Intracranial clot dissolution is associated with embolic signals on transcranial Doppler

Development of a Carotid Artery Thrombolysis (iCAT) Stroke Model in Mice

Development of a mouse carotid artery thrombolysis model of stroke.

iCAT enables assessment of adjunctive antithrombotic therapies on arterial recanalization, cerebral perfusion, and stroke outcomes.

Recanalization with restored cerebral perfusion is the primary goal of thrombolytic therapy in acute ischemic stroke. The identification of adjunctive therapies that can be safely used to enhance thrombolysis in stroke remains an elusive goal. We report here the development of a mouse in situ carotid artery thrombolysis (iCAT) stroke model involving graded cerebral ischemia to induce unihemispheric infarction after thrombotic occlusion of the common carotid artery (CCA). Electrolytic-induced thrombotic occlusion of the left CCA enabled real-time assessment of recanalization and rethrombosis events after thrombolysis with recombinant tissue-type plasminogen activator (rtPA). Concurrent transient stenosis of the right CCA induced unihemispheric hypoperfusion and infarction in the left middle cerebral artery territory. Real-time assessment of thrombolysis revealed recanalization rates <30% in rtPA-treated animals with high rates of rethrombosis. Addition of the direct thrombin inhibitor argatroban increased recanalization rates to 50% and reduced rethrombosis. Paradoxically, this was associated with increased cerebral ischemia and stroke-related mortality (25%-42%). Serial analysis of carotid and cerebral blood flow showed that coadministration of argatroban with rtPA resulted in a marked increase in carotid artery embolization, leading to distal obstruction of the middle cerebral artery. Real-time imaging of carotid thrombi revealed that adjunctive anticoagulation destabilized platelet-rich thrombi at the vessel wall, leading to dislodgement of large platelet emboli. These studies confirm the benefits of anticoagulants in enhancing thrombolysis and large artery recanalization; however, at high levels of anticoagulation (∼3-fold prolongation of activated partial thromboplastin time), this effect is offset by increased incidence of carotid artery embolization and distal middle cerebral artery occlusion. The iCAT stroke model should provide important new insight into the effects of adjunctive antithrombotic agents on real-time thrombus dynamics during thrombolysis and their correlation with stroke outcomes.

Transcranial Doppler ultrasonography (uses, limitations, and potentials): a review article

Background

The additional information that transcranial Doppler can provide as part of a multimodal imaging protocol in many clinical settings has not been evaluated.

Main body

Transcranial Doppler is a bedside procedure used to assess cerebral blood flow velocity via cerebral circulation and pulsatility index (PI). Many diseases can lead to cerebral vessels vasospasm as in subarachnoid hemorrhage and trauma. Cerebral vessels vasospasm represented by abnormal elevation of cerebral blood flow velocity. Intracranial pressure can be monitored by pulsatility index which reflects blood flow resistance in cerebral vessels. Transcranial Doppler ultrasonography is also the unique modality for detection of micro emboli in high-risk patients. Also, it can be used for evaluation of circulatory arrest with subsequent confirmation of brain death

Conclusion

Transcranial Doppler ultrasonography is the only diagnostic modality that provides a reliable assessment of cerebral blood flow patterns in real time. The physiological information obtained from TCD is complementary to the anatomical details obtained from other neuroimaging modalities. TCD is relatively cheap, can be performed bedside, and allows monitoring in acute emergency settings.

Microemboli After Successful Thrombectomy Do Not Affect Outcome but Predict New Embolic Events

Background and Purpose- We aimed to determine if microemboli after endovascular thrombectomy correlate with unfavorable outcomes despite successful recanalization. Methods- This is a prospective multicenter study of consecutive patients with ischemic stroke and occlusion of anterior circulation vessels (terminal internal carotid or main trunk of the middle cerebral artery/first-order branch of the main trunk of the middle cerebral artery segments of middle cerebral artery) after successful thrombectomy (modified Treatment In Cerebral Ischemia grades 2b-3). Microembolic signals (MES) were assessed by 30 minutes of transcranial Doppler monitoring within 72 hours of the last-seen-well time. Major outcomes included modified Rankin Scale at 90 days and infarct volume on head computed tomography at 24 hours. We also assessed early outcomes based on National Institutes of Health Stroke Scale variation and recurrence of stroke, transient ischemic attack, or systemic embolism within 90 days. Results- Among 111 patients, MES were detected in 43 (39%), with a median rate of 4 counts/h (interquartile range 2-12). The occurrence of MES was not associated with a significant difference in modified Rankin Scale (ordinal shift analysis, adjusted odds ratio, 1.06 [95% CI, 0.48-2.34] P=0.85) nor in functional independence (modified Rankin Scale, 0-2: adjusted odds ratio, 0.52 [95% CI, 0.19-1.39] P=0.19). Patients with and without MES had similar infarct volumes (adjusted beta, 11.2 [95% CI, -46.6 to +22.9] P=0.51) on 24-hour computed tomography. MES did predict new embolic events (adjusted Cox hazard ratio, 6.78 [95% CI, 1.63-27.8] P=0.01). Conclusions- MES detected by transcranial Doppler following endovascular treatment of anterior circulation occlusions do not predict clinical or radiological outcome. However, such emboli are an independent marker of recurrent embolic events within 90 days.

