based on the results of 5 randomized clinical trials ( rcts ) , mechanical thrombectomy using the stent - retriever has been approved as standard treatment for acute anterior circulation stroke due to occlusions of the internal carotid artery ( ica ) or the m1 segment of the middle cerebral artery ( mca ) .
recent studies regarding meta - analysis of the 5 rcts showed that stent - retriever thrombectomy is associated with considerable improvement of functional independence compared with standard medical care .
after its acceptance as an effective treatment option , the next steps will be to further establish patient selection criteria and to generalize stent - retriever thrombectomy to a broader class of stroke patients with acute large vessel occlusions . to further broaden treatment indications for stent - retriever thrombectomy ,
although there exist a few studies that have investigated prognostic factors that predict outcomes after stent retriever thrombectomy in patients with acute anterior circulation stroke , these studies are limited by small sample size and the inclusion of patients with posterior circulation stroke [ 4 - 8 ] . thus , this study aimed to investigate clinical , imaging , and procedural factors predictive of good outcome and mortality after stent - retriever thrombectomy in a large cohort of patients with acute anterior circulation stroke
from december 2010 to november 2015 , a total of 356 consecutive patients presenting with acute ischemic stroke due to ica or mca occlusions were treated with stent - retriever thrombectomy at a comprehensive regional stroke center .
mri examinations were performed using a 1.5-t unit ( signa hdxt ; ge medical systems , milwaukee , usa ) .
mri sequences included dwi , gradient echo imaging , flair sequence , 3-dimensional tof mra , and perfusion imaging .
dwi sequences were obtained in the axial plane using a single - shot , spin - echo echo - planar technique with following parameters : tr of 9,000 ms , te of 80 ms , slice thickness of 4 mm , interslice gap of 0 mm , fov of 260260 mm , and b values of 0 and 1,000 sec / mm . of 356 patients , those who had a prestroke modified rankin scale ( mrs ) score 3 ( n=11 ) or concomitant posterior circulation infarctions ( n=8 ) or who were lost to follow - up ( n=2 )
we prospectively collected the following clinical , imaging , and procedural data of these 335 patients : demographic features , cerebrovascular risk factors , nihss scores on admission , use of iv thrombolysis , time to endovascular treatment , procedure time , time to reperfusion , revascularization status , underlying intracranial atherosclerotic stenosis , tandem occlusion at the proximal cervical portion of the ica , intracranial hemorrhage on post - therapeutic ct scans or gradient echo mri , alberta stroke prognosis early ct score ( aspects ) applied to dwi ( dwi - aspects ) , and clinical outcomes at 3 months .
the institutional ethics committee approved this retrospective analysis and waived informed consent based on the study design . upon admission ,
the inclusion criteria for stent - retriever embolectomy were as follows : ( 1 ) the procedure started within 6 hours of symptom onset , ( 2 ) baseline nihss score 4 , ( 3 ) occlusion of ica or mca , ( 4 ) no intracranial hemorrhage detected on the cranial ct or mri , and ( 5 ) infarct volume less than one - third of the mca territory on dwi ( determined as dwi - aspects > 3 ) or non - enhanced ct ( determined by alteplase thrombolysis for acute noninterventional therapy in ischemic stroke [ atlantis ] criteria ) .
for each patient , written informed consent for endovascular therapy was obtained from a family member .
endovascular therapy was performed under conscious sedation . in cases of agitation , an intravenous bolus of midazolam
stent - based thrombectomy with a solitaire stent ( covidien , irvine , usa ) or trevo stent ( stryker , kalamazoo , usa ) was performed as the first - line endovascular treatment .
when stent - based thrombectomy was unsuccessful , additional mechanical approaches were performed , including manual aspiration thrombectomy with a penumbra reperfusion catheter ( penumbra , alameda , usa ) or navien catheter ( covidien , irvine , usa ) .
intracranial angioplasty with or without stenting was performed when severe ( > 70% ) underlying intracranial atherosclerotic stenosis was observed .
