High rate of complete recanalization and dramatic clinical recovery during tPA infusion when continuously monitored with 2-MHz transcranial doppler monitoring

Update on the Serum Biomarkers and Genetic Factors Associated with Safety and Efficacy of rt-PA Treatment in Acute Stroke Patients

An accurate understanding of the mechanisms underlying an individual's response to rt-PA treatment is critical to improve stroke patients' management. We thus reviewed the literature in order to identify biochemical and genetic factors that have been associated with safety and efficacy of rt-PA administration after stroke.

Early changes of tissue perfusion after tissue plasminogen activator in hyperacute ischemic stroke

BACKGROUND AND PURPOSE

it is hypothesized that tissue plasminogen activator rescues brain tissue by improving perfusion. In this study, we aimed to examine acute regional perfusion changes and how they influence infarction and clinical outcome.

METHODS

three sequential MR scans were performed in 15 tissue plasminogen activator-treated patients within 3.5 (tp1), at 6 hours (tp2), and at 1 month (tp3) after stroke onset. "Hypoperfusion" was defined if mean transit time prolongation was more than a threshold (4 thresholds: 3, 4, 5, and 6 seconds). Four regions of interest were classified: (1) "reperfusion"-hypoperfused at tp1, normal at tp2; (2) "nonreperfusion"-hypoperfused at tp1 and tp2; (3) "normal perfusion"-normal at tp1 and tp2; and (4) "new hypoperfusion"-normal at tp1 and hypoperfused at tp2. Risk of infarction was calculated within each region of interest. Associations between tissue perfusion changes and clinical variables were evaluated using stepwise multiple linear regressions. Moreover, the association between National Institutes of Health Stroke Scale changes and perfusion alterations was assessed using linear mixed effect models.

RESULTS

regardless of the mean transit time threshold chosen, the risk of infarction in nonreperfused regions (40% to 68%, thresholds 3 to 6 seconds) was higher than reperfused regions (9% to 30%, P<0.05), and it was higher in new hypoperfusion regions (9% to 33%) than normal perfusion regions (3% to 4%, P<0.05). Volume of new hypoperfusion was significantly associated with onset-to-treatment time and initial hypoperfused volume. Overall relative reperfusion was significantly associated with National Institutes of Health Stroke Scale improvement.

CONCLUSIONS

early tissue perfusion changes influenced final tissue fate. The development of new hypoperfusion may result from delay in tissue plasminogen activator and a large initial lesion.

Changes in blood flow velocity in the radial artery during 1-hour ultrasound monitoring with a 2-MHz transcranial probe--a pilot study

PURPOSE

Multiple biologic effects of ultrasound on the human body have been described. Our aim was to monitor changes in blood flow velocities in the radial artery during continuous pulsed wave Doppler monitoring (DM).

METHODS

Fifteen healthy volunteers (8 males; mean age 55 ± 17 years) underwent two 1-hour sessions of left radial artery DM using a diagnostic transcranial 2-MHz pulsed-wave transducer. Blood flow velocities were recorded twice at 2-minute intervals, for the measurement of peak systolic velocity, end-diastolic velocity, and mean flow velocity, and the calculation of pulsatility index, and resistance index. Insonation was either intermittent (by periods <10 seconds) or continuous during the first session, and conversely during the second session 2 weeks later.

RESULTS

Blood flow velocities and indices fluctuated during both sessions. These changes were symmetrical during the intermittent DM session. In contrast, end-diastolic velocity increased while pulsatility index and resistance index decreased significantly during the continuous DM session (p < 0.05 for all three parameters). The changes in peak systolic velocity and mean flow velocity did not differ between sessions.

CONCLUSIONS

One-hour sonographic Doppler monitoring using a 2-MHz diagnostic transcranial PW Doppler probe may induce peripheral vasorelaxation in humans.

Autonomic neuropathy is associated with impairment of dynamic cerebral autoregulation in type 1 diabetes

HYPOTHESIS

The mechanisms underlying impairment of dynamic cerebral autoregulation in diabetes are not well known. Cardiovascular autonomic neuropathy (CAN) could contribute to dynamic cerebral autoregulation impairment. In this study, we assessed the association between CAN and impairment of dynamic cerebral autoregulation in patients with type 1 diabetes.

METHODS

We evaluated dynamic cerebral autoregulation (DCA) in patients with type 1 diabetes and no history of cerebrovascular disease. DCA was assessed with transcranial Doppler using the correlation coefficient index Mx method. Mx was calculated from slow changes in mean cerebral blood flow velocity and mean arterial blood pressure. Increase in Mx indicates weaker DCA, with a threshold for impaired DCA above 0.3. Moderate CAN was defined as reduced heart rate variability (HRV) on the following tests: deep controlled breathing, Valsalva maneuver or initiation of active standing. Severe CAN was defined as reduced HRV associated with orthostatic hypotension.

RESULTS

60 patients were included (M/F: 33/27; mean age ± SD: 46 years ± 11.5). 23 patients had moderate CAN and 15 patients severe CAN. DCA was impaired in 37 patients. CAN was associated with impaired DCA (p = 0.005). Impairment of DCA was more pronounced in patients with severe CAN (p = 0.019). Glycosylated haemoglobin (HbA1c) was associated with impaired DCA in univariate analysis (p = 0.05). In multivariate analysis, only CAN was associated with impaired DCA (p = 0.007) whereas HbA1c was not (p = 0.161).

CONCLUSIONS

CAN was associated with impaired DCA in type 1 diabetes. The magnitude of DCA impairment increased with the severity of CAN.

