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RATIONALE: The development of closed-loop devices suitable for use in the treatment of epileptic patients would very likely rely on the adequate development of paradigms able to forecast the occurrence of seizures. In this paper, we studied the usefulness of approximate enthropy, of a non-linear paradigm, in this patient population. METHODS: We applied approximate entropy (ApEn) analysis to study the variability in the complexity of the peri-ictal electrocorticogram (ECoG) of patients with refractory epileptic seizures of the temporal lobe origin. Three patients were implanted with chronic subdural grids. The ApEn algorithm measured the complexity of interictal, peri-ictal and ictal phases. We selected one representative channel disclosing interictal activity for each patient and two channels per patient with ictal recordings. RESULTS: In all patients, we found one channel where the interictal activity registered in the ECoG was associated with high complexity and where ApEn was higher than 0.59. But in the other two channels, for each patient that presented interictal/ictal transitions, clinical manifestations of epileptic seizures occurred around 3.5 seconds after the entropy drop, when entropy was below 0.5. In contrast, when entropy was higher than 0.5, clinical manifestation occurred 9.5 seconds after the entropy drop. The 3.5 seconds shorter delay possibly indicates focal activity in the channel analyzed. CONCLUSIONS: Our results suggest that ApEn may be a useful instrument for early detection of epileptic activity. Its application may be indicated for prevention and diagnosis of epileptic seizures. RACIONAL: O desenvolvimento de aparatos retroalimentáveis para o tratamento de pacientes epilépticos dependerá em grande parte do desenvolvimento adequado de paradigmas que possam antever as crises. Neste trabalho, estudamos a utilidade da entropia aproximada (ApEn), um paradigma não-linear, em pacientes portadores de epilepsia. MÉTODOS: Aplicamos a análise de entropia aproximada (ApEn) no estudo de variabilidade da complexidade do eletrocorticograma (ECoG) de pacientes com epilepsia refratária com origem no lobo temporal. Três pacientes foram implantados com matrizes de eletrodos subdurais. O algoritmo ApEn mediu a complexidade das fases interictal, peri-ictal e ictal. Selecionamos um canal representativo de cada paciente manifestando atividade interictal e dois canais de cada paciente com registro ictal. RESULTADOS: Em cada paciente, encontramos um canal cuja atividade interictal registrada no ECoG foi associada a alta complexidade com ApEn maior que 0.59. Nos outros dois canais, para cada paciente que apresentou transição interictal/ictal, as manifestações clínicas das crises epilépticas ocorreram cerca de 3.5 segundos depois após a queda da entropia abaixo de 0.5. Em comparação, quando a entropia foi maior que 0.5, as manifestações clínicas ocorreram 9,5 segundos após a queda da entropia. A curta latência (3.5 segundos) indicou possivelmente o local de início da atividade focal. CONCLUSÕES: Nossos resultados sugerem que ApEn pode ser um instrumento útil na detecção precoce da atividade epiléptica. Sua aplicação pode estar indicada na prevenção ou diagnóstico das crises epilépticas

journal of epilepsy and clinical neurophysiology

Peri-ictal complexity loss as determined by approximate entropy analysis in the electrocorticogram obtained from chronic subdural recordings in patients with refractory temporal lobe epilepsy