PART III - ENDOVASCULAR TREATMENT OF ACUTE ISCHEMIC STROKE
TABLE OF CONTENTS
BOOKSHOP
Updated on June 22, 2020
PART III

Endovascular treatment of acute ischemic stroke

Maxim Mokin, Jason M. Davies, Kenneth V. Snyder, Adnan H. Siddiqui, Elad I. Levy, L. Nelson Hopkins

Summary

Over the last two decades, intraarterial ( IA ) stroke technology has evolved tremendously and is currently the standard treatment of most patients with emergent large vessel occlusion (LVO). Newer-generation devices such as stent retrievers and aspiration catheters allow higher recanalization rates than IA pharmacological thrombolysis and early thrombectomy devices could achieve. Careful patient selection is critical to ensure safety and efficacy of endovascular therapy. A variety of IA approaches is currently available, and selection of the optimal therapeutic intervention is based on clot location and size as well as the anatomy of the affected vessel. In this chapter, we review currently available treatment strategies for IA stroke and discuss relevant studies and their clinical significance and limitations. In addition, we discuss clinical and imaging patient selection criteria for IA treatment of acute and aspiration catheters stroke ( AIS ) and provide illustrative cases.

Introduction

Stroke is the second most common cause of mortality worldwide and is estimated to be the number 1 cause of death and disability in developing countries [1]. Intravenous ( IV ) thrombolysis with recombinant tissue plasminogen activator ( rtPA ) is an effective tool for the treatment of patients with AIS and can be administered within the first 4.5 hours of stroke symptom onset [2, 3]. Unfortunately, because of the associated limited therapeutic time-window and contraindications, approximately only 3–7% of acute stroke patients arriving to hospitals receive IV rtPA [4, 5]. Intraarterial (IA) endovascular stroke interventions are typically reserved for patients with acute stroke due to LVO who present with severe neurological deficits, regardless of eligibility for IV tPA. In this chapter, we review currently available treatment strategies for IA stroke and discuss relevant studies and their clinical significance and limitations. In addition, we discuss clinical and imaging patient selection criteria for IA treatment of acute stroke and provide illustrative cases.

Patient Selection

CLINICAL EVALUATION

The National Institutes of Health Stroke Scale ( NIHSS ) is a commonly used bed-side clinical scale for evaluation of stroke patients [6]. Although several alternative scales for assessment of neurological deficits are available [7, 8], the NIHSS is by far the dominant evaluation tool in both clinical daily practice and research trials. The NIHSS grades independently the patient’s level of consciousness, speech, vision, and motor and sensory domains, with the higher score in each of these categories corresponding to more severe deficits ( Table 1 ). IA stroke interventions are currently reserved for patients with neurologic deficits corresponding to an overall NIHSS score of 6 or higher based on the results of randomized trials of endovascular therapy that are discussed later in this chapter.

Another important clinical assessment scale is the modified Rankin scale ( mRS ) [9], which is used to describe the functional status of stroke patients and is often applied in clinical trials ( Table 2 ). An mRS score of 0–2 at 3 months of follow up is commonly defined as “good” outcome, whereas an mRS score >2 is considered “poor” outcome.

IMAGING OF ACUTE STROKE

Computed tomographic (CT) and magnetic resonance (MR) imaging

Noncontrast brain computed tomography can be performed within seconds and is used as the first-line imaging modality to exclude intracranial hemorrhage when evaluating stroke patients. However, recognition of ischemic stroke within the first few hours of symptom onset is limited with this modality, because CT markers of early ischemia can be very subtle. The Alberta Stroke Program Early CT Score ( ASPECTS ) is a 10-point scoring system of ischemic changes on noncontrast brain CT images in 10 distinct anterior circulation brain regions [10]. The score was designed to improve stroke patient selection for IV thrombolysis and subsequently has been applied to patients undergoing endovascular stroke interventions. A free online training course on the ASPECTS can be found at the following link: www.aspectsinstroke.com ASPECTS ≥6 is considered a favorable imaging pattern for thrombectomy.