Changes in hemocoagulation in acute stroke patients after one-hour sono-thrombolysis using a diagnostic probe

The aim was to monitor the changes in hemocoagulation parameters in acute ischemic stroke (AIS) patients after sono-thrombolysis of the occluded middle cerebral artery using a duplex transcranial probe with 2.0-MHz frequency in Doppler mode. Sixteen AIS patients indicated for intravenous thrombolysis (IVT) (8 males; mean age 68.3 +/- 7.1 y) and 16 AIS patients contraindicated for IVT (11 males; mean age 67.9 +/- 7.9 y) were randomized for sono-thrombolysis (8 + 8 patients) or standard treatment (control group) (8 + 8 patients). The significant decrease of plasminogen activator inhibitor-1, plasminogen and alpha-2-antiplasmin activity by a mean of 60, 32 and 24%, respectively, and the increase of tissue plasminogen activator by a mean of 56% was found after sono-thrombolysis when compared with control group (p < 0.0125); these changes were more evident in patients treated with a combination of sono-thrombolysis and IVT (79, 38, 50 and 82%, respectively) than in patients treated by sono-thrombolysis alone (34, 13, 17 and 30%, respectively).

Equipoise among recanalization strategies

Modern acute ischemic stroke therapy is based on the premise that recanalization and subsequent reperfusion are essential for the preservation of brain tissue and favorable clinical outcomes. We outline key issues that we think underlie equipoise regarding the comparative clinical efficacy of IV recombinant tissue-type plasminogen activator (rt-PA) and intra-arterial (IA) reperfusion therapies for acute ischemic stroke. On the one hand, IV rt-PA therapy has the benefit of speed with presumed lower rates of recanalization of large artery occlusions as compared to IA methods. More recent reports of major arterial occlusions treated with IV rt-PA, as measured by transcranial Doppler and magnetic resonance angiography, demonstrate higher rates of recanalization. Conversely, IA therapies report higher recanalization rates, but are hampered by procedural delays and risks, even failing to be applied at all in occasional patients where time to reperfusion remains a critical factor. Higher rates of recanalization in IA trials using clot-removal devices have not translated into improved patient functional outcome as compared to trials of IV therapy. Combined IV-IA therapy promises to offer advantages of both, but perhaps only when applied in the timeliest of fashions, compared to IV therapy alone. Where equipoise exists, randomizing subjects to either IV rt-PA therapy or IV therapy followed by IA intervention, while incorporating new interventions into the study design, is a rational and appropriate research approach.

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.

Fibrinolytic effects of transparietal ultrasound associated with intravenous infusion of an ultrasound contrast agent: study of a rat model of acute cerebral stroke

The aim of this study was to evaluate the thrombolytic effect of focused transparietal ultrasound in combination with a specific contrast agent (microbubbles) in acute cerebral ischemia. Acute cerebral ischemia was induced in 10 rats by intra-arterial clots injection. Five rats (group 1) were treated with a combination of transparietal ultrasound (probe 2 MHz, acoustic power 500 mW/cm(2)) and intravenous injection of 0.6 mL of the ultrasound contrast agent (UCA) sulfur hexafluoride. Five rats (group 2) were treated by fibrinolytic intravenous infusion (recombinant tissue plasminogen activator). Cerebral cellular energy production was determined by measuring the cellular phosphorylation using phosphorus magnetic spectroscopy before and during ischemia induction and after treatment. Measures were performed on a dedicated 2.35T magnet. The ratio phosphocreatine (P(Cr)) on inorganic phosphate (P(i)), P(Cr)/P(i), estimation of the oxidative phosphorylation metabolism and the intracellular pH (pHi) were measured in the two groups. Compared with the ischemia induction period, both treatments were associated with an increase of P(Cr)/P(i) and pHi values, respectively, +80% and +100% in group 1 (p=0.07) and +100% and +80% in group 2 (p=0.04). There was no significant difference between the two groups for the response treatment. To conclude, treatment with intravenous fibrinolytic infusion and treatment with focused ultrasound in combination with UCA seems to be equally effective in treating acute cerebral ischemia in rats. (E-mail: j.p.tasu@chu-poitiers.fr).

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.

Impact of hyperlipidemia and statins on ischemic stroke outcomes after intra-arterial fibrinolysis and percutaneous mechanical embolectomy

BACKGROUND

Endovascular recanalization therapies are an increasingly employed treatment strategy in acute cerebral ischemia. The determinants of the final clinical outcome after endovascular treatment have been understudied. We investigated the effects of hyperlipidemia and statins on acute ischemic stroke outcomes after endovascular procedures.

METHODS

An inquiry of a prospectively maintained stroke registry was conducted. Endovascular procedures were performed using recombinant tissue plasminogen activator, prourokinase or the Merci device within 12 hours after symptom onset. The analyzed outcomes were revascularization, hemorrhage and excellent functional outcome (Rankin score of 0-1 at 3 months). The analyses included chi(2) and Wilcoxon rank sum, logistic regression (for multivariate analyses with binary outcomes) and linear regression (for continuous outcomes). Significance was set at p < 0.05.

RESULTS

We included 142 patients, 80% treated with intra-arterial fibrinolysis, 22% with percutaneous mechanical embolectomy and 27% treated with intravenous fibrinolysis prior to endovascular intervention. Age (OR = 0.956, 95% CI = 0.927-0.986, p = 0.0041), National Institutes of Health Stroke Scale (NIHSS) score on admission (OR = 0.881, 95% CI = 0.812-0.957, p = 0.0025) and history of hyperlipidemia (OR = 0.284, 95% CI = 0.08-0.99, p = 0.0478) were negatively associated with excellent functional outcome at 3 months. Every 50 mg/dl increment in the total cholesterol level resulted in 64% decrease in the odds of excellent functional outcome (OR = 0.36, 95% CI = 0.447-0.882, p = 0.0253). History of hyperlipidemia decreased the likelihood of neurological improvement (p = 0.0462) and was associated with a higher NIHSS score at 7 days or discharge. Statin use was related to an average 6.5-unit NIHSS decrease at discharge (p = 0.0168). Statins were not associated with increased frequency of recanalization or symptomatic intracerebral hemorrhage.

