Severe Unilateral Carotid Stenosis Research Articles

Numerical investigation of carotid stenosis in three-dimensional aortic-cerebral vasculature: pulsatility index, resistive index, time to peak velocity, and flow characteristics

Haemodynamic correlations among the pulsatility index (PI), resistive index (RI), time to peak velocity (TPV), and mean Reynolds number (ReMean) were numerically investigated during the progression of carotid stenosis (CS), a highly prevalent condition. Fifteen patient-specific CS cases were modeled in the package, SimVascular, by using computed tomography angiography data for the aortic-cerebral vasculature. Computational fluid domains were solved with a stabilized Petrov–Galerkin scheme under Newtonian and incompressible assumptions. A rigid vessel wall was assumed, and the boundary conditions were pulsatile inflow and three-element lumped Windkessel outlets. During the progression, the increase in the TPV resembled that during aortic stenosis, and the parameter was negatively correlated with PI, RI, and ReMean in the ipsilateral cerebral region. The ReMean was inversely related to PI and RI on the contralateral side. In particular, PI and RI in cerebral arteries showed three second-order regression patterns: ‘constant (Group A)’, ‘moderately decreasing (Group B)’, and ‘decreasing (Group C)’. The patterns were defined using a new parameter, mean ratio (lowest mean index/mean index at 0% CS). This parameter could effectively indicate stenosis-driven tendencies in local haemodynamics. Overall, the haemodynamic indices changed drastically during severe unilateral CS, and they reflected both regional and aortic-cerebral flow characteristics.

Risk factors for hyperperfusion-induced intracranial hemorrhage after carotid artery stenting in patients with symptomatic severe carotid stenosis evaluation

BackgroundAnalyzing risk factors for hyperperfusion-induced intracranial hemorrhage (HICH) after carotid artery stenting (CAS) in patients with symptomatic severe carotid stenosis.MethodsThis study retrospectively analyzed clinical data of 210 patients, who had...

Abstract 2762: Asymmetry of The Blood Oxygen Level-Dependent fMRI Response During Hypercapnia Is Reliable to Evaluate Cerebrovascular Reactivity in Patients with Severe Unilateral Carotid Stenosis

Background and Purpose: Previous transcranial Doppler studies have suggested that, in patients with severe carotid stenosis, the lack of cerebrovascular reactivity (CVR) is an independent predictor of ipsilateral stroke. The BOLD (Blood Oxygenation Level-Dependent) fMRI contrast can be used to assess the CVR during normal condition and during hemodynamic stress, like hypercapnia. The purpose of this study is to evaluate the BOLD signal parameters on the Middle Cerebral Artery (MCA) territory, induced by auditory stimulus, during different levels of hypercapnia in patients with severe unilateral carotid stenosis, comparing the ipsilateral hemisphere (IH) to the contralateral hemisphere (CH). Methods: The images were obtained from 16 patients with severe unilateral carotid stenosis. Patients were submitted to an auditory stimulus (3s) in three different conditions: normocapnia and at EtCO2 increase of 5 and 10mmHg. The images were acquired with a 3T Philips MR, preprocessed and analyzed using an autoregressive method. Results: The BOLD signal from the IH was different from the CH during the basal condition and at 5mmHg (p<0.0001), but not at the 10mmHg ETCO2 increase. For each BOLD parameter, the major differences between the hemispheres were seen on the onset time (p<0.0001) and amplitude of BOLD signal (p<0.0001). The width difference was significant between the basal and 10mmhHg increase (p<0.01). In these three parameters, the BOLD signal of the IH presented no significant variations with the CO2 increment. However, the BOLD signal for CH showed an increase on the time-to-onset and width and amplitude decrease. The time to peak parameters of the BOLD signal showed no differences between the hemispheres and at hypercapnic conditions. Conclusion: In our results the IH did not respond to the hypercapnic stress as the CH. Therefore, among patients with severe carotid stenosis, BOLD can reliably identify some that have an exhausted CVR, which cannot respond to a vasodilatory stress like hypercapnia. Future studies using this technique may help to select patients for recanalization procedures.

Preoperative cerebral hemodynamics and shunting during carotid endarterectomy in patients with severe unilateral carotid stenosis

To estimate the possible predictors for the need for shunting during carotid endarterectomy in patients with severe unilateral carotid stenosis based on preoperative transcranial Doppler sonographic examination. One hundred twenty-six patients were included in the study. Pulsatility index, flow acceleration, peak systolic velocity, and mean velocity were measured in the middle cerebral artery (MCA) and anterior cerebral artery on both sides. Cerebrovascular reactivity (CVR) was evaluated in 21 patients with shunts and in 55 patients without shunts. The shunted and nonshunted groups did not differ with regard to demographic and clinical characteristics. The side-to-side difference in peak systolic velocity and mean velocity of the MCA was significantly higher in patients with shunts. CVR were significantly higher in the patients without shunts (36.0 +/- 17.2%) than in patients with shunts (16.6 +/- 11.4%; p = 0.0003). The peak systolic velocity and mean velocity asymmetry of the MCA had relatively low receiver operating characteristics, whereas CVR exhibited a relatively high accuracy in predicting the need for shunting. Low CVR and increased asymmetry of MCA velocities were found in patients who subsequently required shunting during carotid endarterectomy. The relatively low accuracy of the MCA asymmetry should prevent the use of this criterion as a reliable preoperative predictor for shunting during carotid surgery, whereas CVR was more accurate and may prove useful in this setting.

