Detection of asymptomatic cerebral embolic signals with Doppler ultrasound

Micromechanical Force Measurement of Clotted Blood Particle Cohesion: Understanding Thromboembolic Aggregation Mechanisms

PURPOSE

Arterial shear forces may promote the embolization of clotted blood from the surface of thrombi, displacing particles that may occlude vasculature, with increased risk of physiological complications and mortality. Thromboemboli may also collide in vivo to form metastable aggregates that increase vessel occlusion likelihood.

METHODS

A micromechanical force (MMF) apparatus was modified for aqueous applications to study clot-liquid interfacial phenomena between clotted porcine blood particles suspended in modified continuous phases. The MMF measurement is based on visual observation of particle-particle separation, where Hooke's Law is applied to calculate separation force. This technique has previously been deployed to study solid-fluid interfacial phenomena in oil and gas pipelines, providing fundamental insight to cohesive and adhesive properties between solids in multiphase flow systems.

RESULTS

This manuscript introduces distributed inter-particle separation force properties as a function of governing physio-chemical parameters; pre-load (contact) force, contact time, and bulk phase chemical modification. In each experimental campaign, the hysteresis and distributed force properties were analysed, to derive insight as to the governing mechanism of cohesion between particles. Porcine serum, porcine albumin and pharmaceutical agents (alteplase, tranexamic acid and hydrolysed aspirin) reduced the measurement by an order of magnitude from the baseline measurement-the apparatus provides a platform to study how surface-active chemistries impact the solid-fluid interface.

CONCLUSION

These results provide new insight to potential mechanisms of macroscopic thromboembolic aggregation via particles cohering in the vascular system-data that can be directly applied to computational simulations to predict particle fate, better informing the mechanistic developments of embolic occlusion.

Relationship of spontaneous microembolic signals to risk stratification, recurrence, severity, and mortality of ischemic stroke: a prospective study

Introduction

The presence of microembolic signals (MES) during the acute phase of stroke is poorly understood, and its role and clinical application in relation to risk stratification and prognosis in patients remain uncertain. We assessed the prevalence of spontaneous MES in acute stroke and their relationship with risk stratification, stroke recurrence, morbidity, and mortality.

Patients and methods

This was a prospective cohort study conducted in the Stroke Unit. The MES presence was evaluated by transcranial Doppler (TCD) in patients with ischemic stroke within 48 h. The outcomes (risk stratification, morbidity, mortality, and recurrence of a stroke) were followed up for 6 months. The relationship between risk stratification and MES was obtained by odds ratios and that between MES and stroke recurrence, morbidity, and mortality using multiple logistic regression; considering statistical significance at P < 0.05.

Results

Of the 111 patients studied, 70 were men (63.1%) and 90 were white (81.1%), with a median age of 68 years. The MES frequency was 7%. There was a significant relationship between MES and symptomatic carotid disease (OR = 22.7; 95% CI 4.1–125.7; P < 0.001), a shorter time to monitoring (OR = 12.4; 95% CI  1.4–105.4; P = 0.02), and stroke recurrence (OR = 16.83; 95% CI 2.01–141; P = .009).

Discussion

It was observed that the stroke recurrence adjusted for prior stroke was higher and earlier among patients with MES detection. In conclusion, MES demonstrated a significant correlation with symptomatic carotid disease and a shorter DELAY until monitoring, and could be a predictor for the early recurrence of stroke in the long term.

Carotid Angioplasty and Stenting: Will Periprocedural Transcranial Doppler Monitoring Be Important?

Purpose:

To explore the value of transcranial Doppler (TCD) ultrasonography in the periprocedural monitoring of patients undergoing angioplasty procedures for stenosis of the internal carotid artery.

Methods:

Thirty-two patients were included in the study between April 1991 and September 1995 (6 females, 26 males; average age 66 years). All patients were interrogated before and after angioplasty by a standard TCD examination protocol. Intraprocedurally, TCD was used continuously to monitor cerebral blood flow and supply evidence of embolic particulates. Nineteen patients were treated by percutaneous transluminal angioplasty (PTA) alone; the other 13 underwent primary stent (PS) implantation.

Results:

High-intensity transient signals indicative of emboli appeared to be more frequent in the PTA group than in the PS cohort. Preoperative TCD identified 3 (9%) high-risk patients with incompetent collateral pathways through the circle of Willis. Intraoperatively, TCD detected two postdilation carotid occlusions, a sylvian embolism, and one case of arterial spasm. The preprocedural TCD in a patient with contralateral carotid occlusion showed good collateral circulation, providing reassurance during conversion to endarterectomy when an undeployed stent obstructed blood flow. Postoperatively, TCD confirmed restored intracerebral circulation and identified one hyperperfusion syndrome.

Conclusions:

TCD is a simple, relatively inexpensive examination that can preprocedurally identify carotid stenosis patients at high risk for intraoperative cerebral ischemia in whom PTA might be preferable to surgery. During the procedure, TCD can document the benefits of endovascular treatment and offer early detection of ischemic complications.

Advances in imaging of intracranial atherosclerotic disease and implications for treatment

OPINION STATEMENT

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of ischemic stroke worldwide and is associated with a high risk of recurrent stroke despite aggressive therapy. ICAD may lead to cerebral ischemia through a variety of mechanisms, the interactions of which are largely unknown. The use of endovascular therapy for the prevention of stroke related to severe ICAD has been studied but was associated with a higher risk of recurrent stroke and death in the Stenting and Aggressive Medical Management for Preventing Recurrent Stroke in Intracranial Stenosis (SAMMPRIS) study. With advances in diagnostic testing, it may be possible to better delineate the specific mechanism of stroke from ICAD and identify those patients at higher risk for recurrent ischemia. There may be a subset of patients less responsive to medical interventions, such as those with hemodynamic failure as opposed to those with perforator syndromes, who would benefit from medical plaque stabilization or safer endovascular approaches such as angioplasty alone. These will need to be tested in future clinical trials. Overall, symptomatic ICAD remains a high risk condition with suboptimal treatment options.

Correlation between frequency of microembolic signals and efficacy of antiplatelet therapy in symptomatic carotid disease

BACKGROUND AND PURPOSE

The detection of microembolic signals in transcranial-Doppler monitoring is associated with a higher stroke risk. We investigated the correlation between the frequency of microembolic signals and the efficacy of the antiplatelet therapy in patients with a recent symptomatic carotid-artery stenosis.

