Greater effect of stroke thrombolysis in the presence of arterial obstruction

Clinical efficacy of tirofiban combined with a Solitaire stent in treating acute ischemic stroke

This study explores the safety and effect of acute cerebral infarction treatment by microcatheter injection of tirofiban combined with a Solitaire AB stent and/or stent implantation. Emergency cerebral angiograms showing the responsible vascular occlusion of 120 acute cerebral infarction patients who underwent emergency endovascular thrombectomy were included in the study. These patients were randomly divided into two groups using the random number table method: treatment group (n=60) that received thrombectomy (with cerebral artery stents) combined with intracerebral injection of tirofiban and control group (n=60) that only received thrombectomy (with cerebral artery stents alone). The baseline data, cerebral angiography before and after surgery, hospitalization, and follow-up results of patients in these two groups were compared. Furthermore, the incidence of major adverse cerebrovascular events of these two groups was compared (90-day modified Rankin scale, a score of 0–2 indicates a good prognosis). The difference between baseline clinical data and brain angiography between these two groups was not statistically significant. Patients in the treatment group had a higher prevalence of thrombolysis in cerebral infarction grade 2b/3 than patients in the control group (88.3% (53/60) vs 66.7% (40/60), P=0.036). Moreover, the National Institutes of Health Stroke Scale scores 7 days after surgery and the 90-day prognosis were all better for the patients who received tirofiban (P=0.048 and P=0.024). Mechanical thrombectomy with Solitaire AB stents in combination with the injection of tirofiban through a microcatheter appears to be safe and effective for the endovascular treatment of acute ischemic stroke.

Effect of stroke thrombolysis predicted by distal vessel occlusion detection

OBJECTIVE

Among ischemic stroke patients with negative CT angiography (CTA), we aimed to determine the predictive value of enhanced distal vessel occlusion detection using CT perfusion postprocessing (waveletCTA) for the treatment effect of IV thrombolysis (IVT).

METHODS

Patients were selected from 1,851 consecutive patients who had undergone CT perfusion. Inclusion criteria were (1) significant cerebral blood flow (CBF) deficit, (2) no occlusion on CTA, and (3) infarction confirmed on follow-up. Favorable morphologic response was defined as smaller values of final infarction volume divided by initial CBF deficit volume (FIV/CBF). Favorable functional outcome was defined as modified Rankin Scale score of ≤2 after 90 days and decrease in NIH Stroke Scale score of ≥3 from admission to 24 hours (∆NIHSS).

RESULTS

Among patients with negative CTA (n = 107), 58 (54%) showed a distal occlusion on waveletCTA. There was no difference between patients receiving IVT (n = 57) vs supportive care (n = 50) regarding symptom onset, early ischemic changes, perfusion mismatch, or admission NIHSS score (all p > 0.05). In IVT-treated patients, the presence of an occlusion was an independent predictor of a favorable morphologic response (FIV/CBF: β -1.43; 95% confidence interval [CI] -1.96, -0.83; p = 0.001) and functional outcome (90-day modified Rankin Scale: odds ratio 7.68; 95% CI 4.33-11.51; p = 0.039; ∆NIHSS: odds ratio 5.76; 95% CI 3.98-8.27; p = 0.013), while it did not predict outcome in patients receiving supportive care (all p > 0.05).

CONCLUSION

In stroke patients with negative CTA, distal vessel occlusions as detected by waveletCTA are an independent predictor of a favorable response to IVT.

Treatment of stroke with early imaging and revascularization: when to be aggressive?

Neuroimaging has a key role in the assessment and treatment of acute stroke. Cerebral computer tomography is the first step to differentiate hemorragic from ischemic stroke and to detect, in the latter, early signs representative of the lesion severity and predicting a possible hemorrhagic infarction after thrombolytic treatment.Advanced neuroimaging techniques are relevant in the assessment of the ischemic and/or hypo-perfused area, being an essential tool in uncertain situations or when the time of symptoms onset is unavailable, increasing the efficacy and safety of endovenous thrombolysis by enlarging its therapeutic window and leading to more accurate selection of patients to be treated.Moreover, advanced neuroimaging may be of help in choosing the patients to be submitted to endovascular treatment when occlusion of an intracranial artery is documented, either after intravenous thrombolysis or as a primary approach.Here we describe the impact of neuroimaging in the decisional process in acute ischemic stroke, presenting the literature evidence on the topic, especially regarding the recent trials on endovascular treatment.

