Tissue Is More Important than Time in Stroke Patients Being Assessed for Thrombolysis

Prediction of response to thrombolysis in acute stroke using neural network analysis of CT perfusion imaging

BACKGROUND

In ischaemic stroke patients undergoing reperfusion therapy, the amount of salvageable tissue, that is, extent of the ischaemic penumbra, predicts the clinical outcomes. CT perfusion (CTP) enables quantification of penumbral tissues to guide decision making, and current programmes have automated its analysis. More advanced machine learning techniques utilising the CTP maps may improve prediction beyond the ischaemic volume measures.

METHOD

We determined whether applying convolutional neural networks (CNN), a key machine learning technique in modelling image-label relationships, to post-processed CTP maps improved prediction of outcome, assessed by 3 months modified Rankin scale (mRS). Patients who underwent thrombolysis but not thrombectomy were included. CTP maps of a retrospective cohort of 230 patients with middle cerebral artery stroke were used to develop the model, which was validated in an independent cohort of 129 patients.

RESULTS

We constructed a CNN model that predicted a favourable post-thrombolysis outcome (mRS 0-2 at 3 months) with an area under receiver-operator characteristics curve (AUC) of 0.792 (95% CI, 0.707-0.877). This model outperformed a currently clinically used MISTAR software using previously validated thresholds (AUC = 0.583, 95% CI, 0.480-0.686) and a model modified using thresholds from the derivation cohort (AUC = 0.670, 95% CI, 0.571-0.769). By combining CNN-derived features and baseline demographic features, the prediction AUC was improved to 0.865 (95% CI, 0.794-0.936).

CONCLUSION

CNN improved prediction of post-thrombolysis outcome, and may be useful in selecting which patients benefit from thrombolysis.

Determinants of cerebral collateral circulation in acute ischemic stroke due to large vessel occlusion

Introduction

Cerebral collateral circulation has a central role in ischemic stroke pathophysiology, and it is considered to correlate with infarct size, the success of reperfusion therapies, and clinical outcomes. Our aim was to study the factors influencing the development of collaterals in patients with acute ischemic stroke eligible for endovascular treatment.

Materials and methods

We enrolled patients with acute ischemic stroke and large vessel occlusion of anterior circulation potentially eligible for endovascular treatment. Included patients performed multiphase CT angiography to assess collaterals that were graded by the Menon Grading Score. We investigated the associations between clinical factors and collaterals and tested independent associations with logistic (good vs. poor collaterals) and ordinal (collateral grade grouped, Menon 0-2, 3, 4-5) regression analysis adjusting for age, sex, stroke severity, and onset to CT time (OCTT).

Results

We included 520 patients, the mean age was 75 (±13.6) years, 215 (41%) were men, and the median (IQR) NIHSS was 17 (11-22). Good collaterals were present in 323 (62%) patients and were associated with lower NIHSS (median 16 vs. 18; p < 0.001) and left hemisphere involvement (60% vs. 45%; p < 0.001), whereas previous stroke/TIA was more frequent in patients with poor collaterals (17 vs. 26%; p = 0.014). These results were confirmed in both logistic and ordinal regression analyses where good collaterals were associated with lower NIHSS (OR = 0.94; 95% CI = 0.91-0.96; cOR = 0.95; 95% CI = 0.92-0.97, respectively) and left hemisphere stroke (OR = 2.24; 95% CI = 1.52-3.28; cOR = 2.11; 95% CI = 1.46-3.05, respectively), while previous stroke/TIA was associated with poor collaterals (OR = 0.57; 95% CI = 0.36-0.90; cOR = 0.61; 95% CI = 0.40-0.94, respectively). Vascular risk factors, demographics, and pre-stroke treatments did not influence the collateral score.

Discussion

The results of our study suggest that risk factors and demographics do not influence the development of collateral circles, except for a negative relation with previous ischemic events. We confirm an already reported observation of a possible protective effect of collaterals on tissue damage assuming NIHSS as its surrogate. The association between left hemispheric stroke and better collaterals deserves to be further explored. Further efforts are needed to identify the factors that favor the development of collaterals.

