Abstracts

Rationale: Generalized Tonic Clonic (GTC) seizures can cause postictal ventilatory changes, such as hypopnea [1]. In a previously published study, the tonic phase duration was found to predict postictal EEG suppression and postictal unresponsiveness [2]. We clinically observed instances of Postictal Hypopnea (PH) and hypothesized that they may also be correlated with the duration of the tonic phase of GTC seizures. Methods: We examined 63 GTC seizures in 58 patients using a retrospective sequential cohort of Video Electroencephalographic (VEEG)-confirmed epilepsy patients in the Hospital of the University of Pennsylvania Epilepsy Monitoring Unit between February 2004 and April 2010. Retrospective review of VEEG data was used to determine the total duration of: the GTC seizures, the tonic phase alone, and PH. Results: Postictal ventilatory status was clear on video for 59/63 seizures (94%). Of these, 18 (31%) demonstrated PH. The mean duration of PH was 7.9 seconds (median=7; range= 2-25 seconds). There was no difference in the average, total seizure duration in patients with or without PH. We found that a prolonged tonic phase was significantly more likely to be followed by a period of PH (p=0.0002), with the duration of the tonic phase averaged 27.3 seconds for the seizures with PH and 14.3 seconds for the seizures without PH.The longer the duration of the tonic phase the more likely it was to end with PH, consistent with an exposure response curve. When the tonic phase lasted less than 20 seconds, 15% of patients had PH; between 20-39 seconds, 55% of patients had PH; and at greater than 40 seconds, 83% of patients had PH. The likelihood of PH in the latter quartile, greater than 40 seconds of tonic phase, was significantly greater when compared to the group with less than 20 seconds of tonic phase (p=0.002). Conclusions: We found that the duration of the tonic phase of GTC seizures predicts the presence of PH. This is consistent with related findings in the existing literature [2]. GTC seizures are postulated to involve the brainstem, which controls respirations. This may be the anatomic localization of the underlying pathophysiological mechanism [3]. Given the focus on possible respiratory etiology for SUDEP, it is possible that measurement of the tonic phase duration could be a useful clinical variable in SUDEP research. We suggest that the next step in confirming these retrospective findings would be a prospective study into PH and unresponsiveness following prolonged tonic phase GTC seizures. References [1] Bateman LM, Spitz M, Seyal M. Ictal hypoventilation contributes to cardiac arrhythmia and SUDEP: report on two deaths in video-EEG-monitored patients. Epilepsia 2010; 51:916-920. [2]Tao JX, Yung I, Lee A, et al. Tonic phase of a generalized convulsive seizure is an independent predictor of postictal generalized EEG suppression. Epilepsia 2013; 54: 858-865. [3] Engel, Jr, Pedley, T.A. Epilepsy: A Comprehensive Textbook. 2nd Ed. Philadelphia: Lippincott Williams & Wilkins, 2008: 515