Collateral cerebral vascular resistance in patients with significant carotid stenosis

Understanding the role of hemodynamics in the initiation, progression, rupture, and treatment outcome of cerebral aneurysm from medical image-based computational studies

About a decade ago, the first image-based computational hemodynamic studies of cerebral aneurysms were presented. Their potential for clinical applications was the result of a right combination of medical image processing, vascular reconstruction, and grid generation techniques used to reconstruct personalized domains for computational fluid and solid dynamics solvers and data analysis and visualization techniques. A considerable number of studies have captivated the attention of clinicians, neurosurgeons, and neuroradiologists, who realized the ability of those tools to help in understanding the role played by hemodynamics in the natural history and management of intracranial aneurysms. This paper intends to summarize the most relevant results in the field reported during the last years.

Transcervical carotid stenting with internal carotid artery flow reversal: Feasibility and preliminary results

OBJECTIVE

Transfemoral carotid artery stenting (CAS), with or without distal protection, is associated with risk for cerebral and peripheral embolism and access site complications. To establish cerebral protection before crossing the carotid lesion and to avert transfemoral access complications, the present study was undertaken to evaluate a transcervical approach for CAS with carotid flow reversal for cerebral protection.

METHODS

Fifty patients underwent CAS through a transcervical approach. All patients with symptoms had greater than 60% internal carotid artery (ICA) stenosis, and all patients without symptoms had greater than 80% ICA stenosis. Twenty-one patients (42%) had symptomatic disease or ipsilateral stroke, and 8 patients (16%) had contralateral stroke. Four patients (8%) had recurrent stenosis, 7 patients (14%) had contralateral ICA occlusion, and 1 patient (2%) had undergone previous neck radiation. Twenty-seven procedures (54%) were performed with local anesthesia, and 23 (46%) with general anesthesia. Using a cervical cutdown, flow was reversed in the ICA by occluding the common carotid artery and establishing a carotid-jugular vein fistula. Pre-dilation was selective, and 8-mm to 10-mm self-expanding stents were deployed and post-dilated with 5-mm to 6-mm balloons in all cases.

RESULTS

The procedure was technically successful in all patients, without significant residual stenoses. No strokes or deaths occurred. There was 1 wound complication (2%). All patients were discharged within 2 days of surgery. Mean flow reversal time was 21.4 minutes (range, 9-50 minutes). Carotid flow reversal was not tolerated in 2 patients (4%). Early in the experience, carotid flow reversal was not possible in 1 patient, and there were 1 major and 3 minor common carotid artery dissections, which resolved after stent placement. One intraoperative transient ischemic attack (2%) occurred in 1 patient in whom carotid flow was not reversed, and 1 patient with a contralateral ICA occlusion had a contralateral transient ischemic attack. At 1 to 12 months of follow-up, all patients remained asymptomatic, and all but 1 stent remained patent.

CONCLUSION

Transcervical CAS with carotid flow reversal is feasible and safe. It can be done with the patient under local anesthesia, averts the complications of the transfemoral approach, and eliminates the increased complexity and cost of cerebral protection devices. Transcervical CAS is feasible when the transfemoral route is impossible or contraindicated, and may be the procedure of choice in a subset of patients in whom carotid stenting is indicated.

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.

Improved carotid hemodynamics with vertebral reconstruction

This study tests the hypothesis that vertebral artery reconstruction improves carotid distribution hemodynamics during carotid occlusion. Twelve patients with vertebrobasilar symptoms underwent either direct (9) or indirect (3) vertebral reconstruction. There were six proximal vertebral to common carotid reimplantations, one proximal carotid-vertebral bypass and two distal carotid-vertebral bypasses, all with saphenous vein. Three patients with carotid-subclavian or axillo-axillary bypasses performed for symptomatic vertebral steal were studied at the time of carotid endarterectomy. During temporary ipsilateral carotid occlusion, vertebral reconstruction increased carotid back pressure from 39.3 +/- 10.2 mmHg to 46.8 +/- 9.5 mmHg (p less than 0.0001), increased cerebral perfusion pressure from 33.4 +/- 10.8 mmHg to 41.0 +/- 9.1 mmHg (p less than 0.0001), decreased the carotid collateral resistance to cerebral vascular resistance ratio from 1.68 +/- 0.90 to 1.24 +/- 0.64 (p less than 0.001), and increased the ratio of carotid back pressure to mean systemic arterial pressure from 0.452 +/- 0.122 to 0.515 +/- 0.118 (p = 0.0005). These results are presumed due to increased posterior-to-anterior blood flow in the posterior communicating arteries. Direct or indirect vertebral reconstruction may be a consideration in patients with cerebral ischemic symptomatic and nonreconstructible carotid occlusive disease.

