|Year : 2020 | Volume
| Issue : 2 | Page : 56-59
A new era in the management of ischemic stroke: Advent of endovascular mechanical thrombectomy
Mithun G Sattur
Department of Neurosurgery, Medical University of South Carolina, Charleston, South Carolina, USA
|Date of Submission||11-Dec-2019|
|Date of Decision||23-Dec-2019|
|Date of Acceptance||01-Feb-2020|
|Date of Web Publication||18-Apr-2020|
Dr. Mithun G Sattur
96, Jonathan Lucas Street, Suite 301 CSB, MSC 606, Medical University of South Carolina, Charleston 29425, South Carolina
Source of Support: None, Conflict of Interest: None
Reduction in the mortality and disability resulting from acute ischemic stroke translates into restoration of blood flow to ischemic penumbra or tissue-at-risk. Reopening occluded large intracranial arteries is currently possible by timely institution of endovascular mechanical thrombectomy. In this topic, we discuss the physiologic basis of thrombectomy, technical steps and future directions in a concise yet eminently readable manner.
Keywords: Acute stroke, endovascular thrombectomy, National Institutes of Health Stroke Scale, occlusion, penumbra
|How to cite this article:|
Sattur MG. A new era in the management of ischemic stroke: Advent of endovascular mechanical thrombectomy. APIK J Int Med 2020;8:56-9
|How to cite this URL:|
Sattur MG. A new era in the management of ischemic stroke: Advent of endovascular mechanical thrombectomy. APIK J Int Med [serial online] 2020 [cited 2020 May 29];8:56-9. Available from: http://www.ajim.in/text.asp?2020/8/2/56/282852
| Introduction|| |
Adult ischemic stroke carries one of the highest disease burdens to the society all over the world in terms of mortality and disability, including India., Prevention of stroke is, therefore, of paramount importance and comprises chiefly of risk factor modification. Rapid recognition of stroke symptoms and triage is equally important in providing swift treatment to patients. This is especially important because with the advent of endovascular mechanical thrombectomy (EMT), prevention of stroke has a new meaning and lends the concept of reversibility to a disease that was earlier viewed as having a fixed outcome.
| Concept of Ischemic Core and Penumbra|| |
Current stroke therapy is based on the concept of reversible ischemia and optimizing the recovery of tissue at risk. Studies have shown that following occlusion of an intracranial artery, there are distinct yet anatomically overlapping areas of differentially affected brain tissue. Normal cerebral blood flow (CBF) is 50 mL/100 g/min. At the center of the affected area is the ischemic core where the CBF is most severely reduced (to below 10 mL/100 g/min). This represents terminally infarcted tissue, also known as ischemic core. Surrounding this is an area that demonstrates reduced CBF (down to around 20 mL/100 g/min) where neuronal function is reduced but has not yet reached the level of terminal calcium influx and glutamate-induced cytotoxicity. This tissue is potentially salvageable brain where neuronal function can be restored to normal with restoration of normal blood flow. This area constitutes ischemic penumbra and is the focus of stroke therapies including endovascular thrombectomy [Figure 1].
| Clinical Features and National Institutes of Health Stroke Scale|| |
The clinical picture of ischemic stroke presentation is well recognized in most instances. Symptoms that promptly reverse qualify for transient ischemic attack (TIA), but it can be treacherous to not recognize stuttering TIA and progressive symptoms. Classic stroke syndromes can be identified such as middle cerebral artery (MCA) syndrome comprising of contralateral hemiparesis, hemianopsia, neglect, aphasia (on dominant side), and sensory loss. Posterior circulation stroke (vertebrobasilar stroke) constitutes vertigo, ataxia, dysarthria, and cranial nerve deficits. The National Institutes of Health Stroke Scale (NIHSS) is a uniform standard quantification of neurologic deficits that is used to document clinical status at each step of therapy (emergency services first encounter, during transport, after recombinant tissue plasminogen activator [tPA], before and after EMT, discharge NIHSS, and so on). The components of the NIHSS are mentioned in [Table 1]. The total score varies from 0 (normal) to 42 (most severe). Higher NIHSS scores tend to correlate with occlusion of large intracranial arteries, also known as large-vessel occlusion (LVO). It is indeed important to exercise astute clinical judgment to rule out stroke mimics.
