The publication in 2013 of 3 negative randomized trials comparing endovascular treatment (EVT) with IV rtPA vs. IV rtPA alone was really disappointing for the neurointerventional community, even if these trials had several drawbacks restricting their clinical importance.¹ One major drawback was the heterogeneity of endovascular techniques used, and recent studies have established the value of second-generation devices (stent retrievers) in the management of acute ischemic stroke (AIS).² The efficacy of stent-retriever mechanical thrombectomy (MT) was confirmed in a study by Friedrich et al showing that recanalization (TICI 3/2b) was obtained in 78.1% of 73 patients with acute stroke in the anterior circulation.³ Successful recanalization was associated with a final infarct volume significantly smaller compared with insufficient recanalization (TICI 2a and less). The rescue of a large amount of endangered brain tissue was significantly associated with clinical improvement of the patients at 3 months.

The negative 2013 trials have prompted active research in order to improve the results of EVT in AIS, prompting more intense focus on better selection of patients and optimization of endovascular techniques. In an interesting subanalysis of the STAR study, Almekhlafi et al evaluated the impact of Stroke Prognostication using Age and NIHSS Stroke Scale (SPAN) (age + NIHSS score) on clinical outcomes after MT.⁴ SPAN-100-positive patients (SPAN ≥ 100) had a significantly lower proportion of favorable clinical outcomes at 3 months (26.7% vs. 60.8% in SPAN-100-negative; P = .01), despite a similar rate of successful reperfusion. In multivariate analysis, SPAN-100 was a significant predictor of favorable outcome (OR = 0.3) as well as baseline ASPECTS (OR = 1.3) and time from stroke onset to successful revascularization (OR = 0.7). As stated by the authors, the SPAN-100 index may be promising as a simple tool to enhance the patient-selection process for MT.

Improving MT technique requires first an understanding of the mechanisms that can potentially alter the clinical outcome of patients.

One potential mechanism is embolism in previously unaffected vessels. In a nice documented series, Kurre et al showed that anterior cerebral artery emboli occurred in 11.4% of 105 patients with M1 recanalization, leading to 5.7% new infarcts.⁵ This series showed that endovascular recanalization of occluded major anterior cerebral artery branches reduced the risk of ischemia and was not accompanied with adverse events. The authors suggested that recanalization has to be attempted when collateral circulation is poor and accessibility is good. Several strategies are proposed by the authors to reduce the risk of thrombus loss, including improving visualization of the thrombus with advanced imaging techniques, using low-profile microcatheters, positioning of a large-lumen intermediate catheter in the proximity of the thrombus, and using balloon-guided catheters. Further studies are needed to evaluate the value of these different strategies.

Another important issue with MT in AIS treatment is to know whether it is preferable to perform the procedure under general anesthesia or conscious sedation. Soize et al reported a series of 36 patients with AIS treated with MT under conscious sedation.⁶ They showed that MT was feasible in a high percentage of cases (86.1%) and associated with a short procedure delay and a high percentage of good clinical outcomes at 3 months (61.1%). Other series are showing similar results. AIS procedures have to be carried out in the presence of an experienced anesthesiologist, or where these specialists are immediately available. Anesthesiologists can manage untoward events rapidly, including securing the airway.² Conscious sedation can be used if the procedure is feasible according to the clinical status. In the case of agitation, upper airway obstruction, or important pain, general anesthesia can be performed at any time during the management of the patient (before or during the EVT).

Most of the trials dealing with EVT of AIS were conducted in patients with MCA occlusion, which is the cause of approximately 70% of AIS. However, it is important to have an idea of MR results in more challenging situations, like basilar artery occlusion or tandem occlusion. Möhlenbruch et al analyzed the results of MT with stent-retrievers in a series of 24 patients with acute basilar artery occlusion.⁷ Time interval from symptom onset to first angiogram was 125 to 827 minutes. Successful recanalization (TICI 2b/3) by thrombectomy only was observed in 75% of patients. Seven patients had stent placement after MT due to underlying atherosclerotic stenosis. In total, including stent placement, successful recanalization was obtained in 87.5% of patients. As expected, and despite these relatively good recanalization results, clinical outcome was still not optimal, with 29% mortality at 3 months and favorable clinical outcome (mRS 0–2) in only 33% of patients. However, as acute basilar artery occlusion usually has a very bad clinical outcome and IV rtPA has relatively limited efficacy in this situation, MT with a stent retriever is thereby indicated. In addition, underlying atherosclerotic stenosis is not infrequent and must be assessed in order to appropriately conduct endovascular treatment, which in these instances should involve intracranial stenting in addition to MT.

