Change of Hemodynamics and Cerebral Functions After Carotid Artery Revascularization

Overview

The majority (\>80%) of strokes are of ischemic etiology, of which ≈15% to 20% are attributable to atherosclerosis of the extracranial carotid arteries. The primary goal in carotid artery revascularization is to prevent stroke in patients with carotid artery stenosis. Treatment options including carotid endarterectomy (CEA) and carotid artery stenting (CAS). Hence, the investigators aim to compare carotid artery stenting (CAS) with carotid endarterectomy (CEA) in terms of long-term prognostic endpoints. Also, CEA and CAS result in different postoperative geometric features of carotid arteries that entail relevant modifications of rheological parameters, that may be associated with the risk of local complications and carotid artery restenosis. Finally, long-term and sustained cognitive benefits after carotid artery revascularization need further research and evidence.

Hypothesis and Significance: We hypothesize that hemodynamically changes after carotid artery revascularization influence the cerebral function or carotid artery patency. If cognitive improvement or impairment and carotid artery restenosis can be demonstrated relate to hemodynamic remodeling in these patients, then we will have established a new prognostic factor for carotid revascularization independent of the existing study. Specific Aim: 1) To compare the impact of carotid artery revascularization on long-term post-operative baroreceptor function and on cognitive brain function, and analyze their influence on clinical outcome. The specific goal is to assess the potential correlation between post-operative autonomic and cognitive function. 2\) To assess the solicitation on the carotid wall due to CAS as compared to CEA through structural analysis and mechanical modeling. The specific goal is to assess the potential correlation between stenting, wall damage, baroceptor impairment, and late neurological sequelae. 3) To assess the post-operative carotid hemodynamics combining medical image analysis, clinical data, and computer simulations. The specific goal aims at correlating both local (e.g., wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT)) and global phenomena (controlateral flow, arterial stiffening) with baroreflex function and post-operative neurological outcomes. Cognitive Assessment. HALO will use existing cognitive assessment infrastructure. Cognitive assessments in our study must take place prior to revascularization or within two weeks after assignment to medical therapy alone. Testing is repeated at 44 days, and every year thereafter up to 4 years. At each test interval, a composite (mean) Z-score is derived from published normative samples for each test outcome. The primary outcome will be at 1 year in which the change in the composite Z-score from baseline will be calculated. Covariates will include age, education and depression. The test battery will be administered the same way for all enrolled patients. The cognitive domains being assessed in HALO are entirely consistent with those encompassed within the NINDS Common Data Elements (CDE). Imaging protocol. Multimodal MRI, including routine parenchymal sequences and PWI utilizing dynamic susceptibility contrast technique, will be acquired at each participating HALO site. Imaging will take place within 14 days after HALO enrollment and prior to any intervention (carotid artery revascularization). Standardized contrast agent injection protocol, appropriate preparation, and IV setup is used to ensure good scan quality. An antecubital vein IV catheter of 18-20 gauge is required. A test injection will be performed with approximately 10 ml of normal saline solution. MRI image acquisition DWI/ADC (b=0, 1000 s/mm2 applied in each of three principal gradient directions), FLAIR, high-resolution T1, and GRE sequences will be acquired on 1.5-3.0 T scanners equipped with echo-planar imaging capability, using standard clinical protocols at participating HALO sites. Total scanning time will be approximately 40 minutes. PWI acquisition protocol will be standardized across all HALO sites, using sequential T2\*-weighted (gradient echo) EPI time sequence scanning. A modified 2-phase contrast injection scheme will be used to perform CEMRA and DSC perfusion imaging, without need for additional contrast. MRI structural analysis. silent infarct --- non-confluent hyperintense lesion \>1mm on FLAIR sequence on 1-year MRI not present on baseline FLAIR MRI. Cerebral microbleed - hypointense 1-2mm non-confluent lesion on baseline GRE sequence. WMH volume -- White matter hyperintensity volume refers to confluent periventricular high intensity lesions on FLAIR imaging, and will be derived using an automated T2 WMH quantification at the Huston lab. . Analysis. Specific Aim 1. To determine whether cognition can be improved by revascularization among a subset of HALO patients with hemodynamic changes at baseline. The primary hypothesis is to assess if the magnitude of the treatment differences (revascularization versus medical management alone) differs between those with flow failure compared to those without flow failure using the Z-scored cognitive outcomes (C0, C(1). That is, the primary hypothesis is an interaction hypothesis that will be assessed using linear regression, specifically: (C1 - C0) = β0 + β1T + β2F + β3TF + β4C0 + (other covariates), where C1 is the cognitive z-score at year 1, C0 the cognitive z-score at baseline, T the treatment indicator variable, F the flow failure indicator variable, and βi the regression parameters to be estimated. The parameter of interest for the primary hypothesis is then β3 that would assess if the magnitude of treatment difference in the change in cognitive score between baseline and 1-year is similar for those with versus without flow failure. Secondary Aims: To determine if the number of silent infarcts and white matter hyperintensity volume at 1 year is different between the revascularization and the medical-only arms. For the secondary aims we will calculate the number of new silent cerebral infarctions occurring over the first year, and the change in the WMH volume. The approach for analysis of the number of new silent infarcts will depend on the average number and distribution of the number of new infarcts. The analytic approach will be linear regression if the number of new infarcts is large (considered more likely the case), or Poisson Regression if the number is smaller (considered less likely the case). The analysis of the change in WMH will use a linear regression approach.