Electroconvulsive therapy and resistant depression: clinical implications of seizure threshold

Patients with major depressive disorder (MDD) were treated with electroconvulsive therapy (ECT) to determine (1) variability of initial seizure threshold, (2) factors that influence seizure threshold, (3) change in seizure threshold during the ECT course, and (4) relationship of seizure threshold to antidepressant effects.

Seizure threshold was measured by a stimulus titration technique during the first, eighth, and final ECT of medication-free patients who had MDD, endogenous subtype based on Research Diagnostic Criteria and were randomly assigned to three-times-weekly, bilateral, brief pulse ECT (N = 24) or twice-weekly ECT plus one simulated treatment per week (N = 23). Subsequent to the first ECT, stimulus intensity was 1.3 to 1.8 (median = 1.5) times threshold. The Hamilton Rating Scale for Depression (HAM-D) was the primary clinical outcome measure.

Initial seizure threshold varied by 594%. Gender (p = .03), total strength of pre-ECT pharmacotherapy trials (p = .02), and age (p = .12) accounted for 23.9% of the variance. Threshold increased by 42% +/- 26% (p = .0001) from the first to the final ECT, and seizure duration decreased by 33% +/- 28% (p = .0001). Seizure duration and mean stimulus intensity were negatively associated over all treatments (r = -.49, p = .0003). Change in HAM-D score was related to duration of the current depressive episode (r = -.39, p = .006) and total strength of pre-ECT pharmacotherapy trials (r = -.39, p = .008), but not to seizure threshold or duration.

(1) Initial seizure threshold for pulse bilateral ECT is highly variable and not yet amenable to accurate prediction. (2) Stimulus titration allows threshold to be determined on an individual basis and dosage for subsequent treatments to be defined. (3) Seizure duration is of limited value as a sole criterion for the adequacy of treatment when initial threshold is unknown and/or electrical doses that substantially exceed threshold are used. (4) With moderately suprathreshold bilateral ECT, a relationship of seizure threshold to antidepressant response is not demonstrable.