Post-seizure EEG fractal dimension and spectral power predict antidepressant response to unilateral ECT

BACKGROUND Measures of EEG during ECT, for example, smaller post-seizure fractal dimension have predicted antidepressant response. The earlier study on this subject used bilateral ECT. This study aims to examine if this finding holds good even for unilateral ECT, using both fractal dimension and spectral power analysis of EEG. METHODS Fifty-one right-handed, drug-free patients with major depressive disorder received right unilateral ECTs at 2.5 times their seizure threshold. A rater blind to the clinical data measured fractal dimension and spectral power of EEG during their second ECT. Depression was rated using Hamilton's Rating Scale for Depression at baseline and on the 3rd, 7th and 14th days following ECT. RESULTS Thirty-five good quality EEG recordings were analyzed. Seventeen patients reached criteria for early response of more than median percent improvement on HRSD on both 7th and 14th day. Univariate analysis showed smaller fractal dimension and spectral power (greater post-seizure EEG suppression) in early responders compared to the late responders. This was confirmed by multivariate discriminant function analysis. None of the other clinical, treatment or EEG parameters predicted early response. CONCLUSIONS Effective seizure during unilateral ECT may be characterized by high post-seizure EEG suppression.