Quantitative artifact reduction and pharmacologic paralysis improve detection of EEG epileptiform activity in critically ill patients

Abstract

Objective: Epileptiform activity is common in critically ill patients, but movement-related artifacts-including electromyography (EMG) and myoclonus-can obscure EEG, limiting detection of epileptiform activity. We sought to determine the ability of pharmacologic paralysis and quantitative artifact reduction (AR) to improve epileptiform discharge detection.

Methods: Retrospective analysis of patients who underwent continuous EEG monitoring with pharmacologic paralysis. Four reviewers read each patient's EEG pre- and post- both paralysis and AR, and indicated the presence of epileptiform discharges. We compared the interrater reliability (IRR) of identifying discharges at baseline, post-AR, and post-paralysis, and compared the performance of AR and paralysis according to artifact type.

Results: IRR of identifying epileptiform discharges at baseline was slight (N = 30; κ = 0.10) with a trend toward increase post-AR (κ = 0.26, p = 0.053) and a significant increase post-paralysis (κ = 0.51, p = 0.001). AR was as effective as paralysis at improving IRR of identifying discharges in those with high EMG artifact (N = 15; post-AR κ = 0.63, p = 0.009; post-paralysis κ = 0.62, p = 0.006) but not with primarily myoclonus artifact (N = 15).

Conclusions: Paralysis improves detection of epileptiform activity in critically ill patients when movement-related artifact obscures EEG features. AR improves detection as much as paralysis when EMG artifact is high, but is ineffective when the primary source of artifact is myoclonus.

Significance: In the appropriate setting, both AR and paralysis facilitate identification of epileptiform activity in critically ill patients.

Keywords: Continuous video EEG; EEG interpretation; Myoclonus; Neurocritical care.

Fig. 1.

Schematic of study design. Visual representation of the timing and source of baseline (A), post-artifact reduction (AR; B), and post-paralysis (C) EEG clips.

Fig. 2.

Representative baseline and post-artifact reduction (AR) EEG tracings for patients with high and low EMG artifact. Representative images for a patient with high EMG artifact on EEG at baseline (A) and after AR (B), compared to a patient with low EMG artifact at baseline (C) and after AR (D).

Fig. 3.

Interrater reliability (IRR) of baseline, post-artifact reduction (AR), and post-paralysis EEG reads. IRR across multiple conditions. The x-axis indicates the condition (baseline, post-AR, or post-paralysis) and the y-axis shows the IRR as measured by Fleiss’ kappa. The solid line shows the primary analysis of all patients (“All”), the dashed line shows the analysis for patients with high EMG artifact (“High EMG”), and the dotted line shows the analysis for patients with low EMG artifact (“Low EMG”). For the primary analysis, there was a non-significant trend toward improvement in IRR with AR and significant improvement after paralysis. For patients with high EMG artifact, IRR similarly and significantly improved with both AR and paralysis. For patients with low EMG artifact, IRR did not improve after AR but significantly improved after paralysis. The asterisks represent the statistical significance of the difference between a given condition and the baseline condition (hence there is no significance marker above the baseline condition because this is the comparison group). ** = p ≤ 0.01 when compared to baseline, n.s. = not significant.

Fig. 4.

Agreement with clinical report, sensitivity, specificity, and confidence of baseline, post-artifact reduction (AR), and post-paralysis EEG reads. Performance of reviewers at detecting epileptiform discharges across different artifact reduction interventions, as measured by (A) percent agreement with clinical report, (B) sensitivity compared to clinical report, (C) specificity compared to clinical report, (D) reviewer confidence in their interpretation. In each plot, the solid line shows the primary analysis of all patients (N = 30), the dashed line shows the analysis for patients with high EMG artifact (N = 15), and the dotted line shows the analysis for patients with low EMG artifact (N = 15). Stars represent statistical significance of each datapoint compared to the baseline measure of the same condition. * = p ≤ 0.05 when compared to baseline, ^** = p 0.01 when compared to baseline, n.s. = not significant.