Prevalence of impaired cerebrovascular reserve in patients with symptomatic carotid artery disease

Evaluation of cerebrovascular reserve capacity in symptomatic and asymptomatic internal carotid stenosis with transcranial Doppler

Cerebrovascular reserve capacity (CVRC) is a hemodynamic parameter indicating the brain's capacity to overcome ischemia. Transcranial Doppler (TCD) is a useful device to measure CVRC, with high availability and low cost. The aim of the study is to investigate asymptomatic patients with affected CVRC, who could benefit from CEA. One hundred and forty five consecutive patients (60 symptomatic and 65 asymptomatic), with internal carotid artery (ICA) stenosis >70 % and 20 healthy individuals without internal carotid stenosis underwent TCD-inhalation CO(2) tests in order to measure the CVRC in both hemispheres of each patient. CVRC between asymptomatic and symptomatic patients were significantly different in the 95 % confidence interval (CI) as well as the mean CVRC value in contralateral carotid artery. The correlation between CVRC in the carotid artery with stenosis and the existence of symptoms is significant at the 0.01 level. Additionally, symptoms and CVRC of the contralateral carotid artery are also significant at the 0.05 level and CVRC values in asymptomatic patients and the control group at the 0.01 level. None of the covariant factors, except the age, are significantly correlated with CRVC. CVRC could be an early mark-index to evaluate the risk of stroke in this group of patients and to design their therapeutic approach.

M-wave analysis and passive tilt in patients with different degrees of carotid artery disease

BACKGROUND AND PURPOSE

Carotid artery disease (CAD) is able to critically impair cerebral autoregulation which increases the risk for stroke. As therapeutic strategy largely depends on the degree of CAD, we investigated whether this gradation is also related to significant changes in autoregulatory capacity. We applied cross-spectral analysis (CSA) of spontaneous Mayer-wave (M-wave) oscillations and passive tilting (PT) to test cerebral autoregulation.

METHODS

Cerebral autoregulation was tested in 102 patients with carotid stenosis (> or =70%) or occlusion and 14 controls by comparison of continuous transcranial Doppler sonography of the middle cerebral artery and beat-to-beat arterial blood pressure (ABP) during PT to 80 degrees head-up position as well as by CSA of M-waves (3-9 cpm).

RESULTS

The orthostatic decrease of cerebral blood flow velocity (CBFV) was not correlated with the degree of CAD and showed a lower sensitivity and specificity than phase angle shifts between M-waves in ABP and CBFV (sensitivity: 75-80%, specificity: 86%). Phase angles were gradually lowered in carotid stenoses > 70%, but apparently, they were only moderately correlated with the degree of CAD (r = -0.35, P < 0.01). An additional influencing factor seemed to be the sufficiency of collateralization.

CONCLUSIONS

The results show that CSA of M-waves is more appropriate for testing autoregulation than PT. CSA suggests that the capacity to autoregulate depends to a certain extent on the degree of CAD but is also influenced by the sufficiency of collateral pathways and pre-existing strokes.

Carotid endarterectomy improves cognitive function in patients with exhausted cerebrovascular reserve

OBJECTIVE

To investigate changes in cognitive function following carotid endarterectomy (CEA).

DESIGN

Prospective study with controls.

METHODS

CEA patients (n=159) were compared to a urology surgery control group (n=20). In CEA patients cerebrovascular reserve (CVR) was measured preoperatively. During surgery emboli and blood flow velocity in the middle cerebral artery were measured by transcranial Doppler (TCD) and cerebral oxygen saturation (CsO2) by near infrared spectroscopy. Cognitive function was measured preoperatively and at 5 days and 8 weeks postoperatively using a standardised computer battery of tests.

RESULTS

Only 8% of patients had normal CVR bilaterally. The median number of emboli during CEA was 12 (range 0-181). On carotid clamping, TCD velocity fell a median of 41% and cerebral oxygen saturation by 5%. Attention deteriorated compared to controls 5 days following CEA (p=0.003) and this deterioration was related to the rise in TCD velocity on declamping (r=-0.3, p=0.002). Median attention reaction times improved significantly by 8 weeks (p=0.001) especially in patients' with severely impaired CVR before surgery (p=0.02).

