Seizure threshold in a large sample: implications for stimulus dosing strategies in bilateral electroconvulsive therapy: a report from CORE.

Objective: We sought to examine the relationship of seizure threshold (ST) to age and other demographic characteristics in a large sample where ST was determined by the dose titration (DT) method. We also compared the resulting stimulation levels to estimates predicted by an age-based formula, the half-age (HA) method.

Methods: In a multicenter prospective study, patients received a standardized course of bilateral electroconvulsive therapy for major depression using a brief pulse device. The ST was determined at the first treatment using a fixed algorithm of stimulations. Subsequent seizures were induced at a level 50% higher than the empirically determined ST. We only included data from subjects receiving methohexital anesthesia. We correlated ST with demographic and clinical characteristics of the sample. The actual dosing levels at the second treatment were compared with estimates based on HA.

Results: Of the original 531 subjects, 402 met criteria for the current analysis. The ST was positively correlated with age. Male patients had slightly higher ST than female patients. Neither race, severity of illness, psychosis, nor use of psychotropic medications affected ST. Little variability in titrated ST was observed among our patients. An ST of 40 ("percent of charge") or lower was found in 97.5% of patients, with either 20 or 40 in 80% of patients. Ninety-six percent of the patients were treated at the 3 levels of 15%, 30%, or 60%. Estimated HA stimulus levels offered a wider range of choices compared with this particular algorithm used for ST determination at an average level of 18% above the determined ST.

Conclusions: Seizure threshold correlates strongly with age, whereas there is a weaker relation between ST and sex. There was little individual variation of ST determined by the DT method among subjects, possibly because of the wide spacing between steps of this particular titration algorithm. Half-age estimates were 18% above the empirically determined ST. This suggests that the use of the HA estimates at the first treatment may result in fewer stimulations compared with the DT method.