Postictal generalized EEG suppression is not associated with periictal cardiac autonomic instability in people with convulsive seizures

Characteristics of deceased subjects transported to a postmortem imaging center due to unusual death related to epilepsy

OBJECTIVE

Patients with epilepsy have high risk of experiencing uncommon causes of death. This study aimed to evaluate patients who underwent unusual deaths related to epilepsy and identify factors that may contribute to these deaths and may also include sudden unexpected death in epilepsy (SUDEP).

METHODS

We analyzed 5291 cases in which a postmortem imaging (PMI) study was performed using plane CT, because of an unexplained death. A rapid troponin T assay was performed using peripheral blood samples. Clinical information including the cause of death suspected by the attending physician, body position, place of death, medical history, and antiseizure medications was evaluated.

RESULTS

A total of 132 (2.6%) patients had an obvious history of epilepsy, while 5159 individuals had no history of epilepsy (97.4%). Cerebrovascular disease was the cause of death in 1.6% of patients in the group with epilepsy, and this was significantly lower than that in the non-epilepsy group. However, drowning was significantly higher (9.1% vs. 4.4%). Unspecified cause of death was significantly more frequent in the epilepsy group (78.0% vs. 57.8%). Furthermore, the proportion of patients who demonstrated elevation of troponin T levels without prior cardiac disease was significantly higher in the epilepsy group (37.9% vs. 31.1%). At discovery of death, prone position was dominant (30.3%), with deaths occurring most commonly in the bedroom (49.2%). No antiseizure medication had been prescribed in 12% of cases, while 29.5% of patients were taking multiple antiseizure medications.

SIGNIFICANCE

The prevalence of epilepsy in individuals experiencing unusual death was higher than in the general population. Despite PMI studies, no definitive cause of death was identified in a significant proportion of cases. The high troponin T levels may be explained by long intervals between death and examination or by higher incidence of myocardial damage at the time of death.

PLAIN LANGUAGE SUMMARY

This study investigated unusual deaths in epilepsy patients, analyzing 5291 postmortem imaging cases. The results showed that 132 cases (2.6%) had a clear history of epilepsy. In these cases, only 22% cases were explained after postmortem examination, which is less than in non-epilepsy group (42.2%). Cerebrovascular disease was less common in the epilepsy group, while drowning was more common. Elevated troponin T levels, which suggest possibility of myocardial damage or long intervals between death and examination, were also more frequent in the epilepsy group compared to non-epilepsy group.

Impaired post-sleep apnea autonomic arousals in patients with drug-resistant epilepsy

OBJECTIVE

Sudden and unexpected deaths in epilepsy (SUDEP) pathophysiology may involve an interaction between respiratory dysfunction and sleep/wake state regulation. We investigated whether patients with epilepsy exhibit impaired sleep apnea-related arousals.

METHODS

Patients with drug-resistant (N = 20) or drug-sensitive (N = 20) epilepsy and obstructive sleep apnea, as well as patients with sleep apnea but without epilepsy (controls, N = 20) were included. We explored (1) the respiratory arousal threshold based on nadir oxygen saturation, apnea-hypopnea index, and fraction of hypopnea among respiratory events; (2) the cardiac autonomic response to apnea/hypopnea quantified as percentages of changes from the baseline in RR intervals (RRI), high (HF) and low (LF) frequency powers, and LF/HF.

RESULTS

The respiratory arousal threshold did not differ between groups. At arousal onset, RRI decreased (-9.42%) and LF power (179%) and LF/HF ratio (190%) increased. This was followed by an increase in HF power (118%), p < 0.05. The RRI decrease was lower in drug-resistant (-7.40%) than in drug-sensitive patients (-9.94%) and controls (-10.91%), p < 0.05. LF and HF power increases were higher in drug-resistant (188%/126%) than in drug-sensitive patients (172%/126%) and controls (177%/115%), p < 0.05.

CONCLUSIONS

Cardiac reactivity following sleep apnea is impaired in drug-resistant epilepsy.

SIGNIFICANCE

This autonomic dysfunction might contribute to SUDEP pathophysiology.

Association between postictal EEG suppression, postictal autonomic dysfunction, and sudden unexpected death in epilepsy: Evidence from intracranial EEG

OBJECTIVE

The association between postictal electroencephalogram (EEG) suppression (PES), autonomic dysfunction, and Sudden Unexpected Death in Epilepsy (SUDEP) remains poorly understood. We compared PES on simultaneous intracranial and scalp-EEG and evaluated the association of PES with postictal heart rate variability (HRV) and SUDEP outcome.

METHODS

Convulsive seizures were analyzed in patients with drug-resistant epilepsy at 5 centers. Intracranial PES was quantified using the Hilbert transform. HRV was quantified using root mean square of successive differences of interbeat intervals, low-frequency to high-frequency power ratio, and RR-intervals.

RESULTS

There were 64 seizures from 63 patients without SUDEP and 11 seizures from 6 SUDEP patients. PES occurred in 99% and 87% of seizures on intracranial-EEG and scalp-EEG, respectively. Mean PES duration in intracranial and scalp-EEG was similar. Intracranial PES was regional (<90% of channels) in 46% of seizures; scalp PES was generalized in all seizures. Generalized PES showed greater decrease in postictal parasympathetic activity than regional PES. PES duration and extent were similar between patients with and without SUDEP.