when the patient had a tandem occlusion at the proximal cervical portion of the ica , carotid angioplasty and stenting were performed prior to stent - retriever thrombectomy .
revascularization status was assessed on the final angiogram and was classified according to the modified tici scale , and successful revascularization was defined as a modified tici grade of 2b or 3 .
all patients underwent non - enhanced ct scans immediately and 24 hours after endovascular treatment and gradient echo mri 24 - 36 hours after treatment .
intracerebral hemorrhages were assessed on posttreatment ct and gradient echo mr images and classified as hemorrhagic infarction ( hi ) or parenchymal hemorrhage ( ph ) based on the european cooperative acute stroke study ( ecass ) criteria .
symptomatic intracranial hemorrhage was defined as any intracranial hemorrhage that caused neurological deterioration ( increase of 4 points in nihss score or deterioration of 1 point in the level of consciousness on nihss ) .
clinical outcome was assessed by a stroke neurologist using the modified rankin scale ( mrs ) during an outpatient visit 3 months after treatment .
if patients were unable to attend the outpatient clinic , outcomes were obtained via a telephone interview .
first , the relationship between each clinical and procedural characteristic and 3-month outcome was determined . the 2 test or fisher exact test was used for comparing categorical variables , and the mann - whitney u test was used for comparing continuous variables .
second , independent associations between good outcome ( mrs 0 - 2 ) and clinical and procedural factors were determined with a multivariate logistic regression analysis .
the variables tested in the multivariate logistic regression models were those with p<0.05 in the univariate analysis .
third , a multivariate logistic regression analysis was performed to identify independent predictors for mortality at 3 months .
variables with a p value of < 0.05 in the univariate analysis on mortality were included in a multivariate logistic regression analysis .
all statistical analyses were performed with spss software ( version 21.0 ; ibm spss , chicago , il , usa ) . a p value
from december 2010 to november 2015 , a total of 356 consecutive patients presenting with acute ischemic stroke due to ica or mca occlusions were treated with stent - retriever thrombectomy at a comprehensive regional stroke center .
mri examinations were performed using a 1.5-t unit ( signa hdxt ; ge medical systems , milwaukee , usa ) .
mri sequences included dwi , gradient echo imaging , flair sequence , 3-dimensional tof mra , and perfusion imaging .
dwi sequences were obtained in the axial plane using a single - shot , spin - echo echo - planar technique with following parameters : tr of 9,000 ms , te of 80 ms , slice thickness of 4 mm , interslice gap of 0 mm , fov of 260260 mm , and b values of 0 and 1,000 sec / mm . of 356 patients , those who had a prestroke modified rankin scale ( mrs ) score 3 ( n=11 ) or concomitant posterior circulation infarctions ( n=8 ) or who were lost to follow - up ( n=2 )
we prospectively collected the following clinical , imaging , and procedural data of these 335 patients : demographic features , cerebrovascular risk factors , nihss scores on admission , use of iv thrombolysis , time to endovascular treatment , procedure time , time to reperfusion , revascularization status , underlying intracranial atherosclerotic stenosis , tandem occlusion at the proximal cervical portion of the ica , intracranial hemorrhage on post - therapeutic ct scans or gradient echo mri , alberta stroke prognosis early ct score ( aspects ) applied to dwi ( dwi - aspects ) , and clinical outcomes at 3 months .
the institutional ethics committee approved this retrospective analysis and waived informed consent based on the study design .
the inclusion criteria for stent - retriever embolectomy were as follows : ( 1 ) the procedure started within 6 hours of symptom onset , ( 2 ) baseline nihss score 4 , ( 3 ) occlusion of ica or mca , ( 4 ) no intracranial hemorrhage detected on the cranial ct or mri , and ( 5 ) infarct volume less than one - third of the mca territory on dwi ( determined as dwi - aspects > 3 ) or non - enhanced ct ( determined by alteplase thrombolysis for acute noninterventional therapy in ischemic stroke [ atlantis ] criteria ) .
