Ictal hypoxemia in localization-related epilepsy: analysis of incidence, severity and risk factors

Patients' safety in the epilepsy monitoring unit: time for revising practices

PURPOSE OF REVIEW

Long-term video-electroencephalography monitoring (LTM) in epilepsy monitoring units (EMUs) exposes patients to a variety of serious adverse events (SAEs) and safety issues, which have recently caught attention and are summarized in this review.

RECENT FINDINGS

SAEs observed during LTM affect about 10% of patients and include secondary generalized tonic-clonic seizures, seizure clusters and status epilepticus, unusual for the patient; seizure-related falls, injuries, fractures, and aspiration; postictal psychosis; and cardiorespiratory distress, including sudden unexpected death in epilepsy (SUDEP) and near-SUDEP, which were encountered by more than 10% of European and Australian EMUs. Accordingly, 3% of US-based EMUs suffer a death within a 1-year duration census. Many of these SAEs might be promoted by antiepileptic drugs (AEDs) withdrawal, for which no specific guideline is currently available. Current recommendations regarding optimal organization of EMUs, and in particular continuous supervision by a dedicated staff, are not followed by respectively 20 and 26% of European and US-based EMUs.

SUMMARY

SAEs during LTM are a significant concern and might be aggravated by suboptimal EMU organization and staff education. Lack of high-level evidence stands out as the main limiting factor to the development and dissemination of appropriate guidelines.

Cardiorespiratory abnormalities during epileptic seizures

Sudden unexpected death in epilepsy (SUDEP) is a leading cause of death in young and otherwise healthy patients with epilepsy, and sudden death is at least 20 times more common in epilepsy patients as compared to patients without epilepsy. A significant proportion of patients with epilepsy experience cardiac and respiratory complications during seizures. These cardiorespiratory complications are suspected to be a significant risk factor for SUDEP. Sleep physicians are increasingly involved in the care of epilepsy patients and a recognition of these changes in relation to seizures while a patient is under their care may improve their awareness of these potentially life-threatening complications that may occur during sleep studies. This paper details these cardiopulmonary changes that take place in relation to epileptic seizures and how these changes may relate to the occurrence of SUDEP.

Serotonin neurones have anti-convulsant effects and reduce seizure-induced mortality

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. Defects in central control of breathing are important contributors to the pathophysiology of SUDEP, and serotonin (5-HT) system dysfunction may be involved. Here we examined the effect of 5-HT neurone elimination or 5-HT reduction on seizure risk and seizure-induced mortality. Adult Lmx1b(f/f/p) mice, which lack >99% of 5-HT neurones in the CNS, and littermate controls (Lmx1b(f/f)) were subjected to acute seizure induction by maximal electroshock (MES) or pilocarpine, variably including electroencephalography, electrocardiography, plethysmography, mechanical ventilation or pharmacological therapy. Lmx1b(f/f/p) mice had a lower seizure threshold and increased seizure-induced mortality. Breathing ceased during most seizures without recovery, whereas cardiac activity persisted for up to 9 min before terminal arrest. The mortality rate of mice of both genotypes was reduced by mechanical ventilation during the seizure or 5-HT2A receptor agonist pretreatment. The selective serotonin reuptake inhibitor citalopram reduced mortality of Lmx1b(f/f) but not of Lmx1b(f/f/p) mice. In C57BL/6N mice, reduction of 5-HT synthesis with para-chlorophenylalanine increased MES-induced seizure severity but not mortality. We conclude that 5-HT neurones raise seizure threshold and decrease seizure-related mortality. Death ensued from respiratory failure, followed by terminal asystole. Given that SUDEP often occurs in association with generalised seizures, some mechanisms causing death in our model might be shared with those leading to SUDEP. This model may help determine the relationship between seizures, 5-HT system dysfunction, breathing and death, which may lead to novel ways to prevent SUDEP.

The consequences of refractory epilepsy and its treatment

Seizures in some 30% to 40% of patients with epilepsy fail to respond to antiepileptic drugs or other treatments. While much has been made of the risks of new drug therapies, not enough attention has been given to the risks of uncontrolled and progressive epilepsy. This critical review summarizes known risks associated with refractory epilepsy, provides practical clinical recommendations, and indicates areas for future research. Eight international epilepsy experts from Europe, the United States, and South America met on May 4, 2013, to present, review, and discuss relevant concepts, data, and literature on the consequences of refractory epilepsy. While patients with refractory epilepsy represent the minority of the population with epilepsy, they require the overwhelming majority of time, effort, and focus from treating physicians. They also represent the greatest economic and psychosocial burdens. Diagnostic procedures and medical/surgical treatments are not without risks. Overlooked, however, is that these risks are usually smaller than the risks of long-term, uncontrolled seizures. Refractory epilepsy may be progressive, carrying risks of structural damage to the brain and nervous system, comorbidities (osteoporosis, fractures), and increased mortality (from suicide, accidents, sudden unexpected death in epilepsy, pneumonia, vascular disease), as well as psychological (depression, anxiety), educational, social (stigma, driving), and vocational consequences. Adding to this burden is neuropsychiatric impairment caused by underlying epileptogenic processes ("essential comorbidities"), which appears to be independent of the effects of ongoing seizures themselves. Tolerating persistent seizures or chronic medicinal adverse effects has risks and consequences that often outweigh risks of seemingly "more aggressive" treatments. Future research should focus not only on controlling seizures but also on preventing these consequences.

