Aims To evaluate the efficacy and safety of mechanical thrombectomy with the Solitaire FR device in revascularization of patients with acute basilar artery occlusion (ABAO) and to identify the predictive factors for clinical outcome.
Methods This prospective single-center study included 31 patients with acute ischemic stroke attributable to ABAO treated within the first 24 h after onset of symptoms with the Solitaire device. Nineteen patients simultaneously received intravenous thrombolysis. Recanalization rates after stent retrieval were determined and the clinical outcome and mortality rate were assessed 180 days after treatment.
Results The mean ±SD age of the patients was 61±17 years, the median prethrombectomy NIH Stroke Scale score was 38 (IQR 9–38) and the median Glasgow Coma Scale (GCS) score was 7 (IQR 4–14). Successful recanalization (TICI 3 or 2b) was achieved in 23 patients (74%). Five symptomatic intracranial hemorrhages were related to the procedure. Ten symptomatic distal migrations of thrombotic material occurred. A favorable outcome, defined as a modified Rankin Score (mRS) of 0–2, was observed in 35% of patients (11/31). Overall mortality rate was 32% (10/31). In the univariate analysis, elevated baseline glucose (p=0.008) was significantly associated with a poor outcome (mRS >2), whereas a tendency towards significance was observed with age (p=0.06), GCS on admission (p=0.07) and symptom-related lesions on T2 sequences (p=0.10). Patients with successful recanalization tended to have a better outcome (p=0.20).
Conclusion Mechanical thrombectomy with the Solitaire FR device can rapidly and effectively contribute to a high rate of recanalization and improve functional outcome in patients with ABAO and has an acceptable complication rate.
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The prognosis of acute basilar artery occlusion (ABAO) is generally accepted to be poor, with a mortality rate up to 90% and a severe residual deficit in more than 65% of survivors.1 Intravenous recombinant tissue plasminogen activator (rtPA) is the only approved treatment for acute stroke,2 but its efficacy is limited in large intracranial vessel occlusion.3 Early recanalization remains the main prognostic factor for an improved outcome,4–6 but the optimal strategy and most effective time window for treatment have not yet been established.7 ,8 More than half of patients with ABAO treated with intravenous or intra-arterial thrombolysis recanalize, but only 22–24% of these regain functional independence.4
Endovascular mechanical thrombectomy improves the recanalization rate and thus the patient outcome.6 ,9 ,10 One of the most promising devices seems to be the Solitaire FR, a self-expanding and fully retrievable nitinol stent which has a recanalization rate of up to 90% in acute intracerebral artery occlusions.9–11 However, limited studies to date have focused on the safety and effectiveness of mechanical thrombectomy in the posterior circulation.12–15
Our study aimed to analyze the efficacy and safety of mechanical thrombectomy using the Solitaire FR device in patients with ABAO within 24 h of symptom onset to identify the prognostic factors related to clinical outcome.
Selection of patients
This series prospectively analyzed all patients referred to our hospital with a clinical syndrome of ABAO subsequently confirmed by CT angiography (CTA) or MR angiography (MRA) who had been treated by stent-assisted mechanical recanalization between November 2009 and March 2011. The patients’ demographics, risk factors, stroke presentation and severity, time of symptom onset and imaging data were prospectively collected. National Institute of Health Stroke Scale (NIHSS) and Glasgow Coma Scale (GCS) were assessed by a stroke neurologist on admission. An NIHSS score of 38 was assigned to unconscious/comatose patients. Due to the frequent progressive or stepwise presentation, we also noted the time when the clinical symptoms were maximal so maximum NIHSS and GCS scores corresponding to prethrombectomy scores were also determined. The study was approved by the local ethics committee and consent for treatment was obtained from the patients or their family prior to the procedure.
