Pathologic cardiac repolarization in pharmacoresistant epilepsy and its potential role in sudden unexpected death in epilepsy: A case-control study

Practice guideline summary: Sudden unexpected death in epilepsy incidence rates and risk factors: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology and the American Epilepsy Society

OBJECTIVE

To determine the incidence rates of sudden unexpected death in epilepsy (SUDEP) in different epilepsy populations and address the question of whether risk factors for SUDEP have been identified.

METHODS

Systematic review of evidence; modified Grading Recommendations Assessment, Development, and Evaluation process for developing conclusions; recommendations developed by consensus.

RESULTS

Findings for incidence rates based on 12 Class I studies include the following: SUDEP risk in children with epilepsy (aged 0-17 years) is 0.22/1,000 patient-years (95% confidence interval [CI] 0.16-0.31) (moderate confidence in evidence). SUDEP risk increases in adults to 1.2/1,000 patient-years (95% CI 0.64-2.32) (low confidence in evidence). The major risk factor for SUDEP is the occurrence of generalized tonic-clonic seizures (GTCS); the SUDEP risk increases in association with increasing frequency of GTCS occurrence (high confidence in evidence).

RECOMMENDATIONS

Level B: Clinicians caring for young children with epilepsy should inform parents/guardians that in 1 year, SUDEP typically affects 1 in 4,500 children; therefore, 4,499 of 4,500 children will not be affected. Clinicians should inform adult patients with epilepsy that SUDEP typically affects 1 in 1,000 adults with epilepsy per year; therefore, annually 999 of 1,000 adults will not be affected. For persons with epilepsy who continue to experience GTCS, clinicians should continue to actively manage epilepsy therapies to reduce seizures and SUDEP risk while incorporating patient preferences and weighing the risks and benefits of any new approach. Clinicians should inform persons with epilepsy that seizure freedom, particularly freedom from GTCS, is strongly associated with decreased SUDEP risk.

Practice Guideline Summary: Sudden Unexpected Death in Epilepsy Incidence Rates and Risk Factors: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology and the American Epilepsy Society

OBJECTIVE

To determine the incidence rates of sudden unexpected death in epilepsy (SUDEP) in different epilepsy populations and address the question of whether risk factors for SUDEP have been identified.

METHODS

Systematic review of evidence; modified Grading Recommendations Assessment, Development and Evaluation process for developing conclusions; recommendations developed by consensus.

RESULTS

Findings for incidence rates based on 12 Class I studies include the following: SUDEP risk in children with epilepsy (aged 0-17 years) is 0.22/1,000 patient-years (95% CI 0.16-0.31) (high confidence in evidence). SUDEP risk increases in adults to 1.2/1,000 patient-years (95% CI 0.64-2.32) (low confidence in evidence). The major risk factor for SUDEP is the occurrence of generalized tonic-clonic seizures (GTCS); the SUDEP risk increases in association with increasing frequency of GTCS occurrence (high confidence in evidence).

RECOMMENDATIONS

Level B: Clinicians caring for young children with epilepsy should inform parents/guardians that in 1 year, SUDEP typically affects 1 in 4,500 children; therefore, 4,499 of 4,500 children will not be affected. Clinicians should inform adult patients with epilepsy that SUDEP typically affects 1 in 1,000 adults with epilepsy per year; therefore, annually 999 of 1,000 adults will not be affected. For persons with epilepsy who continue to experience GTCS, clinicians should continue to actively manage epilepsy therapies to reduce seizures and SUDEP risk while incorporating patient preferences and weighing the risks and benefits of any new approach. Clinicians should inform persons with epilepsy that seizure freedom, particularly freedom from GTCS, is strongly associated with decreased SUDEP risk.

Unravelling the mysteries of sudden unexpected death in epilepsy

INTRODUCTION

Sudden unexpected death in epilepsy (SUDEP) is the most frequent cause of premature death in epileptic patients. Most SUDEP events occur at night and frequently go unnoticed; the exact pathophysiological mechanisms of this phenomenon therefore remain undetermined. Nevertheless, most cases of SUDEP are attributed to an infrequent yet extremely severe complication of epileptic seizures.