MR diffusion-weighted imaging ( DWI ) reliably detects brain ischemia within minutes of its onset and is often used to quantitatively estimate the size of an ischemic lesion for prognostication [11, 12]. It is estimated that with a DWI lesion volume exceeding 70 cm3, IA stroke intervention is unlikely to lead to good clinical outcomes, even if the revascularization procedure is technically successful [13]. However, there may be clinical benefit in performing thrombectomy in carefully selected patients with a high volume of infarct core [14].

Confirmation of large-vessel occlusion

Before noninvasive imaging ( CT and MR angiography ) of the intracranial vasculature became widely available, clinical examination alone was used to predict whether the stroke was caused by an LVO ( Figure 1 ). Although clinical stroke severity estimated with the NIHSS score can predict the presence of LVO, this association is far from ideal in some cases, especially when the NIHSS score is in the moderate range (8–20) or stroke symptom onset is beyond 6 hours [15, 16].

Evaluation of stroke patients with CT angiography or MR angiography for suspected LVO is critical for estimation of success rates with IV thrombolysis, which strongly depends on the location and extent of the intracranial occlusion. Recanalization rates following IV rtPA and rates of favorable clinical outcomes are much higher in patients with distal middle cerebral artery (MCA) occlusion, in comparison to occlusion of the proximal MCA M1 segment or intracranial ICA. Moreover, basilar artery occlusion [17, 18] and clot length exceeding 8 mm have poor potential for recanalization with IV rtPA alone [19].

In addition to providing important information about clot properties and location, noninvasive imaging offers valuable data about the anatomy of the aortic arch and proximal vasculature. Because a shorter duration of stroke intervention is associated with improved outcomes [20], a preprocedure review of patient anatomy is critical for planning of proper access and devices. For example, recognition of severe tortuosity of the proximal carotid artery or unfavorable arch anatomy (such as a type III arch) might prompt consideration of an alternative access route, such as transcervical access via direct carotid artery puncture [21].

Perfusion and ischemic “penumbra”

CT- and MR-generated perfusion maps are becoming more commonly utilized in clinical practice for identification of irreversibly infarcted brain tissue (known as infarct “core”) and potentially salvageable tissue at risk (known as ischemic “penumbra”). Patients with large ischemic core and little-to-no penumbral tissue are thought to be at high risk for reperfusion hemorrhage and are unlikely to benefit from IA intervention ( Figure 2 ), whereas patients with a higher ischemic penumbra/core mismatch are considered ideal candidates for revascularization ( Figure 3 ) [22, 23, 24]. Perfusion-based selection obviates the limitations of time-based selection of patients for intervention by identifying stroke cases with favorable perfusion when time of onset is unknown or extends beyond the first few hours [25, 26]. Perfusion-based selection of patients for endovascular therapy appears to have the most benefit when applied to patients with symptom onset beyond the first 6 hours, including patients with unwitnessed strokes and wake-up strokes, when ‘last known well’ is used as the time of onset. In fact, there is some evidence that within the first 6 hours of symptom onset, the use of perfusion-based imaging may be ‘harmful’ as it may mistakenly overestimate the degree of irreversible ischemic changes, thus excluding patients from thrombectomy who would otherwise qualify based on CT or MR imaging findings alone .

Grading of revascularization, reperfusion, and collaterals

Although the terms “recanalization” and “reperfusion” are often used interchangeably, they describe two separate phenomena. Reperfusion characterizes the supply of blood (or contrast material, in the case of a cerebral angiogram) to the brain, whereas recanalization describes the status of arterial occlusion and the corresponding downstream flow [28]. The two most commonly used scales in neurointerventional practice are the Thrombolysis in Myocardial Infarction ( TIMI ) ( Table 3 ) and Thrombolysis in Cerebral Infarction ( TICI ) ( Table 4 ) [29, 30]. The TICI scale is superior to the TIMI scale for predicting clinical outcomes after IA stroke interventions and should be used to evaluate the efficacy of thrombectomy procedures [31].

First pass effect ( FPE ) is a novel measure of grading the effectiveness of thrombectomy. FPE is defined as compete recanalization of the occluded segment and its downstream territory achieved with a single pass of a thrombectomy device [32]. This stringent definition has shown that even with the most recent technological advances, FPE is achieved in less than half of thrombectomy cases in real-world practice, indicating the need for continuous innovation and research in this field [32, 33].