CONCLUSIONS

Attention improved at 2 months following CEA in patients with impaired CVR. CEA may offer more than reduced stroke risk to patients with impaired CVR.

Stroke: epidemiology, clinical picture, and risk factors--Part I of III

The aim of this review is to present the current knowledge regarding stroke. It will appear in three parts (in part II the pathogenesis, investigations, and prognosis will be presented, while part III will consist of the management and rehabilitation). In the current part (I) the definitions of the clinical picture are presented. These include: amaurosis fugax, vertebrobasilar transient ischemic attack, and stroke (with good recovery, in evolution and complete). The role of the following risk factors is discussed in detail: age, gender, ethnicity, heredity, hypertension, cigarette smoking, hyperlipidemia, diabetes mellitus, obesity, fibrinogen and clotting factors, oral contraceptives, erythrocytosis and hematocrit level, prior cerebrovascular and other diseases, physical inactivity, diet and alcohol consumption, illicit drug use, and genetic predisposition. In particular, regarding the carotid arteries, the following characteristics are analyzed: atheroma, carotid plaque echomorphology, carotid stenosis, presence of ulcer, local variations in surface deformability, pathological characteristics, and dissection. Finally the significance of the cerebral collateral circulation and the conditions predisposing to cardioembolism and to cerebral hemorrhage are presented.

Patterns of cerebrovascular symptomatology associated with carotid atheroma

The aim of this study was to identify ultrasonic tissue characteristics and stenosis of carotid plaques that correspond to amaurosis fugax, hemispheric transient ischaemic attack, and stroke. At total of 146 symptomatic carotid plaques (136 patients) associated with amaurosis fugax, hemispheric transient ischaemic attack, stroke, and having 50-99% stenosis on duplex, were studied. These plaques were imaged on duplex, captured in a computer and their grey scale median was evaluated to distinguish the dark (low grey scale median) from the bright (high grey scale median) plaques. Stenosis was assessed on duplex. The amaurosis fugax group corresponded to carotid plaques with low grey scale median and severe stenosis, as contrasted with the other two groups (hemispheric transient ischaemic attack and stroke) (P < 0.05). These results suggested that amaurosis fugax was dependent only on the instability of carotid plaques, whereas hemispheric transient ischaemic attack and stroke were both dependent on carotid plaques and other pathogenetic factors.

Estimating normal and pathological dynamic responses in cerebral blood flow velocity to step changes in end-tidal pCO2

The regulation of cerebral blood flow (CBF) following changes in arterial blood pressure (ABP) and end-tidal pCO2 (EtCO2) are of clinical interest in assessing cerebrovascular reserve capacity. Linear finite-impulse-response modelling is applied to ABP, EtCO2 and CBF velocity (CBFV, from transcranial Doppler measurements), which allows the CBFV response to ideal step changes in EtCO2 to be estimated from clinical data showing more sluggish, and additional random variations. The confounding effects of ABP changes provoked by hypercapnia on the CBFV are also corrected for. Data from 56 patients suffering from stenosis of the carotid arteries (with normal or diminished cerebrovascular reactivity to EtCO2 changes--CVRCO2) were analysed. The results show the expected significant differences (p < 0.05) between EtCO2 steps up and down, the significant contribution from ABP variation, and also differences in the dynamic responses of patients with reduced CVRCO2 (p < 0.01 after 10 s). For the latter the CBFV response appears exhausted after about 15 s, whereas for normals CBFV continues to increase. While dispersion of individual step responses remains large, the method gives encouraging results for the non-invasive study of compromised haemodynamics in different patient groups.

Decreased transcranial Doppler carbon dioxide reactivity is associated with disordered cerebral metabolism in patients with internal carotid artery stenosis

PURPOSE

The hemodynamic effect of stenosis of the internal carotid artery (ICA) can be assessed by measuring, with transcranial Doppler (TCD), the carbon dioxide (CO(2)) reactivity of the cerebral vessels. The aim of this study was to determine whether a decreased CO(2) reactivity is associated with a compromised cerebral metabolism, as evaluated with (1)H magnetic resonance spectroscopy (MRS).

