and clot ingestion. ¹⁰ This has been associated with a higher rate of first-pass effect (FPE), complete final recanalization, and lower rates of rescue treatment for aspiration alone or with stent retriever combination techniques.^11,12

There remains a limited amount of clinical data to support the use of Superbore aspiration catheters for the treatment of large vessel occlusions. Rates of FPE and final 2c-3 complete recanalization range from 42% to 68% and 64% to 91%, respectively.^8,13 In another study the Imperative Care Zoom catheter demonstrated utility as an intracranial catheter to support both a combined stent retriever technique and for conventional aspiration using a larger bore catheter. ¹⁴ Both devices were reported to have a good safety profile.

The Millipede⁸⁸ catheter is a Superbore catheter with an 8F outer diameter and 0.088". Superbore lumen. The Millipede⁸⁸ catheter, shown in Figure 1, incorporates a novel rib-and-recess geometry at the distal tip which is intended to increase flexibility and improve navigability in tortuous anatomy enabling the catheter to be taken to the ICA terminus, M1, vertebral and basilar arteries. Millipede⁷⁰ has an internally corrugated profile.

Figure 1.

Millipede⁸⁸ catheter design shows externally corrugated rib and recess design (a) and Millipede⁷⁰ with internal corrugations (b), designed for improved flexibility and navigability.

This study assesses the safety and efficacy of the new Millipede⁸⁸ catheter and Millipede⁷⁰ as a first-line aspiration catheters for endovascular stroke treatment. Currently, aspiration using Millipede⁸⁸ represents off-label use of the catheter. The focus of this study is the technical feasibility (navigation to the target occlusion, recanalization success with and without additional devices) and safety (procedure and catheter-related complications).

Methods

The Millipede⁸⁸ Access Catheter was first cleared for use in the United States in December 2022. All cases in this study were conducted using the newer generation of the device cleared in December 2023 (FDA product code QJP, 242503). The Millipede⁷⁰ Aspiration Catheter was cleared for use in September 2023 (FDA product code NRY, 242503).

Consecutive patients who underwent acute stroke procedures using the second-generation Millipede⁸⁸ Access Catheter between January 2024 and July 2024 were identified. Use of Millipede⁸⁸ was at the operator's discretion. Inclusion criteria for endovascular therapy were ICA, M1, M2, vertebral or basilar occlusions established on CT angiography or non-contrast CT, followed by angiographic confirmation at the time of intervention. If the patients had multiple occlusions or were suspected of having intracranial atherosclerotic disease, they were not included in this series. The local institutional practice was used to determine suitability for treatment; therefore, there were no specific restrictions placed on time from stroke onset to treatment, age, baseline NIHSS score, baseline ASPECTS, or pre-morbid mRS.

Interventional procedure

Procedures were performed under general anesthesia or conscious sedation at the discretion of the physician. Although the procedure was conducted according to physician preference with respect to ancillary devices and choice of catheter for aspiration, broadly it followed the steps outlined below.

A long 8F sheath was placed in the common carotid artery via the common femoral artery and descending aorta. The 8F sheath is analogous to an 8F guide catheter, such as the Neuron Max (Penumbra) or Zoom 088 (Imperative Care), in a traditional thrombectomy procedure and provides proximal support for navigating the Millipede system intracranially. Angiography was performed to confirm the location of the occlusion and to obtain a roadmap. The Millipede⁸⁸ Access Catheter was delivered co-axially over a 6F catheter such as the Millipede⁷⁰ (Perfuze), Sofia Plus (Microvention) or similar. The 6F catheter was advanced through Millipede⁸⁸ to the face of the thrombus over a microcatheter or alternative support catheter and microwire. Millipede⁸⁸ was taken to the target vessel, and as close as possible to the clot face, for distal flow control and distal access. Internal devices were then removed, and a vacuum was applied for up to 2 min.

