Interpretation of embolic phenomena during carotid endarterectomy

Ultrasound-Based Quantification of Emboli during Conventional and Endovascular Aneurysm Repair

Purpose:

To differentiate and quantify the type and number of lower limb emboli occurring during endovascular aneurysm repair, as compared to conventional surgery.

Methods:

Thirty-eight patients underwent elective infrarenal aneurysm repair using a conventional surgical approach in 18 and an endovascular procedure in 20. Emboli were detected using a Doppler ultrasound system with a 2-MHz transducer interrogating the mid superficial femoral artery. Lower limb emboli were differentiated as particulate or gaseous based on the physical distance traversed by the embolic signal.

Results:

Significantly more particulate (median 108 versus 59, p = 0.015) and gaseous (134 versus 46, p = 0.008) emboli were detected during endovascular aneurysm repair as compared to conventional surgery. Clinically, no case of massive microembolization occurred in either group, but one patient in the conventional group required a femoral embolectomy, and three patients undergoing endovascular repair developed self-limiting trash feet postoperatively. In patients undergoing endovascular aortomonoiliac aneurysm repair, there was only a poor correlation between the number of particulate emboli and either procedural duration or operator experience.

Conclusions:

The apparent lack of a relationship between particulate embolization and operative time or technical experience suggests that manipulation of endoluminal devices within the aneurysm sac may not be the sole determinant of intraprocedural embolization. Other as yet undetermined factors may predict patients at high risk for massive embolization.

Relationship between lysophosphatidic acid and matrix metalloproteinase-9 plasma concentrations and carotid atheromatous plaque stability in patients with cerebral infarction

Objective:

To investigate the correlation between plasma lysophosphatidic acid (LPA), matrix metalloproteinase (MMP)-9 and carotid atheromatous plaque stability in patients with cerebral infarction.

Method:

Patients with cerebral infarction underwent carotid artery duplex ultrasonography and transcranial Doppler monitoring for detection of microemboli. Patients were stratified by plaque type (no plaque, intima thickening, unstable plaque, stable plaque) and presence or absence of micoremboli. Plasma LPA and MMP-9 were quantified.

Result:

LPA and MMP-9 concentrations were significantly higher and microemboli positivity was significantly more common in patients with unstable plaque ( n = 21) than the other three groups (intima thickening, n = 16; stable plaque n = 41; no plaque; n = 12). There was a significant positive correlation between LPA and MMP-9 concentrations.

Conclusion:

Plasma LPA and MMP-9 concentrations may be useful biomarkers in the clinical identification and prediction of unstable plaque, and in guiding treatment.

Stratification of intraoperative ischemic impact by somatosensory evoked potential monitoring, diffusion-weighted imaging and magnetic resonance angiography in carotid endarterectomy with routine shunt use

BACKGROUND

Routine shunting to minimize ischemia during carotid endarterectomy (CEA) is controversial. The aim of this study was to stratify the ischemic parameters associated with CEA and evaluate the effect of routine shunting in attempting to mitigate those ischemia.

METHOD

Data from 248 CEAs with routine shunting were retrospectively evaluated. Our assessment included somatosensory evoked potential (SSEP) amplitude reduction more than 50 % and longer than 5 min (SSEP<50%, >5 min), new postoperative diffusion-weighted imaging lesions (new DWI lesions), and severe stenosis as indicated by reduced ipsilateral middle cerebral artery (MCA) signal on preoperative magnetic resonance angiography (MRA asymmetry), as surrogates of hypoperfusion, microembli, and hemodynamic impairment, respectively.

RESULTS

SSEP<50%, >5 min occurred in 15 % of CEAs during cross-clamping, and shunting reversed the SSEP changes. New DWI lesions were observed in 4.1 %. Pre-clamping the common and external carotid artery during dissection (pre-clamp method) decreased the rate of new DWI lesions compared to without pre-clamping (3.5 % vs. 7.5 %, P = 0.22). Occlusion time was significantly longer in the pre-clamp method than without pre-clamping (P < 0.0001). However, the incidence of SSEP<50%, >5 min was not increased with the pre-clamp method (p = 1.0) when using information regarding SSEP and collaterals to modify the speed of shunt manipulation. MRA asymmetry was identified in 39 CEAs (15.8 %) with correction of asymmetry postoperatively. MRA asymmetry correlated with symptomatic hyperperfusion (P = 0.0034). Only three CEAs had symptomatic hyperperfusion (1.2 %) with minimal symptoms. Ten CEAs sustained transient ischemia, symptomatic hyperperfusion, or 30-day-stroke (composite postoperative ischemic symptoms). Logistic regression analysis confirmed that SSEP<50%, >5 min (p = 0.009), new DWI lesions (p = 0.004) and MRA asymmetry (p = 0.042) were independent predictors of　composite postoperative ischemic symptoms.

CONCLUSIONS

SSEP<50%, >5 min, new DWI lesions, and MRA asymmetry were able to stratify the ischemic impacts in CEA. Meticulous routine shunting could mitigate those appropriately.

Improvement and impairment in cognitive function after carotid endarterectomy: comparison of objective and subjective assessments

Objective and subjective assessments of postoperative improvement and impairment in cognition were prospectively compared in patients who underwent carotid endarterectomy (CEA). Each patient underwent subjective cognitive assessment by a neurosurgeon and the patient's next of kin, and neuropsychological testing consisting of five test scores within 7 days before surgery and between 1 and 2 months after surgery. Of 213 patients studied, 24 (11%), 166 (78%), and 23 (11%) patients were defined as having subjectively improved, unchanged, and impaired cognition, respectively, following surgery. In all neuropsychological tests, differences in test scores between the two tests (postoperative test score - preoperative test score) significantly differentiated patients with subjectively improved, unchanged, and impaired cognition after surgery. Receiver operating characteristic analysis showed that the cut-off point for the differences in neuropsychological test scores in detecting subjective improvement and impairment in cognition after surgery was identical to mean +2 standard deviations (SDs) and mean -2 SDs, respectively, of the control value obtained from normal subjects. Of 27 patients with differences in neuropsychological test scores more than the upper cut-off point and 26 patients with differences in neuropsychological test scores less than the lower cut-off point in one or more neuropsychological tests, 24 (89%) and 23 (88%) exhibited subjectively improved and impaired cognition, respectively, after surgery. The present study indicates that neuropsychological test scores reflect the subjective assessment of postoperative change in cognition, and can detect subjective improvement and impairment in cognition after CEA using the optimal cut-off points for the test scores.

Subclinical ischemia verified by somatosensory evoked potential amplitude reduction during carotid endarterectomy: negative effects on cognitive performance

OBJECT

Although the mechanisms underlying neurocognitive changes after carotid endarterectomy (CEA) are poorly understood, intraoperative ischemia and postoperative hemodynamic changes may play a role.

