Stroke and the Neurosurgeon
Peer-Review Report
Mechanical Thrombectomy for Acute Ischemic Stroke Using the MERCI Retriever and Penumbra Aspiration Systems

https://doi.org/10.1016/j.wneu.2011.07.003Get rights and content

Objective

Intracranial large-vessel ischemia is associated with poor clinical outcome and increased mortality. Early reperfusion of ischemic tissue remains the goal of treatment of stroke. Intravenous tissue plasminogen activator (IV tPA) has been shown to improve clinical outcomes for patients who experience ischemic stroke, but it has been shown to be less efficacious for large-vessel occlusions. Mechanical clot extraction provides a therapeutic option for those who are ineligible for, or who do not respond to, conventional ischemic stroke treatment.

Methods

We reviewed the initial studies of the Merci Retriever and Penumbra System for mechanical clot extraction. Baseline patient characteristics, as well as revascularization rates and clinical outcome, were examined.

Results

Baseline National Institutes of Health Stroke Scale scores were greater than those observed in previous IV tPA studies, consistent with large-vessel occlusion. Successful recanalization occurred more frequently than with IV tPA and was associated with improved clinical outcome and mortality. Symptomatic intracranial hemorrhage and mortality rates were greater than those seen with IV tPA.

Conclusions

Mechanical clot extraction can be performed safely in patients with large-vessel occlusions, and successful recanalization resulted in better clinical outcomes than those without. Mechanical thrombectomy provides a therapeutic option for ischemic stroke patients who are ineligible for, or who do not respond to, IV thrombolytics. Further studies, including randomized clinical trials, are needed to validate these findings.

Introduction

Stroke is the leading cause of disability and the third-leading cause of death in the United States. The natural history of intracranial large vessel occlusive disease is particularly poor, with documented mortality rates as high as 90%, depending on the affected vessel (8, 16, 17, 31, 40). Intravenous tissue plasminogen activator (IV tPA) has been shown to be efficacious in the recanalization of occluded intracranial vessels and to improve clinical outcome in patients experiencing ischemic stroke. The authors of a meta-analysis of 53 studies that 2066 patients with acute stroke demonstrated a 46.2% overall recanalization rate with IV fibrinolysis (34). Other investigators have shown, however, that the frequency of recanalization is lower for large vessel occlusions (10, 26, 34, 35, 49). Reported rates range from 28.9% to 54.7% in the middle cerebral artery (MCA), 30% to 80% in the vertebrobasilar (VB) system, and from 5.9% to 13.9% in the internal carotid artery (ICA) (34, 35, 49).

Many acute stroke patients are not candidates for IV tPA. Eligibility is restricted by medical contraindications and stringent exclusion criteria. A narrow time window and inadequate public awareness of stroke symptomatology further limit the number of patients who may benefit from this therapy. It is estimated that only 3%-10% of those patients eligible for IV tPA actually receive the drug (2, 5, 6, 9, 19, 44). Some patients are considered ineligible for treatment because of large areas of ischemia on magnetic resonance imaging (diffusion-weighted imaging sequences). However, several investigators have shown that diffusion-weight imaging changes, once thought to represent infarcted core, can be reversible in the both the anterior and posterior circulation (12, 22, 42, 48, 50).

Endovascular techniques allow for selective treatment via either thrombolytic delivery or mechanical clot extraction in patients who have failed, or are not eligible for, IV tPA. Intra-arterial (IA) tPA administration decreases the undesired effects of systemic infusion and allows for direct delivery to the region of maximal clot burden. Because of the risk of hemorrhage into infarcted tissue, treatment with intra-arterial thrombolytics is limited to a strict six-hour window. Mechanical revascularization establishes vessel patency via clot extraction, providing an alternative treatment for those who are not eligible for, or do not respond to, thrombolytics. Rha and Saver's (34) meta-analysis demonstrated a 63.2% overall recanalization rate for IA thrombolysis and an 83.6% revascularization rate for mechanical therapy. The authors were able to evaluate rates for specific vessels in 1054 patients for IA versus IV therapy. Recanalization was successful in the anterior cerebral artery (ACA) or MCA in 78.4% of patients (vs 54.7% IV), in the VB system in 100% of patients (vs 80% IV), and in the ICA for 77.8% of patients (vs 13.9% IV). Revascularization was significantly associated with good functional outcome, defined as a modified Rankin Score (mRS) (47) ≤2 (58.1% mRS ≤2 for recanalized patients vs 24.8% with no recanalization) and lower mortality (14.4% vs 41.6%) (34). Mechanical revascularization can establish vessel patency without the use of thrombolytic agents. This technique therefore extends the time window of and increases the number of patients eligible for acute stroke treatment. This article will focus on conventional endovascular mechanical recanalization techniques. At this time, there are two devices approved by the Food and Drug Administration (FDA) for endovascular treatment of acute ischemic stroke. These are the Merci Retrieval System (Concentric Medical, Mountain View, California, USA), and the Penumbra System (Penumbra, Alameda, California, USA).

