Transcranial Doppler detected cerebral microembolism following carotid endarterectomy. High microembolic signal loads predict postoperative cerebral ischaemia

Evaluation of the Accuracy in Maximum Intensity Projection Images of Cerebral Computed Tomographic Angiography for the Diagnosis of Cerebral Vasospasm Following Subarachnoid Hemorrhage, in Comparison to Digital Subtraction Angiography

Objective

The purpose of this retrospective study is to determine the accuracy of maximum intensity projection (MIP) images of computed tomographic angiography (CTA) for diagnosis of cerebral vasospasm (CV) following subarachnoid hemorrhage (SAH) compared with that of digital subtraction angiography (DSA).

Materials and Methods

For patients admitted to our hospital for SAH, MIP images of CTA and DSA were checked at admission, and images were taken again 1 week later. This protocol was used in 39 cases. MIP images of CTA and DSA examinations were reviewed by two independent readers.

Results

Accuracy of MIP images of CTA in various arterial segments, using DSA as the gold standard: the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy for different segments varied from 84 to 97, 33–100, 84–100%, 25–85, and 79–97%, respectively, for readers. Accuracy of CTA in various vasospasm severity, using DSA as the gold standard: the sensitivity, specificity, PPV, NPV, and accuracy for different vasospasm severity varied from 44 to 100, 69–100, 36–100%, 61–100, and 88–100%, respectively, for readers. Accuracy of CTA in central segments versus peripheral segments, using DSA as the gold standard: the sensitivity, specificity, PPV, NPV, and accuracy for central segments and peripheral segments varied from 90 to 94, 68–83, 93–97%, 56–69, and 87–93%, respectively, for readers.

Conclusion

MIP imaging of CTA is a useful modality when diagnosing CV after SAH.

Registry report on prediction by Pocock cardiovascular score of cerebral microemboli acutely following carotid endarterectomy

Background

Cerebral microemboli may lead to ischaemic neurological complications after carotid endarterectomy (CEA). The association between classical cardiovascular risk factors and acute cerebral microemboli following carotid surgery has not been studied. The aim of this study was to explore whether an established cardiovascular risk score (Pocock score) predicts the presence of cerebral microemboli acutely after CEA.

Subjects and methods

Pocock scores were assessed for the 670 patients from the Carotid Surgery Registry (age 71±1 (SEM) years, 474 (71%) male, 652 (97%) Caucasian) managed from January 2002 to December 2012 in the Regional Vascular Centre at University Hospitals Coventry and Warwickshire NHS Trust, which serves a population of 950 000. CEA was undertaken in 474 (71%) patients for symptomatic carotid stenosis and in 196 (25%) asymptomatic patients during the same period. 74% of patients were hypertensive, 71% were smokers and 49% had hypercholesterolaemia.

Results

A high Pocock score (≥2.3%) was significantly associated with evidence of cerebral microemboli acutely following CEA (P=0.039, Mann-Whitney (MW) test). A Pocock score (≥2.3%) did not predict patients who required additional antiplatelet therapy (microemboli signal (MES) rate >50 hour^-1: P=0.164, MW test). Receiver operating characteristic analysis also showed that the Pocock score predicts acute postoperative microemboli (area under the curve (AUC) 0.546, 95% CI 0.502 to 0.590, P=0.039) but not a high rate of postoperative microemboli (MES >50 hour⁻¹: AUC 0.546, 95% CI 0.482 to 0.610, P=0.164). A Pocock score ≥2.3% showed a sensitivity of 74% for the presence of acute postoperative cerebral microemboli. A Pocock score ≥2.3% also showed a sensitivity of 77% and a negative predictive value of 90% for patients who developed a high microembolic rate >50 hour⁻¹ after carotid surgery.

Conclusion

These findings demonstrate that the Pocock score could be used as a clinical tool to identify patients at high risk of developing acute postoperative microemboli.

Systematic review and meta-analysis of perioperative and long-term outcomes in patients receiving statin therapy before carotid endarterectomy

BACKGROUND

Carotid endarterectomy (CEA) is associated with perioperative stroke and mortality in a minority of cases. The aim of this systematic review and meta-analysis was to investigate the effect of pre-operative statins on perioperative outcomes in patients undergoing CEA for internal carotid artery (ICA) stenosis.

METHODS

A systematic review of PubMed, Medline, and the Cochrane Database of Systematic Reviews was performed. Studies were included which reported perioperative stroke and/or survival outcomes following CEA for ICA stenosis and compared patients who were and were not taking pre-operative statins. Relevant data were extracted and pooled using meta-analysis.

RESULTS

Seven studies met the inclusion criteria, comprising 21,387 patients. A total of 68.9% (14,976) were administered statins and 31.1% (6657) were statin-free. Pre-operative statin use was higher in patients with a history of cardiac disease (12.2 vs. 23.6% in the statin-free group), diabetes (31.6 vs. 25.1% in the statin-free group), and hypertension (83.5 vs. 72.2% in the statin-free group), while a greater proportion of statin-free patients had symptomatic disease (44.9 vs. 55.5% in the statin-free group). Statins were associated with reduced perioperative stroke in all patients (OR 0.57; 95% CI 0.34-0.95; p = 0.03) and in symptomatic patients (OR 0.57; 95% CI 0.35-0.93; p = 0.03). A trend towards lower perioperative mortality (OR 0.54; 95% CI 0.29, 1.03; p = 0.06) and significantly improved overall survival was observed in the statin group (HR 0.69; 95% CI 0.59-0.81; p < 0.001) at a mean follow-up of 62 months (range 27-76 months).

CONCLUSIONS

Administration of statins before CEA is associated with lower rates of perioperative stroke and improved overall survival. Compliance with optimal medical treatment associated with the use of pre-operative statins may limit the clinical significance of these findings. Future investigation to characterize the potential benefit of statin therapy in patients undergoing CEA for ICA stenosis is warranted.

