How Much Does the Reduced EEG Montage Matter for Seizure Detection?: A Large-Cohort Simulation Study.

Importance: Implantable sub-scalp EEG systems with a small number of channels have emerged as promising solutions for long-term seizure monitoring in patients with epilepsy. How seizure detection performance varies by montage configuration is unknown. Objective: To quantify how automated seizure detection performance differs between full and reduced montages, and how these differences vary by epilepsy characteristics. Design: Retrospective cross-sectional study. Setting: Single-center at the Hospital of the University of Pennsylvania Epilepsy Monitoring Unit (EMU). Participants: EEG data from 2281 consecutive EMU admissions between January 2017 and December 2024 were screened. Admissions with at least one annotated seizure and one interictal clip ≥20 minutes from any seizure were included. Exposure: Computational simulation of published sub-scalp device montages using standard 10-20 EEG channels. Main Outcomes and Measures: The primary outcome was event-based F1 scores evaluated for three published seizure detectors-a one-class support vector machine (SVM), a convolutional neural network (SPaRCNet), and a long short-term memory autoregressive model (NDD)-across montages. Results: A total of 466 admissions from 436 patients (mean [SD] age, 39.0 [14.4] years; 54.4% female) met inclusion criteria, comprising 1683 seizures and 1527 interictal clips. SPaRCNet achieved the highest performance (mean [SD] F1, 0.61 [0.30]), followed by NDD (0.56 [0.28]) and SVM (0.39 [0.25]). Performance decreased by at most 0.09 with reduced montages, depending on detectors. Patient factors accounted for the largest proportion of performance variance (29.2%), followed by detector choice (10.3%). Montage effects were minimal (0.4%), despite variation in optimal montage across detectors. Reduced-montage performance correlated moderately to highly with full-montage performance (ρ=0.29-0.73), suggesting full-montage performance could help identify patients suitable for sub-scalp devices. Missed seizures were associated with lower amplitude and bandpowers than detected seizures, though they remained distinguishable from interictal data. Conclusions and Relevance: Automated seizure detection achieved comparable accuracy, with only modest reductions, under simulated reduced montages. Performance differences were driven primarily by detector- and patient-level factors rather than montage. These findings support the feasibility of accurately detecting seizures with published sub-scalp devices and highlight the need for improved algorithms to optimize performance.