Pragmatic Guidance for EEG Interpretation

E ach patient's induced seizure in electroshock therapy is a controlled experiment. Clinicians apply scalp electrodes, ventilate with oxygen, sedate, paralyze muscles, select energy parameters on the device, stimulate, and expectantly watch unfolding events. Motor movements assure us that the stimulus affected the patient. Facial color changes, heart rate increases, and the monitoring electroencephalogram (EEG) tape shows changing rhythms.After 20 to 100 seconds, the body suddenly relaxes, the auditory warble ends, and oxygenation continues until breathing is assured. We look at the clock or the EEG tape—How long was the seizure? Is the seizure over? The treatment adequate? Is restimulation needed? We selected the stimulus parameters arbitrarily: electrode placement by concerns about cognitive effects, stimulus energy by age and prior experience with this patient, severity of illness, and our understanding of an “effective” treatment. Seizure length is our principal outcome criterion; if very short, we nod to the anesthetist to keep the patient asleep and relaxed, check the electrodes, change energy parameters in the device, and restimulate. We need more reliable criteria that assure that each session is effective in relieving the patient's syndrome. Electroconvulsive therapy (ECT) devices provide a running tape of EEG activity. The rhythms are complex—some are derived from the brain, but many are artifacts of movement or poor electrode placement. Occasionally, the rhythms sufficiently simulate a seizure to be puzzling. Because few psychiatrists are trained in interpreting EEG recordings, how is the clinician to learn? David Semple, an experienced clinician therapist in Edinburgh, offers a well-illustrated guide to seizure patterns, successful seizures, artifacts, anomalies, and EEG terminology. Did a seizure occur? Did it end? Was it adequate? An induced seizure follows a defined pattern. The rhythm starts with low-voltage fast frequencies, amplitudes increase, frequencies slow, and become intermixed with sharp rapid frequency spikes. Slow waves intermixed with spikes appear in multisecond bursts that suddenly end in a flat line. After