Transcranial Doppler Microemboli Monitoring for Stroke Risk Stratification in Blunt Cerebrovascular Injury

OBJECTIVES

To assess whether microemboli burden, assessed noninvasively by bedside transcranial Doppler ultrasonography, correlates with risk of subsequent stroke greater than 24 hours after hospital arrival among patients with blunt cerebrovascular injury. The greater than 24-hour time frame provides a window for transcranial Doppler examinations and therapeutic interventions to prevent stroke.

DESIGN

Retrospective cohort study.

SETTING

Level I trauma center.

PATIENTS

One thousand one hundred forty-six blunt cerebrovascular injury patients over 10 years.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We identified 1,146 blunt cerebrovascular injury patients; 54 (4.7%) experienced stroke detected greater than 24 hours after arrival. Among those with isolated internal carotid artery injuries, five of nine with delayed stroke had positive transcranial Dopplers (at least one microembolus detected with transcranial Dopplers) before stroke, compared with 46 of 248 without (risk ratio, 5.05; 95% CI, 1.41-18.13). Stroke risk increased with the number of microemboli (adjusted risk ratio, 1.03/microembolus/hr; 95% CI, 1.01-1.05) and with persistently positive transcranial Dopplers over multiple days (risk ratio, 16.0; 95% CI, 2.00-127.93). Among patients who sustained an internal carotid artery injury with or without additional vessel injuries, positive transcranial Dopplers predicted stroke after adjusting for ipsilateral and contralateral internal carotid artery injury grade (adjusted risk ratio, 2.91; 95% CI, 1.42-5.97). No patients with isolated vertebral artery injuries had positive transcranial Dopplers before stroke, and positive transcranial Dopplers were not associated with delayed stroke among patients who sustained a vertebral artery injury with or without additional vessel injuries (risk ratio, 0.90; 95% CI, 0.21-3.83).

CONCLUSIONS

Microemboli burden is associated with higher risk of stroke due to internal carotid artery injuries, but monitoring was not useful for vertebral artery injuries.

Transcranial Doppler Monitoring in Carotid Endarterectomy: A Systematic Review and Meta-analysis

OBJECTIVES

To evaluate the efficacy of intraoperative transcranial Doppler monitoring in predicting perioperative strokes after carotid endarterectomy (CEA).

METHODS

An electronic search of PubMed, Embase, and Web of Science databases was conducted for studies on transcranial Doppler monitoring in CEA published from January 1970 through September 2015. All titles and abstracts were independently screened on the basis of predetermined inclusion criteria, which included randomized clinical trials and prospective or retrospective cohort reviews, patients who underwent CEA with intraoperative transcranial Doppler monitoring (either middle cerebral artery velocity [MCAV] or cerebral microembolic signals [MES]) and postoperative neurologic assessments up to 30 days after the surgery, and studies including an abstract, published in English on adult humans 18 years and older with a sample size of 50 or greater.

RESULTS

A total of 25articles with a sample population of 4705 patients were analyzed. Among the study patients, 189 developed perioperative strokes. Transcranial Doppler monitoring (either MCAV or MES) showed specificity of 72.7% (95% confidence interval [CI], 61.2%-81.8%) and sensitivity of 56.1% (95% CI, 46.8%-65.0%) for predicting perioperative strokes. Intraoperative MCAV changes during CEA showed strong specificity of 84.1% (95% CI, 74.4%-90.6) and sensitivity of 49.7% (95% CI, 40.6%-58.8) for predicting perioperative strokes.

CONCLUSIONS

Patients with perioperative strokes are 4 times more likely to have had transcranial Doppler changes (either MCAV or MES) during CEA compared to patients without strokes. Simultaneous MCAV and MES monitoring by transcranial Doppler sonography and combined intraoperative monitoring of transcranial Doppler sonography with somatosensory evoked potentials and electroencephalography during CEA to predict perioperative stroke could not be evaluated because of a lack of clinical studies combining these measures.

Analysis of Risk Factors for Cerebral Microinfarcts after Carotid Endarterectomy and the Relevance of Delayed Cerebral Infarction

Background and Purpose

Carotid endarterectomy (CEA) is performed to prevent cerebral infarction, but a common side effect is cerebral microinfarcts. This study aimed to identify the variables related to the production of microinfarcts during CEA as well as determine their association with delayed postoperative infarction.

Methods

This was a retrospective review of data collected prospectively from 548 patients who underwent CEA. The clinical characteristics of the patients and the incidence rates and causes of microinfarcts were analyzed. Microinfarcts were diagnosed by diffusion-weighted magnetic resonance imaging. The presence of delayed postoperative infarction was compared between microinfarct-positive and microinfarct-negative groups.

Results

In total, 76 (13.86%) patients were diagnosed with microinfarcts. Preoperative neurological symptoms were significantly related to the incidence of microinfarcts [odds ratio (OR)=2.93, 95% confidence interval (CI)=1.72–5.00, p<0.001]. Shunt insertion during CEA was the only significant procedure-related risk factor (OR=1.42, 95% CI=1.00–2.19, p=0.05). The presence of microinfarcts did not significantly increase the incidence of delayed postoperative infarction (p=0.204).

Conclusions

In the present study, risk factors for microinfarcts after CEA included preoperative symptoms and intraoperative shunt insertion. Microinfarcts were not associated with delayed postoperative infarction.

A rabbit model of cerebral microembolic signals for translational research: preclinical validation for aspirin and clopidogrel

Essentials Microembolic signal (MES) is an independent predictor of stroke risk in patients. A rabbit model of cerebral microembolic signals was established. Therapeutic efficacy was demonstrated for aspirin and clopidogrel on microembolic signals. Potential translational value of this preclinical model of MES was demonstrated.

