Dynamic cerebral autoregulation in carotid stenosis before and after carotid stenting

Cerebral Hyperperfusion Syndrome after Carotid Revascularization; Predictors and Complications

BACKGROUND

Cerebral hyperperfusion syndrome (CHS) is a rare but serious complication following carotid artery revascularization. Considering the varying rates observed among carotid endarterectomy (CEA), Transfemoral Carotid Artery Stenting (TFCAS), and Transcarotid Artery Revascularization (TCAR), identifying the predictors and complications of CHS is essential for improving patient outcomes. This study utilizes a national database to investigate the predictors and complications of CHS following carotid revascularizations.

METHODS

We conducted a retrospective analysis of all patients undergoing CEA, TFCAS, and TCAR for carotid artery stenosis in the Vascular Quality Initiative database from 2020 to 2023. Multivariate logistic regression was applied to identify CHS predictors, which were used to develop a risk score calculator. Moreover, we compared the stroke and mortality rates following CHS among the 3 revascularization techniques.

RESULTS

The final cohort in our study included 59,130 (53%) CEAs, 14,064 (13%) TFCAS's, and 37,565 (34%) TCARs. There were 281 cases of CHS (0.25%), and TFCAS was associated with the highest rate of CHS (0.78% vs. 0.22% vs. 0.15%; P < 0.001). After adjusting for potential confounders, TFCAS was associated with almost 3-fold higher risk compared to CEA (adjusted odds ratio (aOR) = 2.87 [95% confidence interval (CI): 1.65-4.9] P < 0.001). On the other hand, TCAR was comparable to CEA. Other predictors of CHS included uncontrolled hypertension, insulin-dependent diabetes, symptomatic status, prior carotid procedure, urgent intervention, and postoperative blood pressure medication. These predictors were used to develop an interactive CHS risk calculator (C-statistic = 0.8). Among patients who developed CHS, TFCAS was associated with a 70% higher risk of inhospital stroke (aOR = 1.7 [95% CI: 1.4-2] P < 0.001) and almost triple the risk of inhospital death (aOR = 2.9 [95% CI: 2.3-3.8] P < 0.001). TCAR and CEA were comparable except for a slight risk of inhospital stroke after TCAR (aOR = 1.2 [95% CI: 1-1.3] P = 0.03).

CONCLUSION

In this multi-institutional national study, we have demonstrated that the type of carotid revascularization significantly influences the risk of CHS and subsequent stroke and mortality, with TFCAS associated with the highest risk. Uncontrolled hypertension was associated with a 2-fold increased risk of CHS, underscoring the importance of tight blood pressure control. We were able to provide a prediction model for CHS based on preoperative factors. Prospective use of this risk calculator might benefit in postoperative monitoring.

Individualized autoregulation-guided arterial blood pressure management in neurocritical care

Cerebral autoregulation (CA) is the physiological process by which cerebral blood flow is maintained during fluctuations in arterial blood pressure (ABP). There are various validated methods to measure CA, either invasively, with intracranial pressure or brain tissue oxygenation monitors, or noninvasively, with transcranial Doppler ultrasound or near-infrared spectroscopy. Utilizing these monitors, researchers have been able to discern CA patterns in several pathological states, such as but not limited to acute ischemic stroke, spontaneous intracranial hemorrhage, aneurysmal subarachnoid hemorrhage, sepsis, and post-cardiac arrest, and they have found CA to be altered in these patients. CA disturbances predispose patients suffering from these ailments to worse outcomes. Much focus has been placed on CA monitoring in these populations, with an emphasis on arterial blood pressure optimization. Many guidelines recommend universal static ABP targets; however, in patients with altered CA, these targets may make them susceptible to hypoperfusion and further neurological injury. Based on this observation, there has been much investigation on individualized ABP goals and their effect on clinical outcomes. The scope of this review includes (1) a summary of the physiology of CA in healthy adults; (2) a review of the evidence on CA monitoring in healthy individuals; (3) a summary of CA changes and its effect on outcomes in various diseased states including acute ischemic stroke, spontaneous intracranial hemorrhage, aneurysmal subarachnoid hemorrhage, sepsis and meningitis, post-cardiac arrest, hypoxic-ischemic encephalopathy, surgery, and moyamoya disease; and (4) a review of the current evidence on individualized ABP changes in various patient populations.