DEVELOPMENT

We conducted a systematic literature search on PubMed. Our review article summarises scientific evidence on the classification, pathophysiological mechanisms, risk factors, biomarkers, and prevention of SUDEP. Likewise, we propose new lines of research and critically analyse findings that are relevant to clinical practice.

CONCLUSIONS

Current knowledge suggests that SUDEP is a heterogeneous phenomenon caused by multiple factors. In most cases, however, SUDEP is thought to be due to postictal cardiorespiratory failure triggered by generalised tonic-clonic seizures and ultimately leading to cardiac arrest. The underlying pathophysiological mechanism involves multiple factors, ranging from genetic predisposition to environmental factors. Risk of SUDEP is higher in young adults with uncontrolled generalised tonic-clonic seizures. However, patients apparently at lower risk may also experience SUDEP. Current research focuses on identifying genetic and neuroimaging biomarkers that may help determine which patients are at high risk for SUDEP. Antiepileptic treatment is the only preventive measure proven effective to date. Night-time monitoring together with early resuscitation may reduce the risk of SUDEP.

Determining factors of electrocardiographic abnormalities in patients with epilepsy: A case-control study

Sudden unexpected death in epilepsy (SUDEP) is a major cause of mortality in young patients with epilepsy (PWE). Although its mechanisms are still poorly understood, they may include cardiorespiratory dysfunction. Standard 12-lead electrocardiograms (ECGs) were obtained from 62 consecutive patients (aged 18-66y) with a definite diagnosis of epilepsy, without seizures at the day of ECG, and 57 healthy controls matched for sex, age and body mass index (BMI). All ECGs were evaluated by a blinded board-certified cardiologist. Patients with symptomatic focal epilepsy represented 90.3% (N=56), of whom 56.4% (N=35) had temporal lobe epilepsy, with a mean duration of 22.02±14.96years of epilepsy. We observed more prolonged P-wave (p<0.0001) and PR interval (p=0.01) in patients than in controls. Additionally, longer QT intervals (p<0.01), pathologic QT dispersion (p<0.01) and left atrial overload (p<0.01) were more common in PWE. Multiple linear regression analysis evidenced age, gender and polytherapy as factors associated with altered ECG. Therefore, routine ECG should be requested in PWE, especially for males, increasing age and in polytherapy. Findings such as longer PR and QT interval, and pathologic QT dispersion, may reflect cardiac structural changes and/or autonomic nervous system dysfunction and indicate a risk for SUDEP.

The role of antiepileptic drugs in sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) primarily affects young adults and is the leading cause of death related directly to seizures. High frequency of generalized tonic-clonic seizures is the most important risk factor, and effective seizure protection is probably the most important measure to prevent these tragic deaths. For several years a potential role of antiepileptic drugs (AEDs) has been discussed, but at present there is wide agreement that choice of AED therapy does not influence the risk. However, although it is well known that the efficacy and safety profiles of AEDs may differ significantly when used in the treatment of genetic epilepsy compared to symptomatic or cryptogenic epilepsy, this has generally been overlooked in epidemiologic studies of possible relationships between AEDs and SUDEP. Consequently important information about drug safety may have been lost. This review challenges the current view that no AED can increase the risk of SUDEP.

Cardiac arrhythmia in a mouse model of sodium channel SCN8A epileptic encephalopathy

Patients with early infantile epileptic encephalopathy (EIEE) are at increased risk for sudden unexpected death in epilepsy (SUDEP). De novo mutations of the sodium channel gene SCN8A, encoding the sodium channel Na_v1.6, result in EIEE13 (OMIM 614558), which has a 10% risk of SUDEP. Here, we investigated the cardiac phenotype of a mouse model expressing the gain of function EIEE13 patient mutation p.Asn1768Asp in Scn8a (Na_v1.6-N1768D). We tested Scn8a^N1768D/+ mice for alterations in cardiac excitability. We observed prolongation of the early stages of action potential (AP) repolarization in mutant myocytes vs. controls. Scn8a^N1768D/+ myocytes were hyperexcitable, with a lowered threshold for AP firing, increased incidence of delayed afterdepolarizations, increased calcium transient duration, increased incidence of diastolic calcium release, and ectopic contractility. Calcium transient duration and diastolic calcium release in the mutant myocytes were tetrodotoxin-sensitive. A selective inhibitor of reverse mode Na/Ca exchange blocked the increased incidence of diastolic calcium release in mutant cells. Scn8a^N1768D/+ mice exhibited bradycardia compared with controls. This difference in heart rate dissipated after administration of norepinephrine, and there were no differences in heart rate in denervated ex vivo hearts, implicating parasympathetic hyperexcitability in the Scn8a^N1768D/+ animals. When challenged with norepinephrine and caffeine to simulate a catecholaminergic surge, Scn8a^N1768D/+ mice showed ventricular arrhythmias. Two of three mutant mice under continuous ECG telemetry recording experienced death, with severe bradycardia preceding asystole. Thus, in addition to central neuron hyperexcitability, Scn8a^N1768D/+ mice have cardiac myoycte and parasympathetic neuron hyperexcitability. Simultaneous dysfunction in these systems may contribute to SUDEP associated with mutations of Scn8a.