SUMMARY

Objectives Cerebral microembolic signals (MESs) detected by transcranial Doppler (TCD) ultrasound constitute an independent predictor of stroke risk and prognosis. The aim of this study was to develop a novel preclinical model of MESs to facilitate translational research. Methods A clinical TCD ultrasound machine was used to detect MESs in the cerebral circulation of New Zealand White rabbits. Technical feasibility was assessed for the measurement of MESs in the middle cerebral artery (MCA) by TCD. FeCl3 -induced carotid arterial thrombosis was optimized for the generation of endogenous microemboli. Ascending doses of two antithrombotic agents (aspirin and clopidogrel) were evaluated individually and in combination for their effects on both arterial thrombosis and MESs in a 30% FeCl3 -induced carotid arterial thrombosis model, along with ex vivo functional assays. Results Dose-dependent FeCl3 -induced arterial thrombosis studies showed that 30% FeCl3 resulted in the most consistent and reproducible MESs in the MCA (3.3 ± 0.7 MESs h(-1) ). Ascending-dose studies showed that the effective doses for 50% inhibition (ED50 ) of thrombus formation, based on integrated blood flow and thrombus weight, respectively, were 3.1 mg kg(-1) and 4.2 mg kg(-1) orally for aspirin, and 0.3 mg kg(-1) and 0.28 mg kg(-1) orally for clopidogrel. The ED50 values for MES incidence were 12.7 mg kg(-1) orally for aspirin, and 0.25 mg kg(-1) orally for clopidogrel. Dual treatment with aspirin (5 mg kg(-1) ) and clopidogel (0.3 mg kg(-1) ) resulted in significant reductions in cerebral MESs (P < 0.05) as compared with monotherapy with either agent. Conclusions Our study demonstrated the successful establishment of the MES model in rabbits, and it may provide translational value for MESs and ischemic stroke research.

Apixaban Inhibits Cerebral Microembolic Signals Derived from Carotid Arterial Thrombosis in Rabbits

Cerebral microembolic signal (MES) is an independent predictor of stroke risk and prognosis. The objective of this study is to assess the effects of apixaban, as a representative of the novel oral anticoagulant class, on a rabbit model of cerebral MES. A clinical transcranial Doppler ultrasound instrument was used to assess MESs in the middle cerebral artery in a 30% FeCl3-induced carotid arterial thrombosis model in male New Zealand White rabbits. Ascending doses of apixaban were evaluated as monotherapy and in combination with aspirin on both arterial thrombosis and MES. Pharmacokinetic and pharmacodynamic responses were also evaluated. The effective dose for 50% inhibition (ED50) of thrombus formation for monotherapy was 0.04 mg/kg per hour apixaban, i.v. (0.03 μM plasma exposure) for the integrated blood flow, 0.13 mg/kg per hour apixaban (0.10 μM plasma exposure) for thrombus weight, and 0.03 mg/kg per hour apixaban (0.02 μM plasma exposure) for MES. Dual treatment with aspirin (5 mg/kg, PO) and apixaban (0.015 mg/kg per hour, i.v.) resulted in a significant reduction in cerebral MES (P < 0.05) compared with monotherapy with either agent. Pharmacokinetic analysis of apixaban and pharmacodynamic assays using activated partial thromboplastin time (aPTT) and prothrombin time (PT) for apixaban- and arachidonic acid-induced platelet aggregation for aspirin were used to confirm the exposure-response relationships. In summary, our study demonstrates that apixaban in a concentration-dependent manner inhibits both arterial thrombosis and MES, suggesting a potential association between factor Xa (FXa) blockade and the reduction in MES in patients at risk of ischemic stroke.

Improvement in cerebral hemodynamic parameters and outcomes after superficial temporal artery-middle cerebral artery bypass in patients with severe stenoocclusive disease of the intracranial internal carotid or middle cerebral arteries

OBJECT

Both the older and the recent extracranial-intracranial (EC-IC) bypass trials for symptomatic carotid occlusion failed to demonstrate a reduction in stroke recurrence. However, the role of superficial temporal artery (STA)-middle cerebral artery (MCA) bypass in patients with symptomatic intracranial stenoocclusive disease has been rarely evaluated. The authors evaluated serial changes in various cerebral hemodynamic parameters in patients with severe stenoocclusive disease of the intracranial internal carotid artery (ICA) or middle cerebral artery (MCA) and impaired cerebral vasodilatory reserve (CVR), treated by STA-MCA bypass surgery or medical treatment.

METHODS

Patients with severe stenoocclusive disease of the intracranial ICA or MCA underwent transcranial Doppler (TCD) ultrasonography and CVR assessment using the breath-holding index (BHI). Patients with impaired BHI (< 0.69) were further evaluated with acetazolamide-challenge technitium-99m hexamethylpropyleneamine oxime ((99m)Tc HMPAO) SPECT. STA-MCA bypass surgery was offered to patients with impaired CVR on SPECT. All patients underwent TCD and SPECT at 4 ± 1 months and were followed up for cerebral ischemic events.

RESULTS

A total of 112 patients were included. This total included 73 men, and the mean age of the entire study population was 56 years (range 23-78 years). (99m)Tc HMPAO SPECT demonstrated impaired CVR in 77 patients (69%). Of these 77 patients, 46 underwent STA-MCA bypass while 31 received best medical treatment. TCD and acetazolamide-challenge (99m)Tc HMPAO SPECT repeated at 4 ± 1 months showed significant improvement in the STA-MCA bypass group. During a mean follow-up of 34 months (range 18-39 months), only 6 (13%) of 46 patients in the bypass group developed cerebral ischemic events, as compared with 14 (45%) of 31 patients receiving medical therapy (absolute risk reduction 32%, p = 0.008).