Non-Invasive Tools in Perioperative Stroke Risk Assessment for Asymptomatic Carotid Artery Stenosis with a Focus on the Circle of Willis

This review aims to explore advancements in perioperative ischemic stroke risk estimation for asymptomatic patients with significant carotid artery stenosis, focusing on Circle of Willis (CoW) morphology based on the CTA or MR diagnostic imaging in the current preoperative diagnostic algorithm. Functional transcranial Doppler (fTCD), near-infrared spectroscopy (NIRS), and optical coherence tomography angiography (OCTA) are discussed in the context of evaluating cerebrovascular reserve capacity and collateral vascular systems, particularly the CoW. These non-invasive diagnostic tools provide additional valuable insights into the cerebral perfusion status. They support biomedical modeling as the gold standard for the prediction of the potential impact of carotid artery stenosis on the hemodynamic changes of cerebral perfusion. Intraoperative risk assessment strategies, including selective shunting, are explored with a focus on CoW variations and their implications for perioperative ischemic stroke and cognitive function decline. By synthesizing these insights, this review underscores the potential of non-invasive diagnostic methods to support clinical decision making and improve asymptomatic patient outcomes by reducing the risk of perioperative ischemic neurological events and preventing further cognitive decline.

Myths and methodologies: Assessment of dynamic cerebral autoregulation by the mean flow index

The mean flow index-usually referred to as Mx-has been used for assessing dynamic cerebral autoregulation (dCA) for almost 30 years. However, concerns have arisen regarding methodological consistency, construct and criterion validity, and test-retest reliability. Methodological nuances, such as choice of input (cerebral perfusion pressure, invasive or non-invasive arterial pressure), pre-processing approach and artefact handling, significantly influence mean flow index values, and previous studies correlating mean flow index with other established dCA metrics are confounded by inherent methodological flaws like heteroscedasticity, while the mean flow index also fails to discriminate individuals with presumed intact versus impaired dCA (discriminatory validity), and its prognostic performance (predictive validity) across various conditions remains inconsistent. The test-retest reliability, both within and between days, is generally poor. At present, no single approach for data collection or pre-processing has proven superior for obtaining the mean flow index, and caution is advised in the further use of mean flow index-based measures for assessing dCA, as current evidence does not support their clinical application.

A systematic review on the assessment of cerebral autoregulation in patients with Large Vessel Occlusion

As the majority of large vessel occlusion (LVO) patients are not treated with revascularization therapies or efficiently revascularized, complementary management strategies are needed. In this article we explore the importance of cerebral autoregulation (CA) assessment in the prediction and/or modification of infarct growth and hemorrhagic transformation. In patients with LVO, these are important factors that affect prognosis. A systematic search of the PubMed, EMBASE databases and a targeted Google search was conducted, resulting in the inclusion of 34 relevant articles. There is an agreement that CA is impaired in patients with LVO; several factors have been identified such as time course, revascularization status, laterality, disease subtype and location, some of which may be potentially modifiable and affect outcomes. The personalized CA assessment of these patients suggests potential for better understanding of the inter-individual variability. Further research is needed for the development of more accurate, noninvasive techniques for continuous monitoring and personalized thresholds for CA.

Hemispheric Asymmetry on the Electroencephalogram during General Anesthesia Responsive to Blood Pressure Manipulations

The electroencephalogram (EEG) has been extensively used to detect ischemia and the need for shunting during carotid endarterectomy. Limited literature exists using EEG data to detect ischemia in other surgeries. This case report depicts a 65-year-old man, with extensive vascular history including complete left carotid occlusion and severe right carotid stenosis, who presented for left first rib resection and left subclavian vein balloon angioplasty. Following induction of general anesthesia, frontal EEG (SedLine; Masimo Corporation, Irvine, CA, USA) demonstrated hemispheric asymmetry, which nearly resolved with vasoactive support. At three distinct periods, discordance reoccurred necessitating a higher mean arterial pressure threshold. This case demonstrates EEG patterns concerning for focal spectrographic ischemia and highlights the potential use of EEG signals to capture hypoperfusion and direct vasoactive therapy.

Retrospective multicenter study on the management of asymptomatic carotid artery stenosis with coexistent unruptured intracerebral aneurysm

AIM OF THE STUDY

To evaluate the results of carotid endarterectomy (CEA) in patients with a concomitant asymptomatic intracranial aneurysm discovered at preoperative diagnostic imaging.

MATERIAL AND METHODS

From January 2000 to December 2020, 75 consecutive patients admitted for surgical treatment of asymptomatic >70% (NASCET) carotid artery stenosis presented at preoperative computed tomography angiography (CTA) with a concomitant, unruptured intracranial aneurysm (UIA). Aneurysm diameter was ≤ 5 mm in 25 patients (Group A), from 6 to 9 mm in 38 patients (Group B) and ≥ 10 mm in 12 patients (Group C). Sixty UIAs (80%) were treated before performing CEA, 10 in Group A (40%), 38 (100%) in Group B and 12 (100%) in Group C. Twenty-five UIAs (42%) were subjected to surgical clipping and 35 (58%) to coiling. The mean time intervals were 48 days (range, 20-55 days) between clipping and CEA, and 8 days (range, 4 -13 days) between coiling and CEA. Carotid endarterectomy (CEA) was standard and performed through eversion of the internal carotid artery (ICA) in 36 patients (48%) and through longitudinal arteriotomy with systematic patch closure in 39 patients (52%). Primary endpoints of the study were mortality and morbidity related to each of the two treatments including any complication occurring during the time interval between the two procedures or within 30 days after the last procedure. Secondary endpoints were mid-term survival and freedom from ischemic or hemorrhagic stroke and carotid restenosis.

