Seizure threshold in ECT: effect of stimulus pulse frequency.

Stimulus parameters, such as pulse width, frequency, and stimulus train duration, affect seizure threshold in electroconvulsive therapy (ECT), although variably. This study examined the effect of low- and high-pulse frequencies of stimulus on seizure threshold and physiological responses to ECT. Twenty-four consenting inpatients prescribed ECT by the treating psychiatrist received bilateral ECT. Threshold was reassessed at second and third ECT sessions in a crossover design. In the second ECT the pulse frequency was randomly either 50 pulses per second (PPS; n=13) or 200 PPS (n=11). In the third ECT, the same was reversed. The seizure threshold and number of subconvulsive stimulations were significantly lower with 50 PPS compared with 200 PPS. There was no significant difference in the cardiovascular responses between the two groups. Lower stimulus frequency is more efficient in inducing a seizure (smaller threshold) without compromising the physiological responses to ECT. Clinical effects of different doses of ECT stimulus must also consider the role of charge rate (frequency of pulses).