There was no significant difference in baseline data between ET + SMT group and SMT group, which made it possible to compare the treatment effects between the two groups. In the ET + SMT group, mRS 0–2 and mRS score in multivariate Logistic regression analysis and linear regression analysis were better than those in the SMT group. ET did significantly improve the living quality of patients with PIS of posterior circulation, and have improved neurologic impairment and survival of patients with a higher deteriorative NIHSS score (NIHSS ≥ 15). Traditional antiplatelet, anticoagulant, reduce blood lipids, improve circulation, difficult to dissolve the mass of stearic plaque or large thrombi, ET can increase the rate of vascular recanalization in patients with low-perfusion watershed infarction caused by large artery stenosis/occlusion, and did not increase the risk of symptomatic intracranial hemorrhage. The risk of SAP and heart failure was similar in both groups. The brain tissue of ischemic penumbra was not completely necrotic, recanalization and blood flow reperfusion were achieved in the early stage of ET. The symptoms of dizziness, paralysis and consciousness disturbance were improved, and the patient could take the initiative to recover, reduce time of ventilator use, bed time and complications, and improve the survival rate. The follow-up results of the two groups showed that patients with low NIHSS score at the time of progression tended to have lower or no significant increase NIHSS score and mRS score 90 days later, with a better prognosis. Conservative treatment could be selected for these patients, but longer follow-up time is needed to verify the long-term prognosis. In this study, 9 patients died, which may be related to the change of the patient's consciousness level affecting swallowing function, vomiting and aspiration, and long-term bed rest, combined with SAP and heart failure during hospitalization. The mortality of patients in the ET + SMT group was lower than that in SMT group, which was statistically different from the previous results of BEST5. This may be related to the small sample size, which needs to be verified by further large-scale studies. In addition, the cases collected during the same period were more willing to choose interventional, which may also result in fewer cases in SMT group than in ET + SMT group. Previous studies on intravascular therapy for ischemic stroke did not include patients with posterior circulation vascular diseases in order to promote intravascular therapy in pursuit of better therapeutic effect. Based on the study of anterior circulation endovascular therapy, the BEST5 study provided the highest level of evidence for thrombectomy for vertebro-basilar artery occlusion, suggesting that ET for stroke patients with acute vertebro-basilar artery occlusion may be safe and feasible. The guidelines suggest that mechanical thrombectomy should be considered after imaging evaluation in patients with acute basilar artery occlusion within 6–24 hours of onset. For patients with large vessel occlusion more than 24 hours after onset, the benefit of mechanical thrombectomy is not clear11. In our study, as a result of some patients have mild onset symptoms, they didn't take it seriously, when they came to the hospital for aggravation, they had missed the best time for treatment, or a lesser degree of disability when aggravated, the patient and his family members did not agree to ET because of the risk of operation, when the pros and cons were weighed again or the disease got worse again, they decided to have ET treatment, the onset-to-ET time tend to be more than 24 hours, deterioration-to-ET time was also more than 24 hours, but we did it to save the ischemic penumbra rather than the core infarct. Animal experiments have shown that the volume of ischemic penumbra changes dynamically and can be identified by MRI12. Due to the existence of collateral circulation, penumbra can persist for a period of time, therefore, delayed reperfusion of ischemic stroke can also improve neurological dysfunction by restoring blood flow to penumbra13, and clinical cases reported that patients can still benefit from ET 3 months or more after onset14. Infarct core was populated by microglial cells, endothelial cells, neural progenitor cells, and neural stem cells after recanalization, additionally, the penumbral region was abundant with neurons and astrocytes, cells in the area around the infarction might help remove debris and release pro-angiogenic, anti-inflammatory, and neuroprotective factors, neural stem cells can differentiate into new blood vessels, astrocytes and neurons, all of these will contribute to the recovery of brain tissue15. Another mechanism for protection of ischemic area is that permanent occlusion can stimulate the liver produce hepatocyte growth factor (HGF), serum release of fibroblast growth factor 21 (FGF21), FGF21 activated the FGFR1/PI3K/Caspase-3 signaling pathway, which attenuated neuronal apoptosis. A similar mechanism was observed for HGF. Bone marrow stem cells can be converted into new neurons, spleen macrophages can remove cellular debris, when recanalization, these beneficial cells and secreted factors reach the infarct area through blood flow and promote the repair of brain tissue16–17. Our research shows that beyond the guidelines for 24 hours, ET can still improve the symptoms of patients with nerve function defect, has potential therapeutic value. MRI/CT perfusion was used in our study, Flair-DWI mismatches18 and ASL-DWI mismatches19 can reveal penumbra, which is conducive to ET. If ET is selected based on the presence of ischemic penumbra, it may be safe and feasible for PIS beyond the traditional 6 hours6. Since NIHSS scores are not sensitive to the posterior circulation, more studies are needed to better define PIS of posterior circulation. At this point, we can use MRI/CT perfusion mismatches to screen patients eligible for ET20. With the improvement of the ability of more accurate and personalized measurement tools to identify the penumbra, it is valuable for suitable patients to ET even days or months after aggravation. Patients with delayed recanalization should be carefully selected according to their condition and be performed by an experienced clinician. For chronic stenosis or occlusion caused by atherosclerosis, ischemic area has certain compensatory ability, symptoms can be mild, there was no significant difference between angioplasty treatment and conservative treatment in these patients21–22, the operation may be delayed after acute phase if the condition was stable and ET was required, but for associated with severe neurologic deficits, especially acute stroke caused by large artery embolism, lack of collateral compensatory, patients with onset nasty, serious, soon consciousness obstacle, reperfusion of the occluded artery should proceed as soon as possible. As a small sample study on the safety of ET for PIS of posterior circulation, linear regression analysis showed that among patients with severe neurological deficits at the time of deterioration (NIHSS ≥ 15), 90-day mRS scores in ET + SMT were 3.33 points lower than those in SMT, and delayed recanalization still benefited, which was consistent with the study on anterior circulation6,23, but the indications for ET should be strictly controlled, age, underlying diseases, baseline NIHSS score, time window of ET, vascular lesions, related risk, willingness of patients and their families and cost of operation should be considered.
Some limitations of the present study must be addressed when interpreting the results. First of all, our study was a retrospective study, reviewing a small sample size database, which limited the ability to rectify differences between the two groups, in this study, only age, sex were adjusted. However, all data were measured by clinicians who were trained to record the data according to hospital standards. Secondly, we assumed that aspirin and clopidogrel were taken regularly for 90 days in two groups, although most of the follow-up of patients with long-term use of antiplatelet drugs or anticoagulant drugs, we don't know whether patients to stop taking one of antiplatelet drugs or replace other antiplatelet drugs, it is impossible to judge whether patients' medication compliance interferes with the study results.