During carotid endarterectomy (CEA), continuous monitoring with electroencephalography (EEG) is routinely used to monitor for cerebral ischemia. We studied the differences in severity of ischemic changes in the EEG between left and right CEA.

Prior studies have concluded that ischemic strokes are more common in the left hemisphere than in the right, and carotid atherosclerotic plaques are larger and more likely to bleed on the left side. This asymmetry may be due to anatomical differences, as the left carotid artery originates directly from the aorta, is larger, and experiences higher pressures than the right carotid artery.

We obtained intraoperative EEG recordings on 88 patients who underwent CEA from 2009 to 2017 and in whom clinically significant ischemic changes were observed on the EEG by visual analysis. All EEG recordings captured eight channels: F3-P3, P3-O1, F3-T3, T3-O1, F4-P4, P4-O2, F4-T4, and T4-O2. For each patient, a Fast Fourier Transform was applied to obtain the power of the alpha band (8-12 Hz) for a 10-minute post-clamp segment when most ischemic changes are observed. We statistically compared the decrease in alpha power in the ipsilateral channels between left and right CEA.

In the immediate 10-minute duration after the carotid artery clamping, the mean decrease in power in the alpha band in the ipsilateral channels was statistically significantly higher in left CEA compared to right CEA (t-statistic = 3.657, p-value = 0.0002).

We speculate that left CEA produces more pronounced cerebral ischemia when the carotid artery is clamped. However, we examined only the alpha band, which is typically the band where ischemic changes are often seen, and other frequency bands should be studied in the future. Further, postsurgical outcomes should be studied to determine if intraoperative differences affect outcomes.