CONCLUSIONS

History of hyperlipidemia may have a negative impact on the outcomes of acute ischemic stroke treated with intra-arterial fibrinolysis or percutaneous mechanical embolectomy. Statin use before and after these procedures may be related to better neurological outcomes. Larger prospective studies are needed to endorse these findings.

Effect of Blood Soluble Clotting Factors on Coagulation Profile

Objective: Recently, mechanical thrombolytic therapy has been introduced as an alternative or adjunct to pharmaceutical thrombolytic therapy in removing thrombus from vascular system. Recurrent thrombosis has been a challenge for thrombolytic therapies. We hypothesize that soluble clotting factors released during a mechanical thrombectomy procedure may be responsible for creating a localized hypercoagulable state and could be one of the underlying causes of recurrent thrombosis. Method: Blood samples were obtained from 20 participants with no history of hypertension, vascular disease, and antiplatelet/anticoagulation therapy. For each whole blood (WB) sample, we measured activated clotting time (ACT) and clotting rate (CR) at the baseline and then with added agitated and nonagitated clot serums. The same set of measurements was performed on platelet-rich plasma (PRP) samples of each participant. We tested for changes in coagulation profile between baseline samples and those with added supernatant serums obtained from autologous blood clot. Result: We observed a significant decrease in ACT for WB with agitated and nonagitated clot serums (49%, P < .0001 and 25%, P = .01, respectively) compared to the baseline WB. The same trend was observed for PRP samples with agitated and nonagitated clot serums (28%, P = .002 and 18%, P = .05, respectively). The CR was increased (a steeper slope) by 83% for samples with added agitated clot serum only (P = .007). Conclusion: We observed a significant change for ACT in WB samples with added clot serums as compared to the baseline WB samples. The results of this study suggest that the soluble substances released from clotting blood have profound procoagulant effects.

Comparison of intravenous alteplase with a combined intravenous-endovascular approach in patients with stroke and confirmed arterial occlusion (RECANALISE study): a prospective cohort study

BACKGROUND

The efficacy of intravenous (IV) alteplase is restricted by the speed of recanalisation and the site of the occlusion. The aim of this study was to ascertain the effect of a combined IV-endovascular approach (intra-arterial alteplase and, if required, additional thrombectomy) in patients with stroke due to arterial occlusion.

METHODS

We compared recanalisation rates, neurological improvement at 24 h, and functional outcome at 3 months between two periods (February, 2002, to March, 2007, vs April, 2007, to October, 2008) in patients in a prospective registry who were treated with different regimens of alteplase within 3 h of symptom onset. Patients with confirmed occlusion who were treated before April, 2007, were treated with IV alteplase; after April, 2007, patients were treated with a systematic IV-endovascular approach. Analysis was by intention to treat.

FINDINGS

46 (87%) of 53 patients treated with the IV-endovascular approach achieved recanalisation versus 56 (52%) of 107 patients in the IV group (adjusted relative risk [RR] 1.49, 95% CI 1.21-1.84; p=0.0002). Early neurological improvement (NIHSS score of 0 or 1 or an improvement of 4 points or more at 24 h) occurred in 32 (60%) patients in the IV-endovascular group and 42 (39%) patients in the IV group (adjusted RR 1.36, 0.97-1.91; p=0.07). Favourable outcome (mRS of 0-2 at 90 days) occurred in 30 (57%) patients in the IV-endovascular group and 47 (44%) patients in the IV group (adjusted RR 1.16, 0.85-1.58; p=0.35). The mortality rate at 90 days was 17% in both groups, and symptomatic intracranial haemorrhage was reported in five (9%) patients in the IV-endovascular group and in 12 (11%) patients in the IV group. Better clinical outcome was associated with recanalisation in both groups and with time to recanalisation in the IV-endovascular group.

INTERPRETATION

An IV-endovascular approach is associated with higher recanalisation rates than is IV alteplase in patients with stroke and confirmed arterial occlusion. In patients treated with an IV-endovascular approach, a shorter time from symptom onset to recanalisation is associated with better clinical outcomes.

Percutaneous transluminal angioplasty and stent placement in acute vessel occlusion: evaluation of new methods for interventional stroke treatment

BACKGROUND AND PURPOSE

The major goal of acute ischemic stroke treatment is fast and sufficient recanalization. Percutaneous transluminal balloon angioplasty (PTA) and/or placement of a stent might achieve both by compressing the thrombus at the occlusion site. This study assesses the feasibility, recanalization rate, and complications of the 2 techniques in an animal model.

MATERIALS AND METHODS

Thirty cranial vessels of 7 swine were occluded by injection of radiopaque thrombi. Fifteen vessel occlusions were treated by PTA alone and 15, by placement of a stent and postdilation. Recanalization was documented immediately after treatment and after 1, 2, and 3 hours. Thromboembolic events and dissections were documented.

RESULTS

PTA was significantly faster to perform (mean, 16.6 minutes versus 33.0 minutes for stent placement; P < .001), but the mean recanalization rate after 1 hour was significantly better after stent placement compared with PTA alone (67.5% versus 14.6%, P < .001). Due to the self-expanding force of the stent, vessel diameter further increased with time, whereas the recanalization result after PTA was prone to reocclusion. Besides thromboembolic events related to the passing maneuvers at the occlusion site, no thrombus fragmentation and embolization occurred during balloon inflation or stent deployment. Flow to side branches could also be restored at the occlusion site because it was possible to direct thrombus compression.

