THE LARGEST LYAPUNOV EXPONENT OF THE EEG DURING ECT SEIZURES AS A MEASURE OF ECT SEIZURE ADEQUACY

Attributes of the electroencephalogram (EEG) recorded during electroco nvulsive therapy (ECT) seizures appear promising for decreasing the un certainty that exists about how to define a therapeutically adequate s eizure. In the present report we study whether one promising and not y et tested ictal EEG measure, the largest Lyapunov exponent (lambda(1)) , is useful in this regard. We calculated lambda(1) from 2 channel ict al EEG data recorded in 25 depressed subjects who received right unila teral ECT. We studied the relationship of lambda(1) to treatment thera peutic outcome and to an indirect measure of treatment therapeutic pot ency, the extent to which the stimulus intensity exceeds the seizure t hreshold. We found lambda(1) could be reliably calculated from ictal E EG data and that the global mean, maximum, and standard deviation of l ambda(1) were smaller in the more therapeutically potent moderately su prathreshold ECT and in therapeutic responders. These results imply a more predictable or consistent pattern of EEG seizure activity over ti me in more therapeutically effective ECT seizures. These findings also suggest the promise of lambda(1) as a marker of ECT seizure therapeut ic adequacy and build on our previous work suggesting that lambda(1) m ay be useful for classifying seizures and for reflecting the relative physiologic impact of seizure activity. (C) 1997 Elsevier Science Irel and Ltd.