A trial of imaging selection and endovascular treatment for ischemic stroke

The exact science of stroke thrombolysis and the quiet art of patient selection

The science of metric-based patient stratification for intravenous thrombolysis, revolutionized by the landmark National Institute of Neurological Disorders and Stroke trial, has transformed acute ischaemic stroke therapy. Recanalization of an occluded artery produces tissue reperfusion that unequivocally improves outcome and function in patients with acute ischaemic stroke. Recanalization can be achieved mainly through intravenous thrombolysis, but other methods such as intra-arterial thrombolysis or mechanical thrombectomy can also be employed. Strict guidelines preclude many patients from being treated by intravenous thrombolysis due to the associated risks. The quiet art of informed patient selection by careful assessment of patient baseline factors and brain imaging could increase the number of eligible patients receiving intravenous thrombolysis. Outside of the existing eligibility criteria, patients may fall into therapeutic 'grey areas' and should be evaluated on a case by case basis. Important factors to consider include time of onset, age, and baseline blood glucose, blood pressure, stroke severity (as measured by National Institutes of Health Stroke Scale) and computer tomography changes (as measured by Alberta Stroke Programme Early Computed Tomography Score). Patients with traditional contraindications such as wake-up stroke, malignancy or dementia may have the potential to receive benefit from intravenous thrombolysis if they have favourable predictors of outcome from both clinical and imaging criteria. A proportion of patients experience complications or do not respond to intravenous thrombolysis. In these patients, other endovascular therapies or a combination of both may be used to provide benefit. Although an evidence-based approach to intravenous thrombolysis for acute ischaemic stroke is pivotal, it is imperative to examine those who might benefit outside of protocol-driven practice.

Simple variables predict miserable outcome after intravenous thrombolysis

BACKGROUND AND PURPOSE

To test the predictability of miserable outcome amongst ischaemic stroke patients receiving intravenous thrombolysis (IVT) based on a simple variables model (SVM) and to compare the model's predictive performance with that of an existing score which includes imaging and laboratory parameters (DRAGON).

METHODS

The SVM consists of the parameters age, independence before stroke, normal Glasgow coma verbal score, able to lift arms and able to walk. In a derivation cohort (n = 1346) and a validation cohort (n = 638) of consecutive IVT-treated stroke patients, the probability estimated by SVM and the observed occurrence of miserable 3-month outcome (modified Rankin score 5-6) were compared. The performances of SVM and the DRAGON score were compared. The area under the receiver operating curve (AUC) (95% confidence interval, CI) and the bootstrapping approach were used to compare the predictive performance.

RESULTS

The AUCs to predict miserable outcome in the derivation cohort were 0.807 (95% CI 0.774-0.838) using the SVM and 0.822 (0.790-0.850) using the DRAGON score (P = 0.3). For the validation cohort, AUCs were 0.786 (0.742-0.829) for the SVM and 0.809 (0.774-0.845) for the DRAGON score (P = 0.23). Only one patient with an SVM probability of >70% for miserable outcome in either cohort had a good outcome whilst 83% had a miserable outcome. An online SVM calculator to estimate the probability of miserable outcome for individual patients is available under http://www.unispital-basel.ch/SVM-Tool.

CONCLUSION

The SVM was similar in accuracy to the DRAGON score for predicting miserable outcome after IVT. As these simple variables are available already at the pre-hospital stage, the SVM may facilitate and accelerate pre-hospital triage of patients at high risk for miserable outcome after IVT towards endovascular treatment.

Good outcome rate of 35% in IV-tPA-treated patients with computed tomography angiography confirmed severe anterior circulation occlusive stroke

BACKGROUND AND PURPOSE

To determine the effect of intravenous tissue plasminogen activator (IV-tPA) on outcomes in patients with severe major anterior circulation ischemic stroke.

