Embolic Signals Research Articles

Ultrasonic plaque echolucency and emboli signals predict stroke in asymptomatic carotid stenosis

Ultrasonic plaque echolucency and emboli signals predict stroke in asymptomatic carotid stenosis

Symptomatic and asymptomatic carotid artery plaque

Carotid atherosclerotic plaques represent both stable and unstable atheromatous lesions. Atherosclerotic plaques that are prone to rupture owing to their intrinsic composition such as a large lipid core, thin fibrous cap and intraplaque hemorrhage are associated with subsequent thromboembolic ischemic events. At least 15–20% of all ischemic strokes are attributable to carotid artery atherosclerosis. Characterization of plaques may enhance the understanding of natural history and ultimately the treatment of atherosclerotic disease. MRI of carotid plaque and embolic signals during transcranial Doppler have identified features beyond luminal stenosis that are predictive of future transient ischemic attacks and stroke. The value of specific therapies to prevent stroke in symptomatic and asymptomatic patients with severe carotid artery stenosis are the subject of current research and analysis of recently published clinical trials that are discussed in this article.

Optimizing Protocols for Risk Prediction in Asymptomatic Carotid Stenosis Using Embolic Signal Detection

Improved methods are required to identify patients with asymptomatic carotid stenosis at high risk for stroke. The Asymptomatic Carotid Emboli Study recently showed embolic signals (ES) detected by transcranial Doppler on 2 recordings that lasted 1-hour independently predict 2-year stroke risk. ES detection is time-consuming, and whether similar predictive information could be obtained from simpler recording protocols is unknown. In a predefined secondary analysis of Asymptomatic Carotid Emboli Study, we looked at the temporal variation of ES. We determined the predictive yield associated with different recording protocols and with the use of a higher threshold to indicate increased risk (≥2 ES). To compare the different recording protocols, sensitivity and specificity analyses were performed using analysis of receiver-operator characteristic curves. Of 477 patients, 467 had baseline recordings adequate for analysis; 77 of these had ES on 1 or both of the 2 recordings. ES status on the 2 recordings was significantly associated (P<0.0001), but there was poor agreement between ES positivity on the 2 recordings (κ=0.266). For the primary outcome of ipsilateral stroke or transient ischemic attack, the use of 2 baseline recordings lasting 1 hour had greater predictive accuracy than either the first baseline recording alone (P=0.0005), a single 30-minute (P<0.0001) recording, or 2 recordings lasting 30 minutes (P<0.0001). For the outcome of ipsilateral stroke alone, two recordings lasting 1 hour had greater predictive accuracy when compared to all other recording protocols (all P<0.0001). Our analysis demonstrates the relative predictive yield of different recording protocols that can be used in application of the technique in clinical practice. Two baseline recordings lasting 1 hour as used in Asymptomatic Carotid Emboli Study gave the best risk prediction.

Ultrasonic plaque echolucency and emboli signals predict stroke in asymptomatic carotid stenosis

Better methods are required to identify patients with asymptomatic carotid stenosis (ACS) at risk of future stroke. Two potential markers of high risk are echolucent plaque morphology on carotid ultrasound and embolic signals (ES) in the ipsilateral middle cerebral artery on transcranial Doppler ultrasound (TCD). We explored the predictive value of a score based on these 2 measures in the prospective, observational, international multicenter Asymptomatic Carotid Emboli Study. A total of 435 recruited subjects with ACS ≥70% had baseline ultrasound images and TCD data available. Subjects were prospectively followed up for 2 years. A total of 164 (37.7%) plaques were graded as echolucent. Plaque echolucency at baseline was associated with an increased risk of ipsilateral stroke alone (hazard ratio [HR] 6.43, 95% confidence interval [CI] 1.36-30.44, p = 0.019). A combined variable of plaque echolucency and ES positivity at baseline was associated with a markedly increased risk of ipsilateral stroke alone (HR 10.61, 95% CI 2.98-37.82, p = 0.0003). This association remained significant after controlling for risk factors, degree of carotid stenosis, and antiplatelet medication. Plaque morphology assessed using a simple, and clinically applicable, visual rating scale predicts ipsilateral stroke risk in ACS. The combination of ES detection and plaque morphology allows a greater prediction than either measure alone and identifies a high-risk group with an annual stroke risk of 8%, and a low-risk group with a risk of <1% per annum. This risk stratification may prove useful in the selection of patients with ACS for endarterectomy.