CONCLUSIONS

Regional intracranial PES can be present despite scalp-EEG demonstrating generalized or no PES. Postictal autonomic dysfunction correlates with the extent of PES.

SIGNIFICANCE

Intracranial-EEG demonstrates changes in autonomic regulatory networks not seen on scalp-EEG.

Automated Analysis of Risk Factors for Postictal Generalized EEG Suppression

Rationale: Currently, there is some ambiguity over the role of postictal generalized electro-encephalographic suppression (PGES) as a biomarker in sudden unexpected death in epilepsy (SUDEP). Visual analysis of PGES, known to be subjective, may account for this. In this study, we set out to perform an analysis of PGES presence and duration using a validated signal processing tool, specifically to examine the association between PGES and seizure features previously reported to be associated with visually analyzed PGES.

Methods: This is a prospective, multicenter epilepsy monitoring study of autonomic and breathing biomarkers of SUDEP in adult patients with intractable epilepsy. We studied videoelectroencephalogram (vEEG) recordings of generalized convulsive seizures (GCS) in a cohort of patients in whom respiratory and vEEG recording were carried out during the evaluation in the epilepsy monitoring unit. A validated automated EEG suppression detection tool was used to determine presence and duration of PGES.

Results: We studied 148 GCS in 87 patients. PGES occurred in 106/148 (71.6%) seizures in 70/87 (80.5%) of patients. PGES mean duration was 38.7 ± 23.7 (37; 1–169) seconds. Presence of tonic phase during GCS, including decerebration, decortication and hemi-decerebration, were 8.29 (CI 2.6–26.39, p = 0.0003), 7.17 (CI 1.29–39.76, p = 0.02), and 4.77 (CI 1.25–18.20, p = 0.02) times more likely to have PGES, respectively. In addition, presence of decerebration (p = 0.004) and decortication (p = 0.02), older age (p = 0.009), and hypoxemia duration (p = 0.03) were associated with longer PGES durations.

Conclusions: In this study, we confirmed observations made with visual analysis, that presence of tonic phase during GCS, longer hypoxemia, and older age are reliably associated with PGES. We found that of the different types of tonic phase posturing, decerebration has the strongest association with PGES, followed by decortication, followed by hemi-decerebration. This suggests that these factors are likely indicative of seizure severity and may or may not be associated with SUDEP. An automated signal processing tool enables objective metrics, and may resolve apparent ambiguities in the role of PGES in SUDEP and seizure severity studies.

Bidirectional relationships of sleep and epilepsy in adults with epilepsy

This targeted review addresses the best accepted and most intriguing recent observations on the complex relationships between sleep and epilepsy. Ten to 15% of all epilepsies are sleep-related. Included in these is sleep-related hypermotor epilepsy, renamed from nocturnal frontal lobe epilepsy by a 2016 consensus conference since 30% of cases are extra-frontal, seizures are related to sleep rather than clock time, and the predominant semiology is hypermotor. Stereo-EEG is providing crucial insights into network activation in sleep-related epilepsies and definition of the epileptogenic zone. Pathologic high-frequency oscillations, a promising biomarker for identifying the epileptogenic zone, are most frequent in NREM sleep, lowest in wakefulness and REM sleep, similar to interictal epileptiform discharges (IEDs). Most sleep-related seizures are followed by awakening or arousal and IEDs cause arousals and increase after arousals, likely contributing to sleep/wake complaints. Sleep/wake disorders are 2-3 times more common in adults with epilepsy than the general population; these comorbidities are associated with poorer quality of life and may impact seizure control. Treatment of sleep apnea reduces seizures in many cases. An emerging area of research is in circadian biology and epilepsy. Over 90% of people with epilepsy have seizures with circadian periodicity, in part related to sleep itself, and the majority of SUDEP cases occur in sleep. Recognizing these bidirectional relationships is important for patient and caregiver education and counseling and optimizing epilepsy outcomes.

Cardiorespiratory and autonomic function in epileptic seizures: A video-EEG monitoring study

PURPOSE

Seizure-induced cardiorespiratory and autonomic dysfunction has long been recognized, and growing evidence points to its implication in sudden unexpected death in epilepsy (SUDEP). However, a comprehensive understanding of cardiorespiratory function in the preictal, ictal, and postictal periods are lacking.

METHODS

We examined continuous cardiorespiratory and autonomic function in 157 seizures (18 convulsive and 139 nonconvulsive) from 70 consecutive patients who had a seizure captured on concurrent video-encephalogram (EEG) monitoring and polysomnography between February 1, 2012 and May 31, 2017. Heart and respiratory rates, heart rate variability (HRV), and oxygen saturation were assessed across four distinct periods: baseline (120 s), preictal (60 s), ictal, and postictal (300 s). Heart and respiratory rates were further followed for up to 60 min after seizure termination to assess return to baseline.