METHODS

Prospectively, 649 patients with acute stroke had admission National Institutes of Health stroke scale (NIHSS) scores, noncontrast computed tomography (CT), CT angiography (CTA), and 6-month outcome assessed using modified Rankin scale. IV-tPA treatment decisions were made before CTA, at the time of noncontrast CT scanning, as per routine clinical protocol. Severe symptoms were defined as NIHSS>10. Poor outcome was defined as modified Rankin scale >2. Major occlusions were identified on CTA. Univariate and multivariate stepwise-forward logistic regression analyses of the full cohort were performed.

RESULTS

Of 649 patients, 188 (29%) patients presented with NIHSS>10, and 64 out of 188 (34%) patients received IV-tPA. Admission NIHSS, large artery occlusion, and IV-tPA all independently predicted good outcomes; however, a significant interaction existed between IV-tPA and occlusion (P<0.001). Of the patients who presented with NIHSS>10 with anterior circulation occlusion, twice the percentage had good outcomes if they received IV-tPA (17 out of 49 patients, 35%) than if they did not (13 out of 77 patients, 17%; P=0.031). The number needed to treat was 7 (95% confidence interval, 3-60).

CONCLUSIONS

IV-tPA treatment resulted in significantly better outcomes in patients with severely symptomatic stroke with major anterior circulation occlusions. The 35% good outcome rate was similar to rates found in endovascular therapy trials. Vascular imaging may help in patient selection and stratification for trials of IV-thrombolytic and endovascular therapies.

Quantitative analysis of hypoperfusion in acute stroke: arterial spin labeling versus dynamic susceptibility contrast

BACKGROUND AND PURPOSE

This study compares the concordance between arterial spin labeling (ASL) and dynamic susceptibility contrast (DSC) for the identification of regional hypoperfusion and diffusion-perfusion mismatch tissue classification using a quantitative method.

METHODS

The inclusion criteria for this retrospective study were as follows: patients with acute ischemic syndrome with symptom onset <24 hours and acquisition of both ASL and DSC MR perfusion. The volumes of infarction and hypoperfused lesions were calculated on ASL and DSC multi-parametric maps. Patients were classified into reperfused, matched, or mismatch groups using time to maximum >6 sec as the reference. In a subset of patients who were successfully recanalized, the identical analysis was performed and the infarction and hypoperfused lesion volumes were used for paired pre- and posttreatment comparisons.

RESULTS

Forty-one patients met our inclusion criteria. Twenty patients underwent successful endovascular revascularization (TICI>2a), resulting in a total of 61 ASL-DSC data pairs for comparison. The hypoperfusion volume on ASL-cerebral blood flow best approximated the DSC-time to peak volume (r=0.83) in pretreatment group and time to maximum (r=0.46) after recanalization. Both ASL-cerebral blood flow and DSC-TTP overestimated the hypoperfusion volume compared with time to maximum volume in pretreatment (F=27.41, P<0.0001) and recanalized patients (F=8.78, P<0.0001).

CONCLUSIONS

ASL-cerebral blood flow overestimates the DSC time to maximum hypoperfusion volume and mismatch classification in patients with acute ischemic syndrome. Continued overestimation of hypoperfused volume after recanalization suggests flow pattern and velocity changes in addition to arterial transit delay can affects the performance of ASL.

Imaging recommendations for acute stroke and transient ischemic attack patients: a joint statement by the American Society of Neuroradiology, the American College of Radiology and the Society of NeuroInterventional Surgery

In the article entitled "Imaging Recommendations for Acute Stroke and Transient Ischemic Attack Patients: A Joint Statement by the American Society of Neuroradiology, the American College of Radiology and the Society of NeuroInterventional Surgery", we are proposing a simple, pragmatic approach that will allow the reader to develop an optimal imaging algorithm for stroke patients at their institution.