Clopidogrel Versus Dipyridamole in Addition to Aspirin in Reducing Embolization Detected with Ambulatory Transcranial Doppler: A Randomized Trial

Background and Purpose—After stroke and transient ischemic attack there is a high early risk of recurrent stroke, particularly in large artery disease. It has been suggested more intensive antiplatelet regimens are required, but trial data are lacking. Treatment efficacy can be evaluated using transcranial Doppler detection of embolic signals. Ambulatory transcranial Doppler has recently been developed; prolonged recording may reduce subject numbers required to determine therapeutic efficacy. In a randomized trial (ISRCTN68019845) with blinded end point evaluation, we determined whether treatment with dipyridamole or clopidogrel, in addition to aspirin, was more effective at reducing embolization. Methods—Consecutive patients with recent symptomatic carotid stenosis were recruited. Ambulatory transcranial Doppler and platelet aggregometry were performed at baseline and 48 hours. Patients, all on aspirin, were randomized to dipyridamole or clopidogrel. Recordings were analyzed offline masked to subject ide...

The von Willebrand Inhibitor ARC1779 Reduces Cerebral Embolization After Carotid Endarterectomy

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. 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. 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. 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.

Clopidogrel Versus Dipyridamole in Addition to Aspirin in Reducing Embolization Detected With Ambulatory Transcranial Doppler

After stroke and transient ischemic attack there is a high early risk of recurrent stroke, particularly in large artery disease. It has been suggested more intensive antiplatelet regimens are required, but trial data are lacking. Treatment efficacy can be evaluated using transcranial Doppler detection of embolic signals. Ambulatory transcranial Doppler has recently been developed; prolonged recording may reduce subject numbers required to determine therapeutic efficacy. In a randomized trial (ISRCTN68019845) with blinded end point evaluation, we determined whether treatment with dipyridamole or clopidogrel, in addition to aspirin, was more effective at reducing embolization. Consecutive patients with recent symptomatic carotid stenosis were recruited. Ambulatory transcranial Doppler and platelet aggregometry were performed at baseline and 48 hours. Patients, all on aspirin, were randomized to dipyridamole or clopidogrel. Recordings were analyzed offline masked to subject identity. Sixty patients were recruited, 30 in each arm. The primary end point of change in embolic signal frequency did not differ between groups (P=0.36). In patients with embolic signals at baseline, there was no difference in reduction in embolic signal frequency: dipyridamole (75.5; SD 17.7%) versus clopidogrel (77.5; SD 20.5%; P=0.77). Baseline platelet aggregation was not different between regimens, but at 48 hours, adenosine 5'-diphosphate aggregation rate (but not collagen) was lower with clopidogrel (P<0.001). Both dipyridamole and clopidogrel reduced embolization to a similar extent. Embolic signals are strong predictors of future stroke rate in this patient group. Our results suggest these 2 treatment regimens have similar efficacy in early secondary prevention of stroke, although this now needs testing in large Phase III trials.

Ischemic Stroke and Cancer: Stroke Severely Impacts Cancer Patients, While Cancer Increases the Number of Strokes