RESULTS

Ictal tachycardia occurred during both convulsive and nonconvulsive seizures, but the maximum rate was higher for convulsive seizures (mean: 138.8 beats/min, 95% confidence interval (CI): 125.3-152.4) compared with nonconvulsive seizures (mean: 105.4 beats/min, 95% CI: 101.2-109.6; p < 0.001). Convulsive seizures were associated with a lower ictal minimum respiratory rate (mean: 0 breaths/min, 95% CI: 0-0) compared with nonconvulsive seizures (mean: 11.0 breaths/min, 95% CI: 9.5-12.6; p < 0.001). Ictal obstructive apnea was associated with convulsive compared with nonconvulsive seizures. The low-frequency (LF) power band of ictal HRV was higher among convulsive seizures than nonconvulsive seizures (ratio of means (ROM): 2.97, 95% CI: 1.34-6.60; p = 0.008). Postictal tachycardia was substantially prolonged, characterized by a longer return to baseline for convulsive seizures (median: 60.0 min, interquartile range (IQR): 46.5-60.0) than nonconvulsive seizures (median: 0.26 min, IQR: 0.008-0.9; p < 0.001). For postictal hyperventilation, the return to baseline was longer in convulsive seizures (median: 25.3 min, IQR: 8.1-60) than nonconvulsive seizures (median: 1.0 min, IQR: 0.07-3.2; p < 0.001). The LF power band of postictal HRV was lower in convulsive seizures than nonconvulsive seizures (ROM: 0.33, 95% CI: 0.11-0.96; p = 0.043). Convulsive seizures with postictal generalized EEG suppression (PGES; n = 12) were associated with lower postictal heart and respiratory rate, and increased HRV, compared with those without (n = 6).

CONCLUSIONS

Profound cardiorespiratory and autonomic dysfunction associated with convulsive seizures may explain why these seizures carry the greatest risk of SUDEP.

Peri-ictal heart rate variability parameters as surrogate markers of seizure severity

This study aims at defining objective parameters reflecting the severity of peri-ictal autonomic changes and their relation to post-ictal generalized electroencephalography (EEG) suppression (PGES), with the view that such changes could be detected by wearable seizure detection systems and prove useful to assess the risk of sudden unexpected death in epilepsy (SUDEP). To this purpose, we assessed peri-ictal changes in heart rate variability (HRV) and correlated them with seizure duration, intensity of electromyography-based ictal muscle activity, and presence and duration of post-ictal generalized EEG suppression (PGES). We evaluated 75 motor seizures from 40 patients, including 61 generalized tonic-clonic seizures (GTCS) and 14 other major motor seizure types. For all major motor seizures, HRV measurements demonstrated a significantly decreased parasympathetic activity and increased sympathetic activity in the post-ictal period. The post-ictal increased sympathetic activity was significantly higher for GTCS as compared with non-GTCS. The degree of peri-ictal decreased parasympathetic activity and increased sympathetic activity was associated with longer PGES (>20 s), longer seizure duration, and greater intensity of ictal muscle activity. Mean post-ictal heart rate (HR) was an independent predictor of PGES duration, seizure duration, and intensity of ictal muscle contraction. Our results indicate that peri-ictal changes in HRV are potential biomarkers of major motor seizure severity.

Periictal electroclinical characteristics of postictal generalized electroencephalographic suppression after generalized convulsive seizures

The aim of this study was to investigate the demographic, clinical, and electrophysiological characteristics of postictal generalized electroencephalography (EEG) suppression (PGES), thereby facilitating the recognition of PGES and providing clues regarding its risk factors, pathophysiology, and relationship with sudden unexpected death in epilepsy patients (SUDEP).We retrospectively reviewed 237 generalized convulsive seizures (GCSs) in 126 patients during long-term video-EEG (VEEG) recordings. The associations of PGES and prolonged PGES (duration >20 seconds) with person- and seizure-specific variables were evaluated independently using SPSS software.Eighty patients (63.5%, 80/126) exhibited PGES after 127 GCSs (53.6%, 127/237) with an average PGES duration of 41.31 ± 24.03 seconds. The tonic phase was significantly prolonged in patients with PGES and prolonged PGES. PGES was independently associated with ictal semiology, which was attributable to the different proportions of GCS type 1. After seizure termination, patients with PGES had a higher percentage of postictal unresponsiveness and immobility, including oropharyngeal immobility. Between prolonged and short-duration PGES, the former was more likely to phase out gradually followed by immediate body movement, whereas the latter tended to have an abrupt, evoked termination followed by delayed body movement.Prolonged tonic duration, GCS type 1, postictal unresponsiveness, and immobility were more prone to occur with PGES, which might imply that hyperactivation of inhibitory neural networks underlies the pathophysiology of PGES and subsequent SUDEP. Any form of periictal bedside care, whether it constitutes effective medical intervention or not, is advisable due to its possible contribution to the interruption of PGES. Regardless of the PGES termination pattern, the neural network resuscitation process was progressive.

Serotonin and sudden unexpected death in epilepsy

Epilepsy is a highly prevalent disease characterized by recurrent, spontaneous seizures. Approximately one-third of epilepsy patients will not achieve seizure freedom with medical management and become refractory to conventional treatments. These patients are at greatest risk for sudden unexpected death in epilepsy (SUDEP). The exact etiology of SUDEP is unknown, but a combination of respiratory, cardiac, neuronal electrographic dysfunction, and arousal impairment is thought to underlie SUDEP. Serotonin (5-HT) is involved in regulation of breathing, sleep/wake states, arousal, and seizure modulation and has been implicated in the pathophysiology of SUDEP. This review explores the current state of understanding of the relationship between 5-HT, epilepsy, and respiratory and autonomic control processes relevant to SUDEP in epilepsy patients and in animal models.