Serotonin and sudden death: differential effects of serotonergic drugs on seizure-induced respiratory arrest in DBA/1 mice

In the DBA/1 mouse model of sudden unexpected death in epilepsy (SUDEP), administration of a selective serotonin (5-HT) reuptake inhibitor (SSRI), fluvoxamine, completely suppressed seizure-induced respiratory arrest (S-IRA) at 30 min after administration (i.p.) in a dose-related manner without blocking audiogenic seizures (AGSz), but another SSRI, paroxetine, reduced S-IRA but with a delayed (24 h) onset and significant toxicity. A serotonin-norepinephrine reuptake inhibitor, venlafaxine, reduced S-IRA incidence, but higher doses were ineffective. A selective 5-HT7 agonist, AS-19, was totally ineffective in reducing S-IRA. In developing DBA/1 mice that had not previously experienced AGSz, administration of a nonselective 5-HT antagonist, cyproheptadine, induced a significantly greater incidence of S-IRA than that of saline. This study confirms that certain drugs that enhance the activation of 5-HT receptors are able to prevent S-IRA, but not all serotonergic drugs are equally effective, which may be relevant to the potential use of these drugs for SUDEP prevention. Serotonergic antagonists may be problematic in patients with epilepsy.

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.

Advantages of respiratory monitoring during video-EEG evaluation to differentiate epileptic seizures from other events

Differentiating between epileptic seizures (ES) and seizure-like nonepileptic events (SLNE) is often difficult using descriptions of seizure semiology. Cardiopulmonary dysfunction is frequent in ES but has not been objectively examined in relation to SLNE. Our purpose was to compare cardiopulmonary dysfunction between ES and SLNE. We prospectively recorded cardiopulmonary function using pulse oximetry, EKG, and respiratory inductance plethysmography (RIP) in 52 ES and 22 SLNE. Comparison of cardiopulmonary complications between ES and SLNE was done using two-sample T-tests and logistic regression. Ictal bradypnea and preictal bradycardia were more frequent in ES than SLNE (p<0.05). Desaturation was found in 57% of ES and in 0% of SLNE (p<0.0001). Oxygen saturation nadir was significantly lower in ES vs. SLNE (p<0.0001). Ictal apnea was present in 31% ES and 9% SLNE (p=0.06). Preictal, ictal, and postictal tachycardia did not significantly differ between ES and SLNE (p>1.0). Cardiorespiratory dysfunction, specifically bradypnea, apnea, preictal bradycardia, and oxygen desaturation, is more frequently seen in ES than in SLNE. Tachycardia was not discriminant between ES and SLNE.

Timing, sleep, and respiration in health and disease

Breathing is perhaps the physiological function that is most vital to human survival. Without breathing and adequate oxygenation of tissues, life ceases. As would be expected for such a vital function, breathing occurs automatically, without the requirement of conscious input. Breathing is subject to regulation by a variety of factors including circadian rhythms and vigilance state. Given the need for breathing to occur continuously with little tolerance for interruption, it is not surprising that breathing is subject to both circadian phase-dependent and vigilance-state-dependent regulation. Similarly, the information regarding respiratory state, including blood-gas concentrations, can affect circadian timing and sleep-wake state. The exact nature of the interactions between breathing, circadian phase, and vigilance state can vary depending upon the species studied and the methodologies employed. These interactions between breathing, circadian phase, and vigilance state may have important implications for a variety of human diseases, including sleep apnea, asthma, sudden unexpected death in epilepsy, and sudden infant death syndrome.

Serotonin: The Anti-SuddenDeathAmine?

Sudden unexpected death in epilepsy (SUDEP) is an exceptionally difficult condition to study in humans. Therefore, translational research in animal models has been very important in defining pathophysiological mechanisms of death and identifying potential treatments. These models are helping define whether the primary mechanism of death is cardiac or respiratory. They have also identified a link to the serotonergic system of the brainstem; this, in turn, led to recognition that SUDEP and sudden infant death syndrome (SIDS) may share a common final pathway in the sequence of events that lead to death.

Early respiratory dysfunction as a biomarker for epileptic encephalopathy

OBJECTIVES

West syndrome is an epileptic encephalopathy starting in infancy with almost continuous interictal epileptic activity, so-called hypsarrhythmia pattern, and therefore is an interesting model for investigating the effect of interictal epileptic activity on autonomic function. It is known that autonomic dysfunction contributes to morbidity and mortality in epilepsy. Our aim is to investigate the effect of interictal epileptic activity in West syndrome on respiratory control.

MATERIALS AND METHODS

Interictal single-lead ECG signals were extracted from 24-h video-EEG recordings in 10 children suffering from West syndrome and 14 control subjects. RR interval time series were calculated, and respiration was derived from the ECG signal. ECG-derived respiration (EDR) signals were computed and time and frequency domain parameters were extracted to characterize the respiration pattern.