| Large-Vessel Occlusion|| |
The large intracranial arteries that are a target for endovascular thrombectomy are intracranial internal carotid artery (ICA), MCA, anterior and posterior cerebral arteries, intracranial vertebral artery, and basilar artery. It is important to note that endovascular thrombectomy cannot be applied for lacunar infarcts.
| Imaging Diagnosis|| |
Plain head computed tomography
The first step in the workup of a patient with acute stroke presentation is to perform a plain head computed tomography (CT) to rule out intracerebral hemorrhage (ICH). Once this is ruled out, the next step is to ascertain if there is established infarcted area and this is achieved by calculating Alberta stroke program early CT Score (ASPECTS) score. It provides a 10-point score for signs of early infarction of the MCA territory on a plain head CT (because anterior circulation stroke is the most common area involved). Hypodensity in each of the territories of the MCA deletes one point on the ASPECTS [Figure 2]. Lower scores indicate increasing infarction and higher risk of hemorrhagic transformation following endovascular therapy. ASPECTS score of 6 and above are indications for endovascular therapy. With tPA, the threshold for withholding treatment is very high and only if more than 1/3rd of the MCA territory.
Computed tomography angiography and computed tomography perfusion
Once ICH is ruled out, the next step is to rule out an LVO because this is a target for endovascular treatment. Along with the CT angiography () for vessel imaging, the protocol involves performing a CTP. Through the estimation of mean transit time (MTT), CBF, and cerebral blood volume (CBV), one can determine the extent of core infarction (irreversible or “matched” deficit where area of decrease in MTT and CBF = decrease in CBV) and penumbra tissue (“mismatch” where area of decrease in MTT and CBF > decrease in CBV) [Figure 3]. This becomes important in selecting patients for EMT especially after the 6-h window. The same information can be obtained with magnetic resonance imaging diffusion-perfusion imaging, but this is time consuming, cumbersome, and expensive compared to CTA.
|Figure 3: Computed tomography perfusion in a patient with large-vessel occlusion and salvageable penumbra|
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Till 2016, intravenous tPA was the standard of care for ischemic stroke when administered to patients without contraindications within 4.5 h since symptom onset. A high proportion of patients with large-vessel intracranial occlusions never saw improvement in clinical status with tPA alone. The advent of several trials (MR CLEAN, EXTEND IA, ESCAPE, SWIFT PRIME, REVASCAT, and THRACE) reporting positive results for EMT paved the way for a revolution in stroke care.,,,,, These studies enrolled patients within 6 h of stroke onset, who had received tPA and who did not have large areas of established infarct (as determined by the ASPECTS score). Two further trials in 2018, DAWN and DEFUSE 3, extended the window of inclusion to 24 h provided there is salvageable penumbra as determined by perfusion scans.,
Therefore, current clinical guidelines recommend EMT for patients who:
- Are over 18 years of age (benefit has been shown even over 80 years of age with proper selection)
- NIHSS ≥6 (though lower scores may qualify on a case-by-case basis)
- Plain CT scan reveals no large areas of infarction (ASPECTS score ≥6)
- CT angiogram demonstrates occlusion of large intracranial vessels (intracranial internal carotid, proximal middle cerebral or M1, proximal anterior cerebral or A1, vertebral or basilar, and proximal posterior cerebral or P1 artery). In select cases, occlusions of second-order arterial branches are also considered for thrombectomy
- May or may not have received tPA (tPA cutoff is 4.5 h)
- For patients presenting over 6 h, CT perfusion demonstrates significant mismatch indicating salvageable penumbra
- Have a good baseline functional status.
| Procedure of Thrombectomy|| |
For the sake of convenience, anterior circulation thrombectomy is described though the procedure is largely same for posterior circulation (vertebrobasilar) too.