Neuroimaging as a Selection Tool and Endpoint in Clinical and Pre-clinical Trials

Standard imaging in acute stroke enables the exclusion of non-stroke structural CNS lesions and cerebral haemorrhage from clinical and pre-clinical ischaemic stroke trials. In this review, the potential benefit of imaging (e.g., angiography and penumbral imaging) as a translational tool for trial recruitment and the use of imaging endpoints are discussed for both clinical and pre-clinical stroke research. The addition of advanced imaging to identify a “responder” population leads to reduced sample size for any given effect size in phase 2 trials and is a potentially cost-efficient means of testing interventions. In pre-clinical studies, technical failures (failed or incomplete vessel occlusion, cerebral haemorrhage) can be excluded early and continuous multimodal imaging of the animal from stroke onset is feasible. Pre- and post-intervention repeat scans provide real time assessment of the intervention over the first 4–6 h. Negative aspects of advanced imaging in animal studies include increased time under general anaesthesia, and, as in clinical studies, a delay in starting the intervention. In clinical phase 3 trial designs, the negative aspects of advanced imaging in patient selection include higher exclusion rates, slower recruitment, overestimated effect size and longer acquisition times. Imaging may identify biological effects with smaller sample size and at earlier time points, compared to standard clinical assessments, and can be adjusted for baseline parameters. Mechanistic insights can be obtained. Pre-clinically, multimodal imaging can non-invasively generate data on a range of parameters, allowing the animal to be recovered for subsequent behavioural testing and/or the brain taken for further molecular or histological analysis.

Recanalization and Reperfusion Therapies of Acute Ischemic Stroke: What have We Learned, What are the Major Research Questions, and Where are We Headed?

Two placebo-controlled trials have shown that early administration of intravenous recombinant tissue plasminogen activator (rt-PA) after ischemic stroke improves outcomes up to 4.5 h after symptoms onset; however, six other trials contradict these results. We also know from analysis of the pooled data that benefits from treatment decrease as time from stroke onset to start of treatment increases. In addition to time, another important factor is patient selection through multimodal imaging, combining data from artery status, and salvageable tissue measures. Nonetheless, at the present time randomized controlled trials (RCTs) cannot demonstrate any beneficial outcomes for neuroimaging mismatch selection after 4.5 h from symptoms onset. By focusing on cases of large arterial occlusion, we know that recanalization is crucial, so endovascular treatment is an approach of interest. The use of intra-arterial thrombolysis was tested in two small RCTs that demonstrated clear benefits in terms of higher recanalization and also in clinical outcomes. But a new paradigm of stroke treatment may have begun with mechanical thrombectomy. In this field, Merci devices have been overtaken by fully deployed closed-cell self-expanding stents (stent-retrievers or “stent-trievers”). However, despite the high rate of recanalization achieved with stent-retrievers compared with other recanalization treatments, the use of these devices cannot clearly demonstrate better outcomes. Thus, futile recanalization occurs when successful recanalization fails to improve functional outcome. Recently, three RCTs, namely synthesis, IMS-III, and MR-rescue, have not been demonstrated any clear benefit for endovascular treatment. Most likely, these trials were not adequately designed to prove the superiority of endovascular treatment because they did not use optimal target populations, vascular status was not evaluated in all patients, relatively high rates of patients did not have enough mismatch, time from baseline neuroimaging to recanalization were too long or the devices used are now obsolete relative to stent-retrievers. Several RCTs currently underway are trying to determine whether bridging therapy is more effective than intravenous treatment and if mechanical thrombectomy is more effective than best medical treatment in patients ineligible for intravenous thrombolysis.