SUBJECTS AND METHODS

Thirty-two patients (mean age: 70 years, 22 men) with a recent symptomatic carotid-artery stenosis underwent 30-minute TCD-monitoring. Twenty-three patients received acetylsalicylic-acid and 9 patients clopidogrel as antiplatelet-therapy. At the same day, the antiplatelet effect was measured with multiple-electrode-impedance aggregometry.

RESULTS

In 20 cases, the qualifying event was a stroke and in 12 cases, a TIA. Twenty-six of the patients had a >50% degree of stenosis. More than one microembolic signals were detected in 13 (40.6%) of the subjects, while multiple-electrode-impedance aggregometry revealed eight low responders (6 acetylsalicylic-acid, 2 clopidogrel). More than one microembolic signals were detected in 6 of the 8 (75.0%) patients with low response, but in only 7 of the 24 subjects (29.2%) with an effective antiplatelet treatment (sensitivity 75%, specificity 70.8%; Fisher's exact test: P = .038).

CONCLUSIONS

Our study suggests that in patients with recent symptomatic carotid-artery stenosis the detection of more than one microembolic signals might serve as a useful marker for the effectiveness of the antiplatelet treatment.

Current diagnosis and management of symptomatic intracranial atherosclerotic disease

PURPOSE OF REVIEW

Intracranial atherosclerotic disease (IAD) is likely the most common cause of stroke world-wide and is associated with a very high risk of recurrence. It results in cerebral ischemia due to a variety of mechanisms, including artery-to-artery embolism, hemodynamic failure, and occlusion of penetrating arteries. New imaging modalities focused on physiological consequences of IAD have become available and recent treatment trials have been completed.

RECENT FINDINGS

We review the traditional imaging modalities, emphasizing the advantages and limitations of each method, and discuss the novel physiological approaches that interrogate physiological process to indicate specific mechanisms of ischemia. These allow deeper understanding of the pathophysiological processes that underlie IAD-related ischemia. The key findings of recent therapeutic trials are reviewed, including the landmark randomized studies showing advantage of antiplatelet agents and risk factor modification, and a significant risk of complications with endovascular approaches.

SUMMARY

Current evidence argues for aggressive medical management and suggests caution with interventional treatments. We propose that mechanistic information will further refine the risk assessment of patients with IAD to offer targeted therapy.

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.

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.

Do carotid surface irregularities correlate with the development of cerebrovascular symptoms? An analysis of the supporting studies, the opposing studies, and the possible pathomechanism

Carotid plaque surface morphology appears to play a controversial role in the occurrence of cerebrovascular symptoms, that is, amaurosis fugax, transient ischemic attacks, and episodes of stroke. A number of researchers favor a strong association between the morphologic abnormalities of the carotid plaque surface and the development of cerebrovascular symptoms. The supporters of this theory have demonstrated that surface contour irregularities not only are important potential sources of flow abnormalities but also contribute significantly to the development of ischemic neurologic symptoms through plaque fragmentation, microthrombi formation, and atheroembolism. However, opposers of this theory also exist. The main arguments for and against this theory, as well as the possible underlying pathomechanism linking the morphology of the carotid plaque surface with the development of cerebrovascular symptoms, are outlined. Detection of carotid surface abnormalities with the aid of angiography or color-flow duplex ultrasonography should play a major role in the early identification of patients at increased risk, this way aiding prompt correction of these usually clinically silent but potentially hazardous lesions.

Clinical application of transcranial Doppler monitoring for embolic signals

A major advantage of transcranial ultrasound is its suitability for continuous monitoring. Microembolic signals (MES) are brief, high-intensity transients that occur when particulate microemboli or gaseous microbubbles pass through the ultrasound beam. These MES have been detected in several clinical scenarios, but rarely in age-matched controls. The detection of MES provides important pathophysiological information in a variety of disorders, but their clinical importance and possible therapeutic implications are still under debate. The present article summarizes the significance of MES in different clinical settings and outlines some of the problems to be resolved so that transcranial ultrasound can be applied in clinical practice.

Do complaints of amaurosis fugax and blurred vision after transcatheter device closure of atrial septal defect indicate microemboli to retinal vessels?

Atrial septal defect (ASD) is a common diagnosis in adults undergoing surgical repair. The aim of the study was to determine if ocular symptoms following treatment are due to microemboli. The study group included 20 adult patients (9 men, 11 women, mean age 57.2 years) with ASD who had undergone successful closure with the Amplatzer occluder. Patients were treated with aspirin or warfarin during the 6 months after the procedure. All were evaluated neurologically and an ocular medical history was obtained. Ocular examination included the 120-point Humphery visual field. Transcranial Doppler (TCD) was performed to monitor the middle cerebral artery. Two patients complained of amaurosis fugax at 1 and 3 months after the procedure, and two patients complained of blurred vision at 3 and 4 months after the procedure. TCD performed within 24 h of the complaints revealed no abnormalities. In all patients, the neurological and ocular examinations, including the visual field test, were normal. In conclusion, microembolic events do not appear to be the cause of the ocular complaints in patients with ASD treated with Amplatzer occluder. Further studies in larger samples are needed to confirm these results.

Do Complaints of Amaurosis Fugax and Blurred Vision after Transcatheter Device Closure of Atrial Septal Defect Indicate Microemboli to Retinal Vessels?

Atrial septal defect (ASD) is a common diagnosis in young adults with congenital heart disease. The aim of this study was to determine if ocular symptoms following percutaneous treatment are due to microemboli. The study group included 20 adult patients (9 men, 11 women, mean age 57.2 years) with ASD who had undergone successful closure with the Amplatzer occluder. The patients were treated with aspirin or warfarin during 6 months after the procedure. All were evaluated neurologically and an ocular medical history was obtained. Ocular examination included the 120-point Humphrey visual field. Transcranial Doppler (TCD) was performed to monitor the middle cerebral artery. Two patients complained of amaurosis fugax at 1 and 3 months after the procedure, and two patients complained of blurred vision at 3 and 4 months after the procedure. TCD performed for 45 minutes within 24 hours of the visual complaints revealed no abnormalities. In all patients, the neurological and ocular examinations, including the visual field test, were normal. In conclusion, microembolic events could not be demonstrated to be the cause of the ocular complaints in patients with ASD treated with Amplatzer occluder. Further studies in larger samples are needed to confirm these results.