BackgroundCancer and ischemic stroke are two of the most common causes of death among the elderly, and associations between them have been reported. However, the main pathomechanisms of stroke in cancer patients are not well known, and can only be established based on accurate knowledge of the characteristics of cancer-related strokes. We review herein recent studies concerning the clinical, laboratory, and radiological features of patients with cancer-related stroke.Main ContentsThis review covers the epidemiology, underlying mechanisms, and acute and preventive treatments for cancer-related stroke. First, the characteristics of stroke (clinical and radiological features) and systemic cancer (type and extent) in patients with cancer-specific stroke are discussed. Second, the role of laboratory tests in the early identification of patients with cancer-specific stroke is discussed. Specifically, serum D-dimer levels (as a marker of a hypercoagulable state) and embolic signals on transcranial Doppler (suggestive of embolic origin) may provide clues regarding changes in the levels of coagulopathy related to cancer and anticoagulation. Finally, strategies for stroke treatment in cancer patients are discussed, emphasizing the importance of preventive strategies (i.e., the use of anticoagulants) over acute revascularization therapy in cancer-related stroke.ConclusionRecent studies have revealed that the characteristics of cancer-related stroke are distinct from those of conventional stroke. Our understanding of the characteristics of cancer-related stroke is essential to the correct management of these patients. The studies presented in this review highlight the importance of a personalized approach in treating stroke patients with cancer.

Peripheral embolic events during endovascular treatment of infra-inguinal chronic total occlusion

Reliance on angiographic detection of peripheral embolic events during endovascular treatment of peripheral arterial disease not only underestimates its true incidence but is the leading cause for underdeveloped embolic protection strategies during peripheral arterial interventions. Detection of distal embolic signals especially during percutaneous treatment of infra-inguinal chronic total occlusions (CTO) remains unknown. We report Doppler ultrasound detection of distal embolic signals, during phases of percutaneous intervention involving recanalization of a superficial femoral artery CTO.

Automatic detection of micro-emboli by means of a generalized autoregressive conditional heteroskedasticity model.

Detection of micro-emboli is of great clinical importance to prevent cerebro-vascular events and to identify the causes of such events. Standard detection techniques implemented in the most commonly used systems are generally based on the passing of an energy threshold. The value of this threshold can be set just above the statistically highest detected energy of a Doppler signal related to circulating blood, i.e., during the systolic phase. This choice of threshold consequently prevents all detection of micro-emboli events whose energy might be lower than the systolic energy. The main idea of our technique was to test adaptively the whiteness of the prediction error between the Doppler signal and a synthetic signal obtained by a GARCH model. By assuming that micro-emboli are unforecasted, we hypothesize that embolic signals are unpredictable. We hypothesize that our new micro-emboli detector is a candidate technique to detect very small micro-emboli. We have tested and compared our new technique to the standard Fourier technique (Fourier). For a probability of detection fixed to 100%, the probability of false alarm of the standard automatic technique is 33% whereas the detector based on the GARCH model is less than 3%. This study demonstrates that our new technique detects micro-emboli hitherto not identified by classical methods.

Rare Detection of Fat Emboli During Venous Duplex Sonography

Fat embolism syndrome (FES) is defined as a variant of posttraumatic pulmonary insufficiency following long-bone musculoskeletal trauma or surgical repair. FES is a serious life-threatening complication characterized by the simultaneous occurrence of pulmonary and neurological symptoms as well as skin and mucosal petechiae. Although frequently asymptomatic and commonly seen following bone manipulation, fatty emboli are rarely found in patients undergoing total joint arthroplasty. Embolic signals from fatty emboli have been detected by transesophageal echocardiography (TTE) and transcranial Doppler (TCD); however, they have rarely been documented in the lower extremity. A patient is described with multiple fatty emboli demonstrated during a venous duplex examination.