RESULTS

In time domain, the standard deviation of the EDR signal is significantly lower in patients with West syndrome compared to control subjects. This finding is an indication of a less variable respiratory rate. In frequency domain, we analyzed the mean power spectrum for the EDR. In patients with West syndrome, there is more activity at the lower frequencies considered to be a risk factor for apneas. Second, there is an attenuated peak at the higher frequency band where normal respiratory rate is to be found, indicating an abnormal breathing pattern.

CONCLUSIONS

Our results show that there is a clear dysfunction in autonomic respiratory control in patients with West syndrome, in between the typical ictal epileptic spasms, compared to control subjects. Respiration is more fixed and contains a higher risk of apneas.

Comparison of cardiorespiratory and EEG abnormalities with seizures in adults and children

Cardiopulmonary dysfunction and postictal generalized EEG suppression (PGES) are proposed as possible risk factors for the occurrence of SUDEP. The evolution of cardiorespiratory abnormalities with seizures has not been systematically studied for any age-related findings. Additionally, not many studies have looked into the possible effect of age-related brain maturation on PGES. The purpose of this study was to compare these SUDEP risk factors in adults versus children. We prospectively recorded cardiopulmonary abnormalities during seizures using pulse oximetry, EKG, and respiratory inductance plethysmography. Linear and logistic regression models adjusting for multiple seizures in a single patient were used to compare the cardiorespiratory and EEG findings between adults and children. We recorded 101 seizures in 26 children and 55 seizures in 22 adults. Ictal central apnea and bradycardia occurred more often in children than in adults (p=0.02 and p=0.008, respectively), while ictal tachycardia occurred more often in adults (p=0.001) than in children. Postictal generalized EEG suppression of longer duration occurred more often in adults (p=0.003) than in children. Minimum O2 saturation and seizure duration/generalization/lateralization did not significantly differ between adults and children (p>0.1). Children had more frontal lobe seizures, and adults had more temporal lobe seizures recorded (p=0.01). There may be an age-related effect on cardiorespiratory and EEG abnormalities associated with seizures, with higher rates of apnea and bradycardia in children and a much higher prevalence of PGES of longer duration in adults. This may indicate why, despite lower rates of cardiopulmonary dysfunction, adults die more frequently from SUDEP than children.

Relation of autonomic and cardiac abnormalities to ventricular fibrillation in a rat model of epilepsy

Cardiac autonomic, conduction, and structural changes may occur in epilepsy and may contribute to sudden unexpected death in epilepsy (SUDEP), e.g. by increasing the risk for ventricular fibrillation (VF). In a model of chronic seizures in rats, we sought to study (1) cardiac and autonomic derangements that accompany the epileptic state, (2) whether chronically seizing rats experienced more significant cardiac effects after severe acute seizures, and (3) the susceptibility of chronically seizing rats to VF arising from autonomic and hypoxemic changes, which commonly occur during seizures. Sprague-Dawely rats were injected with saline or kainic acid to induce chronic seizures. At 2-3 months or 7-11 months after injection, these rats were studied with both 12-lead electrocardiography (to assess heart rate variability and QT dispersion) and echocardiography under ketamine/xylazine or urethane anesthesia. Hearts were subsequently excised, weighed, and examined histologically. Epileptic rats exhibited decreased vagal tone, increased QT dispersion, and eccentric cardiac hypertrophy without significant cardiac fibrosis, especially at 7-11 months post-injection. Of these three findings, vagal tone was inversely correlated with heart weights. Epileptic rats exhibited diminished systolic function compared to controls after severe acute seizures. However, animals with long-standing chronic seizures were less susceptible to autonomic/hypoxemia-driven VF, and their susceptibility inversely correlated with mean left ventricular wall thickness on histology. On the basis of this model, we conclude that cardiac changes accompany epilepsy and these can lead to significant seizure-associated cardiac performance decreases, but these cardiac changes actually lower the probability of VF.

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.

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.

Prevention of sudden unexpected death in epilepsy: a realistic goal?

Sudden unexpected death in epilepsy (SUDEP) represents one of the most severe consequences of drug-resistant epilepsy, for which no evidence-based prevention is available. Development of effective prevention will depend on the following: (1) better understanding of the pathophysiology of SUDEP to define the most appropriate targets of intervention, and (2) identification of risk factors for SUDEP that would allow for the design of feasible clinical trials to test targeted interventions in high-risk populations. The most important known risk factor is the occurrence and frequency of generalized tonic-clonic seizure (GTCS), a seizure type that triggers the majority of witnessed SUDEP. Therefore, one likely way to prevent SUDEP is to minimize the risk of GTCS with optimal medical management and patient education. However, whether one might prevent SUDEP in patients with refractory epilepsy by using more frequent review of antiepileptic treatment and earlier referral for presurgical evaluation, remains to be seen. Another hypothetical strategy to prevent SUDEP is to reduce the risk of GTCS-induced postictal respiratory distress. This might be achieved by using lattice pillow, providing nocturnal supervision, reinforcing interictal serotoninergic tone, and lowering opiate- or adenosine-induced postictal brainstem depression. Promising interventions can be tested first on surrogate markers, such as postictal hypoxia in epilepsy monitoring units (EMUs), before SUDEP trials can be implemented. EMU safety should also be improved to avoid SUDEP occurrence in that setting. Finally, the development of ambulatory SUDEP prevention devices should be encouraged but raises a number of unsolved issues.

