Neurogenic myocardial arrhythmias in experimental focal epilepsy

Amiodarone, a multi-channel blocker, enhances anticonvulsive effect of carbamazepine in the mouse maximal electroshock model

Cardiac arrhythmia may occur in the course of epilepsy. Simultaneous therapy of the two diseases might be complicated by drug interactions since antiarrhythmic and antiepileptic agents share some molecular targets. The aim of this study was to evaluate the influence of amiodarone, an antiarrhythmic drug working as a multi-channel blocker, on the protective activity of four classical antiepileptic drugs in the maximal electroshock test in mice. Amiodarone at doses up to 75 mg/kg did not affect the electroconvulsive threshold in mice. Acute amiodarone at the dose of 75 mg/kg significantly potentiated the anticonvulsive effect of carbamazepine, but not that of valproate, phenytoin or phenobarbital in the maximal electroshock-induced seizures in mice. The antiarrhythmic agent and its combinations with antiepileptic drugs did not impair motor performance or long-term memory in mice, except for the combination of amiodarone and phenobarbital. Brain concentrations of antiepileptic drugs were not changed. Despite favourable impact of amiodarone on the anticonvulsive action of carbamazepine in the maximal electroshock, co-administration of the two drugs should be carefully monitored in clinical conditions. Further studies are necessary to evaluate effects of chronic treatment with amiodarone on seizure activity and the action of antiepileptic drugs.

Activation and involvement of the lateral-posterior nucleus of the thalamus after a single generalized tonic-clonic seizure

The lateral-posterior thalamic nuclei (LP) have been shown to play an important role in controlling epileptic activity. In addition, thalamic atrophy and neuronal loss have been observed in epilepsy. The objective of this study was to investigate whether lateral-posterior neuronal activation may be observed shortly after a single generalized seizure in rats submitted to the pilocarpine model of epilepsy. The results showed an increased lateral-posterior activation as soon as the seizure occurred, suggesting that neuronal loss in the thalamus is not only the consequence of chronic epilepsy.

Arrhythmogenic seizures

Arrhythmogenic seizures may represent one of the mechanisms implicated in sudden unexpected death in epilepsy. Various cardiac changes can be observed during epileptic seizures. However, reports of well-documented, life-threatening cardiac arrhythmias in the literature are scarce. The pathogenesis of these arrhythmias and speculations about the cortical localization of cardioarrhythmogenic triggers are reviewed.

Recurrent unexplained syncope may have a cerebral origin: report of 10 cases of arrhythmogenic epilepsy

BACKGROUND

Despite thorough investigation, approximately 15-20% of syncope cases remain unexplained. An underrecognized cause of syncope may occur when partial epileptic discharges profoundly disrupt normal cardiac rhythm, including cardiac asystole, the so-called arrhythmogenic epilepsy (AE).

AIM

To report initial results of observations of AE in patients with recurrent, unexplained, traumatic and/or convulsive syncope.

METHODS

Ten patients aged 49+/-20 years (median 49.5 years; nine women) underwent complete cardiological (including ambulatory Holter electrocardiogram (ECG), echocardiography and head-up tilt test [plus electrophysiology in four patients]) and neurological (including standard electroencephalogram [EEG], computed tomography [CT] and magnetic resonance imaging scan [MRI]) assessments.

RESULTS

After initial evaluation, neurocardiogenic syncope was suspected in six patients with tilt-induced hypotension+/-bradycardia. Further evaluation (prolonged inpatient video-EEG/ECG monitoring) was undertaken because of non-diagnostic syncope or uncertainty about the diagnosis of neurocardiogenic syncope. While monitored in the neurophysiology lab, a syncopal episode similar to the spontaneous episodes recurred in all 10 patients. Cardiac asystole preceded by partial seizure of temporal onset was documented in nine patients; a second-degree atrioventricular (AV) block with a cardiac rhythm of 30 beats per minute preceded by partial seizure of temporal onset was noted in one patient. Eight patients were treated successfully with antiepileptic drugs; two were refractory to antiepileptic therapy and required pacemaker implantation. No patient had recurrent syncope during a median follow-up of 102.5 months (mean 82.2+/-42; range 16-128 months).

CONCLUSIONS

In patients with recurrent, unexplained, traumatic and/or convulsive syncope, AE should be considered as a possible aetiology.

