BACKGROUND: In electroconvulsive therapy (ECT), the electrical current must pass the scalp, skull, cerebrospinal fluid (CSF) and brain tissues, to sufficiently exceed the seizure threshold (ST).
OBJECTIVE: To investigate the relationship between these anatomical strata of the head and the level of the ST, in both right unilateral (RUL) and bifrontotemporal (BL) ECT.
METHODS: Observational prospective study among 74 mainly depressed patients. STs were measured at the 1st (initial ST), 6th, 12th, 18th and 24th session. MRI scans were acquired before the 1st session. Scalp and skull thickness at electrode sites were measured on T2-weighted images. Volumes of intracranial space (ICV), CSF, gray and white matter, and white matter hyperintensities were estimated using whole brain isovoxel T1-weighted images. Separate multivariate regression analyses for RUL (n = 55) and BL (n = 19) treated groups were used to estimate the predictive values of the MRI variables.
RESULTS: The patients had a mean age of 57.7 ± 14.8 years, and 39% were men. After adjustment for age, gender and ICV, CSF volume strongly and independently predicted initial ST in both RUL (β = 0.31; P = 0.049) and BL ECT (β = 0.64; P = 0.007). Using multilevel regression analysis, CSF volume was associated with ST during the remaining RUL ECT course (β = 0.20; P = 0.02).
CONCLUSIONS: Taking into account the limitations in the titration method and MRI analysis, volume of CSF strongly and independently predicted initial ST. Therefore, the exclusive use of age-based ECT dosing methods may result in suboptimal electrical stimulus dosage in patients with CSF volumes that are not within the average range.