Sudden unexpected death in Dravet syndrome: respiratory and other physiological dysfunctions

Sudden unexpected deaths in epilepsy (SUDEP) occur at an alarming higher rate in patients with Dravet syndrome (DS) than in patients with most other forms of epilepsy. DS is a severe infantile-onset epilepsy caused by a heterozygote loss-of-function mutation in SCN1A, which encodes the voltage-gated-sodium channel NaV 1.1. The mechanisms leading to SUDEP in DS or other epilepsies are not completely understood. Understanding the pathophysiological mechanisms of SUDEP, common to most epilepsies and those specific to DS, may pave the way toward the discovery of effective preventive strategies for these epilepsy-related tragic events.

Endothelial Von Willebrand factor promotes blood-brain barrier flexibility and provides protection from hypoxia and seizures in mice

OBJECTIVE

Aberrant blood-brain barrier (BBB) permeability is a hallmark pathology of many central nervous system diseases. von Willebrand factor (VWF) is stored in endothelial Weibel-Palade bodies from where it is released on activation into plasma and basement membrane. The role of VWF in endothelial homeostasis is unclear. The goal of this study was to assess the role of VWF in disease models associated with increased BBB permeability.

APPROACH AND RESULTS

We did not find any differences in BBB permeability to Evans blue dye at baseline between wild-type and VWF(-/-) animals. We next used 2 models presenting with increased BBB permeability, hypoxia/reoxygenation and pilocarpine-induced status epilepticus, to assess the response of VWF(-/-) animals. In both models, VWF(-/-) mice maintained a tighter BBB than wild-type mice. VWF(-/-) mice fared worse in both conditions, with ≈ 100% of VWF(-/-) mice dying within 120 minutes after pilocarpine administration, whereas >80% of wild-type animals survived. Investigation into the status of tight junction proteins revealed that VWF(-/-) mice expressed more claudin-5 at baseline. In vitro work confirmed that the presence of subendothelial VWF is inhibitory to claudin-5 expression.

CONCLUSIONS

VWF deficiency confers partial preservation of BBB integrity after hypoxia/reoxygenation and seizures. Surprisingly, this decrease in BBB permeability did not result in protection of animals because they demonstrated more severe pathology in both models compared with wild-type animals. These data suggest that a rigid BBB is detrimental (to the organism) during certain disease states and that VWF release may provide desired flexibility under stress.

Effects of age, sex, and sertraline administration on seizure-induced respiratory arrest in the DBA/1 mouse model of sudden unexpected death in epilepsy (SUDEP)

DBA/1 mice are susceptible to audiogenic seizure-induced respiratory arrest (S-IRA), leading to death, which is a model of human sudden unexpected death in epilepsy (SUDEP). Female DBA/1 mice exhibited 71% susceptibility to S-IRA on the third daily test when seizure testing began at postnatal day (PND) 24-30, which was slightly (>10%) but not significantly lower than males. When initial seizure testing was delayed (to >7 weeks of age), DBA/1 mice of both sexes exhibited significantly reduced S-IRA susceptibility, as compared to mice tested initially at PND 24-30. These sex and age issues had not been previously evaluated and may be important for the future use of this SUDEP model. We also observed that 30 min after administering a selective serotonin reuptake inhibitor (SSRI), sertraline (40, 50, or 75 mg/kg i.p.), a significantly reduced S-IRA incidence in DBA/1 mice occurred without blocking seizures, which may be relevant to SUDEP prevention.

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.

Cardiopulmonary complications during pediatric seizures: a prelude to understanding SUDEP

PURPOSE

Sudden unexpected death in epilepsy (SUDEP) is an important, unexplained cause of death in epilepsy. Role of cardiopulmonary abnormalities in the pathophysiology of SUDEP is unclear in the pediatric population. Our objective was to assess cardiopulmonary abnormalities during epileptic seizures in children, with the long-term goal of identifying potential mechanisms of SUDEP.

METHODS

We prospectively recorded cardiopulmonary functions using pulse-oximetry, electrocardiography (ECG), and respiratory inductance plethysmography (RIP). Logistic regression was used to evaluate association of cardiorespiratory findings with seizure characteristics and demographics.

KEY FINDINGS

We recorded 101 seizures in 26 children (average age 3.9 years). RIP provided analyzable data in 78% and pulse-oximetry in 63% seizures. Ictal central apnea was more prevalent in patients with younger age (p = 0.01), temporal lobe (p < 0.001), left-sided (p < 0.01), symptomatic generalized (p = 0.01), longer duration seizures (p < 0.0002), desaturation (p < 0.0001), ictal bradycardia (p < 0.05), and more antiepileptic drugs (AEDs; p < 0.01), and was less prevalent in frontal lobe seizures (p < 0.01). Ictal bradypnea was more prevalent in left-sided (p < 0.05), symptomatic generalized seizures (p < 0.01), and in brain magnetic resonance imaging (MRI) lesions (p < 0.1). Ictal tachypnea was more prevalent in older-age (p = 0.01), female gender (p = 0.05), frontal lobe (p < 0.05), right-sided seizures (p < 0.001), fewer AEDs (p < 0.01), and less prevalent in lesional (p < 0.05) and symptomatic generalized seizures (p < 0.05). Ictal bradycardia was more prevalent in male patients (p < 0.05) longer duration seizures (p < 0.05), desaturation (p = 0.001), and more AEDs (p < 0.05), and was less prevalent in frontal lobe seizures (p = 0.01). Ictal and postictal bradycardia were directly associated (p < 0.05). Desaturation was more prevalent in longer-duration seizures (p < 0.0001), ictal apnea (p < 0.0001), ictal bradycardia (p = 0.001), and more AEDs (p = 0.001).

