Article Text
Abstract
Introduction The low-profile Neuroform Atlas stent received FDA Humanitarian Device Exemption status (HDE) in January 2018 for stent-assisted coil embolization of wide-necked saccular aneurysms. We review and report our results with the Atlas stent in our institution within the first year after its HDE approval.
Methods Our retrospective chart review identified patients treated with the Atlas stent. We analyzed the patient demographics, aneurysm characteristics, stent parameters and configuration, complications, angiographic, and clinical outcomes at discharge.
Results From January to December 2018, 76 Atlas stents were deployed in 58 patients (average 1.3 stents/patient). Median patient age was 63.5 (IQR 56–71) years. Fifty-six (96.6%) patients had elective embolization of unruptured aneurysms, while two (3.4%) patients underwent embolization of a ruptured aneurysm within 2 weeks of subarachnoid hemorrhage. Forty (69.0%) patients were treated with a single stent, 15 (25.9%) with a Y-stent, and three (5.2%) with X-stent configuration. All stent deployments were technically successful. Most stents (82.9%) were the smallest 3 mm diameter devices. Procedural complications included transient stent-associated thrombosis in three (5.2%) patients and aneurysm rupture in one (1.7%). None had distal embolization, associated cerebral infarction, or permanent neurological deficits. Immediate Raymond–Roy 1 occlusion was achieved in 41 (70.7%) patients. Median hospital length of stay for elective aneurysm embolization was 1 day. Excellent outcomes with median National Institute of Health Stroke Scale score 0 (IQR 0–0) and modified Rankin Score 0 (IQR 0–1) were seen for elective patients at discharge.
Conclusion The Neuroform Atlas stent provided a reliable technical and safety profile for the treatment of intracranial wide-neck aneurysms. Further experience is needed to determine long-term durability and safety of this device.
- aneurysm
- angiography
- device
- intervention
- stent
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Introduction
Stent-assisted coil embolization of wide-necked saccular aneurysms provides greater durability and aneurysm occlusion than primary or balloon-assisted coil embolization.1 Several intracranial stents are available, and differ by their delivery microcatheter size and stent cell design.2–5 Until January 2018, most intracranial stents required microcatheters sized 0.021–0.027 inches, and only one closed-cell stent (LVIS Jr, MicroVention, Aliso Viejo, California, USA) could be deployed through a low-profile 0.0165 inch microcatheter in the USA.3 6 The Neuroform Atlas Stent (Stryker, Kalamazoo, Michigan, USA) is a hybrid/open-cell stent, deliverable through a low-profile microcatheter.2 3 7 It received the Food and Drug Administration (FDA) Humanitarian Device Exemption (HDE) in January 2018 for stent-assisted coiling of cerebral aneurysms. There is increasing although still limited experience on its safety and performance.2–4 6 7 We review our single-center experience with the Atlas stent in its first year under HDE status in the USA.
Methods
A retrospective chart review identified patients with wide-necked aneurysms treated with the Atlas stent from January to December 2018. Baseline patient and aneurysm characteristics, stent sizes and configurations, and angiographic and clinical outcomes were reviewed. Outcomes were measured angiographically by the Raymond–Roy Occlusion Classification (RROC). Clinical outcomes were evaluated at discharge and included admission length of stay, modified Rankin Scale (mRS), and National Institute of Health Stroke Scale (NIHSS) scores. All documented complications within 30 days were vetted for their association with the use of the intracranial stent.
We defined subgroups by the history of aneurysm rupture within 14 days of embolization versus elective embolization. Aneurysms undergoing elective embolization were further examined for any effects based on the history of previous rupture or treatment.
