Does carotid stenting with protection make patients smarter?

These interim study results are intriguing, but based on preliminary findings alone there is no way to determine whether carotid artery stenting with distal filter protection (CSP) actually improves memory.

Obvious limitations of this interim report are the small number of patients in the CSP group and the absence of randomization, including a medically treated comparison group. It’s possible the patients selected for CSP somehow had an intrinsically better chance of an improved outcome, which may lead us to falsely generalize the results to the entire patient population.

Furthermore, the CSP group consisted of both symptomatic and asymptomatic patients, but investigators didn’t define what they considered symptomatic.

To avoid misinterpretation, the CSP group should be stratified into symptomatic and asymptomatic, and each of these groups should be well-defined and compared to a control group. Ideally, each CSP and control group should also be stratified by the degree of carotid artery narrowing present, and surveyed for co-morbidities for stroke (e.g. hypertension, diabetes/glucose intolerance, elevated bad cholesterol, obesity, smoking, excess alcohol use, heart disease, etc.).

Without this type of methodology, it’s impossible to know which patients truly benefit most, and how much of the measured cognitive improvement is due to CSP as opposed to other possible interventions, such as the treatment of stroke co-morbidities.

Details of the study methodology, such as patient selection and exclusion criteria, the training and technique used, and the competence of the stenting operators, are lacking. Measurements of carotid narrowing were not performed using the same technology in every patient, and complications of CSP were not reported. The latter is especially important since recurrent narrowing of coronary arteries after stenting has been reported in as many as one third of patients. Carotid stenting could yield similar results.

Additionally, studies have shown that carotid stenting is more likely than CEA to be associated with emboli, especially during the angioplasty phase. Without embolic monitoring, such as real-time Doppler ultrasound or pre- and post-CSP diffusion/perfusion imaging studies, we really don’t know what is happening as far as embolic phenomena are concerned.

The study also raises theoretical questions. Cognitive decline is usually the result of diffuse or multifocal bilateral brain impairment, such as Alzheimers Disease or multiple bilateral strokes, or of a one-sided brain process in certain brain regions, such as the thalamus, hippocampus or perisylvian cortex. The thalamus and hippocampal regions derive their blood supply from the vertebrobasilar arterial system, not the carotid system. Therefore it’s somewhat confounding as to why, in cases of cognitive loss due to diffuse, multifocal, thalamic or hippocampal compromised blood flow, opening up one carotid artery with stenting would result in a significant improvement in cognition.

Lastly, the improvement in cognition was reported in patients six months after CSP. It remains to be seen whether it will be sustained at one year and beyond. It’s possible this study will lead to a revision in our understanding of brain pathways and regions subserving cognitive function, and elucidate the role of vascular disease in cognitive decline. It may also provide more impetus for healthcare providers to screen people at age 35, or even 25, for stroke and heart attack risk factors, and aggressively treat these conditions.

But does CSP make people smarter? It’s too soon to tell. Until larger, randomized and controlled studies are performed, CSP cannot be recommended for routine management of high-grade carotid narrowing. Certain exceptions may exist, such as in the treatment of surgically inaccessible carotid lesions, or in someone who has had neck irradiation or significant trauma. But carotid artery stenting, with or without protective devices, is not yet the standard of care.

Norman Werdiger, MD, is Associate Clinical Professor of Neurology Yale University School of Medicine Assistant Chief of Neurology at Yale-New Haven Hospital.