SIGNIFICANCE

Potentially life-threatening cardiopulmonary abnormalities such as bradycardia, apnea, and hypoxemia in pediatric epileptic seizures are associated with predictable patient and seizure characteristics, including seizure subtype and duration.

Potential mechanisms of sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) accounts for 15% of all deaths in people with epilepsy and 50% in refractory epilepsy. The underlying mechanisms are not well understood, but seizure-induced cardiac and respiratory arrests are involved. The cardiovascular and respiratory systems are subject to precise reflex regulation to ensure appropriate oxygen supply under a wide range of circumstances. Barosensory and chemosensory afferents project into the nucleus tractus solitarius (NTS), which relays systemic data to higher brain centers for integration of homeostatic responses in heart rate, peripheral resistance, respiration, and other autonomic reactions. Being the afferent autonomic gatekeeper, NTS plays a critical role in cardiovascular and respiratory regulation. In the course of studying the kainic acid model, we became aware of progressive neuronal loss in the NTS and noted SUDEP-like deaths in rats with frequent convulsions. Increased autonomic susceptibility with inhalation anesthetics was also observed, often seen after impairment of baroreceptor and chemoreceptor reflex loops. Seizure-induced neuron loss in NTS may play a role impairing the integrative functions of NTS resulting in poor homeostatic responses during seizures and leading to SUDEP.

Autonomic epileptic seizures, autonomic effects of seizures, and SUDEP

Many generalized tonic-clonic seizures are accompanied by profound autonomic changes. However, autonomic seizures and autonomic status epilepticus can also be seen with specific electroclinical syndromes (Panayiotopoulos syndrome), etiologies, and localizations. Such autonomic symptoms may impact cardiorespiratory function. While it is likely that several factors contribute to SUDEP, further study of both ictal respiratory and cardiac changes and underlying neuroanatomical mechanisms involved in autonomic seizure semiology are likely to provide important data to improve our understanding of the pathophysiology of this devastating condition. This paper will review the association between autonomic symptoms and epileptic seizures and will highlight the work of three young investigators. Drs. Lisa Bateman and Brian Moseley will review their work on cardiorespiratory effects of recorded seizures and how this assists in our understanding of SUDEP. Dr. John Millichap will review autonomic seizures and autonomic dysfunctions related to childhood epilepsy and will discuss the importance of expanded research efforts in this field.

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

PURPOSE

Postictal generalized EEG suppression (PGES) seems to be a pathophysiologic hallmark in ictal recordings of sudden unexpected death in epilepsy (SUDEP). It has recently been suggested that presence and duration of PGES might be a predictor of SUDEP risk. Little is known about the etiology of PGES.

METHODS

We conducted a retrospective case-control study in 50 people with convulsive seizures (CS) recorded on digital video-electroencephalography (EEG). One CS per individual was reviewed for presence and duration of PGES by two independent observers: Preictal and postictal heart rate (HR) (1 min before seizure onset and 1, 3, 5, 15, and 30 min after seizure end) and frequency domain measures of heart rate variability (HRV), including the ratio of low frequency (LF) versus high frequency (HF) power, were analyzed. The relationship between PGES and periictal autonomic changes was evaluated, as well as its association with several clinical variables.

KEY FINDINGS

Thirty-seven individuals (74%) exhibited PGES and 13 (26%) did not. CS resulted in a significant increase of periictal HR and the LF/HF ratio. PGES was associated with neither periictal HR (mean HR difference between PGES+ and PGES- seizures: -2 beats per minute [bpm], 95% confidence interval [CI] -10 to +6 bpm) nor HRV change. There was no association between the duration of PGES and periictal HR change. People with PGES were more likely to be asleep before seizure onset (odds ratio [OR] 4.7, 95% CI 1.2-18.3) and had a higher age of onset of epilepsy (median age 15 vs. 4 years).

SIGNIFICANCE

PGES was not associated with substantial changes in measures of cardiac autonomic instability but was more prevalent in CS arising from sleep.

Impact of periictal interventions on respiratory dysfunction, postictal EEG suppression, and postictal immobility

PURPOSE

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related mortality. Seizure-related respiratory dysfunction (RD), the duration of postictal generalized electroencephalography (EEG) suppression (PGES), and duration of postictal immobility (PI) may be important in the pathophysiology of SUDEP. Periictal interventions may reduce the risk of SUDEP.

METHODS

We assessed the impact of periictal nursing interventions on RD, PGES, and PI duration in patients with localization-related epilepsy and secondarily generalized convulsions (GCs) recorded during video-EEG telemetry in the epilepsy monitoring unit. Video-EEG data were retrospectively reviewed. Interventions including administration of supplemental oxygen, oropharyngeal suction, and patient repositioning were evaluated. Interventions were performed based on nursing clinical judgment at the bedside and were not randomized. The two-sided Wilcoxon rank-sum test was used to compare GCs with and those without intervention. Robust simple linear regression was used to assess the association between timing of intervention and duration of hypoxemia (SaO(2) < 90%), PGES, and PI using data from only the first GC for each patient.