CONCLUSIONS

STA-MCA bypass surgery in carefully selected patients with symptomatic severe intracranial stenoocclusive disease of the intracranial ICA or MCA results in significant improvement in hemodynamic parameters and reduction in stroke recurrence.

Prospective validation study of transorbital Doppler ultrasound imaging for the detection of transient cerebral microemboli

BACKGROUND

Transient cerebral microemboli are independent biomarkers of early risk of ischaemic stroke in acute carotid syndromes. Transcranial Doppler imaging (TCD) through the temporal bone is the standard method for detection of cerebral microemboli, but an acoustic temporal bone window for TCD is not available in around one in seven patients. Transorbital Doppler imaging (TOD) has been used when TCD is not possible. The aim of this study was to validate the use of TOD against TCD for detecting cerebral microemboli.

METHODS

The study included patients undergoing elective carotid endarterectomy; all had confirmed temporal and orbital acoustic windows. Subjects gave written informed consent to postoperative TCD and TOD monitoring, which was performed simultaneously for 30 min by two vascular scientists.

RESULTS

The study included 100 patients (mean(s.e.m.) age 72(1) years; 65 men). Microemboli were detected by one or both methods in 40·0 per cent of patients: by TOD and TCD in 24 patients, by TOD alone in ten and by TCD alone in six. For detecting microemboli, TOD had a sensitivity of 80·0 per cent, specificity of 86·1 per cent, positive predictive value of 71·6 per cent and negative predictive value of 91·2 per cent. Bland-Altman analysis revealed no significant bias (bias 0·11 (95 per cent c.i. -0·52 to 0·74) microemboli; P = 0·810) with upper and lower limits of agreement of +6 and -6 microemboli.

CONCLUSION

TOD appears a valid alternative to TCD for detecting microembolic signals in patients with no suitable temporal acoustic window.

Distribution of artificial cerebral microemboli in stroke patients with patent foramen ovale

OBJECTIVES

Patent foramen ovale (PFO) is considered as an important risk factor for cerebrovascular diseases. Nevertheless, the relationship between the distribution of high-intensity transient signals (HITS), resulting from injection of air mixed with saline and detected by transcranial Doppler (TCD), and clinical cerebrovascular syndromes in these patients has not been investigated.

METHODS

Using TCD, we screened 40 patients with stroke or transient ischemic attack (TIA), in whom PFO was proven by transesophageal echocariography (TEE). Of these, 30 patients (75%) with artificially produced HITS either in the middle cerebral artery (MCA) or the basilar artery (BA) were included in the analysis.

RESULTS

Nineteen patients had a stroke or TIA in the carotid territory and 11 patients in the vertebro-basilar territory. HITS were found in the MCA in all 30 patients and in 21 of the 30 patients in the BA. Of the latter, ten patients were in the carotid group and 11 patients were in the veretebro-basilar group, p = 0.011.

CONCLUSION

There is a significant association between the distribution of artificial HITS and the clinical cerebrovascular syndromes.

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.

Intraoperative use of dextran is associated with cardiac complications after carotid endarterectomy

OBJECTIVE

Although dextran has been theorized to diminish the risk of stroke associated with carotid endarterectomy (CEA), variation exists in its use. We evaluated outcomes of dextran use in patients undergoing CEA to clarify its utility.

METHODS

We studied all primary CEAs performed by 89 surgeons within the Vascular Study Group of New England database (2003-2010). Patients were stratified by intraoperative dextran use. Outcomes included perioperative death, stroke, myocardial infarction (MI), and congestive heart failure (CHF). Group and propensity score matching was performed for risk-adjusted comparisons, and multivariable logistic and gamma regressions were used to examine associations between dextran use and outcomes.

RESULTS

There were 6641 CEAs performed, with dextran used in 334 procedures (5%). Dextran-treated and untreated patients were similar in age (70 years) and symptomatic status (25%). Clinical differences between the cohorts were eliminated by statistical adjustment. In crude, group-matched, and propensity-matched analyses, the stroke/death rate was similar for the two cohorts (1.2%). Dextran-treated patients were more likely to suffer postoperative MI (crude: 2.4% vs 1.0%; P = .03; group-matched: 2.4% vs 0.6%; P = .01; propensity-matched: 2.4% vs 0.5%; P = .003) and CHF (2.1% vs 0.6%; P = .01; 2.1% vs 0.5%; P = .01; 2.1% vs 0.2%; P < .001). In multivariable analysis of the crude sample, dextran was associated with a higher risk of postoperative MI (odds ratio, 3.52; 95% confidence interval, 1.62-7.64) and CHF (odds ratio, 5.71; 95% confidence interval, 2.35-13.89).

CONCLUSIONS

Dextran use was not associated with lower perioperative stroke but was associated with higher rates of MI and CHF. Taken together, our findings suggest limited clinical utility for routine use of intraoperative dextran during CEA.

[Detection of micro-embolic signals: a review of the literature]

BACKGROUND

The detection of micro-embolic signals (MES), by transcranial Doppler sonography might be useful for risk stratification in patients with symptomatic and asymptomatic carotid or cerebral artery stenosis, dissections, aortic atheroma, interventional procedures, and right to left cardiac shunts.

AIM

Review of the technique and clinical situations of MES detection.

METHODS

PubMed search from 1990 to 2012.

RESULTS

MES were found in 0,19, 48% versus 0,3, and 12% of patients with symptomatic and asymptomatic inferior than 30, 30 to 69, and 70 to 99% carotid stenosis, respectively. MES were related to the risk of recurrent stroke or transient ischemic attack (TIA). In the ACES study, the absolute annual risk of stroke or TIA after 2 years was 7% with vs 3% without MES. In patients with intracranial stenosis, the risk of stroke recurrence was 48% with vs 7% without MES at 13.6 months follow-up. MES were reported in 25% of the symptomatic versus none of the asymptomatic patients with intracranial stenosis.