Patients were eligible for mechanical thrombectomy if they (1) had a clinical diagnosis of acute stroke in the posterior circulation; (2) were admitted within 24 h after onset of symptoms; (3) had a significant clinical deficit following physician evaluation (no NIHSS limit); (4) underwent an MRI including diffusion-weighted imaging (DWI) before treatment; (5) presented with acute basilar ischemia on MRI that matched the clinical symptoms; and (6) had an ABAO confirmed on catheter angiography.
Patients were excluded if they (1) were pregnant; (2) were aged <18 years; (3) had cerebral imaging that revealed an intracranial hemorrhage, tumor or a subacute infarct; or (4) had a life expectancy of <3 months.
Multimodal MR using a 1.5 T magnet (Intera, Release10, Philips Medical System, Best, The Netherlands; 33 mT/m hypergradients) included a T2 gradient echo, DWI sequences (b0, b500, b1000), apparent diffusion coefficient maps, fluid attenuated inversion recovery (FLAIR), T2 and a circle of Willis time-of-flight sequence.
Collateral flow of the distal basilar artery (BA) was evaluated by CTA or MRA. According to Archer and Horenstein,16 it was graded as ‘present’ if both posterior communicating arteries contributed to the upper BA retrograde filling or as ‘poor or absent’ if the BA was not detectable or was opacified from a single posterior communicating artery. The posterior circulation Alberta Stroke Program Early CT Score (pc-ASPECTS) was assessed on DWI according to the method described by Tei et al.17
Patients received either mechanical thrombectomy following intravenous thrombolysis (bridging therapy) or mechanical thrombectomy alone. With bridging therapy, intravenous rtPA (full dose 0.9 mg/kg with a loading dose of 10%) was administered as soon as possible and patients were transferred to the angiographic suite for thrombectomy. Contraindications to rtPA were: pregnancy, serum glucose >40 mg/dl, known hemorrhagic diathesis or coagulation factor deficiency, oral anticoagulation treatment with INR >1.5, use of heparin within 48 h and a prothrombin time >2 times normal, platelet count <100 000/ml, severe hypertension defined as systolic blood pressure >185 mm Hg or diastolic blood pressure >110 mm Hg despite treatment, and extensive cerebellar ischemia. Endovascular therapy alone was given to patients with a contraindication to intravenous thrombolysis.
Mechanical thrombectomy was performed under general anesthesia with the Solitaire FR device (ev3 Inc, Plymouth, Minnesota, USA), which is CE (Conformité Européenne) certified for thrombectomy. Using a transfemoral approach, a 6 Fr Envoy (Cordis, Miami Lake, Florida, USA) guide catheter was placed into the dominant or most navigable vertebral artery. A 0.21 inch internal diameter microcatheter (Prowler Select Plus; Cordis or Vasco 21; Balt) was navigated distal to the occlusion over a 0.014 inch steerable guidewire which was then exchanged with the thrombectomy device. Once unsheathed, the placement of the Solitaire was evaluated with an angiographic run and was left in place for 2–7 min to allow full expansion of the stent through the thrombus. The device and the delivery microcatheter were subsequently pulled back out together and recovered. Recanalization was assessed with a further angiographic run. The procedure was repeated until a grade 2 Thrombolysis In Cerebral Infarction (TICI) classification was obtained with a maximum of five passes. In cases of major residual stenosis caused by an atherosclerotic plaque, placement of a definitive intracranial stent (Wingspan; Boston Scientific) was applied.
A CT or MRI was routinely performed within 24 h in order to assess the extend of the infarction and/or hemorrhagic complications. If no hemorrhage was present, antiplatelet drugs were commenced.
Successful recanalization was defined as a TICI grade 2b or 3.
In-hospital neurological complications were recorded, including post-procedure hemorrhage and embolic events. Symptomatic intracranial hemorrhage (sICH) was defined as a documented hemorrhage associated with a decline of ≥4 points in the NIHSS score. When patients were analgosedated at the time of imaging, any substantial hemorrhage was assessed and included if agreed upon by two raters (PM, IM). Device-related complications, including vessel perforation, arterial dissection or distal embolization of a previous uninvolved territory, were also reported.