Optimizing prediction scores for poor outcome after intra-arterial therapy in anterior circulation acute ischemic stroke

BACKGROUND AND PURPOSE

Intra-arterial therapy (IAT) promotes recanalization of large artery occlusions in acute ischemic stroke. Despite high recanalization rates, poor clinical outcomes are common. We attempted to optimize a score that combines clinical and imaging variables to more accurately predict poor outcome after IAT in anterior circulation occlusions.

METHODS

Patients with acute ischemic stroke undergoing IAT at University of Texas (UT) Houston for large artery occlusions (middle cerebral artery or internal carotid artery) were reviewed. Independent predictors of poor outcome (modified Rankin Scale, 4-6) were studied. External validation was performed on IAT-treated patients at Emory University.

RESULTS

A total of 163 patients were identified at UT Houston. Independent predictors of poor outcome (P≤0.2) were identified as score variables using sensitivity analysis and logistic regression. Houston Intra-Arterial Therapy 2 (HIAT2) score ranges 0 to 10: age (≤59=0, 60-79=2, ≥80 years=4), glucose (<150=0, ≥150=1), National Institute Health Stroke Scale (≤10=0, 11-20=1, ≥21=2), the Alberta Stroke Program Early CT Score (8-10=0, ≤7=3). Patients with HIAT2≥5 were more likely to have poor outcomes at discharge (odds ratio, 6.43; 95% confidence interval, 2.75-15.02; P<0.001). After adjusting for reperfusion (Thrombolysis in Cerebral Infarction score≥2b) and time from symptom onset to recanalization, HIAT2≥5 remained an independent predictor of poor outcome (odds ratio, 5.88; 95% confidence interval, 1.96-17.64; P=0.02). Results from the cohort of Emory (198 patients) were consistent; patients with HIAT2 score≥5 had 6× greater odds of poor outcome at discharge and at 90 days. HIAT2 outperformed other previously published predictive scores.

CONCLUSIONS

The HIAT2 score, which combines clinical and imaging variables, performed better than all previous scores in predicting poor outcome after IAT for anterior circulation large artery occlusions.

Refining angiographic biomarkers of revascularization: improving outcome prediction after intra-arterial therapy

BACKGROUND AND PURPOSE

Angiographic revascularization grading after intra-arterial stroke therapy is limited by poor standardization, making it unclear which scale is optimal for predicting outcome. Using recently standardized criteria, we sought to compare the prognostic performance of 2 commonly used reperfusion scales.

METHODS

Inclusion criteria for this multicenter retrospective study were acute ischemic stroke attributable to middle cerebral artery M1 occlusion, intra-arterial therapy, and 90-day modified Rankin scale score. Post-intra-arterial therapy reperfusion was graded using the Thrombolysis in Myocardial Infarction (TIMI) and Modified Thrombolysis in Cerebral Infarction (mTICI) scales. The scales were compared for prediction of clinical outcome using receiver-operating characteristic analysis.

RESULTS

Of 308 patients, mean age was 65 years, and median National Institutes of Health Stroke Scale score was 17. The mean time from stroke onset to groin puncture was 305 minutes. There was no difference in the time to treatment between patients grouped by final TIMI (ie, 0 versus 1 versus 2 versus 3) or mTICI grades (ie, 0 versus 1 versus 2a versus 2b versus 3). Good outcome (modified Rankin scale, 0-2) was achieved in 32.5% of patients, and mortality rate was 25.3% at 90 days. There was a 6.3% rate of parenchymal hematoma type 2. In receiver-operating characteristic analysis, mTICI was superior to TIMI for predicting 90-day modified Rankin scale 0 to 2 (c-statistic: 0.74 versus 0.68; P<0.0001). The optimal threshold for identifying a good outcome was mTICI 2b to 3 (sensitivity 78.0%; specificity 66.1%).

CONCLUSIONS

mTICI is superior to TIMI for predicting clinical outcome after intra-arterial therapy. mTICI 2b to 3 is the optimal biomarker for procedural success.