Device
The Atlas stent is a self-expanding nitinol stent with a hybrid open-cell design. The stent has an open-cell structure through most of its length, with the exception of its closed-cell proximal end, which aims to increase device stability when recrossing with a microcatheter. Its largely open-cell design trades off the possibility of recapture and repositioning for greater radial force, and better conformability, wall apposition, and stability. Currently available stent diameters range from 3.0 to 4.5 mm, with lengths between 15 and 30 mm. As the stent is laser-cut from a hypotube, its unexpanded low profile allows for delivery through a microcatheter sized 0.0165–0.017 inches. Following earlier clinical studies, the Atlas stent received FDA approval for use under HDE for aneurysms not amenable to surgical clipping in arteries sized 2.0–4.5 mm in diameter.6
Procedure
Patients with wide-necked aneurysms, defined as a neck ≥4 mm or a dome-to-neck ratio of <2, were selected for coil embolization with Atlas stent assistance. Patient management and endovascular approach were similar between all neurointerventionalists at our institution. All patients were initiated on dual antiplatelet therapy consisting of aspirin, clopidogrel, prasugrel, or ticagrelor for 5–7 days prior to embolization, or through a loading dose. Therapeutic antiplatelet effect was pre-procedurally confirmed by whole blood platelet aggregometry, described earlier.8 Dual antiplatelet therapy was continued for 3–6 months, followed by long-term single antiplatelet therapy.
All patients were treated under general anesthesia with close hemodynamic monitoring. A 6F femoral or radial sheath was placed using a standard technique and connected to heparinized saline flush. Our standard approach uses a coaxial system consisting of a 6F standard guide catheter and one or two 0.0165 or 0.017 inch standard microcatheters, without an intermediate catheter. When using a single microcatheter, the aneurysm was catheterized by crossing the stent construct. With the two-catheter technique, a first (stenting) microcatheter was navigated across the neck of the aneurysm. A second (coiling) microcatheter was then positioned in the aneurysm. The Atlas stent was then advanced to the tip of the stenting microcatheter. After relaxing the forward force in the microcatheter and stent delivery system, the Atlas stent was deployed across the aneurysm neck, jailing the coiling microcatheter. The stenting microcatheter could then advance through the tines of the first stent over a microwire to select another branch for deployment of a second stent in a Y- or X-configuration, if necessary. Coil embolization followed stent deployment. After detachment of the last coil, the microcatheter was cautiously removed from the aneurysm. Follow-up angiography was performed and all catheters were removed from the patient after confirmation of vascular integrity. Vascular closure or manual compression was applied at the puncture site.
Statistical analysis
Angiographic and clinical outcomes between subgroups were compared using the Kruskal–Wallis and Mann–Whitney U tests. Statistical significance was set at an alpha level of 0.05.
Results
Between January and December 2018, a total of 58 patients underwent stent-assisted coiling for wide-necked aneurysms at our institution with the Atlas device. There were 45 women (77.6%) and the median patient age was 63.5 (IQR 56–71) years. The mean±SD aneurysm size was 5.9±2.4 mm. Additional patient characteristics are outlined in table 1.
Only two (3.4%) aneurysms were recently ruptured, with Hunt–Hess grades of 1 in both patients, and modified Fisher scores of 1 and 4. An external ventricular drain was inserted prior to stent-assisted coil embolization in the patient with ventricular hemorrhage and removed 5 days after embolization with no complications despite dual antiplatelet therapy. Of the 56 (96.6%) patients undergoing elective embolization, eight (13.8%) were recurrent, including six (10.3%) previously ruptured and coiled aneurysms. The most common aneurysm location was the anterior communicating artery in 21 (36.2%) patients, followed by the middle cerebral artery bifurcation and basilar artery apex each accounting for nine (15.5%) patients (table 1).
A total of 76 Atlas stents were deployed during the study period. The average number of stents per patient was 1.3. All stents were deployed successfully and as intended (table 2).
In 40 (69.0%) patients, single stents were deployed into the parent from the ipsilateral direct access and 15 (25.9%) patients were treated with overlapping stents in a Y-configuration. An X-configuration was used for three (5.2%) patients with anterior communicating artery aneurysms. As expected with the low profile device, the smallest 3 mm diameter stent was the most commonly used (63 stents; 82.9%). The majority (41 patients, 70.1%) of aneurysms were in smaller or more distal arteries: anterior communicating, middle cerebral bifurcation, anterior cerebral, superior cerebellar, posterior cerebral, and posterior-inferior cerebellar locations (figure 1).