METHODS

Data from 81 patients who underwent unilateral CEA with routine shunt use for carotid artery stenosis were retrospectively evaluated. These patients underwent neuropsychological examinations (NPEs), including assessment by the Wechsler Adult Intelligence Scale-Third Edition and the Wechsler Memory Scale-Revised before and 6 months after CEA. results of NPEs were converted into z scores, from which pre- and postoperative cognitive composite scores (CSpre and CSpost) were obtained. The association between the change of CS between pre- and postoperative NPEs (that is, CSpost - CSpre [CSpost - pre]) and various variables was assessed. These latter variables included ischemic or hemodynamic parameters such as 1) intraoperative hypoperfusion detected by somatosensory evoked potential (SSEP) change-that is, an SSEP amplitude reduction more than 50% and longer than 5 minutes (SSEP< 50%, > 5 min); 2) new lesions on postoperative diffusion-weighted imaging studies; and 3) preexisting hemodynamic impairment. Paired t-tests of the NPE scores were performed to determine the net effect of these factors on neurocognitive function at 6 months.

RESULTS

A significant CSpost - pre decrease was observed in patients with SSEP< 50%, > 5 min when compared with those without SSEP< 50%, > 5 min (-0.225 vs 0.018; p = 0.012). Multiple regression analysis demonstrated that SSEP< 50%, > 5 min independently and negatively correlated with CSpost - pre (p = 0.0020). In the group-rate analysis, postoperative NPE scores were significantly improved relative to preoperative scores.

CONCLUSIONS

Hypoperfusion during cross-clamping, as verified by SSEP amplitude reduction, plays a significant role in the subtle decline in cognition following CEA. However, this detrimental effect was small, and various confounding factors were present. Based on these observations and the group-rate analysis, the authors conclude that successful unilateral CEA with routine shunt use does not adversely affect postoperative cognitive function.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

SELECTIVE VERSUS ROUTINE INTRAOPERATIVE SHUNTING DURING CAROTID ENDARTERECTOMY

OBJECTIVE

The use of intraluminal shunting during carotid endarterectomy (CEA) remains controversial. Over the years, different shunting strategies have been used. More recently, the use of intraoperative electroencephalography and somatosensory evoked potential monitoring with selective intraluminal shunting has been explored. No studies have assessed the independent association of selective versus routine intraluminal shunting to outcomes after CEA.

METHODS

The clinical and radiological records of all patients undergoing CEA from 1994 to 2006 at an academic institution were reviewed retrospectively to assess outcomes at 72 hours. The independent association of selective intraluminal carotid artery shunting during CEA and perioperative stroke within 72 hours was assessed through multivariate logistic regression analysis.

RESULTS

In 1411 patients with both symptomatic and asymptomatic extracranial carotid artery disease, there were a total of 49 (3.5%) perioperative strokes after CEA. There were two (1%) cases of perioperative strokes among 194 patients in the selective shunting group compared with 47 out of 1217 (4%) in the routine shunting group (P = 0.04). Symptomatic carotid artery disease was associated with a twofold increase in the odds of experiencing perioperative stroke (odds ratio, 1.95; 95% confidence interval, 1.08–3.52; P = 0.03). Patients undergoing electrophysiological monitoring with selective intraluminal carotid artery shunting were more than seven times less likely to experience a perioperative stroke (odds ratio, 0.05; 95% confidence interval, 0.01–0.40; P &lt; 0.01). Increasing cumulative surgical volume, particularly more than 200 total cases, was associated with more than a twofold decrease in perioperative stroke (odds ratio, 0.38; 95% confidence interval, 0.20–0.74; P &lt; 0.01).

CONCLUSION

Regardless of symptomatic carotid artery disease or cumulative surgical volume, patients undergoing CEA with intraoperative electroencephalography and somatosensory evoked potential monitoring with selective intraluminal carotid artery shunting had a stroke rate lower than that of the routine shunting group. Selective shunting based on electroencephalography and somatosensory evoked potential monitoring may be superior to the nonselective strategy.

Can Doppler time domain analysis of microembolic signals discriminate between gaseous and solid microemboli in patients with left ventricular assist device?

OBJECTIVE

Microembolic signals (MES) can be detected by transcranial Doppler sonography (TCD). To identify gaseous microemboli the inhalation of oxygen is an established method in patients with prosthetic heart valves. Time domain analysis of sample volume length (SVL) and of frequency modulation showed promising results in the discrimination between solid and gaseous microemboli. We investigated whether these time domain analyses allow the discrimination of different types of microemboli in patients with the non-pulsatile DeBakey left ventricular assist device (LVAD).

MATERIALS AND METHODS

Repeated unilateral detection of MES was performed by TCD in 20 patients supported with DeBakey LVAD. Each monitoring session consisted of 20 minutes without and 20 minutes with inhalation of 100% oxygen (6 l/min). A total of 500 MES, detected with (n=250) or without (n=250) the supply of oxygen, were randomly chosen for offline analysis. The SVL (in cm) was calculated by duration and velocity of the MES measured in the time domain mode. Additionally, frequency modulation of MES was classified into three main types: Without modulation (type I), with gradual changes (type II) and with rapid changes (type III).

RESULTS

With oxygen supply, both prevalence (26.4% versus 36.2%, p<0.01) and mean counts of MES per hour (49+/-293 versus 108+/-550, p<0.001) significantly declined compared with the MES load while breathing room air. There was no significant difference in the SVL of MES under oxygen (0.85+/-0.38 cm) compared with those without oxygen delivery (0.92+/-0.37 cm, p=0.6). Furthermore, no significant differences were noted for the MES frequency modulation types in time domain analysis with regard to oxygen supply.

CONCLUSIONS

The reduction of MES under oxygen delivery confirms the gaseous nature in a substantial number of circulating microemboli produced by the DeBakey LVAD. However, SVL and frequency modulation of MES did not appear to provide valuable information regarding the structural nature of the underlying microembolic material.

Effects of the free radical scavenger, edaravone, on the development of postoperative cognitive impairment in patients undergoing carotid endarterectomy

BACKGROUND

Some patients undergoing carotid endarterectomy (CEA) experience postoperative cognitive impairment. The purpose of the present case cohort study with historical control was to determine whether pretreatment with a novel free radical scavenger, edaravone, could prevent development of cognitive impairment after CEA.

METHODS

Fifty-five patients with ipsilateral internal carotid artery (ICA) stenosis (> or =70%) underwent CEA with administration of edaravone before ICA clamping. Neuropsychological testing was performed preoperatively and at the first postoperative month. Cerebral blood flow was also measured using single-photon emission computed tomography before and immediately after CEA and on the third postoperative day.

RESULTS

Postoperative cognitive impairment was observed in only 1 (2%) patient, who exhibited postoperative cerebral hyperperfusion (cerebral blood flow increase > or =100% compared with preoperative values). Incidence of postoperative cognitive impairment in the control group (92 CEA patients without administration of edaravone) was significantly higher (12%) (P = .0298, control vs treatment group). Logistic regression analysis demonstrated that postoperative cerebral hyperperfusion and absence of pretreatment with edaravone were significant independent predictors of postoperative cognitive impairment.