Imaging recommendations for acute stroke and transient ischemic attack patients: A joint statement by the American Society of Neuroradiology, the American College of Radiology, and the Society of NeuroInterventional Surgery

SUMMARY

Stroke is a leading cause of death and disability worldwide. Imaging plays a critical role in evaluating patients suspected of acute stroke and transient ischemic attack, especially before initiating treatment. Over the past few decades, major advances have occurred in stroke imaging and treatment, including Food and Drug Administration approval of recanalization therapies for the treatment of acute ischemic stroke. A wide variety of imaging techniques has become available to assess vascular lesions and brain tissue status in acute stroke patients. However, the practical challenge for physicians is to understand the multiple facets of these imaging techniques, including which imaging techniques to implement and how to optimally use them, given available resources at their local institution. Important considerations include constraints of time, cost, access to imaging modalities, preferences of treating physicians, availability of expertise, and availability of endovascular therapy. The choice of which imaging techniques to employ is impacted by both the time urgency for evaluation of patients and the complexity of the literature on acute stroke imaging. Ideally, imaging algorithms should incorporate techniques that provide optimal benefit for improved patient outcomes without delaying treatment.

Management of acute ischemic stroke

Stroke is one of the most common causes of morbidity and mortality in hospitalized patients in the United States. A proper understanding of stroke mechanisms helps to guide specific case management. The only therapy approved by the US Food and Drug Administration for the management of acute ischemic stroke is initiation of intravenous recombinant tissue plasminogen activator within 3 hours of symptom onset. Other treatment options include intra-arterial recombinant tissue plasminogen activator, mechanical thrombectomy, clot retrieval, or a combination of these approaches. In this article, we provide an evidence-based review of the diagnostic approach for acute ischemic stroke, including recognizing common stroke mimics. We detail the initial medical management of acute stroke and the medical and surgical therapeutic interventions for patients who have sustained acute ischemic stroke.

Effectiveness of alteplase in the very elderly after acute ischemic stroke

Alteplase has traditionally been the only pharmacologic agent available for treating acute ischemic stroke worldwide, and is considered an effective and safe therapeutic drug for acute cerebral ischemia. However, the drug is usually indicated for use in patients aged <81 years due to insufficient literature regarding the drug’s safety in older individuals. Nevertheless, the elderly can benefit from alteplase after they experience an acute ischemic stroke. Age differences have been observed in the clinical presentation of acute ischemic stroke; however, the safety and efficacy of alteplase for patients with acute ischemic stroke do not depend on age or sex. Evidence of an increasing rate of intracerebral hemorrhage among the elderly with acute ischemic stroke, following alteplase treatment, has not been reported. Severe intracranial hemorrhage is a known side effect of alteplase but is not associated with age in patients with acute ischemic stroke. Alteplase can be used safely and effectively to treat elderly patients who suffer an acute ischemic stroke, including those over the age of 80 years.

Importance of cerebral artery recanalization in patients with stroke with and without neurological improvement after intravenous thrombolysis

BACKGROUND AND PURPOSE

Recanalization status after intravenous thrombolysis (IVT) in patients with ischemic stroke is a reference point to proceed with a rescue reperfusion intervention, although early neurological improvement (NI) may preclude endovascular procedures. We aimed to evaluate the importance of restoration of blood flow at the arterial occlusion site in subgroups of patients with stroke stratified by early NI after IVT.

METHODS

The following patients were recruited from the Safe Implementation of Treatment in Stroke-International Stroke Thrombolysis Register: (1) with baseline vessel occlusion documented by computed tomographic (CT) or magnetic resonance (MR) angiography and follow-up angioimaging between 22 and 36 hours after IVT available; and (2) with dense cerebral artery sign on admission CT scan and results of follow-up CT reported. Recanalization at 24 hours was defined as absence of vessel occlusion or as resolution of dense cerebral artery sign on follow-up 22- to 36-hour imaging. NI was assessed at 2 hours and 24 hours after IVT and was defined as improvement by 20% from baseline National Institute of Health Stroke scale score. Primary outcome measure was independence, defined as modified Rankin scale score 0 to 2 after 3 months.

