Restoration of cerebral blood flow within a short time is the key goal of acute ischemic stroke (AIS) therapy. Although Intravenous or intra-arterial thrombolytic has been shown to be effective for treatment of AIS, due to narrow therapeutic time window, contraindications, risk of symptomatic intracerebral hemorrhage (ICH) and low recanalization rates, endovascular treatment including mechanical thrombectomy (MT) has been widely used as an effective treatment tool for recanalization as it can rapidly improve flow of occluded blood vessels, and promotes recovery of neurological function^2,8,24).

Several instruments have been used and developed for MT. In particular, MT using a self-expanding retrieval stent resulted in a higher recanalization rate^7,23,25,27). Nonetheless, MT using a retrieval stent fails to achieve recanalization in some cases. Recently, permanent stent deployment (SD) as a rescue therapy showed good recanalization rate and favorable outcomes in AIS^{1,3,4,13,14,16,18-20,26,28,29)}. Therefore, in the present study we examined the efficacy of permanent SD to prevent reocclusion after MT with a retrieval stent, and to maintain recanalization state.

From September 2013 to August 2016, 35 consecutive patients who underwent MT using a 4 or 6 mm Solitaire (Medtronic, Irvine, CA, USA) retrieval stent for AIS were included. The enrolled patients were divided into the simple thrombectomy (ST) group or the permanent SD group. We compared demographic data (sex and age), clinical data (hypertension, diabetes mellitus, atrial fibrillation, previous cerebrovascular and cardiovascular disease, initial National Institute of Health Stroke Scale (NIHSS) score, location of thrombus, and the use of intravenous recombinant tissue plasminogen activator and post-thrombectomy results (recanalization, ICH, post-thrombectomy NIHSS score, and modified Rankin Scale [mRS] score at 3 months) between the 2 groups. The degree of vessel recanalization was graded using the thrombolysis in cerebral infarction (TICI) grading system. Successful recanalization was defined as TICI grade 2 or 3. Favorable outcomes were defined as: (1) decrement of NIHSS score ≥4 points; and (2) mRS score 0-3 at 3 months.

All MT interventions were performed under local anesthesia. Usually, a 6F Envoy (Codman, Raynham, MA, USA) guiding catheter was placed in the proximal internal carotid artery. Once the microguidewire crossed the occlusion site, Rebar (Medtronic) microcatheter was advanced over the microwire and navigated distal to the clot. The Solitaire stent was then deployed for 5 to 10 min. Under continuous aspiration through the guiding catheter, the stent was retrieved together with the microcatheter. This procedure was repeated 3 to 5 times to achieve recanalization. When complete reocclusion, distal flow delay, and focal stenotic lesion were found after stent removal, we performed permanent SD. A glycoprotein IIb/IIIa inhibitor (Aggrastat; Merck & Co, Inc., Kenilworth, NJ, USA) was administered intravenously as a loading dose (0.4 mcg/kg) for 30 min, followed by continuous infusion for 24 hr (0.1 mcg/kg/min). Thereafter, dual anti-platelets (acetyl- salicylic acid 100 mg and clopidogrel 75 mg) were given orally.

All continuous variables are presented as the mean±standard deviation. We used the Mann-Whitney U test for continuous variables and the Fisher’s exact test for categorical variables. A 2-tailed value of p≤0.05 was considered statistically significant. All statistical analyses were performed using statistical software (SPSS 20.0 for Windows; SPSS Inc., Chicago, IL, USA).

The demographic and clinical characteristics of the patients are summarized in Table 1. Successful recanalization was achieved in 28 patients (80%) after MT. Ten of the 35 patients were treated with permanent SD. The mean initial NIHSS score was 16.6±4.7 in the ST group and 13.0±4.9 in the SD group. The overall successful recanalization rate (TICI grade 2 or 3) was 84% in the ST group and 70% in the SD group (p=0.381). Procedure-related complications (symptomatic ICH in 1 case, contrast media leakage in 2 cases) occurred in 3 ST patients during MT. The changes in NIHSS score after MT in each patient are shown in Fig. 1. There were no significant differences in favorable outcomes (decrement of NIHSS score ≥4 after MT and mRS score 0-3 at 3 months) between the ST and SD groups (p=0.377 and 0.258, respectively) (Table 2). In subgroup analysis, the reasons for permanent SD in 10 patients were complete reocclusion (n=4), focal stenosis (n=4), proximal vessel tortuosity with imminent therapeutic window (n=1), and distal flow delay with focal stenosis (n=1) (Table 3).