CONCLUSION

Pretreatment with edaravone can prevent development of cognitive impairment after CEA.

Are some strokes preventable? The potential role of transcranial doppler in transient ischaemic attacks of carotid origin

Transient ischaemic attacks (TIA) are more than just ministrokes. The high frequency of early stroke following TIA has resulted in the recent publication of guidelines in the UK. The guidelines recommend that patients attend a neurovascular clinic within 7 days of the index event to expedite investigation and treatment and so reduce the risk of a subsequent (potentially more serious) neurological event. After a TIA or stroke caused by carotid-artery disease, there is an increase in cerebral microemboli detectable by transcranial doppler (TCD). High microembolic loads appear to be surrogate markers for future neurological events, and the pharmacological efficacy of therapeutic interventions can now be rapidly and non-invasively assessed in the clinic or at the bedside. Medical treatments can now be optimised, avoiding the need for urgent or emergency carotid surgery and therefore allowing patients to undergo safer elective surgery when appropriate.

Characteristics of Peripheral Microembolization During Iliac Stenting: Doppler Ultrasound Monitoring

OBJECTIVE

To evaluate the characteristics of distal microembolic signals (MES) during iliac stenting using Doppler ultrasound monitoring.

DESIGN

Prospective clinical study.

METHODS

A 2-MHz probe was used to monitor continuously at the ipsilateral tibioperoneal trunks during technically and hemodynamically successful iliac stenting in 10 patients without infrainguinal occlusive lesion. MESs at guide-wire, balloon, or stent crossing (phase 1), predilatation (phase 2), stent deployment (phase 3), postdilatation (phase 4), and contrast medium or heparinized saline injection (at injection) were analyzed. Differentiation of gaseous emboli from particulate emboli was achieved by calculation of the sample volume length.

RESULTS

No distal embolic complications were observed. Five hundred and forty-one MESs were detected. The MES incidence and intensity in phase 3 were significantly higher than those in phase 1, phase 2, and phase 4 (p<0.05). The MES intensity at injection was significantly higher than that in each of four phases (p<0.0001).

CONCLUSIONS

Both the MES incidence and intensity were highest at stent deployment. Further study is required of microembolism during endovascular procedures in the lower extremities.

Postoperative cerebral hyperperfusion associated with impaired cognitive function in patients undergoing carotid endarterectomy

Object. Cognitive impairment occurs in 20 to 30% of patients following carotid endarterectomy (CEA). The purpose of the present study was to determine whether postoperative cerebral hyperperfusion is associated with impairment of cognitive function in patients undergoing that procedure.

Methods. Cerebral blood flow (CBF) was measured using single-photon emission computerized tomography scanning before and immediately after CEA and on the 3rd postoperative day in 92 patients with ipsilateral internal carotid artery stenosis of 70% or greater. Hyperperfusion post-CEA was defined as a 100% increase or greater in CBF compared with preoperative values. Neuropsychological testing was also performed preoperatively and at the 1-, 3-, and 6-month follow-up examinations.

At the 1-month postoperative neuropsychological assessment, 11 patients (12%) displayed evidence of cognitive impairment. In addition, the incidence of postoperative cognitive impairment in patients with post-CEA hyperperfusion (seven [58%] of 12 patients) was significantly higher than that in patients without post-CEA hyperperfusion (four [5%] of 80 patients; p < 0.0001). A logistic regression analysis demonstrated that post-CEA hyperperfusion was the only significant independent predictor of postoperative cognitive impairment. Of the seven patients in whom post-CEA hyperperfusion and cognitive impairment were identified 1 month postoperatively, four (including three patients with hyperperfusion syndrome) remained cognitively impaired at the 3- and 6-month follow-up examinations.

Conclusions. Postoperative cerebral hyperperfusion is associated with impairment of cognitive function in patients undergoing CEA. Furthermore, the development of hyperperfusion syndrome is associated with the persistence of postoperative cognitive impairment.

Comparison of levels of matrix metalloproteinases, tissue inhibitor of metalloproteinases, interleukins, and tissue necrosis factor in carotid endarterectomy specimens from patients on versus not on statins preoperatively

We performed an observational study on 137 patients undergoing carotid endarterectomy (CEA). Patients on statins were less likely to have had symptoms in the 4 weeks before CEA (p = 0.0049) and were less likely to have spontaneous cerebral embolization detected by transcranial Doppler (p = 0.0459). Carotid plaques retrieved at CEA from patients taking statins revealed significantly lower concentrations of matrix metalloproteinase-1 (p = 0.0176), matrix metalloproteinase-9 (p = 0.0018), and interleukin-6 (p = 0.0005).

Randomized trial of vein versus dacron patching during carotid endarterectomy: Long-term results

BACKGROUND AND PURPOSE

Overviews of randomized patch trials by the Cochrane Collaboration suggest that a policy of routine patching is preferable to routine primary closure. However, there is no systematic evidence that patch type, whether prosthetic or vein, influences outcome after carotid endarterectomy (CEA).

METHODS

Two hundred seventy-three patients were randomized to vein or thin-walled Dacron patch (Hemashield Finesse) closure of the arteriotomy after 276 CEA procedures. Patients were reviewed clinically and with duplex ultrasound scanning at 1, 6, 12, 24, and 36 months or until death. No patients were lost to follow-up. Cumulative statistical analyses are presented for the 264 patients (269 CEAs) who actually received a randomized treatment allocation.

RESULTS

Cumulative freedom from death or ipsilateral stroke at 3 years (including operative events) was 93.0% in the Dacron patch group and 95.5% in the vein group P =.42). Cumulative freedom from death or any stroke was 91.5% after Dacron patch closure and 93.9% after vein closure (P =.46). Cumulative freedom from recurrent stenosis greater than 70% or occlusion at 3 years was 92.9% for patients randomized to the Dacron patch group and 98.4% for patients randomized to the vein group (P =.03). At 3 years the incidence of stroke in the carotid territory not operated on was 1.0% in 93 patients with no contralateral internal carotid artery disease at randomization, and increased to 1.3% in 78 patients with 1% to 69% stenosis, and 2.0% in 51 patients with contralateral 70% to 99% stenosis. No late strokes occurred distal to 42 occluded contralateral internal carotid arteries.

CONCLUSIONS

Patch type has no influence on early operative risk, no association with enhanced patterns of thrombogenicity in the early postoperative period, and no influence on risk for ipsilateral or any stroke at 3 years. Dacron patches were, however, associated with a significantly higher incidence of recurrent stenosis at 3 years, with most occurring within 6 to 12 months of surgery. However, the higher incidence of recurrent stenosis was not associated with a parallel increase in late stroke, and in this study a program of serial ultrasound surveillance could not have prevented one ipsilateral stroke.

