Electroconvulsive Therapy Stimulus Parameters

Abstract

In this paper we review the parameters that define the ECT electrical stimulus and discuss their biophysical roles. We also present the summary metrics of charge and energy that are conventionally used to describe the dose of ECT and the rules commonly deployed to individualize the dose for each patient. We then highlight the limitations of these summary metrics and dosing rules in that they do not adequately capture the roles of the distinct stimulus parameters. Specifically, there is strong theoretical and empirical evidence that stimulus parameters (pulse amplitude, shape, and width, and train frequency, directionality, polarity, and duration) exert unique neurobiological effects that are important for understanding ECT outcomes. Consideration of the distinct stimulus parameters, in conjunction with electrode placement, is central to further optimization of ECT dosing paradigms to improve the risk/benefit ratio. Indeed, manipulation of specific parameters, such as reduction of pulse width and increase in number of pulses, has already resulted in dramatic reduction of adverse side effects, while maintaining efficacy. Furthermore, the manipulation of other parameters, such as current amplitude, which are commonly held at fixed, high values, might be productively examined as additional means of targeting and individualizing the stimulus, potentially reducing side effects. We recommend that ECT dose be defined using all stimulus parameters rather than a summary metric. All stimulus parameters should be noted in treatment records and published reports. To enable research on optimization of dosing paradigms, we suggest that ECT devices provide capabilities to adjust and display all stimulus parameters.

Individualized Low-Amplitude Seizure Therapy: Minimizing Current for Electroconvulsive Therapy and Magnetic Seizure Therapy

“…In fact, for some stimulus parameter ranges, the total charge may increase with decreasing current amplitude (Swartz et al, 2012). The similarity in ST charge among modalities with very different strength and focality of stimulation by virtue of the different stimulus current amplitude supports the view that charge does not capture important dosing tradeoffs in ECT (Peterchev et al, 2010b).…”

“…In contrast, we titrated ST with a train of 500 pulses, which could further reduce the current amplitude required for seizure induction (Liberson, 1948). Finally, the ECT pulse width in the NHP study (0.20 ms) was briefer than conventional ultrabrief ECT pules (0.25-0.30 ms); wider pulses would be expected to have lower amplitude thresholds due to the strength-duration relationship (Liberson, 1945;Peterchev et al, 2010b). Thus, there is converging evidence that seizures can be induced with lower than conventional ECT current amplitude in humans as well.…”

“…At conventional pulse amplitudes, ECT induces an electric field strength that substantially exceeds the neural activation threshold in most brain structures (Deng et al, 2011;Lee et al, 2014), resulting in widespread, nonfocal stimulation. This is higher than necessary to induce seizures since ECT studies dating back to the 1940s as well as several small recent studies demonstrated the feasibility of low-amplitude currents inducing seizures (Liberson, 1953;Nahas et al, 2013;Peterchev et al, 2010b;Rosa et al, 2011Rosa et al, , 2012. Furthermore, magnetic seizure therapy (MST) elicits generalized seizures with an induced electric field that is substantially less intense and more focal than conventional ECT (Deng et al, 2011(Deng et al, , 2013Lee et al, 2014).…”

“…Even when ST is titrated and the dose is set relative to ST, this is done by adjusting the duration and frequency of the stimulus train but not the current amplitude, which does not compensate for the individual variation of the electric field strength in the brain (Peterchev et al, 2010b). Consequently, individual variation in anatomy results in variable strength and focality of the induced electric field, which could account for some of the differences in side effects and therapeutic efficacy across patients (Deng et al, 2014).…”

“…Modifications in ECT technique, including briefer stimulus pulses, unilateral electrode placement, and dosing relative to the individual seizure threshold (ST), have improved the side effect profile of modern ECT without sacrificing its unparalleled efficacy. These modifications reduced the intensity and duration of the electrical stimulus and made it more focal (Lee et al, 2012;Peterchev et al, 2010b;Sackeim, 2004;Sackeim et al, 1994). Nevertheless, a significant proportion of patients receiving ECT still experience adverse effects, which impedes the broader application of this highly effective intervention (Goodman, 2011;Kellner et al, 2010;Semkovska and McLoughlin, 2010;Verwijk et al, 2012).…”