Automated occlusion detection for the diagnosis of acute ischemic stroke: A detailed performance review

INTRODUCTION

Stroke is a leading cause of adult disability and death worldwide. Automated detection of stroke on brain imaging has promise in a time critical environment. We present a method for the automated detection of intracranial occlusions on dynamic CT Angiography (CTA) causing acute ischemic stroke.

METHODS

We derived dynamic CTA images from CT Perfusion (CTP) data and utilised advanced image processing to enhance and display major cerebral blood vessels for symmetry analysis. We reviewed the performance of the algorithm on a cohort of 207 patients from the International Stroke Perfusion Imaging Registry (INSPIRE), with Large Vessel Occlusion (LVO) and non-LVO strokes. Included in the data were images with chronic stroke, various artefacts, incomplete vessel occlusions, and images of poorer quality. All images were annotated by stroke experts. In addition, each image was graded in terms of the difficulty of the task of occlusion detection. Performance was evaluated on the overall cohort, and with respect to occlusion location, collateral grade, and task difficulty. We also evaluated the impact of including additional perfusion data.

RESULTS

Images with a rating of lower difficulty achieved a sensitivity and specificity of 96% and 90%, respectively, while images with a moderate difficulty rating achieved 88% and 50%, respectively. For cases of high difficulty, where more than two experts or additional data were required to reach consensus, sensitivity and specificity was 53% and 11%. The addition of perfusion data to the dCTA images increased the specificity by 38%.

CONCLUSION

We have provided an unbiased interpretation of algorithm performance. Further developments include generalising to conventional CTA and employing the algorithm in a clinical setting for prospective studies.

Preconditioning by Preceding Ischemic Cerebrovascular Events

Background Emerging yet contrasting evidence from animal and human studies associates ischemic preconditioning with improvement of subsequent stroke severity, although long-term outcome remains unclear. The purpose of this study was to analyze how preceding cerebral ischemic events influence subsequent stroke severity and outcome. Methods and Results Data for this retrospective cohort study were extracted from ASTRAL (Acute Stroke Registry and Analysis of Lausanne). This registry includes a sample of all consecutive patients with acute ischemic strokes admitted to the stroke unit and/or intensive care unit of the Lausanne University Hospital, Switzerland. We investigated associations between preceding ischemic events (transient ischemic attacks or ischemic strokes) and the impact on subsequent stroke severity and clinical improvement within 24 hours, measured through National Institute of Health Stroke Scale, as well as 3-month outcome, determined through a shift in the modified Rankin Scale. Of 3530 consecutive patients with ischemic stroke (43% women, median age 73 years), 1001 (28%) had ≥1 preceding cerebral ischemic events (45% transient ischemic attack, 55% ischemic stroke; 31% multiple events). After adjusting for multiple prehospital, clinical, and laboratory confounders, admission stroke severity was significantly lower in patients preconditioned through a preceding ischemic event, but 24-hour improvement was not significant and 3-month outcome was unfavorable. Conclusions Preceding ischemic events were independently associated with a significant reduction in subsequent stroke severity but worsened long-term clinical outcome. These results, if confirmed by future randomized studies, may help design neuroprotective strategies. The unfavorable effect on stroke outcome is probably a consequence of the cumulative disability burden after multiple ischemic events.

A Novel Fast CT Perfusion Core-Penumbra Mismatch Score: Correlation With Stroke Outcome

BACKGROUND

Advanced neuroimaging can identify patients who can most benefit from reperfusion treatment, discriminating between ischemic core and penumbra area in a quick and accurate manner. Despite core-penumbra mismatch being an independent prognostic factor, computed tomography perfusion (CTP) assessment is still debated in hyperacute decision-making. The authors aimed to study a novel CTP mismatch score in emergency settings and to investigate its relation with clinical outcome in acute ischemic stroke patients treated with intravenous thrombolysis (IVT).

METHODS

Neuroimaging and clinical data of 226 consecutive acute ischemic stroke patients were analyzed. The study population was divided into 5 different CTP scores: (0) without perfusion deficit, (1) only penumbra, (2) penumbra > core, (3) core ≥ penumbra, (4) only core. For differences in outcome between treated and nontreated patients, and among CTP core-penumbra groups to be assessed, the authors have evaluated the outcome in terms of National Institutes of Health Stroke Scale (NIHSS) and modified Rankin scale (mRS) at discharge and symptomatic intracerebral hemorrhage.