for each patient , written informed consent for endovascular therapy was obtained from a family member .
endovascular therapy was performed under conscious sedation . in cases of agitation , an intravenous bolus of midazolam
stent - based thrombectomy with a solitaire stent ( covidien , irvine , usa ) or trevo stent ( stryker , kalamazoo , usa ) was performed as the first - line endovascular treatment . when stent - based thrombectomy was unsuccessful , additional mechanical approaches
were performed , including manual aspiration thrombectomy with a penumbra reperfusion catheter ( penumbra , alameda , usa ) or navien catheter ( covidien , irvine , usa ) .
intracranial angioplasty with or without stenting was performed when severe ( > 70% ) underlying intracranial atherosclerotic stenosis was observed .
when the patient had a tandem occlusion at the proximal cervical portion of the ica , carotid angioplasty and stenting were performed prior to stent - retriever thrombectomy .
revascularization status was assessed on the final angiogram and was classified according to the modified tici scale , and successful revascularization was defined as a modified tici grade of 2b or 3 .
all patients underwent non - enhanced ct scans immediately and 24 hours after endovascular treatment and gradient echo mri 24 - 36 hours after treatment .
intracerebral hemorrhages were assessed on posttreatment ct and gradient echo mr images and classified as hemorrhagic infarction ( hi ) or parenchymal hemorrhage ( ph ) based on the european cooperative acute stroke study ( ecass ) criteria .
symptomatic intracranial hemorrhage was defined as any intracranial hemorrhage that caused neurological deterioration ( increase of 4 points in nihss score or deterioration of 1 point in the level of consciousness on nihss ) .
clinical outcome was assessed by a stroke neurologist using the modified rankin scale ( mrs ) during an outpatient visit 3 months after treatment .
if patients were unable to attend the outpatient clinic , outcomes were obtained via a telephone interview .
first , the relationship between each clinical and procedural characteristic and 3-month outcome was determined . the 2 test or fisher exact test was used for comparing categorical variables , and the mann - whitney u test was used for comparing continuous variables .
second , independent associations between good outcome ( mrs 0 - 2 ) and clinical and procedural factors were determined with a multivariate logistic regression analysis .
the variables tested in the multivariate logistic regression models were those with p<0.05 in the univariate analysis .
third , a multivariate logistic regression analysis was performed to identify independent predictors for mortality at 3 months .
variables with a p value of < 0.05 in the univariate analysis on mortality were included in a multivariate logistic regression analysis .
all statistical analyses were performed with spss software ( version 21.0 ; ibm spss , chicago , il , usa ) .
of the 335 patients with acute anterior circulation stroke , 233 patients had occlusions in the mca and 102 in the ica .
successful revascularization ( modified tici 2b or 3 ) was achieved in 81.8% ( n=274/335 ) and a good outcome in 45.1% of patients ( n=151/335 ) .
parenchymal hemorrhage occurred in 8.9% ( n = 30/335 ) and symptomatic hemorrhage in 3.9% ( n=13/335 ) .
seventy - one patients ( 21.2% ) received manual aspiration thrombectomy as a rescue therapy after failed stent - retriever thrombectomy .
forty patients ( 11.9% ) had underlying intracranial atherosclerotic stenosis , and 36 ( 10.7% ) had a tandem occlusion at the proximal cervical portion of the ica .
in the entire cohort ( n=335 ) , the median dwi - aspects was 7 ( iqr , 6 - 8 ) .
patients with good outcome had a higher dwi - aspects score compared to those with poor outcome ( 8 vs. 7 ; or , 1.278 ; p<0.001 ) .
