Changes in middle cerebral artery blood flow after carotid endarterectomy as monitored by transcranial Doppler

OBJECTIVE: By using transcranial Doppler (TCD) it is possible to measure blood flow velocities within the circle of Willis. In this study, TCD was performed before and after carotid endarterectomy (CEA) with the aim to describe cerebral hemodynamics after normalization of the carotid artery blood flow. METHODS: Thirty CEA patients were consecutively entered into the TCD study, whereas 15 patients were referred for postoperative TCD for various clinical reasons. All 45 patients were investigated by using TCD: first preoperatively, then during the first few days after CEA before discharge from the hospital, and finally 3 to 12 months later. In addition, all patients underwent duplex investigation of the internal carotid artery the day before surgery and 3 months postoperatively. For the analysis, the patients were divided into two groups, one with (S-group), suspected postoperative neurologic complications/symptoms and another one without (C-group). Six patients were assigned to the S-group and 37 to the C-group, the latter including two patients who underwent bilateral CEAs. RESULTS: In the whole study group,a significant postoperative increase in systolic flow velocity was recorded bilaterally in the middle cerebral artery (MCA) as measured some days after surgery. The patients in the S-group showed high blood flow velocities mainly in the MCA on the ipsilateral side. A contralateral flow velocity increase did not occur in patients with very severe contralateral stenosis or occlusion (n = 9) if the late follow-up investigation was chosen as a reference value. Twenty patients in the C-group formed a subgroup with high blood pressure and/or headache postoperatively (CB-group) The other 19 patients were referred to as the CA-group. The CB- and S-groups showed more pronounced vessel disease in internal carotid artery on the contralateral side combined with lower collateral capacity in the circle of Willis compared to the CA-group. In the S-group the mean +/- standard deviation peak systolic velocity in ipsilateral MCA increased from a preoperative value of 0.71 +/- 0.22 m/sec to 2.23 +/- 0.72 m/sec (P <.005). In the CB-group, we observed a bilateral MCA blood flow velocity increase from 0.72 +/- 0.18 to 1.35 +/- 0.56 m/sec (P <.0001) on the ipsilateral side and from 0.82 +/- 0.37 to 1.28 +/- 0.66 m/sec (P < 0.001) on the contralateral side. In the CA-group, we observed minor bilateral blood flow velocity increases in the MCA, from 0.79 +/- 0.25 m/sec to 1.03 +/- 0.33 m/sec on the ipsilateral (P <.001) and from 0.70 +/- 0.17 m/sec to 0.93 +/- 0.26 m/sec on the contralateral side (P <.005). At the follow-up 3 to 12 months after surgery, the MCA flow velocities had returned to normal. CONCLUSIONS: Soon after surgery, blood flow velocity increases often bilaterally in the MCA. However a contralateral flow velocity increase did not occur in patients with very severe contralateral stenosis or occlusion if the late follow-up investigation was chosen as a reference value. The clinical significance of bilateral flow velocity increases is uncertain, but very high blood flow velocities might be a signal for cerebrovascular hyperperfusion. In those patients, increased postoperative surveillance is recommended.     

Flow redistribution in the major cerebral arteries after carotid endarterectomy: a study with transcranial Doppler scan

PURPOSE: This open single-center prospective study aimed to determine the redistribution of blood flow within the circle of Willis and through collateral pathways after carotid endarterectomy. Blood flow velocity and flow direction in the major cerebral arteries were determined, both at rest and during CO(2) inhalation. METHODS: Carotid endarterectomy was performed in 148 patients with a 70% or greater diameter stenosis of the internal carotid artery while patients were under general anesthesia. Arteriotomy closure was done with a venous patch. Selective shunting was performed with an electroencephalogram. Baseline blood flow velocity of the basal cerebral arteries was measured by means of transcranial Doppler sonography preoperatively (within 1 week before surgery) and 3 months postoperatively. At the same times, cerebrovascular reactivity was calculated during CO(2) inhalation insonating both middle cerebral arteries. RESULTS: Baseline blood flow velocity in the ipsilateral middle cerebral artery hardly changed 3 months postoperatively, but there was a considerable redistribution of flow in the circle of Willis. This was characterized by a decrease in contribution from the contralateral hemisphere through the anterior communicating artery, reduced cerebropetal flow rates in the ophthalmic artery, and smaller contribution of the posterior collateral sources. The CO(2) reactivity on the side of surgery increased in all patients. In patients with a contralateral occlusion, CO(2) reactivity increased on both sides. The redistribution of flow was most pronounced in patients who needed intraoperative shunting and in patients with a contralateral internal carotid artery occlusion. CONCLUSION: After carotid endarterectomy, flow redistribution, as expressed by changes in blood flow velocity values, occurs in the circle of Willis. The contribution of collateral sources is diminished, and the CO(2) reactivity increases, both of which reflect improvement of the hemodynamic condition. The most improvement occurs in patients with contralateral occlusion.     