RESULTS

One patient died during the 30 days following clipping of a 11 mm diameter UIA of the basilar artery. No other death or complication was observed following CEA and treatment of the UIA, or during the time interval between the two procedures. During median follow-up of 26 months (IQR, 18-30 months), no late stroke and no carotid restenosis were observed. At 22, 27, 29 and 31 months after CEA, four patients in group A underwent surgical clipping of an enlarging intracranial aneurysm, which had not been treated initially due to its small diameter. Cumulative survival rate at 30 months by Kaplan-Meier plots was 83±5%.

CONCLUSIONS

Concomitant asymptomatic carotid artery stenosis and UIA is a rare entity. Our study suggests that in this setting, prior treatment of the UIA followed by CEA is safe.

Reliability of cerebral autoregulation using different measures of perfusion pressure in patients with subarachnoid hemorrhage

Dynamic cerebral autoregulation to spontaneous fluctuations in cerebral perfusion pressure (CPP) is often assessed by transcranial Doppler (TCD) in the time domain, yielding primarily the mean flow index (Mx), or in the frequency domain using transfer function analysis (TFA), yielding gain and phase. For both domains, the measurement of blood pressure is critical. This study assessed the inter-method reliability of dynamic cerebral autoregulation using three different methods of pressure measurement. In 39 patients with aneurysmal subarachnoid hemorrhage, non-invasive arterial blood pressure (ABP), invasive ABP (measured in the radial artery) and CPP were recorded simultaneously with TCD. Intraclass correlation coefficient (ICC) was used to quantify reliability. Mx was higher when calculated using invasive ABP (0.39; 95% confidence interval [95% CI]: 0.33; 0.44) compared to non-invasive ABP, and CPP. The overall ICC showed poor to good reliability (0.65; 95% CI: 0.11; 0.84; n = 69). In the low frequency domain, the comparison between invasively measured ABP and CPP showed good to excellent (normalized gain, ICC: 0.87, 95CI: 0.81; 0.91; n = 96; non-normalized gain: 0.89, 95% CI: 0.84; 0.92; n = 96) and moderate to good reliability (phase, ICC: 0.69, 95% CI: 0.55; 0.79; n = 96), respectively. Different methods for pressure measurement in the assessment of dynamic cerebral autoregulation yield different results and cannot be used interchangeably.

Reliability and validity of the mean flow index (Mx) for assessing cerebral autoregulation in humans: A systematic review of the methodology

Cerebral autoregulation is a complex mechanism that serves to keep cerebral blood flow relatively constant within a wide range of cerebral perfusion pressures. The mean flow index (Mx) is one of several methods to assess dynamic cerebral autoregulation, but its reliability and validity have never been assessed systematically. The purpose of the present systematic review was to evaluate the methodology, reliability and validity of Mx.Based on 128 studies, we found inconsistency in the pre-processing of the recordings and the methods for calculation of Mx. The reliability in terms of repeatability and reproducibility ranged from poor to excellent, with optimal repeatability when comparing overlapping recordings. The discriminatory ability varied depending on the patient populations; in general, those with acute brain injury exhibited a higher Mx than healthy volunteers. The prognostic ability in terms of functional outcome and mortality ranged from chance result to moderate accuracy.Since the methodology was inconsistent between studies, resulting in varying reliability and validity estimates, the results were difficult to compare. The optimal method for deriving Mx is currently unknown.

A narrative review of the pathophysiology of ischemic stroke in carotid plaques: a distinction versus a compromise between hemodynamic and embolic mechanism

Atherosclerotic carotid artery stenosis causes about 10–20% of all ischemic strokes through two main mechanisms: hemodynamic impairment in case of significant stenosis and thromboembolism from an atherosclerotic plaque regardless of the degree of stenosis. The latter is the most frequent mechanism and appear to result from embolization from a vulnerable atherosclerotic plaque or acute occlusion of the carotid artery and propagation of thrombus distally. Downstream infarcts may occur in a territory of major cerebral artery or at the most distal areas between two territories of major cerebral arteries, the so-called watershed (WS), or border zone area. Although WS infarcts, especially deep WS infarct, were historically thought to be due to hemodynamic compromise, the role of microembolism has also been documented, both mechanisms may act synergistically to promote WS infarcts. Routine and more advanced imaging techniques may provide information on the underlying mechanism involved in ipsilateral ischemic stroke. A better understanding of ischemic stroke pathogenesis in carotid stenosis may limit the use of routine non-selective shunt, whose benefit-risk balance is debated, to patients with hemodynamic impairment.