KEY FINDINGS

Data from 39 patients with 105 GCs were analyzed. PGES >2 s occurred following 31 GCs in 16 patients. There were 21 GCs with no intervention (NOINT) and 84 GC with interventions (INT). In the INT group, the duration of hypoxemia was shorter (p = 0.0014) when intervention occurred before hypoxemia onset (mean duration 53.1 s) than when intervention was delayed (mean duration 132.42 s). Linear regression indicated that in GCs with nursing interventions, earlier intervention was associated with shorter duration of hypoxemia (p < 0.0001) and shorter duration of PGES (p = 0.0012). Seizure duration (p < 0.0001) and convulsion duration (p = 0.0457) were shorter with earlier intervention. PI duration was longer for GCs with PGES than GCs without PGES (p < 0.0001). The mean delay to first active nonrespiratory movement following GCs with PGES was 251.96 s and for GC without PGES was 66.06 s. The duration of PI was positively associated with lower SaO(2) nadir (p = 0.003) and longer duration of oxygen desaturation (p = 0.0026). There was no association between PI duration and seizure duration (p = 0.773), between PI duration and PGES duration (p = 0.758), or between PI duration and the timing of first intervention relative to seizure onset (p = 0.823). PGES did not occur in the NOINT group. The mean duration of desaturation was longer (110.9 vs. 49.9 s) (p < 0.0001), mean SaO(2) nadir was lower (72.8% vs. 79.7%) (p = 0.0086), and mean end-tidal CO(2) was higher (58.6 vs. 50.3 mmHg) (p = 0.0359) in the INT group compared with the NOINT group. The duration of the seizure or of the convulsive component was not significantly different between the INT and NOINT groups.

SIGNIFICANCE

Early periictal nursing intervention was associated with reduced duration of RD and reduced duration of PGES. These findings suggest the possibility that such interventions may be effective in reducing the risk of SUDEP in the outpatient setting. Validation of these preliminary data with a prospective study is needed before definitive conclusions can be reached regarding the efficacy of periictal interventions in reducing the risk of SUDEP.

Long-term cardiac rhythm and repolarization abnormalities in refractory focal and generalized epilepsy

This prospective study evaluated 19 individuals with refractory focal or generalized epilepsy utilizing an implantable cardiac loop recorder. Recording averaged 15 months (range 12-19 months) in 18 patients and 1.5 months in one patient. A median of 37 seizures per patient (range 3-657) occurred, with 1,477 seizures total. Cardiac arrhythmias and repolarization abnormalities occurred frequently (in 42% of patients) in refractory epilepsy, particularly during generalized tonic-clonic and tonic seizures. Patients with Lennox-Gastaut syndrome may be at high risk for cardiac abnormalities.

Severe ictal hypoxemia following focal, subclinical temporal electrographic scalp seizure activity

Ictal hypoxemia has been reported in focal seizures and can be particularly severe during sustained seizure activity involving both hemispheres. Oxygen desaturations have been linked to sudden unexplained death in epilepsy (SUDEP). We report a 71-year-old patient with subclinical electrographic seizure discharges involving the left temporal lobe. Electrographic seizures were followed by apneas and severe oxygen desaturations below 70% SpO(2) even after cessation of electrographic scalp seizure activity, suggesting inhibition of respiratory brainstem centers outlasting neocortical seizure activity. Seizures led to disrupted night's sleep due to arousals. Our case illustrates that severe hypoxemia can occur in association with subclinical seizures involving the temporal lobe and after scalp EEG seizure activity has terminated. Electrographic seizures followed by hypoxemia, such as observed in our patient, could contribute to SUDEP without overt clinical seizure activity.

Efficacy of safety signals in the epilepsy monitoring unit (EMU): should we worry?

There is little consensus regarding the critical safety measures to prevent harm in epilepsy monitoring units (EMUs). We sought to determine whether the safety signals (SS) triggered during EMU events differed by seizure type and the efficacy of SS in alerting responders. We screened 468 consecutive EMU admissions from January 2008 until April 2011 for definitive events to evaluate the first 50 events of complex partial seizures (CPS), generalized tonic-clonic seizures (GTC), and psychogenic non-epileptic seizures (PNES). Response to telemetry signal was slower than to push button (PB). When there was PB alarm, response time was slower in patients with PNES. A higher proportion of PNES were triggered by PB. A greater percentage of epileptic seizures were missed compared with PNES. Future studies investigating more effective techniques to capture every epileptic seizure are warranted as 24/7 monitoring by healthcare professionals is not feasible in many settings.