RESULTS

Of 28136 cases registered between December 2003 and November 2009, 5324 cases (19%) met the inclusion criteria. Patients with both NI at 2 hours post-treatment and vessel recanalization had the best chances to achieve independence at 3 months (adjusted odds ratio, 15.8; 95% confidence interval, 12.5-20.0), followed by those who had NI despite persistent occlusion (adjusted odds ratio, 4.7; 95% confidence interval, 3.6-6.1); and those without NI despite recanalization (adjusted odds ratio, 2.7; 95% confidence interval, 2.2-3.3).

CONCLUSIONS

Recanalization of an occluded artery in acute stroke is associated with favorable functional outcome both in patients with and without NI after IVT. In future evaluations of mechanical thrombectomy and other additional strategies, recanalization should be considered in patients with persisting occlusion after IVT even after significant NI.

Acute stroke imaging: recent updates

Acute ischemic stroke imaging is one of the leading causes of death and disability worldwide. Neuroimaging plays a crucial role in early diagnosis and yields essential information regarding tissue integrity, a factor that remains a key therapeutic determinant. Given the widespread public health implications of stroke and central role of neuroimaging in overall management, acute stroke imaging remains a heavily debated, extensively researched, and rapidly evolving subject. There has been recent debate in the scientific community due to divided opinions on the use of CT perfusion and access-related limitations of MRI. In this paper we review and summarize recent updates relevant to acute stroke imaging and propose an imaging paradigm based on the recently available evidence.

Levine SR, Khatri P, Broderick JP, Grotta JC, Kasner SE, Kim D, Meyer BC, Panagos P, Romano J, Scott P. Review, historical context, and clarifications of the NINDS rt-PA stroke trials exclusion criteria: Part 1: rapidly improving stroke symptoms

BACKGROUND AND PURPOSE

Since Food and Drug Administration approval of intravenous tissue-type plasminogen activator (tPA) for treatment of acute ischemic stroke in 1996, it has become clear that several criteria used for exclusion from therapy were not based on actual data or operationally defined for use in clinical practice. All eligibility criteria from the National Institute of Neurological Disorders and Stroke (NINDS) recombinant tPA Stroke Study were adopted within the alteplase package insert as contraindications/warnings. Many clinicians have expressed the need for clarification and better definition of these treatment criteria.

METHODS

A group of investigators who also practice as stroke physicians convened a collaborative endeavor to work toward developing more clinically meaningful and consensus-driven exclusion criteria for intravenous tPA. The first of these exclusion criteria chosen was rapidly improving stroke symptoms (RISS). We reviewed and clarified the historical context and intention with the original investigators, held e-mail discussions, convened an in-person RISS Summit, and obtained the understanding of experienced stroke physicians broadly.

RESULTS

Historically, the intent of this exclusion criterion within the NINDS recombinant tPA Stroke Trial was to avoid treatment of transient ischemic attacks-who would have recovered completely without treatment. There was unanimous consensus that, in the absence of other contraindications, patients who experience improvement of any degree, but have a persisting neurological deficit that is potentially disabling, should be treated with intravenous tPA. This statement is supported from the methods established for the original NINDS trial, on the basis of detailed discussions and interviews with the former NINDS trialists. It was agreed that improvement should only be monitored for the extent of time needed to prepare and administer the intravenous tPA bolus/infusion. An explicit operational definition of RISS was developed by consensus to guide future decision making in acute stroke. There was unanimous agreement that all neurological deficits present at the time of the treatment decision should be considered in the context of individual risk and benefit, as well as the patient's baseline functional status.