After reviewing existing evidence underpinning the contribution of the two mechanisms in downstream ischemic stroke and the various imaging techniques available to investigate them, we will focus on the pathogenesis of WS infarcts that remains debated.

Efficacy and Safety of Emergency Extracranial-Intracranial Bypass for Revascularization within 24 Hours in Resolving Large Artery Occlusion with Intracranial Stenosis

BACKGROUND

Endovascular treatment (EVT) is less effective for intracranial atherosclerosis-induced emergent large vessel occlusion. Extracranial-intracranial (EC-IC) bypass surgery is a possible treatment option to augment cerebral blood flow in the perfusion defect area. We compared the efficacy and safety of EC-IC bypass surgery with those of EVT and maximal medical treatment for acute ischemic stroke.

METHODS

The data from 39 patients, for whom vessel revascularization had failed despite mechanical thrombectomy, were retrospectively analyzed. Of the 39 patients, 22 had undergone percutaneous transluminal angioplasty or intracranial stenting (PTA/S), 10 had undergone emergency EC-IC bypass surgery within 24 hours of symptom onset, and 7 had received maximal medical treatment (MMT) only. The patency, perfusion status, and postoperative infarct volume were evaluated. The clinical outcomes were assessed at 6 months postoperatively using the modified Rankin scale.

RESULTS

The mean reperfusion time was significantly longer for the EC-IC bypass group (14.9 hours) compared with that in the PTA/S group (4.1 hours) and MMT group (7.5 hours; P < 0.05). The postoperative infarct volume on diffusion-weighted magnetic resonance imaging was significantly lower in the emergency EC-IC bypass group (11.3 cm³) than in the MMT group (68.0 cm³) but was not significantly different from that of the PTA/S group (14.0 cm³; P < 0.05). The proportion of patients with a modified Rankin scale score of 0-2 at 6 months after surgery was significantly higher in the EC-IC bypass group (80%) than in the PTA/S (59%) and MMT (14%) groups (P < 0.05).

CONCLUSIONS

Emergency EC-IC bypass surgery is an effective and safe treatment option for intracranial atherosclerosis-induced acute ischemic stroke for which EVT is inadequate.

Hemodynamics in acute stroke: Cerebral and cardiac complications

Hemodynamics is the study of blood flow, where parameters have been defined to quantify blood flow and the relationship with systemic circulatory changes. Understanding these perfusion parameters, the relationship between different blood flow variables and the implications for ischemic injury are outlined in the ensuing discussion. This chapter focuses on the hemodynamic changes that occur in ischemic stroke, and their contribution to ischemic stroke pathophysiology. We discuss the interaction between cardiovascular response and hemodynamic changes in stroke. Studying hemodynamic changes has a key role in stroke prevention, therapeutic implications and prognostic importance in acute ischemic stroke: preexisting hemodynamic and autoregulatory impairments predict the occurrence of stroke. Hemodynamic failure predisposes to the formation of thromboemboli and accelerates infarction due to impairing compensatory mechanisms. In ischemic stroke involving occlusion of a large vessel, persistent collateral circulation leads to preservation of ischemic penumbra and therefore justifying endovascular thrombectomy. Following thrombectomy, impaired autoregulation may lead to reperfusion injury and hemorrhage.

Bilateral Cerebral Hyperperfusion Syndrome Following Carotid Artery Stenting in Stroke - A Case Report

BACKGROUND

Revascularization of the symptomatic carotid artery is performed with endarterectomy or stenting. Rarely, patients may develop cerebral hyperperfusion syndrome (CHS) following revascularization. This usually occurs in the cerebral hemisphere ipsilateral to revascularized carotid stenosis. CHS rarely involves the contralateral hemisphere.

OBJECTIVE

To present a case of CHS involving bilateral cerebral hemispheres following carotid artery stenting in acute ischemic stroke.

CASE DESCRIPTION

A 66-year-old woman presented with right side weakness and aphasia. National Institutes of Health stroke scale score was 27. CT angiogram/perfusion showed high grade left internal carotid artery (ICA) stenosis, left middle cerebral artery (MCA) occlusion, and increased time to peak in left MCA territory. She underwent mechanical thrombectomy with complete reperfusion. Left carotid artery stenting was performed for 85% cervical ICA stenosis with thrombus. She neurologically deteriorated and required intubation after the procedure. Follow-up CT perfusion at 18 hours after thrombectomy showed increased cerebral blood flow and early time to peak in bilateral MCA territories. CT head showed parenchymal hematoma in the left subcortical area with extension to the ventricle. Fluid-attenuated inversion recovery MRI on day 4 showed diffuse white matter hyperintensities in the entire right hemisphere, and left temporal and frontal lobes suggestive of vasogenic edema.