Opposing effects on the phrenic motor pathway attributed to dopamine-D1 and -D3/D2 receptor activation

Previous in vivo studies revealed that dopamine-D1-agonists elevate excitability of ventral respiratory column (VRC) neurons and increase discharge activity in the phrenic motor output through actions in the brainstem. In this in vivo study performed on pentobarbital-anesthetized cats, we show that D1-agonists (SKF-38393, dihydrexidine) given intravenously enhanced discharge activity in VRC inspiratory neurons and the phrenic nerve in two stages; discharge intensity first increased to a peak and then discharge duration increased. Cross-correlation analysis of VRC inspiratory neuron and phrenic nerve discharges showed that both stages increased strength of coupling between medullary inspiratory neurons and the phrenic motoneuron output. Intracellular recording and microiontophoresis experiments indicated that D1-agonists produced their stimulatory effects indirectly through actions on synaptic inputs to VRC inspiratory neurons. Because other laboratories have provided evidence that dopamine acting on other types of receptors depresses respiratory neuron excitability we tested the effects of piribedil, an agonist that activates receptors of the generally depressant D3/D2-dopamine receptor family, on phrenic nerve activity. Piribedil depressed phrenic nerve inspiratory discharge intensity, prolonged discharge duration, slowed burst frequency and slowed rate of action potential augmentation. The effects of piribedil were partially counteracted by intravenous injection of dihydrexidine. We propose that under normal, steady state conditions, D1-receptor-mediated excitatory modulation of phrenic motor output overrides D3/D2-receptor mediated inhibition.

Sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) refers to the sudden death of a seemingly healthy individual with epilepsy, usually occurring during, or immediately after, a tonic-clonic seizure. The frequency of SUDEP varies depending on the severity of the epilepsy, but overall the risk of sudden death is more than 20 times higher than that in the general population. Several different mechanisms probably exist, and most research has focused on seizure-related respiratory depression, cardiac arrhythmia, cerebral depression, and autonomic dysfunction. Data from a pooled analysis of risk factors indicate that the higher the frequency of tonic-clonic seizures, the higher the risk of SUDEP; furthermore, risk of SUDEP is also elevated in male patients, patients with long-duration epilepsy, and those on antiepileptic polytherapy. SUDEP usually occurs when the seizures are not witnessed and often at night. In this Seminar, we provide advice to clinicians on ways to minimise the risk of SUDEP, information to pass on to patients, and medicolegal aspects of these deaths.

Retrospective audit of postictal generalized EEG suppression in telemetry

Sudden unexpected death in epilepsy (SUDEP) has on rare occasions occurred during electroencephalography (EEG) telemetry, and in such cases postictal EEG suppression (PI EEG-SUP) was frequently observed. More recently a retrospective case-control study reported this pattern as a risk factor for SUDEP. We retrospectively audited frequency and electroclinical features of this pattern as well as immediate management following tonic-clonic seizures during telemetry. Forty-eight patients with tonic-clonic seizures were identified from 470 consecutive EEG-videotelemetry reports. Thirteen patients (27%) with PI EEG-SUP (mean duration 38.1 s, range 6-69 s, median 38 s) were compared to 12 randomly selected controls. One seizure was analyzed per individual. Those with PI EEG-SUP were significantly more likely to be motionless after the seizure and have simple nursing interventions performed (suction, oxygen administration, placed in recovery position, vital signs checked). This pattern is relatively common and requires further study as a potential marker for increased mortality in epilepsy.

Ictal central apnea as a predictor for sudden unexpected death in epilepsy

Epidemiological evidence associating ictal hypoventilation during focal seizures with a heightened risk for subsequent sudden unexpected death in epilepsy (SUDEP) is lacking. We describe a patient with temporal lobe epilepsy with two focal seizures recorded in the epilepsy monitoring unit that were associated with central apnea lasting 57 and 58 seconds. During these events, she demonstrated oxygen desaturation down to 68 and 62%. The patient subsequently died at home from autopsy-confirmed SUDEP. The family was not alerted of any seizure activity by the auditory alarm system in her room nor by sleeping in the adjacent room with open doors. This case emphasizes the fact that ictal hypoxia and SUDEP may occur in seizures without noticeable convulsive activity. The report gives credibility to the growing body of literature suggesting that epilepsies affecting the autonomic nervous system may predispose to SUDEP independent of the effects of a secondary generalized convulsion.

Prevention of seizure-induced sudden death in a chronic SUDEP model by semichronic administration of a selective serotonin reuptake inhibitor

DBA/1 mice are a chronically susceptible model of sudden unexpected death in epilepsy (SUDEP) that exhibit chronic audiogenic generalized convulsive seizures (GCSs), leading to death from respiratory arrest (RA) if not resuscitated. Serotonin (5-HT) normally enhances respiration in response to elevated CO(2) levels, which occur during GCSs in humans. Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, increase 5-HT availability. We examined whether fluoxetine can block GCS-induced sudden death in DBA/1 mice. Fluoxetine (15-70 mg/kg ip) was administered acutely with seizure induction at 30minutes or semichronically in five daily doses (20mg/kg/day) with induction after 5 days. Acute fluoxetine (45 or 70 mg/kg) significantly reduced the incidence of RA without blocking seizure susceptibility. Semichronic fluoxetine did not block seizures, but significantly reduced seizure-induced RA, which is consistent with effects of SSRIs on respiration in patients with epilepsy [Bateman LM, Li DS,LiN TC, Seyal M. Epilepsia 2010;51:2211-4]. These findings suggest that treatment with SSRIs should be evaluated for reducing the incidence of SUDEP in patients.