Evaluation of cerebral hemodynamics by transcranial Doppler ultrasonography in carotid endarterectomy

The authors studied the linear blood flow rate (LBFR) in the middle cerebral artery (MCA) which was measured by means of transcranial dopplerography during carotid endarterectomy in 25 patients. Analysis of the results showed that the changes of LBFR in the MCA correlate with alterations in blood pressure: LBFR in the MCA reduced most during compression of the common carotid artery in patients with considerable affection of the contralateral carotid artery. The maximal increase of the blood flow during compression of the common carotid artery occurred when the initial LBFR in the MCA was lowest. After the blood flow in the common carotid artery is restored the LBFR in the MCA is determined by the degree of stenosis of the artery which is operated on and the degree of collateral circulation. The method makes it possible to determine in time the need for additional measures of protection of the brain from ischemia.     

Changes in cerebral blood flow velocity after release of intraoperative tourniquets in humans: a transcranial Doppler study

The effect of release of intraoperative thigh tourniquets on velocity of blood flow in the middle cerebral artery was examined in five patients given general anesthesia with controlled ventilation for lower extremity orthopedic procedures using transcranial Doppler sonography. Middle cerebral artery blood flow velocity increased significantly from 52 +/- 6 (SEM) to 82 +/- 24 cm/s (an increase of 58% +/- 13%) within 4 +/- 1 min after tourniquet release and remained significantly elevated for 7 min. A positive linear correlation was found between middle cerebral artery blood flow velocity and PETCO2 on each occasion (0.97 greater than or equal to r greater than or equal to 0.84, 0.001 greater than P greater than 0.0001) after tourniquet deflation. Assuming a linear relationship between flow velocity and flow, these findings suggest that significant increase in cerebral blood flow can occur after intraoperative tourniquet release and that this increase appears to be mostly CO2-dependent.     

Changes in middle cerebral artery flow velocity and pulsatility index after carotid endarterectomy.

Transcranial Doppler sonography (TCD) was used in 33 patients undergoing carotid endarterectomy (CEA). Mean flow velocity (MCA MV) and the pulsatility index in the middle cerebral artery (MCA PI) were measured pre- and on six occasions postoperatively. The MCA MV was reduced by anaesthesia but was increased postoperatively (+43%, p less than 0.001) compared to the preoperative value and was still increased at late follow-up after several months. The MCA PI, which was lower preoperatively than normally reported in this age group, was not changed by anaesthesia but then rose and remained elevated, i.e. within normal limits 72 h postoperatively (+30%, p less than 0.01) as well as at late follow-up. No significant changes in MCA MV or MCA PI were noted on the contralateral side. The results from this study support earlier findings from invasive studies showing that CEA results in an increased flow in the middle cerebral artery on the operated side and an increased MCA PI suggests an increased resistance on the operated side. The findings are compatible with an increased cerebral blood flow during the first days after CEA and with the operated side supplying a greater part of the cerebral blood flow even several months after surgery.     

Hyperperfusion syndrome after carotid endarterectomy: a transcranial Doppler evaluation

Transcranial Doppler ultrasonography was used to evaluate 2 patients who developed hyperperfusion syndromes after carotid endarterectomy. During the initial postoperative period, each patient had symptoms that were associated with elevated flow velocities in the ipsilateral cerebral vasculature. In addition, vascular resistance of these vessels was found to be abnormally low, as reflected by the Gosling pulsatility index. As the patients' symptoms improved, flow velocities decreased to normal levels and pulsatilities were noted to increase proportionately.     

