Quantification of Microspheres Appearance in Brain Vessels

Transcranial Doppler With Microbubbles: Screening Test to Detect and Grade Right-to-Left Shunt After an Ischemic Stroke: A Literature Review

Right-to-left shunt, mainly due to patent foramen ovale (PFO), is likely responsible for ≈5% of all ischemic strokes and 10% of those occurring in young and middle-aged adults. Randomized clinical trials demonstrated that, in selected young and middle-aged patients with otherwise cryptogenic acute ischemic stroke and high-risk PFO, percutaneous PFO closure is more effective than antiplatelet therapy alone in preventing recurrence. However, PFO is generally a benign finding and is present in about one-quarter of the population. Therefore, in clinical practice, identifying PFOs that are likely to be pathogenetic is crucial for selecting suitable patients for PFO closure to prevent recurrent stroke and to avoid potentially harmful and costly overtreatment. Contrast transthoracic echocardiography has a relatively low sensitivity in detecting PFO, whereas transesophageal echocardiography is currently considered the gold standard for PFO detection. However, it is a relatively invasive procedure and may not always be easily feasible in the subacute setting. Contrast transcranial Doppler is a noninvasive, inexpensive, accurate tool for the detection of right-to-left shunt. We conducted a literature review on the use of contrast transcranial Doppler to detect and grade right-to-left shunt after an acute ischemic stroke and present a clinical workflow proposal for young and middle-aged patients.

Recent advances in targeted delivery of tissue plasminogen activator for enhanced thrombolysis in ischaemic stroke

Tissue plasminogen activator (tPA) is the only FDA approved medical treatment for the ischaemic stroke. However, it associates with some inevitable limitations, including: short therapeutic window, extremely short half-life and low penetration in large clots. Systemic administration may lead to complications such as haemorrhagic conversion in the brain and relapse in the form of re-occlusion. Furthermore, ultrasound has been utilised in combination with contrast agents, echogenic liposome, microspheres or nanoparticles (NPs) carrying tPA for improving thrombolysis - an approach that has resulted in slight improvement of tPA delivery and facilitated thrombolysis. Most of these delivery systems are able to extend the circulating half-life and clot penetration of tPA. Various technologies employed for ameliorated thrombolytic therapy are in different phases, some are in final steps for clinical applications while some others are under investigations for their safety and efficacy in human cases. Here, recent progresses on the thrombolytic therapy using novel nano- and micro-systems incorporating tPA are articulated. Of these, liposomes and microspheres, polymeric NPs and magnetic nanoparticles (MNPs) are discussed. Key technologies implemented for efficient delivery of tPA and advanced thrombolytic therapy and their advantages/disadvantages are further expressed.

Reperfusion therapies of acute ischemic stroke: potentials and failures

Over the past 20 years, clinical research has focused on the development of reperfusion therapies for acute ischemic stroke (AIS), which include the use of systemic intravenous thrombolytics (alteplase, desmoteplase, or tenecteplase), the augmentation of systemic intravenous recanalization with ultrasound, the bridging of intravenous with intra-arterial thrombolysis, the use of multi-modal approaches to reperfusion including thrombectomy and thromboaspiration with different available retrievers. Clinical trials testing these acute reperfusion therapies provided novel insight regarding the comparative safety and efficacy, but also raised new questions and further uncertainty on the field. Intravenous alteplase (tPA) remains the fastest and easiest way to initiate acute stroke reperfusion treatment, and should continue to be the first-line treatment for patients with AIS within 4.5 h from onset. The use of tenecteplase instead of tPA and the augmentation of systemic thrombolysis with ultrasound are both novel therapeutical modalities that may emerge as significant options in AIS treatment. Endovascular treatments for AIS are rapidly evolving due to technological advances in catheter-based interventions and are currently emphasizing speed in order to result in timely restoration of perfusion of still-salvageable, infarcted brain tissue, since delayed recanalization of proximal intracranial occlusions has not been associated with improved clinical outcomes. Comprehensive imaging protocols in AIS may enable better patient selection for endovascular interventions and for testing multi-modal combinatory strategies.

Intravenous thrombolysis in acute ischemic stroke: standard and potential future applications

Acute ischemic stroke is a medical emergency requiring urgent treatment. Randomized clinical trial and Phase IV data have provided unequivocal evidence that intravenous thrombolysis with recombinant tissue plasminogen activator (rt-PA) improves early functional outcomes by restoring brain perfusion. Moreover, these studies have shed substantial light on the factors which are associated with more favorable outcome with tPA and are related to the highest benefit-to-risk ratio. Stroke physicians should consider vascular imaging techniques to aid decision making with thrombolytic therapy. The presence of intracranial occlusion is the target of treatment with early recanalization being the goal. Successful use of intravenous thrombolysis depends on a sound understanding of the decision-making process and organization of the treating team who strives for early treatment initiation and strict adherence to the protocol. Intravenous rt-PA within 4.5 h of onset should now be a standard treatment of acute disabling ischemic stroke throughout the world. This review also summarizes intravenous thrombolysis contraindications as well as the safety of novel reperfusion therapies including tenecteplase, sonothrombolysis and the combination of alteplase with direct thrombin inhibitors or glycoprotein IIb/IIIa receptor antagonists.