CONCLUSIONS

Stent placement and postdilation proved to be much more efficient in terms of acute and short-term vessel recanalization compared with PTA alone.

Advances in transcranial Doppler ultrasonography

Transcranial Doppler ultrasonography (TCD) is the only noninvasive real-time neuroimaging modality for the evaluation of characteristics of blood flow in basal intracerebral vessels that adds physiologic information to structural imaging. TCD has been rapidly evolving from a simple noninvasive diagnostic tool to an imaging modality with a broad spectrum of clinical applications. In acute stroke, TCD can provide rapid information about vascular stenosis and occlusion, the hemodynamic status of the cerebral circulation, and real-time monitoring of recanalization. Extended applications such as vasomotor reactivity testing, emboli monitoring, and right-to-left shunt detection help clinicians ascertain stroke mechanisms at the bedside, plan and monitor treatment, and determine prognosis. In the neurointensive care unit, TCD is useful for detecting increased intracranial pressure and confirming cerebral circulatory arrest. TCD is of established value for screening children with sickle cell disease and detecting and monitoring vasospasm after spontaneous subarachnoid hemorrhage.

Effect of modulated ultrasound parameters on ultrasound-induced thrombolysis

The potential of ultrasound to enhance enzyme-mediated thrombolysis by application of constant operating parameters (COP) has been widely demonstrated. In this study, the effect of ultrasound with modulated operating parameters (MOP) on enzyme-mediated thrombolysis was investigated. The MOP protocol was applied to an in vitro model of thrombolysis. The results were compared to a COP with the equivalent soft tissue thermal index (TIS) over the duration of ultrasound exposure of 30 min (p < 0.14). To explore potential differences in the mechanism responsible for ultrasound-induced thrombolysis, a perfusion model was used to measure changes in average fibrin pore size of clot before, after and during exposure to MOP and COP protocols and cavitational activity was monitored in real time for both protocols using a passive cavitation detection system. The relative lysis enhancement by each COP and MOP protocol compared to alteplase alone yielded values of 33.69 +/- 12.09% and 63.89 +/- 15.02% in a thrombolysis model, respectively (p < 0.007). Both COP and MOP protocols caused an equivalent significant increase in average clot pore size of 2.09 x 10(-2) +/- 0.01 microm and 1.99 x 10(-2) +/- 0.004 microm, respectively (p < 0.74). No signatures of inertial or stable cavitation were observed for either acoustic protocol. In conclusion, due to mechanisms other than cavitation, application of ultrasound with modulated operating parameters has the potential to significantly enhance the relative lysis enhancement compared to application of ultrasound with constant operating parameters.

Safety and efficacy of the sonographic acceleration of the middle cerebral artery recanalization: results of the pilot thrombotripsy study

The aim was to demonstrate the safety and efficacy of continuous ultrasound monitoring of the artery occlusion area (sonothrombotripsy) in patients with acute middle cerebral artery (MCA) occlusion. A total of 52 consecutive patients with acute MCA occlusion were included in the thrombotripsy group. Doppler monitoring of the region of occlusion was performed for up to 45 min. The control group was created from the NAIS study database. Patients were matched for their vascular status, age, sex, artery occlusion, NIHSS at admission, rt-PA treatment and time to the first ultrasound examination. The number of recanalized arteries at 6 and 24 h after the onset of symptoms, the number of independent patients (mRS 0-2 versus 3-6) after 90 d, and the number of serious adverse events were statistically evaluated. In the thrombotripsy group, 19 patients (36.5%) had complete recanalization and 27 (51.9%) patients had partial recanalization at 1 h after the start of the TCCS monitoring. Higher recanalization rates at 6 and 24 h after stoke onset were also seen compared with controls (69.2% versus 7.7% and 92.3% versus 61.5% complete recanalizations, respectively, p < 0.05). Independence (mRS 0-2) at day 90 was achieved by 61.5% of the thrombotripsy patients and 32.7% controls, p < 0.05, odds ratio 1.88 (95% confidence interval = 1.23 - 2.90). In both groups, two symptomatic intracerebral hemorrhages and one symptomatic brain edema occurred. Sonothrombotripsy with diagnostic transcranial duplex technology is safe and may offer benefit in addition to standard of care stroke treatment.

Ultrasound Assisted Thrombolysis in Acute Ischaemic Stroke: Preliminary Experience in Singapore

Background and Aim: Intravenously-administered tissue plasminogen activator (IV-TPA) induces thrombolysis and remains the only FDA-approved therapy for acute ischaemic stroke. IV-TPA thrombolysis has been approved recently in Singapore for acute stroke. Continuous exposure of clot to 2-MHz pulsed-wave transcranial Doppler (TCD) ultrasound during IV-TPA infusion is known to augment thrombolysis. We aimed to determine the feasibility, safety and efficacy of ultrasound-assisted thrombolysis in acute ischaemic stroke in Singapore. Subjects and Methods: Consecutive patients with acute ischaemic stroke due to intracranial arterial-occlusions were treated with standard IV-tPA and continuously monitored with 2-MHz TCD according to the CLOTBUST-trial protocol. Arterial recanalisation was determined with Thrombolysis in Brain Ischemia (TIBI) flow-grading system. Safety and efficacy of ultrasoundassisted thrombolysis were assessed by rates of symptomatic intracranial haemorrhage (sICH) and functional recovery at 1 month, respectively. Results: Five consecutive patients (mean age 58 years, 3 men and 3 of Chinese ethnicity) were included. Mean time elapsed between symptom onset and presentation to emergency room was 98 minutes (range, 50 to 135 minutes) while the mean time interval between symptom onset to IV-TPA bolus was 144 minutes (range, 125 to 180 minutes). Partial or complete recanalisation with reduction in the stroke severity was noted in 4 out of the 5 patients during IV-TPA infusion (mean change in NIHSS = 4 points; range 2 to 8 points). None of our patients developed sICH while 4 patients demonstrated good functional outcome at 1 month. Conclusions: Our preliminary study demonstrates the feasibility, safety and efficacy of ultrasound-assisted thrombolysis in acute ischaemic stroke in Singapore. Continuous TCD-monitoring during IV-TPA infusion provides real-time information, enhances thrombolysis and improves functional outcomes in acute ischaemic stroke. Key words: Acute ischaemic stroke, Thrombolysis, Transcranial Doppler