Use of Transcranial Doppler (TCD) ultrasound in the Neurocritical Care Unit

Transcranial Doppler (TCD) is a portable device that uses a handheld 2-MHz transducer. It is most commonly used in subarachnoid hemorrhage where cerebral blood flow velocities in major intracranial blood vessels are measured to detect vasospasm in the first 2 to 3 weeks. TCD is used to detect vasospasm in traumatic brain injury and post-tumor resection, measurement of cerebral autoregulation and cerebrovascular reactivity, diagnosis of acute arterial occlusions in stroke, screening for patent foramen ovale and monitoring of emboli. It can be used to detect abnormally high intracranial pressure and for confirmation of total cerebral circulatory arrest in brain death.

Thrombolytic therapy for acute ischaemic stroke: what can we do to improve outcomes?

Constant efforts are being made in the stroke community to aim for maximum benefit from thrombolytic therapy since the approval of intravenous recombinant tissue plasminogen activator (rt-PA; alteplase) for the management of acute ischaemic stroke. However, fear of symptomatic haemorrhage secondary to thrombolytic therapy has been a major concern for treating physicians. Certain imaging and clinical variables may help guide the clinician towards better treatment decision making. Aggressive management of some predictive variables that have been shown to be surrogate outcome measures has been related to better clinical outcomes. Achieving faster, safer and complete recanalization with evolving endovascular techniques is routinely practiced to achieve better clinical outcomes. Selection of an 'ideal candidate' for thrombolysis can maximize functional outcomes in these patients. Although speed and safety are the key factors in acute management of stroke patients, there must also be a systematic and organized pattern to assist the stroke physician in making decisions to select the 'ideal candidate' for treatment to maximize results.

Microembolus detection by transcranial Doppler sonography: review of the literature

Transcranial Doppler can detect microembolic signals which are characterized by unidirectional high intensity increase, short duration, random occurrence, and a “whistling” sound. Microembolic signals have been detected in a number of clinical settings: carotid artery stenosis, aortic arch plaques, atrial fibrillation, myocardial infarction, prosthetic heart valves, patent foramen ovale, valvular stenosis, during invasive procedures (angiography, percutaneous transluminal angioplasty), surgery (carotid, cardiopulmonary bypass, orthopedic), and in certain systemic diseases. Microembolic signals are frequent in large artery disease, less commonly detected in cardioembolic stroke, and infrequent in lacunar stroke. This article provides an overview about the current state of technical and clinical aspects of microembolus detection.

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.

Spontaneous recanalization at subacute phase of stroke may be dramatic: A case report

Spontaneous recanalization of the occluded cerebral arteries has occasionally occurred in an acute phase of stroke patients. We report a stroke patient with recanalization at 7 days of onset detected by using continuous transcranial Doppler (TCD) monitoring. After the presence of microembolic signals on TCD display, dynamic flow changes of the middle cerebral artery (MCA) occurred, which represented recanalization of the occluded MCA.