Millipede⁸⁸ is recommended for use in vessels larger than the outer diameter of the catheter (>2.74 mm). If the vessel was deemed too small for Millipede⁸⁸ by the operator, they could instead use the 6F catheter for the primary aspiration of the clot. In that instance, the Millipede⁸⁸ was taken as close as possible to the clot face Figure 2. It was at the physician's discretion whether to conduct additional passes using Millipede⁸⁸ or to switch to an alternative device or technique. Where alternative devices were used, they were delivered through Millipede⁸⁸ placed intracranially for distal access and flow control.

Figure 2.

Mid M1 occlusion treated with Millipede⁸⁸ showing pre-placement of Millipede⁸⁸ at the face of the thrombus, and result following one pass of aspiration.

Evaluation of data

The following parameters were documented: site of occlusion, distal position of Millipede⁸⁸, devices used for aspiration, thrombolysis in cerebral infarction (mTICI) scores (self-assessed by the respective site), recanalization by aspiration alone with Millipede⁸⁸ or Millipede⁷⁰, requirement for additional devices and procedural times (groin to first contact, and groin to final angiography).

Data were collected on catheter-related complications such as vessel dissection, periprocedural hemorrhage due to vessel perforation, and emboli to previously uninvolved territories. For quantification of the neurological deficit, the NIHSS scores on admission and at 24 h were noted. Follow-up imaging was performed to identify symptomatic intracranial hemorrhage, defined as the presence of PH2, SAH, or IVH and an increase of ≥4 points in NIHSS.

Statistics

All statistical analyses were performed using Microsoft Excel. Normally distributed variables were presented as Mean ± SD. Non-normally distributed variables were listed as median and IQR.

Results

Patient demographics and anatomy

In total, 26 patients were included in the analysis. The median age was 66, and 58% were female. The target occlusions were in the anterior circulation in 25 of 26 patients, and of these 56% were on the right side. Occlusions were in the ICA, M1, and basilar arteries in 19%, 77%, and 4% of cases, respectively. The average pre-procedure NIHSS score was 17 ± 5. A summary of patient demographics and baseline characteristics is included in Table 1.

Table 1.

Summary of demographics and baseline characteristics.

Age and sex
Age; median	66
Age; range	36–88
Female sex; %	15 (58%)
NIHSS baseline
Average ± SD	17 ± 5
Range	10–28
Occlusion location; n (%)
Internal carotid artery	5 (19%)
Middle cerebral artery, M1	20 (77%)
Basilar artery	1 (4%)
Right side (%)	14 (56%) a

^aDenominator of 25 since the basilar occlusion is excluded from this calculation.

The target anatomy included Type II or III arches in 54% of cases. S-shape, coiling, or kinking cervical tortuosity was present in 60% of cases according to the Weibull and Fields classification. ¹⁵ All types of carotid siphons according to the Liu classification were encountered. ¹⁶ A summary of the patient anatomy encountered is included in Table 2.

Table 2.

Summary of patient anatomy.

Aortic arch
Type I	11 (42%)
Type II	12 (46%)
Type II	2 (8%)
Not reported	1 (4%)
Cervical ICA tortuosity a
Straight	10 (40%)
S-Shape	12 (48%)
Kink	1 (4%)
Coiling	2 (8%)
Carotid Siphon a
Type IA	5 (20%)
Type IB	9 (36%)
Type II	4 (16%)
Type III	5 (20%)
Type IV	1 (4%)
Not reported	1 (4%)

^aAnterior occlusions only.

Catheter usage and techniques

Either Millipede⁸⁸ or Millipede⁷⁰, or both, was used in all 26 subjects. Millipede⁸⁸ was used in 25 of the 26 patients treated (96%). Millipede⁷⁰ was used in 13 of 26 (50%) patients. For the other 13 cases not using Millipede⁷⁰, the catheters used for internal support were Microvention Sofia Plus (n = 2), Imperative Care Zoom 71 (n = 1), Penumbra ACE 68 (n = 1), Wallaby Phenox Esperance (n = 1), Cerenovus Cereglide 71 (n = 1), Balt Carrier Medium (n = 1), Medtronic Marksman (n = 1), and Route 92 Tenzing 8 (n = 5).

