Stimulus intensity, seizure threshold, and seizure duration: impact on the efficacy and safety of electroconvulsive therapy.

There has been considerable uncertainty in the clinical community on how stimulus dose, seizure threshold, and seizure duration relate to the efficacy and side effects of electroconvulsive therapy (ECT). This article reviews the evidence bearing on these issues. Recent evidence contradicts a number of long-standing views about how to optimize ECT administration. Among these recent observations are findings that (1) generalized seizures that are "adequate" by conventional duration criteria may be produced reliably, yet lack therapeutic properties; (2) the degree to which stimulus intensity exceeds seizure threshold is critical in determining the efficacy of unilateral ECT and also the speed of response with both unilateral and bilateral ECT; (3) the degree to which electrical dose exceeds seizure threshold, not the absolute dose administered, determines dosing effects on clinical outcome and on the magnitude of cognitive deficits; (4) there is marked variability among patients in their seizure thresholds that is related reliably to patient characteristics (sex, age) and treatment factors (electrode placement); and (5) seizure duration alone should not serve as a marker of the adequacy of treatment--there are complex relations between stimulus dosing and seizure duration, with the likelihood that substantially suprathreshold stimulation may result in shorter durations particularly early in the treatment course.