Doppler microembolic load predicts risk of thromboembolic complications in Novacor patients

OBJECTIVE

Left ventricular assist devices have become an established method to bridge patients with end-stage cardiac failure to heart transplantation. Besides infection and bleeding, thromboembolism represents one of the most serious complications. We evaluated the value of microembolic signals in predicting thromboembolic events for individual patients and distinctive left ventricular assist device periods.

METHODS

Twenty patients (14 male) aged 23-57 years supported with the Novacor N100 left ventricular assist device were enrolled in this study. All patients were on effective anticoagulation, 12 patients additionally received antiplatelet therapy. Unilateral detection of microembolic signals was performed once weekly by insonation of the middle cerebral artery using transcranial Doppler sonography for 30 minutes duration. Evidence of clinically manifest thromboembolic events was based on regular questionnaires, clinical examinations, and results of diagnostic procedures.

RESULTS

During a cumulative follow-up of 3876 left ventricular assist device days, 44 thromboembolic complications occurred (incidence, 1.1%) in 15 out of 20 patients. A total of 360 transcranial Doppler sonography monitorings (range, 5-34 per patient) were performed with an overall microembolic signals prevalence of 35.3% and a microembolic signal mean of 2.3 +/- 9.2 per examination. There was a highly significant correlation between the individual microembolic signal activity and the respective incidence of clinical thromboembolism (r = 0.61-0.9; P <.01). Patients with additional antiplatelet treatment had significantly less thromboembolic complications (0.7%) and lower microembolic signal prevalence (18.3%) than those without (2.8% and 65.4%, respectively). Individual patients and left ventricular assist device months with clinical thromboembolization could be identified using the microembolic signal activity with moderate positive (0.37-0.7) and high negative predictive values (0.82-1.0).

CONCLUSIONS

The amount of microembolic signals, serially detected in patients with the Novacor left ventricular assist device, is significantly associated with their incidence of embolic complications. The high negative predictive value of microembolic signals enables to identify those patients and left ventricular assist device periods with particularly low risk of clinical thromboembolization.

Microembolus detection by transcranial doppler sonography

Microembolic signals can be detected by transcranial ultrasound as signals of high intensity and short duration. These signals represent circulating gaseous or solid particles. To optimize the differentiation from artefacts and the background signal and to facilitate the clinical use, several attempts have been made to automatize the detection of microemboli. Microemboli occur spontaneously in various clinical situations but their clinical impact and possible therapeutical implications are still under debate. This article provides a review of the actual literature concerning the current state of technical and clinical aspects of microembolus detection.

Spiral computed tomography angiography (SCTA) and color coded duplex ultrasound (CCDUS): two complementary diagnostic techniques for assessment of extracranial cerebral artery stenosis

Atherosclerotic lesions of the extracranial cerebral arteries account for ischemic stroke in over half of all cases. The risk of stroke associated with symptomatic carotid artery disease is related to the severity of the stenosis. Results of the two major clinical trials, North American Symptomatic Carotid Endarterectomy Trial (NASCET) and European Carotid Surgery Trial (ECST), showed that patients with symptomatic carotid artery disease may benefit from carotid endarterectomy. Therefore, detection and quantification of stenosis are essential. Discrepancies in the angiographic criteria used in both NASCET and ECST trials resulted in continued controversy about the most accurate method of measuring carotid artery stenosis. Moreover, to avoid complications related to the angiography procedure, a good evaluation of vessel wall and plaque composition need to be considered. Both SCTA and CCDUS are non invasive techniques that could overcome angiographic complications and give detailed information on stenosis grading and plaque characteristics. They have been used to evaluate carotid stenosis as a single or combined methods.

111In platelet scintigraphy for the noninvasive detection of carotid plaque thrombosis

BACKGROUND AND PURPOSE

Thrombosis on atherosclerotic lesions in the large extracranial arteries is the main cause of embolization in the distal cerebral circulation and thus is involved in the pathogenesis of ischemic stroke. The assessment of biological characteristics of lesions that are predictive of thrombotic complications might help in stratification of the risk for stroke but is currently imperfect.

METHODS

We compared the performance of (111)In-platelet scintigraphy with blood pool subtraction, ultrasound-based tissue texture analyses, and transcranial Doppler techniques in their ability to predict the occurrence of superficial thrombosis or the presence of a lipid pool in carotid artery plaque specimens removed at the time of carotid endarterectomy in 22 patients with unilateral carotid artery stenosis of >70%.

RESULTS

Positivity at (111)In-platelet scintigraphy was present in 8 patients and correctly identified the presence of thrombosis superimposed on a complicated plaque. Neither tissue texture analysis nor emboli detection by transcranial Doppler, performed in 12 patients, significantly identified plaque thrombosis. None of the techniques used were able to detect the presence of a significant lipid pool inside the plaque.

CONCLUSIONS

Indium-platelet scintigraphy is an accurate noninvasive diagnostic tool to detect thrombotic complications in carotid plaques. Prospective studies should assess its ultimate value in risk stratification, possibly to guide the decision of whether to perform endarterectomy in selected patient categories.

Inapparent hemodynamic insufficiency exacerbates ischemic damage in a rat microembolic stroke model

BACKGROUND AND PURPOSE

Patients with severe carotid artery stenosis may have more severe ischemic damage after embolic stroke than patients without this abnormality. Unilateral proximal carotid occlusion (UCO) alone typically does not induce infarction in normotensive rats. The aim of this study was to investigate whether UCO increases infarct size after microembolic, experimental stroke.

METHODS

Microembolic infarction was induced in 2 groups of Sprague-Dawley rats by injecting 2000 microspheres (50-micrometer diameter) intracranially from the external carotid artery. The common carotid artery (CCA) was either ligated just after the injection (CCA occlusion group, n=8) or left intact (CCA open group, n=8). In the control group (n=4), vehicle without microspheres was injected and the CCA was ligated. Twenty-four hours later, the brains were removed and infarct volumes measured. Perfusion-weighted imaging was used to evaluate the cerebral circulation before and after CCA occlusion with and without microsphere injection in a separate group of animals (n=16).

RESULTS

All animals in the microemboli groups survived and had only a slight hemiparesis 24 hours after occlusion. No neurological deficits were observed in the control group. Infarct volumes were 145+/-57 mm(3) in the CCA occlusion group and 45+/-26 mm(3) in the CCA open group (P <0.01). There were no infarctions detected in the control group. Perfusion-weighted imaging showed that cerebral blood flow decreased after the CCA occlusion in both experiments with and without the microsphere injection.

