Anatomic and Hemodynamic Correlations in Carotid Artery Stenosis
TL;DR: Angiograms in general mimicked the gross appearance of the plaques and predicted the actual degree of stenosis produced but did not identify many diaphragm defects, ulcerations, or small thrombi.
Abstract: Pressures were measured in the carotid arteries of 61 patients proximal and distal to atherosclerotic plaques which were carefully studied by angiography and anatomical dissection.
(1) An atherosclerotic plaque causing a constriction of less than 47% luminal diameter leaving a lumen greater than 3.0 mm in diameter never caused pressure drops of greater than 10 mm Hg. Stenoses of greater than 63% luminal diameter leaving lumens less than 1.0 mm in diameter always caused pressure drops.
(2) Atherosclerotic plaques producing defects which narrowed the lumen fell into a distinct pattern:
(a) Type 1 lesions—This basic lesion filled the bulb of the internal carotid artery near its origin, causing a 1 to 2 cm smooth elliptical encroachment on the lumen.
(b) Type 2 lesions—Short localized areas of thickening in addition to the basic lesion caused bar-like defects of the lumen at the origin of the internal carotid artery or near the distal end of the lesion.
(c) Type 3 lesions—Multiple bar-like defects were sometimes seen.
(d) Type 4 lesions—The areas of increased thickening of the lesion were sometimes quite narrow, producing diaphragm-like defects on the lumen.
Although theoretically these various types of stenoses should produce different hemodynamic changes, insufficient numbers of observations were made to corroborate these presumptions.
(3) Angiograms in general mimicked the gross appearance of the plaques and predicted the actual degree of stenosis produced but did not identify many diaphragm defects, ulcerations, or small thrombi.
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TL;DR: Investigation into the importance of hemodynamic factors in ischemic stroke can now be based on accurate assessment of cerebral (not carotid or vertebrobasilar) hemodynamics in the context of other coexisting epidemiological, clinical, hematological, and angiographic risk factors.
Abstract: During the past decade, technological advances have made it possible to measure regional cerebral hemodynamics in individual patients. Studies performed with these techniques have demonstrated that the degree of carotid stenosis correlates poorly with the hemodynamic status of the ipsilateral cerebral circulation. The primary determinant of cerebral perfusion pressure and blood flow under these circumstances is the adequacy of collateral circulatory pathways. Since collateral circulation varies from patient to patient, there is no critical degree of carotid stenosis that consistently produces hemodynamic compromise of the cerebral circulation. It is, thus, time to abandon the concept of the hemodynamically significant carotid stenosis as it relates to the pathogenesis and treatment of cerebrovascular disease. Measurement of regional cerebral hemodynamics have provided new insight into the pathogenesis of tranisent ischemic attacks and generated some preliminary data on the prognostic and therapeutic importance of chronic reductions in regional cerebral perfusion pressure. Further investigations into the importance of hemodynamic factors in ischemic stroke can now be based on accurate assessment of cerebral (not carotid or vertebrobasilar) hemodynamics in the context of other coexisting epidemiological, clinical, hematological, and angiographic risk factors.
782 citations
TL;DR: A significant relationship was found between the PET measurements of cerebral hemodynamics and the arteriographic circulation pattern and the role of hemodynamic factors in the pathogenesis and treatment of cerebrovascular disease cannot be determined from the severity of carotid artery disease alone.
Abstract: Although the presence of a hemodynamically significant carotid artery lesion is commonly used as an indicator of impaired cerebral circulation, the effect of such lesions on cerebral perfusion pressure and cerebral blood flow has never been determined accurately. We used positron emission tomography (PET) to study 19 patients with unilateral hemodynamically significant carotid artery disease (greater than 66% diameter reduction) and no evidence of cerebral infarction. According to PET measurements in the cerebral hemisphere distal to the lesion, 7 patients had normal cerebral hemodynamics, 8 had reduced perfusion pressure with normal blood flow, and 4 had reduced blood flow. Neither the percent stenosis nor the residual lumen diameter in the carotid artery was a reliable indicator of the hemodynamic status of the cerebral circulation. However, a significant relationship was found between the PET measurements of cerebral hemodynamics and the arteriographic circulation pattern (p = 0.006). The role of hemodynamic factors in the pathogenesis and treatment of cerebrovascular disease cannot be determined from the severity of carotid artery disease alone.
453 citations
TL;DR: There is currently no role for the routine use of neuroimaging tools for the indirect assessment of the hemodynamic effect of atherosclerotic stenosis or occlusion on the distal cerebrovasculature in patients with cerebrovascular disease.
Abstract: Stenosis or occlusion of the major arteries of the head and neck may cause hemodynamic impairment of the distal cerebral circulation. Hemodynamic factors may play an important role in the pathogenesis of ischemic stroke for patients with cerebrovascular disease. Several neuroimaging methods are currently available for the indirect assessment of the hemodynamic effect of atherosclerotic stenosis or occlusion on the distal cerebrovasculature. Because these methods rely on different underlying physiologic mechanisms, they are not interchangeable. Two basic categories of hemodynamic impairment can be assessed with these techniques: Stage 1, in which autoregulatory vasodilation secondary to reduced perfusion pressure is inferred by the measurement of either increased blood volume or an impaired blood flow response to a vasodilatory stimulus; and Stage 2, in which increased oxygen extraction fraction (OEF) is noninvasively but directly measured. The correlation of different Stage 1 methods with each other and with Stage 2 techniques is quite variable. Clinical studies associating different manifestations of hemodynamic impairment with stroke risk often suffer from methodologic problems. The best evidence to date for such an association is for increased OEF measured in patients with symptomatic carotid occlusion. In the absence of data demonstrating improvement in patient outcome, there is currently no role for the routine use of these tools to guide clinical management in patients with cerebrovascular disease.