Evaluating middle cerebral artery collateral blood flow reserve using acetazolamide transcranial Doppler ultrasound in patients with carotid occlusive disease

BACKGROUND: The objective of this study is to examine the utility of acetazolamide TCD ultrasound in the evaluation of MCA collateral blood flow reserve in patients with carotid occlusive disease. METHODS: Acetazolamide TCD and cerebral angiography were performed for 28 carotid territories in 14 patients with carotid occlusive disease. The percentage change in mean blood flow velocity and PI in the MCA was measured before and after 1 g of acetazolamide was administered. The carotid territories were divided into groups according their angiographic findings: (1) mild/moderate (<70%) vs severe (> or =70%) extracranial carotid artery stenosis, and (2) active collateral blood flow to the MCA territory vs no collateral blood flow to the MCA. RESULTS: After acetazolamide injection, the percentage increase in mean MCA velocity for mild/moderate vs severe carotid artery stenosis was 43% +/- 10% and 19% +/- 6%, respectively, indicating less collateral blood flow reserve in patients with severe stenosis (P = .04). The percentage decrease in the PI for MCA territories with vs without angiographic evidence of collateral blood flow was 4.6% +/- 4% and 16% +/- 3%, respectively (P = .04), indicating an exhausted vascular reserve in patients with evidence of active collateral blood flow on angiography. CONCLUSIONS: A decrease in the PI after acetazolamide administration represents a safe and noninvasive indicator of limited collateral blood flow reserve to the MCA territory ipsilateral to an extracranial carotid stenosis. Further study into the role acetazolamide TCD has in the preoperative evaluation of these patients, including threshold values, is warranted.     

Monitoring middle cerebral artery blood velocity during carotid endarterectomy

Transcranial pulsed Doppler ultrasound and spectral analysis were used to monitor blood velocities in the middle cerebral artery of nineteen patients (mean age 61 +/- 9 years) during carotid endarterectomy. A Javid shunt was used in all patients. The intensity weighted mean Doppler frequency for each spectral sweep (at 5 ms intervals) was time-averaged over the cardiac cycle to obtain a mean value for blood velocity in the middle cerebral artery. The range of such values found in the 19 patients was: 12-38 cm s-1 after anaesthesia (baseline); 12-69 cm s-1 during diathermy; 0-30 cm s-1 during carotid clamping; 16-32 cm s-1 during shunting and 18-60 cm s-1 in the recovery room. The average change in middle cerebral artery blood velocity from baseline values showed significant increases during diathermy (P less than 0.005), shunting (P less than 0.05) and in the recovery room (P less than 0.005). Clamping of the internal carotid artery showed a significant decrease in middle cerebral artery blood velocities of all patients (P less than 0.005), three of whom showed no flow in the middle cerebral artery during clamping. Abnormally high amplitude Doppler signals at the commencement of shunting were detected in 17 of the 19 patients. Such Doppler signals are consistent with turbulent blood flow or the introduction of micro-air bubbles by the shunt. Backbleeding in the internal carotid artery before insertion of the shunt was associated with diminished flow in the ipsilateral middle cerebral artery of ten patients, oscillatory forward/reverse flow in three patients and cessation of flow in the remaining six patients.     

The value of transcranial Doppler in predicting cerebral ischaemia during carotid endarterectomy.

OBJECTIVES: transcranial Doppler (TCD) measurement of middle cerebral artery velocity (MCAV) is an indirect method of assessing cerebral blood flow and therefore predicting patients at risk of stroke during carotid endarterectomy (CEA), and may be used to determine the need for shunting. This study evaluates the accuracy of three accepted TCD criteria in predicting the need for a shunt. DESIGN: prospective study. METHODS: one hundred and twenty consecutive CEA were performed under loco/regional anaesthesia. Patients monitored by TCD and Awake neurological examination were included. Shunts were inserted if there was neurological deterioration. Awake patient monitoring was compared with the three TCD criteria. RESULTS: inadequate TCD recordings were obtained in 16 operations (13%). In the remainder (104 cases), 12 developed symptoms of cerebral ischaemia and required a shunt (12%). Comparisons with the three accepted criteria were as follows: (1) m MCAV <30 cm/s had a sensitivity, specificity, PPV and NPV of 92%, 49%, 19%, and 98%, respectively; (2) clamp/pre-clamp ratio <0.6 had a sensitivity, specificity, PPV and NPV of 92%, 75%, 33% and 99%, respectively; (3) greater than 50% reduction in m MCAV had a sensitivity, specificity, PPV and NPV valves of 83%, 77%, 32% and 97%, respectively. CONCLUSIONS: TCD flow velocities are not a reliable method for detecting cerebral ischaemia and therefore determining the need for a shunt in CEA.     