The heart of epilepsy: Current views and future concepts

Cardiovascular (CV) comorbidities are common in people with epilepsy. Several mechanisms explain why these conditions tend to co-exist including causal associations, shared risk factors and those resulting from epilepsy or its treatment. Various arrhythmias occurring during and after seizures have been described. Ictal asystole is the most common cause. The converse phenomenon, arrhythmias causing seizures, appears extremely rare and has only been reported in children following cardioinihibitory syncope. Arrhythmias in epilepsy may not only result from seizure activity but also from a shared genetic susceptibility. Various cardiac and epilepsy genes could be implicated but firm evidence is still lacking. Several antiepileptic drugs (AEDs) triggering conduction abnormalities can also explain the co-existence of arrhythmias in epilepsy. Epidemiological studies have consistently shown that people with epilepsy have a higher prevalence of structural cardiac disease and a poorer CV risk profile than those without epilepsy. Shared CV risk factors, genetics and etiological factors can account for a significant part of the relationship between epilepsy and structural cardiac disease. Seizure activity may cause transient myocardial ischaemia and the Takotsubo syndrome. Additionally, certain AEDs may themselves negatively affect CV risk profile in epilepsy. Here we discuss the fascinating borderland of epilepsy and cardiovascular conditions. The review focuses on epidemiology, clinical presentations and possible mechanisms for shared pathophysiology. It concludes with a discussion of future developments and a call for validated screening instruments and guidelines aiding the early identification and treatment of CV comorbidity in epilepsy.

Baseline elevation and reduction in cardiac electrical instability assessed by quantitative T-wave alternans in patients with drug-resistant epilepsy treated with vagus nerve stimulation in the AspireSR E-36 trial

OBJECTIVE

Reports of cardiac arrhythmias and cardiac pathology at postmortem examination of patients with epilepsy suggest a possible cardiac component of risk for sudden unexpected death in epilepsy (SUDEP). T-wave alternans (TWA) is an established marker of cardiac electrical instability and risk for sudden death in patients with cardiovascular disease. We determined the TWA level before vagus nerve stimulation (VNS) system implantation and subsequently the effect of VNS on TWA in patients with drug-resistant epilepsy.

METHODS

Patients (n=28) from the Seizure Detection and Automatic Magnet Mode Performance Study (E-36), a clinical trial of the AspireSR® VNS Therapy System® (NCT01325623), were monitored with ambulatory electrocardiograms (ECGs) ~2weeks before de novo VNS system implantation and following 2- to 4-week VNS titration during a protocol-specified 3- to 5-day epilepsy monitoring unit stay with concurrent EEG/ECG recordings. The TWA level was assessed interictally by the Modified Moving Average (MMA) method.

RESULTS

At preimplantation baseline, TWA was elevated above the 47-μV abnormality cutpoint in 23 (82%) patients with drug-resistant epilepsy. In 16 (70%) patients, TWA level was reduced during VNS treatment to <47μV, thereby converting positive TWA test results to negative. Peak TWA level in all 28 patients improved (group mean, 43%, from 72±4.3 to 41±2.3μV; p<0.0001). Vagus nerve stimulation was not associated with reduced heart rate (77±1.4 to 75±1.4beats/min; p=0.18). Heart rate variability was unchanged.

SIGNIFICANCE

These findings suggest significant interictal cardiac electrical instability in this population of patients with drug-resistant epilepsy and suggest that VNS may be a novel approach to reducing risk.