Thrombolysis in ischemic stroke without arterial occlusion at presentation

BACKGROUND AND PURPOSE

None of the randomized trials of intravenous tissue-type plasminogen activator reported vascular imaging acquired before thrombolysis. Efficacy of tissue-type plasminogen activator in stroke without arterial occlusion on vascular imaging remains unknown and speculative.

METHODS

We performed a retrospective, multicenter study to collect data of patients who presented to participating centers during a 5-year period with ischemic stroke diagnosed by clinical examination and MRI and with imaging evidence of no vascular occlusion. These patients were divided into 2 groups: those who received thrombolytic therapy and those who did not. Primary outcome measure of the study was excellent clinical outcome defined as modified Rankin Scale of 0 to 1 at 90 days from stroke onset. Secondary outcome measures were good clinical outcome (modified Rankin Scale, 0-2) and perfect outcome (modified Rankin Scale, 0). Safety outcome measures were incidence of symptomatic intracerebral hemorrhage and poor outcome (modified Rankin Scale, 4-6).

RESULTS

A total of 256 patients met study criteria, 103 with thrombolysis and 153 without. Logistic regression analysis showed that patients who received thrombolysis had more frequent excellent outcomes with odds ratio of 3.79 (P<0.01). Symptomatic intracerebral hemorrhage was more frequent in thrombolysis group (4.9 versus 0.7%; P=0.04). Thrombolysis led to more frequent excellent outcome in nonlacunar group with odds ratio 4.90 (P<0.01) and more frequent perfect outcome in lacunar group with odds ratio 8.25 (P<0.01).

CONCLUSIONS

This study provides crucial data that patients with ischemic stroke who do not have visible arterial occlusion at presentation may benefit from thrombolysis.

Imaging predictors of outcome following intravenous thrombolysis in acute stroke

Intravenous tissue plasminogen activator is the only approved medical treatment for patients with acute ischemic stroke. While it is associated with excellent clinical outcome in about 30 %, even with timely thrombolysis administration, certain strokes continue to evolve and lead to poor outcomes. Several studies have attempted to identify predictors of outcome despite timely thrombolysis. Persistence of a proximal clot burden and large vessel occlusion following thrombolysis are markers for patients who may potentially benefit from advanced treatment modalities like intra-arterial thrombolysis and thrombectomy. Timely brain imaging and interpretation play a crucial role in providing these treatment decisions. In this review, various imaging predictors of poor outcome among patients with acute ischemic stroke treated with intravenous thrombolysis are outlined. Despite identification of these imaging predictors, thrombolysis should not be withheld, as it may still be beneficial in a subset of patients. Knowledge of these predictors may set benchmarks for selecting candidates who may potentially benefit from advanced management strategies in future trials.

Is vascular imaging valuable prior to administration of intravenous tissue plasminogen activator?

Our goals were to explore whether performing computerized tomography angiography (CTA) prior to administration of tissue plasminogen activator (tPA) delays treatment and impacts outcome in patients with proximal middle cerebral artery occlusions (pMCAO). Patients with pMCAO with a National Institutes of Health Stroke scale (NIHSS) score >10 were identified from a prospective Stroke Registry. Patients underwent multi-parametric imaging studies whenever possible. Patients who underwent CTA were compared to those who only had non-contrast CT scan. Disability was measured with the modified Rankin Scale. Logistic regression was used to determine outcome modifiers. We included 73 patients (median age 73 years, 52% men) with moderate-severe stroke (median admission NIHSS 14). Of those, 44 underwent CTA and 29 did not. There were no differences between the groups in risk factor profile or baseline characteristics including stroke severity and door to needle, door to imaging or imaging to treatment times. At 90 days post-stroke there were no statistically significant differences in outcomes between the groups. On multivariate analysis, performing CTA had no impact on the chance of obtaining favorable outcome. In conclusion, CTA does not have a major impact on outcome in patients with pMCAO treated with tPA. Therefore, performing CTA should be considered on an individual basis prior to administration of tPA.