Inadequate acoustical temporal bone window in patients with a transient ischemic attack or minor stroke: role of skull thickness and bone density

Transcranial Doppler (TCD) ultrasonography may provide important diagnostic and prognostic information in patients with ischemic stroke or transient ischemic attack. TCD also enhances the effect of thrombolytic treatment in patients with acute stroke. In some patients, especially elderly women, TCD cannot be performed because of temporal bone window failure (WF). We investigated whether skull thickness or bone density on computed tomography scans predicts WF. In 182 patients with a transient ischemic attack or minor ischemic stroke, skull thickness and bone density measurements were made at the level of the temporal bone window. Multiple logistic regression analysis was used to relate independent variables to WF and to adjust the estimates for possible confounding factors. TCD signals were absent on the symptomatic side in 22 female and 11 male patients (18%). Both skull thickness and radiodensity at the level of the temporal bone window were strongly related to WF as well as age and female gender. After adjustment according to age and gender, skull thickness at the temporal bone window was an independent prognostic factor of WF (odds ratio [OR]: 2.3 per mm increase in skull thickness, 95% confidence interval [CI]: 1.4 to 3.8). Radiodensity of the temporal bone decreased with age in women (-52 HU per 10 y over 50 y of age, 95% CI: -73 to -30) but in men (-10 HU per 10 y over 50 y of age, 95% CI: -33 to 13), no statistically significant association was observed. We computed probabilities of WF for each patient individually. With a probability cut point of 50%, 33% of the patients with WF and 97% of the patient without WF were correctly identified. The area under the receiver operating characteristic (ROC) curve of this simple prediction model including age, gender and skull thickness was 0.88; the area under the ROC curve of a gender-stratified model including age, skull thickness and radiodensity was 0.90. This difference was not statistically or clinically significant p = 0.13). WF is more common in women because density of the temporal bone in elderly women is low. Absence of WF can be predicted by a combination of three simple parameters: skull thickness, age and gender. This may help to select patients with ischemic stroke for diagnostic TCD screening and to facilitate targeted delivery of ultrasound-enhanced thrombolysis.

Intravenous recombinant tissue plasminogen activator improves arterial recanalization rates and reduces infarct volumes in patients with hyperdense artery sign on baseline computed tomography

BACKGROUND

We sought to evaluate arterial recanalization as measured by changes in the presence of hyperdense artery sign (HAS) on initial and 24-hour computed tomography scans in patients treated with recombinant tissue plasminogen activator (rt-PA) or placebo, and to assess the effect of rt-PA on patient outcomes in this population.

METHODS

Patients in the National Institute of Neurological Disorders and Stroke (NINDS) rt-PA Stroke Trial composed the study group. We determined the percentage of patients with HAS in rt-PA- and placebo-treated groups who had persistence (HAS +/+) or resolution (HAS +/-) of HAS on 24-hour computed tomography, and compared outcomes in those with resolution or persistence of the sign in these treatment groups.

RESULTS

Baseline HAS occurred in 79 of 604 eligible patients (13%). The two treatment groups were similar, although patients treated with rt-PA were significantly older. Of the 79 patients with HAS on baseline computed tomography scan, 14 of 37 (38%) treated with rt-PA had resolution of HAS at 24 hours compared with 7 of 42 (17%) treated with placebo (P = .03). Infarct volumes at 24 hours were significantly smaller in patients treated with rt-PA with resolution of the sign, compared with those who had persistence of the sign (P = .004). In our analysis, functional outcomes were not significantly improved based on resolution of HAS in either treatment group. There were 4 symptomatic ICHs in the rt-PA-treated group with HAS as compared with two in the placebo-treated group.

CONCLUSION

Among patients with HAS at baseline in the NINDS rt-PA Stroke Trial, intravenous rt-PA increased recanalization as measured by resolution of HAS and reduced infarct volumes at 24 hours.

Recanalization between 1 and 24 hours after t-PA therapy is a strong predictor of cerebral hemorrhage in acute ischemic stroke patients

BACKGROUND AND PURPOSE

Intravenous administration of tissue plasminogen activator (t-PA) can improve clinical outcomes in patients with acute ischemic stroke. The most important complication of t-PA therapy is intracerebral hemorrhage (ICH). The aim of this study was to use serial MRI studies to identify independent predictors of symptomatic and asymptomatic ICH after t-PA therapy.

METHODS

Consecutive anterior-circulation ischemic stroke patients treated with t-PA within 3 h of stroke onset were studied prospectively. To identify the presence of recanalization in the occluded arteries and the presence of ICH, MRI, including diffusion weighted imaging (DWI), T2*, and magnetic resonance angiography (MRA), was performed before and 1 h, 24 h, and 5-7 days after t-PA thrombolysis. The independent predictors of ICH were determined using multivariate logistic regression analysis.