Seizure-related cardiac repolarization abnormalities are associated with ictal hypoxemia

PURPOSE

Cardiac arrhythmias and respiratory disturbances have been proposed as likely causes for sudden unexpected death in epilepsy. Oxygen desaturation occurs in one-third of patients with localization-related epilepsy (LRE) undergoing inpatient video-electroencephalography (EEG) telemetry (VET) as part of their presurgical workup. Ictal-related oxygen desaturation is accompanied by hypercapnia. Both abnormal lengthening and shortening of the corrected QT interval (QTc) on electrocardiography (ECG) have been reported with seizures. QTc abnormalities are associated with increased risk of sudden cardiac death. We hypothesized that there may be an association between ictal hypoxemia and cardiac repolarization abnormalities.

METHODS

VET data from patients with refractory LRE were analyzed. Consecutive patients having at least one seizure with accompanying oxygen desaturation below 90% and artifact-free ECG data were selected. ECG during the 1 min prior to seizure onset (PRE) and during the ictal/postictal period with accompanying oxygen desaturation below 90% (DESAT) was analyzed. Consecutive QT and RR intervals were measured. In the same patients, DESAT seizures were compared with seizures without accompanying oxygen desaturation below 90% (NODESAT). For NODESAT seizures, QT and RR intervals for 2 min after seizure onset were measured.

KEY FINDINGS

Thirty-seven DESAT seizures were analyzed in 17 patients with localization-related epilepsy. A total of 2,448 QT and RR intervals were analyzed during PRE. During DESAT, 1,554 QT and RR intervals were analyzed. Twelve of the 17 patients had at least one NODESAT seizure. A total of 19 NODESAT seizures were analyzed, including 1,558 QT and RR intervals during PRE and 3,408 QT and RR intervals during NODESAT. The odds ratio for an abnormally prolonged (>457 ms) QTcH (Hodges correction method) during DESAT relative to PRE was 10.64 (p < 0.0001). The odds ratio for an abnormally shortened (<372 ms) QTcH during DESAT relative to PRE was 1.65 (p < 0.0001). Seizure-related shortening and prolongation of QTc during DESAT were also observed when Fridericia correction of the QT was applied. During DESAT seizures, the mean range of QT values (QTr) (61.14 ms) was significantly different from that during PRE (44.43 ms) (p = 0.01). There was a significant association between DESAT QTr and oxygen saturation nadir (p = 0.025) and between DESAT QTr and duration of oxygen desaturation (p < 0.0001). Both QTcH prolongation and shortening also occurred with NODESAT seizures. A seizure-associated prolonged QTcH was more likely during DESAT than NODESAT, with an odds ratio of 4.30 (p < 0.0001). A seizure-associated shortened QTcH was more likely during DESAT than NODESAT with an odds ratio of 2.13 (p < 0.0001).

SIGNIFICANCE

We have shown that the likelihood of abnormal QTcH prolongation is increased 4.3-fold with seizures that are associated with oxygen desaturation when compared with seizures that are not accompanied with oxygen desaturation. The likelihood of abnormally shortened QTcH increases with seizures that are accompanied by oxygen desaturation with an odds ratio of 2.13 compared with that in seizures without desaturations. There is a significant association between the depth and duration of oxygen desaturation and QTr increase. These findings may be related to the pathophysiology of SUDEP.

Differences in serotonin receptor expression in the brainstem may explain the differential ability of a serotonin agonist to block seizure-induced sudden death in DBA/2 vs. DBA/1 mice

DBA mice are models of sudden unexpected death in epilepsy (SUDEP) that exhibit audiogenic generalized convulsive seizures (GCS), ending in death due to respiratory arrest (RA). Serotonin (5-HT) normally enhances respiration in response to elevated CO(2) levels, which occur during GCS in patients. Fluoxetine, a selective serotonin reuptake inhibitor (SSRI), blocks GCS-induced SUDEP in both DBA/2 and DBA/1 mice. This study examined the effects of a 5-HT(2B/2C) agonist (m-chlorophenylpiperazine, mCPP) to test the generality of serotonergic effects on DBA mice. In DBA/2 mice mCPP pre-treatment [5 or 10 (but not 2) mg/kg, i.p.] significantly reduced RA incidence without blocking seizure susceptibility. However, in DBA/1 mice mCPP in doses up to 40mg/kg was ineffective in blocking seizure-induced RA, and 60mg/kg was toxic. The cause of this strain difference was perplexing. Previous studies showed that brainstem 5-HT receptor protein expression was abnormal in DBA/2 mice. Therefore, expression of 5-HT receptor proteins in the medial-caudal brainstem of DBA/1 mice was evaluated using Western blots. In DBA1/mice 5-HT(2C) and 5-HT(3B) receptor expression levels were significantly reduced, as seen previously in DBA/2 mice. However, 5-HT(2B) receptor expression was also reduced in DBA/1 mice, contrasting with the 5-HT(2B) receptor elevation seen in DBA/2 mice. This difference may explain the differential effects of the 5-HT(2B/2C) agonist in these SUDEP models. mCPP blocked RA in DBA/2 mice and concomitantly reduced tonic seizures, which also occurs. Fluoxetine is the only agent tested that blocks RA selectively in these SUDEP models, which may be clinically relevant.