RESULTS

A decrease in NIHSS was statistically greater in IVT-treated patients compared to nontreated patients showing only penumbra (ΔNIHSS%: 80.0% vs. 50.0%; P=0.0023) or no perfusion deficit (ΔNIHSS%: 89.4% vs. 61.5%; P=0.027) on CTP maps. The same trend was found in other groups without significant difference. A significant correlation was found in IVT patients between core/penumbra score and outcome in terms of ΔNIHSS (Kendall τ=-0.19; P=0.004).

CONCLUSIONS

The authors proposed a novel immediate CTP assessment to score perfusion mismatch in emergency settings to guide clinicians' decision-making for aggressive treatment and to prevent stroke-related disability.

A physiological perspective of the associations between hydration status and CTP neuroimaging parameters in hyper-acute ischaemic stroke patients

Hypohydration may be associated with vascular diseases, poor prognosis and worse outcomes in stroke. The underlying mechanisms have not yet been completely investigated, although some studies suggested potential associations with brain perfusion and collaterals status. Despite the potentially different mechanisms promoting serum or urine biomarkers of hypohydration, few studies have investigated both markers separately. A prospective descriptive study was conducted in stroke patients admitted to a stroke unit <4.5 h from symptoms onset. All patients underwent neurological evaluation and whole-brain computed tomography perfusion (CTP) upon admission. Blood and urine samples were immediately collected at admission, and patients were defined as "hypohydrated" (HYP) if blood urea nitrogen-to-creatinine ratio was >15 and "underhydrated" (UND) if urine osmolality was >500 mOsm/kg. CTP images were processed to calculate core, penumbra, their mismatch and total hypoperfused volume. Forty-six patients were included and were grouped according to hydration status. Despite no different NIHSS at baseline, at CTP HYP was independently associated with core-penumbra mismatch (β: -0.157, 95% CI: -0.305 to -0.009; p = .04), while UND was independently associated with the total hypoperfused volume (β: 31.502, 95% CI: 8.522-54.481; p = .01). Using CTP imaging, this study proposes a physiological insight of some possible mechanisms associated with the better outcomes observed in acute stroke patients when properly hydrated. These results suggest different associations between hydration status and CTP parameters depending on serum or urine biomarkers in the hyper-acute phase and encourage the association between hydration status and stroke characteristics.

Tissue no-reflow despite full recanalization following thrombectomy for anterior circulation stroke with proximal occlusion: A clinical study

Despite early thrombectomy, a sizeable fraction of acute stroke patients with large vessel occlusion have poor outcome. The no-reflow phenomenon, i.e. impaired microvascular reperfusion despite complete recanalization, may contribute to such "futile recanalizations". Although well reported in animal models, no-reflow is still poorly characterized in man. From a large prospective thrombectomy database, we included all patients with intracranial proximal occlusion, complete recanalization (modified thrombolysis in cerebral infarction score 2c-3), and availability of both baseline and 24 h follow-up MRI including arterial spin labeling perfusion mapping. No-reflow was operationally defined as i) hypoperfusion ≥40% relative to contralateral homologous region, assessed with both visual (two independent investigators) and automatic image analysis, and ii) infarction on follow-up MRI. Thirty-three patients were eligible (median age: 70 years, NIHSS: 18, and stroke onset-to-recanalization delay: 208 min). The operational criteria were met in one patient only, consistently with the visual and automatic analyses. This patient recanalized 160 min after stroke onset and had excellent functional outcome. In our cohort of patients with complete and stable recanalization following thrombectomy for intracranial proximal occlusion, severe ipsilateral hypoperfusion on follow-up imaging associated with newly developed infarction was a rare occurrence. Thus, no-reflow may be infrequent in human stroke and may not substantially contribute to futile recanalizations.

Plasmin Generation Potential and Recanalization in Acute Ischaemic Stroke; an Observational Cohort Study of Stroke Biobank Samples

Rationale: More than half of patients who receive thrombolysis for acute ischaemic stroke fail to recanalize. Elucidating biological factors which predict recanalization could identify therapeutic targets for increasing thrombolysis success.