Elevation in Plasma MMP-9 Following Carotid Endarterectomy is Associated with Particulate Cerebral Embolisation

OBJECTIVES

To study plasma MMP-9 levels before and after carotid endarterectomy (CEA).

DESIGN

Observational study.

METHODS

Pre-operative (morning of surgery) and post-operative (48 h) plasma samples were obtained from 75 consecutive patients undergoing CEA. MMP-9 concentrations were quantified using ELISA. Transcranial Doppler monitoring was performed on each patient to detect particulate embolisation during the dissection phase of the CEA, until the application of carotid clamps.

RESULTS

The median post-operative plasma MMP-9 level of emboli-positive patients was significantly higher than their median pre-operative value (14.9 ng/ml vs. 8.8 ng/ml; p=0.038). However, no significant difference was seen in the plasma MMP-9 level of emboli-negative patients (7.7 ng/ml vs. 7.1 ng/ml; p=0.364). A greater rise was seen in the median plasma MMP-9 levels of those patients suffering >2 emboli (from 3.4 to 19.3 ng/ml; p=0.041) than those patients suffering 1 or 2 emboli (from 10.1 to 12.8 ng/ml; p=0.340).

CONCLUSIONS

Plasma MMP-9 only rises after CEA in patients with evidence of embolisation. This increase is more pronounced in those with high numbers of emboli. These data suggest that the increase in MMP-9 is due to cerebral damage caused by embolisation.

Patients' thromboembolic potential after carotid endarterectomy is related to the platelets' sensitivity to adenosine diphosphate

Background and purpose Postoperative microemboli in patients undergoing carotid endarterectomy are a significant risk factor for stroke. These emboli can be detected by intraoperative transcranial Doppler monitoring. They are not linked to technical error and are variable between patients. As it is known that platelets play a key role in arterial thrombosis, it was hypothesized that a patient's risk of postoperative carotid thrombosis was linked to the individual's platelet response to physiologic agonists.

METHODS

Blood samples from 120 patients undergoing carotid endarterectomy were analyzed before surgery. Platelet aggregation was measured in response to adenosine diphosphate (ADP) (0.5 to 4 micromol/L), collagen (10 to 50 mg/mL), and arachidonic acid (3 or 6 micromol/L), and fibrinogen binding to GPIIb-IIIa was measured by whole blood flow cytometry in response to ADP (0.1 to 10 micromol/L) and thrombin (0.02 to 0.16 micro/mL). Patients underwent intraoperative transcranial Doppler monitoring for 3 hours after surgery, and platelet functional data of those who had >25 emboli in this period (n = 22) were compared with the data of those with <25 emboli (n = 88).

RESULTS

The platelet response to ADP was significantly higher in the patients with >25 emboli, as measured both by aggregometry (P =.0012) and by flow cytometry (P <.0001). Platelet aggregation with collagen was also significantly higher in this group (P =.0018), but the response to thrombin was not statistically different in the two groups. In addition, there was no difference in the response to arachidonic acid between the groups.

CONCLUSION

The platelet response to ADP may be linked to clinical outcome, and thus, specific ADP receptor inhibitors may be appropriate for this group of patients.

The Excess of Strokes in Female Patients after CEA is due to their Increased Thromboembolic Potential—Analysis of 775 Cases

INTRODUCTION

Women suffer an excess of complications following arterial surgery, including an increased stroke risk following CEA. In order to investigate this further we studied men and women's thromboembolic potential following CEA.

METHOD

Analysis of prospectively collected data on 775 consecutive CEAs performed between October 1995 and October 2001, to identify the number of microembolic events detected following CEA.

RESULTS

Overall women had a 2.2 fold increase in the number of postoperative emboli detected (95% CI 1.2-3.3). Of those patients with significant numbers of postoperative emboli (>25), 68% were female against 22% for men (p=0.009). In order to prevent progression onto postoperative thrombotic stroke 9.7% of women were treated with intravenous Dextran-40 therapy, as opposed to only 2.7% of men (p=0.013). There were no significant differences between men and women's preoperative risk factors and/or factors relating to their operation.

CONCLUSION

It is possible that women's excess of postoperative complications following arterial surgery is related to their apparent increased thromboembolic potential following acute arterial injury.

MP3 compression of Doppler ultrasound signals

The effect of lossy, MP3 compression on spectral parameters derived from Doppler ultrasound (US) signals was investigated. Compression was tested on signals acquired from two sources: 1. phase quadrature and 2. stereo audio directional output. A total of 11, 10-s acquisitions of Doppler US signal were collected from each source at three sites in a flow phantom. Doppler signals were digitized at 44.1 kHz and compressed using four grades of MP3 compression (in kilobits per second, kbps; compression ratios in brackets): 1400 kbps (uncompressed), 128 kbps (11:1), 64 kbps (22:1) and 32 kbps (44:1). Doppler spectra were characterized by peak velocity, mean velocity, spectral width, integrated power and ratio of spectral power between negative and positive velocities. The results suggest that MP3 compression on digital Doppler US signals is feasible at 128 kbps, with a resulting 11:1 compression ratio, without compromising clinically relevant information. Higher compression ratios led to significant differences for both signal sources when compared with the uncompressed signals.

Asymptomatic embolisation in non-valvular atrial fibrillation and its relationship to anticoagulation therapy

OBJECTIVE

A prospective study to determine the prevalence of embolic signals (ES) detected with transcranial Doppler ultrasound (TCD) in subjects with non-valvular atrial fibrillation (NVAF) who were and were not taking anticoagulants.

METHODS

Sixty-eight subjects with NVAF taking warfarin and sixty-three NVAF subjects not taking warfarin were recruited from the cardiology department. No patients had suffered a previous stroke or clinical systemic embolisation. Thirty subjects in sinus rhythm were recruited as controls. TCD recordings were performed bilaterally from the middle cerebral arteries for 1 h. In 126 subjects (96%) the recording was repeated 1 week later. All Doppler recordings were reviewed blindly by an observer for ES.

RESULTS

After one recording ES were detected in one warfarin NVAF subject (1.5%), four non-warfarin NVAF subjects (6.3%) and no sinus rhythm controls. Following both recordings ES were detected in one warfarin NVAF subject (1.5%) and seven non-warfarin NVAF subjects (11.9%) P = 0.017.

CONCLUSIONS

Asymptomatic ES can be detected in a minority of subjects with NVAF. These signals were significantly less common in NVAF subjects taking warfarin, and this is consistent with asymptomatic ES having clinical significance in this disease. TCD detection of ES may have application in patients with NVAF for risk stratification, and assessment of the efficacy of new anti-platelet and anti-thrombotic regimens in the condition. Further large prospective studies are required to determine whether ES predict stroke risk in this patient group.