CONCLUSIONS

UCO alone does not induce ischemic damage, but it worsens ischemic lesion size after multiple microemboli. This is probably due to the slight cerebral perfusion insufficiency caused by UCO. These results suggest that patients with cerebral hemodynamic insufficiency, such as those with severe carotid stenosis, may have increased ischemic damage after microembolic events.

Cerebral oligaemia episode triggers free radical formation and late cognitive deficiencies

Sixty minutes of cerebral oligaemic hypoxia, induced by bilateral clamping of the carotid arteries (BCCA) in pentobarbital-anaesthetized normotensive rats, induces a late progressive cognitive decline when compared with sham-operated controls. Analysis at BCCA of hippocampal metabolism using microdialysis showed increased release of glutamate, aspartate and gamma-aminobutyric acid, followed by a progressive rise in the formation of hydroxyl free radicals measured as 2,3-dihydroxybenzoic acid (2,3-DHBA), their reaction product with salicylate, though only in the re-perfusion phase. In the striatum increased dopamine release occurred during BCCA, whereas glutamate and aspartate showed an increase only during the late re-perfusion phase. gamma-Aminobutyric acid (GABA) concentration increased during BCCA and early re-perfusion. An increase in 2,3-DHBA was seen during BCCA, and persisted over 2 h of re-perfusion. Six and 13 months after surgery, though not as early as 3 months, BCCA-treated rats perform worse than sham-operated controls in a water-maze, where decreased swimming speed reveals striatal dysfunction, while hippocampal dysfunction manifested as diminished spatial bias. These results show that cerebral oligaemia, similarly to cerebral ischaemia, leads to increased extracellular dopamine, aspartate and glutamate, and the production of hydroxyl radicals in structures associated with learning and memory processes. Unlike cerebral ischaemia, in cerebral oligaemia the appearance of spatial memory deficits is delayed.

Four-dimensional ultrasonographic characterization of plaque surface motion in patients with symptomatic and asymptomatic carotid artery stenosis

BACKGROUND AND PURPOSE

In vitro studies of atherosclerotic plaque fracture mechanics suggest that analysis of local variations in surface deformability may provide information on relative vulnerability to plaque fissuring or rupture. We investigated plaque surface deformations in patients with symptomatic and asymptomatic carotid artery disease using 4-dimensional ultrasonography and techniques for measuring optical flow.

METHODS

Four-dimensional ultrasound examinations of carotid artery plaques were performed in 23 asymptomatic and 22 symptomatic patients with 50% to 90% stenosis of the internal carotid artery. Plaque surface motion during 1 cardiac cycle was computed with a hierarchical model-based motion estimator. Results were compared with plaque echogenicity and surface structure.

RESULTS

Of the 45 patients examined, plaque surface motion estimates were obtained for 18 asymptomatic and 13 symptomatic patients. There were no significant differences in echogenicity or surface structure of asymptomatic and symptomatic plaques (P>0.05). Results of motion estimation showed that asymptomatic plaques had surface motion vectors of equal orientation and magnitude to those of the internal carotid artery, whereas symptomatic plaques demonstrated evidence of inherent plaque movement. There was no significant difference in maximal plaque velocity between symptomatic and asymptomatic plaques (P<0.14). Maximal discrepant surface velocity (MDSV) in symptomatic plaques was 3.85+/-1.26 mm/s (mean+/-SD), which was significantly higher (P<0.001) than MDSV of asymptomatic plaques with 0.58+/-0.42 mm/s (mean+/-SD).

CONCLUSIONS

++MDSV of carotid artery plaques is significantly different in asymptomatic and symptomatic disease. Further studies are warranted to determine whether plaque surface motion patterns can identify vulnerable plaques in patients with carotid artery stenosis.

Reduced release of tissue factor by application of a centrifugal pump during cardiopulmonary bypass

The application of a centrifugal pump might lead to a reduced release of tissue factor (TF) due to less blood cell damage. This could result in a decrease in activation of the extrinsic pathway of coagulation and embolus formation. In the present study, 60 patients undergoing coronary artery bypass grafting were randomly assigned to a centrifugal or a roller pump. Plasma concentrations of TF, thrombin-antithrombin complex (TAT), and prothrombin fragments F1 + 2 were investigated before, during, and after cardiopulmonary bypass (CPB). Embolus detection was performed at the arterial line of CPB and transcranially by Doppler ultrasound. The centrifugal pump group revealed a lower TF release (area under the curve during CPB) when compared with the roller pump group [5661 (696-10359) vs 12681 (6383-17538) microg x min/l; median (lower - upper quartiles); P = 0.009]. In contrast, TAT and F1 + 2 formation did not differ between the groups, and neither did the total embolus count of both Doppler systems. Embolus counts did not correlate with TAT or F1 + 2 formation. In conclusion, the reduction in TF release by the application of a centrifugal pump seems to have little consequence on total thrombin formation. Since the applied Doppler systems seem to detect mainly microbubbles, conclusions regarding differences between the two pumps in the formation of thrombofibrinous clots cannot be drawn.

Transcranial Doppler detection of microemboli during percutaneous transluminal coronary angioplasty

BACKGROUND AND PURPOSE

The use of percutaneous transluminal coronary angioplasty (PTCA) to treat coronary artery disease is now commonplace. The occurrence of microemboli during invasive procedures such as cardiac angiography and bypass surgery is well documented, although neurological complications are relatively uncommon. To date, no investigation has been undertaken of the frequency or nature of microemboli occurring during PTCA or of the correlation with aortic atheroma.

METHODS

Twenty patients having elective PTCA underwent examination by transcranial Doppler ultrasonography (TCD) to detect left middle cerebral artery microemboli occurring during the procedure. Blinded off-line analysis correlated microembolic signal counts on TCD with the components of each stage of the PTCA. Patients later underwent transesophageal (TEE) echocardiography, with measurements made of the thickness of the intima and atheroma in the ascending and descending thoracic aortic arch by cardiologists blinded to the TCD results.

RESULTS

A total of 973 microembolic signals were detected (mean+/-SD, 48.7+/-36.7 per patient); 196 (20%) occurred on movement of the PTCA catheter and wire around the aortic arch, 84 (9%) with other PTCA catheter-associated movements, and 679 (70%) in association with injection of solutions (eg, saline and contrast). Mean signal counts during contrast injection were significantly greater than during the other 3 phases (P<0.001). No neurological events occurred in the study. Although not statistically significant, there was a trend toward greater microembolic signal counts with the number of times the catheter was passed around the aortic arch and the amount of arch atheroma detected by transesophageal echocardiography.