The extent of pial collateral flow is described using the American Society of Interventional and Therapeutic Neuroradiology collateral grading system [29]. The scale ranges from 0 (no visible collateral flow) to 4 (complete and robust collateral flow in the entire ischemic area by retrograde perfusion). Patients with poorly developed collaterals are at risk for greater infarct growth [34]. Multiphase CT angiography ( mCTA ) can be used to evaluate the extent of collaterals to select candidates for thrombectomy [35, 36]. Patients with good or moderate collaterals are more likely to demonstrate improvement in clinical deficits than patients with poor collaterals. mCTA was used to select patients in the Endovascular Treatment for Small Core and Anterior Circulation Proximal Occlusion with Emphasis on Minimizing CT to Recanalization Times (ESCAPE) trial [37].

Endovascular approaches to stroke

PHARMACOLOGICAL THROMBOLYSIS

In this approach, a small dose of a thrombolytic agent (most commonly rtPA) is injected through a microcatheter that is positioned proximally to or inside the thrombus ( Figure 4 ).

FOCUS BOX 1IA pharmacological thrombolysis, key points
  • Used primarily as an adjunct treatment to aspiration or stent retriever thrombectomy
  • Can be delivered via a small microcatheter positioned proximal to or inside the thrombus
  • Contrast injection is performed through the microcatheter to ensure its satisfactory position and no perforation/active contrast extravasation
  • rtPA is administered at rate of 1 mg/min, maximal dose of 10–20 mg. Frequently repeat angiography is performed to assess for revascularization
  • Very gentle microwire manipulation can be used for adjunctive treatment (using a “J” tip is safer than a straight tip)
  • Additional use of glycoprotein IIb/IIIa inhibitors is controversial

Recanalization rates with this treatment are modest, especially with larger clot burden [38]. Because of this, IA rtPA is rarely used as a primary treatment of acute stroke. Its role is reserved for more distal occlusions, which can be difficult to reach with other devices, or as an adjunct to other thrombectomy devices, when distal embolization is observed. IA infusion of rtPA is sometimes combined with gentle microwire manipulation to facilitate thrombus breakdown. Pharmacological thrombolysis alone is rarely used these days, even for small more distal occlusions, where highly trackable smaller lumen aspiration catheters or smaller profile stent retrievers are preferred.

MECHANICAL THROMBECTOMY

The introduction of the Merci retriever (Stryker, Kalamazoo, Michigan, USA) was a real breakthrough in the endovascular treatment of stroke [39, 40]. The principle of trapping the thrombus inside the “corkscrew”-like designed Merci device and subsequently mechanically extracting clot from intracranial vasculature ultimately established a foundation for newer-generation devices. The utility of the Merci retriever in current acute stroke interventions has declined dramatically, and the device is no longer in use since the publication of the Solitaire With the Intention For Thrombectomy ( SWIFT ) and Thrombectomy Revascularization of Large Vessel Occlusions in Acute ischemic stroke ( TREVO 2 ) trials, which established the superiority of newer generation devices in achieving revascularization and good clinical outcomes [41, 42]. Stent retrievers were the most widely used class of thrombectomy devices in a series of randomized trials of endovascular versus medical therapy of stroke from LVO.

ASPIRATION THROMBECTOMY

The Penumbra aspiration system (Penumbra Inc., Alameda, California, USA) works by mechanical debulking of the thrombus with specially designed separators under continuous direct aspiration through a reperfusion catheter that is positioned proximally to the occlusion site. In the Penumbra Pivotal Stroke trial, 82% of patients demonstrated TIMI 2–3 revascularization, but only 25% achieved a good clinical outcome at the 3-month follow up [43] ( Focus Box 2 ).This system was a predecessor to a variety of aspiration catheters currently used in clinical practice

These larger diameter, highly navigable and trackable catheters (such as the JET family of reperfusion catheters from Penumbra Inc., SOFIA catheters from MicroVention, or Vecta by Stryker) have been used for direct aspiration – the approach most commonly referred to as the A direct aspiration first pass technique ( ADAPT ) [44]. With the ADAPT, a large-bore aspiration catheter is advanced over a microcatheter (or even sometimes over the micro guide wire alone) and put in direct contact with the thrombus ( Figure 5 ).