The nature of microemboli in patients with artificial heart valves

Cognitive decline has recently been found to be associated with microemboli in cerebral vessels in patients with artificial heart valves. The authors sought to determine the nature of such microemboli, that is, whether they are gaseous or solid, by comparing their characteristics to those of artificially generated air emboli in patients with patent foramen ovale (PFO). Three hundred and forty-eight microemboli were recorded in 11 patients with artificial valves (all taking coumadin), and 86 microemboli were recorded in response to intravenous injection of saline agitated with air in 8 PFO patients. No difference in intensity, duration, or relative velocity of microemboli was found between groups. The authors conclude that microemboli generated from artificial heart valves are generally gaseous and not solid.

Determinants of carotid microembolization

PURPOSE

Earlier studies have highlighted risk factors for perioperative stroke after carotid endarterectomy, such as female sex, preoperative symptoms, and cerebral infarction. In this study, we investigated the relationship between these factors and perioperative microembolization.

METHODS

A total of 235 patients were entered in the study at two centers. Transcranial Doppler ultrasound scanning was possible in 190 patients (81%) and was performed for 1 hour preoperatively and continuously intraoperatively as a means of detecting microemboli and monitoring mean middle cerebral artery velocity. The findings of transcranial Doppler ultrasound scanning were related to perioperative risk factors by means of univariate analysis.

RESULTS

Microemboli were detected in 28 (15%), 79 (42%), and 98 (52%) patients preoperatively, during carotid artery dissection, and after closure of the artery, respectively. Having 10 or more emboli after carotid artery closure was more common in women (P = .04) and in patients with symptomatic carotid artery disease (P = .04) and was demonstrated in three of the six patients who had a perioperative stroke. These three patients also had preoperative evidence of cerebral infarction and an intraoperative middle cerebral artery velocity less than 40 cm/s.

CONCLUSION

In this study, perioperative microembolization was more common in women and patients with symptomatic carotid artery disease. These findings may explain the increased risk of carotid surgery in these patients.

Patients' thromboembolic potential between bilateral carotid endarterectomies remains stable over time

OBJECTIVES

There is limited understanding of the reasons underlying post-CEA carotid thrombosis. Clinicians have often implicated operative technique, such as patch type or shunting, however the evidence for this is limited. We have studied whether it is the patients themselves who are prothrombotic, by studying the rates of emboli detection in patients undergoing bilateral CEAs at separate time points.

MATERIALS AND METHODS

Sixteen patients (3 women) underwent CEA during the study period, all of whom were taking aspirin. CEA was performed in a standardised manner throughout the study. All patients were monitored for 3 h postoperatively using a 2 MHz fixed head probe.

RESULTS

Those patients who had no emboli detected on TCD after the first operation, had a mean of 2.5 emboli after the second operation. Patients with emboli after the first operation had a mean of 41.3 emboli after the second CEA (MWU test, p=0.02). The dose of aspirin administered did not affect emboli rates. Correlation of the number of emboli detected after the first CEA with the second CEA gave a significant correlation ( p=0.038).

CONCLUSIONS

There appear to be factors relating to the patient that places some individuals at an increased risk of thrombotic stroke. Further elucidation of these factors may enable more effective, targeted therapy to be applied in the prevention of arterial thrombosis.

Hemodynamic conditions at the carotid bifurcation during protective common carotid occlusion

OBJECTIVES

Carotid angioplasty and stenting procedures are associated with an obligatory release of particulate debris into the distal cerebral circulation. Although most of the emboli are small and do not result in symptomatic neurologic deficits, some may be large enough to cause stroke. For this reason, a variety of filters and balloon occlusion devices have been employed as adjuvants to decrease the risk of distal embolization during carotid stenting. Some of these devices rely on the arrest of antegrade blood flow with the use of inflow arrest. The present study was undertaken to investigate the hemodynamic conditions that exist at the carotid bifurcation during common carotid artery (CCA) occlusion.

METHODS

Internal carotid artery (ICA) and external carotid artery (ECA) stump pressures were measured in 29 patients undergoing carotid endarterectomy. Duplex ultrasound scanning was used to measure the direction and velocity of blood flow in the ICA and ECA with the CCA cross-clamped but the ICA and ECA open, a clinical scenario analogous to CCA balloon occlusion at the time of carotid angioplasty and stenting. The direction and magnitude of ICA and ECA flow were compared with the stump pressures to determine whether a correlation existed between these variables.

RESULTS

The mean stump pressure in the ICA and ECA averaged 56 +/- 16 and 53 +/- 12 mm Hg, respectively. The ICA systolic stump pressure was lower than the ECA systolic stump pressure in six patients (21%), and all of these patients had persistent antegrade systolic duplex blood flow by duplex interrogation during CCA occlusion. The ICA systolic stump pressure exceeded the ECA systolic stump pressure in 19 patients (66%), and all of these patients had retrograde ICA flow during systole. Diastolic flow was also well correlated with the magnitude of the ICA/ECA stump pressure differential, with antegrade diastolic ICA blood flow in all nine patients with an ICA diastolic stump pressure less than the ECA diastolic stump pressure. None of the 10 patients with ICA diastolic stump pressure greater than ICA diastolic stump pressure maintained antegrade ICA diastolic flow, but four of these patients had flow to zero in diastole. Overall, 13 of 29 patients (45%) could be surmised to be at risk for distal embolization to the brain based on the persistence of some element of either systolic or diastolic antegrade ICA flow during common carotid occlusion.

CONCLUSIONS

Common carotid occlusion alone appears insufficient to protect against distal embolization during manipulations of the carotid bifurcation. Persistent systolic or diastolic antegrade blood flow occurs in a high proportion of patients, lending credence to the use of additional protective strategies to ameliorate the risk of embolic complications.

Cerebral protection systems for distal emboli during carotid artery interventions

Carotid angioplasty and stenting is associated with liberation of cerebral emboli that can cause periprocedural stroke. There are currently three classes of emboli protection devices (EPDs) that are undergoing feasibility studies and one randomized clinical trial. Preliminary data from a small series appear to be promising, and there appears to be attenuation of embolic signals on a cerebral Doppler exam with EPD use. However, rare strokes and patient intolerance due to imposed ischemia have been observed. The advantages and disadvantages of each EPD class and the issues involving clinical trials and surrogate end points in this area of study are discussed.

Automated embolus identification using a rule-based expert system

Transcranial Doppler ultrasound (US) can be used to detect microemboli in the cerebral circulation, but is still limited because it usually relies on "human experts" (HEs) to identify signals corresponding to embolic events. The purpose of this study was to develop an automatic system that could replace the HE and, thus, make the technique more widely applicable and, potentially, more reliable. An expert system, based around a digital signal-processing board, analysed Doppler signal patterns in both the time domain and frequency domain. The system was trained and tested on Doppler signals recorded during the dissection and recovery phases of carotid endarterectomy. It was tested with 74 separate 2.5-min recordings that contained at least 575 artefacts in addition to 253 s of diathermy interference. The results were compared with the results obtained by three HEs. Using a "gold-standard" that classified any event detected by the majority of HEs as an embolus, the automatic system displayed a sensitivity of 94.7% and a specificity of 95.1% for 1151 candidate events 7 dB or more above the clutter (signal-to-clutter ratio, SCR, > or = 7 dB), and 89.6% and 95.3%, respectively, for 2098 candidate events with SCR > or = 5 dB. The system had a very similar performance to individual HEs for SCR > or = 7dB, and was only marginally worse for SCR > or = 5 dB.