CONCLUSION

This case highlights bilateral cerebral hyperperfusion syndrome characterized by neurological worsening, imaging findings of parenchymal hemorrhage, vasogenic edema and increased cerebral blood flow without any new ischemic lesions. The involvement of bilateral hemispheres in the absence of significant contralateral carotid stenosis is unique in this case.

Cerebrovacular Reserve Predicts the Cerebral Hyperperfusion Syndrome After Carotid Endarterectomy

BACKGROUND

Cerebral hyperperfusion syndrome is a rare but potentially severe complication of carotid artery revascularisation that develops under conditions of resistant postoperative hypertension and impaired cerebrovascular autoregulation.

OBJECTIVE

Was to determine which preoperative and operative factors affect the development of cerebral hyperperfusion syndrome after carotid endarterectomy.

METHODS

This prospective observational study enrolled 93 asymptomatic patients who underwent carotid endarterectomy. Cerebral hyperperfusion was registered in patients who had 100% postoperative increase in mean flow in middle cerebral artery registered by Transcranial Doppler ultrasound. Cerebral hyperperfusion syndrome was diagnosed in patients with cerebral hyperperfusion who postoperatively developed at least one of the symptoms. Pre-operative and operative risk factors for cerebral hyperperfusion syndrome were analysed by multivariate binary logistic regression.

RESULTS

Out of 93 operated patients, cerebral hyperperfusion was registered in 23 and cerebral hyperperfusion syndrome in 18 patients. Risk factors for cerebral hyperperfusion syndrome were included in the binary logistic regression model. Incomplete Circle of Willis morphology on 3D TOF magnetic resonance image (p = 0.002), Breath holding index below the 0.69 cut-off (p = 0.006), positive criteria for insufficient collateral flow through circle of Willis registered by TCD (p = 0.03), and poorly controlled hypertension (p = 0.023) showed statistically significant independent predictive value for cerebral hyperperfusion syndrome. The model was statistically significant (p = 0.012) and correctly classified 90.3 % of patients.

CONCLUSIONS

Incomplete circle of Willis and insufficient collateral flow, low cerebrovascular reserve, and poorly regulated hypertension are significant predictors of post- carotid endarterectomy hyperperfusion development.

Cerebral Autoregulation in Stroke

PURPOSE OF REVIEW

Cerebral autoregulation (CA) is a mechanism that maintains cerebral blood flow constant despite fluctuations in systemic arterial blood pressure. This review will focus on recent studies that measured CA non-invasively in acute cerebrovascular events, a feature unique to the transcranial Doppler ultrasound. We will summarize the rationale for CA assessment in acute cerebrovascular disorders and specifically evaluate the existing data on the value of CA measures in relation to clinical severity, guiding management decisions, and prognostication.

RECENT FINDINGS

Existing data suggest that CA is generally impaired in various cerebrovascular disorders. In patients with small vessel ischemic stroke, CA has been shown to be impaired in both hemispheres, whereas in large territorial strokes, CA impairment has been limited to the affected hemisphere. In these latter patients, impaired CA is also predictive of secondary complications such as hemorrhagic transformation and cerebral edema, hence worse functional outcome. In patients with carotid stenosis, impaired CA may also be associated with a higher ipsilateral hemispheric stroke risk. CA is also strongly linked to outcome in patients with intracranial hemorrhage. In patients with intraparenchymal hemorrhage, CA impairment correlated with clinical and imaging severity, whereas in those with subarachnoid hemorrhage, CA measures have a predictive value for development of delayed cerebral ischemia and radiographic vasospasm. Assessment of CA is increasingly more accessible in acute cerebrovascular disorders and promises to be a valuable measure in guiding hemodynamic management and predicting secondary complication, thus enhancing the care of these patients in the acute setting.

Multiple blood flow measurements before and after carotid artery stenting via phase-contrast magnetic resonance imaging: An observational study

