Latencies from intracranial seizure onset to ictal tachycardia: A comparison to surface EEG patterns and other clinical signs

Abstract

Objective: Information on the relative timing of electroencephalography (EEG) seizure onset, ictal tachycardia (ITC), and first other clinical seizure manifestations is crucial for an understanding of the potential benefit of ITC-detection based closed-loop intervention systems for epilepsy treatment. This study analyzes the temporal relation of ITC, other clinical signs, and seizure onset in relation to intracranial and surface EEG.

Methods: Seventy-eight seizures with ITC from 13 patients undergoing invasive EEG recordings with simultaneous recordings of electrocardiography (ECG), intracranial EEG (iEEG) and surface EEG, and video recordings to determine clinical onset were analyzed. Latencies for ITC were calculated for thresholds of 100 bpm and for a 20% heart rate increase above baseline obtained 60 s prior to seizure onset on iEEG. Patient-based, seizure-based, and seizure origin-based analyses were performed.

Results: Mean latencies between seizure onset in invasive EEG and the following onset of ITC in the seizure- and patient-based analysis for both thresholds varied between 21.6 and 23.7 s, showing that ITC is an ictal rather a preictal phenomenon. In 10 of 13 patients and in 56 of 78 seizures, at least one of the thresholds for ITC was crossed before any other clinical sign. In the majority of cases, ITC also preceded ictal onset as determined in surface EEG. Latencies to ictal tachycardia were shorter for hippocampal than for extrahippocampal temporal seizure onset. ITC occurred earlier in right than in left temporal seizures.

Significance: iEEG preceded other seizure manifestations, but ictal tachycardia was an early sign particularly in mesial temporal and in right temporal seizure onset and often preceded not only other clinical manifestations but also first visible patterns in surface EEG. Detection of ictal tachycardia was thus the best noninvasively assessed marker for closed-loop interventions in this multimodally assessed patient group.

Keywords: Clinical onset; Closed-loop stimulation; Epilepsy; Ictal tachycardia; Intracranial EEG; Seizure-onset zone.