Randomized trial of vein versus Dacron patching during carotid endarterectomy: influence of patch type on postoperative embolization

PURPOSE

A recent overview indicated that although routine patching is safer than routine primary closure after carotid endarterectomy (CEA), there is no systematic evidence that patch type influences outcome. However, most surgeons still believe that prosthetic patches are probably more thrombogenic than vein patches. This study tested the hypothesis that there was no difference in thrombogenicity between the different patch types.

METHODS

A total of 274 patients undergoing 276 CEAs were randomized to either Dacron-patch closure (n = 137) or vein-patch closure (n = 139). All patients with an accessible cranial window were monitored for 3 hours postoperatively with transcranial Doppler scanning (TCD). The number of emboli and rate of embolization were quantified with the requirement for selective dextran therapy to control high rates of postoperative embolization. All patients were assessed postoperatively and again at 30 days by a neurologist, and all patients underwent a duplex examination at 30 days.

RESULTS

The 30-day death/any stroke rate was 2.2% for patients in the Dacron-patch group and 3.6% for patients in the vein-patch group (P =.72). Patients in the Dacron-patch group had a higher incidence of postoperative emboli (median, 5; interquartile range, 0-10.5) than patients in the vein-patch group (median, 3; interquartile range, 1-17; P =.028). However, the incidence of detecting more than 50 emboli was virtually identical, and patch type had no effect on the incidence of high-rate, sustained embolization that required dextran therapy (5.3% for Dacron, 3.7% for vein). No patient had a carotid thrombosis at 30 days.

CONCLUSION

Sustained, high-rate embolization, previously shown to be highly predictive of progression to carotid thrombosis, appears to be patient dependent, rather than related to patch type.

Plasma MMP-9 - a marker of carotid plaque instability

OBJECTIVES

to investigate whether peripheral blood levels of matrix metalloproteinases (MMPs) or their inhibitors are altered in patients with particulate cerebral embolisation.

DESIGN

a prospective study.

MATERIALS AND METHODS

using sandwich enzyme immunoassay, plasma levels of MMPs-1, -2, -3 and -9, plus TIMPs-1 and -2 were quantified in 70 consecutive patients undergoing carotid endarterectomy. Patients were monitored with transcranial Doppler (TCD) preoperatively and during the dissection phase of the operation to detect those with spontaneous particulate embolisation (n =21).

RESULTS

the plasma level of MMP-9 was significantly higher in those patients with evidence of spontaneous embolisation compared to those without. There were no differences in other MMP levels, or plasma concentrations of TIMPs.

CONCLUSIONS

plasma MMP-9 levels are elevated in patients with particulate cerebral embolisation, and this may represent a novel marker of atherosclerotic plaque instability.

Reducing the risk of carotid surgery: a 7-year audit of the role of monitoring and quality control assessment

BACKGROUND AND PURPOSE

The current risk of stroke after carotid endarterectomy may be worse than reported in the international trials. Because studies have suggested that most operative strokes follow surgeon error, the aim of the current study was to audit the impact of introducing a strategy of perioperative monitoring and quality control assessment on outcome.

METHODS

A total of 500 patients underwent carotid endarterectomy with intraoperative transcranial Doppler scan monitoring, completion angioscopy, and 3 hours of postoperative transcranial Doppler scan monitoring. The last of these guided selective dextran therapy in patients with high rates of postoperative embolization, which in previous series has been shown to be highly predictive of progression to thromboembolic stroke.

RESULTS

Intimal flaps were repaired in 3% of patients and luminal thrombus removed in 4% of patients. The rate of intraoperative stroke was 0.2%. A total of 313 patients had more than one embolus detected postoperatively (96% within 2 hours of flow restoration), but only 22 patients had sustained embolization requiring dextran. Embolization ceased in all but one patient receiving dextran, although the dose had to be increased in seven patients (36%). One patient was unable to receive adequate dextran therapy because of severe cardiac failure. Overall, the 30-day death/stroke rate was 2.2%, no patient had a perioperative stroke because of carotid thrombosis, and the rate of ipsilateral embolic stroke was 0.8%. Most complications resulted from cardiac pathology or intracranial hemorrhage.

CONCLUSIONS

A program of monitoring and quality control assessment has been associated with a 60% decrease in the operative risk in comparison with that observed before implementation of the protocol.

Transcranial Doppler assessment of cerebral embolic disorders

Transcranial Doppler ultrasound allows noninvasive monitoring of the large intracranial vessels. Microembolic signals (MES) have been observed under a variety of circumstances, especially in symptomatic carotid stenosis, high-risk cardiac conditions, and surgical procedures (such as carotid endarterectomy and cardiopulmonary bypass surgery). Technical considerations have presented numerous challenges to the interpretation of these signals, many of which appear to represent small emboli traveling in the blood flow. The technical aspects of these MES are discussed and their significance in relation to cerebral ischemia and its prevention are examined in some detail.

Eversion carotid endarterectomy generates fewer microemboli than standard carotid endarterectomy

OBJECTIVES

to test whether the occurrence of microembolism differed between eversion and standard carotid endarterectomy (CEA).

DESIGN

prospective, non-randomised transcranial Doppler (TCD) monitoring study of 61 patients.

MATERIALS AND METHODS

eversion CEA was performed in 27 and standard CEA in 34 patients. Surgery was performed under general anaesthesia. Three (5%) patients had a shunt inserted based on continuous EEG monitoring. Continuous middle cerebral artery TCD monitoring (EME, TC-4040) was performed intraoperatively and for 45 min postoperatively on day 1, day 2-3, day 4-5 and after 3 months. Unidirectional signals lasting >25 ms, having intensities of >9 dB were considered to represent embolic events.

RESULTS

intraoperative embolic events were detected in 50 (93%) of 54 patients in whom successful intraoperative TCD monitoring was achieved. Events occurred most frequently immediately following clamp release (85%), without difference between the two techniques. Embolic events were encountered postoperatively in four (15%) and 16 (48%) patients having eversion and standard CEA, respectively (p< 0.02). Four patients developed new neurological symptoms equally distributed between eversion and standard CEA. Two (3%) deficits were permanent and two transient. The patency of the carotid bifurcation was confirmed in all instances with duplex scanning.

CONCLUSION

we identified a surprisingly high number of postoperative embolic events as detected with transcranial Doppler in patients who had undergone carotid surgery using standard endarterectomy, as compared to patients who underwent eversion endarterectomy. Whether this difference has any clinical implication has yet to be proved.