Section snippets

Merci Retrieval System

The Merci device was initially approved by the FDA in 2004 as a Humanitarian-Use Device. A Humanitarian Device Exemption is granted for products used to treat a disease or condition that affects 4000 patients or fewer per year in the United States. The newest version of the device is approved via a 510k clearance, meaning that it has been shown to be equivalent in safety and efficacy to a device that has already been approved for a particular indication. The retriever is also approved for the

Penumbra System

The Penumbra system was approved for use in the United States in 2008, also under a 510k clearance from the FDA. It is currently approved for use in ischemic stroke in Europe, Australia, and parts of Asia. In the United States, its intended use is for “the revascularization of patients with acute ischemic stroke secondary to intracranial large vessel occlusive disease (in the internal carotid, middle cerebral – M1 and M2 segments, basilar, and vertebral arteries) within 8 hours of symptom

Future Directions

At this time, the Penumbra device is indicated for use in patients with symptoms for eight hours or less. Although the Merci retriever was approved for use without a time window, many physicians use eight hours as the maximum time limit for treatment on the basis of previous mechanical thrombectomy studies. However, the authors of several recent papers have challenged the traditional dogma that eligibility for endovascular stroke therapy should be limited by strict temporal criteria. These

Conclusions

The data from mechanical thrombectomy studies indicate that in carefully selected patients, recanalization of large vessel occlusions can be achieved safely. Successful revascularization results in more favorable clinical outcomes and decreased mortality when compared with persistent vessel occlusion. These findings are critical in light of the poor natural history and lack of treatment options for the majority of stroke patients. Each of these devices had increased risk of sICH and mortality

References (50)

  • Y. Loh et al.

    Preprocedural basal ganglionic infarction increases the risk of hemorrhagic transformation but not worse outcome following successful recanalization of acute middle cerebral artery occlusions

    World Neurosurg

    (2010)
  • H.L. Lutsep et al.

    Vertebrobasilar revascularization rates and outcomes in the MERCI and Multi-MERCI trials

    J Stroke Cerebrovasc Dis

    (2008)
  • A. Abou-Chebl et al.

    Conscious Sedation Versus General Anesthesia During Endovascular Therapy for Acute Anterior Circulation Stroke: preliminary results from a retrospective, multicenter study

    Stroke

    (2010)
  • A. Abou-Chebl

    Endovascular treatment of acute ischemic stroke may be safely performed with no time window limit in appropriately selected patients

    Stroke

    (2010)
  • H.P. Adams et al.

    Guidelines for the early management of adults with ischemic stroke: a guideline from the American Heart Association/American Stroke Association Stroke Council, Clinical Cardiology Council, Cardiovascular Radiology and Intervention Council, and the Atherosclerotic Peripheral Vascular Disease and Quality of Care Outcomes in Research Interdisciplinary Working Groups: The American Academy of Neurology affirms the value of this guideline as an educational tool for neurologists

    Circulation

    (2007)
  • W.L. Baker et al.

    Neurothrombectomy devices for the treatment of acute ischemic stroke: state of the evidence

    Ann Intern Med

    (2011)
  • K.Z. Bambauer et al.

    Reasons why few patients with acute stroke receive tissue plasminogen activator

    Arch Neurol

    (2006)
  • P.A. Barber et al.

    Why are stroke patients excluded from TPA therapy?

    Neurology

    (2001)
  • A. Bose et al.

    The Penumbra System: a mechanical device for the treatment of acute stroke due to thromboembolism

    AJNR Am J Neuroradiol

    (2008)
  • T. Brandt et al.

    thrombolytic therapy of acute basilar artery occlusion

    Stroke

    (1996)
  • Prioritizing interventions to improve rates of thrombolysis for ischemic stroke

    Neurology

    (2005)
  • G.J. del Zoppo et al.

    Recombinant tissue plasminogen activator in acute thrombotic and embolic stroke

    Ann Neurol

    (1992)
  • T.G. Devlin et al.

    The Merci Retrieval System for Acute StrokeThe Southeast Regional Stroke Center Experience

    Neurocrit Care

    (2007)
  • J. Fiehler et al.

    Predictors of apparent diffusion coefficient normalization in stroke patients

    Stroke

    (2004)
  • A. Furlan et al.

    Intra-arterial prourokinase for acute ischemic strokeThe PROACT II Study: a randomized controlled trial

    JAMA

    (1999)
  • Y.P. Gobin et al.

    MERCI 1: a phase 1 study of mechanical embolus removal in cerebral ischemia

    Stroke

    (2004)
  • I.Q. Grunwald et al.

    Revascularization in acute ischaemic stroke using the penumbra system: the first single center experience

    Eur J Neurol

    (2009)
  • W. Hacke et al.

    “Malignant” middle cerebral artery territory infarctionclinical course and prognostic signs

    Arch Neurol

    (1996)
  • O. Jansen et al.

    Thrombolytic therapy in acute occlusion of the intracranial internal carotid artery bifurcation

    AJNR Am J Neuroradiol

    (1995)
  • S.A. Josephson et al.

    Comparison of mechanical embolectomy and intraarterial thrombolysis in acute ischemic stroke with the MCA: MERCI and Multi MERCI compared to PROAACT II

    Neurocrit Care

    (2009)
  • I.L. Katzan et al.

    Use of tissue-type plasminogen activator for acute ischemic strokeThe Cleveland Area Experience

    JAMA

    (2000)
  • P. Khatri

    Neurothrombectomy devices for acute ischemic stroke: a state of uncertainty

    Ann Intern Med

    (2011)
  • C.S. Kidwell et al.

    Thrombolytic toxicity: blood brain barrier disruption in human ischemic stroke

    Cerebrovasc Dis

    (2008)
  • C.S. Kidwell et al.

    Thrombolytic reversal of acute human cerebral ischemic injury shown by diffusion/perfusion magnetic resonance imaging

    Ann Neurol

    (2000)
  • D. Kim et al.

    Endovascular mechanical clot retrieval in a broad ischemic stroke cohort

    AJNR Am J Neuroradiol

    (2006)
  • Cited by (0)

    Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

    View full text