Cerebral Hemodynamics in Symptomatic and Asymptomatic Patients with Severe Unilateral Carotid Stenosis before and after Carotid Endarterectomy

Data concerning hemodynamic status prior to and after carotid endarterectomy (CEA) in symptomatic and asymptomatic patients is insufficient. Transcranial Doppler (TCD) provides information regarding compensatory collateral flow as well as mechanisms of cerebral autoregulation in patients with carotid stenosis. Forty eight symptomatic and 81 asymptomatic patients with unilateral severe carotid stenosis were examined by TCD before and in early postoperative period after CEA. Cigarette smoking was the only risk factor significantly more frequent in symptomatic patients. Preoperative anterior cerebral artery (ACA) and middle cerebral artery (MCA) asymmetry, basilar artery velocity and number of ophthalmic arteries with reversed flow, were not significantly different between the two groups. Pulsatility index, cerebrovascular reactivity and flow acceleration on the side of stenosis were significantly lower in symptomatic patients. After surgery there was a significant improvement of all TCD parameters in symptomatic as well as asymptomatic patients. The exhausted ability of cerebral autoregulation is an important factor differentiating between symptomatic and asymptomatic patients with severe carotid stenosis. Successful surgery provides good recovery of cerebral hemodynamics in both symptomatic and asymptomatic patients.

1360 Cerebral hemodynamics in symptomatic and asymptomatic patients with severe unilateral carotid stenosis before and after carotid endarterectomy : TCD evaluation

1360 Cerebral hemodynamics in symptomatic and asymptomatic patients with severe unilateral carotid stenosis before and after carotid endarterectomy : TCD evaluation

Mutual Information and Assesment of Dynamic Cerebral Autoregulation

The assessment of dynamic cerebral autoregulation (DCA) and cerebral hemodynamics is a central task in patients suffering from cerebrovascular diseases or from stroke. We present an investigation of the DCA assessment on the basis of mutual information (MI) analysis in patients suffering from severe unilateral carotid stenosis and a control group of healthy volunteers. Besides the evaluation of the MI approach a comparison with various other approaches and validated DCA parameters is presented. We find significant differences between the healthy volunteers and the patients suffering from stenosis in the new approaches and the validated DCA parameters. Moreover side-to-side differences ipsi- and contralateral to the stenosis are found. Finally, the concordance of the various approaches for DCA assessment is discussed.

Dynamic cerebral autoregulation and collateral flow patterns in patients with severe carotid stenosis or occlusion.

The quality of collateral blood supply in carotid disease is pivotal for the resulting hemodynamic compromise. However, the interrelation between different patterns of collateral blood flow and actual impairment of cerebral autoregulation (CAR) has not been analyzed so far. Dynamic CAR was assessed noninvasively by the phase shift between respiratory-induced 0.1-Hz oscillations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) in 101 patients with severe unilateral carotid stenosis (> or = 75%) or occlusion. CO(2)-vasomotor reactivity was assessed via inhalation of 7% CO(2). Spontaneously activated collaterals via primary (anterior/posterior communicating artery, type I, n = 65) and secondary (ophthalmic artery / leptomeningeal with or without primary pathways, group II, n = 24) pathways were assessed by transcranial Doppler/duplex sonography. Signs of functional stenosis in the anterior collateral pathways were subsumed under type III (n = 12). Best dynamic CAR (phase shift) on affected sides was observed for type I (n = 65), in which values did not differ significantly from contralateral sides. Reduced phase shift values were present in type II; poorest values were observed for type III. CO(2)-reactivity differed mainly between type I and the other types. A less distinct differentiation of autoregulatory impairment was found when dividing patients into groups of different degrees of stenosis. Symptomatic patients (previous TIA/stroke) were significantly less frequent in the group with type I collateral flow and had significantly lower phase shift and CO(2)-reactivity values. In conclusion, we found that dynamic CAR is substantially impaired if secondary collateral pathways are activated or if functional stenosis in the activated anterior collateral pathway is present. These hemodynamic constellations are also associated with a higher proportion of clinically symptomatic patients. Determination of dynamic CAR by transfer function analysis represents a convenient, sensitive method for detection of cerebral hemodynamic compromise in obstructive carotid disease.