Who to target in sudden unexpected death in epilepsy prevention and how? Risk factors, biomarkers, and intervention study designs

The risk of dying suddenly and unexpectedly is increased 24- to 28-fold among young people with epilepsy compared to the general population, but the incidence of sudden unexpected death in epilepsy (SUDEP) varies markedly depending on the epilepsy population. This article first reviews risk factors and biomarkers for SUDEP with the overall aim of enabling identification of epilepsy populations with different risk levels as a background for a discussion of possible intervention strategies. The by far most important clinical risk factor is frequency of generalized tonic-clonic seizures (GTCS), but nocturnal seizures, early age at onset, and long duration of epilepsy have been identified as additional risk factors. Lack of antiepileptic drug (AED) treatment or, in the context of clinical trials, adjunctive placebo versus active treatment is associated with increased risks. Despite considerable research, reliable electrophysiologic (electrocardiography [ECG] or electroencephalography [EEG]) biomarkers of SUDEP risk remain to be established. This is an important limitation for prevention strategies and intervention studies. There is a lack of biomarkers for SUDEP, and until validated biomarkers are found, the endpoint of interventions to prevent SUDEP must be SUDEP itself. These interventions, be they pharmacologic, seizure-detection devices, or nocturnal supervision, require large numbers. Possible methods for assessing prevention measures include public health community interventions, self-management, and more traditional (and much more expensive) randomized clinical trials.

Furthering our understanding of SUDEP: the role of animal models

Sudden and unexpected death in epilepsy (SUDEP) is the most common type of death among patients with epilepsy. Here, we address the importance of the experimental models in search of the mechanisms underlying SUDEP. Most studies have investigated the cardiovascular responses in animal models of epilepsy. However, there are few proposed SUDEP models in literature. Hypoventilation, apnea, respiratory distress, pulmonary hypertension, autonomic dysregulation and arrhythmia are common findings in epilepsy models. Impairments on adenosinergic and serotonergic systems, brainstem spreading depolarization, seizure-activation of neural substrates related to cardiorespiratory control, altered autonomic control, and mutations on sodium and potassium channels are hypothesis suggested. Overall, current research highlights the evident multifactorial nature of SUDEP, which involves acute and chronic aspects ranging from systemic to molecular alterations. Thus, we are convinced that elucidation and prevention of SUDEP can be achieved only through the interaction between basic and clinical science.

Impaired Serotonergic Brainstem Function during and after Seizures

Impaired breathing, cardiac function, and arousal during and after seizures are important causes of morbidity and mortality. Previous work suggests that these changes are associated with depressed brainstem function in the ictal and post-ictal periods. Lower brainstem serotonergic systems are postulated to play an important role in cardiorespiratory changes during and after seizures, whereas upper brainstem serotonergic and other systems regulate arousal. However, direct demonstration of seizure-associated neuronal activity changes in brainstem serotonergic regions has been lacking. Here, we performed multiunit and single-unit recordings from medullary raphe and midbrain dorsal raphe nuclei in an established rat seizure model while measuring changes in breathing rate and depth as well as heart rate. Serotonergic neurons were identified by immunohistochemistry. Respiratory rate, tidal volume, and minute ventilation were all significantly decreased during and after seizures in this model. We found that population firing of neurons in the medullary and midbrain raphe on multiunit recordings was significantly decreased during the ictal and post-ictal periods. Single-unit recordings from identified serotonergic neurons in the medullary raphe revealed highly consistently decreased firing during and after seizures. In contrast, firing of midbrain raphe serotonergic neurons was more variable, with a mixture of increases and decreases. The markedly suppressed firing of medullary serotonergic neurons supports their possible role in simultaneously impaired cardiorespiratory function in seizures. Decreased arousal likely arises from depressed population activity of several neuronal pools in the upper brainstem and forebrain. These findings have important implications for preventing morbidity and mortality in people living with epilepsy.

SIGNIFICANCE STATEMENT

Seizures often cause impaired breathing, cardiac dysfunction, and loss of consciousness. The brainstem and, specifically, brainstem serotonin neurons are thought to play an important role in controlling breathing, cardiac function, and arousal. We used an established rat seizure model to study the overall neuronal activity in the brainstem as well as firing of specific serotonin neurons while measuring cardiorespiratory function. Our results demonstrated overall decreases in brainstem neuronal activity and marked downregulation of lower brainstem serotonin neuronal firing in association with decreased breathing and heart rate during and after seizures. These findings point the way toward new treatments to augment brainstem function and serotonin, aiming to prevent seizure complications and reduce morbidity and mortality in people living with epilepsy.