CONCLUSIONS

Microemboli detected on TCD are a common occurrence during PTCA but are largely asymptomatic. The majority of microembolic signals are most probably gaseous in origin and do not appear to be related to the extent of aortic atheroma or to clinical events.

Helical CT angiography in the preoperative evaluation of carotid artery stenosis

PURPOSE

To determine the utility and accuracy of helical CT angiography (CTA) in the evaluation of carotid artery stenosis.

METHODS

A comparison of CTA and conventional arteriogram was performed in 53 patients undergoing evaluation for carotid artery stenosis. Ninety-six carotid systems were evaluable. CTA stenosis was determined by the percent of area reduction seen on axial images through the level of greatest narrowing. MIP images were used to identify the point of maximal stenosis and to visualize overall vascular anatomy. The percent diameter stenosis was measured on conventional arteriograms using strict North American Symptomatic Carotid Endarterectomy Trial (NASCET) and European Carotid Surgery Trial (ECST) criteria.

RESULTS

Significant correlation was found between CTA and arteriography (NASCET method R=0.87, ECST method R=0.87, p < 0.001). Using NASCET >60% as an indicator for disease, CTA had a sensitivity of 87%, specificity of 90%, accuracy of 89%, negative predictive value of 88%, and positive predictive value of 89%. CTA identified plaque characteristics such as ulcerations (8), occlusion (10), fatty plaques (22), calcifications (48), and fibrosis (2). CTA underestimated 2 cases of short segment stenoses because of volume averaging, but this discrepancy was detected by duplex scan. No complications or renal dysfunction occurred with CTA; 1 patient became symptomatic during arteriography, necessitating termination of the procedure.

CONCLUSION

CTA is a safe, non-invasive technique that precisely measures carotid artery area reduction and highly correlates to conventional arteriography. With this new technology, the current standards for carotid artery imaging may need to be reevaluated, and the precise role for helical CTA more clearly defined.

Temporal variability of asymptomatic embolization in carotid artery stenosis and optimal recording protocols

BACKGROUND AND PURPOSE

Although asymptomatic embolization can be detected in patients with carotid artery stenosis, its temporal variability is unclear. An understanding of this is important in designing optimal recording protocols for future prospective studies of the predictive value of embolic signals (ES). We determined the effect of repeating and extending recording times in patients with symptomatic and asymptomatic carotid stenosis.

METHODS

In 20 asymptomatic and 20 symptomatic subjects with > 60% carotid stenosis, we used transcranial Doppler ultrasound to record for ES in the ipsilateral middle cerebral artery. Three 1-hour recordings were performed on three separate days, and on one occasion (not necessarily the first) the recording was extended to 2 hours. The recordings were saved onto digital tape for subsequent blinded analysis.

RESULTS

Marked temporal variability was seen in symptomatic patients in whom the cumulative proportion of subjects with ES increased from 10 (50%) after a single hour of recording to 12 (60%) and 15 (75%) after two and three recordings, respectively. Extending the recording to 2 hours increased the yield of ES-positive patients from 6 (30%) to 8 (40%). In symptomatic patients there was excellent agreement between whether patients were positive for ES during each of two consecutive 1-hour recordings (kappa = 0.78, P = 0.0003) but poor agreement between the results of two single-hour recordings performed on different days (kappa = 0.22, P = 0.27). In asymptomatic patients, 4 (20%) were ES positive during the first hour; this increased to 5 (25%) after the recording was repeated once, with no further increase after the third recording. Extending the recording to 2 hours increased the yield from 3 (15%) to 7 (35%). In contrast to symptomatic stenoses, in patients with asymptomatic stenoses there was fair agreement between whether patients were ES positive on two consecutive 1-hour recordings (kappa = 0.49, P = 0.01) or two single-hour recordings performed on different days (kappa = 0.48, P = 0.02). Symptomatic subjects were more likely to have ES (when all 1-hour recordings were considered, 24/60 versus 10/60; P = 0.0046). ES in symptomatic subjects had a higher relative intensity increase than in asymptomatic subjects (P = 0.01).

CONCLUSIONS

The temporal variability of ES needs to be taken into account in the design of optimal recording protocols and comparisons of results from different studies. Extending the duration of recording beyond an hour in symptomatic stenoses is of less value, but repeating the recording on a different day will often identify additional subjects with ES. In intervention studies in symptomatic patients, the time since last symptoms must be considered. In asymptomatic stenosis, extending the duration of recording beyond an hour will increase the proportion of patients positive for ES.

Technical report: Combined carotid bifurcation endarterectomy and intra-operative transluminal angioplasty of a proximal common carotid artery stenosis: an alternative to extrathoracic bypass

A method of management of a dual stenoses affecting the proximal common carotid artery and the internal carotid artery, the tandem lesion, is described in two cases. The combination of a surgical endarterectomy of the internal carotid artery narrowing and percutaneous balloon dilatation of the more proximal common carotid artery narrowing, via the arteriotomy site, with clamping of the internal carotid artery was successfully employed to avoid an extrathoracic bypass procedure.

Alterations of neuropsychological function and cerebral glucose metabolism after cardiac surgery are not related only to intraoperative microembolic events

BACKGROUND AND PURPOSE

High-intensity transient signals (HITS) during cardiac surgery are capable of causing encephalopathy and cognitive deficits. This study was undertaken to determine whether intraoperative HITS cause alterations of neuropsychological function (NPF) and/or cerebral glucose metabolism (CMRGlc), even in a low-risk patient group, and whether induced changes are interrelated.

METHODS

Eighteen patients without signs of cerebrovascular disease underwent elective coronary artery bypass grafting (CABG), and two of these additionally underwent valve replacement in normothermia. Intraoperatively, HITS were recorded by means of transcranial Doppler ultrasonography (TCD). Perioperatively, NPF and CMRGlc were assessed using a standardized complex test battery and positron emission tomography with 18F-2-fluoro-2-deoxy-D-glucose (FDG-PET), respectively.