The mystery of sudden death: mechanisms for risks

This review addresses the possible overlapping mechanisms that may apply to the risk of sudden unexpected death occurring in epilepsy and in cardiac disease. It explores the interaction between the central and peripheral autonomic nervous systems and the cardiopulmonary systems. Included is a discussion of the potential interactive role of genetically determined subtle cardiac risk factors for arrhythmias with a predisposition for seizure-related cardiac arrhythmias. We address the possible mechanisms that are operant in producing both epileptogenic and cardiogenic arrhythmias. Finally, we speculate about potential preventive measures to minimize the risk of both sudden unexpected death in epilepsy and sudden cardiac death.

Sudden death in epilepsy: An experimental animal model

INTRODUCTION

The physiopathogenetic mechanisms possibly involved in sudden unexplained epileptic death (SUDEP), were investigated in the hemispherectomized rat.

METHODS

For this purpose, paroxysmal activity, vagal nerve firing, systemic blood pressure (BP), pulmonary artery pressure, and ECG were simultaneously recorded in an experimental animal model of epilepsy. Recordings were performed in basal conditions and during paroxysmal activity induced by topical application of penicillin-G at hypothalamic and mesencephalic level. During the experiment were also performed hemogas analysis and at end, samples of lung tissue were processed for histology.

RESULTS

Activation of hypothalamic (HEF) and mesencephalic (MEF) epileptic foci induced a significant increase of spontaneous vagal nerve firing that was strictly correlated to ECG impairments and hypotension. When paroxysmal activity extinguished, vagal nerve activity and cardiovascular parameters returned to basal conditions. However, in 25% of the animals, co-activation of HEF and MEF always triggered a vagal hypertone which was temporally correlated to cardiac arrhythmias, but also to hyperkalemia, acidosis, pulmonary hypertension and to animal death. Histological control in lungs of deceased animals showed an alveolar and perivessel oedema with an oedematous infiltration in the alveolar and bronchial spaces and mucous secretion. During ictal activity, comparison between survived and deceased animals showed significant differences in the incidence of ECG impairment of pulmonary artery pressures, pO2, and pCO2 pressures, and [K+], [HCO3-], and [pH], concentrations.

DISCUSSION

A possible explanation of the above observations is discussed in relationship to SUDEP physiopathogenesis.

Coroner and medical examiner documentation of sudden unexplained deaths in epilepsy

BACKGROUND

Prevalence data for sudden unexplained death in epilepsy (SUDEP) are hampered by its underuse as a final diagnosis on death certificates in appropriate cases. Few data exist about how coroners (COs) and medical examiners (MEs) in the United States use the diagnosis of SUDEP.

METHODS

A survey instrument that addressed demographics, professional background, annual cases of epilepsy, seizure history, percentage of post-mortem examinations, cause of death, and use of SUDEP as a diagnosis was sent to all COs and MEs in the United States. Unadjusted comparisons between categorical variables used chi2 tests. A multiple regression model examined the odds of respondents considering SUDEP to be a valid diagnosis.

RESULTS

Of 2995 surveys, 80.7% went to COs and 19.3% to MEs. The response rate was 15.9% for COs and 21.8% for MEs. Acknowledgment of SUDEP as a valid entity was greatest among pathologists (83.5%) versus other physicians and non-physicians (P< .001) and correlated with higher autopsy rates and seeing more cases of epilepsy. In actual practice, SUDEP was not used routinely as a death certificate diagnosis in most cases with no cause of death found at autopsy by any group in the survey regardless of title, educational background, location, autopsy rate, or number of seizure cases seen annually.

CONCLUSIONS

SUDEP appears to be an underused final diagnosis by COs and MEs throughout the United States. There is a need to educate officials at all levels about this diagnosis in persons who have epilepsy with no other cause of death.

Does epilepsy surgery lower the mortality of drug-resistant epilepsy?

Drug-resistant epilepsy has proved to be associated with an increased standardized mortality ratio (SMR), primarily due to seizure-related fatalities including sudden unexpected death (SUDEP). Recent studies have suggested that the surgical cure of temporal lobe epilepsy (TLE) was likely to normalize the SMR of patients suffering from refractory TLE. However, these studies raise a number of methodological issues, which have not always been fully addressed. Some conclusions have relied on previously reported data, indicating a SMR of approximately 5, and a SUDEP incidence of 9/1000 patient-years in drug-resistant epilepsy. In fact, as shown in this review, SMR varied considerably, from 2 to 16, in the various series of patients with refractory epilepsy, whereas the average SUDEP incidence in the same populations was calculated at 3.7/1000 patient-years. Other conclusions were based on the comparison of either surgically and medically treated patients, or cured and non-cured operated patients. In both situations, the two groups included a different proportion of excellent and poor surgical candidates. The biological differences that distinguish these two populations might explain part of the differences observed in their mortality rate, regardless of the effect of surgery. In particular, temporal-plus epilepsies involving the insula, the frontal orbital, or the frontal operculum region, might favour ictal arrhythmias, central apnoea and secondary generalization, which in turn would increase the risk of SUDEP. Future studies are thus warranted to specifically address these issues.