Millipede⁸⁸ was successfully navigated to the target vessel in 96% (24/25) of cases. In one instance it was not possible to navigate Millipede⁸⁸ or the 6F catheter (Sofia Plus) to the target vessel. Therefore, a Medtronic Solitaire 4 × 40 stentriever was used in a combination technique. In that case, Sofia Plus was brought to the M1 following stentriever deployment, while Millipede⁸⁸ remained in the communicating segment of the ICA.

In 92% of patients in which Millipede⁷⁰ was used (12/13), it successfully navigated to the clot face. In one instance the Millipede⁷⁰ snagged at the ophthalmic artery, but the Millipede⁸⁸ advanced to the M1 over the Phenom 21 microcatheter (Medtronic).

Millipede⁸⁸ was used for the first pass aspiration in 85% (22/26) of occlusions. Millipede⁷⁰ was used for the first pass aspiration in two cases (7.5%). A combination technique (stentriever + aspiration) was used in the remaining two cases (7.5%).

Reperfusion success and outcomes

For M1 occlusions, Millipede⁸⁸ was used for first-pass aspiration in 80% (16/20) of cases. For the remaining four M1 occlusions, first-line aspiration was performed with Millipede⁷⁰ in two cases, and a combination technique (stentriever + aspiration) was used in the remaining two cases. All ICA and basilar occlusions were treated using Millipede⁸⁸ aspiration as the first line.

Successful reperfusion (mTICI ≥ 2b) and excellent reperfusion (mTICI ≥ 2c) on final angiography were obtained in 96% and 88% of patients, respectively. First-pass effect mTICI ≥ 2c was achieved in 69% of patients across all patients and in 73% of those in whom Millipede⁸⁸ was used for first-pass aspiration. A summary is shown in Table 3.

Table 3.

Summary of reperfusion success.

First pass reperfusion (All)
Modified first-pass effect mTICI ≥ 2b	21/26 (81%)
First-pass effect mTICI ≥ 2c	18/26 (69%)
Final reperfusion (All)
mTICI ≥ 2b	25/26 (96%)
mTICI ≥ 2c	23/26 (88%)
Reperfusion using Millipede88
Modified first-pass effect mTICI ≥ 2b	19/22 (86%)
First-pass effect mTICI ≥ 2c	16/22 (73%)

The median number of passes was 1. Time from groin access to first clot contact was within 15 and 30 min in 67% and 96% of cases, respectively. Groin to final angiography was within 20 and 40 min in 63% and 88% of cases, respectively. A summary of the procedural metrics can be found in Table 4.

Table 4.

Summary of procedural efficiency.

Number of passes
Median number of passes	1
Average number of passes (SD)	1.4 ± 0.8
Average number of passes to achieve mTICI ≥ 2c (SD)	1.3 ± 0.5
Time from groin to clot contact a
<15 min	16/24 (67%)
15–30 min	7/24 (29%)
>30 min	1/24 (4%)
Groin to final reperfusion a
<20 min	15/24 (63%)
20–40 min	6/24 (25%)
>40 min	3/24 (12%)
Stentriever usage	2/26 (8%)

The average NIHSS at 24 h^a was 9.2 ± 8.3. The average change in NIHSS from baseline to 24 h^a was 8.2 ± 8.9. No adverse events or safety concerns were reported^‡. There were no reports of sICH at 24 h.^a

^aMissing data for two patients.

Discussion

The advent of Superbore catheters, which are suitable for intracranial delivery, represents a significant shift in technology for mechanical thrombectomy. In this case series, the rate of FPE was 73% when Millipede⁸⁸ was used for aspiration on the first pass. This compares favorably to the literature which reports rates from 42% to 68% in retrospective with 088". catheters.^8,13

The ultimate goal of mechanical thrombectomy is to achieve an FPE rate of 100%; however, there are many reasons why this may never be achieved. For example, the widespread use of thrombolytics means in many instances the clot may already be fragmented, resulting in tandem distal occlusions which will invariably require multiple passes. The presence of underlying ICAD (excluded in this series), present in about 9% of LVO cases, may prevent complete recanalization using any technique. ¹⁷ Additionally, and particularly for ICA occlusions, the clot burden may be distributed in three vessels (ICA, M1, ACA) and may be simply too large for a single-pass approach to be reliable. Rates of FPE of 60% to 75% are possibly approaching a theoretical maximum which can be achieved using contact aspiration. However, this does not mean excellent results cannot be achieved on final angiography using Superbore aspiration as the first line. In this series, the final mTICI 2c-3 was achieved in 88% of cases. This compares favorably to conventional 6F contact aspiration techniques which range from 56% to 80%^18–20.