Angiographic outcomes were assessed at completion of coil embolization. Forty-one (70.7%) patients achieved an RROC of 1 and 12 (20.7%) patients achieved an RROC of 2 (table 3).
There was no difference in median RROC between patients with recent rupture and those undergoing elective embolization. Median admission length of stay was 1.0 (IQR 1.0–2.0) day for all patients. There was a significant difference between patients undergoing elective embolization (1.0 day, IQR 1–1.3) and those with subarachnoid hemorrhage due to aneurysm rupture (13.5 days, IQR 13.3–13.8; p=0.002).
Discharge NIHSS score was excellent for all patients, accounting for no significant neurological deficits in patients with elective embolization and mild deficits with a median NIHSS of 1.5 in the two patients with ruptured aneurysms (table 3). Functional status at discharge similarly remained excellent (median mRS 0, IQR 0–1) for most patients with elective embolization, and was mildly impaired in patients with ruptured aneurysms (mRS of 1 and 2, respectively).
There were no differences in median RROC, admission length of stay, discharge NIHSS and mRS among patients undergoing elective embolization, irrespective of history of previous rupture or treatment.
Complications
Neurologic complications related to stent-assisted embolization occurred in four (6.9%) patients overall, with none resulting in permanent neurologic deficit. Three (5.2%) patients had transient intraprocedural thrombosis, which was treated with intra-arterial tirofiban or abciximab infusion through a microcatheter positioned immediately proximal to the clot. Fractionated doses were infused through the microcatheter, with intermittent follow-up angiography and up to a maximum of tirofiban 25 μg/kg or abciximab 0.25 mg/kg. The thrombi resolved in all patients, with no distal embolization or cerebral infarction.
In one of these cases (1.7%), the thrombus formation was likely secondary to coil herniation. During elective treatment of a right A1–A2 junction aneurysm, a 3 mm x 15 mm Atlas stent was initially deployed across the neck of the aneurysm. Subsequent embolization was uneventful until delivery of the last coil, when several loops of a previously detached coil herniated. Follow-up angiography demonstrated thrombus build-up and flow limitation in the right A2 segment, and a 3 mm x 24 mm Atlas stent was then deployed distal to the initial stent in a telescoped fashion, jailing the herniated coil loops.
Aneurysm rupture occurred in one (1.7%) patient during elective coiling of a 7 mm basilar apex aneurysm. Increased pressure near the tip of the jailed microcatheter and its immobilization by the radial force of two overlapping Atlas stents in a Y-stent construct likely contributed to the unexpected forward motion of the microcatheter with resulting aneurysm rupture. Heparin was reversed, blood pressure was lowered, and the aneurysm was rapidly secured with additional coiling. Despite an immediate postoperative right abducens palsy and left upper extremity drift, the patient was eventually discharged home on post-procedural day 11 without any permanent neurologic deficits.
Discussion
We treated 58 patients with wide-necked intracranial aneurysms by Atlas stent-assisted coil embolization within the first year after its HDE approval in the USA. To the best of our knowledge, this is currently the largest series of its kind. Our results demonstrate 100% technical success rate, good immediate angiographic results, and excellent clinical outcomes at discharge, without significant safety concerns.
We report technical success rates similar to recently published experience with the Neuroform Atlas stent. In our series, successful deployment to the intended position and configuration was achieved in all of the patients, similar to previously reported success rates of 93–100%.3 6 9 This rate is also similar to contemporary low-profile stents such as the LVIS Jr and Leo Baby.2 5 10 The reliable and accurate deployment is attributable to the minimal foreshortening and stability of its laser-cut and open-cell design.2 In comparison with other low-profile stents, immediate occlusion rates range between 44% and 75% in LVIS Jr and LEO Baby case series.3 5 11 12 We achieved a similar immediate RROC 1 occlusion rate of 70.7%, comparable with rates of 57–63% in previous Atlas case series.3 6
The most common configuration in our series was a single stent deployment in the parent vessel to assist coiling. In addition, over 25% of our patients were treated with Y-stenting and 5% of patients with X-stenting. The number of aneurysms treated with a two-stent construct varies widely in published series. Ten Brinck et al treated 10 (37%) of their 27 patients with Y-stenting.9 Ulfert et al used Y-stenting in two (5.4%) of 37 patients.2 In the HDE Atlas cohort, three (10%) patients had a Y-stent configuration.6 In our experience, the Atlas stent has a minimal risk of displacement or foreshortening during delivery of the second stent, either when deployed through the proximal end of the first stent, or when crossing an open cell. This stability results from the stent’s hybrid cell design and its deliverability with low-profile microcatheters. Case series and a meta-analysis of complications directly related to Y-stenting, using the Enterprise, Neuroform, LVIS and LVIS Jr stents, report rates up to 8.9%.13 14 In contrast, no Y-stenting related complications were observed in our Atlas series and none have been reported in the reviewed literature.
