Outcomes of mechanical thrombectomy with pre-intravenous thrombolysis: a systematic review and meta-analysis

Efficacy and safety of intravenous tenecteplase compared to alteplase before mechanical thrombectomy in acute ischemic stroke: a meta-analysis

BACKGROUND

The benefits and risks of tenecteplase (TNK) versus alteplase (ALT) have recently been assessed in acute ischemic stroke (AIS) patients undergoing mechanical thrombectomy (MT) with diverse results. Due to its high fibrin specificity and lack of excitotoxicity, TNK may have a higher efficacy and safety profile. This study aimed to evaluate the benefits and risks of TNK compared to ALT in AIS patients prior to thrombectomy.

METHODS

We systematically searched four key databases, PubMed, Embase, Web of Science and Cochrane Library until January 27, 2024 for clinical studies evaluating the effects of TNK versus ALT in patients with large vessel occlusion undergoing MT. A random-effect meta-analysis was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Ten studies involving 3722 patients receiving TNK (1266 patients) or ALT (2456 patients) were included (age: 69.05 ± 14.95 years; 55.64% male). Compared to ALT-treated patients, TNK-treated patients demonstrated significantly higher rates of early recanalization (odds ratio 2.02, 95%-confidence interval 1.20-3.38, p = 0.008) without increased risk of symptomatic intracerebral hemorrhage (1.06, 0.64-1.76, p = 0.82) or intracerebral hemorrhage (1.21, 0.66-2.25, p = 0.54). TNK-treated patients showed similar rates of functional independence at 90 days (1.13, 0.87-1.46, p = 0.37) as ALT-treated patients, but lower rates of mortality within 90 days (0.65, 0.44-0.96, p = 0.03).

CONCLUSION

TNK is superior to ALT in achieving early recanalization and is associated with lower mortality within 90 days in AIS patients undergoing MT. Compared with ALT, TNK does not significantly alter functional independence at 90 days, symptomatic intracerebral hemorrhage or intracerebral hemorrhage.

Impact of atrial fibrillation on the treatment effect of bridging thrombolysis in ischemic stroke patients undergoing endovascular thrombectomy: a multicenter international cohort study

BACKGROUND

The role of bridging intravenous thrombolysis (IVT) before endovascular thrombectomy (EVT) in the treatment of acute ischemic stroke (AIS) remains debatable. Atrial fibrillation (AF) associated strokes may be associated with reduced treatment effect from IVT. This study compares the effect of bridging IVT in AF and non-AF patients.

METHODS

This retrospective cohort study comprised anterior circulation large vessel occlusion (LVO) AIS patients receiving EVT alone or bridging IVT plus EVT within 6 hours of symptom onset. Primary outcome was good functional outcome defined as modified Rankin Scale (mRS) 0-2 at 90 days. Secondary outcomes were successful reperfusion defined as expanded Thrombolysis In Cerebral Infarction (eTICI) grading ≥2b flow, symptomatic intracerebral hemorrhage (sICH), and in-hospital mortality.

RESULTS

We included 705 patients (314 AF and 391 non-AF patients). The mean age was 68.6 years and 53.9% were male. The odds of good functional outcomes with bridging IVT was higher in the non-AF (adjusted odds ratio (aOR) 2.28, 95% CI 1.06 to 4.91, P=0.035) compared with the AF subgroups (aOR 1.89, 95% CI 0.89 to 4.01, P=0.097). However, this did not constitute a significant effect modification by the presence of AF on bridging IVT (interaction aOR 0.12, 95% CI -1.94 to 2.18, P=0.455). The rate of successful reperfusion, sICH, and mortality were similar between bridging IVT and EVT for both AF and non-AF patients.

CONCLUSION

The presence of AF did not modify the treatment effect of bridging IVT. Further individual patient data meta-analysis of randomized trials may shed light on the comparative efficacy of bridging IVT in AF versus non-AF LVO strokes.