Hypothesis: We hypothesize that individual patient plasmin potential, as measured by in vitro response to recombinant tissue-type plasminogen activator (rt-PA), is a biomarker of rt-PA response, and that patients with greater plasmin response are more likely to recanalize early.

Methods: This study will use historical samples from the Barcelona Stroke Thrombolysis Biobank, comprised of 350 pre-thrombolysis plasma samples from ischaemic stroke patients who received serial transcranial-Doppler (TCD) measurements before and after thrombolysis. The plasmin potential of each patient will be measured using the level of plasmin-antiplasmin complex (PAP) generated after in-vitro addition of rt-PA. Levels of antiplasmin, plasminogen, t-PA activity, and PAI-1 activity will also be determined. Association between plasmin potential variables and time to recanalization [assessed on serial TCD using the thrombolysis in brain ischemia (TIBI) score] will be assessed using Cox proportional hazards models, adjusted for potential confounders.

Outcomes: The primary outcome will be time to recanalization detected by TCD (defined as TIBI ≥4). Secondary outcomes will be recanalization within 6-h and recanalization and/or haemorrhagic transformation at 24-h. This analysis will utilize an expanded cohort including ~120 patients from the Targeting Optimal Thrombolysis Outcomes (TOTO) study.

Discussion: If association between proteolytic response to rt-PA and recanalization is confirmed, future clinical treatment may customize thrombolytic therapy to maximize outcomes and minimize adverse effects for individual patients.

A CT perfusion based model predicts outcome in wake-up stroke patients treated with recombinant tissue plasminogen activator

OBJECTIVE

Advanced neuroimaging has proved to be pivotal in the management of acute ischemic stroke. The use of CT perfusion (CTP) core and penumbra parameters to predict the outcome in wake-up stroke (WUS) patients in everyday clinical scenarios has not yet been investigated. The aim of our study was to investigate the predictive power of CTP parameters on functional and morphological outcomes in WUS patients treated with recombinant tissue plasminogen activator (rTPA).

APPROACH

We analyzed clinical data and processed CTP images of 83 consecutive WUS patients treated with rTPA. The predictive power of whole-brain CTP features and of the clinical stroke-related parameters to predict the National Institutes of Health Stroke Scale (NIHSS) score at the seventh day and ischemic lesion volume outcome was investigated by means of multivariate regression analysis as well as least absolute shrinkage and selection operator (LASSO) modeling.

MAIN RESULTS

Multivariate analysis showed that CTP core volume (β = 0.403, p = 0.000), NIHSS at admission (β = 0.323, p = 0.005) and Alberta Stroke Program Early CT (ASPECT) score (β = -0.224, p = 0.012) predict NIHSS at 7 days, while total hypoperfused volume (β = 0.542, p = 0.000) and core volume on CTP (β =0.441, p = 0.000) predict infarct lesion volume at follow-up CT. The LASSO modeling approach confirmed the significant predictive power of CTP core volume, total hypoperfused CTP volume, NIHSS at baseline and ASPECT score, producing a sparse model with adequate reliability (the root mean square error on a previously unseen testing dataset was 3.68).

SIGNIFICANCE

Our findings highlight the importance of CT multimodal imaging features for decision-making and prediction in the hyperacute phase of WUS. The predictive model supports the hypothesis that an irreversible necrotic core rather than the extent of the penumbra is the main prognostic factor in WUS patients treated with rTPA.

The accuracy of ischemic core perfusion thresholds varies according to time to recanalization in stroke patients treated with mechanical thrombectomy: A comprehensive whole-brain computed tomography perfusion study