Dead in the Night: Sleep-Wake and Time-Of-Day Influences on Sudden Unexpected Death in Epilepsy

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related death in patients with refractory epilepsy. Convergent lines of evidence suggest that SUDEP occurs due to seizure induced perturbation of respiratory, cardiac, and electrocerebral function as well as potential predisposing factors. It is consistently observed that SUDEP happens more during the night and the early hours of the morning. The aim of this review is to discuss evidence from patient cases, clinical studies, and animal research which is pertinent to the nocturnality of SUDEP. There are a number of factors which might contribute to the nighttime predilection of SUDEP. These factors fall into four categories: influences of (1) being unwitnessed, (2) lying prone in bed, (3) sleep-wake state, and (4) circadian rhythms. During the night, seizures are more likely to be unwitnessed; therefore, it is less likely that another person would be able to administer a lifesaving intervention. Patients are more likely to be prone on a bed following a nocturnal seizure. Being prone in the accouterments of a bed during the postictal period might impair breathing and increase SUDEP risk. Sleep typically happens at night and seizures which emerge from sleep might be more dangerous. Lastly, there are circadian changes to physiology during the night which might facilitate SUDEP. These possible explanations for the nocturnality of SUDEP are not mutually exclusive. The increased rate of SUDEP during the night is likely multifactorial involving both situational factors, such as being without a witness and prone, and physiological changes due to the influence of sleep and circadian rhythms. Understanding the causal elements in the nocturnality of SUDEP may be critical to the development of effective preventive countermeasures.

Heart rate variability measurement in epilepsy: How can we move from research to clinical practice?

Our objective was to critically evaluate the literature surrounding heart rate variability (HRV) in people with epilepsy and to make recommendations as to how future research could be directed to facilitate and accelerate integration into clinical practice. We reviewed relevant HRV publications including those involving human subjects with seizures. HRV has been studied in patients with epilepsy for more than 30 years and, overall, patients with epilepsy display altered interictal HRV, suggesting a shift in autonomic balance toward sympathetic dominance. This derangement appears more severe in those with temporal lobe epilepsy and drug-resistant epilepsy. Normal diurnal variation in HRV is also disturbed in at least some people with epilepsy, but this aspect has received less study. Some therapeutic interventions, including vagus nerve stimulation and antiepileptic medications, may partially normalize altered HRV, but studies in this area are sometimes contradictory. During seizures, the changes in HRV may be complex, but the general trend is toward a further increase in sympathetic overactivity. Research in HRV in people with epilepsy has been limited by inconsistent experimental protocols and studies that are often underpowered. HRV measurement has the potential to aid clinical epilepsy management in several possible ways. HRV may be useful in predicting which patients are likely to benefit from surgical interventions such as vagus nerve stimulation and focal cerebral resection. As well, HRV could eventually have utility as a biomarker of risk for sudden unexpected death in epilepsy (SUDEP). However, at present, the inconsistent measurement protocols used in research are hindering translation into clinical practice. A minimum protocol for HRV evaluation, to be used in all studies involving epilepsy patients, is necessary to eventually allow HRV to become a useful tool for clinicians. We propose a straightforward protocol, involving 5-minute measurements of root mean square of successive differences in wakefulness and light sleep.

Sudden unexpected death in epilepsy: ongoing challenges in finding mechanisms and prevention

Purpose/aim of the study: To summarize recent studies on the pathophysiology and preventive strategies for SUDEP. Materials and methods: Databases and literature review. Results: Patients with epilepsy have a significantly higher risk of death than the general population. Sudden unexpected death in epilepsy (SUDEP) is the leading cause of sudden death among patients with epilepsy. Despite on-going research, there are still deficits in our knowledge about the mechanisms, genetic factors, and prevention of SUDEP. Current evidence suggests that cardiac arrhythmias, respiratory dysfunction, and brainstem arousal system dysfunction are the major mechanisms of SUDEP, and animal models support the role of neurotransmitters, especially serotonin and adenosine, in pathophysiology of SUDEP. Several mutations in the neurocardiogenic channelopathy genes have been identified as a possible cause of epilepsy and increased SUDEP risk. The lack of awareness that SUDEP can be a potential cause of premature death has been found in several surveys. In addition, medical legal cases demonstrate the need for more education about this condition. Several preventive strategies to reduce SUDEP have been proposed, including effective seizure control, nocturnal supervision, seizure monitoring, devices to protect the airway, and selective serotonin reuptake inhibitors. Further research is needed to determine the efficacy of these interventions. Conclusions: The major mechanisms of SUDEP include cardiac arrhythmias, respiratory dysfunction, and brainstem arousal system dysfunction. Effective control of seizures is the only effective strategy to prevent SUDEP. Other preventive interventions require more research.