RESULTS

41 patients (21 males, 20 females; mean age, 73.2+/-10.7 years) were enrolled, and 19 ICHs (1 symptomatic, 18 asymptomatic) were observed on T2*. The initial MRA demonstrated occluded brain arteries in 31 patients (75.6%), of which follow-up MRA at 1 h, 24 h, and 5-7 days after t-PA therapy revealed recanalization in 48.4%, 80.0%, and 90.0% of patients, respectively. The frequency of recanalization within 1 h after t-PA therapy did not differ between ICH and No-ICH groups, but the ICH group had more frequent recanalization between 1 h and 24 h after t-PA than the No-ICH group (50.0% vs. 4.5%, P=0.001). The ICH group had arterial fibrillation (AF) more frequently than the No-ICH group (78.9% vs. 27.3%, P=0.001). Compared to the No-ICH group, the NIHSS score was higher (16.4+/-5.7 vs. 11.5+/-6.5, P=0.011) and the ASPECTS-DWI value (a normal DWI has an ASPECTS-DWI value of 11 points) was lower (7.3+/-2.4 vs. 8.9+/-1.9, P=0.019) in the ICH group. Multivariate logistic regression analysis demonstrated that the presence of recanalization between 1 and 24 h after the end of t-PA infusion (OR: 20.2; CI: 1.0-340.9; P=0.037) was the only independent predictor of ICH.

CONCLUSION

Recanalization of occluded arteries between 1 and 24 h but not within 1 h after t-PA infusion should be independently associated with symptomatic and asymptomatic ICH after t-PA therapy.

Comparative in vitro study of five mechanical embolectomy systems: effectiveness of clot removal and risk of distal embolization

INTRODUCTION

We report an in vitro study comparing the effectiveness of clot removal and clot fragmentation of five embolectomy systems.

METHODS

A flow model was embolized with fresh and old thrombi, occluding an inner diameter of 2-5 mm simulating internal carotid artery (ICA), basilar artery (BA) and middle cerebral artery (MCA) branch occlusion. Embolectomy was performed using five retrieval systems: CATCH (Balt), Merci retriever (Concentric), InTime and Attracter (Boston Scientific), and the Phenox Clot Retriever (Phenox). Clot removal and evidence and type of thrombus fragmentation and distal embolization were recorded.

RESULTS

There were no observable differences attributable to thrombus age. The Merci, CATCH and Phenox Clot Retriever were equally able to mobilize and remove thrombi with the exception of one particularly firm clot. There were marked differences in terms of thrombus fragmentation and distal embolization. All devices produced micro- and macrofragments during penetration and retrieval. The Phenox Clot Retriever was able to filter fragments. The InTime and Attracter devices failed to retrieve thrombi in this model and achieved partial removal at best with a tendency towards thrombus displacement and fragmentation.

CONCLUSION

Within limits, the experimental setup was appropriate for generating occlusions of diameter 2-5 mm of various lengths, simulating ICA, BA and MCA thromboembolism. In this model, thrombus mobilization appeared to be less dependent upon the individual design of the retrieval system than on thrombus fragmentation. The ability to prevent distal embolization is, however, strongly dependent on the ability of a thrombectomy device to capture fragments that are generated during removal of the device.

Alberta Stroke Program Early CT Scoring of CT perfusion in early stroke visualization and assessment

BACKGROUND AND PURPOSE

Qualitative CT perfusion (CTP) assessment by using the Alberta Stroke Program Early CT Score (ASPECTS) allows rapid calculation of infarct extent for middle cerebral artery infarcts. Published thresholds exist for noncontrast CT (NCCT) ASPECTS, which may distinguish outcome/complication risk, but early ischemic signs are difficult to detect. We hypothesized that different ASPECTS thresholds exist for CTP parameters versus NCCT and that these may be superior at predicting clinical and radiologic outcome in the acute setting.

MATERIALS AND METHODS

Thirty-six baseline acute stroke NCCT and CTP studies within 3 hours of symptoms were blindly reviewed by 3 neuroradiologists, and ASPECTS were assigned. Treatment response was defined as major neurologic improvement when a > or =8-point National Institutes of Health Stroke Scale improvement at 24 hours occurred. Follow-up NCCT ASPECTS and 90-day modified Rankin score (mRS) were radiologic and clinical reference standards. Receiver operating characteristic curves derived optimal thresholds for outcome.

RESULTS

Cerebral blood volume and NCCT ASPECTS had similar radiologic correlations (0.6 and 0.5, respectively) and best predicted infarct size in the absence of major neurologic improvement. A NCCT ASPECT threshold of 7 and a cerebral blood volume threshold of 8 discriminated patients with poor follow-up scans (P < .0002 and P = .0001) and mRS < or =2 (P = .001 and P < .001). Only cerebral blood volume predicted major neurologic improvement (P = .02). Interobserver agreement was substantial (intraclass correlation coefficient, 0.69). Cerebral blood volume ASPECTS sensitivity, specificity, positive predictive value, and negative predictive value for clinical outcome were 60%, 100%, 100%, and 45%, respectively. No patients with cerebral blood volume ASPECTS <8 achieved good clinical outcome.

CONCLUSION

Cerebral blood volume ASPECTS is equivalent to NCCT for predicting radiologic outcome but may have an additional benefit in predicting patients with major neurologic improvement.

Influence of thrombin-activatable fibrinolysis inhibitor and plasminogen activator inhibitor-1 gene polymorphisms on tissue-type plasminogen activator-induced recanalization in ischemic stroke patients

OBJECTIVE

Endogenous resistance to tissue-type plasminogen activator (t-PA) might decrease the benefit of thrombolysis-induced recanalization. Thrombin-activatable fibrinolysis inhibitor (TAFI) and plasminogen activator inhibitor-1 (PAI-1) are fibrinolysis inhibitors. TAFI removes residues from partially degraded fibrin that in turn eliminates plasminogen binding sites; PAI-1 directly inhibits the activity of t-PA. We aimed to study whether the presence of two common functional polymorphisms of the TAFI and PAI-1 genes influence rates of recanalization of the middle cerebral artery (MCA) among t-PA-treated stroke patients.