Clinical evidence comparing bridging and direct endovascular thrombectomy: progress and controversies

Clinical evidence comparing bridging endovascular thrombectomy (bEVT) with intravenous thrombolysis and direct endovascular thrombectomy (dEVT) without thrombolysis for patients with acute ischemic stroke (AIS) presented directly to an EVT-capable center is overwhelming but inconsistent. This study aimed to analyze the progress and controversies in clinical evidence based on current meta-analyses. Three databases, including MEDLINE, EMBASE, and the Cochrane Library, were searched. Relevant data were extracted and reviewed from the pooled studies. The Assessment of Multiple Systematic Review (AMSTAR-2) was used for quality assessment. Twenty-five meta-analyses were finally included. There were 56% (14/25) from Asian countries, 20% (5/25) from North America, and 24% (6/25) from Europe. The majority (72%, 18/25) of evidence arose in a short period from 2020 to 2022 with the serial publication of four randomized controlled trials (RCTs). Among the 25 meta-analyses, 11 pooled at least three RCTs but there is substantial overlap among seven (five recruited the same four RCTs solely and two recruited the same three RCTs solely). Meanwhile, quality rating based on AMSTAR-2 showed 16 'high' rated studies (64%). For functional independence, 40% (10/25) of studies favored bEVT and 60% showed neutral results. For symptomatic intracerebral hemorrhage, most studies (82.6%, 19/23) showed no significant difference. Non-RCT studies contributed to evidence favoring bEVT. Current RCTs provide an update of clinical evidence comparing bEVT and dEVT. However, they simultaneously contribute to an unnecessary overlap among studies. Contemporary observational studies demonstrated different but possibly confounded evidence. Thus, this issue still requires more clinical evidence under standard procedures.

Impact of ongoing intravenous thrombolysis until completion of endovascular treatment in large vessel occlusion stroke patients

Background

Recent studies have implied that ongoing intravenous thrombolysis (IVT) during endovascular treatment (ET) improves functional outcomes in patients who have undergone stroke caused by a large vessel occlusion (LVO). In this study, we investigated the effect of ongoing IVT until completion of ET on procedure duration, first-pass thrombectomy rate, and periprocedural complications.

Methods

We analyzed patients from the German Stroke Registry-Endovascular Treatment dataset, collected between June 2015 and December 2021. Primary outcomes were modified Rankin Scale (mRS) score after 3 months and achievement of a Thrombolysis In Cerebral Infarction (TICI) score of 2b-3. Secondary parameters included ET duration, first-pass thrombectomy, and periprocedural complications.

Results

Of the 13,082 patients in the dataset, 1,639 met the study inclusion criteria. A total of n = 317 patients (19.3%) underwent ongoing IVT until completion of ET, while IVT was completed prior to ET in 1,322 patients (80.7%). Ongoing IVT was associated with higher rates of achievement of an mRS score of 0-2 (or a back-to-baseline) after 3 months [odds ratio (OR) 1.53; 95% confidence interval (CI) 1.08-2.17]. Furthermore, ongoing IVT was predictive of achievement of a TICI score of 2b-3 (OR 1.37; 95% CI 1.03-1.83) and of first-pass thrombectomy (OR 2.07; 95% CI 1.51-2.84), while reducing the rate of peri-interventional complications (OR 0.64; 95% CI 0.44-0.94) and reducing ET duration by 24 min [β = -24.35; 95% CI -32.92-(-15.79)].

Conclusion

Our findings suggest that ongoing IVT until ET completion has a favorable impact on both clinical and angiographic outcomes, as well as on periprocedural conditions, regardless of the overall time intervals involved. Therefore, rapid ET after IVT should be sought in order to take advantage of the additive effect of ongoing IVT during ET. Future studies should consider IVT timing in the context of ET as a potential confounder and treatment target.

Symptomatic Intracranial Hemorrhage after Ischemic Stroke Treated with Bridging Revascularization Therapy

