Determinants of Seizure Threshold in ECT: Benzodiazepine Use, Anesthetic Dosage, and Other Factors

Abstract

The electrical dosage of the ECT stimulus impacts on efficacy and cognitive side effects, yet seizure threshold (ST) may vary as much as 50-fold across patients. It would be desirable to predict ST on the basis of patient and treatment characteristics. In particular, concerns have been raised that benzodiazepine use and higher dosage of barbiturate anesthetics elevate ST. In a three-site study, ST was quantified at the first ECT session using an identical empirical titration procedure in 294 patients who met RDC and DSM-IIIR criteria for a major depressive episode. ST varied over a 35-fold range across patients treated with right unilateral (RUL) (n = 267) and bilateral (BL) (n = 27) ECT. Higher ST was associated with BL electrode placement (p = 0.001). Among patients treated with RUL ECT, univariate analyses indicated that higher ST was associated with advanced age (p < 0.001), male gender (p < 0.001), greater burden of medical illness (p < 0.001), weight (p < 0.01), duration of mood disorder (p < 0.01), and history of previous ECT (p < 0.05). Average lorazepam dose in the 48 hours prior to ECT was not associated with ST, but was associated with decreased seizure duration (p < 0.01). Absolute, but not weight-adjusted, methohexital dose was associated with ST (p < 0.01). Multivariate analyses in patients treated with unilateral ECT showed that only 27.6% of the variance in ST (p < 0.0001) could be predicted. In the multivariate analyses, only age (p = 0.0001), gender (p = 0.01), and methohexital dose (p = 0.0001) were independently related to ST. Low dosage of lorazepam and methohexital dosage below 1 mg/kg are unlikely to impact on ST. Given the limited capacity to predict ST, empirical titration remains the only accurate method to determine electrical dosage in RUL ECT.

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

“…Our analysis did not reveal weight as a significant predictor of ST either. This is largely consistent with clinical ECT data (Boylan et al, 2000;Chung, 2006;van Waarde et al, 2013c), except for a small predictive power of body mass index on BL ECT ST in one study (Chung, 2006).…”

“…We observed inverse dependencies of motor and EEG seizure duration on age, as well as of EEG seizure duration on individual ST, consistent with clinical ECT with conventional dosing strategies (Boylan et al, 2000;Chung, 2002;Coffey et al, 1995;Rasimas et al, 2007). The reported significant interaction effect of session and stimulation modality on EEG seizure duration may be due to particularly long seizures occurring in arbitrary sessions that are different across the modalities.…”

“…The ability of this MT to explain 63.1% of the ST variance in our study is notable as known predictors of conventionally titrated ST for a given electrode placement explain less than 40% of the variance (Boylan et al, 2000;Chung, 2006;Galvez et al, 2015;Sackeim et al, 1994;van Waarde et al, 2013c). The strong correlation between MT and amplitude-titrated ST supports the explanation that the interindividual ST variability is influenced by individual anatomical parameters that also affect the MT.…”

“…After accounting for electrode placement, age is the strongest predictor of conventionally titrated ST, although it explains only 10-30% of the ST variance (Boylan et al, 2000;Chung, 2006;Galvez et al, 2015;van Waarde et al, 2013c). Amplitude-titrated ST in unanesthetized patients also increases with age (Liberson, 1948).…”

Subjective Memory Immediately Following Electroconvulsive Therapy

“…If electrical doses are not adequately adjusted to age and sex, this could contribute to the increased risk of SMW among women and younger patients. 31,32 The optimal dosing strategy is yet to be determined.…”