The ictal bradycardia syndrome: Localization and lateralization

Britton J, Ghearing G, Benarroch E, and Cascino G(2006) The ictal bradycardia syndrome: Localization and lateralization. Epilepsia 47:4 737–44.

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Abstract: PURPOSE: Previous studies have established the importance of the insular cortex and temporal lobe in cardiovascular autonomic modulation. Some investigators, based on the results of cortical stimulation response, functional imaging, EEG recordings of seizures, and lesional studies, have suggested that cardiac sympathetic and parasympathetic function may be lateralized, with sympathetic representation lateralized to the right insula, and parasympathetic, to the left. These studies have suggested that ictal bradycardia is most commonly a manifestation of activation of the left temporal and insular cortex. However, the evidence for this is inconsistent. We sought to assess critically the predictable value of ictal bradycardia for seizure localization and lateralization. METHODS: In this study, we reviewed the localization of seizure activity in 13 consecutive patients with ictal bradycardia diagnosed during prolonged video-EEG monitoring at Mayo Clinic Rochester. The localization of electrographic seizure activity at seizure onset and bradycardia onset was identified in all patients. In addition, we performed a comprehensive review of the ictal bradycardia literature focusing on localization of seizure activity in ictal bradycardia cases. RESULTS: All occurrences of ictal bradycardia in the 13 identified patients were associated with temporal lobe-onset seizures. However, no consistent lateralization of seizure activity was found at onset of seizure activity or at onset of bradycardia in this population. Seizure activity was bilateral at bradycardia onset in nine of 13 patients. The results from the literature review also showed that a predominance of patients had bilateral activity at bradycardia onset; however, more of the ictal bradycardia cases from the literature had left hemispheric localization of seizure onset. CONCLUSIONS: Ictal bradycardia most often occurs in association with bilateral hemispheric seizure activity and is not a consistent lateralizing sign in localizing seizure onset. Our data do not support the existence of a strictly unilateral parasympathetic cardiomotor representation in the left hemisphere, as has been suggested.

Keywords: Partial seizures, Bradycardia, SUDEP, Epilepsy, EEG monitoring

Context

• Combined meta-analysis and original retrospective study, from Mayo Clinic, Minnesota, US, designed to address lateralization of cortical control of autonomic function. In the original study, ictal bradycardia was strongly associated with temporal lobe seizures but no clear link with either hemisphere was evident for onset either of seizure or of bradycardia. The analysis of previous studies showed bilateral seizure activity at the time of bradycardia onset in about half of the cases, with the other half split between either hemisphere. Literature review showed bradycardia-linked seizures began in the left hemisphere roughly 60% of the time. Bradycardia was defined as an R-R interval greater than 2 s. Delay to onset of bradycardia ranged from 10 to > 100 s, with average approximately 20 s. Bradycardia was often seen in bilateral seizures. The authors conclude that their study does not support evidence of lateralization effects in ictal bradycardia as reported in Oppenheimer et al. They refer to Epstein et al. as one of several studies that failed to find a link of altered temporal lobe function and bradycardia.

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