(1) Background: bridging revascularization therapy is now the standard of care in patients with ischemic stroke due to large vessel occlusion. This study aimed to determine the frequency of symptomatic intracranial hemorrhage (sICH) related to this treatment, and to assess contributing factors and patients' outcomes. (2) Methods: consecutive ischemic stroke patients treated with bridging therapy were prospectively enrolled. sICH (intracranial hemorrhage with an increase in NIHSS score of ≥4 points) was assessed on imaging at 24 h. The functional status of patients was measured at 6 months using the mRS score; (3) Results: 176 patients were included (mean age 68.7 ± 1.2 years, 52.3% women), among whom 15 (8.5%) had sICH. Patients with sICH had more frequent alcohol abuse (30.1% versus 9.7%, p = 0.023), prestroke use of dual antiplatelet therapy (14.3% versus 1.3%, p = 0.002), higher NIHSS scores at admission (median score 20.5 versus 15, p = 0.01), greater systolic blood pressure upon admission, more frequent vascular intracranial calcifications (p = 0.004), leukoaraiosis (p = 0.001), and intracranial atheroma (p = 0.02), and higher neutrophil-to-lymphocyte ratios (p = 0.02) and neutrophil-to-platelet ratios (p = 0.04). At 6-month follow-up, 9 (60%) patients with sICH died, versus 18% of patients without sICH (p < 0.001). Only 1 (7%) patient with sICH had a good functional outcome, defined as an mRS score of 0 to 2, versus 51% of patients without sICH. (4) Conclusions: one in twelve ischemic stroke patients treated with bridging therapy suffered sICH. Given the observed poor outcomes after sICH, further studies are required to better identify patients at risk to help clinicians in guiding therapeutic strategies.

Endovascular thrombectomy with or without intravenous alteplase in acute stroke: a systematic review and meta-analysis of randomized clinical trials

BACKGROUND AND PURPOSE

This study investigated clinical outcomes after direct endovascular thrombectomy (EVT) compared to bridging therapy (EVT with prior intravenous alteplase) in acute stroke within 4.5 h after onset.

METHODS

PubMed and Embase were searched for eligible randomized controlled trials. The primary outcome was the rates of neurological functional independence defined as modified Rankin scale score 0-2 at 90 days, whose non-inferiority margin was set at - 15%, - 10%, - 6.5%, - 5%, and - 1.3% for its risk difference (RD).

RESULTS

We included six studies enrolling 2334 participants. The crude cumulative rates of functional independence were 49.0% with direct EVT vs 50.9% with bridging therapy, without significant difference (Odd ratio [OR] = 0.93, 95% confidence interval [CI] 0.79-1.09) between two groups, where the pooled RD was - 2% (95% CI - 6 to 2%) whose lower 95% CI bound fell within non-inferiority margins of - 15%, - 10%, -6.5%, but not - 5% and - 1.3%. Between the two groups, no significant difference was found in excellent function rate (30.2% vs 30.6%, OR = 0.99, 95% CI 0.82-1.18) with RD of 0% (95% CI - 3 to 4%), mortality rate (16.0% vs 15.0%, OR = 1.08, 95% CI 0.86-1.35) with RD of 1% (95% CI - 2 to 4%), and symptomatic intracranial hemorrhage rate (4.3% vs 5.0%, OR = 0.86, 95% CI 0.58-1.27) with RD of 0% (95% CI - 2 to 1%).

CONCLUSIONS

No statistical difference was found in functional and safety outcomes between direct EVT and bridging therapy groups in acute stroke within 4.5 h after symptom onset. EVT alone was non-inferior to bridging therapy for several, but not the more stringent, non-inferiority margins.

Direct Endovascular Thrombectomy or With Prior Intravenous Thrombolysis for Acute Ischemic Stroke: A Meta-Analysis

Background and purpose: It is unclear whether endovascular thrombectomy alone compared with intravenous thrombolysis combination with endovascular thrombectomy can achieve similar neurological outcomes in patients with acute large vessel occlusion stroke. We aimed to perform a systematic review and meta-analysis of randomized controlled trials to compare endovascular thrombectomy alone or intravenous thrombolysis plus endovascular thrombectomy in this population.

Methods: We systematically searched PubMed, Embase, and ClinicalTrials.gov. We restricted our search to randomized clinical trials that examined the clinical outcomes of endovascular thrombectomy alone vs. intravenous thrombolysis plus endovascular thrombectomy. The Cochrane risk of bias tool was used to assess study quality. Random-effects meta-analyses were used for evaluating all outcomes.