CONCLUSIONS

A structured framework and quantitative approach toward defining RISS emerged through expert opinion and consensus. The term, RISS, should be reserved for those who improve to a mild deficit, specifically one which is perceived to be nondisabling. This is recommended to guide decision making on intravenous tPA eligibility going forward, including the design of future studies. An additional study of patients with rapid improvement to nonmild deficits is not justified because these patients should be treated.

Quantification of errors in ordinal outcome scales using shannon entropy: effect on sample size calculations

Objective

Clinical trial outcomes often involve an ordinal scale of subjective functional assessments but the optimal way to quantify results is not clear. In stroke, the most commonly used scale, the modified Rankin Score (mRS), a range of scores (“Shift”) is proposed as superior to dichotomization because of greater information transfer. The influence of known uncertainties in mRS assessment has not been quantified. We hypothesized that errors caused by uncertainties could be quantified by applying information theory. Using Shannon’s model, we quantified errors of the “Shift” compared to dichotomized outcomes using published distributions of mRS uncertainties and applied this model to clinical trials.

Methods

We identified 35 randomized stroke trials that met inclusion criteria. Each trial’s mRS distribution was multiplied with the noise distribution from published mRS inter-rater variability to generate an error percentage for “shift” and dichotomized cut-points. For the SAINT I neuroprotectant trial, considered positive by “shift” mRS while the larger follow-up SAINT II trial was negative, we recalculated sample size required if classification uncertainty was taken into account.

Results

Considering the full mRS range, error rate was 26.1%±5.31 (Mean±SD). Error rates were lower for all dichotomizations tested using cut-points (e.g. mRS 1; 6.8%±2.89; overall p<0.001). Taking errors into account, SAINT I would have required 24% more subjects than were randomized.

Conclusion

We show when uncertainty in assessments is considered, the lowest error rates are with dichotomization. While using the full range of mRS is conceptually appealing, a gain of information is counter-balanced by a decrease in reliability. The resultant errors need to be considered since sample size may otherwise be underestimated. In principle, we have outlined an approach to error estimation for any condition in which there are uncertainties in outcome assessment. We provide the user with programs to calculate and incorporate errors into sample size estimation.

Efficacy of peripheral interventional radiologists performing endovascular stroke therapy guided by CT perfusion triage of patients

PURPOSE

To assess safety and efficacy of intraarterial mechanical thrombectomy for treatment of ischemic stroke in a community hospital by peripheral interventional radiologists employing computed tomography (CT) perfusion imaging for patient selection.

MATERIALS AND METHODS

Forty patients, 11 men (27.5%) and 29 women (72.5%), were treated between February 2008 and October 2011. Eligible patients had a National Institutes of Health Stroke Scale (NIHSS) score greater than 8 and diagnosis of large-vessel ischemic stroke by head CT angiogram, and met previously reported CT perfusion imaging triage criteria.

RESULTS

The baseline NIHSS score was 18.0 ± 7.9 (range, 8-35). Sixteen patients (40%) had a baseline NIHSS score greater than 20. Symptom onset was unknown in five patients. Symptom onset to device time in the remaining 35 patients was 254.8 minutes ± 150.9 (range, 75-775 min). A total of 65% of patients showed thrombolysis in cerebral infarction (TICI) 2a, 2b, or 3 flow following the procedure. Symptomatic intracranial hemorrhage was seen in four patients (10.0%). At 90 days, 32 patients (80%) were alive and eight (20%) had died. The modified Rankin scale (mRS) score at 90 days was no more than 2 in 20 patients (50.0%). The mean mRS score at 90 days was 2.9 ± 2.0 (range, 0-6). NIHSS score at 90 days was 5.1 ± 6.1 (range, 0-24). In patients with successful recanalization (ie, TICI 2 or 3 flow), a good clinical outcome (ie, mRS score ≤ 2) was achieved in 65.3% of patients (mean, 2.4 ± 1.9; range, 0-6), and 90-day mortality rate was 15.4%, compared with 28.6% in patients with TICI 0/1 flow.

