An evaluation of ambulatory, cassette EEG monitoring: II. Detection of interictal abnormalities.

Although they are clearly useful for generalized ictal events, the ability of ambulatory, cassette EEG systems to detect interictal abnormalities routinely remains in question. The EEGs of 25 patients have been simultaneously monitored by cable telemetry and Oxford Medilog recorder, using a three-channel montage. Output from the cassette recorder amplifiers was of high fidelity compared to cable telemetry, and EEG reproduction from tape suffered only minimal signal degradation. Ambulatory EEG detection rate for interictal abnormalities averaged 85% and was commensurate with the montage design study. Perceptual demand during video scanning, including the recognition of normal transients and artifacts, was addressed as an important limiting factor. Ambulatory EEG monitoring by cassette recorder appears to be a useful intermediate-level screening technique for epileptiform abnormalities, both ictal and interictal.