Clinical pharmacology: drugs as a benefit and/or risk in sudden unexpected death in epilepsy?

Death may be the consequence of natural or unnatural causes, such as accidents, homicide, and suicide, which have no relationship to the disease of epilepsy. Direct causes of death include status epilepticus, and indirect causes may be head trauma or drowning subsequent to a seizure. When death occurs suddenly and without explanation, the term sudden unexpected unexplained death is used. Unexplained is a term that clinicians and research scientists are working to clarify. Numerous preclinical animal studies have been conducted as models for sudden death and have led to clinical studies in persons with epilepsy. These studies show that sympathetic nerve stimulation, ouabain, or coronary occlusion increased temporal dispersion of recovery of ventricular excitability and led to an underlying electrical instability that predisposed the ventricularmyocardium to arrhythmia. Cardiac arrhythmias in an animal model for ouabain-induced toxicity were associated with neural autonomic dysfunction. Neural discharges were characterized by increases, decreases, or no change in the discharge of postganglionic cardiac sympathetic nerves monitored simultaneously, predisposing to cardiac arrhythmia. Stimulation of the sympathetic ventrolateral cardiac nerve produced a shift in the origin of the pacemaker and tachyarrhythmias because the nerve is not uniformly distributed to the various regions of the heart but is localized to the atrioventricular junctional and ventricular regions. Such nonuniform distribution of sympathetic nerves would also contribute to initiation of arrhythmia as a nonuniform neural discharge occurred. Studies examining the physiology and pharmacology of this finding in multiple animal models found that subconvulsant, interictal discharge was associated with autonomic cardiac neural non-uniform discharge and cardiac arrhythmias. As a result of further investigations, Lathers and Schraeder edited a book in 1990 that summarized the clinical problem of sudden unexpected death and epilepsy (SUDEP). The contributors concluded that there was a paucity of clinical data addressing the mechanism of death. Regulatory response resulting from the consequent increased awareness of SUDEP occurred in 1993, when the FDA focused attention of practitioners and pharmaceutical manufacturers on the question of whether use of anticonvulsant drugs contributes to or prevents sudden unexpected death in epileptic persons. The FDA-convened panel of scientists considered the prevalence of sudden unexpected death in patients involved in studies associated with developing new anticonvulsant drugs and reviewed data on the risk of sudden unexpected death in patients taking lamotrigine. The risk of SUDEP was no different from thatfound in the young epilepsy population in general. Estimated SUDEP rates in patients receiving the new anticonvulsant drugs lamotrigine, gabapentin, topiramate, tigabine, and zonisamide were found to be similar to those in patients receiving standard anticonvulsant drugs, suggesting that SUDEP rates reflect population rates and not a specific drug effect. The FDA required warning labels on the risk of SUDEP in association with the use of each of the above-mentioned drugs. Another effect of bringing SUDEP to the attention of epilepsy researchers has been the expansion of basic science and the development of epidemiological and clinical studies directed at this phenomenon. Results from some of these studies are discussed in this article.

Autonomic nervous system activity and life threatening arrhythmias in experimental epilepsy

In the present study the possible derangement of the autonomic system and its influence in life threatening arrhythmias were analysed during paroxysmal activity. In hemispherectomized rats a paroxysmal activation of the hypothalamic and mesencephalic cardioarrhythmogenic triggers was performed by topical application of penicillin-G. Blood gas parameters and electrical activity of the thalamus, hypothalamus, vagal nerve fibre, ECG and arterial blood pressure were simultaneously monitored in basal conditions and repeated after the appearance of paroxysmal activity. Temporal correlation analysis was carried out. Results showed that during activation of these triggers, the spontaneous vagal nerve fibre activity significantly increased and triggered the appearance of cardiac arrhythmias which could become life threatening and induce animal death when blood gas and electrolytic parameters were simultaneously impaired. These experiments suggest that fatal evolution of the heart impairment is related not only to an autonomic cardiac trigger, but also to a concomitant metabolic derangement, which most likely shares the same autonomic origin.

