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Endovascular Therapies in Acute Ischemic Stroke Diogo C. Haussen, MD1

Dileep R. Yavagal, MD1

1 Department of Neurology and Neurosurgery, University of Miami

Miller School of Medicine / Jackson Memorial Hospital, Miami, Florida.

Address for correspondence Dileep R. Yavagal, MD, University of Miami Miller School of Medicine / Jackson Memorial Hospital, 1120 NW 14th St, Suite 1356, Miami, FL 33136 (e-mail: [email protected]).

Abstract Keywords

► stroke ► endovascular procedures ► thrombectomy ► randomized controlled trials

Intraarterial therapy for acute ischemic stroke (AIS) was originally described five decades ago. Since then, the endovascular management of AIS endovascular therapy has advanced swiftly, and a promising body of evidence informing patient selection and interventional techniques has accrued. The authors discuss the evolution of endovascular therapy for AIS, including a review of recently published landmark clinical trials.

Introduction Stroke is a leading cause of long-term disability in the Western hemisphere. Acute ischemic stroke accounts for  85% of stroke and results most commonly from a sudden occlusion of major craniocervical or cerebral vessels. Following initial reports of angiographically confirmed cases of carotid or major cerebral artery thrombosis in the early 1950s,1–3 a surgical approach to this condition was proposed.4 Soon afterwards, the first report of endovascular therapy for acute ischemic stroke was reported in a patient with proximal internal carotid artery occlusion who concomitantly underwent intraarterial (IA) and intravenous fibrinolysin (plasmin) infusion. Although the angiographic and clinical results were suboptimal, this description paved the way for IA investigations in acute ischemic stroke.5 The field of endovascular therapy has advanced swiftly recently with the accrual of a growing body of scientific evidence. Here we discuss the recent developments in the endovascular management of AIS.

Chemical Thrombolysis and Initial Thrombectomy Experience Multiple anecdotal reports and small series demonstrated that the use of IA thrombolysis could be beneficial in the

Issue Theme Advanced Cerebrovascular Disease Management; Guest Editor, Jason Mackey, MD, MS

management of AIS. Intraarterial chemical thrombolysis was demonstrated to be safe and efficacious in the late 1990s.6,7 The Prolyse in Acute Cerebral Thromboembolism (PROACT II) was a randomized, controlled, multicenter, open-label clinical trial with blinded follow-up that compared the administration of IA urokinase plus intravenous (IV) heparin (n ¼ 121) versus IV heparin alone (n ¼ 59) in patients with middle cerebral artery (MCA) occlusions. Despite a symptomatic hemorrhage rate of 10%, IA therapy was associated with clear absolute clinical benefits (40% vs. 25% with modified Rankin score  2 at 90 days).7 The benefits were largely attributed to the high rate of MCA recanalization in the interventional arm. Using the Thrombolysis in Myocardial Ischemia (TIMI) Scale scoring method, TIMI II-III in the control arm was dismally low at 18% versus 66% after 2 hours of thrombolytic infusion. A brief discussion of recanalization scales is pertinent at this point. The TIMI grading scale was designed for evaluation of recanalization in myocardial ischemia, and was posteriorly adapted to the cerebral circulation. Unfortunately, multiple different definitions have been utilized across stroke trials, making it difficult to accurately compare recanalization rates.8 Good recanalization was typically defined by incomplete or slow distal branch filling (TIMI II) or by full perfusion with filling of all distal branches (TIMI III).9 Recently, a consensus was published reinforcing the better interrater

Copyright © 2013 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.

DOI http://dx.doi.org/ 10.1055/s-0033-1364219. ISSN 0271-8235.

This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.

Semin Neurol 2013;33:441–447.

