Repeated generalized seizures can produce calcified cardiac lesions in DBA/1 mice

Audiogenic epileptic DBA/2 mice strain as a model of genetic reflex seizures and SUDEP

Epilepsy is a chronic neurological disease characterized by abnormal brain activity, which results in repeated spontaneous seizures. Sudden unexpected death in epilepsy (SUDEP) is the leading cause of seizure-related premature death, particularly in drug-resistant epilepsy patients. The etiology of SUDEP is a structural injury to the brain that is not fully understood, but it is frequently associated with poorly controlled and repeated generalized tonic-clonic seizures (GTCSs) that cause cardiorespiratory and autonomic dysfunctions, indicating the involvement of the brainstem. Both respiratory and cardiac abnormalities have been observed in SUDEP, but not much progress has been made in their prevention. Owing to the complexity of SUDEP, experimental animal models have been used to investigate cardiac and/or respiratory dysregulation due to or associated with epileptic seizures that may contribute to death in humans. Numerous rodent models, especially mouse models, have been developed to better understand epilepsy and SUDEP physiopathology. This review synthesizes the current knowledge about dilute brown agouti coat color (DBA/2) mice as a possible SUDEP model because respiratory arrest (RA) and sudden death induced by audiogenic generalized seizures (AGSs) have been observed in these animals. Respiratory/cardiac dysfunction, brainstem arousal system dysfunction, and alteration of the neurotransmitter systems, which are observed in human SUDEP, have also been observed in these mice. In particular, serotonin (5-HT) alteration and adenosine neurotransmission appear to contribute to not only the pathophysiological mechanisms of medication but also seizure-related respiratory dysfunctions in this animal model. These neurotransmitter systems could be the relevant targets for medication development for chronic epilepsy and SUDEP prevention. We reviewed data on AGSs in DBA/2 mice and the relevance of this model of generalized tonic-clonic epilepsy to human SUDEP. Furthermore, the advantages of using this strain prone to AGSs for the identification of possible new therapeutic targets and treatment options have also been assessed.

The mechanism of sudden unexpected death in epilepsy: A mini review

Sudden unexpected death in epilepsy (SUDEP) is defined as a sudden, unexpected, non-traumatic, non-drowning death in a person with epilepsy. SUDEP is generally considered to result from seizure-related cardiac dysfunction, respiratory depression, autonomic nervous dysfunction, or brain dysfunction. Frequency of generalized tonic clonic seizures (GTCS), prone posture, and refractory epilepsy are considered risk factors. SUDEP has also been associated with inherited cardiac ion channel disease and severe obstructive sleep apnea. Most previous studies of SUDEP mechanisms have focused on cardiac and respiratory dysfunction and imbalance of the neural regulatory system. Cardiac-related mechanisms include reduction in heart rate variability and prolongation of QT interval, which can lead to arrhythmias. Laryngospasm and amygdala activation may cause obstructive and central apnea, respectively. Neural mechanisms include impairment of 5-HT and adenosine neuromodulation. The research to date regarding molecular mechanisms of SUDEP is relatively limited. Most studies have focused on p-glycoprotein, catecholamines, potassium channels, and the renin-angiotensin system, all of which affect cardiac and respiratory function.

The role of monoaminergic neurons in modulating respiration during sleep and the connection with SUDEP

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death among epilepsy patients, occurring even more frequently in cases with anti-epileptic drug resistance. Despite some advancements in characterizing SUDEP, the underlying mechanism remains incompletely understood. This review summarizes the latest advances in our understanding of the pathogenic mechanisms of SUDEP, in order to identify possible targets for the development of new strategies to prevent SUDEP. Based on our previous research along with the current literature, we focus on the role of sleep-disordered breathing (SDB) and its related neural mechanisms to consider the possible roles of monoaminergic neurons in the modulation of respiration during sleep and the occurrence of SUDEP. Overall, this review suggests that targeting the monoaminergic neurons is a promising approach to preventing SUDEP. The proposed roles of SDB and related monoaminergic neural mechanisms in SUDEP provide new insights for explaining the pathogenesis of SUDEP.

Acute and chronic cardiorespiratory consequences of focal intrahippocampal administration of seizure-inducing agents. Implications for SUDEP

The risk factors for SUDEP are undoubtedly heterogenous but the main factor is the frequency of generalized tonic-clonic seizures with apnoea and/or cardiac abnormalities likely precipitating the lethal event. By its very nature modelling SUDEP experimentally is challenging, yet insights into the nature of the lethal event and precipitating factors are vital in order to understand and prevent fatalities. Acute animal models, which induce status epilepticus (SE), can be used to help understand pathophysiological processes during and following seizures, which sometimes lead to death. The most commonly used method to induce seizures and status epilepticus is systemic administration of an ictogenic agent. Microinjection of such agents into restricted regions within the brain induces a more localised epileptic focus and circumvents the risk of direct actions on cardiorespiratory control centres. Both approaches have revealed substantial cardiovascular and respiratory consequences, including death as a result of apnoea, which may be of central origin, obstructive due to laryngospasm or, at least in genetically modified mice, a result of spreading depolarisation to medullary respiratory control centres. SUDEP is by definition a result of epilepsy, which in turn is diagnosed on the basis of two or more unprovoked seizures. The incidence of tonic-clonic seizures is the main risk factor, raising the possibility that repeated seizures cause cumulative pathological and/or pathophysiological changes that contribute to the risk of SUDEP. Chronic experimental models, which induce repeated seizures that in some cases lead to death, do show progressive development of pathophysiological changes in the myocardium, e.g. prolongation of QT the interval of the ECG or, over longer periods, ventricular hypertrophy. However, the currently available evidence indicates that seizure-related deaths are primarily due to apnoeas, but cardiac factors, particularly cumulative cardiac pathophysiologies due to repeated seizures, are potential contributing factors.

