Abstracts

Rationale: Digital electroencephalogram (EEG) techniques have developed rapidly in recording, reviewing, and storing EEG. This recent technical advantage now enables us to record, analyze and interpret the EEG data with a wide range of time constant (TC). If long TC is chosen (e.g., 2s), slow activities are emphasized in comparison to the conventional setting. It may be beneficial for detecting slow EEG activities including the after-slow activity of epileptiform discharges (EDs). However, from the clinical and practical view point, there was no systematic analysis in the detection of after-slow activity of EDs among different TC in the digital EEG era. Furthermore, sharp transients (Sts) were anecdotally defined as sharp EEG activity with less after-slow, and thus reflecting little or no epileptic nature, but no study was done to endorse this operational definition in clinical EEG as compared with EDs. Here we try to clarify whether longer TC is useful in the detection of after-slow activity of EDs and consequently useful to differentiate between EDs and Sts, as compared with that of conventional setting of TC. Methods: 46 after-slow activities, preceded by 19 sharp waves (Sws), 5 spikes (Sps) and 22 Sts, were employed from 35 patients with epilepsy (16 men and 19 women; mean age of 39.1 ± 12.8 years, 26 with partial epilepsy and 9 with generalized epilepsy). These activities were retrospectively analyzed about total area size with three different TC, i.e., longer (2s), conventional (0.3s) and shorter (0.1s) conditions. The total area size and total duration of after-slow were also compared between EDs and Sts with TC of 0.3s. Institutional Review Board approved the entire protocol. Results: The EDs showed significantly larger total area size of after-slow than that of Sts with TC 0.3s (p < 0.001) according to their definition. Among 46 after-slow activities, 31 (preceded by 19 Sws, 5 Sps and 7 Sts), 2 (Sts) and 13 (Sts) activities showed the largest total area size with TC of 2s, 0.3s and 0.1s, respectively. The total area size of after-slow of EDs in TC 2s was significantly larger than those in TC 0.1s and 0.3s (p < 0.001). In contrast, there was no significant difference in total area size of after-slow of Sts among three different TC. Regarding comparison of the total duration of after-slow activity between EDs and Sts with TC 0.3s, it was significantly longer in the former than the latter (p < 0.001).  In case of the ambiguous waveform, EEG displayed with TC of 2s clearly delineate EDs than that of 0.3s. Conclusions: These results suggest that longer TC setting is beneficial for differentiation between after-slow activity of EDs and that of Sts. It was caused by the slower frequency of after-slow of the EDs than that of the Sts. These findings may endorse the current operational definition of EDs and Sts. Funding: Training Program of Leaders for Integrated Medical System.