in univariate analysis , the following variables were identified as predictors of a good outcome at 3 months : younger age , absence of hypertension , dwi - aspects , mca occlusions ( vs. ica occlusions ) , low baseline nihss , no need for rescue therapy , successful revascularization , absence of parenchymal hemorrhage or symptomatic hemorrhage , shorter procedure time , and a shorter time to revascularization . when dichotomized , patients aged 80 years had more frequent poor outcome ( mrs 3 - 6 ) than those aged < 80 years ( 69.6% vs. 51.1% ; or , 2.2 ; p=0.007 ) in univariate analysis . in multivariate analysis , younger age ( or , 0.965
; 95% ci , 0.944 - 0.986 ; p=0.001 ) , successful revascularization ( or , 4.658 ; 95% ci , 2.240 - 9.689 ; p<0.001 ) , low baseline nihss ( or , 0.908 ; 95% ci , 0.855 - 0.965 ; p=0.002 ) , and absence of parenchymal hemorrhage ( or , 0.150 ; 95% ci , 0.049 - 0.460 ; p=0.001 ) were independent predictors of good outcome at 3 months ( table 2 ) .
in univariate analysis , age , history of previous stroke / transient ischemic attack ( tia ) , revascularization status , symptomatic hemorrhage , and baseline nihss score were associated with mortality at 3 months .
patients aged 80 years had a higher mortality rate than those aged < 80 years ( 18.8% vs. 8.6% ; or , 2.2 ; p=0.015 ) in univariate analysis . in multivariate analysis , age ( or , 1.043 ; 95% ci , 1.002 - 1.086 ; p=0.041 ) , history of previous stroke / tia ( or , 3.124 ; 95% ci , 1.340 - 7.281 ; p=0.008 ) , revascularization ( or , 0.171 ; 95% ci , 0.079 - 0.370 ; p<0.001 ) , and parenchymal hemorrhage ( or , 2.961 ; 95% ci , 1.059 - 8.276 ; p=0.038 ) were independent predictors of mortality at 3 months ( table 3 ) .
the main findings of our study are summarized as follows : 1 ) age , revascularization status , and parenchymal hemorrhage are significant independent predictors of not only good clinical outcome but also mortality at 3 months ; 2 ) in addition , nihss score on admission is independently associated with good outcome , whereas a history of previous stroke / tia is independently associated with mortality .
several studies have evaluated independent predictors of clinical outcome after stent - retriever thrombectomy in patients with acute ischemic stroke due to intracranial large vessel occlusion [ 4 - 8 ] .
these previous studies have identified that younger age , lower admission nihss score , successful recanalization , shorter procedure time , smaller early ischemic changes on pretreatment ct , and lower serum glucose level were independent predictors of good outcome [ 4 - 8 ] .
symptomatic ich , baseline dwi - aspect score , baseline nihss 20 , and onset to recanalization > 5 hours have been identified as independent predictors of mortality after stent - retriever thrombectomy . however , these studies are limited by small sample sizes and inclusion of posterior circulation stroke .
the strengths of our study include a large sample size , inclusion of only anterior circulation stroke , and consistency in patient selection and endovascular procedures . in our study , age
a good outcome was significantly less frequent among patients 80 years than among those < 80 years ( 30.4% vs. 48.9% ) and mortality was significantly more frequent among patients 80 years ( 18.8% vs. 8.6% ) in the present study .
patient age 80 years was associated with a 2.2-fold increase in both poor outcome and mortality compared with the younger cohort .
the results of our study are in agreement with those of north american solitaire stent - retriever acute stroke ( nasa ) registry , which included 354 patients . in the nasa registry
, patients > 80 years showed less favorable outcome ( 27.3% vs. 45.4% , p=0.02 ) and increased mortality ( 43.9% vs. 27.3% , p=0.01 ) compared with patients 80 years in age .
however , a meta - analysis of 4 recent randomized trials showed a trend toward better outcome ( mrs 0 - 2 at 90 days ; 38% vs. 19% ) and a significant reduction in mortality ( 20% vs. 41% , adjusted or 3.7 ; p=0.01 ) in patients 80 years who received solitaire stent thrombectomy when compared to those received medical treatment alone .
thus , old age should not be used as exclusion criteria for stent - retriever thrombectomy in patients with acute large vessel occlusions .
