Cardiac dysfunction during status epilepticus in the neonatal pig

β adrenergic blockade prevents cardiac dysfunction following status epilepticus in rats

Status epilepticus (SE) can result in temporary cardiac dysfunction in patients, characterized by reduced ejection fraction, decreased ventricular contractility, and alterations in electrical activity of the heart. Although reversible, the cardiac effects of seizures are acutely life threatening, and may contribute to the delayed mortality following SE. The precise mechanisms mediating acute cardiac dysfunctions are not known. These studies evaluated effects of self-sustaining limbic SE in rats on cardiac performance 24h following seizures, and determined if sympathetic nervous system activation during seizures contributed to cardiac dysfunction. Rats subjected to SE received either vehicle (saline) or the B1 adrenergic antagonist atenolol (AT) prior to and during 90 min of seizure activity. Control rats were similarly treated, except they did not undergo seizures. Twenty-four hours after SE, animals were anesthetized and catheterized for measurement of cardiac performance variables. Animals undergoing SE demonstrated significantly reduced cardiac output, decreased ventricular contractility and relaxation, increased blood pressure, and prolonged QT interval. However, heart rate was not altered. Treatment with AT prevented all changes in cardiac performance due to SE, and attenuated the increase in QT interval. These data demonstrate that SE in the rat results in cardiac dysfunction 24h following seizures, mediated by the sympathetic nervous system.

Status epilepticus induces cardiac myofilament damage and increased susceptibility to arrhythmias in rats

Status epilepticus (SE) is a seizure or series of seizures that persist for >30 min and often results in mortality. Death rarely occurs during or immediately following seizure activity, but usually within 30 days. Although ventricular arrhythmias have been implicated in SE-related mortality, the effects of this prolonged seizure activity on the cardiac function and susceptibility to arrhythmias have not been directly investigated. We evaluated myocardial damage, alterations in cardiac electrical activity, and susceptibility to experimentally induced arrhythmias produced by SE in rats. SE resulted in seizure-related increases in blood pressure, heart rate, and the first derivative of pressure, as well as modest, diffuse myocyte damage assessed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining. Ten to twelve days following seizures, electrocardiographic recordings showed arrhythmogenic alterations in cardiac electrical activity, denoted by prolonged QT interval corrected for heart rate and QT dispersion. Finally, SE increased susceptibility to experimentally induced (intravenous aconitine) cardiac arrhythmias. These data suggest that SE produces tachycardic ischemia following the activation of the sympathetic nervous system, resulting in cardiac myofilament damage, arrhythmogenic alterations in cardiac electrical activity, and increased susceptibility to ventricular arrhythmias.

Ischemic stroke mimicking acute myocardial infarction, a diagnostic dilemma

Neurocardiogenic dysfunction is described in acute neurological injury. We report a case of ischemic stroke mimicking acute myocardial infarction.

Poor outcome after hypoxia-ischemia in newborns is associated with physiological abnormalities during early recovery. Possible relevance to secondary brain injury after head trauma in infants

"Secondary hypoxia/ischemia" (i.e. regional impairment of oxygen and substrate delivery) results in secondary deterioration after traumatic brain injury in adults as well as in children and infants. However, detailed analysis regarding critical physiological abnormalities resulting from hypoxia/ischemia in the immature brain, e.g. acid-base-status, serum glucose levels and brain temperature, and their influence on outcome, are only available from non-traumatic experimental models. In recent studies on hypoxic/asphyxic cardiac arrest in neonatal piglets, we were able to predict short-term outcome using specific physiologic abnormalities immediately after the insult. Severe acidosis, low serum glucose levels and fever after resuscitation were associated with an adverse neurologic recovery one day after the insult. The occurrence of clinically apparent seizure activity during later recovery increased mortality (epileptic state), and survivors had greater neocortical and striatal brain damage. Brain damage after transient hypoxia/ischemia and "secondary brain injury" after head trauma may have some mechanistic overlap, and these findings on physiological predictors of outcome may also apply to pathologic conditions in the post-traumatic immature brain. Evaluation of data from other models of brain injury will be important to develop candidate treatment strategies for head-injured infants and children and may help to initiate specific studies about the possible role of these physiological predictors of brain damage in the traumatically injured immature brain.

