Studies of dosage, seizure threshold, and seizure duration in ECT

Seizure threshold, defined as the minimal electrical dosage necessary to elicit adequate generalized seizure, was determined throughout the course of electroconvulsive therapy (ECT) in depressed patients randomly assigned to bilateral and right unilateral treatment, with brief pulse, constant current stimulation. In Study 1, it was found that seizure threshold may be more accurately measured using the unit of charge compared to the traditional unit of watt-second. In Study 2, it was found that seizure threshold was associated with seizure duration. Patients with high thresholds had shorter seizure durations. This indicated that the seizure threshold measure assesses in part functional neural activity. In Study 3, it was found that failure for seizure threshold to increase substantially over the course of ECT was associated with poor clinical outcome. In Study 4, it was found that electrical dosage at threshold was not related to magnitude of acute cognitive impairments. This suggested that the degree to which dosage exceeds threshold may be more strongly tied to adverse effects than the absolute dosage administered to patients. Implications of the data are discussed, particularly in relation to a hypothesized link between the anticonvulsant properties of ECT and its mechanism of therapeutic action.