Because outcome tends to be better for patients with ABAO after a longer follow-up, we evaluated them at ≥180 days. Clinical outcome measures included NIHSS score, mRS score, Barthel index and mortality. Favorable outcome was defined as an mRS score ≤2.
Descriptive analysis included frequencies and percentages for categorical variables and mean and SD or median (IQR) (25–75%) for continuous variables. Patients with a favorable outcome were compared with those with a poor outcome using the Student t test or Wilcoxon rank test for continuous variables and the χ2 test or Fisher exact test for categorical variables. Univariate logistic regression was used to identify predictors of clinical evolution. Statistical analyses were performed using SAS V.9.1 (SAS Institute, Cary, North Carolina, USA).
Between November 2009 and March 2011, 31 consecutive patients (15 men) of mean±SD age 61±17 years with ABAO were treated by stent-assisted mechanical recanalization in our center. Their baseline clinical and radiological features are presented in table 1. The median NIHSS score on admission was 14 (IQR 7–38) and the median GCS was 11 (IQR 7–15). Prethrombectomy clinical status was more severe, with median scores of 38 (IQR 9–38) for NIHSS and 7 (IQR 4–14) for GCS. The median time interval between symptom onset and admission to our stroke center was 357 min (IQR 125–437); this time was unknown for six patients including two ‘wake-up’ strokes. All patients were reported to have been symptom-free within the previous 24 h by their family. The mean±SD DWI pc-ASPECT score was 6±2. Eighteen patients had symptom-related lesions on T2 sequence. The median time interval from symptom onset to MRI was 334 min (IQR 160–480).
All patients showed complete occlusion of the BA (TICI 0). The occlusion site was the proximal BA in 4 cases (13%), the mid BA in 8 cases (26%) and the distal BA in 19 patients (61%). Collateral flow was graded as ‘present’ in 19 patients (61%). Infarct etiology according to the TOAST classification was cardioembolic in 16 patients (52%), atherothrombotic in 5 (16%), vertebral dissection in 2 (6%) and undetermined in 8 (26%).
Nineteen patients (61%) received bridging therapy. Twelve patients had contraindications to intravenous thrombolysis including the use of oral anticoagulants, heparin, endocarditis and extensive cerebellar ischemia. The mean number of passes with the thrombectomy device was 2 (range 1–4) (table 2).
The thrombectomy procedure failed in four cases because of an inability to advance and deploy the stent in the BA (n=3) or to pull it back after deployment (n=1). Angioplasty and stenting of the mid BA were performed following thrombectomy failure in one patient which resulted in a favorable outcome. Successful recanalization (TICI ≥2b) was achieved in 23 patients (74%) and TICI 3 was achieved in 64.5%. The mean time from groin puncture to maximum final TICI was 61 min (range 15–243). The mean±SD time from symptom onset to recanalization was 512±258 min and 410±187 min from onset of maximal symptoms.
Ten embolic infarcts in a new territory (cerebellar (n=7), brainstem (n=1) and occipital lobe (n=2)) were observed on DWI in nine patients; however, they were related to severe neurological deterioration or death in only two patients (table 2).
Five patients experienced mild to moderate clinical sequelae (gait ataxia, abnormal visual field). One patient developed a post-procedural vertebral dissection with infarction of the posterior inferior cerebellar artery. No arterial perforation was encountered.
Five cases of sICH (16%) related to the acute therapy occurred within the first 31 h (cerebellar (n=3), brainstem (n=2) and temporal lobe (n=1)). Two of these patients had been previously treated with intravenous thrombolysis. One patient died from a large symptomatic posterior fossa hematoma.