The use of MT with a retrieval stent was recently reported to have excellent efficacy^{2,5-7,12,15,21-23,25,27)}. Furthermore, the safety problems related to the procedure were lower or similar to those of other methods^{2,5,7,15,22,23,27)}.

However, MT using a retrieval stent may fail in some patients, resulting in a significant increase in mortality¹¹⁾. Because recanalization of the occluded vessel in AIS treatment is closely related to good prognosis, recanalization of the occluded vessels is the most important factors for effective treatment^8,24).

Repeated MT using a retrieval stent can result in vessel injury, such as perforation or dissection, leading to a symptomatic ICH. Delayed stenosis or reocclusion may also occur due to vascular intimal injury^9,10). Furthermore, the migration of thromboembolic fragments may be problematic during retrieval using a stent, while some emboli may not be affected by the thrombolytic agent due to mature and fibrinous consistency, and MT may be difficult if the emboli are firmly attached to the vessel intima. In addition, in cases where a stenotic lesion contains an atherosclerotic plaque, recanalization using simple MT is often difficult.

Thus, permanent stent placement is considered as a rescue therapy when recanalization fails or MT is difficult. Indeed, recent studies have shown that permanent stent placement is effective method in treating AIS^{1,3,4,13,14,16,18-20,26,28,29)}.

Permanent stent placement as a rescue therapy has several potential advantages. First, there is no need for multiple repetitive procedures, which allows rapid recanalization and is less likely to damage blood vessels. Second, recanalization can be achieved by compressing and fixing the thrombus to the vessel wall, even if a mature and fibrinous clot exists or a thrombus is strongly attached to the vessel wall. Third, even if there is a stenotic lesion containing an atherosclerotic plaque, recanalization with permanent stent placement is advantageous as it may slightly widen the vessel. Nevertheless, although there was no evidence of in-stent stenosis in patients at 6-month follow-up after permanent stent placement, there are some concerns such as late reocclusion and in-stent stenosis associated with permanent stent placement^9,17). Several studies have also reported increased tendency for bleeding because of dual antiplatelet medication after permanent stent placement^16,19,20).

In this study, symptomatic ICH did not occur in SD group, but there was no statistical significance. In our study, 35 patients with AIS were enrolled and 10 patients underwent permanent stent placement. It is reasonable to compare the usefulness of permanent SD as a rescue therapy in failed MT group. However, due to small sample size and the changes of MT protocol during study period, we did not directly compare ST group with SD group following failed MT. In subgroup analysis, permanent stent placement was effective, when focal stenosis or complete reocclusion was evident but the thrombus did not come out. In addition, higher rate of permanent SD compared with other studies may be attributed to the small sample size. Nevertheless, we found no differences in favorable outcome between the 2 groups, suggesting that the efficacy of permanent stent placement as a rescue therapy after failure of MT may equivalent to patients receiving simple MT.

Our study has several limitations. First, this study was limited by its retrospective nature and small sample size. Second, we did not perform permanent SD in the earlier period of study. During study period, MT protocol was changed to perform permanent SD based on consensus among attending physicians (neurologists and interventionists). Therefore, direct comparison of the degree of recanalization rate and clinical outcomes in this heterogenous group may cofound our results. In addition, late reocclusion and in-stent thrombosis caused by permanent stent placement were not evaluated as the follow-up period was short.

Permanent SD showed high potential for flow restoration in the reoccluded vessel, especially when simple MT had failed. A long-term follow-up is required to verify the incidence of late complications. Previous presentation: Oral presentation at Annual Meeting of Society of Korean Endovascular Neurosurgeons, 2016