Differentiating motor phenomena in tilt-induced syncope and convulsive seizures

Objective

We assessed motor phenomena in syncope and convulsive seizures to aid differential diagnosis and understand the pathophysiologic correlates.

Methods

We studied video-EEG recordings of tilt-induced syncope and convulsive seizures in participants aged 15 years and older. Syncope was defined as (1) loss of consciousness (video-assessed), (2) circulatory changes (accelerating blood pressure decrease with or without bradycardia/asystole), and (3) EEG changes (“slow” or “slow-flat-slow”). We assessed myoclonic jerks and tonic postures of the arms and noted time of occurrence, laterality, synchrony, and rhythmicity (mean consecutive differences of interclonic intervals).

Results

Video-EEG records of 65 syncope cases and 50 convulsive seizures were included. In syncope, postures occurred in 42 cases (65%) and jerks in 33 (51%). Fewer jerks occurred in syncope (median 2, range 1–19) compared to convulsive seizures (median 48, range 20–191; p < 0.001). Jerks were more rhythmic in seizures compared to syncope (p < 0.001). Atonia was seen in all syncope cases, while this was not observed in any seizure. Jerks predominantly occurred during the slow and postures during the flat EEG phase.

Conclusions

Jerks and tonic postures were common in syncope, but semiology differed from convulsive seizures. The lack of overlap in the number of jerks suggests that less than 10 indicates syncope and more than 20 a convulsive seizure: the “10/20 rule.” Loss of tone strongly favors syncope. The EEG correlates imply that jerks in syncope are likely of cortical origin, whereas tonic postures may result from brainstem disinhibition.

Association of sleep with sudden unexpected death in epilepsy

OBJECTIVE

The objective of this study was to determine the association of sleep with sudden unexpected death in epilepsy (SUDEP).

METHODS

We conducted a systematic review and meta-analysis based on literature search from databases PubMed, Web of Science, and Scopus using keywords "SUDEP", or "sudden unexpected death in epilepsy", or "sudden unexplained death in epilepsy". Sudden unexpected death in epilepsy was considered to occur during sleep if the patient was found in bed, if the SUDEP cases were documented as in sleep, or if the patient was found at bedside on the bedroom floor.

RESULTS

Circadian pattern was documented in 880 of the 1025 SUDEP cases in 67 studies meeting the inclusion and exclusion criteria. Of the 880 SUDEP cases, 69.3% occurred during sleep and 30.7% occurred during wakefulness. Sudden unexpected death in epilepsy was significantly associated with sleep as compared to wakefulness (P<0.001). In the subgroup of 272 cases in which circadian pattern and age were documented, patients 40years old or younger were more likely to die in sleep than those older than 40years (OR: 2.0; 95% CI=1.0, 3.8; P=0.05). In the subgroup of 114 cases in which both circadian pattern and body position at the time of death were documented, 87.6% (95% CI=81.1%, 94.2%) of patients who died during sleep were in the prone position, whereas 52.9% (95% CI=24.7%, 81.1%) of patients who died during wakefulness were in the prone position. Patients with nocturnal seizures were 6.3 times more likely to die in a prone position than those with diurnal seizures (OR: 6.3; 95% CI=2.0, 19.5; P=0.002).

CONCLUSIONS

There is a strong association of SUDEP with sleep, suggesting that sleep is a significant risk factor for SUDEP. Although the risks of SUDEP associated with sleep are unknown and likely multifactorial, the prone position might be an important contributory factor.

Dynamics of convulsive seizure termination and postictal generalized EEG suppression

It is not fully understood how seizures terminate and why some seizures are followed by a period of complete brain activity suppression, postictal generalized EEG suppression. This is clinically relevant as there is a potential association between postictal generalized EEG suppression, cardiorespiratory arrest and sudden death following a seizure. We combined human encephalographic seizure data with data of a computational model of seizures to elucidate the neuronal network dynamics underlying seizure termination and the postictal generalized EEG suppression state. A multi-unit computational neural mass model of epileptic seizure termination and postictal recovery was developed. The model provided three predictions that were validated in EEG recordings of 48 convulsive seizures from 48 subjects with refractory focal epilepsy (20 females, age range 15-61 years). The duration of ictal and postictal generalized EEG suppression periods in human EEG followed a gamma probability distribution indicative of a deterministic process (shape parameter 2.6 and 1.5, respectively) as predicted by the model. In the model and in humans, the time between two clonic bursts increased exponentially from the start of the clonic phase of the seizure. The terminal interclonic interval, calculated using the projected terminal value of the log-linear fit of the clonic frequency decrease was correlated with the presence and duration of postictal suppression. The projected terminal interclonic interval explained 41% of the variation in postictal generalized EEG suppression duration (P < 0.02). Conversely, postictal generalized EEG suppression duration explained 34% of the variation in the last interclonic interval duration. Our findings suggest that postictal generalized EEG suppression is a separate brain state and that seizure termination is a plastic and autonomous process, reflected in increased duration of interclonic intervals that determine the duration of postictal generalized EEG suppression.