CONCLUSIONS

Peripheral interventional radiologists who use CT perfusion imaging for patient triage can have good neurologic outcomes and provide sustainable, safe, and complete around-the-clock coverage for endovascular stroke treatment.

Status of endovascular interventions to treat acute ischemic stroke

OPINION STATEMENT

Acute stroke is a major component of neurology and one of few neurologic emergencies. Despite many efforts to increase treatment of acute ischemic stroke, we are still not able to treat a significant percentage of patients with intravenous tPA, typically because of time restrictions. Unfortunately, many patients do not present to medical attention within the short window for tPA administration. In addition, there are numerous contraindications for tPA, which make more patients ineligible. Endovascular treatment for acute ischemic stroke may help to expand the number of patients treated by extending the time window beyond the 3 to 4.5 hour constraints of IV tPA, and including patients with tPA contraindications such as use of oral anticoagulants. However, several recent studies have raised questions regarding the utility and efficacy of these procedures. These studies should not discourage endovascular treatment of acute stroke, but should lead us to ask more questions and be proactive in seeking answers, and should make us carefully select the patient population to receive the treatment. Future studies should take advantage of the lessons learned from these recent trials, including the importance of using vascular imaging for inclusion criteria, and of utilizing the latest and most advanced devices and techniques. Endovascular therapy will continue to evolve into what will hopefully be a clinically significant alternative therapy for acute ischemic stroke.

Use of perfusion imaging and other imaging techniques to assess risks/benefits of acute stroke interventions

The advent of multimodal neuroimaging has provided acute stroke care providers with an armamentarium of sophisticated imaging options to utilize for guidance in clinical decision-making and management of acute ischemic stroke patients. Here, we propose a framework and potential algorithm-based methodology for imaging modality selection and utilization for the purpose of achieving optimal stroke clinical care. We first review imaging options that may best inform decision-making regarding revascularization eligibility, with a focus on the imaging modalities that best identify critical inclusion and exclusion criteria. Next, we review imaging methods that may guide the successful achievement of revascularization once it has been deemed desirable and feasible. Further, we review imaging modalities that may best assist in both the noninterventional care of acute stroke as well as the identification of stroke-mimics. Finally, we review imaging techniques under current investigation that show promise to improve future acute stroke management.

Acute stroke management in patients with known or suspected atrial fibrillation

Atrial fibrillation (AF) is an important cause of ischemic stroke, especially in older individuals. Strokes attributed to AF are often large and result in a high rate of fatality. The new oral anticoagulants offer advantages over warfarin in terms of dosing, pharmacokinetic characteristics, and lower rates of intracranial hemorrhage, but pose new management questions for physicians treating these patients. The management of acute stroke is not modified by the presence of AF, but is unique with respect to management of anticoagulation in the hyperacute and acute phases. We will review and discuss acute treatment options in anticoagulated patients with ischemic stroke, anticoagulation discontinuation, and timing of initiation with old and new oral anticoagulants, and managing intracranial hemorrhage in anticoagulated patients. We will end by briefly discussing investigations of stroke patients with suspected cardioembolic stroke.

Trials of endovascular therapies or collaterals?

Several landmark clinical trials of endovascular therapy for acute ischemic stroke have recently jolted the concerted multidisciplinary efforts to develop effective revascularization strategies. Further consideration of these four endovascular stroke trials published in the last year suggests a more fundamental question: are these trials of specific treatments or have the results simply reflected the importance of underlying pathophysiology? Data from IMS III, MR RESCUE, SWIFT and TREVO2 consistently demonstrate the dramatic impact of collateral perfusion in acute ischemic stroke. Such collateral, or parallel, trials of the underlying pathophysiology in stroke reveal that diagnosis or selection of optimal candidates may be paramount to the specific drug or device therapy. Future trials of endovascular therapies may harness the influential role of collaterals as critical selection criteria for intervention, with triage based on imaging rather than time alone. Treating the optimal patient may be more important than chasing an elusive magical therapy.