No patient was lost to follow-up (median follow-up time 240 days (IQR 22–365)). The mortality rate was 32% (10/31). The mean neurological scores measured at the last visit were 6 (range 0–23) for NIHSS, 69 (range 0–100) for Barthel index and 2.6 (range 0–5) for mRS. A favorable outcome (mRS 0–2) was seen in 11 patients, which represented 35% of all patients and 52% of the survivors (including 10 of the 23 successfully recanalized patients and 1 non-recanalized patient).
Predictive factors for clinical outcome
In a univariate analysis, poor outcome (mRS >2) was associated with a raised glucose level (p=0.008; table 1). Procedural complications were not linked with clinical outcome (p=0.98). Age (p=0.06), GCS at presentation (p=0.07) and symptom-related lesions on T2 sequences (p=0.10) tended to be associated with clinical outcome, but did not reach significance. Patients with successful recanalization (43% vs 12%, p=0.20) showed a non-significant trend towards a better outcome.
The mean time between symptom onset and recanalization tended to be lower in patients with a poor outcome than in those with a favorable outcome (411±178 min vs 663±296 min, p=0.03; table 2). Moreover, compared with those with a favorable outcome, patients with a poor outcome more frequently had a severe clinical presentation with tetraplegia at admission (100% vs 17%, p=0.05), a severe presenting course with a maximal deficit from onset (67% vs 0%, p=0.08) and poor or absent collateral flow (100% vs 17%, p=0.05).
In this series we have demonstrated that mechanical thrombectomy with the Solitaire device can rapidly and effectively restore flow in ABAO within 24 h of severe stroke symptom onset and can improve patients’ outcome.
Our results compare favorably with the good outcome rate of 5–21% (mRS score 0–3), the mortality rate of 40–86% and the presence of severe residual deficit in ≥65% of survivors reported in other studies on the outcome of ABAO after conventional treatment.1 Our study shows better results than those previously published for intravenous or intra-arterial thrombolysis in terms of rate of successful revascularization (74% vs 53–65%), frequency of good outcome (35% vs 20–24%) and mortality rate (32% vs 50–56%).4 ,18 Our successful revascularization and favorable functional outcome rates are comparable to those reported for ABAO treated with multimodal reperfusion therapy or a MERCI device5 ,6 ,19–23 and our mortality rate was lower. The mean time for the Solitaire procedure was less than half of that with the MERCI device (61 min vs 139 min) and the mean number of pass attempts was lower (2 vs 3).
Only a few recent trials on mechanical thrombectomy have focused on ABAO. Roth et al13 analyzed 12 patients with ABAO who were treated using Penumbra (a device for aspiration thrombectomy) and intravenous thrombolysis. Andersson et al12 examined 28 cases of ABAO using different clot retrievers and supplemental therapies such as intra-arterial thrombolysis and balloon angioplasty. Mordasini et al14 used a multimodal treatment that included a Solitaire FR device and combined thrombectomy with thromboaspiration, intravenous or intra-arterial thrombolysis, mechanical and percutaneous angioplasty/stent placement in 14 patients. In the most recent study, Espinosa et al15 treated 18 patients with a vertebrobasilar occlusion with direct thrombectomy by a stent retriever (Solitaire or Trevo).
Our rate of successful recanalization (74%) is comparable to that obtained in other series (64–100%).12–15 The mRS score of 0–2 in our series was 35%, compared with 33% in the study by Roth et al,13 57% in Andersson et al,12 28.6% in Mordasini et al14 and 50% in Espinosa et al.15 Our patients had a mortality rate of 32% compared with 33% in the series of Roth et al,13 21% in Andersson et al,12 35.7% in Mordasini et al14 and 22.2% in Espinosa et al.15 All these results indicate the technical feasibility and application of mechanical thrombectomy using stent retrieval to treat ABAO.