CONCLUSION

Detection of MES is feasible and reproducible for multicenter studies, using rigourous methodology and long lasting recordings. It may contribute to risk stratification, especially in patients with extra- or intracranial stenosis.

Microembolic Signals in Acute Posterior Circulation Cerebral Ischemia

Background and Purpose—

The clinical significance of microembolic signals (MES) in the posterior circulation remains unclear. The aim of this study was to investigate the sources and consequences of MES in acute posterior circulation cerebral ischemia.

Methods—

We evaluated a total of 140 consecutive patients (93 males, mean age 62.9 years) who had acute posterior circulation cerebral ischemia. The MES monitoring was conducted at the basilar artery through the suboccipital window for a 30-minute period.

Results—

MES were detected in 18 (12.9%) of the 140 patients. Clinical characteristics and laboratory data did not differ between the MES-positive and MES-negative groups. Intracranial vertebrobasilar artery (VBA) stenosis was independently associated with the presence of MES (odds ratio, 9.85; 95% confidence interval, 1.22–79.48; P =0.032), whereas the patients with vertebral artery stenosis that was limited to the extracranial portion did not show an association. Microembolic signals occurred significantly more frequently in patients with severe degree of VBA stenosis compared to those with nonsignificant stenosis (odds ratio, 9.88; 95% confidence interval, 1.23–79.07; P =0.031). In a subgroup analysis of the 79 patients who had lesions on diffusion-weighted images and relevant VBA stenosis, the MES-positive group showed more frequent embolic infarction ( P =0.010) and multiple lesion patterns ( P =0.007) than single perforating infarctions.

Conclusions—

In acute posterior circulation cerebral ischemia, intracranial and severe VBA stenosis is associated with MES and may be its root causes. The presence of MES in VBA stenosis suggests that multiple and embolic type infarctions are the mechanisms of stroke.

An innovative method for detecting surgical errors using indocyanine green angiography during carotid endarterectomy: a preliminary investigation

BACKGROUND

Carotid endarterectomy (CEA) is the most effective treatment method of carotid stenosis or occlusion. Surgeons typically check the blood flow in each vessel using Duplex Doppler ultrasonography or radiocontrast angiography in order to prevent postoperative complications. Embolic cerebral infarction on the ipsilateral side has been reported in 4-7% of patients undergoing CEA despite a tolerable blood flow reported by Duplex ultrasonography. This study was designed to evaluate a new intraoperative method for detecting technical errors during CEA using indocyanine green (ICG) angiography.

METHODS

Six consecutive patients with severe carotid stenosis or occlusion underwent CEA. Both ICG angiography and Doppler ultrasonography were performed before the carotid arterial incision and after the carotid arterial suture. After injecting ICG dye via an intravenous route, the internal surface, atheroma, and flow defect were visualized with a microscope.

RESULTS

In ICG angiography, stenotic lesions could be identified as regions of relatively dark signal intensity. Magnified real-time images could be created using a microscope with an infrared filter, including three-dimensional images and detailed images of the inner lumen. These images could then be compared with the results of Doppler ultrasonography. In the six cases assessed by both ICG angiography and Doppler ultrasonography, all Doppler results were acceptable. However, one patient underwent revision surgery because a fluttering atheroma was detected by ICG angiography. ICG angiography could assume the extent of severe stenotic area. ICG angiography could also detect mobile lesions such as a fluttering atheroma.

CONCLUSIONS

Intraoperative ICG angiography before arteriotomy is useful to determine the precise stenotic area and the shape of the associated plaque. ICG angiography after an arteriotomy site is sutured is also useful for detecting residual stenosis or fluttering atheroma. ICG angiography could be an alternative method to Doppler ultrasonography for ensuring a complete and successful operation and preventing complications.

Silent cerebral events in asymptomatic carotid stenosis

BACKGROUND

Approximately 20% of strokes are attributable to carotid stenosis. However, the number of asymptomatic patients needed to prevent one stroke or death with endarterectomy is high at 17 to 32. There is a clear need to identify asymptomatic individuals at high risk of developing future ischemic events to improve the cost-effectiveness of surgery. Our aim was to examine the evidence for subclinical microembolization and silent brain infarction in the prediction of stroke in asymptomatic carotid stenosis using transcranial Doppler (TCD), computed tomography (CT), and magnetic resonance imaging (MRI).

METHODS

The review was conducted according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Articles regarding humans between 1966 and 2010 were identified through systematic searches of Pubmed, MEDLINE, and EMBASE electronic databases using a predetermined search algorithm.

RESULTS

Fifty-eight full text articles met the inclusion criteria. A median of 28% of microemboli positive patients experienced a stroke or transient ischemic attack during follow-up compared with 2% of microemboli negative patients (P = .001). The same was true for the end point of stroke alone with a median of 10% of microemboli positive patients experiencing a stroke vs 1% of microemboli negative patients (P = .004). A specific pattern of silent CT infarctions was related to future stroke risk (odds ratio [OR] = 4.6; confidence interval [CI] = 3.0-7.2; P < .0001). There are no prospective MRI studies linking silent infarction and stroke risk.

CONCLUSIONS

There is level 1 evidence for the use of TCD to detect microembolization as a risk stratification tool. However, this technique requires further investigation as a stroke prevention tool and would be complemented by improvements in carotid plaque imaging.

The von Willebrand inhibitor ARC1779 reduces cerebral embolization after carotid endarterectomy: a randomized trial

BACKGROUND AND PURPOSE

Inhibition of von Willebrand factor offers a novel approach to prevention of stroke and myocardial ischemia but has not yet been demonstrated to show efficacy on clinically relevant end points. ARC1779 is an aptamer that inhibits the prothrombotic function of von Willebrand factor by binding to the A1 domain of von Willebrand factor and thereby blocking its interaction with glycoprotein. Phase 1 studies suggest it inhibits platelet aggregation with less increase in bleeding than conventional antiplatelet agents. The effect of ARC 1779 on cerebral emboli immediately after carotid endarterectomy was investigated in a randomized clinical trial.