The open-cell body of the Atlas stent is the most distinguishing feature from other currently available microstents. While its resulting higher radial force provides the benefit of stability, additional caution is warranted when coiling through a jailed microcatheter. As in our patients, the Atlas stent’s greater stability can translate into decreased microcatheter yield against pressure build-up within the aneurysm during coil deployment, with risk of intra-procedural rupture. Another well-recognized limitation stemming from its open-cell body is the inability to resheath the stent after initial deployment. However, in our experience, the Atlas stent’s reliability has largely obviated the need for repositioning and its use has not been limited by this feature.
It is important also to note that the majority of the stents (82.9%) we successfully deployed were the smallest 3 mm diameter devices. A large proportion of the aneurysms (70.1%) we treated were located in smaller-caliber distal vasculature, such as the anterior communicating and anterior cerebral region, middle cerebral artery bifurcation, and even the posterior inferior cerebellar and superior cerebellar arteries. These vascular territories were typically considered more difficult and riskier to access with larger microcatheters and stent delivery systems in the past. Due to its favorable low profile delivery system, the Atlas stent is expected to further expand the list of endovascularly treatable aneurysms for the benefit of more patients in the future.
Limitations
There are several limitations of this study. Our experience with the Atlas stent is limited to its first year of FDA approval through HDE, therefore we do not yet have long-term follow-up data on durability and long-term efficacy. However, as occlusion rates are expected to increase over time, we expect a higher rate of complete occlusion at 1 year follow-up as reported in prior studies.3 5 6 12 15 In addition, although our cohort includes patients with recently ruptured aneurysms, the sample size is small and we cannot conclude safety in using the Atlas stent in this population. Our case series is also limited to Atlas stent-assisted coiling of wide-necked aneurysms and does not include our direct comparative experience with other low-profile intracranial stents.
Conclusion
Our single-center study is currently one of the largest available series of stent-assisted coil embolization with the Neuroform Atlas stent. Our results suggest that the Atlas stent is technically safe and results in good early occlusion rates for the treatment of wide-necked aneurysms in both anterior and posterior intracranial circulations. Further experience and long-term follow-up data are needed to establish the durability and efficacy of this device.
References
Footnotes
Contributors JT: drafting of manuscript, interpretation of data, data analysis, acquisition of data, critical revision of manuscript. JH: drafting of manuscript, acquisition of data, interpretation of data, critical revision of manuscript. NM, ME: acquisition of data, critical revision of manuscript. MSH, MB, PAR, LS: interpretation of data, critical revision of manuscript. TM: acquisition of data, interpretation of data, critical revision of manuscript. GT: study conception and supervision, drafting of manuscript, acquisition of data, interpretation of data, critical revision of manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests MB is a consultant for Rebound Therapeutics and Stryker Neurovascular. MSH is a consultant for Cerenovus. PAR is on the Medical Advisory Board for Mehana Medical, Stryker Neurovascular, Medtronic Neurovascular, Perflow Medical, and has an Equity Position in Mehana Medical, Perflow Medical, and Bard Neurovascular. GT is a consultant for Dynamed EBSCO.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Anonymized data may be shared by request from a qualified investigator in compliance with our Institution’s data sharing policies.
Patient consent for publication Not required.