Results: Total three randomized controlled trials with 1,092 individuals enrolled were included in the meta-analysis, including 543 (49.7%) who received endovascular thrombectomy alone and 549 (50.3%) who received intravenous thrombolysis plus endovascular thrombectomy. The primary outcome of 90-day functional independence (modified Rankin scale (mRS) score ≤ 2) was 44.6% (242/543) in the endovascular thrombectomy alone group vs. 42.8% (235/549) in the alteplase with endovascular thrombectomy group (odds ratio (OR), 1.08 [95% CI, 0.85–1.38]; P = 0.0539). Among pre-specified secondary outcomes, no significant between-group differences were found in excellent outcome (mRS score ≤ 1) (OR, 1.12 [95% CI, 0.85–1.47]; P = 0.418), mortality at 90 days (OR, 0.93 [95% CI, 0.68–1.29]; P = 0.673), successful reperfusion (thrombolysis in cerebral infarction 2b-3) (OR, 0.75 [95% CI, 0.54–1.05]; P = 0.099), and symptomatic intracranial hemorrhage (OR, 0.72 [95% CI, 0.45–1.15]; P = 0.171).

Conclusions: Among patients with acute ischemic stroke in the anterior circulation within 4.5 h from the onset, endovascular thrombectomy alone was non-inferior to combined intravenous thrombolysis and endovascular thrombectomy.

Thrombolytic strategies for ischemic stroke in the thrombectomy era

Twenty-five years ago, intravenous thrombolysis has revolutionized the care of patients with acute ischemic stroke. Since 2015, randomized clinical trials have demonstrated that mechanical thrombectomy improves functional outcome in stroke patients over intravenous thrombolysis alone. More recently, three randomized clinical trials have suggested that mechanical thrombectomy alone is noninferior to a combined strategy with both intravenous thrombolysis and mechanical thrombectomy. In the present review, we will present the last clinical and preclinical studies on the use of thrombolysis in stroke patients in the modern thrombectomy era. At the cost of a potential increased risk of hemorrhagic transformation, thrombolysis may promote arterial recanalization before thrombectomy, improve the rate of successful recanalization after thrombectomy, and restore microcirculation patency downstream of the main thrombus. Besides, new thrombolytic strategies targeting tissue-type plasminogen activator resistant thrombi are being developed, which could strengthen the beneficial effects of thrombolysis without carrying additional pro-hemorrhagic effects. For instance, tenecteplase has shown improved rate of recanalization compared with tissue-type plasminogen activator (alteplase). Beyond fibrinolysis, DNA- and von Willebrand factor-targeted thrombolytic strategies have shown promising results in experimental models of ischemic stroke. New combined strategies, improved thrombolytics, and dedicated clinical trials in selected patients are eagerly awaited to further improve functional outcome in stroke.

Endovascular Thrombectomy Versus Bridging Thrombolysis: Real-World Efficacy and Safety Analysis Based on a Nationwide Registry Study

Background

It was uncertain if direct endovascular thrombectomy (ET) was superior to bridging thrombolysis (BT) for patients with acute ischemic stroke caused by large‐vessel occlusions. We aimed to examine real‐world clinical outcomes of ET using nationwide registry data in China and to compare the efficacy and safety between BT and direct ET.

Methods and Results

Patients treated with ET from a nationwide registry study in China were included. Rapid neurological improvement, intracranial hemorrhage, and in‐hospital mortality were compared between the 2 groups using multivariate logistic models and propensity‐score matching analyses. A total of 7674 patients from 592 stroke centers were included. The median onset‐to‐puncture time, onset‐to‐door time, and door to puncture time were 290, 170, and 99 minutes, respectively. A total of 2069 (27.0%) patients received BT treatment. Patients in the BT group had a significantly shorter onset‐to‐puncture time (235 versus 323 minutes; P<0.001) and onset‐to‐door time (90 versus 222 minutes; P<0.001) compared with the direct ET group. The prior use of intravenous thrombolysis was associated with a higher rate of rapid neurological improvement (adjusted odds ratio [OR], 0.83; 95% CI, 0.71–0.96) and higher risk of intracranial hemorrhage (adjusted OR, 1.46; 95% CI, 1.18–1.80) in multivariate analyses and propensity‐score matching analyses.

Conclusions

This study reflects the current application of ET in China. More patients received direct ET than BT. Our results suggested that favorable short‐term outcomes could be achieved with BT compared with direct ET. Higher risk of intracranial hemorrhage was observed in the BT group.

