The efficacy and risk factors of mechanical thrombectomy for the treatment of vertebrobasilar artery occlusion: a single center study

Introduction

Acute stroke, including ischemic stroke and hemorrhagic stroke, is one of the most life-threatening diseases that leads to neurological disabilities (1). Previous studies have suggested that ischemic stroke is more common than hemorrhagic stroke (2). Ischemic stroke can be caused by the occlusion of different cerebral vessels, and vertebrobasilar artery occlusion (VBAO) accounts for approximately 20% of all acute ischemic strokes (3). Despite its relatively low incidence, acute VBAO is the most dangerous type of cerebral vessel occlusion and can be caused by severe local atherosclerotic stenosis or distant embolization (4), with the former being more common (5). Without any specific treatment, the mortality rate of patients with acute ischemic stroke caused by VBAO is approximately 80–90% (6). Therefore, effective treatments for VBAO have attracted much attention globally.

Unfortunately, antithrombotic agents yield poor rates of recanalization of cerebral vessels in ischemic stroke patients (7). Intravenous or intra-arterial thrombolysis is more commonly used for the treatment of ischemic stroke, however, the rates of recanalization are also not satisfactory, reaching only as high as 65% (8). In the recent decade, mechanical thrombectomy has emerged as a promising treatment for acute ischemic stroke. Nevertheless, the outcomes of mechanical thrombectomy may vary depending on the mechanism of cerebral vascular occlusion (9). The rate of reperfusion using mechanical thrombectomy may decrease slightly in patients with severe local atherosclerotic stenosis because the retrieval of the stent may result in damage to atherosclerotic plaques that then leads to the development of acute thrombosis (10). In addition, the resistance caused by atherosclerotic stenosis during the procedure of mechanical thrombectomy may tear some cerebral vessels and induce intracerebral hemorrhage (10). Despite these complications, mechanical thrombectomy has been reported to have a higher rate of recanalization and lower mortality in ischemic stroke patients compared to intravenous or intra-arterial thrombolysis (11-13). However, only a limited number of studies have investigated the efficacy of mechanical thrombectomy in acute ischemic stroke patients caused by VBAO, especially in the Chinese population.

This single-center report analyzed the efficacy of mechanical thrombectomy in VBAO patients. In addition, the risk factors of poor outcomes in these patients were identified. We present the following article in accordance with the STROBE reporting checklist (available at http://dx.doi.org/10.21037/apm-21-614).

Methods

Study design and patient selection

This retrospective study enrolled 65 patients with acute ischemic stroke caused by VBAO at the Department of Neurology in our hospital between March 1, 2016 and August 31, 2019. The following patients were included in this study: patients who were older than 18 years; patients diagnosed with acute ischemic stroke caused by VBAO due to severe local atherosclerotic stenosis; patients with a pc-ASPECTS (posterior circulation acute stroke prognosis early CT score) no less than 6 points; patients with a NIHSS score (National Institutes of Health stroke scale) no less than 6 points; and patients who had received mechanical thrombectomy treatment. Mechanical thrombectomy was performed dependent on the clinical judgement of experienced neurologists in our department. The following patients were excluded from this study: patient with intracerebral hemorrhage confirmed by computed tomography at diagnosis; patients with a history of intracerebral hemorrhage or cerebral tumor; patients with pc-ASPECTS score less than 6 points; patients with NIHSS score less than 6 points; and patients who had been diagnosed with renal dysfunction or failure. This study was reviewed and approved by the institutional review board of Taixing People’s Hospital and all procedures were in accordance with the Declaration of Helsinki (as revised in 2013). Written informed consent from patients was not required due the retrospective nature of the study.

Data collection

Patient demographic and clinical data were collected retrospectively. Demographic data collated included patient age, gender, body mass index, previous history of stroke, and other comorbidities (such as hypertension, diabetes, hyperlipidemia, and chronic heart disease). Clinical data collated included the site of occlusion, baseline pcASPECTS and NIHSS scores, the duration of the occlusion, the duration of the treatment procedure, the use of angioplasty (balloon dilation and stent placement), and the rate of residual stenosis. The time of wake-up stroke onset was defined as the last normal time of the patient on the previous day. The collection of data and the scores of pcASPECTS and NIHSS were performed by two independent investigators and any disagreements were resolved by a third investigator.

All mechanical thrombectomy interventions were performed by skilled neurologists. In patients where mechanical thrombectomy failed to achieve successful reperfusion, transluminal angioplasty was performed using balloon dilation and stent placement. Tirofiban was intravenously administered during the angioplasty procedure.