RESULTS

Intraoperatively, the number of HITS ranged from 90 to 1710 per patient and hemisphere, more on the right side than on the left (P<.05). HITS occurred primarily during cardiopulmonary bypass (71.3%) and, to a lesser extent, during aortic manipulation (22.2%). Changes in global and regional CMRGlc between first (one day preoperatively) and second (8 to 12 days postoperatively) FDG-PET scans were mild. No correlations were found between the number of HITS, age of patient, duration of cardiac ischemia or cardiopulmonary bypass and the changes in CMRGlc. In patients with recorded HITS and a postoperative decrease of regional CMRGlc (n=11), the maximal decrease of rCMR Glc in each hemisphere below the individual global change of CMRGlc correlated with the number of HITS (r= -0.46, P<.05). Limitations in NPF occurred 8 to 12 days postoperatively, resolved within 3 months, and were not found to be correlated to the absolute number of HITS or changes in CMRGlc.

CONCLUSIONS

HITS during cardiac surgery can cause alterations of both NPF and CMRGlc, even in a low-risk patient group. However, the number of HITS and changes in NPF and CMRGlc are not necessarily interrelated, which indicates that (1) the location of brain damage related to HITS is more important for the development of NPF than is the absolute number of HITS, and (2) factors in addition to HITS might contribute to surgery-related brain damage.

Microembolic signals and intraoperative stroke in carotid endarterectomy

OBJECTIVES

Microembolic signals (high-intensity transient signals, HITS) detected by means of transcranial Doppler sonography (TCD) may be relevant for intraoperative strokes in carotid endarterectomy (CEA).

MATERIAL AND METHODS

An intraoperative HITS detection study was performed on 77 patients (63 men, 14 women, mean age+/-SD, 64+/-8 years) with a total of 81 CEAs. Using the Scandinavian Stroke Scale the patients were clinically examined by a neurologist preoperatively and postoperatively within 6 h. A deterioration of the Scandinavian Stroke Scale was considered an intraoperative stroke if persisting longer than 24 h. Cranial computed tomography (CT scan) was performed preoperatively and 3 to 5 days postoperatively. By means of TCD total HITS count and mean blood velocity changes, for shunting, were recorded sufficiently in the middle cerebral artery in 79 CEAs.

RESULTS

HITS were significantly more frequent in symptomatic [n = 53; HITS: median, 15 (range 1-159)] than in asymptomatic stenoses [n = 26; HITS: 6.5 (0-41); P < 0.001]. An intraoperative stroke in the hemisphere ipsilateral to the operation occurred in eight of the 81 CEAs. On postoperative CT scans, five of the eight strokes showed new corresponding territorial infarctions. In the three strokes without new CT lesions, the mean blood velocity changes after clamping indicated normal cerebral perfusion. Total HITS count was significantly higher in procedures with intraoperative strokes [n = 8; HITS: 33 (11-159)] than in the uncomplicated [n = 71; HITS: 10 (0-62); P = 0.002]. No stroke occurred in 37 CEAs with 10 or less HITS, but eight in 42 CEAs with 11 or more HITS [P = 0.006; relative risk 1.23 (95% confidence interval: 1.06 to 1.43)].

CONCLUSION

Microembolism seems clinically relevant in carotid endarterectomy. Asymptomatic patients may run a lower risk of intraoperative embolization.

Clinically silent microemboli in patients with artificial prosthetic aortic valves are predominantly gaseous and not solid

BACKGROUND AND PURPOSE

Microembolic signals (MES) are frequently observed by transcranial Doppler ultrasound after prosthetic heart valve implantation. Whether these MES are due to solid or gaseous particles is uncertain. We hypothesized that MES are gaseous and that if they are due to cavitation effects, their occurrence should respond to changes of dissolved oxygen concentration in the blood.

METHODS

Transcranial monitoring of MES was performed in five patients with prosthetic aortic valves, who inspired 100% oxygen through a facial mask. In one patient 100% oxygen was administered under hyperbaric (2.5 kPa) conditions in a hyperbaric chamber.

RESULTS

Inspiration of 100% oxygen reduced the total number of MES from 96/30 min to 2/30 min. Increasing the concentration of dissolved oxygen in the hyperbaric chamber led to an increase from 0.3 MES per minute (1.0 kPa) to 0.9 MES per minute (2.5 kPa).

CONCLUSIONS

The dependence of occurrence of MES in patients with prosthetic cardiac valves on the oxygen partial pressure in blood provides strong evidence that these microemboli are gaseous.

High-intensity transient signals in patients with cerebral ischemia

BACKGROUND AND PURPOSE

This study investigated the diagnostic relevance of transcranial Doppler monitoring for the detection of high-intensity transient signals (HITS) in patients with recent cerebral ischemic events of various origins.

METHODS

We prospectively performed bilateral transcranial Doppler monitoring (mean, 48 +/- 8 minutes) from both middle cerebral arteries in 280 patients with an acute (< 4 weeks) cerebral ischemic event in the middle cerebral artery territory and in 118 asymptomatic control subjects. HITS were analyzed according to a standardized protocol.

RESULTS

Symptomatic patients had a significantly (P < .001) higher rate (9.3%) of HITS than asymptomatic control subjects (1.7%). Patients with reversible ischemia (4.2%) and patients with suspected small-vessel syndromes (4.5%) had lower rates of HITS (P < .05) than those with large-vessel territory strokes (14.2%). Brain imaging (CT/MRI) results corresponded with this observation: the occurrence of HITS was significantly higher (P < .001) in patients with a pattern of large-vessel territorial brain infarction (19.0%) than in those with lacunar lesions (0%) or unidentified ischemic lesions (3.4%). Patients with identified sources of potential embolism (12.9%) had HITS (P < .001) more frequently than those without (0%). Patients with cardiac sources of embolism (excluding artificial heart valves) showed fewer HITS (6.2%) than patients with vascular sources (17.1%).

CONCLUSIONS

The results indicate that HITS occur predominantly in patients with large-vessel territory stroke patterns and persisting deficits that are most likely due to artery-to-artery or cardiogenic embolism. In contrast, patients with small-vessel disease and rapid recovery only occasionally present with HITS. Thus, the detection of HITS may substantially support the classification of the individual pathogenesis of cerebral ischemia, particularly when multiple risk constellations for stroke coexist.