Technique and clinical results of carotid stump back-pressure to determine selective shunting during carotid endarterectomy

A method of confirming carotid back pressure accuracy, variability during carotid clamping, and the clinical results with a modified back pressure shunt criterion were evaluated in 665 carotid endarterectomies. Mean arterial pressure, back pressure, and internal jugular vein pressure were measured. Cerebral perfusion pressure (back pressure-jugular vein pressure) and the collateral to hemisphere vascular resistance ratio, (ratio = [arterial pressure-back pressure]/[back pressure-jugular vein pressure]) were calculated. A shunt was used when cerebral perfusion pressure less than 18 mm Hg. Back pressure accuracy was confirmed by test occlusion of the internal carotid artery distal to the plaque. Initial back pressure values were falsely high in 83 (12.5%) carotid endarterectomies. The mean SD (n = 665, mm Hg) were arterial pressure = 84.0 +/- 9.06, back pressure = 41.0 +/- 15.9, jugular vein pressure = 6.2 +/- 3.9, cerebral perfusion pressure = 35.1 +/- 5.7, and resistance ratio = 1.85 +/- 1.44. Perfusion pressure was less than 18 mm Hg in 82 (12.3%), of which 74 (11.1%) were shunted, and 8 (1.2%) had perfusion pressure increased greater than or equal to 18 mm Hg during carotid endarterectomy with phenylephrine. Back pressure was less than 25 mm Hg in 107 (16.1%), less than or equal to 25 in 114 (17.1%), and less than 50 mm Hg in 481 (72.3%). Pressures were continuously monitored during 28 carotid endarterectomies, and all had a positive linear relationship between arterial pressure and back pressure, and minimal variability in the back pressure/arterial pressure and resistance ratios. Only two patients (0.3%) had a new neurologic deficit in the first 12 hours after carotid endarterectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Linear response of collateral cerebral perfusion pressure during carotid clamping

Phenylephrine is frequently used to increase systemic arterial pressure during carotid endarterectomy. However, little is known of its effect on collateral cerebral perfusion pressure, particularly in patients with high collateral cerebral vascular resistance who are at increased risk of cerebral ischemia during carotid clamping. We tested the hypothesis that this subset of patients can have collateral perfusion pressure, and hence collateral cerebral blood flow, increased in a predictable way by elevating systemic arterial pressure. We measured mean systemic arterial pressure (Pa), jugular venous pressure (Pv), and mean carotid back pressure (Pc), and calculated collateral cerebral perfusion pressure (P = Pc - Pv) and the ratio of collateral to ipsilateral hemisphere cerebral vascular resistance (Rc/Rh) in 18 patients with low P. Initial measurements were Pa = 84 +/- 8.8 (mm Hg, mean +/- SD), Pv = 7.8 +/- 3.9, Pc = 26 +/- 5.1, P = 18 +/- 4.5 and Rc/Rh = 3.4 +/- 1.15. During phenylephrine infusion, Pa = 108 +/- 11, Pc = 32 +/- 6.5, and P = 24 +/- 7.2, increases of 29, 23, and 33%, respectively (P less than 0.05). Unchanged were Pv = 8.2 +/- 4.1 (5%) and Rc/Rh = 3.5 +/- 1.30 (3%) (P greater than 0.8). The latter two findings indicate that cerebral perfusion pressure and mean systemic arterial pressure are linearly related according to the fluid mechanics equation governing these parameters: Pa = P(Rc/Rh + 1) + Pv. These results support the use of phenylephrine to increase collateral blood flow during carotid endarterectomy in patients with low cerebral perfusion pressure.

The relationship of early hypertension following carotid endarterectomy to intraoperative cerebral ischemia

The relationship between early hypertension following carotid endarterectomy, and intraoperative cerebral ischemia was investigated. Two measures of the adequacy of collateral cerebral circulation during carotid clamping were used: collateral cerebral perfusion pressure (delta P), and the ratio of collateral to ipsilateral cerebral vascular resistance (R/R). Change in blood pressure was measured by the ratio of mean early post to preendarterectomy pressure (P/P). Nitroprusside or nitroglycerin (NN) was used after endarterectomy to maintain systolic blood pressure less than 160 mmHg. The mean values for NN (n = 26) and no NN (n = 81) groups were: delta P = 30.0 and 40.2 mmHg (p less than 0.001); R/R = 1.93 and 1.24 (p less than 0.005); and P/P = 1.03 and 0.857 (p less than 0.001 p by unpaired t test). Linear regression analysis of the two measures of cerebral perfusion with the ratio of post-to preoperative blood pressure gave correlation coefficients between 0.629 and 0.841 with a probability that the slope of the regression line greater than 0 of less than 0.01. Low delta P and high R/R correlate with early postcarotid endarterectomy hypertension. These results support the hypothesis that one determinant of early post endarterectomy hypertension is inadequate collateral cerebral circulation during carotid clamping.