Variation of ictal electroencephalographic regularity with low-, moderate-, and high-dose stimuli during right unilateral electroconvulsive therapy

Background: Previous work has demonstrated changes in electroencephalographic (EEG) ictal morphology during electroconvulsive therapy (ECT) as stimulus intensity is increased from barely suprathreshold to moderately suprathreshold. Our study reports on the reactivity of seizure regularity ratings in 11 subjects receiving right unilateral (RUL) ECT as the stimulus is varied over a wider range of intensities from low to medium, then high dose. Methods: The stimulus intensity of all 11 subjects was first increased from barely suprathreshold to moderately suprathreshold, and then randomized to either stay at a moderately suprathreshold dose or increase to a high dose. The regularity of the EEG ictal discharge was visually measured on a seven-point scale. Results: We found that seizure regularity increases as the stimulus intensity moves from the barely suprathreshold to the moderately suprathreshold dosage, but did not increase further when the stimulus increased to a high dose. Conclusions: These results suggest that EEG regularity is unlikely to distinguish moderately suprathreshold from markedly suprathreshold stimuli during RUL ECT.