Previous studies have shown that increasing the inner diameter of aspiration catheters can lead to better revascularization performance and improved clinical outcomes. ²¹ Therefore, using larger 088 in. catheters, such as Millipede⁸⁸, for aspiration was expected to further enhance these outcomes due to the larger lumen and greater aspiration force. Indeed, in vitro research demonstrated that the Millipede⁸⁸ achieved superior reperfusion compared to the SOFIA Plus and ACE 068 devices. ²² Additionally, the larger 8F outer diameter of the Millipede⁸⁸ provides better distal flow control, complete clot ingestion, and flow-reversal in the target vessel, reducing distal emboli which is not always possible with 6F catheters. ²² The results of this case series are aligned with the in-vitro data, showing a greater FPE rate when the Millipede⁸⁸ is used for aspiration compared to studies using 6F contact aspiration techniques.^18,19,23

In this series, the procedural times were low, though it is likely that they could have been further reduced as follows; Millipede⁸⁸ Access Catheter was delivered over both a microcatheter and intermediate 6F catheter to reduce the ledge effect and prevent potential snagging on the ophthalmic artery in this series. A new class of delivery assist catheters that combine the functionality of the microcatheter, and intermediate catheter has been developed, including Tenzing (Route 92 Medical) and Zipline (Perfuze Ltd). These catheters are likely to simplify the procedure and increase the chances of successfully reaching the clot. Millipede⁸⁸ is delivered through an 8F Long Sheath. This is broadly aligned with contact aspiration using large bore aspiration catheters which use a 6F Long Sheath for support. However, existing 8F long sheaths such as Flexor Shuttle (Cook Medical), Destination (Terumo), and Super Arrow-Flex (Teleflex) have been in use for over 15 years, and do not provide the navigability of newer 6F sheaths designed specifically for neurovascular use. 8F long sheaths customized for delivery to the neurovasculature over challenging aortic arch anatomy are likely to improve procedural efficiency further.

In this study, there were no procedural complications or reports of sICH. This is aligned with other studies that have reported promising safety profiles for other Superbore 088 intracranial catheters such as the Route 92 Medical Hi-Point 88, and the Imperative Care Zoom 88.^8,24 In this study, users took a conservative approach, only advancing Millipede⁸⁸ into the target vessel if it was perceived to be large enough to comfortably accept the catheter. A more pragmatic approach has been reported by Campos et al., in which the 8F 2.6 mm outer diameter Zoom catheter navigated MCA segments of 2.4 ± 0.1 mm, without any hemorrhagic or periprocedural complications noted. ²⁵ Safe navigation through small MCA segments of Superbore aspiration catheters relies on flexible and maneuverable designs, advanced materials, and the expertise of interventionalists, all of which minimize the risk of vascular damage.

A limitation of this study is that it was a retrospective review of cases. Reperfusion scores were self-reported instead of being read by an independent core lab. A prospective, controlled single-arm study of the Millipede catheters called MARRS recently finished enrolling in the United States, France, and Spain and will provide higher-level evidence for the Perfuze Millipede⁸⁸ and Millipede⁷⁰ Aspiration Catheters.

Conclusions

In this analysis, Millipede⁸⁸ and Millipede⁷⁰ catheters were evaluated in a real-world setting. High rates of successful and excellent reperfusion were achieved. Navigation was successful in the vast majority of cases without the requirement of a stentriever. There were no adverse events reported, and there were no reported symptomatic intracranial hemorrhages.

Abbreviations

FPE

first-pass effect

ICA

internal carotid artery

LVO

large vessel occlusion

MCA

middle cerebral artery

MT

mechanical thrombectomy

mTICI

modified thrombolysis in cerebral infarction score

NIHSS

National Institutes of Health Stroke Scale