Automated Video Detection of Epileptic Convulsion Slowing as a Precursor for Post-Seizure Neuronal Collapse

Automated monitoring and alerting for adverse events in people with epilepsy can provide higher security and quality of life for those who suffer from this debilitating condition. Recently, we found a relation between clonic slowing at the end of a convulsive seizure (CS) and the occurrence and duration of a subsequent period of postictal generalized EEG suppression (PGES). Prolonged periods of PGES can be predicted by the amount of progressive increase of interclonic intervals (ICIs) during the seizure. The purpose of the present study is to develop an automated, remote video sensing-based algorithm for real-time detection of significant clonic slowing that can be used to alert for PGES. This may help preventing sudden unexpected death in epilepsy (SUDEP). The technique is based on our previously published optical flow video sequence processing paradigm that was applied for automated detection of major motor seizures. Here, we introduce an integral Radon-like transformation on the time–frequency wavelet spectrum to detect log–linear frequency changes during the seizure. We validate the automated detection and quantification of the ICI increase by comparison to the results from manually processed electroencephalography (EEG) traces as “gold standard”. We studied 48 cases of convulsive seizures for which synchronized EEG-video recordings were available. In most cases, the spectral ridges obtained from Gabor-wavelet transformations of the optical flow group velocities were in close proximity to the ICI traces detected manually from EEG data during the seizure. The quantification of the slowing-down effect measured by the dominant angle in the Radon transformed spectrum was significantly correlated with the exponential ICI increase factors obtained from manual detection. If this effect is validated as a reliable precursor of PGES periods that lead to or increase the probability of SUDEP, the proposed method would provide an efficient alerting device.

Local brain activity persists during apparently generalized postictal EEG suppression

OBJECTIVES

Postictal generalized EEG suppression (PGES) frequently occurs after generalized convulsive seizures (GCS) and may be involved in the pathophysiology of sudden unexpected death in epilepsy (SUDEP). It is usually determined using conventional scalp EEG which is likely to miss cerebral activity in deeper brain structures. Here, we examined intracranial EEG activity after GCS to unravel the pattern and extent of local brain activity during apparent PGES on scalp EEG (s-PGES).

METHODS

We retrospectively reviewed electroencephalographic data of people with chronic epilepsy who had GCS during presurgical video-EEG monitoring using simultaneous intracranial and scalp EEG (10-20 system) electrodes.

RESULTS

Twenty-five GCS (20 with s-PGES) of 15 patients with an average number of 88±42 intracranial electrode contacts were included. The majority of GCS with s-PGES (18 of 20) displayed persisting or reemerging intracranial EEG activity during apparent PGES on scalp EEG. Three patterns were identified: Pattern 1 (11 GCS, 6 patients) consisted of continuous local interictal activity; Pattern 2 (5 GCS, 5 patients) displayed suppressed EEG activity at all intracranial contacts in the early phase of s-PGES, but reemerging local brain activity before s-PGES dissolved; and Pattern 3 (2 GCS, 2 patients) showed persistent local ictal activity during s-PGES. Persisting intracranial EEG activity at PGES onset on scalp EEG was present in 10±14% (range: 0 to 42%) of all intracranial contacts and mostly in the temporal lobe.

CONCLUSIONS

Our results reveal that, during apparently generalized postictal EEG suppression, local brain activity persists or reemerges in most GCS. Possible implications of this localized neuronal activity in the context of SUDEP are discussed in the paper.

Prone sleeping and SUDEP risk: The dynamics of body positions in nonfatal convulsive seizures

BACKGROUND

Most victims of sudden unexpected death in epilepsy (SUDEP) are found prone with signs suggestive of an unwitnessed convulsive seizure (CS). Prone sleeping has been proposed as a risk factor for SUDEP. Little is known, however, about the change of body position during the course of CSs.

METHODS

We retrospectively reviewed video-EEG data and assessed body positions during the course of CSs, until there was a physical interaction by nursing staff with the subject.

RESULTS

We identified 180 CSs in 90 individuals. In 16 of the 180 CSs (9%), the subject started in or turned to the prone position. Of the seven CSs that started in the prone position, three turned to a lateral position during the CS. In 13 CSs, the subject was in prone position at time of nursing intervention; nine (69%) of these started in a nonprone position.

DISCUSSION

Our data suggest that the prone position occurs infrequently in closely supervised nonfatal CSs, a notable contrast to the number of victims of SUDEP found prone. Whether prone sleeping prior to CSs increases SUDEP risk, however, remains speculative, as body position during the course of a CS appeared to be dynamic.

Postictal immobility and generalized EEG suppression are associated with the severity of respiratory dysfunction

OBJECTIVE

The pathophysiology of sudden unexpected death in epilepsy (SUDEP) remains undetermined. Seizures are accompanied by respiratory dysfunction (RD). Postictal generalized electroencephalography (EEG) suppression (PGES) may follow generalized tonic-clonic seizures (GTCS). Following GTCS patients have impaired arousal and may be motionless. Patients with SUDEP are usually prone. Postictal immobility (PI) may contribute to SUDEP by not permitting repositioning of the head to allow unimpeded ventilation. To determine whether RD and/or ictal characteristics are associated with PI, we analyzed patients with GTCS in the epilepsy monitoring unit.

METHOD

We investigated for associations between PI duration and PGES, ictal/postictal oxygen saturation (SpO2 ), end-tidal CO2 (ETCO2 ), seizure localization, duration, and tonic and total convulsive phase duration. We investigated for linkage between PGES and these measures.