our study suggests that successful recanalization is still a strong predictor of clinical outcome after endovascular treatment for acute ischemic stroke in this recent era of mechanical thrombectomy . in the present study , successful recanalization ( defined as modified tici 2b )
occurred in 82% of patients and was the most powerful independent predictor of both good clinical outcome and mortality .
our results are consistent with 2 previous reports , which demonstrated that successful recanalization is one of the independent predictors of good outcome . with regard to association between recanalization and mortality ,
the nasa registry showed that successfully recanalized patients had lower mortality ( 25.2% vs. 46.9% , p<0.001 in a univariate analysis ) after solitaire stent thrombectomy . in the nasa registry , proximal occlusion ( ica or basilar artery occlusion ) , high admission nihss score ( 18 ) , and need for rescue therapy were predictors of mortality in successfully recanalized patients .
the results of our study together with previous studies strongly suggest that neurointerventionalists should make every effort to achieve successful recanalization in order to increase good outcome and decrease mortality .
parenchymal hemorrhage is considered the most catastrophic complication of reperfusion therapy for acute ischemic stroke and is known to be one of predictors of clinical outcome . in our study , parenchymal hemorrhage occurred in 8.9% of patients .
patients with parenchymal hemorrhage had good outcome less frequently ( 13.3% vs. 48.2% ) and mortality more frequently ( 23.3% vs. 9.5% ) compared to those without it .
our findings are consistent with a recent multicenter retrospective study , which included 1,122 patients with anterior circulation large vessel occlusion strokes who received multimodal endovascular therapy . in that study ,
parenchymal hemorrhage occurred in 8.6% of patients ( 96 of 1122 ) and was associated with a higher rate of poor outcome ( or=6.24 , p<0.001 ) and higher mortality ( or=3.52 , p<0.001 ) . in that study , atrial fibrillation ( or=1.61 , p=0.045 ) was an independent predictor of parenchymal hemorrhage .
in addition , mishra et al .   suggested that the presence of a severely hypoperfused lesion on pretreatment imaging ( defined as a very low cerebral blood volume on perfusion mri ) is a strong predictor of parenchymal hemorrhage ( or=33 , p<0.001 ) in patients undergoing endovascular therapy for acute stroke .
however , there was no significant clinical or procedural predictor of parenchymal hemorrhage in univariate or multivariate analysis in our study .
although the occurrence of parenchymal hemorrhage after endovascular therapy is multifactorial , careful patient selection based on pretreatment imaging studies , judicious management of blood pressure , and reduced use of contrast agents and thrombolytic drugs during the endovascular procedure are all needed to decrease the occurrence of parenchymal hemorrhage . interestingly , a history of previous stroke / tia was independently associated with mortality in our study , which has not been previously reported in stent retriever thrombectomy studies .
mortality occurred more frequently in patients with previous stroke / tia ( 23.1% vs. 8.5% ) than those without it .
although this is a novel finding in studies regarding mechanical thrombectomy using stent retrievers , a history of previous stroke / tia has been found as a predictor of short - term and long - term mortality in patients with acute ischemic stroke compared with healthy control subjects in observational studies .
the results of our study and previous studies indicate that more improved management of vascular risks is needed to prevent secondary stroke and subsequent cardiovascular mortality in patients with first - ever stroke . in our study , nihss score on admission was independently associated with good outcome but not with mortality .
reported that baseline nihss score ( or=1.228 , p=0.002 ) was an independent predictor of poor outcome at 3 months .
jiang et al .   showed that patients with lower baseline nihss score ( score < 20 ) had good outcome less frequently ( 21.1% vs. 56.9% , or=5.25 ) compared with those nihss score 20 .
in addition , shi et al .   reported that baseline nihss score was an independent predictor of functional dependence ( mrs 3 - 6 ) despite successful revascularization ( or=1.13 , p=0.0074 ) in 109 patients treated with the trevo stent - retriever .
however , like advanced age , severe stroke should not be used as exclusion criteria because patients with severe stroke do even worse with medical therapy alone .
