Structural Stability of Carotid Plaque and Symptomatology

This study examines the relationship between the structural stability of carotid atherosclerotic plaque forming at the bifurcation of the common internal/external carotids and the ability of such lesions to cause disease. The theory behind this work is the hypothesis that carotid atherosclerotic stroke presents not only as a classical episodic clinical condition, but may also involve elements of a continuous process involving large and small vessel circulations, microcirculatory changes, cellular metabolic resistance to ischemia and micro embolic events. Recent studies suggest for every recognized clinical stroke, 5 silent strokes take place.

The patient implications are enormous as imaging suggests 11 million "silent strokes" occur yearly in the US with poor understanding of the pathophysiology or cognitive consequences for our patients. Within this framework, the investigators choose to study the hypothesis that carotid artery atherosclerosis is likely to cause microemboli, as well as classic macroemboli, which may result in more subtle disturbances than those ordinarily detected by more obvious clinical events such as stroke and transient ischemia attacks.

Understanding the structural plaque abnormalities that render a carotid plaque unstable and at risk of embolization would help to predict and treat individuals who are likely to suffer not only classic episodic major strokes, but also cognitive impairment from the contribution of microemboli to this overall disease process. The investigators have previously described a non-invasive ultrasound-based measure of plaque structural stability which will be further studied in this proposal. This study will expand on previous work performed at the University of Wisconsin-Madison, and will include patients with carotid artery stenosis, both with and without classic stroke symptoms, as well as a control group of patients without known atherosclerotic disease. Current treatments for carotid artery stenosis include either carotid endarterectomy to remove plaque or carotid stenting using a expandable metal coil to prevent the artery from narrowing.

In the previous version of this protocol, the investigators have enrolled 95 -subjects (75 patient-subjects and 20 control-subjects) with no safety concerns. Findings include new understanding of the relatively of atherosclerosis and cognition as well as the basic pathophysiology of atherosclerotic large to small vessel disease.

The study will run for 5 years from IRB approval with potential to further expand it. All patient-subjects will have a baseline and 1-year follow-up, ultrasound, TCD, blood collection and cognitive study to see if endarterectomy or stenting (endovascular) affected pre-op change. Change in cognition will be compared to report studies in the normal control group. In past, carotid patients have been recruited at a greater pace. Given the complexity of these studies the investigators anticipate recruitment and complete analysis of 20 patients/year. During this time initial psychological testing will be done pre-operatively. During the final year of the study, the data analysis of the plaque ultrasounds, and histopathology and 1-year follow-up the patient received in the last year of recruitment will take place. The investigators can recruit additional patients to fill any missing data points if these results identify a subset of classically asymptomatic patients with significant carotid plaques and microemboli causing vascular cognitive decline.

• Specific Aim 1: Atherosclerosis, plaque elasticity, strain defects and histopathology of plaque. This aim will study the relationship of structural instability in the carotid plaques with histopathologic evidence for fissuring of the plaques that may represent a micro-emboli source. The determination of a structural defect causing abnormal strain measurements in a carotid atherosclerotic plaque will be important in understanding the pathophysiology of this disorder, as well as, addressing future treatment strategies, which could include preventing angiogenesis, thrombosis, or abnormal cholesterol deposit within the plaque.
• Specific Aim 2: Plaque strain deficits and microemboli. In this aim, the investigators will preoperatively measure the structural stability of each plaque ultrasonically while simultaneously recording distally for the presence of microemboli over time within the carotid system. Statistical analysis will establish the structural instability signature that predicts ongoing subclinical microemboli.
• Specific Aim 3: Plaque strain deficits, microemboli, and cognition. This aim will analyze increased elasticity strain within carotid plaques as measured preoperatively with ultrasound and correlate these parameters with cognition
• Specific Aim 4: Blood RNA expression profiles can be used as biomarkers to identify the patients with a higher risk of plaque instability. This aim will analyze the mRNA and microRNA expression profiles of the blood and the excised plaque samples from patients with stable and ruptured carotid atherosclerotic plaques. The RNA analysis will be conducted with the microarrays.