After carotid artery stenting, the procurement of information about blood flow redistribution among brain-feeding arteries and its time trend is essential to understanding a patient’s physiological background and to determine their care regimen. Cerebral blood flow has been measured twice following carotid artery stenting in few previous studies, with some discrepancies in the results. The purpose of this study was to measure cerebral blood flow at multiple time points after carotid artery stenting, and to elucidate the time trend of cerebral blood flow and redistribution among arteries. Blood flow rates in 11 subjects were measured preoperatively, at one day, one week, and about three months, respectively after carotid artery stenting by using phase-contrast magnetic resonance imaging. The target vessels were the bilateral internal carotid arteries, the basilar artery, and the bilateral middle cerebral arteries. Lumen was semi-automatically defined using an algorithm utilizing pulsatility. The results showed that blood flow rates in the stented internal carotid artery and the ipsilateral middle cerebral artery increased following carotid artery stenting. Blood flow rates in the contralateral internal carotid artery and the basilar artery gradually declined, and they were lower than the preoperative values at three months after stenting. The sum of blood flow rates of the bilateral internal carotid arteries and the basilar artery increased after carotid artery stenting, and then decreased over the next three months. There was no significant change in the blood flow rate in the contralateral middle cerebral artery. From these results, it was concluded that redistribution among the bilateral internal carotid arteries and the basilar artery occurs after carotid artery stenting, and that it takes months thereafter to reach another equilibrium.

Comparing Different Recording Lengths of Dynamic Cerebral Autoregulation: 5 versus 10 Minutes

We compared the dynamic cerebral autoregulation (dCA) indices between 5- and 10-minute data lengths by analyzing 37 patients with ischemic stroke and 51 controls in this study. Correlation coefficient (Mx) and transfer function analysis were applied for dCA analysis. Mx and phase shift in all frequency bands were not significantly different between 5- and 10-minute recordings [mean difference: Mx = 0.02; phase shift of very low frequency (0.02–0.07 Hz) = 0.3°, low frequency (0.07–0.20 Hz) = 0.6°, and high frequency (0.20–0.50 Hz) = 0.1°]. However, the gains in all frequency bands of a 5-minute recording were slightly but significantly higher than those of a 10-minute recording (mean difference of gain: very low frequency = 0.05 cm/s/mmHg, low frequency = 0.11 cm/s/mmHg, and high frequency = 0.14 cm/s/mmHg). The intraclass correlation coefficients between all dCA indices of 5- and 10-minute recordings were favorable, especially in Mx (0.93), phase shift in very low frequency (0.87), and gain in very low frequency (0.94). The areas under the receiver operating characteristic curve for stroke diagnosis between 5- and 10-minute recordings were not different. We concluded that dCA assessed by using a 5-minute recording is not significantly different from that using a 10-minute recording in the clinical application.

Predictive Value of Dynamic Cerebral Autoregulation Assessment in Surgical Management of Patients with High-Grade Carotid Artery Stenosis

Dynamic cerebral autoregulation (DCA) capacity along with the degree of internal carotid artery (ICA) stenosis and characteristics of the plaque can also play an important role in selection of appropriate treatment strategy. This study aims to classify the patients with severe ICA stenosis according to preoperative state of DCA and to assess its dynamics after surgery. Thirty-five patients with severe ICA stenosis having different clinical type of disease underwent reconstructive surgery. DCA was assessed with transfer function analysis (TFA) by calculating phase shift (PS) between Mayer waves of blood flow velocity (BFV) and blood pressure (BP) before and after operation. In 18 cases, regardless of clinical type, preoperative PS on ipsilateral side was within the normal range and did not change considerably after surgery. In other 17 cases preoperative PS was reliably lower both in patients with symptomatic and asymptomatic stenosis. Surgical reconstruction led to restoration of impaired DCA evidenced by significant increase of PS in postoperative period. Our data suggest that regardless clinical type of disease various state of DCA may be present in patients with severe ICA stenosis. This finding can contribute to establishing the optimal treatment strategy, and first of all for asymptomatic patients. Patients with compromised DCA should be considered as ones with higher risk of stroke and first candidates for reconstructive surgery.

[Severe carotid stenosis: cerebral autoregulation in the ipsilateral region]

AIM

To study cerebral autoregulation (CA) in region of the stenotic carotid artery.

MATERIAL AND METHODS

The study involved 35 patients with critical stenosis of the carotid arteries, including 24 patients were asymptomatic and 11 patients with symptomatic course. Blood flow velocity in middle cerebral arteries was monitored using Multi Dop X (DWL, Germany) with simultaneous noninvasive systemic blood pressure registration (CNAP, Austria). CA was assessed by calculating the phase shift (PS) between spontaneous oscillations of blood flow velocity and blood pressure within the range of systemic Mayer waves (80-120 mHz).

RESULTS

In 18 patients, the CA indicators were in the normal range (PS 1.2±0.3 rad). Seventeen patients, including asymptomatic as well as symptomatic types, had impaired CA (PS 0.2±0.2 rad and 0.3±0.2 rad, respectively). Reconstructive surgery, irrespective of clinical manifestations, led to the significant increase in PS (p<0.001) in the early postoperative period (0.9±0.5 and 0.9±0.3 rad, respectively).

CONCLUSION

A significant variability in the cerebrovascular reserve capacity in symptomatic and asymptomatic types of carotid artery stenosis was found. CA can be used in determining the indications for surgical treatment and evaluation of its effectiveness in patients with stenosis of carotid arteries.