[Bradycardia as an epileptic manifestation in temporal epilepsy: report of a case]

We describe a patient who had cardiac arrhythmia as epileptic manifestation. In a 34-year-old woman who had many episodes of loss of consciousness, the simultaneous ECG and video-EEG monitoring recorded bradycardia with a short episode of asystole (4 seconds) and left temporal rhythmic theta activity on EEG. MRI showed a small mass lesion in the left parahippocampal gyrus. Alterations in cardiac rhythm have been reported in epileptic seizures and tachycardia is the most common finding associated with them; bradyarrhythmia during seizures was uncommon. Many interconnections among insular cortex, limbic system and hypothalamus, may be responsible for vegetative manifestations in temporal lobe epilepsy.

Kindled seizures activate both branches of the autonomic nervous system

Amygdaloid kindled seizures in the rat induce an abrupt elevation of blood pressure accompanied by a significant decrease in heart rate. The autonomic pharmacology of this response was examined in unanesthetized kindled rats. Muscarinic receptor blockade with atropine (1 mg/kg, intravenous (i.v.)) abolished the seizure-induced bradycardia. The seizure-induced hypertension was unaffected by beta-adrenergic blockade with timolol (1 mg/kg, i.v.), but was reduced by phentolamine (5 mg/kg, subcutaneous (s.c.)), an alpha-adrenergic receptor antagonist. A chemical sympathectomy was induced with 6-hydroxydopamine (100 mg/kg, i.v.), an agent that does not cross the blood-brain barrier. This eliminated the pressor response but did not completely block the seizure-induced bradycardia. The effectiveness of 6-hydroxydopamine was tested with tyramine (0.5 mg/kg, i.v.) an agent that releases endogenous catecholamines. These results indicate amygdaloid kindled seizures activate both branches of the autonomic nervous system. The bradycardia was mediated by the parasympathetic system; the pressor response was caused by an increase in peripheral resistance due to alpha-adrenergic receptor activation. More important, these findings show that kindling is a useful seizure model for future studies on the effect of seizures on cardiovascular function and possible mechanisms of seizure-related sudden unexplained death.

Bradycardia induced from stimulation of the left versus right central nucleus of the amygdala

Studies have demonstrated that the predominant effect of stimulation of the central nucleus of the amygdala is one of heart rate deceleration. Anatomical studies have shown that projections from the central nucleus to the cardioinhibitory neurons in the medulla are ipsilateral and that projections of the left or right vagal efferents to the heart innervate different nodal points. The results of this study suggest that stimulation of the central nucleus of the amygdala from either the left or right hemisphere produced similar increases in heart period. These results are discussed in terms of the effects of the localization of epileptic foci in the temporal lobes on the cardiovascular system.

Immobilization stress induces c-fos and c-jun immediate early genes expression in the heart

Emotional stress is considered to be one of the etiological factors in ischemic heart disease (IHD) and sudden cardiac death (SCD), mechanisms of which are poorly understood. Immediate early genes (IEGs), such as c-fos and c-jun are used as tools for detection of cellular activation. Male Wistar rats were exposed to acute immobilization (IMO). IMO stress for 30 min induced c-fos and c-jun mRNAs expression in the myocardium and the smooth muscle layer of the coronary arteries. IMO stress for 2 h also induced Fos and Jun like-immunoreactivities in the same regions. Distribution of IEG mRNAs and their protein products in the myocardium was not uniform but rather localized. These data provided histological evidence for an early cellular event in the stress response whose consequences could result in activation of tissues in the myocardium and coronary arterial smooth muscle cells which play a role in the pathophysiological changes in IHD and SCD.

The effect of amygdaloid kindling on heart period and heart period variability

Two studies were conducted on rats to assess the effects of amygdaloid kindling on baseline measures of heart period and heart period variance. The results indicate that seizure activity was associated with increased vagal influence on heart period marked by sinus bradycardia and decreased beat-to-beat variability. The resultant bradycardia was enhanced following each seizure and persisted for at least a one-week period of time. The results are discussed in terms of the role of vagal tone in influencing abnormal cardiac patterns which could result in sudden unexplained death in some epileptic patients.