Primary sensory and forebrain motor systems in the newborn brain are preferentially damaged by hypoxia-ischemia

Cerebral hypoxia-ischemia causes encephalopathy and neurologic disabilities in newborns by unclear mechanisms. We tested the hypothesis that hypoxia-ischemia causes brain damage in newborns that is system-preferential and related to regional oxidative metabolism. One-week-old piglets were subjected to 30 minutes of hypoxia and then seven minutes of airway occlusion, producing asphyxic cardiac arrest, followed by cardiopulmonary resuscitation and four-day recovery. Brain injury in hypoxic-ischemia piglets (n = 6) compared to controls (n = 5) was analyzed by hematoxylin-eosin, Nissl, and silver staining, relationships between regional vulnerability and oxidative metabolism were evaluated by cytochrome oxidase histochemistry. Profile counting-based estimates showed that 13% and 27% of neurons in layers II/III and layers of somatosensory cortex had ischemic cytopathology, respectively; CA1 neuronal perikarya appeared undamaged, and < 10% of CA3 and CA4 neurons were injured; and neuronal damage was 79% in putamen, 17% in caudate, but nucleus accumbens was undamaged. Injury was found preferentially in primary sensory neocortices (particularly somatosensory cortex), basal ganglia (predominantly putamen, subthalamic nucleus, and substantia nigra reticulata), ventral thalamus, geniculate nuclei, and tectal nuclei. In sham piglets, vulnerable region generally had higher cytochrome oxidase levels than less vulnerable areas. Postischemic alterations in cytochrome oxidase were regional and laminar, with reductions (31-66%) occurring in vulnerable regions and increases (20%) in less vulnerable areas. We conclude that neonatal hypoxia-ischemia causes highly organized, system-preferential and topographic encephalopathy, targeting regions that function in sensorimotor integration and movement control. This distribution of neonatal encephalopathy is dictated possibly by regional function, mitochondrial activity, and connectivity.

Recurrent seizures alter renal function and plasma atrial natriuretic peptide levels in rats

Status epilepticus can lead to impaired renal function, which has been attributed to complications of myoglobinuria. We confirmed changes in renal function in the absence of myoglobinuria by measuring renal hemodynamics, fluid and electrolyte excretions, and plasma levels of renin and atrial natriuretic peptide (ANP) before and after a 30-min period of recurrent generalized seizures in anesthetized, paralyzed rats. Renal plasma flow (RPF), renal blood flow (RBF) and glomerular filtration rate (GFR) decreased by approximately 60% after seizures. In contrast, urinary sodium excretion, urine flow, and plasma ANP levels increased approximately threefold. Urinary potassium excretion and plasma renin levels were unchanged. Renal function is profoundly altered after 30 min of seizures, primarily due to intense renal vasoconstriction precipitating a dramatic reduction in GFR. The concomitant increases in sodium and urine excretion may be mediated by the marked increase in plasma ANP levels. The decreases in GFR and RBF might contribute to the renal failure observed in some patients after status epilepticus.

Immunological aspects of experimental allergic encephalomyelitis and multiple sclerosis

Multiple sclerosis (MS) is the most frequent, demyelinating disease of the central nervous system (CNS) in Northern Europeans and North Americans. Despite intensive research its etiology is still unknown, but a T cell-mediated autoimmune pathogenesis is likely to be responsible for the demyelination. This hypothesis is based both on findings in MS patients and studies of an experimental animal model for demyelinating diseases, experimental allergic encephalomyelitis (EAE). Experiments in EAE have not only demonstrated which myelin antigens are able to induce the demyelinating process but also have determined the characteristics of encephalitogenic T cells, that is, their fine specificity, major histocompatibility complex (MHC) restriction, lymphokine secretion, activation requirements, and T cell receptor (TCR) usage. Based on these findings, highly specific and efficient immune interventions have been designed in EAE and have raised hopes that similar approaches could modulate the disease process in MS. Although the examination of the myelin-specific T cell response in MS patients has shown parallels to EAE, this remains an area of intensive research because a number of questions remain. This review summarizes the important lessons from EAE, examines recent findings in MS, and discusses current concepts about how the disease process develops and which steps might be taken to modulate it.

Cardiac output and regional hemodynamics during recurrent seizures in rats

Altered cardiovascular function in status epilepticus may contribute to mortality and morbidity in patients. We investigated changes in cardiac output and regional hemodynamics during 2 h of recurrent PTZ-induced seizures in anesthetized, paralyzed rats using radioactive microspheres, thermodilution methods, and the pulsed Doppler technique. Cardiac output fell 30-60% during recurrent seizures in 17 of 27 animals. The fall in cardiac output was sudden in onset and occurred primarily in association with seizures accompanied by prolonged increases in MABP but no change in central venous pressure. Total peripheral resistance (TPR) rose during early seizures in association with vasoconstriction of renal and certain splanchnic vascular beds. Ictal increases in TPR became attenuated during late seizures, due to failure of renal and splanchnic beds to constrict. Therefore, derangements in both cardiac and vascular function occur during late seizures. These derangements may contribute to both cerebral hypoperfusion and sudden death in status epilepticus.