Cardiac arrhythmias during or after epileptic seizures

Seizure-related cardiac arrhythmias are frequently reported and have been implicated as potential pathomechanisms of Sudden Unexpected Death in Epilepsy (SUDEP). We attempted to identify clinical profiles associated with various (post)ictal cardiac arrhythmias. We conducted a systematic search from the first date available to July 2013 on the combination of two terms: 'cardiac arrhythmias' and 'epilepsy'. The databases searched were PubMed, Embase (OVID version), Web of Science and COCHRANE Library. We attempted to identify all case reports and case series. We identified seven distinct patterns of (post)ictal cardiac arrhythmias: ictal asystole (103 cases), postictal asystole (13 cases), ictal bradycardia (25 cases), ictal atrioventricular (AV)-conduction block (11 cases), postictal AV-conduction block (2 cases), (post)ictal atrial flutter/atrial fibrillation (14 cases) and postictal ventricular fibrillation (3 cases). Ictal asystole had a mean prevalence of 0.318% (95% CI 0.316% to 0.320%) in people with refractory epilepsy who underwent video-EEG monitoring. Ictal asystole, bradycardia and AV-conduction block were self-limiting in all but one of the cases and seen during focal dyscognitive seizures. Seizure onset was mostly temporal (91%) without consistent lateralisation. Postictal arrhythmias were mostly found following convulsive seizures and often associated with (near) SUDEP. The contrasting clinical profiles of ictal and postictal arrhythmias suggest different pathomechanisms. Postictal rather than ictal arrhythmias seem of greater importance to the pathophysiology of SUDEP.

Cardiac and autonomic mechanisms contributing to SUDEP

Sudden unexpected death in epilepsy is likely caused by a cascade of events affecting the vegetative nervous system leading to cardiorespiratory failure and death. Multiple genetic, electrophysiological, neurochemical, and pharmacological cardiac alterations have been associated with epilepsy, which can affect autonomic regulation of the heart and predispose patients to sudden unexpected death in epilepsy. These cardiac and autonomic changes are more frequently seen in patients with longstanding and medication refractory epilepsy and may be a prerequisite for sudden unexpected death in epilepsy. Cardiac changes are also observed within the immediate periictal period in patients with and without preexisting cardiac pathology and could be the tipping point in the cascade of events compromising autonomic, respiratory, and cardiac function during an epileptic convulsion. Better understanding if and how these cardiac alterations can make a particular individual with epilepsy more susceptible to sudden unexpected death in epilepsy will hopefully lead us to more effective preventative strategies.

Third International Congress on Epilepsy, Brain, and Mind: Part 2

Epilepsy is both a disease of the brain and the mind. Here, we present the second of two papers with extended summaries of selected presentations of the Third International Congress on Epilepsy, Brain and Mind (April 3-5, 2014; Brno, Czech Republic). Humanistic, biologic, and therapeutic aspects of epilepsy, particularly those related to the mind, were discussed. The extended summaries provide current overviews of epilepsy, cognitive impairment, and treatment, including brain functional connectivity and functional organization; juvenile myoclonic epilepsy; cognitive problems in newly diagnosed epilepsy; SUDEP including studies on prevention and involvement of the serotoninergic system; aggression and antiepileptic drugs; body, mind, and brain, including pain, orientation, the "self-location", Gourmand syndrome, and obesity; euphoria, obsessions, and compulsions; and circumstantiality and psychiatric comorbidities.