Shear-mediated dilation of the internal carotid artery occurs independent of hypercapnia

Evidence for shear stress as a regulator of carotid artery dilation in response to increased arterial CO2 was recently demonstrated in humans during sustained elevations in CO2 (hypercapnia); however, the relative contributions of CO2 and shear stress to this response remains unclear. We examined the hypothesis that, after a 30-s transient increase in arterial CO2 tension and consequent increase in internal carotid artery shear stress, internal carotid artery diameter would increase, indicating shear-mediated dilation, in the absence of concurrent hypercapnia. In 27 healthy participants, partial pressures of end-tidal O2 and CO2, ventilation (pneumotachography), blood pressure (finger photoplethysmography), heart rate (electrocardiogram), internal carotid artery flow, diameter, and shear stress (high-resolution duplex ultrasound), and middle cerebral artery blood velocity (transcranial Doppler) were measured during 4-min steady-state and transient 30-s hypercapnic tests (both +9 mmHg CO2). Internal carotid artery dilation was lower in the transient compared with steady-state hypercapnia (3.3 ± 1.9 vs. 5.3 ± 2.9%, respectively, P < 0.03). Increases in internal carotid artery shear stress preceded increases in diameter in both transient (time: 16.8 ± 13.2 vs. 59.4 ± 60.3 s, P < 0.01) and steady-state (time: 18.2 ± 14.2 vs. 110.3 ± 79.6 s, P < 0.01) tests. Internal carotid artery dilation was positively correlated with shear rate area under the curve in the transient ( r2 = 0.44, P < 0.01) but not steady-state ( r2 = 0.02, P = 0.53) trial. Collectively, these results suggest that hypercapnia induces shear-mediated dilation of the internal carotid artery in humans. This study further promotes the application and development of hypercapnia as a clinical strategy for the assessment of cerebrovascular vasodilatory function and health in humans.

NEW & NOTEWORTHY Shear stress dilates the internal carotid artery in humans. This vasodilatory response occurs independent of other physiological factors, as demonstrated by our transient CO2 test, and is strongly correlated to shear area under the curve. Assessing carotid shear-mediated dilation may provide a future avenue for assessing cerebrovascular health and the risk of cerebrovascular events.

Brain perfusion evaluated by perfusion-weighted magnetic resonance imaging before and after stenting internal carotid artery stenosis in asymptomatic and symptomatic patients

PURPOSE

To evaluate the brain perfusion with MRI perfusion weighted imaging (PWI) before and after ICA stenting in asymptomatic and symptomatic patients.

MATERIALS AND METHODS

PWI was performed 3-21 days before and 3 days after ICA stenting in 31 asymptomatic patients with ICA >70% stenosis - Group I, and in 14 symptomatic patients with ICA >50% stenosis - Group II. PWI was evaluated qualitatively and quantitatively in 5 cerebral territories with: mean transit time (MTT), cerebral blood volume (CBV) and cerebral blood flow (CBF). Mean values of perfusion parameters were measured before and after stenting ΔMTT, ΔCBV, ΔCBF were calculated as subtraction of after-treatment values from those before treatment.

RESULTS

In qualitative evaluation after ICA stenting perfusion was normalized in 21 patients (80.8%) in Group I and in 8 patients (80%) in Group II. In quantitative estimation MTT decreased significantly after CAS on stented side vs. non-stented side in all examined patients regardless of the group, p<0.05. MTT decreased more in Group II than in Group I in all territories (p<0.05) with the exception of temporal lobe. CBV and CBF have shown insignificant differences.

Assessment of dynamic cerebral autoregulation in patients with basilar artery stenosis

Background and Aims

Previous studies have shown impaired cerebral autoregulation (CA) in carotid and middle cerebral artery (MCA) stenosis/occlusion. Little is known about CA in patients with basilar artery (BA) stenosis. We therefore investigated dynamic CA patterns in BA stenosis using transfer function analysis (TFA).

Methods

We measured spontaneous oscillations of blood flow velocity (CBFV) in the right posterior cerebral artery (PCA), and left MCA and mean arterial pressure (ABP) continuously in 25 patients with BA stenosis (moderate n=16 with 50-69% occlusion and severe n=9 with ≥70% occlusion) and 22 healthy volunteers in supine position during 6 circles per minute deep breath. Analysis was based on the ‘black-box’ model of transfer function deriving phase and gain in both PCA and MCA.

Results

Though changes of phase shift and gain between the patients and healthy controls were observed in MCA, the differences are however not significant. Phase shift in PCA was significantly decreased in severe stenosis when comparing with healthy controls and moderate stenosis (4.2±34.2° VS 41.1±40.4°, 4.2±34.2° VS 34.2±27.2°, both p<0.05), whilst the gain in PCA is increased for moderate BA stenosis and decreased for severe BA stenosis. Furthermore, we found that phase shift were almost abolished in patients with ischemic stroke who developed unfavorable clinical outcome (mRs>2) on the 90 days after stroke onset.

