EEG Seizure Measurement

ECT device manufacturers provide some quantification of the EEG changes. The clinical Thymatron? DGx device made by Somatics Inc. provides three quantitative measures of the seizure EEG: seizure energy index (integration of total energy of the seizure), postictal suppression index (degree of suppression at end of the seizure) and endpoint concordance index (a measure of the relation of the endpoints of the EMG and the EEG seizure determinations when simultaneously recorded).

In 1997, Somatics introduced a proprietary computer-assisted EEG analysis system for use with their ECT device to obtain the EEG power spectral and coherence analytic measures for routine clinical use.

In their new Spectrum 5000Q device, the Mecta Corporation makes available the EEG algorithms derived from research by Krystal and Weiner (1994) and licensed from Duke University to assist clinicians in better determining the quality and efficacy of individual seizures. The clinical significance of these measures has not been prospectively examined, yet the measures provide accessible quantitative indices of the seizure EEG which hold the promise of clinical application and provide the means for establishing their validity (Kellner and Fink, 1996).

For immediate application, clinicians can visually examine the available EEG outputs for evidence of good seizure intensity and generalization. The present criteria for an effective seizure include a synchronous, well-developed, symmetrical ictal structure with high amplitude relative to baseline; a distinct spike and slow wave midictal phase; pronounced postictal suppression; and a substantial tachycardia response. These are reasonable criteria based on present experience. Another measure, that of interhemispheric coherence (symmetry), can be roughly estimated visually from a two-channel EEG recording when care is taken to position the recording electrodes symmetrically over both hemispheres.

Examples of inadequate and adequate seizures are shown in Figures 1, 2a and 2b. These samples are derived from an ongoing study involving energy dosing estimates in the first treatment of a 69-year-old man with recurrent major depression. In the first two stimulations, 10% (50 millicoulombs) and 20% (100 millicoulombs) energies were applied. In the third application, 40% (201 millicoulombs) energy was applied. Electrode placement was bilateral.

Interseizure EEG

In patients receiving a course of ECT, EEG recordings made in the days after treatments showed profound and persistent effects. With repeated seizures, the EEG showed a progressive increase in amplitudes, a slowing and greater rhythmicity of frequencies, and the development of burst patterns. These changes in EEG characteristics were related to the number of treatments, their frequency, type of energy and electrical dosage, clinical diagnosis, patient age and clinical outcome (Fink and Kahn, 1957).

The improvement in patient behavior from the Fink and Kahn (1957) study (observed as a decrease in psychosis, lifting of depressed mood and decrease in psychomotor agitation) was associated with the development of high degrees of EEG change. The EEG characteristics predicted which patients had improved and which had not.

The association was quantitative � the greater the degree of slowing of EEG frequencies and the earlier that "high degree" slowing appeared, the earlier and more dramatic was the change in behavior. Elderly patients developed EEG changes early while younger adults were often slow in showing the changes. In some patients the EEG did not slow despite many treatments, except when the treatments were given more frequently during the week.

The association between ECT-induced interictal EEG slowing and improvement in depression was confirmed by Sackeim et al. (1996). EEG records were examined at different times during the treatment course in 62 depressed patients who received either unilateral or bilateral ECT at threshold or high-dose energies. ECT produced a marked short-term increase in delta and theta power, the former of which resulted from effective forms of ECT. The changes in the EEG were no longer present at two-month follow-up. The authors concluded that the induction of EEG slow-wave activity in the prefrontal cortex was tied to the efficacy of ECT.

An important clinical application of EEG methodology is in determining the adequacy of a course of ECT. When a clinical change does not occur in a timely fashion, the interseizure EEG can be examined visually or by computer analysis. Failure of the EEG from the frontal leads to show well-defined delta and theta activity after several treatments suggests that the individual treatments were inadequate. At such times, the treatment technique should be reexamined for adequacy (i.e., sufficient electrical dosage, choice of electrode placement, concurrent drug use), or the frequency of the treatments should be increased. If the patient fails to improve despite apparently sufficient EEG slowing, the diagnosis and treatment plan should be reexamined.

The renewed interest in the seizure EEG as a marker of seizure adequacy, and in the interseizure EEG as a marker of ECT course adequacy is likely to underlie the next phase of research into the physiology of ECT.

Dr. Fink is professor of psychiatry and neurology at the State University of New York at Stony Brook. He is the author of Convulsive Therapy: Theory and Practice (Raven Press), and founder of the quarterly journal, Convulsive Therapy.

Dr. Abrams is professor of psychiatry at the Chicago Medical School. He has conducted basic science and clinical research on ECT for more than 25 years and has written over 70 articles, books and chapters on ECT.

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