METHODS

Patients undergoing carotid endarterectomy were randomized double-blind to ARC1779 or placebo administered intravenously. Transcranial Doppler recording, to detect cerebral embolic signals, was performed in the first 3 hours postoperatively. The primary end point was time to first embolic signals.

RESULTS

Thirty-six patients were recruited, 18 in each arm. The Kaplan-Meier median time to first embolic signals was 83.6 minutes for ARC1779 compared with 5.5 minutes for placebo. Using Cox proportional hazards embolic signals occurred statistically significantly later on ARC1779 (P=0.007). Reduced embolic signals counts were correlated with inhibition of von Willebrand factor activity (P=0.03). Increased perioperative bleeding and anemia were seen with ARC1779.

CONCLUSIONS

von Willebrand factor inhibition reduces thromboembolism in humans. It may play a role in treatment of stroke and myocardial ischemia. The extent to which bleeding complications occur in nonoperated patients needs to be assessed in further studies. Clinical Trial Registration- URL: http://clinicaltrials.gov. Unique identifier: NCT00742612.

Perioperative transorbital Doppler flow imaging offers an alternative to transcranial Doppler monitoring in those patients without a temporal bone acoustic window

Transcranial Doppler has been used to identify microembolic signals before, during and after carotid endarterectomy, but 10% to 15% of patients are reported not to have suitable temporal bone window. The aim of this study was to assess the feasibility of transorbital Doppler monitoring of patients with absent temporal bone acoustic window. Between 2005 and 2008, those patients with absent temporal bone acoustic window were assessed for a transorbital acoustic window. During the study period, 318 carotid endarterectomy were performed. In the 29 (9.1%) with absent temporal bone acoustic window, 25 (86%) had satisfactory transorbital acoustic windows, consequently only four (1.2%) of patients could not be monitored postoperatively. One patient required postoperative transorbital acoustic windows directed glycoprotein IIb/IIIa receptor antagonist infusion due to excessive carotid microembolisation to prevent stroke. This is the first description of the use of transorbital flow imaging to determine postoperative cerebral blood flow, microembolic load and to direct the use of intravenous antiplatelet agents.

Microemboli monitoring by trans-cranial doppler in patient with acute cardioemboliogenic stroke due to atrial myxoma

This is the first reported attempt to examine the emboliogenic potential of cardiac myxoma in patients with acute stroke through the monitoring of microembolic signals (MES) by transcranial doppler. A 43-year old woman was brought to the emergency department because of acute onset of generalized tonic-clonic seizures and left hemiplegia. A CT scan of the brain demonstrated a large acute infraction in the territory of the right middle cerebral artery (MCA) and another smaller one in the territory of the posterior cerebral artery on the same side. Trans-cranial doppler (TCD) microemboli monitoring did not reveal MES. Transesophagial echocardiography (TEE) identified a 5 cm left atrial mass, which was highly suspected to be an atrial myxoma attached to the interatrial septum and prolapsed through the mitral valve. After the TEE results were obtained, another TCD monitoring was performed. Again, there were no MES found in either of the MCAs.Our findings showed the absence of MES on two consecutive TCD examinations, suggesting a spontaneous occurrence, rather than the permanent presence, of embolization, even in the most acute phase of stroke. Thus, the tendency of myxomas to spontaneously produce multiple emboli emphasizes the need for the surgical excision of myxomas.

Treatment of stroke after carotid endarterectomy using intravenous abciximab

A 59-year old man developed perioperative stroke following left carotid endarterectomy seconday to thrombosis at the endarterectomy site. Transcranial Doppler ultrasonography revealed very frequent microembolization in the left middle cerebral artery territory. The patient was successfully treated with intravenous abciximab with complete neurological recovery.

Low molecular weight heparin significantly reduces embolisation after carotid endarterectomy--a randomised controlled trial

OBJECTIVES

The administration of unfractionated heparin (UFH) prior to carotid clamping during carotid endarterectomy (CEA) transiently increases the platelet aggregation response to arachidonic acid (AA) despite the use of aspirin. We hypothesized that this phenomenon might be reduced by using low molecular weight heparin (LMWH) resulting in fewer emboli in the early post-operative period.

METHODS

183 aspirinated patients undergoing CEA were randomised to 5000 IU UFH (n=91) or 2500 IU LMWH (dalteparin, n=92) prior to carotid clamping. End-points were: transcranial Doppler (TCD) measurement of embolisation, effect on bleeding and platelet aggregation to AA and adenosine 5'-diphosphate (ADP).

RESULTS

Patients randomised to UFH had twice the odds of experiencing a higher number of emboli in the first 3h after CEA, than those randomised to LMWH (p=0.04). This was not associated with increased bleeding (mean time from flow restoration to operation end: 23 min (UFH) vs. 24 min (LMWH), p=0.18). Platelet aggregation to AA increased significantly following heparinisation, but was unaffected by heparin type (p=0.90). The platelets of patients randomised to LMWH exhibited significantly lower aggregation to ADP compared to UFH (p<0.0001).

CONCLUSIONS

Intravenous LMWH is associated with a significant reduction in post-operative embolisation without increased bleeding. The higher rate of embolisation seen with UFH may be mediated by increased platelet aggregation to ADP, rather than to AA.

Carotid endarterectomy performed in the morning is associated with increased cerebral microembolization

OBJECTIVES

Platelet function exhibits circadian variation with highest levels of activity in the morning and plays a central role in arterial thrombotic events, including thrombotic stroke following carotid endarterectomy (CEA). Prior to the platelet-rich thrombus occluding the carotid artery, multiple embolic signals are detected in the middle cerebral artery using transcranial Doppler ultrasound. We hypothesized that patients undergoing CEA early in the day may be at an increased stroke risk and this would manifest as an increased postoperative embolic count.

