The Ictal Bradycardia Syndrome: Localization and Lateralization

Abstract

Summary: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.

Clinical cues for detecting ictal asystole

“…Some have suggested ictal bradycardia may have lateralizing value as well. However our analysis of the dynamic EEG/ECG recordings of patients with ictal bradycardia in a previous publication suggested that bitemporal activation was present at bradycardia onset in the majority of patients, providing no clear evidence for the existence of a consistently lateralized cardiac parasympathetic representation in the central autonomic network [3].…”

“…These patients are theorized to have a lower seizure threshold, and the period of hypoxia-ischemia provokes the seizure [1]. Ictal bradycardia occurs most often in the setting of temporal lobe epilepsy, and has only been described during partial seizures [3]. It has been hypothesized that seizures may lead to the stimulation of regions of the brain, such as the insula, cingulate cortex, amygdala, or hypothalamus which regulate cardiac outflow through connection to brainstem and spinal cord nuclei [2].…”

Movement-induced heart rate changes in epileptic and non-epileptic seizures

“…Although sinus tachycardia is by far the most commonly reported autonomic change during seizures 4 , bradycardia and many other types of arrhythmias have been described during focal or generalized epileptic events 6,8,9 . Its mechanisms may include altered baroreflex function, decreased total autonomic variability and relative increase in baseline sympathetic tone, which may further explain the propensity to cardiac arrhythmias and sudden death in epileptic patients 11 .…”

“…Several studies have demonstrated that heart rate (Hr) is usually increased during seizures [1][2][3][4][5][6][7] , but bradycardia 8 and even cardiac asystole 9 can occasionally occur during temporal lobe seizures. opherk et al 7 demonstrated that ictal Hr analysis could aid in differentiating non-convulsive epileptic seizures from non-epileptic events.…”

Combined Neuro-Cardiogenic Epilepsy Syndromes and Novel Mechanistic Insights

“…Importantly, several clinical studies have documented abnormalities of the heart rhythm in SUDEP patients suggesting the possibility of co-existing or even synergistic neuro-cardiogenic mechanisms (Britton et al, 2006;Johnson et al, 2009;Nei et al, 2000;Opherk et al, 2002;Zijlmans et al, 2002). Indeed, sudden death caused by dysrhythmia of the heart (in cardiovascular sciences also referred to as arrhythmia) represents a frequent cause of electrical organ dysfunction in the general population.…”