Epileptic heart: A clinical syndromic approach

Prevention of premature death in patients with chronic epilepsy remains a major challenge. Multiple pathophysiologic factors have been implicated, with intense investigation of cardiorespiratory mechanisms. Up to four in five patients with chronic epilepsy exhibit cardiovascular comorbidities. These findings led us to propose the concept of an "epileptic heart," defined as "a heart and coronary vasculature damaged by chronic epilepsy as a result of repeated surges in catecholamines and hypoxemia leading to electrical and mechanical dysfunction." Among the most prominent changes documented in the literature are high incidence of myocardial infarction and arrhythmia, altered autonomic tone, diastolic dysfunction, hyperlipidemia, and accelerated atherosclerosis. This suite of pathologic changes prompted us to propose for the first time in this review a syndromic approach for improved clinical detection of the epileptic heart condition. In this review, we discuss the key pathophysiologic mechanisms underlying the candidate criteria along with standard and novel techniques that permit evaluation of each of these factors. Specifically, we present evidence of the utility of standard 12-lead, ambulatory, and multiday patch-based electrocardiograms, along with measures of cardiac electrical instability, including T-wave alternans, heart rate variability to detect altered autonomic tone, echocardiography to detect diastolic dysfunction, and plasma biomarkers for assessing hyperlipidemia and accelerated atherosclerosis. Ultimately, the proposed clinical syndromic approach is intended to improve monitoring and evaluation of cardiac risk in patients with chronic epilepsy to foster improved therapeutic strategies to reduce premature cardiac death.

Cardiorespiratory findings in epilepsy: A recent review on outcomes and pathophysiology

Epilepsy is a debilitating disorder of uncontrollable recurrent seizures that occurs as a result of imbalances in the brain excitatory and inhibitory neuronal signals, that could stem from a range of functional and structural neuronal impairments. Globally, nearly 70 million people are negatively impacted by epilepsy and its comorbidities. One such comorbidity is the effect epilepsy has on the autonomic nervous system (ANS), which plays a role in the control of blood circulation, respiration and gastrointestinal function. These epilepsy-induced impairments in the circulatory and respiratory systems may contribute toward sudden unexpected death in epilepsy (SUDEP). Although, various hypotheses have been proposed regarding the role of epilepsy on ANS, the linking pathological mechanism still remains unclear. Channelopathies and seizure-induced damages in ANS-control brain structures were some of the causal/pathological candidates of cardiorespiratory comorbidities in epilepsy patients, especially in those who were drug resistant. However, emerging preclinical research suggest that neurotransmitter/receptor dysfunction and synaptic changes in the ANS may also contribute to the epilepsy-related autonomic disorders. Thus, pathological mechanisms of cardiorespiratory dysfunction should be elucidated by considering the modifications in anatomy and physiology of the autonomic system caused by seizures. In this regard, we present a comprehensive review of the current literature, both clinical and preclinical animal studies, on the cardiorespiratory findings in epilepsy and elucidate the possible pathological mechanisms of these findings, in hopes to prevent SUDEP especially in patients who are drug resistant.

The number and periodicity of seizures induce cardiac remodeling and changes in micro-RNA expression in rats submitted to electric amygdala kindling model of epilepsy

Generalized tonic-clonic seizures (GTCS) are the main risk factor for sudden unexpected death in epilepsy (SUDEP). Also, among the several mechanisms underlying SUDEP there is the cardiac dysfunction. So, we aimed to evaluate the impact of the number of seizures on heart function and morphology in rats with epilepsy. Rats were randomized into three groups: Sham (without epilepsy), 5 S, and 10 S groups, referred as rats with epilepsy with a total of 5 or 10 GTCS, respectively. Epilepsy was induced by electrical amygdala kindling. The ventricular function was analyzed by the Langendorff technique and challenged by ischemia/reperfusion protocol. Cardiac fibrosis and hypertrophy were analyzed by histology. We also analyzed cardiac metalloproteinases (MMP2 and MMP9), ERK 1/2 and phosphorylated ERK1/2 (P-ERK) by western blot; microRNA-21 and -320 by RT-PCR; and oxidative stress (TBARS, catalase activity and nitrite) by biochemical analysis. Only the 5S group presented decreased values of ventricular function at before ischemia/reperfusion (baseline): intraventricular systolic pressure, developed intraventricular pressure, positive and negative dP/dt. During ischemia/reperfusion protocol, the variation of the ventricular function did not differ among groups. Both 5S and 10S groups had increased cardiomyocyte hypertrophy and fibrosis compared to Sham, but in the 5S group, these alterations were higher than in the 10S group. The 5S group increased in microRNA-21 and decreased in microRNA-320 expression compared to Sham and the 10S group. The 10S group increased in MMP9 and decreased in P-ERK/ERK expression, and increased in nitrite content compared to both Sham and the 5S group. Therefore, seizures impair cardiac function and morphology, probably through microRNA modulation. The continuation of seizures seems to exert a preconditioning-like stimulus that fails to compensate the cardiac tissue alteration.

