Overlooking the obvious? Influence of electrolyte concentrations on seizure quality parameters in electroconvulsive therapy

Clinical response to electroconvulsive therapy (ECT) depends on eliciting a generalized seizure. Though there are multiple ictal and other parameters to assess seizure quality, factors that influence these parameters have only been identified to a limited extend in antecedent studies (e.g., stimulus dosage, age). In the context of ECT, electrolyte concentrations have hardly been investigated so far—although hyponatremia is one well-known clinical factor to increase the risk of spontaneous seizures. In 31 patients with unipolar or bipolar depressive disorder, blood concentrations of sodium (Na), potassium (K), and calcium (Ca) were measured immediately prior to repeated sessions of maintenance ECT. Generalized linear mixed models were used to analyze the influence of Na, K, and Ca on seven seizure quality parameters: postictal suppression index (PSI), maximum sustained coherence (MSC), midictal amplitude, average seizure energy index, seizure duration (EEG/motor), and peak heart rate. Results show a statistically significant relationship between the serum sodium level and MSC: in the model, a reduction of 1 mmol/l led to an increase in interhemispheric coherence of 0.678%. The further markers remained unaffected by changes in electrolyte concentrations. This finding provides first evidence that a lower blood concentration of sodium could enhance the quality of ECT-induced seizures in terms of higher interhemispheric coherence.