Endovascular Therapies in Acute Ischemic Stroke

Haussen, Yavagal

reliability and ability of the mTICI (modified therapy in cerebral ischemia) scale in predicting outcome.10 mTICI 2a is represented by antegrade reperfusion of less than half of the occluded target artery previously ischemic territory, while mTICI 2b is defined by antegrade reperfusion of more than half of the previously occluded target artery ischemic territory (e.g., in two major divisions of the MCA and their territories). mTICI 3 is described by complete antegrade reperfusion at the capillary level, with absence of visualized occlusion in all distal branches. Data from multiple studies show mTICI 2b-3 to have a high accuracy for discriminating good and bad outcomes, being therefore recommended as a reperfusion endpoint for studies. The previously utilized TICI scale is similar to the mTICI, with the distinction that TICI 2a is denoted by less than two-thirds reperfusion of the ischemic territory, while TICI 2b by more than two-thirds. Maceration of the clot with a microwire was being diffusely utilized at the time PROACT II was published, whereas snare devices and balloon angioplasty were becoming commonly utilized options.11–13 The EKOS System was described in 2003 in a phase 1 study. It consisted of a microinfusion catheter with an ultrasound element at the distal tip that provided an ultrasound energy source to alter the structure of the thrombus and enhance thrombolysis by facilitating t-PA penetration.14 The interventional treatment evolved rapidly to mechanical thrombectomy devices specifically designed for intracranial embolectomy, with the approval of the Merci and Penumbra systems. The Merci retrieval system (Concentric Medical, Mountain View, CA) was introduced in 2004, and consisted of a corkscrew-shaped nitinol device designed to specifically engage thrombus present in the cerebral circulation.15 The MERCI Trial was a single-arm study that included 151 patients ineligible for IV t-PA presenting within 8 hours and reported a 7.8% symptomatic hemorrhage rate and a 46% recanalization rate (TIMI IIIII).16 Of note, patients with MCA, ICA, and basilar and vertebral occlusions were included. Modified Rankin Scale (mRS)  2 were observed in 27.7% of the subjects. The potential for an extended time window, improved symptomatic hemorrhages rates, and the possibility of treating ICA terminus occlusions were promising advances. The Multi-MERCI Trial further investigated whether a newer generation Merci retrieval system would be safe and effective in 164 patients and included cases in which IV t-PA was concomitantly used.17 Recanalization was observed in 57.3% (and in 69.5% after adjunctive IA t-PA therapy), symptomatic hemorrhage in 9.8%, and good clinical outcome (mRS  2) in 36%, which represented better trends for revascularization and clinical outcomes. The Penumbra system (Penumbra, Oakland, CA) consists of a reperfusion thromboaspiration catheter connected to an aspiration pump. The catheter is conventionally positioned in the face of the clot while a microwire (with an olive at its distal end) is moved back and forth macerating/debulking the clot and clearing the microcatheter path. The Penumbra Pivotal Stroke Trial enrolled 125 patients within 8 hours of onset aiming to demonstrate equivalence to the Merci clot retriever. Good clinical outcome (mRS  2) was observed in 25% of patients with a symptomatic hemorrhage rate of 11.2% Seminars in Neurology

Vol. 33

No. 5/2013

and TIMI II-III recanalization rates of 81.6%.18 Comparing the different devices regarding revascularization, hemorrhage rates and clinical outcomes is problematic, and should be done cautiously given the heterogeneous populations and methodology (►Table 1). In 2006, two series describing the use of intracranial stent placement for cases of failed thrombolysis were published, citing high recanalization rates (TICI 2 or 3 ¼ 79% and TIMI 2– 3 ¼ 90%).19,20 The stent deployment was suggested to immediately restore flow by entrapping the thrombus between the vessel wall and the stent struts.21 Despite the promising results, there was some concern related to the need for double antiplatelet therapy in the setting of acute infarct due to the permanent implantation.

Newer-Generation Thrombectomy Devices and Techniques Stent retrievers constitute the newer-generation devices for stroke intervention. The technique follows the aforementioned theoretical principles of conventional self-expanding stents, in which an immediate perfusing channel is created upon deployment in addition to providing high revascularization rates. The technique has the major advantage of allowing retraction of the thrombus entrapped in the stent struts, such that the clot is typically not disrupted but rather extracted entirely.22 These characteristics permit repeated passes and avoid the requirement of antithrombotics. Most of the reports involve the Solitaire AB (ev3 Inc, Plymouth, MN), which was originally developed for stentassisted coiling of intracranial aneurysms. A pilot study was published in 2010, describing its use for flow restoration in 20 anterior circulation ischemic stroke patients who presented within 8 hours of onset. Half of the patients received IV t-PA, 90% of the patients achieved TICI 2b-3, 10% developed symptomatic hemorrhage, and 45% of patients achieved mRS  2. Other reports followed with similar results.23,24 Other stent retrievers are currently being studied, including the Trevo retriever (Stryker Neurovascular, Kalamazoo, MI), Revive system (Codman & Shurtleff, Inc, Raynham, MA), and Aperio (Acandis GmbH & Co. KG, Pforzheim, Germany). The studied populations in the aforementioned series and trials are relatively small and considerably different. Imaging selection and outcome measurements (including multiple different definitions of revascularization) varied substantially. Nevertheless, the stent retrievers were thought likely superior to older devices and this was confirmed with the publication of the TREVO 2 and Solitaire with the Intention for Thrombectony (SWIFT) trials.25,26 The TREVO 2 was an open-label randomized controlled multicenter trial that included 178 patients with large-vessel occlusion within 8 hours of stroke onset comparing the TREVO retriever with the Merci retriever. The authors found that 86% of the patients assigned to the stent retriever achieved TICI 2–3 reperfusion versus 60% in the Merci group with comparable symptomatic hemorrhage rates. Clinical outcomes were also superior in the stent retriever group (mRS  2 in 40% compared with 22% in the Merci group).25

This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.

442

66%

Overall (TIMI/mTICI 2–3)

10%

25%

Mortality

SICH

40%

mRS  2 at 90 days

CLINICAL OUTCOMES

9.8%

34%

36%

68%

65%

67%

1.6

32%

11%

32%

25%

18%

9%

18%

21%

0%

20%

17%

27%

\

24%

77%

\

23%

59%

18%

84%

40%

122cc

19

61

30

No penumbra

Endovascular therapies in acute ischemic stroke.

Intraarterial therapy for acute ischemic stroke (AIS) was originally described five decades ago. Since then, the endovascular management of AIS endova...
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