METHODS

Sixty-six patients with unilateral or bilateral stenosis of the ICA, who were scheduled for carotid endarterectomy (CEA) and who had undergone both a TCD CO(2) reactivity test and a MRS examination, were included in this study. The ICA stenosis on one side (CEA side) was always more than 70%, and the extent of the stenosis on the contralateral side varied.

RESULTS

The CO(2) reactivity and the N-acetyl aspartate (NAA)/choline ratio were correlated in both hemispheres (r =.43; P <.001). Patients with an ICA occlusion contralateral to the CEA side are especially at risk for disordered cerebral hemodynamics and metabolism; in the contralateral hemisphere, the mean CO(2) reactivity and NAA/choline ratio were abnormal (18% and 1.52, respectively), and lactate was present in 85% of the patients. Changes indicative of disordered hemodynamics were found more often in symptomatic than in asymptomatic patients.

CONCLUSION

A decreased CO(2) reactivity appears to be associated with a disordered cerebral metabolism. Patients with severe bilateral ICA stenosis are at risk for disordered cerebral metabolism and hemodynamics. Therefore, the indication for CEA based on the degree of ICA stenosis and clinical grounds might be refined with an additional test, such as the TCD CO(2) reactivity test.

Can cerebrovascular reactivity be assessed without measuring blood pressure in patients with carotid artery disease?

BACKGROUND AND PURPOSE

Conventional methods of assessing cerebrovascular reactivity (CVR) omit the influence of blood pressure (BP). This study demonstrates the significant influence of BP during the assessment of CVR in patients with carotid artery disease.

METHODS

In 56 subjects the CVR was bilaterally assessed by measurement of cerebral blood flow velocity change in response to inhalation of 5% CO2 in air while BP was continuously monitored. Three methods of calculating the CVR were used: the conventional ratio between relative cerebral blood flow velocity and end-tidal CO2, simple linear regression, and multiple linear regression analysis (MLRA). The clinical significance of the difference in CVR indices was evaluated. The Bland-Altman test was applied to quantify the comparability and bias between measurements. The magnitude and significance of a change in BP during the CVR assessment were calculated in conjunction with an estimate of the velocity change attributed to the BP. The statistical significance of the data segment length on the variability and magnitude of the CVR index was computed.

RESULTS

The value of the CVR index was reduced by 20% and 6% in comparison to the conventional ratio approach when MLRA and linear regression were applied, respectively. With the use of MLRA, in 96% of cases the value of the BP coefficient was statistically significant, and in four patients the increase in velocity was primarily attributed to the increase in BP.

CONCLUSIONS

The influence of BP is significant and requires consideration when the CVR index is calculated in patients with carotid artery disease.

Symptoms, stenosis and carotid plaque morphology. Is plaque morphology relevant?

OBJECTIVES

To study the relationship between carotid plaque morphology and the degree of stenosis on Duplex ultrasonography and symptoms.

DESIGN

Prospective open clinical study.

METHODS

2,590 patients with 5,180 carotid arteries were scanned, 4,560 were initially analysed in terms of symptoms but 54 were excluded, leaving a total of 4,258.

RESULTS

Localising symptoms were present with respect to 1,342 vessels (29.4%). Two-thirds of symptomatic patients had normal carotid arteries. Tight stenosis (80-99%) was more likely to be associated with symptoms than low-grade (20-79%) stenosis (chi 2 = 28.0, p < 0.0001). Plaque type was identified in 1,558 bifurcations (36.6%). Heterogeneous type I & II plaques accounted for one third of plaques. There was a relationship between plaque morphology and degree of stenosis. At < 20% stenosis only 4.4% of plaques were heterogeneous whereas at 80-99% stenosis 84.5% of plaques were heterogeneous. Amaurosis fugax was the only symptom that had any association with a particular plaque morphology. Seventy-two percent of plaques associated with this symptom were heterogeneous in nature.

CONCLUSIONS

Carotid plaque morphology and degree of internal carotid stenosis are mutually dependent factors and both reflect the severity of atherosclerotic disease. Plaque morphology does not add to the sensitivity of stenosis in predicting the presence of symptoms.