RESULTS

Seventy patients with 181 GTCS and available SpO2 and/or ETCO2 data were studied. Simple linear regression analysis by seizures showed that PI duration was associated with peak periictal ETCO2 (p = 0.03), duration of oxygen desaturation (p = 0.005) and with SpO2 nadir (p = 0.02). PI duration was not associated with tonic, convulsive phase or total seizure duration. Analysis by patients also showed significant association of PI with RD. Duration of PI was longer following seizures with PGES (p < 0.001). PGES was not associated with the tonic, convulsive phase or total seizure duration. SpO2 nadir was lower in seizures with PGES (p = 0.046), ETCO2 peak change (p = 0.003) was higher, and duration of ETCO2 elevation (p = 0.03) was longer. Multivariable regression analysis showed that PGES and severe RD were associated with PI duration.

SIGNIFICANCE

The duration of PI and presence of PGES are associated with periictal RD. The duration of PI is also associated with the presence of PGES. Seizure duration or duration of the convulsive phase is not associated with PI or PGES. Interventions aimed at reversing impaired arousal and PI may reduce SUDEP risk.

Postictal generalized EEG suppression and SUDEP: a review

SUMMARY

Sudden unexpected death in epilepsy (SUDEP) remains a leading cause of epilepsy-related death, and yet, its pathogenic mechanisms remain ill-defined. Although epidemiological studies of SUDEP in heterogenous populations have established a number of clinical associations, evaluation and stratification of individual risk remains difficult. Thus, potential markers as predictors of risk of SUDEP are important not only clinically but also for research on SUDEP prevention. Recordings from rare monitored cases of SUDEP demonstrate postictal generalized EEG suppression after terminal seizures, raising expectations that postictal generalized EEG suppression may identify individuals at higher risk. In this review, we consider the literature on postictal generalized EEG suppression and evaluate its relevance and utility as a possible marker of SUDEP.

Mechanisms of sudden unexplained death in epilepsy

PURPOSE OF REVIEW

Human and experimental research has identified cardioautonomic and respiratory dysfunction as a frequent accompaniment in human and animal model events of sudden unexpected death in epilepsy (SUDEP). This review aims to provide an overview of the scientific evidence behind the currently accepted risk factors and working hypotheses regarding SUDEP pathophysiology.

RECENT FINDINGS

Epidemiological analysis of public health burden of SUDEP has shown that it rates second only to stroke in the years of potential life lost. Clinical and experimental studies uncovered the dynamic cardiorespiratory dysfunction interictally and imminently to SUDEP, and model systems have facilitated discoveries in SUDEP mechanistic understanding and application of pilot therapeutic interventions. Pilot molecular profiling of human SUDEP has uncovered complex genomic structure in the candidate gene network.

SUMMARY

Extensive clinical and experimental work has established a rationale for the conceptual thinking about SUDEP mechanisms. The application of the global molecular profiling will be invaluable in unraveling the individually unique genomic complexities and interactions that underlie the physiological signature of each patient. At the same time, sophisticated model systems will be critical in the iterative translation of human genetics, physiology, pharmacological interventions, and in testing preventive interventions.

Mechanisms of sudden unexpected death in epilepsy: the pathway to prevention

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy, with an estimated 35% lifetime risk in this patient population. There is a surprising lack of awareness among patients and physicians of this increased risk of sudden death: in a recent survey, only 33% of Canadian paediatricians who treated patients with epilepsy knew the term SUDEP. Controversy prevails over whether cardiac arrhythmia or respiratory arrest is more important as the primary cause of death. Effective preventive strategies in high-risk patients will rely on definition of the mechanisms that lead from seizures to death. Here, we summarize evidence for the mechanisms that cause cardiac, respiratory and arousal abnormalities during the ictal and postictal period. We highlight potential cellular mechanisms underlying these abnormalities, such as a defect in the serotonergic system, ictal adenosine release, and changes in autonomic output. We discuss genetic mutations that cause Dravet and long QT syndromes, both of which are linked with increased risk of sudden death. We then highlight possible preventive interventions that are likely to decrease SUDEP incidence, including respiratory monitoring in epilepsy monitoring units and overnight supervision. Finally, we discuss treatments, such as selective serotonin reuptake inhibitors, that might be personalized to a specific genetic or pathological defect.

Incidence and mechanisms of cardiorespiratory arrests in epilepsy monitoring units (MORTEMUS): a retrospective study

BACKGROUND

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in people with chronic refractory epilepsy. Very rarely, SUDEP occurs in epilepsy monitoring units, providing highly informative data for its still elusive pathophysiology. The MORTEMUS study expanded these data through comprehensive evaluation of cardiorespiratory arrests encountered in epilepsy monitoring units worldwide.

METHODS

Between Jan 1, 2008, and Dec 29, 2009, we did a systematic retrospective survey of epilepsy monitoring units located in Europe, Israel, Australia, and New Zealand, to retrieve data for all cardiorespiratory arrests recorded in these units and estimate their incidence. Epilepsy monitoring units from other regions were invited to report similar cases to further explore the mechanisms. An expert panel reviewed data, including video electroencephalogram (VEEG) and electrocardiogram material at the time of cardiorespiratory arrests whenever available.