Computed tomography perfusion (CTP) allows the estimation of pretreatment ischemic core after acute ischemic stroke. However, CTP-derived ischemic core may overestimate final infarct volume. We aimed to evaluate the accuracy of CTP-derived ischemic core for the prediction of final infarct volume according to time from stroke onset to recanalization in 104 patients achieving complete recanalization after mechanical thrombectomy who had a pretreatment CTP and a 24-h follow-up MRI-DWI. A range of CTP thresholds was explored in perfusion maps at constant increments for ischemic core calculation. Time to recanalization modified significantly the association between ischemic core and DWI lesion in a non-linear fashion (p-interaction = 0.018). Patients with recanalization before 4.5 h had significantly lower intraclass correlation coefficient (ICC) values between CTP-predicted ischemic core and DWI lesion (n = 54; best threshold relative cerebral blood flow (rCBF) < 25%, ICC = 0.673, 95% CI = 0.495-0.797) than those with later recanalization (n = 50; best threshold rCBF < 30%, ICC = 0.887, 95% CI = 0.811-0.935, p = 0.013), as well as poorer spatial lesion agreement. The significance of the associations between CTP-derived ischemic core and clinical outcome at 90 days was lost in patients recanalized before 4.5 h. CTP-derived ischemic core must be interpreted with caution given its dependency on time to recanalization, primarily in patients with higher chances of early recanalization.

Mechanical recanalization for acute bilateral cerebral artery occlusion - literature overview with a case

Background

Acute bilateral internal carotid artery (ICA) and/or middle cerebral artery (MCA) occlusion is extremely rare and associated with poor clinical outcomes. There are only a few reports in the literature about mechanical thrombectomy being performed for acute bilateral occlusions. The treatment strategies and prognoses (clinical outcomes) are therefore unclear.

Methods

A systematic review of the literature was performed through several electronic databases with the following search terms: acute bilateral stroke, mechanical recanalization and thrombectomy.

Results

In the literature, we identified five reports of six patients with bilateral ICA and/or MCA occlusion treated with mechanical recanalization. Additionally, we report our experience with a subsequent contralateral large brain artery occlusion during intravenous thrombolytic therapy, where the outcome after mechanical thrombectomy was not dependent on the time from stroke onset but rather on the capacity of collateral circulation exclusively.

Conclusions

Acute bilateral cerebral (ICA and/or MCA) occlusion leads to sudden severe neurological deficits (comas) with unpredicted prognoses, even when mechanical recanalization is available. As the collateral capacity seems to be more important than the absolute time to flow restoration in determining the outcomes, simultaneous thrombectomy by itself probably does not lead to improved functional outcomes.

Factors delaying intravenous thrombolytic therapy in acute ischaemic stroke: a systematic review of the literature

BACKGROUND/AIMS

This review examined factors that delay thrombolysis and what management strategies are currently employed to minimise this delay, with the aim of suggesting future directions to overcome bottlenecks in treatment delivery.

METHODS

A systematic review was performed according to PRISMA guidelines. The search strategy included a combination of synonyms and controlled vocabularies from Medical Subject Headings (MeSH) and EmTree covering brain ischemia, cerebrovascular accident, fibrinolytic therapy and Alteplase. The search was conducted using Medline (OVID), Embase (OVID), PubMed and Cochrane Library databases using truncations and Boolean operators. The literature search excluded review articles, trial protocols, opinion pieces and case reports. Inclusion criteria were: (1) The article directly related to thrombolysis in ischaemic stroke, and (2) The article examined at least one factor contributing to delay in thrombolytic therapy.

RESULTS

One hundred and fifty-two studies were included. Pre-hospital factors resulted in the greatest delay to thrombolysis administration. In-hospital factors relating to assessment, imaging and thrombolysis administration also contributed. Long onset-to-needle times were more common in those with atypical, or less severe, symptoms, the elderly, patients from lower socioeconomic backgrounds, and those living alone. Various strategies currently exist to reduce delays. Processes which have achieved the greatest improvements in time to thrombolysis are those which integrate out-of-hospital and in-hospital processes, such as the Helsinki model.

CONCLUSION

Further integrated processes are required to maximise patient benefit from thrombolysis. Expansion of community education to incorporate less common symptoms and provision of alert pagers for patients may provide further reduction in thrombolysis times.

Interpreting CT perfusion in stroke

CT perfusion images can be rapidly obtained on all modern CT scanners and easily incorporated into an acute stroke imaging protocol. Here we discuss the technique of CT perfusion imaging, how to interpret the data and how it can contribute to the diagnosis of acute stroke and selection of patients for treatment. Many patients with acute stroke are excluded from reperfusion therapy if the onset time is not known or if they present outside of traditional treatment time windows. There is a growing body of evidence supporting the use of perfusion imaging in these patients to identify patterns of brain perfusion that are favourable for recanalisation therapy.