Conclusion

Dynamic CA in PCA reduces in patients with severe BA stenosis and those with ischemic stroke who present poor outcome in 90 days after stroke onset. Phase shift might be a sensitive index prompting impaired CA in posterior circulation.

Nonlinear and conventional biosignal analyses applied to tilt table test for evaluating autonomic nervous system and autoregulation

Tilt table test (TTT) is a standard examination for patients with suspected autonomic nervous system (ANS) dysfunction or uncertain causes of syncope. Currently, the analytical method based on blood pressure (BP) or heart rate (HR) changes during the TTT is linear but normal physiological modulations of BP and HR are thought to be predominately nonlinear. Therefore, this study consists of two parts: the first part is analyzing the HR during TTT which is compared to three methods to distinguish normal controls and subjects with ANS dysfunction. The first method is power spectrum density (PSD), while the second method is detrended fluctuation analysis (DFA), and the third method is multiscale entropy (MSE) to calculate the complexity of system. The second part of the study is to analyze BP and cerebral blood flow velocity (CBFV) changes during TTT. Two measures were used to compare the results, namely correlation coefficient analysis (nMxa) and MSE. The first part of this study has concluded that the ratio of the low frequency power to total power of PSD, and MSE methods are better than DFA to distinguish the difference between normal controls and patients groups. While in the second part, the nMxa of the three stages moving average window is better than the nMxa with all three stages together. Furthermore the analysis of BP data using MSE is better than CBFV data.

Cerebral hemodynamic benefits after contralateral carotid artery stenting in patients with internal carotid artery occlusion

CEA contralateral to an ICA occlusion is considered a surgical risk, and CAS may be an alternative for these patients. Our goal was to examine whether CAS improves cerebral hemodynamics on the treated side and on the side of the ICA occlusion, on the basis of measurement of CBF and CVR by using SPECT. The subjects were 8 patients who underwent contralateral CAS. Resting CBF and CVR to acetazolamide were measured by using (123)I-IMP SPECT before and chronically (3-6 months) after CAS. Resting CBF was also measured immediately (<2 hours) after CAS by using (123)I-IMP SPECT. There were no significant differences in resting CBF in both hemispheres immediately after CAS. However, resting CBF and CVR both significantly increased in the chronic period in both hemispheres. Contralateral CAS in patients with ICA occlusion resulted in cerebral hemodynamic improvement on the treated side and on the side of ICA occlusion.

Acute increase of complexity in the neurocardiovascular dynamics following carotid stenting

OBJECTIVE

Percutaneous carotid angioplasty and stenting (CAS) has been used to improve cerebral circulation and autoregulation. However, whether CAS ameliorates the autonomic regulatory dynamics remains unclear. This prospective study examines the neurocardiovascular dynamics following carotid stenting.

METHODS

Thirty minutes electrocardiograms were recorded at three different time points (pre-operative, 1-h post-operative, 1-day post-operative) on twelve male patients (mean age 70.8 ± 9.6 years) receiving unilateral primary CAS. The HR data were analyzed by the conventional heart rate variability (HRV) and the multiscale entropy (MSE) methods; the former associates with autonomic activities and the latter quantifies the regulatory complexity of heart beat intervals. Loss of complexity at multiple scales has been associated with decoupled regulatory network in vivo.

RESULTS

Conventional HRV indices showed no difference after CAS. Complexity indices increased significantly on scales 2-8 at 1-h and on scales 2-3 1-day post-treatment. The lower scale MSE (1-5) correlated with the frequency components of conventional HRV indices. The increased complexity could imply a restoration of the neurocardiovascular dynamics on the path to a healthier state.

CONCLUSIONS

Primary CAS can induce a recovery in the neurocardiovascular regulatory dynamics in patients with high-grade carotid stenosis.

Hyperperfusion syndrome after carotid revascularization

Cerebral hyperperfusion syndrome is a rare, serious complication of carotid revascularization either after carotid endarterectomy or carotid stent placement. Impaired cerebral autoregulation and post-revascularization changes in cerebral hemodynamics are the main mechanisms involved in the development of the syndrome. Hyperperfusion syndrome may be fatal once an intracranial hemorrhage occurs. This article reviews the literature, intending to make a synthesis of all new data concerning the clinical manifestations of hyperperfusion syndrome, the pathophysiologic pathways involved in its development, the prediction, and the appropriate management. Also, a review of the most recent series of hyperperfusion syndrome following carotid revascularization, both with classic open endarterectomy and carotid artery stenting has been performed.