The role of the cerebral capillaries in acute ischemic stroke: the extended penumbra model

The pathophysiology of cerebral ischemia is traditionally understood in relation to reductions in cerebral blood flow (CBF). However, a recent reanalysis of the flow-diffusion equation shows that increased capillary transit time heterogeneity (CTTH) can reduce the oxygen extraction efficacy in brain tissue for a given CBF. Changes in capillary morphology are typical of conditions predisposing to stroke and of experimental ischemia. Changes in capillary flow patterns have been observed by direct microscopy in animal models of ischemia and by indirect methods in humans stroke, but their metabolic significance remain unclear. We modeled the effects of progressive increases in CTTH on the way in which brain tissue can secure sufficient oxygen to meet its metabolic needs. Our analysis predicts that as CTTH increases, CBF responses to functional activation and to vasodilators must be suppressed to maintain sufficient tissue oxygenation. Reductions in CBF, increases in CTTH, and combinations thereof can seemingly trigger a critical lack of oxygen in brain tissue, and the restoration of capillary perfusion patterns therefore appears to be crucial for the restoration of the tissue oxygenation after ischemic episodes. In this review, we discuss the possible implications of these findings for the prevention, diagnosis, and treatment of acute stroke.

Advanced imaging to extend the therapeutic time window of acute ischemic stroke

Reperfusion therapy for acute stroke has evolved from the initial use of intravenous tissue plasminogen activator (tPA) within 3 hours of symptom onset to more recent guideline-recommended use up to 4.5 hours. In addition, endovascular therapy is increasingly utilized for stroke treatment and is typically initiated up to 8 hours after onset. Recent studies demonstrate that imaging of the ischemic penumbra with diffusion/perfusion magnetic resonance imaging (MRI) can identify subgroups of patients who are likely to improve following successful reperfusion (Target Mismatch profile) and others who are at increased risk for hemorrhage and poor clinical outcomes (Malignant profile). New data indicate that stent retriever devices provide better recanalization efficacy and clinical outcomes than the previously available mechanical thrombectomy devices. Going forward, we believe that the use of penumbral imaging with validated MRI techniques, as well as the currently less well-validated computed tomography (CT) perfusion approach, will maximize benefit and reduce the risk of adverse events and poor outcomes when used both early after stroke onset and at later time points. New trials that feature diffusion/perfusion MRI or CT perfusion-based patient selection for treatment with intravenous tPA and or endovascular therapies versus nonreperfused control groups are planned or in progress. We predict that these trials will confirm the hypothesis that penumbral imaging can enhance patient selection and extend the therapeutic time window for acute ischemic stroke.

How baseline severity affects efficacy and safety outcomes in acute ischemic stroke intervention trials

Baseline severity of stroke may be an important predictor of efficacy and safety outcomes in acute stroke intervention trials. This summary explores definitions of baseline variables and outcomes used to measure stroke severity, efficacy, and safety. In addition, the discussion here reviews select acute ischemic stroke intravenous thrombolytic studies, such as the National Institute of Neurological Disorders and Stroke rt-PA Stroke Study and European Cooperative Acute Stroke Studies, select neuroprotectant and endovascular clot retrieval device studies, and large cooperative databases, such as the Virtual International Stroke Trials Archive and Safe Implementation of Treatment in Stroke-International Stroke Thrombolysis Registry, to explore relationships between baseline stroke severity and other possible factors associated with efficacy and safety outcomes. The NIH Stroke Scale and modified Rankin scale will be featured as major stroke outcome measures, based on frequency of use and reliability, familiarity, adaptability, and comparability.

Timing of thrombolysis for acute ischemic stroke: "timing is everything" or "everyone is different"

It is indisputable that in the first 2 to 3 hours of an acute ischemic, the best strategy to maximize recovery is robustly time-based and depends on getting the artery open as soon as possible. The second law of thermodynamics and the underappreciated effect of clot consistency and size must be accounted for in our efforts to minimize time to recanalization within the first 2 to 3 hours. It is also clear that at later time intervals, beyond 4.5 hours, few patients completely recover even with sustained complete recanalization, and that the ability to recover depends more on physiologic tissue issues than on the duration of the occlusion. Clinical factors as well as imaging should be used to select patients who may benefit from delayed attempts at reperfusion.