FOCUS BOX 2Aspiration thrombectomy, key points
  • Requires a large-bore guide catheter (examples: Neuron MAX 088 from Penumbra, 6-French (F) Cook Shuttle long sheath from Cook Medical (Bloomington, Indiana, USA), or 8-9F balloon-guide catheter
  • Choice of reperfusion catheter depends on the location of occlusion: use the JET family of aspiration catheters from Penumbra, Inc. or SOFIA 6F from MicroVention for ICA-terminus and proximal M1 MCA occlusions, JET D catheter from Penumbra, Inc. or SOFIA 5F from MicroVention for M2 MCA occlusions.
  • In cases of tortuous anatomy, an aspiration catheter can be advanced over a 3MAX catheter and 0.014-0.018-inch microwire
  • Continuous aspiration can be achieved manually using a 20-cc syringe or by connecting to the aspiration pump

Next, direct aspiration with a pump or manually with a syringe is applied to extract the clot. The advantages of this approach include its simplicity and the low cost of the procedure. If direct aspiration alone is unsuccessful in removing the clot, a stent retriever (or another rescue device) is delivered through the aspiration catheter to perform stent-retriever thrombectomy.

The Adapt versus StEnt Retriever (ASTER) and COMParison of direct ASpiration versus Stent retriever as first approach (COMPASS) trials have shown that recanalization rates, clinical outcomes, and safety of the ADAPT approach to thrombectomy are similar to those of using a stent retriever as the primary treatment strategy [45, 46]. Additionally, the ADAPT approach may provide a cost-effectiveness advantage for the treatment of AIS from LVO [47].

STENT RETRIEVERS

These devices are manufactured by several companies and vary in length, radial force, and distal tip design (open vs. closed) but all share the same principle – unsheathing of the stent retriever when positioned directly inside the thrombus with subsequent thrombus entrapment within the stent struts. Once the stent retriever is deployed, it apposes the clot against the vessel wall and achieves rapid recanalization, allowing instant reperfusion of the distal territory, a concept called “temporary endovascular bypass.” After a few minutes, once the clot becomes fully engaged within the stent retriever struts, both the clot and stent retriever are retracted into the guide catheter ( Figure 6, Focus Box 3 ).

FOCUS BOX 3Stent retriever thrombectomy, key points
  • 0.021–0.027-inch microcatheters can be used to deliver most stentrievers
  • The microcatheter is advanced over the microwire through the thrombus and microinjection is performed to ensure adequate position of the microcatheter
  • The stent retriever is unsheathed under direct fluoroscopy, and the interventionist waits 3-5 minutes to allow the stent retriever struts to engage the clot
  • If successful revascularization is not achieved, repeat thrombectomy attempts with the same device are recommended (typically 3 attempts are recommended, depending on the manufacturer). If still unsuccessful, consider changes the size or brand of the stent retriever.
  • If using a balloon-guide catheter, inflating the balloon during the retrieval step might decrease the chance of inadvertent distal embolization
  • For the combined stent retriever + aspiration thrombectomy approach, a large-bore guide (examples; Neuron MAX 088 from Penumbra, 6F Cook Shuttle long sheath from Cook Medical, 9F balloon-guide catheter from Stryker) that can accommodate an appropriately-sized aspiration catheter. The proximal end of the stent retriever is engaged within the tip of the aspiration catheter to facilitate capturing the clot.

Randomized trials of stent retrievers

The Solitaire (Medtronic, Dublin, Ireland) stent retriever and Trevo stentriever (Stryker, Kalamazoo, Michigan, USA) have been studied most extensively. Both devices were compared to the Merci retriever in two randomized trials. The SWIFT trial tested the Solitaire FR stent retriever, and the Trevo stentriever was evaluated in the TREVO 2 trial [41, 42]. Both trials included patients who were treated within the first 8 hours of stroke symptom onset; each reported higher rates of successful revascularization and favorable clinical outcome with stent retrievers in strokes caused by LVO.