METHODS

Data were collected prospectively on 235 patients undergoing primary CEA. Accurate start and finish times were recorded in addition to the number of postoperative emboli detected in the first three hours after CEA using transcranial Doppler (TCD) monitoring.

RESULTS

For operations finishing before midday, there was a 3.6-fold increase in the number of emboli detected relative to afternoon finishes (53.2 vs 14.8, P = .002) with similar results for starts before 10:30 AM (48.1 vs 14.7, P =.002). There was also a significant correlation between start time and emboli count (P = .02). Of the 55 patients with no postoperative emboli, only 19 had a morning start (relative risk 0.63, P = .011). Patients were 6.9 times more likely to require treatment with Dextran-40 to prevent progression onto a thrombotic stroke if their CEA finished before midday (P = .008).

CONCLUSION

There is a significantly increased rate of postoperative embolization for operations begun earlier in the day. Carotid endarterectomies performed in the afternoon may be at less risk of developing postoperative thrombotic stroke.

Detection of microembolic signals using power M-mode Doppler sonography in acute stroke patients with intracranial artery stenosis

PURPOSE

Microembolic signals (MES) can be detected in a variety of clinical situations using conventional transcranial Doppler (TCD) sonography. We studied the prevalence of positive MESs in acute stroke patients with intracranial artery stenosis using power M-mode Doppler (PMD) sonography and also tested the feasibility of this new technique.

METHOD

Thirty-three consecutive acute ischemic stroke or transient ischemic attack patients with intracranial large artery occlusive disease were enrolled. PMD/TCD monitoring for 30 minutes was used for MES detection downstream of the stenotic artery within 1 week after stroke onset. Clinical risk factors in emboli-positive and emboli-negative patients were assessed.

RESULTS

MESs were detected in 21% (7/33) of patients. No significant differences were found in clinical risk factors between emboli-positive and emboli-negative patients.

CONCLUSION

PMD sonography to detect MESs in acute stroke patients is feasible and may be used in future clinical trials regarding MES detection.

Transcranial Doppler ultrasonography-directed intravenous glycoprotein IIb/IIIa receptor antagonist therapy to control transient cerebral microemboli before and after carotid endarterectomy

BACKGROUND

Patients with a transient focal neurological deficit, critical carotid stenosis and/or microemboli detected by transcranial Doppler ultrasonography (TCD) have a significant risk of stroke. The effect of tirofiban, a selective glycoprotein IIb/IIIa inhibitor, was assessed in patients with microembolic signals on TCD after transient ischaemic attacks or carotid endarterectomy (CEA).

METHODS

Thirty-three patients with microemboli on TCD (13 symptomatic preoperative, 19 postoperative, one both) were treated with tirofiban between 2002 and 2007. All patients had carotid stenosis greater than 70 per cent. TCD monitoring was used during and after tirofiban therapy.

RESULTS

The median (range) rate of microemboli decreased from 22 (4-260) per h before surgery and 81 (44-216) per h after surgery to 0 (0-9) per h in both groups (P < 0.001, Mann-Whitney U test). This occurred rapidly (preoperative median 30 min; postoperative median 45 min) and was well tolerated in all patients, with no serious adverse effects.

CONCLUSION

Cerebral microemboli were controlled by tirofiban both before and after CEA. Further study is required to compare the relative efficacy of tirofiban and dextran.

Embolic Doppler ultrasound signal detection using continuous wavelet transform to detect multiple vascular emboli

BACKGROUND

Ischemic stroke is mainly caused by embolism. Vascular emboli can be solid or gaseous and can be non-invasively registered by transcranial Doppler ultrasound as microembolic signals (MESs). The existing methods are limited as they do not distinguish between cases in which a single embolus is present and those in which multiple emboli -- perhaps a mix of those gaseous and solid in nature -- are present. In a previous in vitro study, we have developed a wavelet-based algorithm to detect multiple emboli. We proceed with this technique to investigate whether it could prove useful in patients.

METHOD

MESs were collected during emboli monitoring from patients undergoing carotid artery stenting and from patients having middle cerebral artery stenosis, and continuous wavelet transform was used to detect multiple emboli.

RESULTS

From 17 MESs recorded from middle cerebral artery stenosis patients, we found no multiple MES. From 306 MESs recorded from carotid stenting, we found 31 multiple MESs.

CONCLUSION

Multiple emboli were detected and quantified in patients using continuous wavelet transform. These were difficult to observe using conventional analysis techniques.

Techniques in carotid artery surgery

✓The major objective in carotid endarterectomy is to achieve safe and complete removal of intimal plaque and provide lasting, nonstenotic closure. Controversy exists as to which technical variation best achieves this. In this paper, the authors review the operative nuances and outcomes with conventional and eversion endarterectomy, with a focus on the latter. The views expressed reflect specific neurosurgical and vascular perspectives in the context of a multi-disciplinary stroke unit, where carotid stenosis is managed with all available open and endovascular means. The neurosurgical approach was almost entirely conventional endarterectomy with primary repair, while the vascular surgeons used the eversion method with few exceptions.

Enhanced Detection of Thromboemboli With the Use of Targeted Microbubbles

Background and Purpose— Targeted ultrasound contrast agents have recently been developed to adhere selectively to specific pathogenic materials such as plaque or thrombus. Administration of such microbubbles has potential to aid transcranial Doppler ultrasound (TCD) detection of emboli and to act as markers for distinguishing one embolic material from another. The purpose of this study was to investigate whether TCD detection of circulating thrombus emboli would be enhanced by the addition of targeted microbubbles.