Relative hypoperfusion in rat cerebral cortex during recurrent seizures

Focal cortical CBF and oxygenation were measured in rats during repetitive seizures to determine whether CBF is maintained above a critical level for adequate delivery of O2. Cerebral oxygenation was determined by measuring relative changes in the oxidation/reduction level of cytochrome aa3 and CBF was measured by the washout of H2. During early seizures, cortical CBF increased to 350% of control and cortical oxygenation also rose markedly. During later seizures, both the increases in CBF and in cortical oxygenation were attenuated progressively. This was accompanied also by attenuation of the associated increases in MABP. Cortical oxygenation decreased during a seizure if the increase in CBF failed to exceed 150-200% of control, defining the critical CBF value. Ventilating the rats on 97% O2 resulted in restoration of the seizure-associated increases in cortical oxygenation in 50% of the cases. The elevation of inspired O2 was effective only if CBF increased once again above 150-200% of control, confirming that the critical CBF lies within this range of values. We conclude that CBF must rise greater than 200% of control levels to provide sufficient O2 to meet the enhanced metabolic requirements of repetitive seizures.

In vivo 31P and in vitro 1H nuclear magnetic resonance study of hypoglycemia during neonatal seizure

To examine the hypothesis that hypoglycemia has an adverse effect on brain energy state during seizure, neonatal dogs were subjected to bicuculline-induced seizure while hyperglycemic, normoglycemic, or hypoglycemic. Cerebral blood flow increased and remained elevated in all animals subjected to seizure, regardless of blood or brain glucose concentration. In vivo 31P nuclear magnetic resonance spectroscopy disclosed a small (10-20%) decrease in adenosine triphosphate levels and a greater (20-40%) decline in phosphocreatine levels in animals experiencing seizure, irrespective of whether they were hyper-, normo-, or hypoglycemic. In vitro analysis of brain extracts with 1H nuclear magnetic resonance spectroscopy disclosed a significant elevation of lactate in all seizing animals. There were differences in brain alanine, glycine, and beta-hydroxybutyrate levels between the hyperglycemia-seizure and hypoglycemia-seizure groups. Alternate substrates such as lactate, fatty acids, or amino acids may be used when neonatal seizure is complicated by hypoglycemia, thereby preventing further deterioration of brain metabolic state.

Epileptogenesis and the immature brain

Epidemiological studies indicate that the incidence of seizures is highest early in life. This report discusses the experimental data derived from studies of focal epileptogenesis of the immature brain in tandem with ongoing maturational changes. During development, neurons have characteristic neurophysiological properties. Local interictal discharges are long in duration, lack a stereotypic morphology, and have limited fields. Yet the immature brain is very susceptible to the development of bilateral, although asynchronous, seizures and status epilepticus induced by amygdala kindling or by convulsant drugs. This increased seizure susceptibility may be due to a functional immaturity of a substantia nigra, GABA-sensitive output system. The morbidity of convulsions occurring early in life may not be as grave as previously thought in terms of subsequent acquisition of "normal" developmental milestones. The propensity to develop recurrent convulsions in adulthood is not related to the severity of a single seizure in infancy. Although multiple severe seizures may predispose animals to the development of seizures later in life, this is not a unique feature of the immature brain, since it also occurs in the adult brain. Finally, there is evidence that the immature brain may respond to anticonvulsant drugs differently from its mature counterpart; these findings emphasize the need to develop new antiepileptic therapies that take into account the maturational state of the brain.

Mental deterioration in epilepsy

A variety of factors could potentially influence the occurrence of mental deterioration in epilepsy, including seizure type, age of seizure onset, seizure duration, and seizure severity. The available literature suggests that measures of severity are more predictive of progressive decreases in intellectual functioning. There is also evidence suggesting that seizure severity and cognitive deterioration might both be the result of underlying pathophysiologic abnormalities in some cases. In the majority of patients with epilepsy, however, with relatively less severe disease, there is little evidence for cognitive deterioration. Total seizure number also has an inverse correlation with level of psychosocial functioning in some studies, whereas others have found that patients with emotional difficulties have fewer seizures. In the case of emotional deterioration, the impact of interpersonal relationships and other environmental factors upon psychosocial outcome seems clear, and the evidence for specific pathophysiologic explanations for emotional deterioration, less convincing.