Coagulopathy and embolic signal in cancer patients with ischemic stroke

It has been reported that embolic signal (ES) detected by transcranial Doppler (TCD) has clinical significance, especially in patients with recent stroke attributable to arterial or cardiac embolism. Therefore, we conducted this study to determine whether the prevalence of ES is high in ischemic stroke patients with cancer and related to hypercoagulopathy. We prospectively studied cancer patients with acute ischemic stroke within the middle cerebral artery (MCA) distribution on diffusion-weighted imaging. Conventional stroke mechanisms (CSMs) were determined using cardiologic and vascular studies. Additionally, the coagulation status was assessed based on the serum D-dimer levels, and TCD monitoring was performed on both MCAs for 30 minutes to detect ES. Clinical features including vascular risk factors, characteristics of ischemic stroke, and cancer and laboratory findings associated with the presence of ES were evaluated. A total of 74 patients were finally included in this study. ES was more commonly observed in patients without CSMs (22 of 38 patients, 57.9%) than in those with CSMs (12 of 36 patients, 33.3%) (p = 0.034). Moreover, ES was more commonly detected in patients with high D-dimer levels (p < 0.001), and D-dimer levels were significantly correlated with the number of ESs in patients without CSMs (r = 0.732, p < 0.001), but were poorly correlated in patients with CSMs (r = 0.152, p = 0.375). Higher levels of D-dimer (odds ratio [OR], 1.082 per 1 microg/ml increase; 95% confidence interval [CI], 1.014-1.154) and adenocarcinoma (OR, 3.829; 95% CI, 1.23-13.052) were independently associated with the presence of ES. The use of anticoagulants dramatically decreased the D-dimer levels. A high prevalence of ES was observed in cancer patients with ischemic stroke, especially in those without CSMs. Elevated D-dimer levels were independently associated with ES, and decreased dramatically with the use of anticoagulants. ANN NEUROL 2010;68:213-219.

Asymptomatic embolisation for prediction of stroke in the Asymptomatic Carotid Emboli Study (ACES): a prospective observational study

SummaryBackgroundWhether surgery is beneficial for patients with asymptomatic carotid stenosis is controversial. Better methods of identifying patients who are likely to develop stroke would improve the risk–benefit ratio for carotid endarterectomy. We aimed to investigate whether detection of asymptomatic embolic signals by use of transcranial doppler (TCD) could predict stroke risk in patients with asymptomatic carotid stenosis.MethodsThe Asymptomatic Carotid Emboli Study (ACES) was a prospective observational study in patients with asymptomatic carotid stenosis of at least 70% from 26 centres worldwide. To detect the presence of embolic signals, patients had two 1 h TCD recordings from the ipsilateral middle cerebral artery at baseline and one 1 h recording at 6, 12, and 18 months. Patients were followed up for 2 years. The primary endpoint was ipsilateral stroke and transient ischaemic attack. All recordings were analysed centrally by investigators masked to patient identity.Findings482 patients were recruited, of whom 467 had evaluable recordings. Embolic signals were present in 77 of 467 patients at baseline. The hazard ratio for the risk of ipsilateral stroke and transient ischaemic attack from baseline to 2 years in patients with embolic signals compared with those without was 2·54 (95% CI 1·20–5·36; p=0·015). For ipsilateral stroke alone, the hazard ratio was 5·57 (1·61–19·32; p=0·007). The absolute annual risk of ipsilateral stroke or transient ischaemic attack between baseline and 2 years was 7·13% in patients with embolic signals and 3·04% in those without, and for ipsilateral stroke was 3·62% in patients with embolic signals and 0·70% in those without. The hazard ratio for the risk of ipsilateral stroke and transient ischaemic attack for patients who had embolic signals on the recording preceding the next 6-month follow-up compared with those who did not was 2·63 (95% CI 1·01–6·88; p=0·049), and for ipsilateral stroke alone the hazard ratio was 6·37 (1·59–25·57; p=0·009). Controlling for antiplatelet therapy, degree of stenosis, and other risk factors did not alter the results.InterpretationDetection of asymptomatic embolisation on TCD can be used to identify patients with asymptomatic carotid stenosis who are at a higher risk of stroke and transient ischaemic attack, and also those with a low absolute stroke risk. Assessment of the presence of embolic signals on TCD might be useful in the selection of patients with asymptomatic carotid stenosis who are likely to benefit from endarterectomy.FundingBritish Heart Foundation.