388 citations
TL;DR: An increase in the regional vasodilatory capacity was observed postoperatively in the majority of patients, while 9 patients showed a significant redistribution of flow in favor of the non-occluded side and two patients showed even a paradoxical decrease in focal CBF preoperatively, i.e., a "steal" effect.
Abstract: Cerebral blood flow (CBF) was measured by xenon-133 inhalation tomography in 18 patients with cerebrovascular disease before and 4 months after extracranial-intracranial bypass surgery. Only patients who showed a reduced CBF in areas that were intact on the CT scan and relevant to the clinical and angiographical findings were operated. The majority of the patients had suffered a minor stroke with or without subsequent transient ischemic attacks. They were studied at least 6 weeks following the stroke. All patients had an occlusion of the relevant internal carotid artery. To identify preoperatively the patients with a compromised collateral circulation and hence reduced CBF due to reduced perfusion pressure, a cerebral vasodilatory stress test was performed using acetazolamide (Diamox). In normal subjects, Diamox has been shown to increase tomographic CBF without change of the flow distribution. In the present series 9 patients showed a significant redistribution of flow in favor of the non-occluded side ("positive" Diamox test). Two of these 9 patients showed even a paradoxical decrease in focal CBF preoperatively, i.e., a "steal" effect. These 2 patients were the only patients who improved in focal CBF after shunting. The remaining 9 patients all showed uniform flow responses ("negative" Diamox test), and none of these increased in focal CBF postoperatively. The finding of an unchanged flow map postoperatively confirmed that the low flow areas were not due to restricted flow via collateral pathways. However, an increase in the regional vasodilatory capacity was observed postoperatively in the majority of patients.
281 citations
TL;DR: Although causality cannot be inferred from these data and plausible underlying mechanisms remain undetermined, preceding febrile infection may play an important part in the development of brain infarction in young and middle aged patients.
Abstract: The role of preceding infection as a risk factor for ischaemic stroke was investigated in a case-control study of 54 consecutive patients under 50 years of age with brain infarction and 54 randomly selected controls from the community matched for sex and age. Information about previous illnesses, smoking, consumption of alcohol, and use of drugs was taken. A blood sample was analysed for standard biochemical variables and serum cholesterol, high density lipoprotein cholesterol, triglyceride, and fasting blood glucose concentrations determined. Titres of antimicrobial antibodies against various bacteria, including Staphylococcus, Streptococcus, Yersinia, and Salmonella and several viruses were determined. Febrile infection was found in patients during the month before the brain infarction significantly more often than in controls one month before their examination (19 patients v three controls; estimated relative risk 9.0 (95% confidence interval 2.2 to 80.0)). The most common preceding febrile infection was respiratory infection (80%). Infections preceding brain infarction were mostly of bacterial origin based on cultural, serological, and clinical data. In conditional logistic regression analysis for matched pairs the effect of preceding febrile infection remained significant (estimated relative risk 14.5 (95% confidence interval 1.9 to 112.3)) when tested with triglyceride concentration, hypertension, smoking, and preceding intoxication with alcohol. Although causality cannot be inferred from these data and plausible underlying mechanisms remain undetermined, preceding febrile infection may play an important part in the development of brain infarction in young and middle aged patients.
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"Anatomic and Hemodynamic Correlatio..." refers background in this paper
...Unfortunately, it was not possible to identify small thrombi or ulcerations on angiograms in the 20% of specimens demonits component parts and the hemodynamic effects of these parts were individually analyzed.(2) The hemodynamically dominant component of an arterial stenosis is its outflow tract, i....
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TL;DR: It has been found that patients with a considerable reduction in pressure, e.g., 60 per cent or greater, require a longer period for closure of the clamp and are more likely to have a neurologic complication as a result of ligation than patients with less reduction in Pressure.
Abstract: F oR the past 1~ years in our clinic, determinations of intravascular pressure have been carried out, in a nun> ber of patients undergoing gradual ligation of the common carotid ar tery for the t reatment of intraerania] ancurysms, particularly those situated on the internal carotid artery. These measurements have been made at the t ime of application of the clamp to determine the per-cent reduction in pressure in the distal carotid system following occlusion of the proximal common caroti(l artery. In general, it has been found that patients with a considerable reduction in pressure, e.g., 60 per cent or greater, require a longer period for closure of the clamp and are more likely' to have a neurologic complication as a result of ligation than patients with less reduction in pressure, t lowever, the relationship of reduction in pressure to lhe rate of neurologic complications has not always been as predicted. For inslanee, we have observed serious neurologic complications as a result, of closure of the claml) in patients with a reduction in pressure less than 40 per cent and, contrariwise, patients in whom the reduction in pressure has been as high as 70 per cenl have tolerated gradual closure without difficulty. I t is felt that all accurate knowledge of blood flow through the carotid ar tery 1o be ligated might provide more information regarding the change in intracranial circulatory dynamics a t tendant upon carotid liga-
75 citations