Abstracts

Rationale: Amplitude-integrated electroencephalography (aEEG) is a tool for continuously monitoring brain function and now widely used in neonatal intensive care units. Background aEEG pattern most-cited nowadays is classified into the following five categories: flat tracing (FT), continuous extremely low voltage (CLV), burst–suppression (BS), discontinuous normal voltage (DNV), and continuous normal voltage (CNV). Here, we report an additional aEEG background pattern seen in infants with hypoxic-ischemic encephalopathy (HIE). Methods: We studied 32 hospitalized infants with HIE treated with therapeutic hypothermia (TH) at Anjo Kosei Hospital between January 2012 and March 2017. Conventional EEG was recorded at bedside using a bipolar montage with at least eight surface electrodes (AF3–C3, C3–O1, AF4–C4, C4–O2, AF3–T3, T3–O1, AF4–T4, and T4–O2) according to the international 10–20 system. This was combined with electrocardiography and respiratory movement assessment using a Nihon Kohden EEG Neurofax (Nihon Kohden, Tokyo, Japan). aEEG was  simultaneously displayed with conventional EEG. We evaluated aEEG patterns according to a classification reported previously by Hellström-Westas. Neurodevelopmental outcome was assessed at 18 months old. Results: Of the 32 infants studied, 5 infants (16%) had a unique aEEG pattern characterized by repetitive, rhythmic wave with elevation of both the lower and upper borders, with maximal amplitude and cyclicity of approximately 30 -50µV and 3-5 minutes. We designated this pattern as “pseudo-sawtooth” (PST) because of its resemblance to the repetitive seizure pattern on aEEG known as saw tooth pattern. However, the raw EEG of PST pattern did not show rhythmic activity nor evolutional change of seizures. Frequency analysis of the PST pattern demonstrated rhythmic burst evolution from 1-3 delta frequency to 6-12 Hz power. Evolution lasted about 40 seconds and its cyclicity was about 3-5 minutes. All 5 infants with the PST pattern later had true seizures within 48 hours after birth, which showed seizure pattern or true saw-tooth pattern on aEEG. The presence of the PST pattern was associated with poorer neurodevelopmental outcome at 18 months old. Conclusions: The PST pattern is a novel aEEG finding seen in infants with HIE. To recognize PST pattern is important for physicians because 1) the pattern is not uncommon, 2) it mimics seizure pattern on aEEG, and 3) it might predict poorer neurodevelopmental outcome. Funding: The study was not supported by any funding.