Central deficiency of norepinephrine synthesis and norepinephrinergic neurotransmission contributes to seizure-induced respiratory arrest

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of mortality in patients with intractable epilepsy. However, the pathogenesis of SUDEP seems to be poorly understood. Our previous findings showed that the incidence of seizure-induced respiratory arrest (S-IRA) was markedly reduced by atomoxetine in a murine SUDEP model. Because the central norepinephrine α-1 receptor (NEα-1R) plays a vital role in regulating respiratory function, we hypothesized that the suppression of S-IRA by atomoxetine was mediated by NE/NEα-1R interactions that can be reversed by NEα-1R antagonism. We examined whether atomoxetine-mediated suppression of S-IRA evoked by either acoustic stimulation or pentylenetetrazole (PTZ) in DBA/1 mice can be reversed by intraperitoneal (IP) and intracerebroventricular (ICV) administration of prazosin, a selective antagonist of NEα-1R. The content and activity of tyrosine hydroxylase (TH), a rate-limiting enzyme for NE synthesis, in the lower brainstem was measured by ELISA. Electroencephalograms (EEG) were obtained from using the PTZ-evoked SUDEP model. In our models, atomoxetine-mediated suppression of S-IRA evoked by either acoustic stimulation or PTZ was significantly reversed by low doses of IP and ICV prazosin. Neither repetitive acoustic stimulation nor S-IRA reduced TH levels in lower brainstem. However, the enzyme activity of TH levels in lower brainstem was significantly increased by mechanical ventilation with DBA/1 mice, which makes the dying DBA/1 mice suffering from S-IRA and SUDEP recover. EEG data showed that although the protective effect of atomoxetine was reversed by prazosin, neither drug suppressed EEG activity. These data suggest that deficient synthesis of NE and norepinephrinergic neurotransmission contributed to S-IRA and that the NEα-1R is a potential therapeutic target for the prevention of SUDEP.

The Epileptic Heart: Concept and clinical evidence

Sudden unexpected death in epilepsy (SUDEP) is generally considered to result from a seizure, typically convulsive and usually but not always occurring during sleep, followed by a sequence of events in the postictal period starting with respiratory distress and progressing to eventual cardiac asystole and death. Yet, recent community-based studies indicate a 3-fold greater incidence of sudden cardiac death in patients with chronic epilepsy than in the general population, and that in 66% of cases, the cardiac arrest occurred during routine daily activity and without a temporal relationship with a typical seizure. To distinguish a primarily cardiac cause of death in patients with epilepsy from the above description of SUDEP, we propose the concept of the "Epileptic Heart" as "a heart and coronary vasculature damaged by chronic epilepsy as a result of repeated surges in catecholamines and hypoxemia leading to electrical and mechanical dysfunction." This review starts with an overview of the pathophysiological and other lines of evidence supporting the biological plausibility of the Epileptic Heart, followed by a description of tools that have been used to generate new electrocardiogram (EKG)-derived data in patients with epilepsy that strongly support the Epileptic Heart concept and its propensity to cause sudden cardiac death in patients with epilepsy independent of an immediately preceding seizure.

[Sudden unexpected death in epilepsy (SUDEP) : Epidemiology, cardiac and other risk factors]

Sudden unexpected death in epilepsy (SUDEP) is one of the most frequent epilepsy-related causes of death. The incidence of SUDEP is estimated to be approximately 1.2/1000 person-years (PY); however, it varies considerably depending on disease-specific and demographic factors. The estimated incidence of SUDEP in children seems to be significantly lower (0.22/1000 PY) than in adults but recent studies in children (>12 years) indicated a similar incidence to that of adults. Based on these estimations, approximately 700 SUDEP cases would be expected in Germany annually but no reliable data or epidemiological studies on SUDEP are available. Various risk factors and predictors for SUDEP have been investigated, e.g. age, seizure frequency, number of antiepileptic drugs, non-compliance and comorbidities, with sometimes contradictory results. This is understandable given that the exact mechanisms of SUDEP are unclear; however, it is very likely that the frequency of (nocturnal) generalized tonic-clonic seizures is the most important risk factor. Nocturnal monitoring of seizures (using devices) or the presence of another person at night may represent important factors to reduce the risk of SUDEP. Thus, seizure control and seizure monitoring are, according to current knowledge, the most important factors to avoid SUDEP. Some recent studies have contributed to a better understanding of possible pathomechanisms of SUDEP; however, further research is needed to identify predictive clinical factors and biomarkers and in particular to prevent SUDEP.