The management of tandem occlusion is still unclear. Stampfl et al reported the treatment of combined intracranial anterior circulation occlusion and high-grade proximal stenosis or occlusion of the ipsilateral cervical ICA in 24 patients.⁸ In the great majority of patients (21/24) the treatment was started with ICA stent implantation, while intracranial thrombectomy was performed secondarily. These treatments were performed in reverse order in 3 patients. ICA stent implantation was successfully achieved in all cases. Fifteen patients (62.5%) had a successful recanalization (TICI 2b/3), but a good clinical outcome was obtained in only 29.2% of patients, with death in 16.6%. It was not possible in this series to compare both approaches (ICA stenting first or reverse technique) as the second group was too small (3 patients). However, it is of interest to know whether the reverse technique (MT first) results in earlier recanalization, potentially improving the clinical outcome. Another question that must be answered is whether ICA stenting is always necessary and must be done at the acute phase of AIS. Certainly, angioplasty/stenting should be the first step when no other access to the intracranial occlusion is available.

MT with a stent retriever is actually the endovascular treatment of preference for patients with AIS. Results of randomized trials comparing this treatment with IV rtPA are warranted to know its exact indications. As of now, MT is already indicated when IV rtPA is contraindicated or fails. Better selection of patients and refinement of the technique, together with improved timing management for AIS, will contribute to the improvement of clinical outcome of patients treated with MT.

Disclosures

LP is a consultant for Codman, Covidien/eV3, Microvention, Sequent, and Stryker.

References

1. Pierot L, Gralla J, Cognard C, et al. Mechanical thrombectomy after IMS III, Synthesis, and MR-RESCUE. AJNR Am J Neuroradiol 2013;34:1671–73, 10.3174/ajnr.A3654
2. Soize S, Benaissa A, Wakhloo A, et al. Techniques for the endovascular treatment of acute ischemic stroke. Stroke (in press)
3. Friedrich B, Kertels O, Bach D, et al. Fate of the penumbra after mechanical thrombectomy. AJNR Am J Neuroradiol 2014;35:972–72, 10.3174/ajnr.A3769
4. Almekhlafi MA, Davalos A, Bonafe A, et al. Impact of age and baseline NIHSS scores on clinical outcomes in the Mechanical Thrombectomy Using Solitaire FR in Acute Ischemic Stroke Study. AJNR Am J Neuroradiol 2014;35:1337–40, 10.3174/ajnr.A3855.
5. Kuure W, Vorlaender K, Aguilar-Perez M, et al. Frequency and relevance of anterior cerebral artery embolism caused by mechanical thrombectomy of middle cerebral artery occlusion. AJNR Am J Neuroradiol 2013;34:1606–11, 10.3174/ajnr.A3462
6. Soize S, Kadziolka K, Estrade L, et al. Mechanical thrombectomy in acute stroke: prospective pilot trial of the Solitaire FR device while under conscious sedation. AJNR Am J Neuroradiol 2013;34:360–365, 10.3174/ajnr.A3200
7. Mölhenbruch M, Stampfl S, Behrens L, et al. Mechanical thrombectomy with stent retrievers in acute basilar artery occlusion. AJNR Am J Neuroradiol 2014;35:959–64, 10.3174/ajnr.A3796
8. Stampfl S, Ringleb PA, Möhlenbruch M, et al. Emergency cervical internal carotid artery stenting in combination with intracranial thrombectomy in acute stroke. AJNR Am J Neuroradiol 2014;35:741–46, 10.3174/ajnr.A3763

 

Image modified from: Friedrich B, Kertels O, Bach D, et al. Fate of the penumbra after mechanical thrombectomy.