High-amplitude short infraslow activity (SISA) with burst suppression: A potential marker of ictogenicity in critical...

Infraslow activity (ISA) <.1 Hz is supposed to represent epileptogenicity; however, its activity is rarely recorded in clinical practice. Therefore, we have focused on the previously reported short infraslow activity (SISA) with a time constant (TC) of 2 s, always accompanied by burst suppression in acute anoxic encephalopathy (AnE). As the association between SISA and seizures has not been evaluated, this study aimed to elucidate the ictogenicity of SISA.

Electroencephalographies (EEGs) were evaluated in 16 consecutive comatose patients who showed burst suppression in 1155 EEGs at two tertiary emergency care facilities. Eight of these patients had acute AnE (acute AnE group), whereas the remaining patients had metabolic encephalopathy or were sedated for status epilepticus (nonacute AnE group). SISA was defined as a waveform with a duration of >3 s and an amplitude >10 μV with a 2 s TC. The SISA amplitude was compared between patients with and without posthypoxic myoclonus or acute symptomatic seizures.

SISA was observed in all patients. Acute symptomatic seizure or posthypoxic myoclonus occurred in seven of eight patients in the acute AnE group but none in the nonacute AnE group. The SISA amplitude was significantly higher in seven patients with acute symptomatic seizure or posthypoxic myoclonus than in nine without them. Furthermore, high-amplitude SISA (>120 μV) was specific for acute symptomatic seizure or posthypoxic myoclonus occurrence.

High-amplitude SISA accompanied by burst suppression is associated with acute symptomatic seizure or posthypoxic myoclonus and can be an ictogenicity marker in critical care patients.