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EEG Monitoring in ECT: A Guide to Treatment Efficacy

EEG Monitoring in ECT: A Guide to Treatment Efficacy

For over 50 years we clinicians have administered electroconvulsive therapy with little to guide us in deciding whether or not a particular induced seizure is an effective treatment. At first we thought that piloerection or pupillary dilatation predicted the efficacy of a seizure, but these signs were difficult to assess and were never subjected to controlled experiments.

The duration of the motor seizure was examined next, and in evaluations of the seizures in unilateral and bilateral ECT, it seemed reasonable to opine that a minimum of 25 seconds defined a good seizure (Fink and Johnson, 1982). In studies of unilateral and bilateral ECT with threshold and suprathresh-old energy dosing, motor seizure durations were greater than 25 seconds, yet the threshold-unilateral condition yielded ineffective courses of treatment (Sackeim et al., 1993). Indeed, the new experience finds that longer seizures are not necessarily better for determining efficacy (Nobler et al., 1993; Krystal et al., 1995; McCall et al., 1995; Shapira et al., 1996). The occurrence of a prolonged, poorly developed, low-voltage seizure of indeterminate length and poor postictal suppression is a clear call for restimulation at a higher dose, with the expectation of inducing a shorter, better developed and clinically more effective seizure.

The Seizure EEG

Modern brief pulse ECT devices provide the facility to monitor the seizure by an electroencephalogram, an electrocardiogram, and lately, an electromyogram. For a decade it has been feasible to examine the electrographic characteristics of the EEG seizure as well as its duration. The EEG usually develops patterned sequences consisting of high voltage sharp waves and spikes, followed by rhythmic slow waves that end abruptly in a well-defined endpoint. In some treatments, however, spike activity is poorly defined and the slow waves are irregular and not of particularly high voltage. It is also difficult to define the endpoint, with the record showing a waxing and waning period followed by an imprecise termination. Could these patterns be related to treatment efficacy?

One suggestion was that bilaterally induced seizures were characterized by greater midseizure ictal amplitude in the two to five hertz frequency band than those induced by unilateral ECT (Krystal et al., 1993). Moreover, the seizures in bilateral ECT showed greater interhemispheric symmetry (coherence) during the seizure and more pronounced suppression (flattening) of EEG frequencies in the immediate postictal period. In other words, bilaterally induced seizures were more intense and more widely distributed throughout both hemispheres than seizures induced with unilateral stimulation.

The clinical relevance of these observations derives from the frequently reported therapeutic advantage of bilateral over unilateral ECT in the relief of depression (Abrams, 1986; Sackeim et al., 1993). The apparent validity of these observations led others to specifically examine the clinical predictive value of the described EEG patterns.

The EEG data of Nobler et al. (1993) came from studies of patients receiving either unilateral or bilateral ECT and energy stimulation either at threshold or two and one-half times threshold (Sackeim et al., 1993; 1996). The patients who received threshold unilateral ECT fared poorly compared to those who received bilateral ECT. Regardless of the electrode placement, however, those patients who exhibited greater midictal EEG slow-wave amplitude and greater postictal EEG suppression experienced greater clinical improvement and relief of depression (Nobler et al., 1993), confirming the observations by Krystal et al. (1993). Greater immediate post-stimulus and midictal EEG spectral amplitudes, greater immediate post-stimulus interhemispheric coherence and greater postictal suppression were reported with higher dose stimuli (two and one-half times threshold) compared to barely suprathreshold stimuli (Krystal et al., 1995). In another study, clinical improvement in depression correlated best with evidence for an immediate postictal reduction both in EEG amplitude and coherence (Krystal et al., 1996).

These analyses of the seizure EEG show promise of defining a clinically effective seizure. The available brief pulse ECT devices allow visual examination of the seizure record so that we can estimate the presence and duration of spike activity and the development of rhythmic high voltage slow wave activity, measure the duration of total seizure activity, and evaluate the endpoint of the fit (precise or imprecise).

In recent research studies, the methods of EEG analysis have been complex. Investigators often use sophisticated multichannel instrumentation recorders and EEG-analytic
computer systems that are not usually available in clinical settings, but their elegant findings
are consistent with the visual observations of the records provided by clinical ECT devices.

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