Infralow Activity on Intracranial EEG: A Systematic Review: Characteristics, Recording Methods and Predictive Value...

ObjectivesWe aimed to clarify the occurrence pattern of icDCs (ictal direct-current shifts), its recording parameters, polarity, and amplitude and to elucidate whether icDCs correlated with histology and the resection of the core area of icDCs is associated with favorable outcomes. Methods We carried out a systematic review according to the PRISMA statement. We searched for studies describing intracranial direct current shift, intracranial slow potential shift (SPS), or intracranial infralow activity AND surgical outcome. Results There is a marked heterogenicity in the recording parameters of icDCs, and in the method of intracranial evaluation (SEEG, subdural electrodes or both); icDCs can be obtained in more than 90% of patients with epilepsy evaluated with intracranial electrodes and in more than 90% of the seizures; icDCs is an electrical phenomenon with very high amplitude, with positive or negative polarity and prolonged duration, seen before or during seizure onset; IcDCs are best recorded with a time constant of 10 s, and setting LFF at 0.01 to 0.016 Hz and variable HFF; it seems preferable to evaluate them with an epoch of 300 s. IcDCs are not specific to any subjacent pathology. icDCs increases the probability of being seizure-free by 30.5. Conclusion Infralow activity can be assessed during intracranial recording with sEEG or subdural electrodes. Infralow activity is a prolonged baseline shift, with a very high amplitude appearing before or with the seizure onset. This might not be related to the subjacent pathology, but it helps delineate the zone to remove.