baseline aspects measured by ct or mri has been found to be an independent predictor of clinical outcome after stent retriever thrombectomy in two previous studies . in the present study ,
dwi - aspects was significantly higher in patients with good outcome than those with poor outcome in a univariate analysis ( or=1.278 , per 1-point increase , p<0.001 ) . however , dwi - aspects was not an independent predictor of both good outcome and mortality in multivariate analyses .
similarly , a recent study showed that there were no differences in outcomes between patients with high dwi - aspect scores of 7 - 10 and those with intermediate scores of 4 - 6 who underwent stent retriever thrombectomy for acute anterior circulation stroke .
this finding may be because of the high rate of successful revascularization with stent retrievers in that study and the disparity between aspect score and infarct lesion volume .
in addition , some potential confounding factors , such as blood glucose level were not analyzed in our study .
admission blood glucose level is known to be associated with poor outcome , increased hemorrhage , and mortality following iv thrombolysis or stent - retriever thrombectomy .
we did not analyze blood glucose level in this study because it was missing for some patients .
finally , the fact that 21.2% of patients received manual aspiration thrombectomy as a rescue therapy after failed stent - retriever thrombectomy may limit the accuracy of data in regard to interpretation related to the value of stent retriever thrombectomy .
in conclusion , age , revascularization status , and parenchymal hemorrhage are independently associated with both good outcome and mortality after stent - retriever thrombectomy in patients with acute anterior circulation stroke .
in addition , nihss score on admission is independently associated with good outcome , whereas a history of previous stroke is independently associated with mortality .
our results suggest that achieving successful revascularization and trying to reduce parenchymal hemorrhage are priorities when performing stent retriever thrombectomy in patients with acute anterior circulation stroke .
the data also suggest a novel finding that a history of previous stroke / tia can be considered a predictor of mortality in patients receiving stent retriever thrombectomy .
 background and purpose predictive factors associated with stent - retriever thrombectomy for patients with acute anterior circulation stroke remain to be elucidated . this study aimed to investigate clinical and procedural factors predictive of good outcome and mortality after stent - retriever thrombectomy in a large cohort of patients with acute anterior circulation stroke.methods we analyzed clinical and procedural data in 335 patients with acute anterior circulation stroke treated with stent - retriever thrombectomy . 
 a good outcome was defined as a modified rankin scale score of 0 to 2 at 3 months . 
 the associations between clinical , imaging , and procedural factors and good outcome and mortality , respectively , were evaluated using logistic regression analysis.results using multivariate analysis , age ( odds ratio [ or ] , 0.965 ; 95% confidence interval [ ci ] , 0.944 - 0.986 ; p=0.001 ) , successful revascularization ( or , 4.658 ; 95% ci , 2.240 - 9.689 ; p<0.001 ) , parenchymal hemorrhage ( or , 0.150 ; 95% ci , 0.049 - 0.460 ; p=0.001 ) , and baseline nihss score ( or , 0.908 ; 95% ci , 0.855 - 0.965 ; p=0.002 ) were independent predictors of good outcome . 
 independent predictors of mortality were age ( or , 1.043 ; 95% ci , 1.002 - 1.086 ; p=0.041 ) , successful revascularization ( or , 0.171 ; 95% ci , 0.079 - 0.370 ; p<0.001 ) , parenchymal hemorrhage ( or , 2.961 ; 95% ci , 1.059 - 8.276 ; p=0.038 ) , and a history of previous stroke / tia ( or , 3.124 ; 95% ci , 1.340 - 7.281 ; p=0.008).conclusions age , revascularization status , and parenchymal hemorrhage are independent predictors of both good outcome and mortality after stent retriever thrombectomy for acute anterior circulation stroke . in addition , nihss score on admission is independently associated with good outcome , whereas a history of previous stroke is independently associated with mortality . 
Introduction
Methods
Patients
Endovascular treatment
Statistical analysis
Results
Discussion
Conclusions