In SWIFT, the primary efficacy endpoint (TIMI 2–3 recanalization without the use of rescue treatment and with no symptomatic intracerebral hemorrhage [sICH]) showed an absolute difference of 37% in favor of the Solitaire device . At 3 months, 58% of patients had a good clinical outcome with the Solitaire versus only 33% with the Merci. In TREVO 2, the TICI 2–3 rates were 86% in the Trevo group and 60% in the Merci group. More patients treated with the Trevo stentriever had good long-term outcomes (absolute difference 18%).

Clinical experience from centers around the world has confirmed the high success rate of stent retrievers in patients with acute stroke, comparable to the results of SWIFT and TREVO 2 [48, 49, 50, 51, 52].

Retrievable stents were the primary thrombectomy device used in the series of the first “positive” landmark randomized trials of endovascular stroke therapy ( Table 5) [37, 53, 54, 55, 56], which proved the superiority and effectiveness of IA interventions over medical therapy alone, including the use of IV rtPA. Stent retrievers were also the dominant thrombectomy device in the two most recent trials of endovascular therapy that evaluated thrombectomy at late time windows of up to 16 and 24 hours from symptom onset: Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution (DEFUSE 3) and Clinical Mismatch in the Triage of Wake Up and Late Presenting Strokes Undergoing Neurointervention With Trevo (DAWN) [57, 58].

Combined stent retriever and aspiration thrombectomy

Unlike in trials that require adherence to protocols to test the performance of a single device per stroke case, in daily clinical practice, a variety of different devices are often needed to achieve successful recanalization. A combination stent retriever and direct aspiration thrombectomy technique is often performed because of a theoretical reduction in the chance of distal embolization, which can occur when a part of the clot breaks off while withdrawing the stent retriever and clot together from the occluded vessel [61]. In this technique, a large-bore catheter (similar to those used in aspiration thrombectomy technique, such as the JET7 (Penumbra) or 6F SOFIA (MicroVention) reperfusion catheters, is connected to an aspiration catheter creating negative pressure and capturing emboli while the stent retriever is withdrawn into the catheter ( Figure 7 , Focus Box 3 ).

PRIMARY STENTING

Stenting with permanently implanted intracranial stents has not yet established itself as a primary treatment of intracranial large-vessel occlusion, largely because of the success with temporarily deployed stent retrievers, which are dominating the field. In a prospective series of 20 patients from a single center, primary stenting was successful in achieving TIMI 2–3 recanalization in all patients, with 11 patients (55%) demonstrating favorable angiographic and clinical results at 6 months [62, 63]. Intracranial stenting can be used as a rescue treatment for patients in whom other thrombectomy devices fail, and it requires dual antiplatelet therapy to prevent instent thrombosis.

Randomized trials of stroke therapies

Earlier randomized clinical trials (Interventional Management of Stroke [IMS] III, Mechanical Retrieval and Recanalization of Stroke Clots Using Embolectomy [MR RESCUE], and Synthesis Expansion: A Randomized Controlled Trial on Intra-Arterial Versus Intravenous Thrombolysis in Acute Ischemic Stroke [SYNTHESIS Expansion]) compared endovascular stroke therapies to systemic thrombolysis and medical management of patients with acute stroke [64, 65, 66]. Although these trials did not demonstrate the overall benefit of catheter-based therapy over traditional treatment with IV thrombolysis or antiplatelet therapy, they showed the safety of IA revascularization and identified subgroups of patients who can benefit the most from such therapies.

It should be noted that a large proportion of patients in these trials were treated with IA pharmacological thrombolysis and early-generation thrombectomy approaches (Merci and Penumbra systems), whereas stent retrievers were used in few patients. Other criticisms include failure to utilize noninvasive imaging to confirm LVO in many cases and delays in initiating IA therapy [67, 68]. Nevertheless, these trials laid the foundation for the next generation of stroke trials, which compared modern mechanical stroke thrombectomy devices (mostly stent retrievers) with medical therapy alone ( Table 5 ). The five ‘next-generation’ trials [37, 53, 54, 55, 56] had some variations in inclusion criteria such as age, time window for randomization, and specific imaging criteria.