The quest for arterial recanalization in acute ischemic stroke-the past, present and the future

Ischemic stroke is one of the major causes of mortality and long-term disability. In the recent past, only very few treatment options were available and a considerable proportion of stroke survivors remained permanently disabled. However, over the last 2 decades rapid advances in acute stroke care have resulted in a corresponding improvement in mortality rates and functional outcomes. In this review, we describe the evolution of systemic thrombolytic agents and various interventional devices, their current status as well as some of the future prospects. We reviewed literature pertaining to acute ischemic stroke reperfusion treatment. We explored the current accepted treatment strategies to attain cerebral reperfusion via intravenous modalities and compare and contrast them within the boundaries of their clinical trials. Subsequently we reviewed the trials for interventional devices for acute ischemic stroke, categorizing them into thrombectomy devices, aspiration devices, clot disruption devices and thrombus entrapment devices. Finally we surveyed several of the alternative reperfusion strategies available. We also shed some light on the controversies surrounding the current strategies of treatment of acute ischemic stroke. Acute invasive interventional strategies continue to improve along with the noninvasive modalities. Both approaches appear promising. We conducted a comprehensive chronological review of the existing treatments as well as upcoming remedies for acute ischemic stroke.

The role of sonolysis and sonothrombolysis in acute ischemic stroke: a systematic review and meta-analysis of randomized controlled trials and case-control studies

OBJECTIVES

To assess the evidence on the safety and efficacy of sonothrombolysis in acute stroke.

SEARCH METHODS

Electronic databases and grey literature were searched under different MeSH terms from 1970 to present.

SELECTION CRITERIA

Randomized control trials (RCTs) and case control studies (CCSs) on sonolysis and sonothrombolysis alone or with microsphere in acute stroke patients (>18 old). Outcome measures included complete recanalization (CR) at 1-2 and 24 hours, 3 months modified Rankin Scale (mRS), and symptomatic intracerebral hemorrhage (sICH). Data was extracted to Review Manager software.

RESULTS

Fifty-seven studies were retrieved and analyzed. Ten studies (7 RCTs and 3 CCSs) were included in our meta-analysis, which revealed that sonolysis and sonothrombolysis are safe (OR of sICH: 1.14; 95% confidence interval (CI): 0.56- 2.34;P=0.71) and effective (OR of CR at 1-2 hours: 2.95;95% CI: 1.81-4.81;P<0.00001) and have more than two-fold higher likelihood of favourable long-term outcome (3-month mRS 0-2; OR: 2.20; CI:1.52-3.19;P<0.0001). Further subgroup analysis based on the presence of microsphere revealed that it is safe (OR of sICH: 1.18; CI:0.433.24;P=0.75) and effective (OR of CR: 2.61; CI: 1.36-4.99;P=0.004). Subgroup analysis based on sonolysis revealed to be safe and effective.

CONCLUSIONS

This novel treatment appears safe and effective. The evidence of microsphere as an enhancement of sonothrombolysis is evolving.

Current and future recanalization strategies for acute ischemic stroke

In a quest for stroke treatment, reperfusion proved to be the first key to the puzzle. Systemic tissue plasminogen activator (tPA), the first and currently the only approved treatment, is also the fastest way to initiate thrombolyis for acute ischemic stroke. tPA works by induction of mostly partial recanalization since stroke patients often have large thrombus burden. Thus, early augmentation of fibrinolysis and multi-modal approach to improve recanalization are desirable. This review focuses on the following strategies available to clinicians now or being tested in clinical trials: (a) faster initiation of tPA infusion; (b) sonothrombolysis; (c) intra-arterial revascularization, bridging intravenous and intra-arterial thrombolysis, mechanical thrombectomy and aspiration; and (d) novel experimental approaches. Despite these technological advances, no single strategy was yet proven to be a 'silver bullet' solution to reverse acute ischemic stroke. Better outcomes are expected with faster treatment leading to early, at times just partial flow improvement rather than achieving complete recanalization with lengthy procedures. Arterial re-occlusion can occur with any of these approaches, and it remains a challenge since it leads to poor outcomes and no clinical trial data are available yet to determine safe strategies to prevent or reverse re-occlusion.

