Burst suppression: a more valid marker of postictal central inhibition?

A valid marker to predict seizure adequacy in electroconvulsive therapy (ECT) is still missing. Postictal suppression has been claimed to correlate with the antidepressive effectiveness of an induced seizure. Postictal suppression index (PSI) is derived from a short time span of electroencephalographic recording at seizure termination, and, alternatively, burst suppression (BS) index is defined as the percentage of suppressed epochs within a predefined time period.

In a retrospective study including 9 patients with a total of 104 recorded ECT sessions, we compared the influence of variables that are known to alter seizure adequacy like age, stimulation dose, electrode position, and the number of the consecutive ECT sessions on both indices, PSI versus BS index.

For PSI, electrode positioning turned out to be a significant independent variable, with bilateral placement revealing higher PSI. Electroconvulsive therapy session number was significant for BS index, with lower burst suppression in higher ECT session number. In contrast to PSI, BS index turned out to be a significant covariate of seizure duration. Postictal suppression index and BS index did not show linear but a significant rank correlation.

We report first data about postictal BS index in ECT. As a measure of postictal electrical suppression, BS index appears as robust as PSI. Burst suppression index decreases during an individual ECT course, which presumably reflects the anticonvulsive effect of ECT. Less artifact-prone methods of automatic quantification of electrical suppression could improve precise determination of individual seizure adequacy.