Because thrombectomy was initiated within the first 6 hours of symptom onset in most patients enrolled in the five trials, the guidelines that followed these five trials did not give strong recommendations in support of endovascular therapy beyond the 6-hour window.

The aforementioned DEFUSE 3 and DAWN trials demonstrated a strong benefit of thrombectomy versus medical therapy in patients with symptom onset up to 16 or 24 hours, including wake-up strokes [57, 58]. Both trials relied on the use of perfusion imaging to exclude patients with large core infarcts. The American Heart Association (AHA) issued a new set of stroke guidelines recommending thrombectomy up to 24 hours in patients with anterior circulation LVO AIS immediately after the publication of these two trials [69]. However, the AHA limited its recommendations to patients who would otherwise meet the criteria of these trials. In a real-world setting, most patients present with one or more clinical or imaging criteria that would make them ineligible for the criteria of a randomized trial. Nevertheless, this should not be the reason to exclude considerations of thrombectomy for such patients – thrombectomy is a procedure that has been proven to be safe and highly effective. Although the treatment effect may be not as robust as that in patients who qualify for all of the clinical trial criteria, there is accumulating evidence that thrombectomy is equally effective even in those patients who do not meet top-tier criteria.

GUIDELINES

The AHA released several corrected versions of the guidelines for the management of AIS after the publication of DAWN and DEFUSE 3 data, the most recent one dating December 2019 [59] (Focus Box 4). The European Stroke Organization also updated its guidelines on mechanical thrombectomy of AIS in 2018 [60] (Focus Box 5).

At the 2020 International Stroke Conference, the results of the Efficiency of alone endovascular therapy for acute ischemic stroke patients ( SKIP ) trial of thrombectomy with versus without IV tPA (alteplase) were announced [70]. The trial showed no added benefit of IV tPA in patients treated with thrombectomy [70]. Moreover, fewer intracranial hemorrhages were seen in patients treated with the direct thrombectomy approach versus in patients with bridging therapy. These findings have not been incorporated into the AHA or ESO guidelines to officially recommend withholding IV tPA in patients treated with thrombectomy.

FOCUS BOX 4Summary of the 2019 AHA/ASA update on endovascular management of acute stroke (adapted from Corrections [authors anonymous], [59])
  • Strongest evidence supports mechanical thrombectomy for patients with ICA or MCA M1 occlusion and NIHSS and ASPECTS ≥6 in whom treatment can be initiated within 6 hours of stroke onset.
  • In carefully selected patients, such as those with more distal occlusions, posterior circulation occlusion, and NIHSS <6 or ASPECTS <6, mechanical thrombectomy within 6 hours may be reasonable.
  • In carefully selected patients within 6 to 24 hours of symptom onset, including wake-up strokes, mechanical thrombectomy is indicated in patients who meet DAWN and DEFUSE 3 eligibility criteria.
  • Direct aspiration is noninferior to stent retriever use.
  • The choice of anesthesia (conscious or general) can be individualized (previous recommendations favored conscious sedation over general).
FOCUS BOX 5Summary of the 2018 European Stroke Organisation (ESO) - European Society for Minimally Invasive Neurological Therapy (ESMINT) guidelines on endovascular management of acute stroke (adapted from Turc et al. [60])
  • There is high-quality evidence to recommend thrombectomy plus best medical management (including IV tPA) in patients with LVO AIS within 6 hours after symptom onset.
  • There is a moderate quality of evidence to recommend thrombectomy plus best medical management in the 6-24 hour time window in patients meeting the eligibility criteria of published randomized trials.