Scn1b deletion leads to increased tetrodotoxin-sensitive sodium current, altered intracellular calcium homeostasis and arrhythmias in murine hearts

KEY POINTS

Na(+) current (INa) results from the integrated function of a molecular aggregate (the voltage-gated Na(+) channel complex) that includes the β subunit family. Mutations or rare variants in Scn1b (encoding the β1 and β1B subunits) have been associated with various inherited arrhythmogenic syndromes, including Brugada syndrome and sudden unexpected death in patients with epilepsy. We used Scn1b null mice to understand better the relation between Scn1b expression, and cardiac electrical function. Loss of Scn1b caused, among other effects, increased amplitude of tetrodotoxin-sensitive INa, delayed after-depolarizations, triggered beats, delayed Ca(2+) transients, frequent spontaneous calcium release events and increased susceptibility to polymorphic ventricular arrhythmias. Most alterations in Ca(2+) homeostasis were prevented by 100 nM tetrodotoxin. We propose that life-threatening arrhythmias in patients with mutations in Scn1b, a gene classically defined as ancillary to the Na(+) channel α subunit, can be partly consequent to disrupted intracellular Ca(2+) homeostasis.

ABSTRACT

Na(+) current (INa) is determined not only by the properties of the pore-forming voltage-gated Na(+) channel (VGSC) α subunit, but also by the integrated function of a molecular aggregate (the VGSC complex) that includes the VGSC β subunit family. Mutations or rare variants in Scn1b (encoding the β1 and β1B subunits) have been associated with various inherited arrhythmogenic syndromes, including cases of Brugada syndrome and sudden unexpected death in patients with epilepsy. Here, we have used Scn1b null mouse models to understand better the relation between Scn1b expression, and cardiac electrical function. Using a combination of macropatch and scanning ion conductance microscopy we show that loss of Scn1b in juvenile null animals resulted in increased tetrodotoxin-sensitive INa but only in the cell midsection, even before full T-tubule formation; the latter occurred concurrent with increased message abundance for the neuronal Scn3a mRNA, suggesting increased abundance of tetrodotoxin-sensitive NaV 1.3 protein and yet its exclusion from the region of the intercalated disc. Ventricular myocytes from cardiac-specific adult Scn1b null animals showed increased Scn3a message, prolonged action potential repolarization, presence of delayed after-depolarizations and triggered beats, delayed Ca(2+) transients and frequent spontaneous Ca(2+) release events and at the whole heart level, increased susceptibility to polymorphic ventricular arrhythmias. Most alterations in Ca(2+) homeostasis were prevented by 100 nM tetrodotoxin. Our results suggest that life-threatening arrhythmias in patients with mutations in Scn1b, a gene classically defined as ancillary to the Na(+) channel α subunit, can be partly consequent to disrupted intracellular Ca(2+) homeostasis in ventricular myocytes.

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 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.

Altered cardiac electrophysiology and SUDEP in a model of Dravet syndrome

Objective

Dravet syndrome is a severe form of intractable pediatric epilepsy with a high incidence of SUDEP: Sudden Unexpected Death in epilepsy. Cardiac arrhythmias are a proposed cause for some cases of SUDEP, yet the susceptibility and potential mechanism of arrhythmogenesis in Dravet syndrome remain unknown. The majority of Dravet syndrome patients have denovo mutations in SCN1A, resulting in haploinsufficiency. We propose that, in addition to neuronal hyperexcitability, SCN1A haploinsufficiency alters cardiac electrical function and produces arrhythmias, providing a potential mechanism for SUDEP.

Methods

Postnatal day 15-21 heterozygous SCN1A-R1407X knock-in mice, expressing a human Dravet syndrome mutation, were used to investigate a possible cardiac phenotype. A combination of single cell electrophysiology and invivo electrocardiogram (ECG) recordings were performed.

Results

We observed a 2-fold increase in both transient and persistent Na⁺ current density in isolated Dravet syndrome ventricular myocytes that resulted from increased activity of a tetrodotoxin-resistant Na⁺ current, likely Na_v1.5. Dravet syndrome myocytes exhibited increased excitability, action potential duration prolongation, and triggered activity. Continuous radiotelemetric ECG recordings showed QT prolongation, ventricular ectopic foci, idioventricular rhythms, beat-to-beat variability, ventricular fibrillation, and focal bradycardia. Spontaneous deaths were recorded in 2 DS mice, and a third became moribund and required euthanasia.

Interpretation

These data from single cell and whole animal experiments suggest that altered cardiac electrical function in Dravet syndrome may contribute to the susceptibility for arrhythmogenesis and SUDEP. These mechanistic insights may lead to critical risk assessment and intervention in human patients.