METHODS AND RESULTS

TAFI and PAI-1 polymorphism determinations were performed by restriction fragment length polymorphism mapping and conventional sequencing in 139 patients with strokes involving the MCA and who received t-PA within 3 h. Recanalization was diagnosed by means of transcranial Doppler. No association was found between PAI-1 4 G/5 G polymorphism and recanalization rate. Dyslipidemia and TAFI Thr325Ile polymorphism were the main variables associated with recanalization resistance by the end of t-PA infusion: odds ratio (OR) 4.1 [95% confidence interval (95% CI) 1.6-10.8, P = 0.003] and OR 5.6 (95% CI 1.2-20, P = 0.031), respectively. The combination of the two polymorphisms doubled the risk of absence of recanalization: OR 11.1 (95% CI 1.4-89.8, P = 0.025).

CONCLUSIONS

Polymorphic fibrinolysis inhibitor genes influence t-PA-induced recanalization resistance in ischemic stroke patients, especially when coexisting in the same patient. Efforts to individualize thrombolytic treatments are required.

Combined intravenous and intra-arterial approach in acute stroke treatment

Despite the significant improvement in the outcome of ischaemic stroke with the use of intravenous recombinant tissue plasminogen activator, experience has shown limitations of the sole use of this approach in acute stroke treatment. This has encouraged the search for alternative managements for acute stroke. The combined use of intravenous/intra-arterial therapy is one such alternate treatment, if used in the right setting. In this review, the authors discuss the advantages and limitations of using this approach, together with an overview of the available therapies used through each route. The authors discuss the process of patient selection using clinical, as well as state of the art imaging modalities.

Beyond intravenous thrombolysis

The National Institute of Neurological Disorders and Stroke trial of recombinant tissue plasminogen activator has been considered a landmark study in the acute treatment of ischemic stroke. Unfortunately, only a small percentage of all ischemic stroke patients presents to the hospital in time to receive the drug. Moreover, the recannalization rate of a major artery occlusion, such as the proximal middle cerebral artery or top of the internal carotid artery occlusion, after intravenous (IV) thrombolytic therapy has been disappointingly low. Since the Food and Drug Administration's approval of IV plasminogen activator, there have been numerous randomized clinical trials investigating the safety and efficacy of different thrombolytics administered in various time frames. In addition to the IV administration, efforts have been made in order to study the radiographic as well as clinical effects of intra-arterial (IA) thrombolysis. The combination of IV and IA thrombolysis has been studied. For patients who do not qualify for receiving chemical thrombolysis, new devices have been developed for mechanical thrombectomy. Angioplasty and stenting procedures are being performed more frequently than in the past as one of the treatment modalities for acute ischemic stroke patients. Relentless research effort is being made internationally in order to fight the devastating disease which now goes beyond the conventional IV thrombolysis.

Changes in haemocoagulation in healthy volunteers after a 1-hour thrombotripsy using a diagnostic 2–4 MHz transcranial probe

INTRODUCTION

The aim was to monitor the changes in haemocoagulation parameters in healthy volunteers after a thrombotripsy with 1-hour transcranial Doppler monitoring using a 2-4 MHz probe.

MATERIALS AND METHODS

About 10 healthy volunteers underwent a 1-hour thrombotripsy of the middle cerebral artery (MCA), thrombotripsy of the radial artery and a standard 20-min neurosonologic examination (NSE) in 2-week intervals. Platelet count, aPTT, prothrombin time, fibrinogen, D-dimers, tPA, FDP, alpha-2-antiplasmin (AP), plasminogen, PAI-1 antigen, time of euglobulin clot lysis (ECL), homocysteine, and lipoprotein (a) were examined before, at the end and 24 h after a thrombotripsy. All adverse events were monitored.

RESULTS

After a thrombotripsy of the MCA, PAI-1 antigen, tPA antigen, fibrinogen and AP activity were significantly decreased by a mean of 32, 23, 7, and 4% respectively (P < 0.05 in all cases). After a thrombotripsy of the RA, there was a significant decrease in tPA antigen alone by an average of 14% (P < 0.05). Standard NSE did not affect any of the measured factors.

CONCLUSIONS

Thrombotripsy with 1-hour TCD monitoring using a 2-4 MHz diagnostic probe may affect the fibrinolytic system in humans.

Clinical applications of focused ultrasound-the brain

This paper provides a historic and contemporary overview of the use of focused ultrasound for treating brain disorders.

Ultrasound-enhanced thrombolysis in acute ischemic stroke: potential, failures, and safety

Experimental and pilot clinical evidence shows that thrombolysis with intravenous tissue plasminogen activator (TPA) can be enhanced with ultrasound. Ultrasound delivers mechanical pressure waves to the clot, thus exposing more thrombus surface to circulating drug. The international multicenter phase II CLOTBUST trial showed that, in patients with acute ischemic stroke, transcranial Doppler (TCD) monitoring augments TPA-induced arterial recanalization, with a nonsignificant trend toward an increased rate of recovery from stroke, compared with placebo. In the CLOTBUST trial, the dramatic clinical recovery from stroke coupled with complete recanalization within 2 hours after TPA bolus occurred in 25% of patients treated with TPA + TCD (n = 63), compared with 8% of those who received TPA alone (n = 63, P = 0.02). Different results were achieved in smaller studies that used transcranial color-coded duplex sonography (TCCD) and a nonimaging therapeutic ultrasound system. The findings of the TRUMBI trial (26 patients) underscored the adverse bioeffects of mid-kilohertz (300 kHz) ultrasound, such as promotion of bleeding in brain areas both affected and unaffected by ischemia. Exposure to multifrequency, multielement duplex ultrasound resulted in a trend toward a higher risk of hemorrhagic transformation. To further enhance the ability of TPA to break up thrombi, current ongoing clinical trials include phase II studies of a single-beam, 2-MHz TCD with perflutren lipid microspheres. Enhancement of intra-arterial TPA delivery is being clinically tested with 1.7-2.1 MHz pulsed-wave ultrasound (EKOS catheter). Multinational dose escalation studies of microspheres and the development of an operator-independent ultrasound device are underway.

