Electrical dose and seizure threshold: relations to clinical outcome and cognitive effects in bifrontal, bitemporal,...

In patients allocated blindly and randomly to receive bitemporal, right unilateral, or bifrontal electroconvulsive therapy, seizure length, electrophysiologic characteristics (dynamic impedance, seizure threshold, and changes in threshold), and the degree of suprathreshold stimulation were recorded. The relations of these variables to clinical outcome and cognitive effects were determined. There were no differences in seizure length between groups, and there were no significant correlations between seizure length and any measure of clinical response. There were substantial differences between the groups in mean charge per treatment, with the right unilateral group receiving lower doses than either bilateral group. Convulsion time was inversely related to applied charge and the rate of increase in charge. There were no significant correlations between impedance, charge, energy, or rate of increase in charge on the one hand, and clinical improvement on the other. The increase in threshold during the course of treatment was not related to clinical change. Cognitive impairment was related to electrical dose only in the bifrontal group, which showed the least degree of treatment-induced intellectual dysfunction. Compared with bitemporal or right unilateral treatment, bifrontal electroconvulsive therapy yields the best ratio of benefits to side effects and should be given at threshold level to minimize cognitive loss.