FINDINGS

147 (92%) of 160 units responded to the survey. 29 cardiorespiratory arrests, including 16 SUDEP (14 at night), nine near SUDEP, and four deaths from other causes, were reported. Cardiorespiratory data, available for ten cases of SUDEP, showed a consistent and previously unrecognised pattern whereby rapid breathing (18-50 breaths per min) developed after secondary generalised tonic-clonic seizure, followed within 3 min by transient or terminal cardiorespiratory dysfunction. Where transient, this dysfunction later recurred with terminal apnoea occurring within 11 min of the end of the seizure, followed by cardiac arrest. SUDEP incidence in adult epilepsy monitoring units was 5·1 (95% CI 2·6-9·2) per 1000 patient-years, with a risk of 1·2 (0·6-2·1) per 10,000 VEEG monitorings, probably aggravated by suboptimum supervision and possibly by antiepileptic drug withdrawal.

INTERPRETATION

SUDEP in epilepsy monitoring units primarily follows an early postictal, centrally mediated, severe alteration of respiratory and cardiac function induced by generalised tonic-clonic seizure, leading to immediate death or a short period of partly restored cardiorespiratory function followed by terminal apnoea then cardiac arrest. Improved supervision is warranted in epilepsy monitoring units, in particular during night time.

FUNDING

Commission of European Affairs of the International League Against Epilepsy.

Periictal autonomic dysfunction and generalized postictal EEG suppression in convulsive seizures arising from sleep and wakefulness

Sleep appears to be an independent risk factor of sudden unexpected death in epilepsy (SUDEP). We retrospectively determined the periictal electrophysiological characteristics of nocturnal and diurnal generalized convulsive seizures (GCSs) in 109 patients. Our data showed that preictal heart rate (HR) was significantly lower in 46 patients with nocturnal GCSs than in 63 patients with diurnal GCSs (p=0.002). However, there was no significant difference in postictal HR and respiratory rate (RR), total seizure duration, total convulsive phase, tonic phase, and clonic phase. Meanwhile, postictal generalized EEG suppression (PGES) was observed in 52.4% of the patients with diurnal GCSs and 67.4% of the patients with nocturnal GCSs. Duration of PGES was 38.2±17.3s in patients with diurnal GCSs and 49.5±21.7s in patients with nocturnal GCSs. There was also no significant difference in the prevalence (p=0.118) and duration (p=0.044, Bonferroni-corrected significant level: α=0.00625) of PGES in the two patient groups. Therefore, there is no clear evidence to attribute the SUDEP risk associated with sleep to postictal autonomic dysfunction and PGES, as compared to wakefulness.

Postictal generalized EEG suppression: an inconsistent finding in people with multiple seizures

OBJECTIVE

To determine the consistency and facilitating cofactors of postictal generalized EEG suppression (PGES) of >20 seconds after convulsive seizures (CS), a suggested predictor of sudden unexpected death in epilepsy risk.

METHODS

We retrospectively reviewed video-EEG data of people with ≥2 recorded CS. Presence and duration of PGES were assessed by 2 independent observers blinded to patient status. Intraindividual consistency of PGES >20 seconds was determined and correlations with clinical characteristics were analyzed after correction for individual effects and the varying number of seizures.

RESULTS

One hundred fifty-four seizures in 59 people were analyzed. PGES >20 seconds was found in 37 individuals (63%) and 57 (37%) of CS. The proportion of persons in whom PGES occurred consistently (presence or absence of PGES >20 seconds in all CS) was lower in those with more CS. PGES of >20 seconds was more frequent in seizures arising from sleep (odds ratio 3.29, 95% confidence interval 1.21-8.96) and when antiepileptic medication was tapered (odds ratio 4.80, 95% confidence interval 1.27-18.14).

CONCLUSION

Apparent PGES consistency was less frequent in people with more CS recorded, suggesting that PGES is an inconsistent finding in any one individual. Thus, we believe that PGES >20 seconds is not a reliable predictor of sudden unexpected death in epilepsy. Sleep and antiepileptic drug reduction appear to facilitate the occurrence of PGES.

Sudden unexpected death in epilepsy: fatal post-ictal respiratory and arousal mechanisms

Sudden unexplained death in epilepsy (SUDEP) is the cause of premature death of up to 17% of all patients with epilepsy and as many as 50% with chronic refractory epilepsy. However, SUDEP is not widely recognized to exist. The etiology of SUDEP remains unclear, but growing evidence points to peri-ictal respiratory, cardiac, or autonomic nervous system dysfunction. How seizures affect these systems remains uncertain. Here we focus on respiratory mechanisms believed to underlie SUDEP. We highlight clinical evidence that indicates peri-ictal hypoxemia occurs in a large percentage of patients due to central apnea, and identify the proposed anatomical regions of the brain governing these responses. In addition, we discuss animal models used to study peri-ictal respiratory depression. We highlight the role 5-HT neurons play in respiratory control, chemoreception, and arousal. Finally, we discuss the evidence that 5-HT deficits contribute to SUDEP and sudden infant death syndrome and the striking similarities between the two.