Cerebellar and mesencephalic influence on bulbar penicillin-G epileptogenesis in rats

The influence of the cerebellum and mesencephalon on epileptic bulbar discharge induced by topical application of penicillin-G on the floor of the IVth ventricle was analyzed in rats. Bulbar multiunit activity was recorded at different depths. The animals were divided into two main groups: totally cerebellectomized rats (Group I) and lobus anterior cerebellectomized rats (Group II). Each main group was further subdivided into two subgroups: animals with intact mesencephalon and animals with transected mesencephalon. In Group I: the total cerebellectomy, in intact mesencephalic rats (first subgroup) induced a sudden disappearance of bulbar epileptic discharge. The mid-collicular transection (second subgroup) produced the immediate disappearance of bulbar paroxysms and the total cerebellectomy, subsequently performed, further decreased the spontaneous firing rate. In Group II: (first subgroup) the lobus anterior ablation in rats with intact mesencephalon, significantly enhanced the paroxysmal discharge. In the second subgroup, where the midcollicular transection had provoked the disappearance of bulbar paroxysms, the lobus anterior ablation induced the immediate reappearance of the paroxysmal activity. The penicillin-G epileptogenic activity showed a different intensity at different depths in the bulb with a maximum intensity at the level of the vestibular nuclei. In conclusion, the present study shows that both the mesencephalon and the cerebellum have a facilitating influence on bulbar epileptic discharge induced by the topical application of the GABA antagonist. However, not all the cerebellum has a facilitating effect, because the anterior lobus was found to have an inhibitory influence on bulbar discharge.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of phenobarbital on autonomic function and epileptogenic activity induced by the hippocampal injection of penicillin in cats

This study addressed whether penicillin-induced epileptiform discharges in the right hippocampus produced associated autonomic dysfunction. The study also examined the effect of phenobarbital on the heart rate and blood pressure changes that were induced by the epileptiform discharges. The delay in onset of epileptiform activity at the site of injection ranged from 1 second to 16 minutes, and consisted of interictal discharges or ictal discharges. With the onset of epileptiform activity, blood pressure and heart rate increased significantly from control (P < .05). Electrocardiogram alterations included: P-R interval changes; increased P-wave amplitude; QRS complex changes; T-wave inversion; and ST elevation. Phenobarbital 20 mg/kg intravenously suppressed the epileptogenic activity and depressed the blood pressure and heart rate below control (P < .05). In an additional series of experiments, penicillin G injected into the right hippocampus in five cats produced epileptiform activity and increased the blood pressure and the heart rate significantly from the control (P < .05). Phenobarbital (20 mg/kg, intravenously, and 40 mg/kg, intravenously) also prevented the penicillin-induced epileptiform activity. Phenobarbital (40 mg/kg, intravenously) reversed the effect of penicillin on the blood pressure and heart rate, to levels significantly below that of control (P < .05). Phenobarbital diminished both epileptiform activity and autonomic dysfunction. The autonomic dysfunction related to epileptiform activity induced by focal hippocampal administration of penicillin was similar to that induced by the intravenous administration of pentylenetetrazol.

The brainstem cardioarrhythmogenic triggers and their possible role in sudden epileptic death

The cardiovascular effects of simultaneous activation of hypothalamic and mesencephalic cardioarrhythmogenic triggers were studied in hemispherectomized rats. Paroxysmal activity of hypothalamic neurons (HEF), elicited by topical application of penicillin G on the thalamus, triggered short-lasting bradyarrhythmic episodes, up to a maximum of 6 s, and alterations in repolarization. In the hypothalamic neurons, an additional penicillin G epileptic focus at mesencephalic level (MEF) induced the enhancement of paroxysmal activity by a recruitment of new units and potentiation of their background activity. HEF+MEF triggered second-degree 2:1-8:1 atrioventricular (A-V) blocks, impairment of the A-V conduction, alterations in the recovery phase and bundle branch blocks. After HEF, the arterial blood pressure decreased by 4-6%. HEF+MEF induced a further reduction of 17% in systolic pressure only. It is possible that the enhancement of the HEF following MEF could depend on MEF spreading upward. The HEF, in turn, by spreading downward could influence the MEF and so activate, between HEF and MEF, a circuitry with reciprocal co-excitation that could explain the more serious cardiovascular alterations observed during HEF+MEF compared with those observed during HEF only or during MEF only. However, this cardiovascular impairment, which must be neurogenic in origin as it was observed in animals with normal acid-base and blood parameter values, did not induce heart death. Thus, additional concomitances must be considered, such as metabolic derangement which can occur during seizures, to explain sudden death in epileptic patients. Some aspects of metabolic complications in cardiac activity during epilepsy are also discussed.