经颅多普勒超声预警颈动脉内膜切除术后脑高灌注综合征

目的 通过经颅多普勒超声(TCD)脑血流监测,探索预警颈动脉内膜切除术(CEA)后脑高灌注综合征(CHS)发生的新方法.方法 2009年8月至2011年12月进行CEA前瞻性临床试验.TCD共测量夹闭前、开放后、离室前血压稳定后3个时间点大脑中动脉收缩期血流速度.计算术中脑血流速度增加比例(VR1)和术后脑血流速度增加比例(VR2).通过计算灵敏度、特异度、阳性预测值、阴性预测值、受试者工作特征曲线(ROC)下面积分析VR1、VR2预警CHS的能力.结果 共76例病例入组.6例VR1＞ 100％,18例VR2＞ 100％.共10例患者被诊断为CHS,其中3例VR1＞100％,7例VR2＞ 100％.VR1和VR2预警CHS发生的ROC下面积分别为0.636和0.728.当VR1取切点100％时,其灵敏度为30％,特异度95％,阳性预测值和阴性预测值分别为50％和90％;当VR2取切点100％时,其灵敏度为70％,特异度83％,阳性预测值、阴性预测值分别为39％及95％,明显优于VR1.结论 血压稳定条件下增加监测离室前的脑血流变化对预警CEA术后CHS的发生十分有效,VR2＞ 100％能较好预测CHS的发生并排除阴性病例.     

Thiopental effect on cerebral blood flow during carotid endarterectomy

To investigate the effect of thiopental on cerebral blood flow (CBF) during carotid endarterectomy, five patients receiving isoflurane-N2O anesthesia were studied. During the period of temporary bypass shunting, a baseline CBF was measured using i.v. Xe washout, and global CBF was calculated from the mean of 10 detectors. Thiopental was given in a dose sufficient (mean 4.5, range 2.6-5.8 mg/kg) to result in burst-suppression on the electroencephalogram (EEG) of approximately 1:1 duration and CBF was measured again. Data were compared using repeated measures analysis of variance. Thiopental significantly reduced mean (+/-SE) CBF (ml/100 g/min) from 37 +/- 6 to 18 +/- 2 (p <0.02). Corresponding PaCO2 (mm Hg) values were 42.8 +/- 1.2 and 41.2 +/- 1.6 and mean systemic blood pressure (mm Hg) was 101 +/- 3 and 100 +/- 6, respectively (NS). Mean % change in CBF was 48 +/- 5 (range 32-62%). There was no relationship between the dose administered and the change in CBF. During steady-state anesthesia, a small dose of thiopental capable of suppressing EEG resulted in a profound reduction in CBF.     

The significance of posttraumatic increase in cerebral blood flow velocity: a transcranial Doppler ultrasound study.

Using transcranial doppler ultrasonography, cerebral blood flow velocity was measured daily from both middle cerebral arteries in 121 patients who had suffered minor (n = 55), moderate (n = 16), or severe (n = 50) brain injury. Serial computed tomographic scans were performed to identify noncontusion-related infarction (NCI). Cerebral perfusion pressure was monitored continuously in 41 patients who had severe head injury; of these, 22 had continuous measurement of arterial and jugular bulb venous oxygen (SJO2) saturation. Abnormally high mean flow velocity (greater than 100 cm/s) was observed in 23 patients (minor injury, n = 3; moderate injury, n = 3; severe injury, n = 17), but was recorded only when cerebral perfusion pressure exceeded 60 mm Hg (P less than 0.0001). Fourteen patients who underwent SJO2 monitoring developed increased mean flow velocity (MFV). In 6, the arterial-jugular venous oxygen content difference (AVDO2) was below 4 ml/dl, indicating global cerebral hyperemia. All had bilateral elevation of MFV, and 6 of the 8 nonhyperemic patients (AVDO2, 4-9 ml/dl) had a unilateral increase of MFV (P = 0.018). Four of the 23 patients with increased MFV developed NCI, as compared with none of the patients without elevated MFV (P = 0.015). All patients with NCI had suffered severe brain injury, had unilateral elevation of MFV in the terriory of the relevant cerebral vessel, and had received therapy to correct reduced cerebral perfusion pressure (P = 0.008). NCI did not occur in any patient with increased MFV that was associated with global hyperemia.     

