Endovascular Management of Large Vessel Occlusion in Acute Ischemic Stroke

Abbreviations and Acronyms

ASPECTS, Alberta Stroke Program Early CT Score; ASTER, Contact Aspiration vs. Stent Retriever for Successful Revascularization; CAST, Committee on Subspecialty Training; COMPASS, Comparison of Direct Aspiration vs. Stent Retriever as a First Approach; CPSSS, Cincinnati Prehospital Stroke Severity Scale; CSC, Comprehensive Stroke Center; CT, computed tomography; CTA, CT angiography; CTP, CT perfusion; ECASS, European Cooperative Acute Stroke Study; ELVO, emergent large vessel occlusion; DWI, diffusion-weighted imaging; ENDOLOW, Endovascular Therapy for Low NIHSS Ischemic Strokes; FDA, Food & Drug Administration; ICA, internal carotid artery; IV, intravenous; LAMS, Los Angeles Motor Scale; LVO, large vessel occlusion; MCA, middle cerebral artery; MR, magnetic resonance; MRA, MR angiography; MRI, MR imaging; MRP, MR perfusion; NCCT, noncontrast computed tomography; NIHSS, National Institutes of Health Stroke Scale; Penumbra Separator 3D, A Randomized, Concurrent Controlled Trial to Assess the Safety and Effectiveness of the Separator 3D as a Component of the Penumbra System in the Revascularization of Large Vessel Occlusion in Acute Ischemic Stroke; RACE, Rapid Arterial oCclusion Evaluation; rtPA, recombinant tissue plasminogen activator; TESLA, Thrombectomy for Emergent Salvage of Large Anterior Circulation Ischemic Stroke; TSC, thrombectomy-capable stroke center.

Clinical Examination

The National Institutes of Health Stroke Scale (NIHSS) is the most frequently used scale for evaluation and triage of stroke patients. This scale is composed of 11 items such as level of alertness, motor, sensory or speech deficits, each of which is scored based on the severity of specific neurological deficits ( Table 95.1 ). According to most stroke guidelines, candidates for endovascular therapy generally have a score of 6 or above. In most endovascular trials and registries, the majority of patients who are treated with endovascular therapy present with severe debilitating neurologic deficits; as such, their average NIHSS scores typically fall within a 15–20 range. The role of endovascular therapy in patients with “mild” neurological deficits (that is, NIHSS score of <6) is not well established. Although evidence from post-hoc analysis suggests that endovascular therapy may be of benefit in this patient population, it has not been confirmed in randomized clinical trials specifically targeting this population. Ongoing trials, such as Endovascular Therapy for Low NIHSS Ischemic Strokes (ENDOLOW; ClinicalTrials.gov identifier: NCT04167527), are evaluating the benefit of endovascular therapy in patients with mild neurologic deficits.

In addition to the NIHSS, there are multiple clinical tools that are designed to predict the likelihood of emergent large vessel occlusion (ELVO) as the cause of stroke in order to identify patients who are most likely to benefit from thrombectomy. Such clinical tools are often used in the prehospital setting when the first responders need to make a swift decision regarding the most appropriate stroke triage in each individual case. The Los Angeles Motor Scale (LAMS), Cincinnati Prehospital Stroke Severity Scale (CPSS), and Rapid Arterial oCclusion Evaluation (RACE) are some of the examples of such ELVO detection tools ( Tables 95.2–95.4 )

Imaging

The two main questions that various stroke imaging modalities are designed to answer are whether a patient is experiencing a stroke from ELVO and whether endovascular therapy is indicated. Approximately 15%–20% of acute strokes are caused by ELVO, and computed tomography angiography (CTA) is currently the most widely used modality performed in the emergency department to confirm or exclude any potential targets for thrombectomy. The choice of imaging modality to determine whether thrombectomy should or should not be performed in an individual stroke caused by ELVO varies greatly and has been a subject of ongoing debate. The Alberta Stroke Program Early CT Score (ASPECTS), magnetic resonance imaging (MRI), advanced CT perfusion (CTP) imaging, and assessment of collaterals can be used individually or in combination. The choice often depends on unique workflow patterns at individual centers, geographical aspects, and patient populations being treated.

Alberta Stroke Program Early CT Score

ASPECTS is a noncontrast computed tomography (NCCT)-based scoring system with scores ranging from 0 to 10; it is used to evaluate the extent of early ischemic changes in the territory of the middle cerebral artery (MCA) ( Fig. 95.1 ). Significant variations in agreement, especially among operators with limited experience in interpreting ASPECTS, and dependence on high-resolution imaging workstations for accurate scoring are the limitations that have led to the creation of various automated ASPECTS platforms, so called “eASPECTS” ( Fig. 95.2 ). Automated ASPECTS notification allows fast imaging assessment, which can be done on a variety of devices including smart phones and tablets, which is highly practical and convenient. Endovascular treatment is indicated for ASPECTS of 6 and higher. Patients with lower ASPECTS are at risk of reperfusion hemorrhage and are less likely to achieve good clinical outcomes than patients with ASPECTS 6–10. However, in comparison to standard medical therapy alone, even in patients with values in the low ASPECTS range, there is still a potential benefit of endovascular recanalization. Thrombectomy for Emergent Salvage of Large Anterior Circulation Ischemic Stroke (TESLA; ClinicalTrials.gov identifier: NCT03805308) is an ongoing randomized clinical trial of anterior circulation stroke with ASPECTS 2–5. The objective of this trial is to help determine the safety and efficacy of endovascular therapy in patients with large ischemic stroke burden.

Perfusion Imaging

Another common imaging modality used in an acute stroke setting is perfusion imaging, especially in patients with late onset of stroke symptom onset, unknown time of stroke onset, or last known well or wake-up strokes. MR- and CT-based perfusion studies help in assessing the volume of irreversibly infarcted brain tissue (ischemic core) and relative volume of potentially salvageable tissue at risk (ischemic penumbra). CTP is preferred over magnetic resonance perfusion (MRP) as this can be performed in the same setting as CTA in an additional 4 to 5 minutes. The practice of routine CTP and/or MRP varies between different centers as it depends on physician preference. At some comprehensive stroke centers, perfusion imaging is reserved for unclear or challenging cases, e.g., awake stroke or stroke with late presentation, while other centers routinely perform CTP for all cases of stroke.

Automated software imaging tools such as RAPID AI (iSchemaView, Menlo Park, CA) allows rapid evaluation of CT- and MR-generated perfusion maps on a desktop, tablet, or smartphone ( Fig. 95.3 ). Perfusion imaging allows estimation of irreversibly infarcted brain (known as “core”) and salvageable tissue at risk (ischemic “penumbra”). It should be noted that within the first few hours of stroke onset, perfusion imaging may overestimate the true extent of irreversible injury, the phenomenon known as “ghost infarct core,” arguing against its use in clinical decision-making during the early hours (typically, the first 6 hours) of stroke symptom onset.