Ultrasound Identification and Lysis of Clots

Poor recovery after systemic tissue plasminogen activator (tPA) therapy could result from the initial severity of ischemic insult and slow and incomplete thrombolysis. Persisting arterial occlusions can be identified at bedside using portable diagnostic ultrasound by detecting residual flow signals around the thrombus (thrombolysis in brain ischemia [TIBI] flow grades). A narrow pulsed ultrasound beam can be steadily aimed at the thrombus/residual flow interface, exposing more thrombus surface and structures to tPA, and tPA activity can be enhanced with 2 MHz transcranial Doppler (TCD). A randomized, multicenter, clinical trial called CLOTBUST (Combined Lysis of Thrombus in Brain ischemia using transcranial Ultrasound and Systemic tPA) trial showed a 49% rate of complete recanalization or dramatic clinical recovery from stroke within 2 hours after tPA bolus when tPA infusion was continuously monitored with TCD, compared with 30% among patients who received tPA without ultrasound monitoring (P=0.03, number needed to treat, 5). Early complete recanalization was sustained at 2 hours by 38% of monitored patients compared with 12.7% controls. The CLOTBUST Trial showed a trend toward sustaining complete recovery at 3 months (41.5% versus 28%, modified Rankin Scale scores 0 to 1), subject for a pivotal phase III trial. Ultrasound is an inexpensive, noninvasive, real-time monitoring tool to identify nonresponders to systemic tPA and select patients with persisting occlusions for intraarterial interventions. Early brain perfusion augmentation, complete recanalization, and dramatic clinical recovery are feasible goals for ultrasound-enhanced thrombolysis.

Systemic Thrombolysis With Recombinant Tissue Plasminogen Activator and Tirofiban in Acute Middle Cerebral Artery Occlusion

Background and Purpose— In acute ischemic stroke, thrombolytic treatment with recombinant tissue plasminogen activator (rtPA) is limited by a concomitant activation of the coagulatory system, leading to incomplete or delayed reperfusion, microcirculatory disturbances, or even repeated vessel occlusions. Our pilot study sought to assess the therapeutic potential of a new treatment strategy combining rtPA at reduced dosages with a platelet glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitory agent in acute middle cerebral artery occlusion.

Methods— Nineteen patients suffering from acute middle cerebral artery occlusion (Thrombolysis in Myocardial Infarction [TIMI] flow grade 0 to 1) underwent combined intravenous thrombolytic treatment using rtPA at reduced dosages and the GPIIb/IIIa antagonist tirofiban. Stroke MRI (diffusion- and perfusion-weighted imaging) and MR angiography were performed at baseline and between days 1 and 2 after treatment. Clinical scores (National Institutes of Health Stroke Scale and modified Rankin Scale) were assessed at baseline and after 1 week.

Results— Middle cerebral artery recanalization (TIMI flow grade 2 and 3) occurred in 13 of 19 patients (68%). The ischemic lesion on follow-up MRI was significantly smaller in patients with recanalization compared with those without recanalization ( P =0.001). Only patients with recanalization improved neurologically ( P <0.001). Because no symptomatic hemorrhage was observed, the power of our study to detect a symptomatic bleeding rate of ≥8% was at least 80%.

Conclusions— Combined thrombolysis with a GPIIb/IIIa antagonist and rtPA at reduced dosages is promising but cannot be recommended for general use before prospective randomized clinical trials are completed.

Neuroendovascular Rescue: Interventional Treatment of Acute Ischemic Stroke

Stroke continues to be a major health problem for our society. Despite the proven effectiveness of intravenous tissue plasminogen activator (t-PA) for the treatment of acute ischemic stroke, only a minority of patients qualify for this type of therapy. Furthermore, the existing literature has demonstrated that t-PA is not as effective in the treatment of occlusion of large cerebral arteries. The benefit-to-risk assessment of this subpopulation of stroke patients makes them the best candidates for neuroendovascular rescue. This term refers to the intra-arterial application of techniques designed to promote arterial recanalization, and includes intra-arterial thrombolysis and antithrombotic agents, direct mechanical disruption, angioplasty, stenting, embolectomy, and vasoactive pharmacologic intervention. The timing and choice of these procedures, as well as the care of the patient prior to, during, and after the intervention, requires a highly focused and expert approach.

Velocity of microemboli and transit time from the heart to the brain in patients with patent foramen ovale and artificial heart valves

There is no information about the physical behavior of microemboli en route from their source to the cerebral vessels. Microemboli could abide to a certain laminae, and have a consistent velocity, or wander between different laminae, and keep changing their velocity. Two hundred and seventy four microemboli were recorded by transcranial Doppler (TCD) in six patients with artificial valves, and 119 microemboli were recorded in response to i.v. injection of saline agitated with air in eight patent foramen ovale (PFO) patients. Transit time of microemboli, calculated based on their arrival time at the cerebral vessel (site of monitoring) was explored as a possible function of their measured velocity at the detection point. In the PFO group, the relation between embolus velocity and transit time was: embolus velocityPFO = -41.8 * transit time + 100.6, whereas for the artificial heart valve group it was: embolus velocityValve = -22.6 * transit time + 67.1. Transit time, in both clinical groups, was inversely related to velocity (p < 0.001), thus, early appearing emboli had higher velocity and vice versa. The inverse relation between transit time and measured terminal velocity implies a consistent velocity per microemboli en route, in both groups. Thus, a flow abided to a certain laminae seems to characterize microemboli.