Endovascular Treatment With and Without Intravenous Thrombolysis in Large Vessel Occlusions Stroke: A Systematic Review and Meta-Analysis

Background: Previous studies have shown conflicting results about the benefits of pretreatment with intravenous thrombolysis before endovascular treatment (EVT) in patients with acute ischemic stroke (AIS) with large vessel occlusions (LVOs). This study aimed to investigate the clinical efficacy and safety of EVT alone vs. bridging therapy (BT) in patients with AIS with LVOs. Methods: A systematic review with meta-analysis of all available studies comparing clinical outcomes between BT and EVT alone was conducted by searching the National Center for Biotechnology Information/National Library of Medicine PubMed and Web of Science databases for relevant literature from database inception to October 20, 2020. Results: A total of 93 studies enrolling 45,190 patients were included in the present analysis. In both unadjusted and adjusted analyses, BT was associated with a higher likelihood of 90-day good outcome (crude odds ratio [cOR] 1.361, 95% confidence interval [CI] 1.234-1.502 and adjusted OR [aOR] 1.369, 95% CI 1.217-1.540) and successful reperfusion (cOR 1.271, 95% CI 1.149-1.406 and aOR 1.267, 95% CI 1.095-1.465) and lower odds of 90-day mortality (cOR 0.619, 95% CI 0.560-0.684 and aOR 0.718, 95% CI 0.594-0.868) than EVT alone. The two groups did not differ in the occurrence of symptomatic intracranial hemorrhage (sICH) (cOR 1.062, 95% CI 0.915-1.232 and aOR 1.20, 95% CI 0.95-1.47), 24-h early recovery (cOR 1.306, 95% CI 0.906-1.881 and aOR 1.46, 95% CI 0.46-2.19), and number of thrombectomy device passes ≤ 2 (aOR 1.466, 95% CI 0.983-2.185) after sensitivity analyses and adjustment for publication bias. Conclusions: BT provides more benefits than EVT alone in terms of clinical functional outcomes without compromising safety in AIS patients with LVOs.

Impact of bridging thrombolysis on clinical outcome in stroke patients undergoing endovascular thrombectomy: a retrospective analysis of a regional stroke registry

Purpose

It is unclear whether stroke patients undergoing endovascular thrombectomy (EVT) should receive bridging intravenous thrombolysis (IVT), if eligible. This study aims at analyzing the impact of bridging IVT on short-term clinical outcome.

Methods

In a prospective regional stroke registry, all stroke patients with premorbid modified Rankin Scale (mRS) score of 0–2 who were admitted within 4.5 h after onset and treated with EVT were analyzed retrospectively. Patients receiving “IVT prior to EVT” (IVEVT) were compared to those undergoing “EVT only” regarding the ratio of good outcome, discharge mRS, mRS shift, hospital mortality, and occurrence of symptomatic intracranial hemorrhage.

Results

In total, 2022 patients were included, 816 patients (40.4%) achieved good clinical outcome; 1293 patients (63.9%) received bridging IVT. There was no significant difference between both groups regarding the ratio of good outcome (IVEVT 41.4% vs. EVT 38.5%, P = 0.231), discharge mRS (median, IVEVT 3 vs. EVT 3, P = 0.178), mRS shift (median, IVEVT 3 vs. EVT 3, P = 0.960), and hospital mortality (IVEVT 19.3% vs. EVT 19.5%, P = 0.984). Bridging IVT was not a predictor of outcome (adjusted OR 1.00, 95% CI 0.79–1.26, P = 0.979). However, it was an independent predictor of symptomatic intracranial hemorrhage (adjusted OR 1.79, 95% CI 1.21–2.72, P = 0.005).

Conclusions

The results of the present study suggest that bridging IVT does not seem to improve short-term clinical outcome of patients undergoing EVT. Nonetheless, there might be a subgroup of patients that benefits from IVT. This needs to be addressed in randomized controlled trials.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00234-020-02619-1.

Endovascular treatment of acute ischemic stroke

Endovascular treatment of acute ischemic stroke has become the first choice of treatment in large cerebral vessel occlusions, with a very high efficacy in terms of revascularization and reducing disability of affected patients. Revolutionizing acute therapy, it induced important paradigm shifts in the concepts of time and salvageable brain. In this review we focus on the current concepts of patient selection, imaging, techniques and perspectives of endovascular stroke treatment.