Assessment of ophthalmic artery collateral pathway in the hemispheric cerebral hemodynamics in patients with severe unilateral carotid stenosis

The role of ophthalmic artery collateral pathway in hemispheric hemodynamics in patients with severe carotid stenosis is controversial. The aim of the present study was to address this question comparing the asymmetry of the velocity in middle and anterior cerebral arteries (MCAs and ACAs) and cerebrovascular reactivity (CVR) in MCA on stenotic side in the patients with unilateral severe stenosis of internal carotid artery (ICA) in patients with and without ophthalmic artery collateral pathway. The cohort of 118 patients with carotid stenosis was prospectively assembled. Fifty patients who had severe unilateral ICA stenosis (71%-99%) by Duplex Ultrasound (DUS) were observed by transcranial Doppler (TCD). Cerebral blood flow velocity in MCA and ACA in both sides, direction of blood flow in ophthalmic artery (OA) and CVR on the side of stenosis were determined. There were 14 patients with retrograde blood flow in OA (Group I). The remaining 36 patients with anterograde flow in OA composed Group II. The degree of interarterial asymmetry of peak and mean velocity (Vpeak and Vmean) in MCA and ACA and CVR in MCA were compared in both groups. The degree of ACA asymmetry by Vpeak was 44.0% ± 6.9% in Group I and 38.3% ± 3.9% in Group II ( p= 0.49), by Vmean 40.3% ± 6.7% and 36.6% ± 3.8% ( p= 0.63) respectively. The degree of MCA asymmetry by Vpeak was 24.2% ± 2.8% in Group I and 19.5% ± 5.0% in Group II (p = 0.42), by Vmean 23.5% ± 2.9% and 20.6% ± 5.1% (p = 0.63) respectively. CVR in Group I was 26.1% ± 6.1%, in Group II 29.0% ± 6.7% (p = 0.65). The ophthalmic collateral pathway has no influence on hemispheric cerebral hemodynamics in patients with severe unilateral carotid stenosis.

Vasomotor response to CO2 and L-Arginine in patients with severe internal carotid artery stenosis; pre- and post-surgical evaluation with transcranial Doppler.

Carotid artery disease may cause both thromboembolism and cerebral blood flow disturbances, particularly in subjects with impaired hemodynamic compensatory mechanisms. The aim of this study was to evaluate by transcranial Doppler (TCD) the hemodynamic changes induced by CO2 and L-Arginine stimulation in a selected population with severe unilateral carotid stenosis (70-80%), before and after carotid endarterectomy, in order to determine the effect of surgery in the vascular hemodynamics of these patients. We studied 20 subjects (mean age 66.4 years) consecutively admitted to our institute with ischemia and unilateral severe internal carotid artery stenosis (70-80%) detected by Color Doppler. All patients underwent arterial digital subtraction angiography to confirm the ultrasonographic evaluation. TCD was performed bilaterally; blood flow velocity was monitored during CO2 and L-Arginine stimulation both in basal conditions and three months after surgery. After endarterectomy, mean velocity increased in response to both stimuli with a trend toward statistical significance. A significantly lower reactivity to L-Arginine on the stenotic side was found in the pre-operative phase: this asymmetrical reactivity was no longer observable after carotid endarterectomy. We found a statistically significant difference in L-Arginine reactivity in the stenotic side of patients with severe unilateral internal carotid stenosis. This is probably related to an alteration of the endothelium function due to the carotid pathology, since the abnormalities disappeared three months after endarterectomy.

Cerebral vasoreactivity in unilateral carotid artery disease. A comparison of blood flow velocity and regional cerebral blood flow measurements.

Hemodynamic information obtained by assessing cerebral vasoreactivity is of clinical interest and may have prognostic significance in patients with occlusive carotid disease. The aim of this study was to compare the results of transcranial Doppler and regional cerebral blood flow studies when used to assess cerebral vasoreactivity. Blood flow velocities in both middle cerebral arteries and regional cerebral blood flow in their respective perfusion territories were compared in 52 patients with severe unilateral carotid stenosis or occlusion. The studies were first performed under basal conditions and repeated after the intravenous administration of 1 g acetazolamide. Asymmetry (normal compared with pathological side) in middle cerebral artery blood velocity increase was significantly greater than the asymmetry in cerebral blood flow increase in the perfusion territories of the arteries. A significant correlation (r = .63, P < .0001) was found between asymmetry in percent velocity increase and asymmetry in absolute cerebral blood flow increase. The two methods agreed in their assessment of either a normal or a reduced vasoreactivity in 38 subjects and disagreed in 14. In six of the latter patients, who had no evidence of cerebral infarction, the asymmetry in velocity increase was abnormal, whereas asymmetry in flow increase was assessed as normal. We found a good correlation between the asymmetry in regional cerebral blood flow increase in the middle cerebral artery perfusion territories and asymmetry in the velocity increase in the middle cerebral arteries after administration of acetazolamide. These results suggest that transcranial Doppler examination combined with the acetazolamide test may be used in clinical situations to assess cerebral vasoreactivity.