Atrial fibrillation after acute stroke

BACKGROUND AND PURPOSE

Atrial fibrillation (AF) is a risk factor for stroke, although it may not always be directly responsible for the stroke. On the other hand, cardiac arrhythmias and electrocardiographic changes have been reported after ischemic stroke and numerous other intracranial pathologies. We tested the hypothesis that some patients with acute stroke may develop transient AF as a consequence of the stroke.

METHODS

This study was based on 1,661 patients with first-ever stroke consecutively hospitalized and prospectively included into the Lausanne Stroke Registry. "Recent AF" was defined as AF discovered at or after ("after-admission" AF) admission in patients without any previous history of AF. Populations with recent AF and after-admission AF were compared for AF evolution, risk factors, and lesion type and distribution with patients with previous history of AF (known AF) and with patients with another recognized cardiac source of embolism (cardioembolic).

RESULTS

Twenty-four patients had recent AF on admission, and 17 developed it a few hours to 3 days after stroke. AF disappeared after a few days in 26 (63%; 94% of after-admission AF) patients. Stroke was a primary hematoma in 9.8% of patients with recent AF, 2.8% of patients with known AF, and 0.9% (p < 0.001) of patients with cardiac source of embolism. Parietoinsular (32%) and brain stem (11%) involvement were more common in recent AF than in cardioembolic stroke in general (16.7% and 6.7%, respectively; p < 0.05).

CONCLUSIONS

AF discovered after an acute stroke lasted no more than a few days, suggesting that it may have occurred as a consequence of the stroke. This possibility is emphasized by the significant predominance in patients with recent AF of primary hematoma, which cannot be caused by AF, and of parietoinsular and brain stem involvement, which are experimentally known as arrhythmogenic. This hypothesis should be considered in patients with acute stroke and previously unknown AF before therapeutic decisions are made.

Syncope--brain or heart? A case report

A 44-year-old man suffered from recurrent episodes of unconsciousness, without any other concomitant manifestations. After routine workup, EEG and CT had proven nondiagnostic, prolonged Holter monitoring revealed a single episode of asystole, lasting 7.6 seconds. A pacemaker was inserted but did not abolish his episodic syncope. Subsequently, long-term EEG recording revealed epileptiform activity with independent foci in both temporal lobes. Antiepileptic treatment relieved the patient of his symptoms. This case illustrates the intimate relationship between the heart and the brain that sometimes lies behind syncope.

The sudden unexplained death syndrome in epilepsy: demographic, clinical, and postmortem features

Sudden unexplained death syndrome (SUDS) accounts for about 10% of deaths in patients with epilepsy. It is associated with subtherapeutic postmortem serum antiepileptic drug (AED) levels but no anatomic cause of death on autopsy. The mechanisms of death are not known. We investigated 44 cases of SUDS for details of seizure history, treatment, medical and psychological history, events at the time of death, and postmortem findings. Cases of status epilepticus, drowning or other identifiable causes of death were excluded. Two groups emerged: five children with uncontrolled seizures receiving multiple AEDs and good compliance with medications, and 39 adults with less frequent seizures, often receiving monotherapy, but noncompliant with medications. Four children (80%) but only one adult (3%) had fully therapeutic postmortem AED levels. Sixty-three percent of adults recently had experienced an unusually stressful life event. Investigation of the circumstances at the time of death suggested two possible modes of death: (a) a seizure with an immediately fatal arrhythmia, or, (b) a seizure, recovery, then delayed secondary respiratory arrest or arrhythmia. Even though the mechanisms of death are unknown, the risk of SUDS may be reduced by encouraging patients to be compliant with medications, especially in times of unusual life stress.