Microembolism in Carotid Artery Disease

Abnormal high intensity transient signals detectable with transcranial Doppler (TCD) sonography have been associated with formed cerebral microembolism. Using long-term TCD monitoring, these clinically silent microembolic events can be observed in patients with cerebrovascular disease. Downstream of high grade internal carotid artery (ICA) stenosis, they occur significantly more frequently in neurologically symptomatic than in asymptomatic patients. Although the occurrence of microemboli is random, the individual rate underlies circadian fluctuations and seems to decline within the first weeks after an ischemic event. Pathoanatomic work suggests that luminal ulcer and thrombosis of the stenosed ICA are the major sources of microemboli. Thus, by tapping into an important pathomechanism, the detection of clinically silent cerebral microembolism appears to provide paraclinical evidence of "unstable carotid artery disease" and may help to evaluate more specific treatment strategies. (ECHOCARDIOGRAPHY, Volume 13, September 1996)

How good is intercenter agreement in the identification of embolic signals in carotid artery disease?

BACKGROUND AND PURPOSE

There has been concern regarding the reproducibility of the detection of embolic signals, particularly in patients with carotid artery stenosis in whom the signals are of low intensity. No published studies have examined inter-center agreement in reporting specific embolic signals or the factors responsible for any lack of agreement. We examined reproducibility between two centers in which widely differing proportions of embolic signals have previously been reported in patients with carotid artery stenosis.

METHODS

Recordings from the middle cerebral artery of eight patients with ipsilateral carotid artery stenosis in whom embolic signals had been detected during a previously study were independently examined by three experienced observers in one center and by one experienced observer in another center. We calculated agreement within and between centers by estimating the probability that one observer would identify a specific embolic signal if other observers had identified it (a probability of 1 indicates complete agreement). The influence of different characteristics of the embolic signal on the probability of its detection as an embolic signal was determined.

RESULTS

A high level of agreement in the identification of specific embolic signals was found. This was similar between all observers (.90), between the three observers in one center (.89), and between observers in the two different centers (.94). The probability of detection was independently related to the relative intensity of the embolic signal (P<.0001). It was less (although significantly) independently related to the position of the embolic signal in the cardiac cycle (P=.02), with signals in systole being more reliably detected. There was no independent relationship between the probability of detection and either the duration of the embolic signal or the velocity at the maximum intensity increase. The use of threshold intensity as a criterion for embolic signal detection increased interobserver agreement but reduced the sensitivity in detecting signals.

CONCLUSIONS

The high level of interobserver agreement suggests that the technique is sufficiently reproducible for clinical use.

Carotid angioplasty and stenting: will periprocedural transcranial Doppler monitoring be important?

PURPOSE

To explore the value of transcranial Doppler (TCD) ultrasonography in the periprocedural monitoring of patients undergoing angioplasty procedures for stenosis of the internal carotid artery.

METHODS

Thirty-two patients were included in the study between April 1991 and September 1995 (6 females, 26 males; average age 66 years). All patients were interrogated before and after angioplasty by a standard TCD examination protocol. Intraprocedurally, TCD was used continuously to monitor cerebral blood flow and supply evidence of embolic particulates. Nineteen patients were treated by percutaneous transluminal angioplasty (PTA) alone; the other 13 underwent primary stent (PS) implantation.

RESULTS

High-intensity transient signals indicative of emboli appeared to be more frequent in the PTA group than in the PS cohort. Preoperative TCD identified 3 (9%) high-risk patients with incompetent collateral pathways through the circle of Willis. Intraoperatively, TCD detected two postdilation carotid occlusions, a sylvian embolism, and one case of arterial spasm. The preprocedural TCD in a patient with contralateral carotid occlusion showed good collateral circulation, providing reassurance during conversion to endarterectomy when an undeployed stent obstructed blood flow. Postoperatively, TCD confirmed restored intracerebral circulation and identified one hyperperfusion syndrome.

CONCLUSIONS

TCD is a simple, relatively inexpensive examination that can preprocedurally identify carotid stenosis patients at high risk for intraoperative cerebral ischemia in whom PTA might be preferable to surgery. During the procedure, TCD can document the benefits of endovascular treatment and offer early detection of ischemic complications.

Occurrence of transcranial Doppler high-intensity transient signals in patients with potential cardiac sources of embolism. A prospective study

BACKGROUND AND PURPOSE

Cerebral emboli can be recognized by typical "high-intensity transient signals" (HITS) in the transcranial Doppler (TCD) spectral curves. Patients with potential cardiac sources of embolism are at higher risk for stroke.

METHODS

We examined the frequency of HITS in the left middle cerebral artery (MCA) with TCD over periods of 30 minutes in 100 patients having potential cardiac sources of embolism, as indicated by transthoracic or transesophageal echocardiography.

RESULTS

Thirty-six (36%) of the patients presented with HITS. Sex, age, sufficient anticoagulation level, antiplatelet therapy, neurological symptoms, and a history of thrombosis had no influence on the prevalence and number of HITS. The patients with a single echocardiographic diagnosis were separated into eight echocardiographically defined groups: patients with (1) atrial fibrillation, (2) coronary artery disease plus ejection fraction of more than 30% including at least three wall segments of hypokinesia/akinesia, (3) coronary artery disease with less than 30% ejection fraction, (4) dilated cardiomyopathy, (5) infectious endocarditis, (6) aortic stenosis, (7) mitral stenosis, and (8) patent foramen ovale. A significant difference in HITS occurrence could not be found in any of the defined groups. Only patients with infectious endocarditis showed a tendency for a higher HITS prevalence.

CONCLUSIONS

HITS are common phenomena in patients with potential cardiac sources of embolism. The clinical relevance of these HITS remains unclear.

Importance of time-window overlap in the detection and analysis of embolic signals

BACKGROUND AND PURPOSE

The detection of asymptomatic embolic signals by Doppler ultrasound may offer a powerful investigational tool in the management of cerebrovascular disease. However, early studies, particularly in patients with carotid artery disease, have reported very different frequencies of embolic signals. While this may reflect differences in patient groups and the criteria used for embolic signal identification, the degree of time-window overlap may be important. If this is insufficient, some embolic signals may fall between two time windows and not appear on the spectral display. Furthermore, the use of nonrectangular time windows, such as the Hanning window, may result in variation of the intensity of an embolic signal depending on where it is detected within the time window.

METHODS

To test the importance of this potential problem, the same 25 embolic signals recorded as the audio signal on digital audiotape were each played repeatedly through a transcranial Doppler ultrasound (TCD) system using fast Fourier transform analysis. An older system with no time-window overlap was used, and a more modern system was also used in which three different degrees of overlap were used: -9%, 27%, and 57%. The number of signals audible but not appearing on the spectral display was recorded. The variability in the relative intensity increase for the same embolic signal played repeatedly was estimated by calculating the coefficient of variation of the relative intensity increase.