Interictal 12-lead electrocardiography in patients with epilepsy

Interictal electrocardiographic predictors of sudden unexpected death in epilepsy (SUDEP) are unknown. This study was designed to identify the unique features of the interictal 12-lead electrocardiogram (EKG) in patients with epileptic seizures. We conducted a retrospective chart review of adult patients below the age of 65 admitted to our epilepsy monitoring unit. Using EEG telemetry data, we classified patients as having nonepileptic seizures (NESs), probable epilepsy (PE), or definite epilepsy (DE) and analyzed 12-lead EKGs obtained on admission. Patients with NESs were assigned as the control group. We included patients taking antipsychotic and/or antidepressant medications but excluded patients with medical conditions or taking other medications that would otherwise confound EKG measurements. Out of the 1007 charts reviewed, 195 patients were included in our analysis, and extensive subgroup analyses were performed. We found that patients with definite localization-related epilepsy displayed a significantly longer average PR interval (162.1 ms) than patients with NESs (148.8 ms). This effect was pronounced in female patients and did not vary with the number of antiepileptic drugs (AEDs) prescribed. In contrast to previous studies, mean QTc intervals were not significantly different between DE (428 ms) and NESs (422.6 ms). However, within females, this difference reached statistical significance (DE: 434.6 ms, NESs: 424.6 ms). Antiepileptic drug polytherapy was associated with a significantly lower QTc interval (416 ms in patients on 4-6 drugs and 436.4 ms in patients on 0-1 drugs). Levetiracetam was the most commonly used AED and was associated with the longest average PR (163 ms) and QTc (432 ms) intervals. The mean QRS axis displayed a significant leftward shift in patients with localization-related epilepsy (35.6° versus 54.3° in patients with NESs) and also in female patients with DE (42.1° versus 55.4° in female patients with NESs). No differences were observed between patients with left versus right hemisphere seizure foci. Overall, these findings may reflect cardiac structural changes and/or alterations in autonomic tone that deserve closer study. Further, longer-term prospective studies are required to understand how these electrocardiographic signatures may predict sudden unexpected death in epilepsy.

Loss-of-function KCNH2 mutation in a family with long QT syndrome, epilepsy, and sudden death

There has been increased interest in a possible association between epilepsy channelopathies and cardiac arrhythmias, such as long QT syndrome (LQTS). We report a kindred that features LQTS, idiopathic epilepsy, and increased risk of sudden death. Genetic study showed a previously unreported heterozygous point mutation (c.246T>C) in the KCNH2 gene. Functional studies showed that the mutation induces severe loss of function. This observation provides further evidence for a possible link between idiopathic epilepsy and LQTS.

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.

QT and P wave dispersion and heart rate variability in patients with Dravet syndrome

SCN1A mutations are found in up to 80 % of patients with Dravet syndrome (DS), and the sudden unexpected death in epilepsy (SUDEP) rate is higher in DS than in most forms of severe epilepsy. The aim of this study is to examine the autonomic cardiac function and the risk of arrhythmia in DS patients by evaluating QT and P wave dispersion and heart rate variability (HRV) using standard electrocardiography (ECG) and 24-h ECG. The study group consisted of 15 patients (9 boys and 6 girls aged 3.5-17 years) who were genetically diagnosed with DS. The control group comprised 20 healthy subjects, 13 boys and 7 girls aged 4-17 years. P wave dispersion (44.6 ± 3.5 ms), QT dispersion (58.8 ± 7.5 ms) and QTc dispersion (70.8 ± 7.4 ms) were significantly higher in DS patients as compared to the control group (p < 0.001 for all values). However, there was no significant difference in PR, QT or QTc length between the groups. 24-h Holter ECG showed that all HRV parameters were significantly lower in patients with DS. The decreased HRV and increased P wave and QT dispersion seen in DS patients are important signs of autonomic dysfunction with increased adrenergic tone. To determine whether autonomic dysfunction is correlated with SUDEP in DS, long-term electrocardiographic monitoring and wider prospective studies are necessary.

Ictal modulation of cardiac repolarization, but not of heart rate, is lateralized in mesial temporal lobe epilepsy

Objectives

Human and animal studies provided controversial data on asymmetric cortical representation of cardiac function, which may partially be due to different study designs and inter-individual variability. Here, we investigated whether seizure-related changes in heart rate (HR) and cardiac repolarization depend on the side of seizure-activity in people with mesial temporal lobe epilepsy (mTLE).