Dynamics and embolic activity of symptomatic intra-cranial cerebral artery stenoses

OBJECTIVE

To investigate the occurrence of microembolic signals (MES) and hemodynamic features in patients with acute symptomatic intracranial cerebral artery stenoses by transcranial Doppler (TCD).

MATERIAL AND METHODS

Twelve patients with acute hemispheric ischemic events and corresponding intracranial cerebral artery stenoses as identified by TCD, and exclusion of extracranial or cardiac emboli sources were repeatedly studied by TCD monitoring of the affected and the contralateral vessel. The occurrence of MES and MES clusters (> or =3 MES per second) and of flow velocity changes was examined.

RESULTS

Nine patients presented with MES in the affected artery during the first measurement. In seven patients sudden flow velocity changes could be detected in the affected vessel. In five patients these changes were accompanied by MES clusters. MES and velocity changes disappeared in all patients during follow-up, and the degree of stenosis decreased in nine patients.

CONCLUSIONS

The high prevalence of MES and sudden velocity changes in acute intracranial cerebral artery stenoses indicates that acute intracranial stenoses may be formed at least in part by mobile thrombotic material.

Controversies about tissue plasminogen activator: extending the window of therapy

The management of stroke has undergone significant development over the past 15 years. Perhaps the single most important landmark has been the approval by the Food and Drug Administration of intravenous (IV) tissue plasminogen activator (t-PA) for the treatment of ischemic stroke. However, the approval of this drug has not met with unanimous support by the medical community and, at present, only a minority of stroke patients receive t-PA. Although this is partly due to the fact that many patients do not meet criteria for treatment with IV t-PA, others simply do not arrive at medical facilities sufficiently early to be safely managed using thrombolysis. The appropriate use of IV t-PA in the treatment of ischemic stroke requires proper selection of patients and strict adherence to clinical protocols of treatment. The ideal stroke patient for treatment with IV t-PA is one who suffers occlusion of a small artery that leads to a disabling deficit.

Speed of intracranial clot lysis with intravenous tissue plasminogen activator therapy: sonographic classification and short-term improvement

BACKGROUND

Arterial recanalization precedes clinical improvement or may lead to hemorrhage or reperfusion injury. Speed of clot lysis was not previously measured in human stroke.

METHODS AND RESULTS

Transcranial Doppler (TCD) and the National Institutes of Health Stroke Scale (NIHSS) were used to monitor consecutive patients receiving intravenous tissue plasminogen activator (tPA), before tPA bolus and at 24 hours. Patients with complete or partial recanalization of the middle cerebral or basilar artery on TCD were studied. Recanalization was classified a priori as sudden (abrupt appearance of a normal or stenotic low-resistance signal), stepwise (flow improvement over 1 to 29 minutes), or slow (>/=30 minutes). Recanalization was documented in 43 tPA-treated patients (age 68+/-17 years; NIHSS score 16.8+/-6, median 15 points). tPA bolus was given at a mean of 135+/-61 minutes after symptom onset. Recanalization began at a median of 17 minutes and was completed at 35 minutes after tPA bolus, with mean duration of recanalization of 23+/-16 minutes. Recanalization was sudden in 5, stepwise in 23, and slow in 15 patients. Faster recanalization predicted better short-term improvement (P=0.03). At 24 hours, 80%, 30%, and 13% of patients in these respective recanalization groups had NIHSS scores of 0 to 3. Symptomatic hemorrhage occurred in only 1 patient, who had stepwise recanalization 5.5 hours after stroke onset. Slow or partial recanalization with dampened flow signal was found in 53% of patients with total NIHSS scores >10 points at 24 hours (P=0.01). Complete recanalization (n=25) occurred faster (median 10 minutes) than partial recanalization (n=18; median 30 minutes; P=0.0001).

CONCLUSIONS

Rapid arterial recanalization is associated with better short-term improvement, mostly likely because of faster and more complete clot breakup with low resistance of the distal circulatory bed. Slow (>/=30 minutes) flow improvement and dampened flow signal are less favorable prognostic signs. These findings may be evaluated to assist with selection of patients for additional pharmacological or interventional treatment.