RESULTS

With the older system, 39/500 (7.8%) of embolic signals were missed. With the newer system, the number of embolic signals missed was fewer and decreased with increasing degrees of overlap (10/500 for -9% overlap, 1/500 for 27% overlap, and 0/500 for 57% overlap). For those setups in which embolic signals were missed, there was a highly significant relationship between duration of embolic signal and number of signals missed. In parallel with these results, the coefficient of variation of the relative intensity increase became progressively less with increasing degrees of time-window overlap. For all processing setups, the coefficient of variation was greater for the less intense and shorter duration signals, but this dependence, as estimated by the slope of the regression line, became less strong with higher degrees of overlap.

CONCLUSIONS

Inadequate degrees of fast Fourier transform time-window overlap will result in the failure of current TCD machines to detect embolic signals. Furthermore, this and the time windowing currently usually used may result in variability in the relative intensity increase of identical embolic signals. These factors need to be taken into account when comparing data on the frequencies of embolic signals recorded by different researchers and in the design of future TCD equipment.

Asymptomatic cerebral embolic signals in patients with carotid stenosis. Correlation with appearance of plaque ulceration on angiography

BACKGROUND AND PURPOSE

Asymptomatic cerebral emboli may be detected in patients with carotid stenosis by transcranial Doppler ultrasonography of the middle cerebral artery (MCA). The aim of this study was to determine the angiographic correlates of such embolic signals.

METHODS

Doppler signals from 48 MCAs in 26 patients with carotid stenosis that was either symptomatic (n = 20) or asymptomatic (n = 6) were recorded for 40 minutes. The grade of carotid stenosis and the ulcerated or nonulcerated appearance of the plaque were assessed using the criteria of the North American Symptomatic Carotid Endarterectomy Trial.

RESULTS

Embolic signals were detected in 8 MCAs from 7 patients; 4 (50%) of these MCAs were clinically symptomatic compared with 16 (40%) without embolic signal. Although there was a trend toward more severe stenosis in the cases with embolic signals, this was not significant (mean +/- SD, 67 +/- 29% versus 55 +/- 36%). In contrast, an image of ulceration was found on ipsilateral carotid angiography in 5 cases (63%) with embolic signals and in only 9 cases (23%) without embolic signals (odds ratio, 5.74; 95% confidence interval, 1.15 to 28.79, by multivariate regression analysis).

CONCLUSIONS

This study demonstrates that the occurrence of embolic signals in patients with carotid stenosis is associated with the appearance of plaque ulceration on angiography.

Carotid Stenosis Index. A new method of measuring internal carotid artery stenosis

BACKGROUND AND PURPOSE

Current methods of measuring carotid stenosis such as those used in the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and European Carotid Surgery Trial (ECST) have limitations caused by difficulties in measuring the normal width of the distal internal carotid artery (ICA) or the carotid bulb.

METHODS

We developed a new technique, the Carotid Stenosis Index (CSI), based on the known anatomic relationship between the common carotid artery (CCA) and ICA (1.2 x CCA diameter=proximal ICA diameter). The normal ICA diameter can therefore be calculated from direct measurement of the CCA. Three blinded observers evaluated the angiograms of 57 patients (114 carotid arteries), previously screened with duplex ultrasonography, using the NASCET, ECST, and CSI methods. In a subset of 30 patients undergoing carotid endarterectomy, comparison was also made to computerized carotid plaque planimetry.

RESULTS

The NASCET method could only be applied correctly in 89% and the ECST method in 95% of cases because of overlying vessels or inadequate views of the distal ICA or carotid bulb. An additional 9% of NASCET cases had a "negative" stenosis, in which the stenosis is wider than the distal ICA. The CSI method was applicable in 99% of cases. Interobserver comparison using ANOVA revealed significant differences using NASCET (P < .0001) and ECST (P <.001) but not CSI (P = NS). NASCET had a sevenfold variation (P < .01) and ECST a twofold variation (P < .01) in results compared with CSI. The intraobserver reliability was 0.87 for NASCET, 0.86 for ECST, and 0.90 for CSI. However, the 95% confidence intervals for an individual measurement by an observer were +/- 30% for NASCET, +/- 19% for ECST, and +/- 15% for CSI. With linear methods of measurement there were significant differences between NASCET and CSI (P < .0001) and ECST (P < .0001) but not between CSI and ECST. A comparison of area derivations of these methods to carotid plaque planimetry revealed significant differences from NASCET (P <.0001) but not ECST, CSI, or duplex methods. A CSI nomogram was created, allowing measurement of both linear and area percent stenosis.

CONCLUSIONS

CSI is the most reliable validated method of measuring carotid stenosis, and it correlates with duplex and carotid pathology.

Carotid angioplasty. Detection of embolic signals during and after the procedure

BACKGROUND AND PURPOSE

Carotid angioplasty may offer an effective treatment for carotid stenosis, but there has been concern about the incidence and clinical consequences of distal embolization. Transcranial Doppler monitoring in carotid endarterectomy has demonstrated embolic signals during this procedure. We used this technique in patients undergoing carotid angioplasty.

METHODS

Transcranial Doppler ultrasound was used to monitor for embolic signals in the ipsilateral middle cerebral artery before and during 10 technically successful carotid angioplasties and at various standardized times in the following month.

RESULTS

In the month before angioplasty asymptomatic embolic signals were detected in 3 of 10 patients. During angioplasty multiple embolic signals were detected immediately after balloon inflation in 9 of 10 subjects. A minor ipsilateral cerebral ischemic event occurred in 1 of these 9, but the other 8 were asymptomatic. Embolic signals were common immediately after the procedure and intra-arterial femoral catheter removal (8 of 10 subjects) but thereafter became less frequent and were present in 1 of 5 at 4 hours, 2 of 10 at 48 hours, 1 of 6 at 7 days, and 1 of 10 at 1 month.

CONCLUSIONS

Embolization at the time of carotid angioplasty is very common but usually asymptomatic; monitoring by means of Doppler ultrasound will allow the effectiveness of measures to reduce this embolization to be studied. Late embolization occurs in a minority of patients and may account for the small but significant risk of delayed stroke. Doppler monitoring may allow identification of patients at risk and assessment of the effectiveness of prophylactic therapy.