Outcomes

All enrolled patients in this study were retrospectively interviewed by telephone or internet for at least 3 months. The primary outcome in this study was the modified Rankin scale (mRS) score within 90 days. Patients with a mRS score between 0 and 3 points were defined as having satisfactory outcomes while those with more than 3 points were defined as having unsatisfactory outcomes. Secondary outcomes included in-hospital mortality, the rate of recanalization, and the rate of intracerebral hemorrhage due to mechanical thrombectomy.

Statistical analysis

Statistical analyses were performed using SPSS 20.0 (IBM Corp., Armonk, New York, USA). Categorical variables were presented with frequencies and percentages, and continuous variables were presented with median and interquartile range (IQR). Comparisons between patients having satisfactory and unsatisfactory outcomes were performed using chi-square test for categorical variables and Manne-Whitney U test for continuous variables. The risk factors of satisfactory outcomes were assessed using logistic regression analysis. All collected variables were initially analyzed by univariate logistic regression to determine potential risk factors of satisfactory outcomes and these potential risk factors were then further analyzed using multivariate logistic regression to determine eventual risk factors. A P value <0.05 was considered statistically significant.

Results

According to the inclusion and exclusion criteria, 65 patients were finally enrolled in this study. All enrolled patients were diagnosed with acute ischemic stroke caused by VBAO due to severe local atherosclerotic stenosis. The demographic and clinical data are shown in Table 1. The median age of the patients was 69.0 (63.0–78.0) years and 48 patients (73.8%) were male. The majority of patients had a normal body mass index. A total of 9 patients had a previous history of stroke. There were 45, 12, 16, and 4 patients with hypertension, diabetes, hyperlipidemia, and chronic heart disease, respectively. The most common site of occlusion was the distal basilar artery, detected in 40.0% of patients, followed by the middle basilar artery, the proximal basilar artery, and the vertebral artery. Median baseline scores of pcASPECTS and NIHSS were 9.0 (8.0–10.0) and 21.0 (11.0–24.5), respectively. The median duration of occlusion was 9.5 (7.0–13.5) hours and the median duration of the treatment procedure was 94.0 (71.5–136.0) minutes. A total of 19 patients received angioplasty as mechanical thrombectomy failed to achieve successful reperfusion in these patients. There were 28 patients with residual stenosis of more than 50% after treatment with mechanical thrombectomy.

Table 1 Demographic and clinical data of all the enrolled patients in this study
Full table

The mRS scores for the patients are listed in Table 2. Approximately 50% of patients had a mRS score of 0 or 1 point within 90 days after treatment with mechanical thrombectomy. A total of 14 patients died within 90 days and had a mRS score of 6 points. Secondary outcomes including in-hospital mortality, recanalization, and intracerebral hemorrhage are shown in Table 2. After treatment with mechanical thrombectomy, 11 patients died in hospital. A total of 7 patients required recanalization and 9 patients suffered from intracerebral hemorrhage.

Table 2 Primary and secondary outcomes of the study
Full table

Patients were divided into two groups according to the mRS score, patients with satisfactory outcomes and patients with unsatisfactory outcomes. Most of the demographic and clinical data between the two groups were not significantly different (Table 3). However, patients in the satisfactory outcome group were younger compared to patients in the unsatisfactory outcome group [65.5 (60.0–73.0) vs. 76.0 (65.5–82.0), P=0.010]. Fewer patients in the satisfactory outcome group had hypertension compared to those in the unsatisfactory outcome group [29 (66.0%) vs. 16 (88.9%), P=0.039]. Patients in the satisfactory outcome group had significantly higher baseline pcASPECTS scores and lower baseline NIHSS scores compared to the unsatisfactory outcome group [9.0 (9.0–10.0) vs. 9.0 (8.0–9.0), P=0.013; and 18.0 (14.0–21.5) versus 24.5 (23.0–26.0), P<0.001, respectively]. In addition, more patients in the unsatisfactory outcome group had residual stenosis after mechanical thrombectomy compared to the satisfactory outcome group [12 (66.7%) vs. 16 (38.3%), P=0.017].

Table 3 Comparisons of the demographic and clinical data between patients with satisfactory outcomes and patients with unsatisfactory outcomes
Full table

Multivariate logistic regression was used to determine the risk factors of unsatisfactory outcomes (Table 4). Older age, lower baseline pcASPECTS score, higher baseline NIHSS score, and residual stenosis were related to a higher incidence of unsatisfactory outcomes. Hypertension was associated with the incidence of unsatisfactory outcomes in the univariate analysis, however no significant impact was observed during the multivariate analysis. Moreover, risk factors of in-hospital mortality were assessed by multivariate logistic regression (Table 5). Similar to risk factors of unsatisfactory outcomes, older age, lower baseline pcASPECTS, higher baseline NIHSS, and residual stenosis were related to in-hospital mortality. Primary and secondary outcomes of the patients are shown in Table 6 according to age, baseline pcASPECTS, baseline NIHSS, and residual stenosis.

