EEG manifestations during ECT: effects of electrode placement and stimulus intensity

This study examined the ictal electroencephalographic (EEG) characteristics of four forms of electroconvulsive therapy (ECT) known to differ in efficacy. Previously, we demonstrated that titrated, low-dose right unilateral ECT reliably produces generalized seizures of adequate duration, but is remarkably weak in antidepressant effects. Using a new rating scale, we found that specific features of the ictal and immediate postictal EEG varied significantly with ECT stimulus intensity and electrode placement. The low-dose right unilateral condition differed from more effective forms of ECT in having the longest polyspike phase duration, averaging twice that of the other conditions; it was also the condition least likely to manifest bioelectric suppression immediately following seizure termination. In contrast, high-dose bilateral ECT--a treatment with particularly rapid antidepressant effects--resulted in the greatest peak slow-wave amplitude in both hemispheres. Total seizure duration did not differ among the four treatment conditions. These findings indicate that seizure duration is not a useful marker of therapeutic efficacy, and instead provide preliminary evidence that other features of the EEG may be more useful markers of treatment adequacy.