Review of stroke thrombolytics

The cornerstone of acute ischemic stroke treatment relies on rapid clearance of an offending thrombus in the cerebrovascular system. There are various drugs and different methods of assessment to select patients more likely to respond to treatment. Current clinical guidelines recommend the administration of intravenous alteplase (following a brain noncontract CT to exclude hemorrhage) within 4.5 hours of stroke onset. Because of the short therapeutic time window, the risk of hemorrhage, and relatively limited efficacy of alteplase for large clot burden, research is ongoing to find more effective and safer reperfusion therapy, as well as focussing on refinement of patient selection for acute reperfusion treatment. Studies using advanced imaging (incorporating perfusion CT or diffusion/perfusion MRI) may allow us to use thrombolytics, or possibly endovascular therapy, in an extended time window. Recent clinical trials have suggested that Tenecteplase, used in conjunction with advanced imaging selection, resulted in more effective reperfusion than alteplase, which translated into increased clinical benefit. Studies using Desmoteplase have suggested its potential benefit in a sub-group of patients with large artery occlusion and salveageable tissue, in an extended time window. Other ways to improve acute reperfusion approaches are being actively explored, including endovascular therapy, and the enhancement of thrombolysis by ultrasound insonation of the clot (sono-thrombolysis).

Magnetic resonance imaging of ischemia viability thresholds and the neurovascular unit

Neuroimaging has improved our understanding of the evolution of stroke at discreet time points helping to identify irreversibly damaged and potentially reversible ischemic brain. Neuroimaging has also contributed considerably to the basic premise of acute stroke therapy which is to salvage some portion of the ischemic region from evolving into infarction, and by doing so, maintaining brain function and improving outcome. The term neurovascular unit (NVU) broadens the concept of the ischemic penumbra by linking the microcirculation with neuronal-glial interactions during ischemia reperfusion. Strategies that attempt to preserve the individual components (endothelium, glia and neurons) of the NVU are unlikely to be helpful if blood flow is not fully restored to the microcirculation. Magnetic resonance imaging (MRI) is the foremost imaging technology able to bridge both basic science and the clinic via non-invasive real time high-resolution anatomical delineation of disease manifestations at the molecular and ionic level. Current MRI based technologies have focused on the mismatch between perfusion-weighted imaging (PWI) and diffusion weighted imaging (DWI) signals to estimate the tissue that could be saved if reperfusion was achieved. Future directions of MRI may focus on the discordance of recanalization and reperfusion, providing complimentary pathophysiological information to current compartmental paradigms of infarct core (DWI) and penumbra (PWI) with imaging information related to cerebral blood flow, BBB permeability, inflammation, and oedema formation in the early acute phase. In this review we outline advances in our understanding of stroke pathophysiology with imaging, transcending animal stroke models to human stroke, and describing the potential translation of MRI to image important interactions relevant to acute stroke at the interface of the neurovascular unit.

Magnetic resonance imaging to visualize stroke and characterize stroke recovery: a review

The global burden of stroke continues to grow. Although stroke prevention strategies (e.g., medications, diet, and exercise) can contribute to risk reduction, options for acute interventions (e.g., thrombolytic therapy for ischemic stroke) are limited to the minority of patients. The remaining patients are often left with profound neurological disabilities that substantially impact quality of life, economic productivity, and increase caregiver burden. In the last decade, however, the future outlook for such patients has been tempered by movement toward the view that the brain is capable of reorganizing after injury. Many now view brain recovery after stroke as an area of scientific research with large potential for therapeutic advances, far into the future (Broderick and William, 2004). As a probe of brain anatomy, function and physiology, magnetic resonance imaging (MRI) is a non-invasive and highly versatile modality that promises to play a particularly important role in such research. Here we provide a basic review of MRI physical principles and applications for assessing stroke, looking toward the future role MRI may play in improving stroke rehabilitation methods and stroke recovery.