Stimulus Electrode Placement

Electroconvulsive Therapy: Stimulus Electrode Placement

For many years, stimulus electrodes were applied bitemporally, with midpoints of the electrodes approximately 1 inch above the midpoint of a line connecting the external canthus with the upper tip of the tragus (the small cartilaginous structure in the anterior region of the external ear). This type of electrode placement is called bilateral (BL) ECT. In 1958, Lancaster and colleagues developed an alternative placement in which the stimulus electrodes were both placed over the cerebral hemisphere opposite the one believed to be dominant for speech, thereby relatively sparing verbal memory function (Lancaster et al. 1958). This technique is called right unilateral (RUL) ECT.

Since that study, there have been dozens of additional investigations focusing on the efficacy and safety of various RUL types versus the more traditional BL ECT (reviewed in Abrams 1997a). These studies have, for the most part, tended to demonstrate three general types of findings: 1) memory impairment, particularly left hemisphere function, is less likely, less severe, and less persistent with RUL ECT; 2) the antidepressant effect of BL ECT may be more rapid or pronounced than with RUL ECT, at least under certain circumstances; and 3) optimization of RUL technique can maximize its therapeutic potency. It is now known, for example, that RUL ECT administered using a frontotemporal to high centroparietal (just lateral to the vertex of the scalp) configuration (d'Elia 1970) in combination with a stimulus intensity that is at least moderately suprathreshold has significant efficacy, though not necessarily equivalent to BL ECT in some patients (Sackeim et al. 1991, 1993). More recent preliminary data indicate that when RUL ECT is administered at a stimulus intensity that is markedly above the seizure threshold in intensity (500% above threshold), the efficacy may become equivalent to that of BL ECT (Sackeim et al. 2000). Interestingly, although such increases in RUL ECT stimulus intensity are associated with a rise in level of amnesia, this effect is less than that observed with BL ECT. Further studies are needed to indicate how to optimally administer RUL ECT and to determine when BL ECT may be needed. In the meantime, each practitioner must choose the electrode placement and stimulus intensity on the basis of a case-by-case analysis of anticipated benefits versus likely risks (American Psychiatric Association Committee on ECT 2000).

Electroconvulsive Therapy Introduction Indications