LncRNA MACC1-AS1 attenuates microvascular endothelial cell injury and promotes angiogenesis under hypoxic conditions via modulating miR-6867-5p/TWIST1 in human brain microvascular endothelial cells

Background

Hypoxia following ischemic stroke is a common cause of brain insults. Mounting evidence suggests that long non-coding RNAs (lncRNAs) play a vital role in regulating certain physiological and pathological processes including ischemic stroke. For the first time, the present study investigated the effects and mechanism of LncRNA MACC1-AS1 on hypoxia-induced human brain microvascular endothelial cells (HBMECs).

Methods

LncRNA MACC1-AS1 levels in HBMECs were detected via reverse transcription quantitative polymerase chain reaction (RT-qPCR) assay. Reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT), were detected using their respective kits. Flow cytometry and clone formation assay were performed to evaluate the effects of lncRNA MACC1-AS1 on cell apoptosis and cell proliferation respectively. Angiogenesis capacity was evaluated via tube formation assay. Transwell migration assay was performed for assessment of cell migration, Western blot assay was performed for measurement of Twist1 and VE-cadherin level, and permeability assay was performed for evaluation of the cell barrier function. The target gene was predicted via bioinformatics online tool and validated through luciferase reporter assay and RNA pull-down assay.

Results

LncRNA MACC1-AS1 was downregulated in hypoxia-induced HBMECs. Overexpression of LncRNA MACC1-AS1 reduced cell apoptosis and oxidative stress, while promoting cell proliferation, migration, and angiogenesis. Moreover, LncRNA MACC1-AS1 overexpression reduced cell permeability and elevated VE-cadherin level, which contributed to maintaining cell barrier function. TWIST1 was validated as the target of miR-6867-5p which was further targeted by lncRNA MACC1-AS1. Thus, LncRNA MACC1-AS1 functions in hypoxia-induced HBMECs by regulating miR-6867-5p/TWIST1.

Conclusions

In this study, we found that LncRNA MACC1-AS1 exerted a protective role in hypoxia-induced HBMECs via regulating miR-6867-5p/TWIST1, indicating a new therapeutic strategy for future ischemic stroke therapy.

Direct admission versus secondary transfer for acute ischemic stroke patients treated with thrombectomy: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Randomized controlled trials have demonstrated that mechanical thrombectomy (MT) could provide more benefit than standard medical care for acute ischemic stroke (AIS) patients due to emergent large vessel occlusion. However, most primary stroke centers (PSCs) are unable to perform MT, and MT can only be performed in comprehensive stroke centers (CSCs) with on-site interventional neuroradiologic services. Therefore, there is an ongoing debate regarding whether patients with suspected AIS should be directly admitted to CSCs or secondarily transferred to CSCs from PSCs. This meta-analysis was aimed to investigate the two transportation paradigms of direct admission and secondary transfer, which one could provide more benefit for AIS patients treated with MT.

METHODS

We conducted a systematic review and meta-analysis through searching PubMed, Embase and the Cochrane Library database up to March 2020. Primary outcomes are as follows: symptomatic intracerebral hemorrhage (sICH) within 7 days; favorable functional outcome at 3 months; mortality in hospital; mortality at 3 months; and successful recanalization rate.

RESULTS

Our pooled results showed that patients directly admitted to CSCs had higher chances of achieving a favorable functional outcome at 3 months than those secondarily transferred to CSCs (OR = 1.26; 95% CI, 1.12-1.42; P < 0.001). In addition, no significant difference was found between the two transportation paradigms in the rate of sICH (OR = 0.86; 95% CI, 0.62-1.18; P = 0.35), mortality in hospital (OR = 0.84; 95% CI, 0.51-1.39; P = 0.51), mortality at 3 months (OR = 1.01; 95% CI, 0.85-1.21; P = 0.91), and successful recanalization (OR = 1.03; 95% CI, 0.88-1.20; P = 0.74). However, in the 100% bridging thrombolysis usage rate subgroup, our subgroup analysis indicated that no difference was found in any outcome between the two transportation paradigms.

CONCLUSION

Patients with AIS directly admitted to CSCs for MT may be a feasible transportation paradigm for AIS patients. However, more large-scale randomized prospective trials are required to further investigate this issue.