Patent foramen ovale is not associated with an increased risk of stroke recurrence

Despite numerous studies suggesting a relationship between paradoxical embolism from a patent foramen ovale (PFO) and stroke, the role of PFO as a risk factor for cerebral ischaemia remains controversial. We therefore sought to determine the association between a RLS detected by contrast-enhanced transcranial Doppler ultrasonography (c-TCD) and recurrent stroke in an unselected population sample. We analyzed the records of 763 patients with diagnosis of cerebral ischaemia at our institution. All patients had undergone TCD-based detection of RLS. Embolic signals have been measured both under resting conditions and after performing a Valsalva maneuver. For follow-up, all patients were contacted by mail, which included a standardized questionnaire. Endpoints of follow-up were defined as recurrence of cerebral ischaemia, occurrence of myocardial infarction or death from any cause. Follow-up data were available in 639 patients (83.7%). At baseline, a RLS was detected in 140 (28%) men and in 114 (42%) women. Ten shunt-carriers (1.6%) and 32 patients (5.0%) without RLS had suffered a recurrent stroke. After adjustment for age, sex, and atrial fibrillation, the hazard ratio of RLS for stroke recurrence was 0.86 (95% CI 0.41-1.79). The condition of RLS at rest adjusted for age, sex, stroke subtype, and cardiovascular risk factors was not found to increase the risk of stroke substantially (HR 1.16 [95% CI 0.41-3.29]) Our data suggest that the risk of recurrent stroke in subjects with PFO is not significantly increased in comparison with subject without it.

Prevalence of Embolic Signals in Acute Coronary Syndromes

The purpose of this study was to assess the prevalence of embolic signals (ES) in acute coronary syndromes (ACS) and their association with stroke. From December 2004 to October 2006, 209 consecutive patients with ACS (without prosthetic heart valves or previous stroke) were studied within 72 hours of symptom onset. Patients underwent ES monitoring in both middle cerebral arteries by transcranial Doppler for 30 minutes. Median follow-up was 14 months after discharge. Patients were treated according to current European Society Cardiology guidelines. Specifically, 92% of patients received heparin(s), 100% aspirin, 92% clopidogrel, 67% intravenous glycoprotein IIb/IIIa inhibitors, 9% fibrinolysis, and 67% underwent angioplasty. ES were detected in 7 patients (prevalence 3.4%; 95% CI, 1.4 to 6.8). Except for a higher prevalence of ES in patients with unstable angina versus other ACS categories (8.5% versus 1.9%, P=0.047), none of the factors among baseline characteristics, clinical features, ACS treatment, and cardiac findings were associated with the presence of ES. During hospitalization, 3 patients without ES had cerebrovascular events (one stroke and 2 transient ischemic attacks), whereas no cerebrovascular events occurred in patients with ES. The prevalence of ES among hospitalized patients with ACS is currently low, possibly because of improvement in ACS treatment. In this ACS sample, ES did not appear associated with short-term risk of cerebrovascular events.

Doppler Embolic Signals in Cerebrovascular Disease and Prediction of Stroke Risk

Background and Purpose— Asymptomatic embolic signals (ES) detected using transcranial Doppler have been reported in patients with potential cerebral embolic sources. They may be useful in risk stratification and in assessing therapies. First, it is essential to show whether they predict stroke risk. Methods— A systematic review and meta-analysis was performed to determine the prognostic value of ES in different potential cerebral embolic sources. Studies were identified that used transcranial Doppler to detect ES and included prospective stroke/TIA follow-up. Numbers of ES-positive and ES-negative patients were extracted with stroke/TIA and stroke alone outcomes. Results— ES are most frequent in large artery disease, less frequent in cardioembolic stroke, and infrequent in lacunar stroke. Data relating ES to future stroke risk were available for acute stroke, large artery disease, and the perioperative period of carotid endarterectomy. For symptomatic carotid stenosis, ES predicted stroke alone (OR, 9.57; 95%CI, 1.54 to 59.38; P =0.02) and stroke/TIA (OR, 6.36; 95% CI, 2.90–13.96; P &lt;0.00001). For asymptomatic carotid stenosis, ES predicted stroke alone (OR, 7.46; 95% CI, 2.24–24.89; P =0.001) and stroke/TIA (OR, 12.00; 95% CI, 2.43–59.34; P =0.002) but with heterogeneity ( P =0.004). In acute stroke ES predicted stroke alone (OR, 2.44; 95% CI, 1.17–5.08; P =0.02) and stroke/TIA (OR, 3.71; 95% CI, 1.64–8.38; P =0.002). A high frequency of ES immediately after carotid endarterectomy predicted stroke alone (OR, 24.54; 95% CI, 7.88–76.43; P &lt;0.00001) and stroke/TIA (OR, 32.04; 95% CI, 11.36–90.39; P &lt;0.00001). Conclusion— ES predict stroke risk in acute stroke, symptomatic carotid stenosis, and postoperatively after carotid endarterectomy; in asymptomatic carotid stenosis, data are less robust. In these conditions ES may be useful in risk stratification and in assessing therapeutic efficacy. For other embolic sources, further prospective data are required.