Methods— Binding of microbubbles to the surface of the thrombus was confirmed by scanning electron microscopy. Targeted and control bubbles were then introduced to thrombus and tissue-mimicking material circulated under pulsatile-flow conditions in an in vitro flow rig. Embolic signal intensities before and after introduction of the bubbles were measured by TCD.

Results— Targeted microbubbles enhanced TCD signal intensities from thrombus emboli by up to 13 dB. The bubbles were capable of binding to moving thrombus when injected into the flow circuit in low concentrations (≈36 bubbles per 100 mL) and were retained on the thrombus under pulsatile-flow conditions. Signal intensities from similarly sized pieces of tissue-mimicking material were not enhanced by injection of targeted bubbles.

Conclusions— Injection of appropriately targeted microbubbles significantly enhances TCD detection of circulating thrombus emboli in vitro.

Extensive hemispheric cerebral infarction

BACKGROUND AND PURPOSE

Patients with extensive hemispheric cerebral infarction have a high incidence of mortality and serious morbidity. Because of their poor prognosis, they warrant attention; however, in acute stroke therapy trials they do not appear to benefit from treatment. We sought to determine the clinical features, pathophysiological mechanisms, and outcome in a series of cases with radiologically defined extensive hemispheric infarction.

METHODS

Cases of extensive hemispheric infarction were ascretained retrospectively from stroke admissions during a 5-year period. Extensive hemispheric infarction was defined radiologically as infarction involving greater than 75% of the middle cerebral artery territory, with or without involvement of the adjacent anterior or posterior cerebral artery territories. Clinical, risk factor, and stroke mechanism data were compared with that of a control group of ischemic stroke patients admitted during the same period.

RESULTS

Extensive hemispheric infarction occurred in 53 of 1,440 cases of ischemic stroke (3.7%). Infarction involved the middle cerebral artery territory alone in 79% of cases, and the adjacent anterior or posterior cerebral artery territories as well as 21% of cases. A cardioembolic mechanism was likely in 58% of cases; 42% had atrial fibrillation. When compared with the control group, a cardioembolic mechanism was the only feature more frequently associated with extensive hemispheric infarction. The overall in-hospital mortality rate was 52%; 84% of those discharged from hospital required nursing home care because of severe disability.

CONCLUSION

Although uncommon, extensive hemispheric infarction is an important stroke subtype with dramatic and easily recognizable presenting clinical features, frequent cardio-embolic mechanism, an extremely poor outcome, and failure to benefit from most experimental acute stroke therapies.

Influence of Antiplatelet Therapy on Cerebral Micro-Emboli after Carotid Endarterectomy using Postoperative Transcranial Doppler Monitoring

AIM

To study the effect of different antiplatelet regimens (APT) on the rate of postoperative TCD registered micro-embolic signals (MES) following carotid endarterectomy (CEA).

DESIGN

Prospective, randomised, double-blinded, pilot study.

METHODS

The study group of 102 CEA patients (76 men, mean age 66.8 years) was randomised to routine Asasantin (Dipyridamole 200mg/Aspirin 25mg) twice daily (group I; n=39), Asasantin plus 75 mg Clopidogrel once daily (group II; n=33), or Asasantin plus Rheomacrodex (Dextran 40) 100g/L iv; 500 ml (group III; n=30). TCD monitoring of the ipsilateral middle cerebral artery for the occurrence of MES was performed intra-operatively and during the second postoperative hour following CEA. Primary endpoints were the rate of postoperative emboli and the occurrence of cerebrovascular complications. Secondary endpoint was any adverse bleeding.

RESULTS

There were no deaths or major strokes. We observed 2 intraoperative TIA's (group II and III) and 1 postoperative minor stroke (group I). In comparison with placebo, Clopidogrel or Rheomacrodex in addition to Asasantin produced no significant reduction in the number of postoperative MES. There was no significant difference between the number of postoperative MES and different antiplatelet regimens. The incidence of bleeding complications was not significantly different between the 3 APT groups.

CONCLUSION

In the present study, we could not show a significant influence of different antiplatelet regimens on TCD detected postoperative embolization following CEA.

Therapeutic benefit of low-dose clopidogrel in patients undergoing carotid surgery is linked to variability in the platelet adenosine diphosphate response and patients' weight

BACKGROUND AND PURPOSE

We have previously shown that a single 75-mg tablet of clopidogrel, taken before carotid endarterectomy, significantly reduces postoperative embolization, a marker of thromboembolic stroke. This study explores the antiplatelet effect of this submaximal dose.

METHODS

Fifty-six patients on long-term aspirin (150 mg) were randomized to 75 mg clopidogrel or placebo before carotid endarterectomy. Blood samples were taken pre- and postdrug administration and at the end of surgery to measure platelet activation and adenosine diphosphate (ADP) response by flow cytometry and aggregometry.

RESULTS

Surgery produced a significant rise in platelet activation in vivo as evidenced by a rise in the percentage of monocyte-platelet aggregates in patients given placebo, but this was not seen in patients receiving clopidogrel. Before surgery, clopidogrel produced a significant reduction in the platelet response to ADP; for example, with 10(-6)M ADP, 77.32+/-2.3% bound fibrinogen in placebo group compared with 67.16+/-3.1% after clopidogrel (P=0.01). This was accentuated after surgery when the percentage of platelets binding fibrinogen in response to ADP was 76.53+/-2.2% in patients given placebo and 62.84+/-3.3% in the clopidogrel group (P=0.002). Similar differences were seen over a range of ADP concentrations and by aggregometry. Platelet responsiveness before treatment was highly variable and was positively correlated with the inhibitory effect of clopidogrel; patients with the highest baseline response to ADP showed the greatest response to clopidogrel. A negative correlation was seen between the effect of clopidogrel and patients' weight (r=0.57; P=0.002).

CONCLUSIONS

These results explain how a single 75-mg dose of clopidogrel produces a significant clinical impact on embolization.