The patient is wheeled to the neuroendovascular surgery (NES) angiography suite from the emergency room or the CT scan room. The key difference between a regular or cardiology angiography suite and the NES suite is that the latter comprises biplanar angiography to acquire simultaneous anteroposterior and lateral images. Sedation or general endotracheal is used.
Typically, transfemoral access is used although increasingly, transradial approaches are being adopted across the world especially with stent retriever use.
The procedure involves typically using a short or long femoral sheath or radial access sheath that is the starting point for securing arterial access. The next set of catheters used are arranged in a “triaxial” fashion. From outside to inside, this consists of progressively smaller devices: guide catheter or guide sheath (placed in the ICA), aspiration catheter (guided to the intracranial clot), and microcatheter (which is navigated over a microwire into branches of the MCA). To provide perspective about the sizes of these catheters, the ICA at the skull base intracranially measures about 5–6 mm and the MCA's main trunk measures about 3–4 mm. The triaxial set is navigated up across the aortic arch into the common carotid artery on the affected side. Under roadmap guidance, the system is then navigated into the ICA, and the aspiration catheter is “corked” against the clot to aspirate it [Figure 4]. The microcatheter is typically navigated earlier beyond the clot and can be used to deploy the stent retriever to capture clot and deliver it into the aspiration catheter. The process can be repeated multiple times to obtain recanalization, although recent studies have demonstrated diminishing benefit if procedure times exceed 35 min. Closure devices can be used to secure the arterial access site. The overall success rate of thrombectomy is 71% and failure occurs in 29%, but more recent series demonstrate higher recanalization rates.
|Figure 4: Acute right middle cerebral artery occlusion (left) and successful endovascular thrombectomy with recanalization|
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Following recanalization, patients are managed in the neuro-intensive care unit with strict blood pressure control for those with complete recanalization, i.e., thrombolysis in cerebral infarction 2B and above (under 120–140 mmHg systolic to prevent reperfusion hemorrhage). Close attention to respiratory care, nutrition via enteral feeding, deep-venous thrombosis prophylaxis, and physical and occupational therapy is maintained. Patients who experience incomplete or failed recanalization are monitored for infarct-related edema and raised intracranial pressure which requires hyperosmolar therapy. Severe edema necessitates decompressive craniectomy.
Periprocedural antiplatelet and antithrombotic therapy
This depends more on the tPA administration than on the thrombectomy procedure and is typically safe after 24 h.
Concomitant occlusion or high-grade stenosis of the extracranial cervical artery (carotid or vertebral) is termed tandem stenosis and is seen in nearly 15% of patients with intracranial LVO. This adds an additional layer of complexity, but favorable recanalization rates of around 60%–80% are possible even in this population. The order of recanalization, that is “neck- first” or “head- first,” varies between centers and likely does not affect the outcome. The extracranial stenosis or occlusion can be managed with angioplasty alone or with stent placement. Studies have shown that dual antiplatelet therapy in this situation is safe.
Coincident with the establishment of telestroke programs, there has been a significant development in robotic systems that are being developed with the ultimate aim of remote stroke thrombectomy. Newer devices are constantly being developed for improving the technical ability to extract intravascular clots. These include both aspiration catheters and stent retrievers. Simultaneously, there are ongoing efforts at introducing better drugs and indications for intravenous thrombolysis and neuroprotection. For example, a Phase III, prospective, double-blind, randomized, placebo-controlled trial to assess the efficacy and safety of tenecteplase in patients presenting between 4.5 and 24 h (late presentation) is being investigated in the TIMELESS trial (ClinicalTrials.gov-NCT03785678).
One must not overlook the indispensable role of primary prevention of stroke by primary care teams through risk factor modification via education and treatment of hypertension, diabetes mellitus, smoking, hyperlipidemia, and physical activity maintenance.
The authors would like to thank Dr. G. B. Sattur and Dr. Ameet G. Sattur, who provided editorial assistance for drafting the manuscript.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]