Comparing Continuous to Brief Intermittent EEG for Detecting Ictal Activity

Jonathan Elmer, MD

New data from a University of Pittsburgh study is shining light on the apparent ineffectiveness of intermittent electroencephalography (EEG) compared to continuous EEG for detecting ictal activity following cardiac arrest.

Results of the study indicated brief intermittent monitoring was insensitive for detecting potentially treatable seizures but may prove useful for guiding multimodality prediction of outcomes following hospital discharge in patients who were comatose following cardiac arrest.

With some data suggesting up to half of all cardiac arrest patients who are comatose after resuscitation have EEG activity, a team of investigators—led by Jonathan Elmer, MD—designed a study to assess whether EEG monitoring could improve detection and determine the necessary duration of such observation. To do so, investigators identified 2 cohorts of consecutive patients from the University of Pittsburgh Medical Center (UPMC) Presbyterian Hospital and University of Alabama (UAB) Birmingham Hospital from September 2010 through 2018.

From these medical centers, investigators obtained a cohort of 759 patients that met their inclusion criteria. For the purpose of their analysis, investigators excluded patients who experienced cardiac arrest as a result of trauma or a neurological catastrophe. Additionally, patients who underwent fewer than 24 hours of monitoring and those with interruptions in monitoring totaling more than 10% of the overall observation period were also excluded.

Investigators noted the standard of care at both hospitals included in the study included monitoring patients with continuous EEG except in cases with rapid awakening prior to monitoring initiation, early limitations of care because of prior advanced directives, refractory multisystem organ failure or rearrest, or nonsurvivable cerebral edema on initial brain imaging.

Of note, investigators categorized EEG patterns as risk factors if less likely to be prognostically or clinically important but instead reflective of epileptiform potential and events if strongly associated with outcome or likely to cause secondary brain injury. Additionally, 2 sets of definitions were tested in the analysis—the first was designed to detect prognostic events and the other was designed to detect potentially treatable seizures.

Of the 759 patients included in the study, 584 were from UPMC Presbyterian Hospital and 175 were from UAB Birmingham Hospital. Patients in the Pittsburgh cohort had a mean age of 57 (17) years and 37.2% were female. In the Alabama cohort, the mean 58 (16) years and 36.6% were female.

The mean age of the overall study cohort was 58 (17) years, 37% of participants were female. Epileptiform EEG was observed in 414 (54.5%) participants and 26 (3.4%) developed potentially treatable seizures.

Results of the analyses indicate brief intermittent EEG, which investigators defined as 20 minutes or less, had an estimated sensitivity of 66% (95% CI, 62%-69%) to 68% (95% CI, 66%-70%). Results also suggested between 0-51 hours of continuous monitoring were needed, depending on initial continuity of EEG, to achieve 95% sensitivity for detecting prognostic epileptiform events.

When assessing for ability to detect potentially treatable seizures, results indicated brief intermittent EEG had a sensitivity of 7% (95% CI, 4%-12%) to 8% (95% CI, 4%-12%)—investigators pointed out between 0 to 53 hours of continuous monitoring were needed to achieve 95% sensitivity. Results also suggested brief intermittent EEG and continuous EEG had similar effectiveness for predicting neurological outcome.

Investigators noted multiple limitations within their study. Limitations included limited prognostic data from the Alabama cohort, limited generalizability, and inability to account for unmeasured confounders, among others.

This study, “Sensitivity of Continuous Electroencephalography to Detect Ictal Activity After Cardiac Arrest,” was published in JAMA Network Open.