Methods

To account for inter-individual variability, EEG and ECG data were reviewed from patients with medically refractory mTLE undergoing pre-surgical video-EEG telemetry with at least 2 seizures arising from each hippocampus as assessed by bilateral hippocampal depths electrodes. RR and QT intervals were determined at different timepoints using a one-lead ECG. QT intervals were corrected for HR (QTc) using 4 established formulas.

Results

Eighty-two seizures of 15 patients were analyzed. HR increased by ∼30% during hippocampal activity irrespective of the side (p = 0.411). QTc intervals were lengthened to a significantly greater extent during left hippocampal seizures (e.g. difference of QT intervals between preictal and ictal state using Bazett’s formula; left side 32.0±5.3 ms, right side 15.6±7.7 ms; p = 0.016). Abnormal QTc prolongation occurred in 7 of 41 left hippocampal seizures of 4 patients, and only in 2 of 37 right hippocampal seizures of 2 patients.

Conclusions

Seizure-related modulation of cardiac repolarization, but not of HR, appears to depend on the side of ictal activity, strengthening the hypothesis of asymmetric cerebral representation of cardiac function. The clinical relevance of this is unclear, but may indicate an increased risk of abnormal ictal QT prolongation in people with left mTLE.

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.

Seizures following hippocampal kindling induce QT interval prolongation and increased susceptibility to arrhythmias in rats

The prolonged seizures of status epilepticus produce chronic arrhythmogenic changes in cardiac function. This study was designed to determine if repeated, self-limiting seizures administered to kindled rats induce similar cardiac dysfunction. Multiple seizures administered to rats following hippocampal kindling resulted in cardiac QT interval prolongation and increased susceptibility to experimental arrhythmias. These data suggest that multiple, self-limiting seizures of intractable epilepsy may have cardiac effects that can contribute to sudden unexpected death in epilepsy (SUDEP).

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.

Epilepsy is a risk factor for sudden cardiac arrest in the general population

BACKGROUND

People with epilepsy are at increased risk for sudden death. The most prevalent cause of sudden death in the general population is sudden cardiac arrest (SCA) due to ventricular fibrillation (VF). SCA may contribute to the increased incidence of sudden death in people with epilepsy. We assessed whether the risk for SCA is increased in epilepsy by determining the risk for SCA among people with active epilepsy in a community-based study.

METHODS AND RESULTS

This investigation was part of the Amsterdam Resuscitation Studies (ARREST) in the Netherlands. It was designed to assess SCA risk in the general population. All SCA cases in the study area were identified and matched to controls (by age, sex, and SCA date). A diagnosis of active epilepsy was ascertained in all cases and controls. Relative risk for SCA was estimated by calculating the adjusted odds ratios using conditional logistic regression (adjustment was made for known risk factors for SCA). We identified 1019 cases of SCA with ECG-documented VF, and matched them to 2834 controls. There were 12 people with active epilepsy among cases and 12 among controls. Epilepsy was associated with a three-fold increased risk for SCA (adjusted OR 2.9 [95%CI 1.1-8.0.], p=0.034). The risk for SCA in epilepsy was particularly increased in young and females.

CONCLUSION

Epilepsy in the general population seems to be associated with an increased risk for SCA.

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.

Comparison of corrected QT interval as measured on electroencephalography versus 12-lead electrocardiography in children with a history of syncope

Long QT syndrome can present with neurological manifestations, including syncope and seizure-like activity. These patients often receive an initial neurologic evaluation, including electroencephalography (EEG). Our previous retrospective study suggested an increased prevalence of prolonged corrected QT interval (QTc) measured during the EEG of patients with syncope. The aim of the current study is to assess the accuracy of the EEG QTc reading compared with the nonsimultaneous 12-lead electrocardiography (ECG) in children with syncope. Abnormal QTc was defined as ≥450 ms in boys, ≥460 ms in girls. Forty-two children were included. There was no significant correlation between QTc readings in the EEG and ECG. EEG failed to identify 2 children with prolonged QTc in the ECG and overestimated the QTc in 3 children with normal QTc in the ECG. This study suggests that interpretation of the QTc segment during an EEG is limited. Further studies with simultaneous EEG and 12-lead ECG are warranted.

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.