Penicillin-induced paroxysmal activity in brainstem neurons

The spontaneous electrical activity of single mesencephalic and bulbar neurons was recorded in hemispherectomized rats, following topical application of the GABA-antagonist penicillin-G on the mesencephalon or on the rhombencephalon, to investigate whether these structures could develop a specific penicillin paroxysmal activity independently of the upper structures. Twenty minutes following penicillin-G, the mesencephalic neurons developed paroxysmal activity characterized by a significant increase in the spontaneous electrical activity, the appearance of multiunit activity and, frequently, phasic activity with rhythmical outbursts. The paroxysmal activity at bulbar level appeared later than that observed in the mesencephalon and was characterized by a significant increase of the spontaneous firing rate of the neurons, single short bursts and sometimes rhythmical outbursts. The bulbar outbursts always discharged at lower frequency than those at the mesencephalic level. Following a midcollicular transection the paroxysmal bulbar activity abruptly disappeared. This phenomenon might be explained by a loss of facilitation from superior structures on the bulbar neurons which in roditors show a poor GABA-receptor distribution. In other words, penicillin alone, due to the scarcity of GABA receptors, might not be sufficient to induce paroxysmal activity in bulbar neurons but the simultaneous presence of both the superior facilitation and the drug might enhance neuronal excitability to a critical level. However, the diffusion of the drug upwards to the mesencephalon, with consequent activation of a system allowing the downward propagation of paroxysmal activity, cannot be excluded. In conclusion, while the mesencephalic neurons demonstrate a proper ability to develop penicillin paroxysmal discharge, the bulbar neurons must be sustained by intact connections with upper structures to be able to do so.

Analysis of central cardioarrhythmogenic triggers in experimental epilepsy

The cardioarrhythmogenic potential of epileptic foci induced at mesencephalic and rhombencephalic levels was analyzed in hemispherectomized rats. Topical application of penicillin-G onto the mesencephalic quadrigeminal lamina or onto the fourth ventricle induced paroxysmal activity at the mesencephalic or bulbar neurone level. At the mesencephalic levels, the paroxysmal activity was characterized by a significant increase in the spontaneous frequency of the neurones, with the appearance of multiunit activity and rhythmical outbursts. The simultaneous recording of myocardial electrical activity and blood pressure showed that the paroxysmal activity triggered short-latency sinus bradyarrhythmias with wandering of the sinus pacemaker, the appearance of biphasic or negative P waves, some premature ventricular contractions and non-significant reduction of systolic and diastolic pressures. When the paroxysmal activity stopped, the cardiac rhythm and blood pressure returned to basal values. At the bulbar level, the paroxysmal activity appeared with longer latency and usually the rhythmical outbursts were not observed. Following bulbar paroxysmal activity only short-lasting episodes of sinus bradyarrhythmias appeared. Midcollicular transection eliminated paroxysmal activity at the bulbar level, and blood pressure and cardiac rhythm resumed basal values. After transection, an additional application of convulsant drug (penicillin-G or pentylenetetrazole) onto the fourth ventricle did not induce the reappearance of paroxysmal activity and the consequent cardiovascular alterations. The results showed the existence of a cardioarrhythmogenic trigger localized at the mesencephalic level which spreads paroxysmal activity upwards. A hypothesis to explain the appearance of fetal haemodynamic modifications and life-threatening arrhythmias has been proposed.

Kindled seizures elevate blood pressure and induce cardiac arrhythmias

The effect of kindled seizures on the cardiovascular system was examined in amygdaloid kindled rats. The most prominent cardiovascular response during a generalized kindled seizure was an abrupt 50% increase in mean arterial pressure (MAP) lasting 20-30 s after initiation of the seizure. Superimposed on this change in blood pressure (BP) was a profound bradycardia characterized by a rate about half that recorded before stimulation. Changes in heart rate (HR) and BP observed during amygdaloid kindled seizures were similar to those observed during secondary spontaneous seizures. These effects apparently are independent of the kindling stimulus because stimulus-induced cardiovascular changes were not present at the beginning of the kindling process. These results suggest that the kindling seizure model is useful to study the underlying mechanisms of seizure-induced cardiac arrhythmias and possibly the clinical phenomenon of sudden unexplained death in epileptic patients.

Bradycardia and syncope as manifestations of partial epilepsy

Although transient increases in heart rate typically occur, bradycardia has infrequently been noted in association with partial seizures. Five patients with temporal lobe epilepsy are described in whom sinus bradyarrhythmias and syncope were prominent manifestations of seizure activity. Partial improvement occurred in one of two patients in whom a permanent pacemaker was implanted before a diagnosis of epilepsy was established. Treatment with phenytoin or carbamazepine resulted in nearly complete resolution of symptoms in all five patients. Because pacemaker implantation does not prevent recurrent symptoms, but anticonvulsant therapy does, this experience underscores the importance of considering the diagnosis of partial epilepsy in selected patients with sinus bradyarrhythmias and syncope.