颈动脉内膜剥脱术治疗颈动脉狭窄58例临床分析

目的 评估颈动脉内膜剥脱术治疗颅外颈动脉狭窄的疗效,并探讨经颅多普勒超声(transcranial Doppler,TCD)的价值. 方法回顾性分析2002年1月至2008年12月采用颈动脉内膜剥脱术治疗的58例颅外颈动脉狭窄的资料.40例伴有不同程度的脑缺血症状,18例无明显症状.颈动脉狭窄程度均在70%以上.41例行内膜剥脱后动脉单纯缝合,9例采用人工材料(涤纶)补片成形,8例行自体静脉补片成形.32例在TCD的监测下完成,26例没有采用TCD监测,28例则采用临时转流管. 结果手术成功率为100%,无死亡率.术前有腩缺血症状的40例患者中,术后大多数患者有不同程度的恢复.未采用TCD组患者5例(19.2%)术后出现脑血流过度灌注.采用TCD者未发现过度灌注的并发症.53例患者获随访,随访率为91.4%;随访时间为15～86个月,平均42.5个月.死亡5例.3例出现术后再狭窄(5.7%),其中2例接受颈动脉支架成形术,1例仍在观察随访中.结论 颈动脉内膜剥脱术治疗颅外颈动脉狭窄是一种安全、有效的措施;TCD监测对于转流管的选择提供重要依据,并对预防术后过度脑灌注具有指导作用.     

Instantaneous measurement of blood flow velocity in internal carotid arteries by pulsed Doppler in cerebral arteriovenous malformations

Hemodynamics (systolic rate: VS and diastolic rate: VD) of internal carotid artery blood flow was determined by pulsed Doppler combined with ultrasound scans to measure instantaneous flow rate in 8 patients with cerebral arteriovenous malformations. Values obtained were compared with those in 10 healthy volunteers. Measurement of the diastolic fraction a = (formula: see text) appears to be a valid method for assessing severity of this malformation and the importance of its output. Repeated tests in one patients operated upon by several stages demonstrated the importance of a blood shunt after ablation of lesions.     

Stump pressure and transcranial Doppler for predicting shunting in carotid endarterectomy.

OBJECTIVES: to compare stump pressure (SP) and transcranial Doppler (TCD) with neurologic monitoring during carotid endarterectomy (CEA). MATERIALS: one hundred and forty-seven CEAs performed under local anaesthesia. METHODS: neurologic monitoring and SP were performed in all cases, while mean velocity of the middle cerebral artery (mvMCA) by TCD was done in 140/147 (95%) cases. Shunts were applied in all cases on the basis of neurologic monitoring. The following haemodynamic criteria have been compared to neurologic monitoring: (a) <25 mmHg SP; (b) <50 mmHg SP; (c) < or =10 cm/s mvMCA after carotid occlusion; (d) > or =70 decrease of mvMCA after carotid occlusion. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated for each haemodynamic criterion. RESULTS: shunt was used in 18/147 (12.2%) cases. With regards to <25 mmHg SP, < or =50 mmHg SP, < or =10 cm/s mvMCA after carotid occlusion, and > or =70 decrease of mvMCA after carotid occlusion, sensitivity resulted 33, 89, 80 and 80%, respectively. Specificity resulted 96, 82, 97 and 96%, respectively. Positive predictive value resulted 55, 41, 75 and 71%, respectively. Negative predictive value 91, 98, 98 and 98%, respectively. Accuracy resulted 88, 76, 89 and 94%, respectively. CONCLUSIONS: none of the haemodynamic criteria by SP and TCD resulted absolutely reliable in predicting the need for carotid shunt.     

Influence of antiplatelet therapy on cerebral micro-emboli after carotid endarterectomy using postoperative transcranial Doppler monitoring.