Transcranial focused ultrasound surgery

The development of high-intensity ultrasound technology into a system for performing image-guided noninvasive ultrasound neurosurgery has developed at a relatively rapid pace in the past few years. Magnetic resonance imaging has contributed significantly to this development by providing a modality by which percutaneous ultrasound treatments can be preoperatively planned, intraoperatively guided and postoperatively evaluated for safety and efficacy. Especially in the case of transcranial ultrasound therapies, the structural identification and thermal monitoring of cortical structures is essential to avoid overheating at the skull-brain interface and to avoid the sonication of critical structures. This chapter briefly describes the physics of transmitting ultrasound through the skull and the technological advances that circumvented the physical limits imposed by the skull bone. The integration of magnetic resonance guidance and monitoring is detailed, along with an overview of ongoing studies with a commercially developed magnetic resonance imaging-compatible hemispherical transducer array.

Mechanical interventions to treat acute stroke

The approach to stroke therapy has historically been limited due to the existence of relatively few treatment options and the necessity for action within 3 hours of symptom onset. As neuroimaging technology advances, fertile new ground is revealed for novel therapies. Recently, a number of exciting mechanical systems have been developed with potential efficacy even hours after cerebrovascular occlusion: endovascular clot disruption, endovascular clot extraction, and angioplasty with stenting are currently under study, with promising initial results. With more options, each with greater effectiveness in a particular clinical scenario, the physician is now better equipped than ever to treat acute ischemic stroke successfully.

Role of transcranial Doppler ultrasonography in evaluation of patients with cerebrovascular disease

Transcranial Doppler ultrasonography (TCD) is the only noninvasive examination method that enables the reliable evaluation of blood flow from the basal intracerebral vessels, adding physiologic information to the anatomic images. TCD is relatively inexpensive, can be performed at bedside, and allows monitoring in acute emergency settings and for prolonged periods with a high temporal resolution, making it ideal for studying dynamic cerebrovascular responses. In acute stroke, TCD is capable of providing rapid information about the hemodynamic status of the cerebral circulation and monitoring recanalization in real-time, with a potential for enhancing tissue plasminogen activator-induced thrombolysis. Extended applications such as emboli monitoring, right-to-left shunt detection, and vasomotor reactivity make TCD an important and valuable tool for evaluating stroke mechanisms, planning and monitoring treatment, and determining prognosis.

Ultrasound enhanced thrombolysis: applications in acute cerebral ischemia

Intravenous tissue plasminogen activator (TPA) improves patient chances to recover from stroke by inducing mostly partial recanalization of large intracranial thrombi. TPA activity can be enhanced with ultrasound including 2 MHz transcranial Doppler (TCD). TCD identifies residual blood flow signals around thrombi, and, by delivering mechanical pressure waves, exposes more thrombus surface to circulating TPA. The international multi-center CLOTBUST trial showed that ultrasound enhances thrombolytic activity of a drug in humans thereby confirming multi-disciplinary experimental research conducted worldwide for the past 30 years.

In the CLOTBUST trial, the dramatic clinical recovery from stroke coupled with complete recanalization within 2 hours after TPA bolus occurred in 25% of patients treated with TPA+TCD compared to 8% who received TPA alone (p=0.02). Complete clearance of a thrombus and dramatic recovery of brain functions during treatment are feasible goals for ultrasound-enhanced thrombolysis that can lead to sustained recovery. An early boost in brain perfusion seen in the Target CLOTBUST group resulted in a trend of 13% more patients achieving favorable outcome at 3 months, subject for a pivotal trial. However, different results were achieved in a small TRUMBI trial and another study that used Transcranial Color-Coded Duplex Sonography (TCCD). Adverse bio-effects of mid-KHz (300) ultrasound promote bleeding, including brain areas not-affected by ischemia while exposure to multi-frequency / multi-element duplex ultrasound resulted in a trend towards higher risk of hemorrhagic transformations.

To further enhance the ability of TPA to break up thrombi, current ongoing clinical trials include phase II studies of a single beam 2 MHz TCD with perflutren-lipid microspheres. Enhancement of intra-arterial TPA delivery is being clinically tested with 1.7-2.1 MHz pulsed wave ultrasound (EKOS catheter). Multi-national dose escalation studies of microspheres and the development of an operator independent ultrasound device are underway.

Anesthetic-mediated protection/preconditioning during cerebral ischemia

Cerebral ischemia is a multi-faceted neurodegenerative pathology that causes cellular injury to neurons within the central nervous system. In light of the underlying mechanisms being elucidated, clinical trials to find possible neuroprotectants to date have failed, thus highlighting the need for new putative targets to offer protection. Recent evidence has clearly shown that anesthetics can confer significant protection and or induce a preconditioning effect against cerebral ischemia-induced injury. This review will focus on the putative protection/preconditioning that is afforded by anesthetics, their possible interaction with GABA(A) and glutamate receptors and two-pore potassium channels. In addition, the interaction with inflammatory, apoptotic and underlying molecular (particularly immediately early genes and inducible nitric oxide synthase etc) pathways, the activation of K(ATP) channels and the ability to provide lasting protection will also be addressed.