With regard to hemorrhagic complications, the rate of sICH related to the procedure was acceptable at 16%. Bridging therapy was not associated with a greater risk of sICH. However, this rate was higher than that reported with intravenous or intra-arterial thrombolysis alone4 ,18 ,24 but was comparable to other interventional studies.6 ,19–23
In our series, 10 symptomatic distal embolic events occurred and seemed to be the most common procedural complication of this technique in the posterior circulation.14 This high rate of embolic events may be due to the anatomic specificity of the posterior circulation which is supplied by a single main artery. Moreover, in the posterior circulation, the use of proximal balloon occlusion for flow reversal during retrieval is not applicable so the risk of a distal thromboembolic event is potentially increased. To avoid these adverse events, Mordasini et al14 used the largest possible guide catheter to ensure safe catheterization of the vertebral artery. This achieved flow reduction and enabled effective aspiration during retrieval, and resulted in no thromboembolic events in their series.
Despite sICHs and adverse embolic strokes, the outcome and mortality rates in our cohort were clearly better than the natural history of ABAO.1 Previous authors have reported that many factors can predict a favorable functional outcome in this disease, even during the early period following stroke onset. Among these are age (<60 years),1 ,21 atrial fibrillation,21 presentation with fluctuating symptoms or maximum deficit from onset,1 GCS at presentation,20 ,21 ,24 NIHSS <14,23 presence of collateral flow,22 ,25 treatment time window,5 ,23 ,26 multimodal therapy6 ,21 ,22 and good recanalization.4 ,6 ,18 ,23 ,24 In our study, age, severe deficit at presentation, presenting course, collateral flow and revascularization tended to be associated with clinical outcome but failed to reach significance. Patients with a raised baseline glucose level (p=0.008) were at higher risk of having a poor outcome. This is known to increase the risk of poor functional recovery even in non-diabetic stroke survivors. The mean time between symptom onset and recanalization tended to be lower in our patients who had a poor outcome than in those with a favorable outcome (p=0.03). This shorter delay can be explained, at least in part, by the fact that patients who had a severe clinical presentation (tetraplegia or coma) were treated earlier. For these patients, the median time from onset of maximal symptoms to treatment was 220 min (IQR 120–365) compared with 458 min (IQR 187–575) for those with a mild to moderate deficit (p=0.047).
The effective therapeutic window has not yet been established for the posterior circulation. The current findings suggest that the application of rigid temporal exclusion criteria is not warranted.8 It seems important to consider factors such as delay to maximal symptoms and anatomical characteristics including collateral flow or the extent of a brain stem infarction as assessed by DWI. Tei et al17 found in 132 patients with a posterior circulation infarction that a pc-ASPECTS of >7 was an independent predictor for a favorable functional outcome. In our cohort this score did not correlate significantly with clinical outcome. Nevertheless, our population was quite different from that of Tei et al whose patients had less severe symptoms and did not exclusively include patients with ABAO. An easy-to-use pretreatment DWI brainstem score taken within a shorter time after the onset of stroke may be useful in this specific population, but this remains to be established.
This single-center study which exclusively included patients with ABAO was composed of a very homogeneous population and no patients were lost during follow-up. However, by focusing on such a specific population and because the number of patients was relatively small, there was limited statistical power despite the fact that this is one of the largest stent retriever series in patients with ABAO.
Our preliminary observations suggest that the Solitaire FR device combines the advantages of prompt flow restoration and mechanical thrombectomy with the potential for a good clinical outcome. The technical outcomes of patients with ABAO could be improved by avoiding embolic complications. A large prospective multicenter study comparing intravenous thrombolysis with bridging therapy with a Solitaire device is needed to confirm our results and to identify further clinical and radiological factors that contribute to a good outcome.
We thank Erika Nogue and Valérie Macioce for their assistance with the statistical analysis and with preparing the manuscript.
Contributors All authors contributed to the conception, design, analysis, interpretation of the data, drafting of the article and revising it critically for important intellectual content. All authors gave final approval of the version to be published.
Competing interests None.
Ethics approval Ethics approval was obtained from the research ethics committee of CHRU Montpellier.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement A more thorough description of the data than is presented above is available on request.
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