AIM: To study the effect of different antiplatelet regimens (APT) on the rate of postoperative TCD registered micro-embolic signals (MES) following carotid endarterectomy (CEA). DESIGN: Prospective, randomised, double-blinded, pilot study. METHODS: The study group of 102 CEA patients (76 men, mean age 66.8 years) was randomised to routine Asasantin (Dipyridamole 200mg/Aspirin 25mg) twice daily (group I; n=39), Asasantin plus 75 mg Clopidogrel once daily (group II; n=33), or Asasantin plus Rheomacrodex (Dextran 40) 100g/L iv; 500 ml (group III; n=30). TCD monitoring of the ipsilateral middle cerebral artery for the occurrence of MES was performed intra-operatively and during the second postoperative hour following CEA. Primary endpoints were the rate of postoperative emboli and the occurrence of cerebrovascular complications. Secondary endpoint was any adverse bleeding. RESULTS: There were no deaths or major strokes. We observed 2 intraoperative TIA's (group II and III) and 1 postoperative minor stroke (group I). In comparison with placebo, Clopidogrel or Rheomacrodex in addition to Asasantin produced no significant reduction in the number of postoperative MES. There was no significant difference between the number of postoperative MES and different antiplatelet regimens. The incidence of bleeding complications was not significantly different between the 3 APT groups. CONCLUSION: In the present study, we could not show a significant influence of different antiplatelet regimens on TCD detected postoperative embolization following CEA.     

Evaluation of posttraumatic cerebral blood flow velocities by transcranial Doppler ultrasonography

Thirty-five patients were admitted to the hospital with Glasgow coma scale scores of 4 to 7 after severe, blunt head injury. Blood flow velocities of the middle cerebral artery (MCA) and the ipsilateral internal carotid artery (ICA), high in the neck, were recorded noninvasively by Doppler ultrasonography. Serial examinations were begun within 48 hours of trauma and continued until the patient either died or was discharged. Spasm of the MCA was assumed if the ratio of the velocity of blood flow in the MCA (VMCA) to the velocity of blood flow in the ICA (VICA) exceeded 3 (normal value, 1.7 +/- 0.4). In cases of severe MCA spasm, this ratio is higher because of increased flow velocity in the MCA and reduced flow in the ICA due to increased cerebrovascular resistance. Higher MCA velocities with VMCA/VICA above 3, consistent with MCA spasm, were found in 14 of the 35 patients (40%). The increase began as early as 48 hours after injury, reached a maximum between Days 5 and 7, and lasted until 2 weeks after injury. There was a significant correlation between the occurrence of vasospasm and the quantity of cisternal or intracerebral blood seen on a computed tomographic scan. No correlation was found with the age of the patients, the Glasgow coma scale score at admission, the intracranial pressure, or the functional outcome 6 months after injury. The occurrence of a secondary infarction in a patient with severe MCA spasm suggests that, at least in some cases, spasm may influence the prognosis.     

Microemboli detected by transcranial Doppler monitoring in patients during carotid angioplasty versus carotid endarterectomy

Microemboli, as detected by transcranial Doppler monitoring, have been shown to be a potential cause of strokes after carotid endarterectomy. We retrospectively reviewed 105 patients who underwent transcranial Doppler monitoring during 112 procedures for the treatment of 115 carotid bifurcation stenoses: 40 by percutaneous angioplasty with stenting and 75 by carotid endarterectomy. In PTAS procedures (n = 40), there was a mean of 74.0 emboli per stenosis (range 0-398, P = 0.0001) with 4 neurologic events per patient (P = 0.08). In CEA procedures (n = 76), there was a mean of 8.8. emboli per stenosis (range 0-102, P= 0.0001) with 1 neurologic event per patient (P = 0.08). The post-procedural neurological events in the percutaneous angioplasty with stenting population included two strokes (5.6%) and two transient ischemia attacks (5.6%). Microemboli for each of these cases totalled 133, 17, 29 and 47 (with one shower), respectively. One postoperative carotid endarterectomy patient was noted to have a stroke (1.4%), with 48 microemboli noted during that procedure. The mean emboli rate for percutaneous angioplasty with stenting patients with neurological events was 59.0: without complications it was 85.1. The mean emboli rate for carotid endarterectomy patients without complications was 8.3. Three percutaneous angioplasty with stenting patients had no emboli (7.5%), whereas 29 carotid endarterectomy patients had no emboli (38.7%). CONCLUSION: The percutaneous angioplasty with stenting procedure is associated with more than eight times the rate of microemboli seen during carotid endarterectomy when evaluated with transcranial Doppler monitoring. Larger patient groups are needed to determine if this greater embolization rate has an associated risk of higher morbidity or mortality.