Sonothrombolysis: an emerging modality for the management of stroke

OBJECTIVE

Ischemic stroke and intracranial hemorrhage remain a persistent scourge in Western civilization. Therefore, novel therapeutic modalities are desperately needed to expand the current limitations of treatment. Sonothrombolysis possesses the potential to fill this void because it has experienced a dramatic evolution from the time of early conceptualization in the 1960s. This process began in the realm of peripheral and cardiovascular disease and has since progressed to encompass intracranial pathologies. Our purpose is to provide a comprehensive review of the historical progression and existing state of knowledge, including underlying mechanisms as well as evidence for clinical application of ultrasound thrombolysis.

METHODS

Using MEDLINE, in addition to cross-referencing existing publications, a meticulous appraisal of the literature was conducted. Additionally, personal communications were used as appropriate.

RESULTS

This appraisal revealed several different technologies close to broad clinical use. However, fundamental questions remain, especially in regard to transcranial high-intensity focused ultrasound. Currently, the evidence supporting low intensity ultrasound's potential in isolation, without tissue plasminogen, remains uncertain; however, possibilities exist in the form of microbubbles to allow for focal augmentation with minimal systemic consequences. Alternatively, the literature clearly demonstrates, the efficacy of high-intensity focused ultrasound for independent thrombolysis.

CONCLUSION

Sonothrombolysis exists as a promising modality for the noninvasive or minimally invasive management of stroke, both ischemic and hemorrhagic. Further research facilitating clinical application is warranted.

Transcranial ultrasound in clinical sonothrombolysis (TUCSON) trial

OBJECTIVE

Microspheres (microS) reach intracranial occlusions and transmit energy momentum from an ultrasound wave to residual flow to promote recanalization. We report a randomized multicenter phase II trial of microS dose escalation with systemic thrombolysis.

METHODS

Stroke patients receiving 0.9mg/kg tissue plasminogen activator (tPA) with pretreatment proximal intracranial occlusions on transcranial Doppler (TCD) were randomized (2:1 ratio) to microS (MRX-801) infusion over 90 minutes (Cohort 1, 1.4ml; Cohort 2, 2.8ml) with continuous TCD insonation, whereas controls received tPA and brief TCD assessments. The primary endpoint was symptomatic intracerebral hemorrhage (sICH) within 36 hours after tPA.

RESULTS

Among 35 patients (Cohort 1 = 12, Cohort 2 = 11, controls = 12) no sICH occurred in Cohort 1 and controls, whereas 3 (27%, 2 fatal) sICHs occurred in Cohort 2 (p = 0.028). Sustained complete recanalization/clinical recovery rates (end of TCD monitoring/3 month) were 67%/75% for Cohort 1, 46%/50% for Cohort 2, and 33%/36% for controls (p = 0.255/0.167). The median time to any recanalization tended to be shorter in Cohort 1 (30 min; interquartile range [IQR], 6) and Cohort 2 (30 min; IQR, 69) compared to controls (60 min; IQR, 5; p = 0.054). Although patients with sICH had similar screening and pretreatment systolic blood pressure (SBP) levels in comparison to the rest, higher SBP levels were documented in sICH+ patients at 30 minutes, 60 minutes, 90 minutes, and 24-36 hours following tPA bolus.

INTERPRETATION

Perflutren lipid microS can be safely combined with systemic tPA and ultrasound at a dose of 1.4ml. Safety concerns in the second dose tier may necessitate extended enrollment and further experiments to determine the mechanisms by which microspheres interact with tissues. In both dose tiers, sonothrombolysis with microS and tPA shows a trend toward higher early recanalization and clinical recovery rates compared to standard intravenous tPA therapy. Ann Neurol 2009;66:28-38.

Ultrasound Enhancement of Fibrinolysis

Systemic administration of tissue plasminogen activator (tPA) remains the fastest way to initiate treatment for acute ischemic stroke. The presence of a proximal arterial occlusion should not be viewed as an insurmountable predictor of tPA failure. Because tPA works by induction of partial recanalization of large thrombi, early augmentation of fibrinolysis to improve recanalization is desirable. This augmentation is feasible and can be safely achieved at the bedside with diagnostic Doppler ultrasound. In the CLOTBUST trial, 83% of patients achieved any recanalization (46% complete, 27% partial) with tPA+transcranial Doppler vs 50% (17% complete, 33% partial) with tPA alone within 2 hours of treatment ( P <0.001). Sustained, complete recanalization at 2 hours was 38% vs 13%, respectively ( P =0.03). A recent meta-analysis of 6 randomized and 3 nonrandomized clinical studies of sonothrombolysis showed that any diagnostic ultrasound monitoring can at least double the chance of early complete arterial recanalization at no increase in the risk of symptomatic intracerebral hemorrhage. Because application in humans of frequencies below the diagnostic range resulted in increased symptomatic bleeding rates, mechanisms by which megahertz and kilohertz frequencies interact with the clot–residual flow interface and endothelium are currently under renewed investigations. Catheter-based ultrasound delivery to arterial thrombi and intraventricular clots is the subject of ongoing clinical trials. Addition of gaseous perflutren-lipid microspheres to tPA and transcranial Doppler can further facilitate early flow improvement, with a 50% rate of early, complete recanalization in a recent feasibility study. Transcranial ultrasound delivery in an operator-independent and dose-controlled manner is being tested in a clinical trial.