Middle cerebral artery anatomy and characteristics of embolic signals: a dual gate computer simulation study

In terms of microembolic signal (MES) detection, the anatomy of the middle cerebral artery (MCA) mainstem has only scarcely been considered. The vessel itself, however, could be at least partly responsible for the enormous variation when calculating the essential time difference (deltat) values of MES using the dual-gate technique. Therefore, we studied the time characteristics of MES in a computer simulation applying an anatomically realistic vessel and a dual-gate TCD approach. Three different MCA anatomies and two MES to blood intensities were simulated as well as two different sample volume settings. The MES length (proximal sample volume t1; distal sample volume t2) and deltat were calculated for different angles of insonation and sample volume depths. The calculations of the time characteristics of MES showed extreme variation, with only modest changes of the insonation angle (t1 4-34 ms; deltat 9-27 ms) or the sample volume depth (t1 7-27 ms; deltat 6-32 ms). The variation could be considerably reduced with modified TCD settings i.e., a shorter gate separation combined with a shorter receiver gate time in the distal sample volume (deltat with changing insonation angles 6-19 ms; deltat with changing insonation depths 13-17 ms). These results not only urge us to a cautious interpretation of the properties of single MES, but also contribute to an understanding of the marked deltat variation using the dual-gate technique.

Transcranial Doppler directed dextran therapy in the prevention of carotid thrombosis: three hour monitoring is as effective as six hours

BACKGROUND

Six hours' monitoring by transcranial Doppler (TCD) has been successful in directing Dextran therapy in patients at high risk of thrombotic stroke after carotid endarterectomy (CEA).

OBJECTIVES

Is 3 h of routine monitoring as effective as 6 h in the prevention of early postoperative thrombotic stroke?

DESIGN

Prospective, consecutive study in all patients with an accessible cranial window.

METHODS

One hundred and sixty-six patients undergoing CEA underwent 3 h of postoperative monitoring by TCD. Any patient with > 25 emboli detected in any 10 min period or those with emboli that distorted the arterial waveform were commenced on an incremental infusion of dextran 40.

RESULTS

The majority of patients destined to embolise will do so within the first 2 postoperative hours. Dextran therapy was instituted in nine patients (5%) and rapidly controlled this phase of embolisation although the dose had to be increased in three (33%). No patient suffered a postoperative carotid thrombosis but one suffered a minor stroke on day 5 and was found to have profuse embolisation on TCD; high dose dextran therapy was again instituted, the embolus count rate fell rapidly and he made a good recovery thereafter. Overall, the death and disabling stroke rate was 1.2% and the death/any stroke rate was 2.4%.

CONCLUSION

Three hours of postoperative TCD monitoring is as effective as 6 h in the prevention of postoperative carotid thrombosis.

A policy of quality control assessment helps to reduce the risk of intraoperative stroke during carotid endarterectomy

OBJECTIVES

A pilot study in our unit suggested that a combination of transcranial Doppler (TCD) plus completion angioscopy reduced incidence of intra-operative stroke (i.e. patients recovering from anaesthesia with a new deficit) during carotid endarterectomy (CEA). The aim of the current study was to see whether routine implementation of this policy was both feasible and associated with a continued reduction in the rate of intraoperative stroke (IOS).

MATERIALS AND METHODS

Prospective study in 252 consecutive patients undergoing carotid endarterectomy between March 1995 and December 1996.

RESULTS

Continuous TCD monitoring was possible in 229 patients (91%), while 238 patients (94%) underwent angioscopic examination. Overall, angioscopy identified an intimal flap requiring correction in six patients (2.5%), whilst intraluminal thrombus was removed in a further six patients (2.5%). No patient in this series recovered from anaesthesia with an IOS, but the rate of postoperative stroke was 2.8%.

CONCLUSIONS

Our policy of TCD plus angioscopy has continued to contribute towards a sustained reduction in the risk of IOS following CEA, but requires access to reliable equipment and technical support. However, a policy of intraoperative quality control assessment may not necessarily alter the rate of postoperative stroke.

Time domain analysis of embolic signals can be used in place of high-resolution Wigner analysis when classifying gaseous and particulate emboli

The sample-volume length (SVL) of an embolic signal has previously been used to differentiate between gaseous and particulate emboli and has been calculated using high-resolution Wigner analysis. Although successful, this method of analysis is not widely available to other groups using transcranial Doppler ultrasound (TCD) to classify emboli. The SVL of embolic signals can also be calculated using time domain analysis, which is a far simpler method and potentially available to all TCD users. The aim of this study was to compare the SVL of embolic signals calculated using Wigner analysis and time domain analysis to assess whether or not time domain analysis can replace Wigner analysis to classify emboli. In total, 215 particulate and 100 gaseous emboli were recorded onto digital audiotape and analysed off-line. Two SVLs for each embolic signal were calculated by measuring embolic duration and velocity in the time domain and with Wigner analysis. Receiver operator characteristic (ROC) curves were plotted to assess the optimum SVL threshold for each method, and levels of sensitivity and specificity were defined. The optimum SVL threshold using Wigner analysis was 1.28 cm, yielding 93% sensitivity and 97% specificity. Using time domain analysis, the optimum threshold was 1.12 cm, yielding 90% sensitivity and 96% specificity. The methods were compared statistically (chi2) using their optimum thresholds, and were found not to be statistically different for classifying particles p=0.283) or gaseous emboli (p=0.700). This study has shown that the SVL of embolic signals, used to differentiate particulate from gaseous emboli, can be calculated more simply in the time domain, which yields as accurate results as calculating the SVL using Wigner analysis.

The effect of perioperative embolisation on visual function in patients undergoing carotid endarterectomy

OBJECTIVES

To investigate the effect of carotid artery embolisation detected by transcranial Doppler (TCD) monitoring during carotid endarterectomy (CEA) on visual function.

DESIGN

A prospective study. Visual function was assessed by an independent ophthalmalogist.

MATERIALS

One hundred consecutive patients undergoing carotid endarterectomy.

METHODS

All patients underwent pre- and postoperative retinal fundoscopy and automated visual field analysis. Intraoperative emboli were detected by continuous TCD monitoring of the middle cerebral artery.

RESULTS

Preoperatively, six patients had fundoscopic evidence of silent retinal embolisation, five patients had visible emboli associated with amaurosis fugax. Visual field analysis found no significant difference between ipsi- and contralateral eye scores. Only patients with occlusions of major retinal vessels had clinically reduced visual function. Intraoperatively TCD identified embolisation in 83/91 of monitored operations. Postoperatively, ipsilateral visual field scores deteriorated while contralateral eye scores remained unchanged, however only one new retinal embolus was detected. The incidence of TCD detected embolisation was not associated with a corresponding deterioration in postoperative visual function.

CONCLUSIONS

(1) A group of patients can be identified who experience "silent" retinal embolisation prior to CEA. (2) Clinically significant retinal embolisation resulting from CEA is uncommon. (3) CEA is associated with a deterioration in the visual field scores for the ipsilateral eye compared with the contralateral eye but the mechanism for this small but significant deterioration remains unclear.