Table 4 Multivariate logistic regression analysis for the risk factors of satisfactory outcomes
Full table

Table 5 Multivariate logistic regression analysis for the risk factors of in-hospital mortality
Full table

Table 6 Primary and secondary outcomes of enrolled patients according to age, baseline pcASPECTS, baseline NIHSS, and residual stenosis
Full table

Discussion

Previous studies have investigated the efficacy of mechanical thrombectomy in patients with acute ischemic stroke caused by severe local atherosclerotic stenosis and distant embolization (3-5,8,10,14,15). However, it is possible that different mechanisms of acute ischemic stroke may results in different patient prognosis and hence this study only enrolled patients with acute ischemic stroke caused by VBAO due to severe local atherosclerotic stenosis. The results indicated that approximately 70% of patients in this study achieved a relatively satisfactory outcome. The risk factors of unsatisfactory outcomes included older age, lower baseline pcASPECTS, higher baseline NIHSS, and residual stenosis after mechanical thrombectomy. These results provided some evidence for the application of mechanical thrombectomy in the treatment of acute ischemic stroke caused by VBAO.

The application of mechanical thrombectomy in the treatment of acute ischemic stroke has been studied for many years. The incidence of satisfactory outcomes in this study was approximately 70%, which is similar to previous studies of acute ischemic stroke caused by occlusion of other arteries (16,17). Furthermore, in agreement with previous studies (18,19), the mortality rate in this study was 17% within 90 days after the procedure. These results indicated that the efficacy of mechanical thrombectomy in these patients is relatively stable despite the different sites of occlusion. Symptomatic intracerebral hemorrhage is the most significant postoperative complication of mechanical thrombectomy. The meta-analysis by Dmytriw et al. reported that the pooled rate of symptomatic intracranial hemorrhage was 5.9% in tandem acute ischemic stroke patients receiving mechanical thrombectomy (19). Wang et al. detected a rate of 8.7% in acute mild ischemic stroke patients with large vessel occlusion (20). Compared with these studies, the rate of intracranial hemorrhage in our study was relatively high, up to 13.8%. This may be related to the nursing care of postoperative patients in our hospital and could be improved in the future.

Numerous studies have confirmed that age is significantly associated with the prognosis of acute stroke patients (12,21,22). This current study further confirmed the important role of age in the unsatisfactory outcomes and in-hospital mortality. In practice, the age of patients in our study was relatively young compared with some other studies (23,24). Sojka et al. reported that the mortality after 90 days was as high as 47.4% in acute ischemic stroke patients aged more than 90 years old (25). The baseline pcASPECTS and NIHSS scores represent the severity of stroke in patients, which in turn determines the prognosis of patients to a large extent, and this is confirmed by this study and previous investigations (12,16). Residual stenosis has seldomly been identified as a risk factor of unsatisfactory outcomes in stroke patients. However, this study found that residual stenosis may be detrimental to the prognosis of patients irrespective of whether stenosis was greater or less than 70%. Indeed, residual stenosis may be related to a higher occurrence of re-occlusion. Our study also identified some other variables as risk factors of unsatisfactory outcomes in acute ischemic stroke patients caused by VBAO, however, these results were not statistically significant. Indeed, other reports have suggested that onset-to-recanalization time and being female may be risk factors of unsatisfactory outcomes in stroke patients (5,24). Further studies are needed to determine all the risk factors in the prognosis of acute ischemic stroke patients.

There are some limitations to this study. First, the retrospective design and the small number of patients were the most significant limitations, and may result in errors in the data collected and may not reflect the situation in a broader population. Second, this investigation was a single center study, and the results may only apply to this center. Third, some patients failed to achieve successful reperfusion by mechanical thrombectomy, and transluminal angioplasty was performed using balloon dilation and stent placement which may have affected the results in this study.

Conclusions

This study investigated the efficacy of mechanical thrombectomy in the treatment of patients with acute ischemic stroke caused by VBAO and identified potential risk factors of unsatisfactory outcomes within 90 days. These results further confirmed the important role of mechanical thrombectomy and may provide some basis for improving the prognosis of these patients.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at http://dx.doi.org/10.21037/apm-21-614

Data Sharing Statement: Available at http://dx.doi.org/10.21037/apm-21-614

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/apm-21-614). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was reviewed and approved by the institutional review board of Taixing People’s Hospital and all procedures were in accordance with the Declaration of Helsinki (as revised in 2013). Written informed consent from patients was not required due the retrospective nature of the study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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(English Language Editor: J. Teoh)