Exciting findings have also been reported for the first time in the field of neuroprotection for patients specifically treated with endovascular therapies [71]. Safety and Efficacy of NA-1 in Subjects Undergoing Endovascular Thrombectomy for Stroke ( ESCAPE-NA1 ) was the first randomized trial evaluating neuroprotection specifically in patients with emergent LVO treated with endovascular therapy. The trial tested the safey and efficacy of the neuroprotective agent nerinetide in patients treated with thrombectomy. Although the overall findings of the study were ‘negative,’ there was a significant benefit of using nerinetide in a subgroup of patients who did not receive IV tPA. The authors concluded that IV tPA may have had an unanticipated drug–drug interaction with nerinetide, attenuating its protective effect.

Complications associated with IA stroke treatment

INTRACEREBRAL HEMORRHAGE

ICH is the most feared complication associated with the endovascular treatment of AIS. According to the definition applied in the National Institute of Neurological Disorders and Stroke (NINDS) IV rtPA stroke trial, hemorrhage is considered symptomatic if associated with any clinical decline in neurological examination and sICH is associated with increased mortality [3, 72]. The European Cooperative Acute Stroke Study (ECASS) investigators’ definition of sICH is more specific; it implies neurologic deterioration by at least 4 NIHSS score points [73]. The rate of sICH was on the order of 10–15% in the first trials of endovascular therapies that included IA pharmacological thrombolysis and mechanical thrombectomy with the Merci device [38, 39, 74]. A much lower rate of sICH (2–4%) was seen in the two more recent trials of the Solitaire and Trevo stent retriever devices, indicating their improved safety profiles [41, 42]].

ICH can have a variable appearance on noninvasive imaging, based on its radiographic classification [72]. Hemorrhagic infarction is defined as the presence of petechial hemorrhages along the margins of or within the infarct core and typically has benign outcomes [73]. Parenchymal hematomas are characterized by a larger hemorrhage size with the presence of mass effect and are more alarming. Of those, parenchymal hematoma type 2, which occupies more than one-third of the infarcted area with significant mass effect [73], carries the worst clinical prognosis with high mortality rates.

ICH is sometimes difficult to differentiate from the postprocedure contrast medium staining that is often seen immediately after a stroke intervention. In such cases, serial noncontrast CT examinations or MR imaging with a gradient echo sequence can be used to differentiate between the two.

DISTAL EMBOLIZATION

Embolization of distal vessels can occur during mechanical thrombectomy ( Figure 7 [D] ). Depending on the location of the distal embolization, the caliber of the affected vessel, and the anticipated clinical consequence, the management of this complication can vary from a conservative approach to additional thrombectomy attempts and local administration of pharmacological thrombolytic agents. The use of a balloon guide catheter might decrease the risk of distal embolization [75].

PERFORATION

Vessel perforation can occur when attempting to cross the occlusion with a microwire or microcatheter, which is a maneuver that is performed “blindly” because the arterial system cannot be visualized beyond the occlusion site. Intimal injury can occur when retrieving a thrombectomy device (such as a stent retriever). Rescue techniques include reversal of the systemic effect of heparinization with protamine sulfate (heparin is always administered at the start of an endovascular intervention), and temporary inflation of a small balloon at the perforation site, if active contrast extravasation is observed [76].

Conclusion

Over the last two decades, IA stroke technology has evolved tremendously. Newer-generation devices such as stent retrievers allow higher recanalization rates than IA pharmacological thrombolysis and early thrombectomy devices could achieve. Careful patient selection is critical to ensure safety and efficacy of endovascular therapy. A variety of IA approaches is currently available, and selection of the optimal therapeutic intervention is based on clot location and size as well as the anatomy of the affected vessel.

Personal Perspective – L. Nelson Hopkins

The neurointerventional field is perhaps the most rapidly evolving branch of currently available minimally invasive endovascular disciplines. Over the last decade, multiple IA devices for the treatment of AIS due to LVO have been developed. Research confirms that new-generation devices, such as stent retrievers and aspiration catheters, allow higher recanalization rates leading to improved clinical outcomes, in comparison to early thrombectomy tools. Yet, more research is needed to establish the most effective ways to intervene in stroke and reverse neurologic deficits. The focus should now be shifted to patient care elements before the patient arrives at the angiography suite, including improving public awareness of stroke symptoms, technological innovations for accurate and rapid detection of LVO, and developing stroke systems of care capable of providing the best available treatment.

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