Intra-arterial administration of microbubbles and continuous 2-MHz ultrasound insonation to enhance intra-arterial thrombolysis

BACKGROUND

Microbubbles (MB) and ultrasound have been shown to enhance thrombolysis. We sought to evaluate safety and efficacy on middle cerebral artery (MCA) recanalization of local MB administration during intra-arterial (IA) thrombolysis and continuous transcranial Doppler (TCD) monitoring.

METHODS

Patients with acute M1-MCA occlusion were treated with intravenous tissue plasminogen activator (iv-tPA) and continuously monitored with TCD. If recanalization was not achieved during first-hour bridging IA-rescue was adopted: MB + tPA direct intraclot microcatheter infusion. TCD flow monitoring allowed continuous insonation at clot location. Recanalization was angiographically assessed (thrombolysis in cerebral infarction [TICI] score) and compared with simultaneous TCD data. IA procedures were stopped at 6 hours. Recanalization was reassessed at 12 hours (TCD). Neurological status was repeatedly assessed (National Institutes of Health Stroke Scale [NIHSS]). At three months, patients were considered independent if mRS <or= 2.

RESULTS

Of the 18 included patients (mean age 72), 16 received standard iv-tPA (.9 mg/kg). Nine patients were recanalized during tPA infusion and 9 patients underwent IA-rescue procedures. Median pre-IA NIHSS score: 20. Median time to IA initiation was 175 +/- 63 minutes. Mean IA doses were tPA = 10 +/- 3 mg and MB = 3 +/- 1 mL. TCD monitoring allowed direct visualization of massive MB arrival during every administration. In-procedure recanalization was observed in 78% (n= 7): complete-TICI3 in 22% (n= 2), partial-TICI2 in 56% (n= 5). Perfect correlation was observed between TICI and TCD scores. At 12 hours complete recanalization increased to 56%, partial to 22%. One patient (11%) experienced symptomatic intracranial hemorrhage accounting for the only death. Median NIHSS evolution was 12 at 24 hours and 10 at discharge. At 3 months 4 patients (44%) were independent.

CONCLUSION

The combination of ultrasound and IA MB and tPA may be a strategy to enhance the thrombolytic effect and increase recanalization rates.

A pilot randomized clinical safety study of sonothrombolysis augmentation with ultrasound-activated perflutren-lipid microspheres for acute ischemic stroke

BACKGROUND AND PURPOSE

Ultrasound transiently expands perflutren-lipid microspheres (muS), transmitting energy momentum to surrounding fluids. We report a pilot safety/feasibility study of ultrasound-activated muS with systemic tissue plasminogen activator (tPA).

METHODS

Stroke subjects treated within 3 hours had abnormal Thrombolysis in Brain Ischemia (TIBI) residual flow grades 0 to 3 before tPA on transcranial Doppler (TCD). Randomization included Controls (tPA+TCD) or Target (tPA+TCD+2.8 mL microS). The primary safety end point was symptomatic intracranial hemorrhage (sICH) with worsening by >or=4 NIHSS points within 72 hours.

RESULTS

Fifteen subjects were randomized 3:1 to Target, n=12 or Control, n=3. After treatment, asymptomatic ICH occurred in 3 Target and 1 Control, and sICH was not seen in any study subject. muS reached MCA occlusions in all Target subjects at velocities higher than surrounding residual red blood cell flow: 39.8+/-11.3 vs 28.8+/-13.8 cm/s, P<0.001. In 75% of subjects, microS permeated to areas with no pretreatment residual flow, and in 83% residual flow velocity improved at a median of 30 minutes from start of microS infusion (range 30 s to 120 minutes) by a median of 17 cm/s (118% above pretreatment values). To provide perspective, current study recanalization rates were compared with the tPA control arm of the CLOTBUST trial: complete recanalization 50% versus 18%, partial 33% versus 33%, none 17% versus 49%, P=0.028. At 2 hours, sustained complete recanalization was 42% versus 13%, P=0.003, and NIHSS scores 0 to 3 were reached by 17% versus 8%, P=0.456.

CONCLUSIONS

Perflutren microS reached and permeated beyond intracranial occlusions with no increase in sICH after systemic thrombolysis suggesting feasibility of further microS dose-escalation studies and development of drug delivery to tissues with compromised perfusion.