Variability of velocity and duration of microembolic signals detected by bigated transcranial Doppler sonography in carotid endarterectomy

OBJECTIVE

To differentiate between gaseous and particular microemboli in carotid surgery one clinical approach is the interpretation of the effective sample volume length (SVL). We investigated whether such a clinical interpretation is based on reproducible measurements.

METHODS

Microembolic signals (MES) recorded during carotid endarterectomy by a bigated transcranial Doppler device were analyzed off-line. In the two sample volumes, the duration and the velocity of the MES were measured by two observers independently from each other twice within 2 weeks. The SVL of the MES were calculated by multiplying duration with velocity.

RESULTS

In the anatomical proximal sample volume 215 MES were recorded of which 203 (94.5%) were also present in the distal. The SVL medians of the MES were 2.2-4.1 mm lower in the distal than in the proximal sample volume as a result of lower velocity and shorter duration of the MES in the distal sample volume. The median of the paired differences of the SVL was 0.2 mm (interquartile range: 0.0-1.2) in the proximal sample volume and 0.8 mm (0.2-1.8) in the distal sample volume for observer 1, and 0.6 mm (0.4-2.2) and 0.9 mm (0.5-1.6) for observer 2. The median of the paired differences of the SVL between the observers was 1.4 mm (1.2-2.9) in the proximal sample volume and 1.6 mm (1.3-3.0) in the distal.

CONCLUSION

The intra- and interobserver agreement on calculating SVL is good. However, the depth of insonation influences some features of embolic signals.

Provision of training in carotid surgery does not compromise patient safety

BACKGROUND

Vascular surgeons perceive that carotid endarterectomy carries a higher risk of stroke if performed by a surgical trainee. Accordingly, some trainees consider that they receive a less than adequate training in carotid surgery before taking up a consultant position. The aim of this study was to establish whether the stroke rate was adversely affected if carotid endarterectomy was performed by a surgical trainee under consultant supervision.

METHODS

This was a prospective study of 151 consecutive patients undergoing carotid endarterectomy between 1 January and 31 December 1996 using a standardized technique including intraoperative and postoperative transcranial Doppler monitoring and completion angioscopy.

RESULTS

The overall mortality and/or disabling stroke rate was 0.7 per cent (one of 151 patients), whereas the mortality and/or any stroke rate was 1.3 per cent (two of 151). Surgical trainees performed 82 of 151 carotid endarterectomies, with a mortality rate of 1 per cent and a mortality and/or any stroke rate of 2 per cent. There was no significant difference in the incidence of retained thrombus or intimal flaps between trainees and consultants as detected by angioscopy.

CONCLUSION

Vascular surgical trainees can receive a comprehensive training in carotid artery surgery without incurring an unacceptable increase in operative risk.

Quality control during carotid endarterectomy

Although some form of quality control assessment is standard practice following virtually all forms of peripheral vascular reconstruction, it is seldom applied to carotid endarterectomy. This is despite the fact that the complications following endarterectomy can be catastrophic, are often related to technical error and are not easily remedied. A number of novel quality control techniques are now available. This review article summarizes the application of these methods to ensuring optimal surgical practice in patients undergoing carotid endarterectomy.

The narrow band hypothesis: an interesting approach for high-intensity transient signals (HITS) detection

We propose a new approach to detect microemboli automatically using the narrow band hypothesis. An initial database of 560 peripheral arterial Doppler high-intensity transient signals (HITS) was created to study microemboli and to define the normal limits to be used in our method. When a HITS occurs, our approach consists of modelling the Doppler signal using amplitude and frequency wave modulation. A threshold was defined experimentally using this database and then applied to 38 recordings from 12 patients. Using another database, six expert Doppler users reported 140, 176, 155, 161, 161 and 146 HITS, corresponding to a total of 197 different observed HITS. When an event was detected by 6, 5, 4, 3, 2 and 1 of the observers, the sensitivity of the automatic detection was 94.8%, 75.9%, 55.6%, 42.9%, 30% and 0%, respectively. The sensitivity of our automatic detection thus is highly associated with the likelihood (defined as the ratio of observers in agreement to the total number of observers) of an event: r = 0.99 for p < 0.0001. Although future research would result in improvement of the specificity, the narrow band hypothesis appears to be a promising technique for the detection of HITS.

Experience with transcranial Doppler monitoring reduces the incidence of particulate embolization during carotid endarterectomy

BACKGROUND

The aim of this study was to investigate whether the introduction of routine transcranial Doppler (TCD) ultrasonography during carotid endarterectomy reduces the incidence of microembolization by altering operative technique.

METHODS

The number and nature of microemboli detected during the first 75 consecutive carotid endarterectomies performed with TCD monitoring during 1992-1993 (group 1) were compared with those in a similar series of 75 consecutive patients undergoing carotid endarterectomy in 1995 (group 2), after substantial experience (210 patients) with TCD monitoring. Emboli were classified as either particulate or gaseous.

RESULTS

In patients with evidence of particulate emboli during the dissection phase of the operation, the total number of particulate emboli fell significantly in patients in group 2 (P = 0.019). Similarly, in patients in whom microembolization was detected on immediate opening of the shunt, the total number of microemboli also fell significantly in group 2 (P = 0.003). Overall, the median (95 per cent confidence interval) number of particulate emboli detected during the entire procedure fell significantly from 21 (16-29) in group 1 to 9 (7-14) in group 2 (P = 0.0008).

CONCLUSIONS

TCD monitoring plays an important role in the training and quality control of carotid endarterectomy and helps significantly to reduce the amount of microembolization.

Prevention of postoperative thrombotic stroke after carotid endarterectomy: the role of transcranial Doppler ultrasound

PURPOSE

To determine the incidence of particulate embolization after carotid endarterectomy (CEA), the effect of dextran-40 infusion in patients with sustained postoperative embolization, and the impact of transcranial Doppler (TCD) monitoring plus adjuvant dextran therapy on the rate of postoperative carotid thrombosis.

METHODS

Prospective study in 100 patients who underwent CEA with 6-hour postoperative monitoring using a TCD that was modified to allow automatic, intermittent recording from the ipsilateral middle cerebral artery waveform (10 minute sample every 30 minutes). An incremental dextran-40 infusion was commenced if 25 or more emboli were detected in any 10-minute period.

RESULTS

Overall, 48% of patients had one or more emboli detected in the postoperative period, particularly in the first 2 hours. However, sustained embolization that required Dextran therapy developed in only five patients. In each case, the rate of embolization rapidly diminished.

CONCLUSIONS

A small proportion of patients have sustained embolization after CEA, which in previous studies has been shown to be highly predictive of thrombotic stroke. Intervention with dextran reduced and subsequently stopped all the emboli in those in whom it was used and contributed to a 0% perioperative morbidity and mortality rate in this series.