The Asymptomatic Carotid Emboli Study: Study Design and Baseline Results

Better methods of identifying which patients with asymptomatic carotid stenosis will develop stroke, are required to improve the risk-benefit ratio of carotid endarterectomy. A promising method is the detection of asymptomatic embolic signals using transcranial Doppler. Embolic signals predict stroke risk in symptomatic carotid stenosis, but their predictive role in asymptomatic carotid stenosis is uncertain. The Asymptomatic Carotid Emboli Study is a prospective observational study in patients with asymptomatic carotid stenosis> or =70%. Two 1-h transcranial Doppler recordings from the ipsilateral middle cerebral artery are performed at baseline, and a single-hour recording is performed at 6, 12 and 18 months. Follow-up is for 2 years. All recordings are centrally blinded to subject identity during analysis. The primary hypothesis is: do embolic signals on either of two 1-h recordings at entry predict ipsilateral transient ischaemic attack and stroke risk over the following 2 years? The major secondary hypothesis is: does the presence of embolic signals on a single-hour-long recording at baseline or at 6, 12 or 18 months predict ipsilateral transient ischaemic attack and stroke risk over the subsequent 6-month period? Recruitment was completed in October 2007 with 482 subjects. At the baseline, the proportion of subjects with embolic signals was 10.7% on recording 1, 10.8% on recording 2 and 16.7% on either of the two recordings. Embolic signal prevalence on the two recordings was significantly associated (chi(2) 27.48, P<0.0005). Patients without embolic signals were more likely to be treated with antiplatelets (90.8 vs 76.9%, P<0.0005) and this difference persisted on multivariate analysis. Asymptomatic Carotid Emboli Study will determine whether embolic signal is a useful predictor in asymptomatic carotid stenosis, and detection allows its predictive value to be compared with clinical features, imaging parameters and ultrasound plaque morphology. Baseline data show antiplatelet therapy is associated with fewer embolic signals.

Thrombus Size and Doppler Embolic Signal Intensity

Background: Migration of thrombus through the cerebral arteries is a common cause of stroke. Thrombus emboli can be detected non-invasively using Doppler ultrasound, but even where the embolus composition is known, there is currently no method for estimating the size of an embolus based on the returned ultrasound signal. Here we report the results of in vitro experiments investigating the relationship between size and embolic signal intensity for fresh thrombus emboli with a view to estimating the sizes of thrombi detected following carotid surgery. Method: Thrombi were formed from whole blood using the ‘Chandler loop’ method under flow conditions similar to those associated with arterial thrombus formation in vivo. A total of 390 Doppler embolic signals were then measured from 37 pieces of thrombus circulated in a pulsatile closed-flow circuit. The dimensions of each of the thrombi were measured before and after circulation using an optical microscope. Relationships between thrombus size and embolic signal properties were then investigated using standard statistical methods with a view to size estimation of thrombi during clinical monitoring. Results: Although embolic signals generally became more intense with increasing thrombus size, strong oscillations due to resonance effects were observed. Pearson tests revealed strong positive correlations between embolus diameter, signal intensity and duration (r > 0.8, p ≤ 0.01). Conclusions: This study provides experimental evidence supporting theoretical predictions relating Doppler embolic signal intensity to thrombus size. In our discussion, we tentatively suggest how this information might be used to size emboli in clinical practice.

0017: Ultrasound Detection of Cerebral Emboli, the State of the Art

To provide an overview of the current state-of-the-art of detection of cerebral emboli with transcranial Doppler, including methods of distinguishing embolic signals from artifacts, of distinguishing between particulate and gaseous emboli, and of sizing emboli.

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

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. 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. 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). 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.