Interictal alterations of cardiovagal function in chronic epilepsy

Exercise-induced central and peripheral sympathetic activity in a community-based group of epilepsy patients differ from healthy controls

Ictal and interictal activity within the autonomic nervous system is characterized by a sympathetic overshoot in people with epilepsy. This autonomic dysfunction is assumed to be driven by alterations in the central autonomic network. In this study, exercise-induced changes of the interrelation of central and peripheral autonomic activity in patients with epilepsy was assessed. 21 patients with epilepsy (16 seizure-free), and 21 healthy matched controls performed an exhaustive bicycle ergometer test. Immediately before and after the exercise test, resting state electroencephalography measurements (Brain Products GmbH, 128-channel actiCHamp) of 5 min were carried out to investigate functional connectivity assessed by phase locking value in source space for whole brain, central autonomic network and visual network. Additionally, 1-lead ECG (Brain products GmbH) was performed to analyze parasympathetic (root mean square of successive differences (RMSSD) of the heart rate variability) and sympathetic activity (electrodermal activity (meanEDA)). MeanEDA increased (p < 0.001) and RMSSD decreased (p < 0.001) from pre to post-exercise in both groups. Correlation coefficients of meanEDA and central autonomic network functional connectivity differed significantly between the groups (p = 0.004) after exercise. Both patients with epilepsy and normal control subjects revealed the expected physiological peripheral autonomic responses to acute exhaustive exercise, but alterations of the correlation between central autonomic and peripheral sympathetic activity may indicate a different sympathetic reactivity after exercise in patients with epilepsy. The clinical relevance of this finding and its modulators (seizures, anti-seizure medication, etc.) still needs to be elucidated.

Assessing epilepsy-related autonomic manifestations: Beyond cardiac and respiratory investigations

The Autonomic Nervous System (ANS) regulates many critical physiological functions. Its control relies on cortical input, especially limbic areas, which are often involved in epilepsy. Peri-ictal autonomic dysfunction is now well documented, but inter-ictal dysregulation is less studied. In this review, we discuss the available data on epilepsy-related autonomic dysfunction and the objective tests available. Epilepsy is associated with sympathetic-parasympathetic imbalance and a shift towards sympathetic dominance. Objective tests report alterations in heart rate, baroreflex function, cerebral autoregulation, sweat glands activity, thermoregulation, gastrointestinal and urinary function. However, some tests have found contradictory results and many tests suffer from a lack of sensitivity and reproducibility. Further study on interictal ANS function is required to further understand autonomic dysregulation and the potential association with clinically-relevant complications, including risk of Sudden Unexpected Death In Epilepsy (SUDEP).

Early transient dysautonomia predicts the risk of infantile epileptic spasm syndrome onset: A prospective cohort study

Background

Infantile epileptic spasm syndrome (IESS) is an age-dependent epileptic encephalopathy with a significant risk of developmental regression. This study investigates the association between heart rate variability (HRV) in infants at risk of IESS and the clinical onset of IESS.

Methods

Sixty neonates at risk of IESS were prospectively followed from birth to 12 months with simultaneous electroencephalogram (EEG) and electrocardiogram recordings for 60 min at every 2-month interval. HRV metrics were calculated from 5 min time-epoch during sleep including frequency domain measures, Poincare analysis including cardiac vagal index (CVI) and cardiac sympathetic index (CSI), and detrended fluctuation analysis (DFA α1, DFA α2). To assess the effect of each HRV metric at the 2-month baseline on the time until the first occurrence of either hypsarrhythmia on EEG and/or clinical spasm, univariate cox-proportional hazard models were fitted for each HRV metric.

Results

Infantile epileptic spasm syndrome was diagnosed in 20/60 (33%) of the cohort in a 12-month follow-up and 3 (5%) were lost to follow-up. The median age of developing hypsarrhythmia was 25 (7-53) weeks and clinical spasms at 24 (8-40) weeks. Three (5%) patients had clinical spasms without hypsarrhythmia, and 5 (8%) patients had hypsarrhythmia before clinical spasms at the initial presentation. The infants with high CSI (hazard ratio 2.5, 95% CI 1.2-5.2, P = 0.01) and high DFA α1 (hazard ratio 16, 95% CI 1.1-240, P = 0.04) at 2 months were more likely to develop hypsarrhythmia by the first year of age. There was a trend toward decreasing CSI and DFA α1 and increasing CVI in the first 8 months of age.

Conclusion

Our data suggest that relative sympathetic predominance at an early age of 2 months may be a potential predictor for developing IESS. Hence, early HRV patterns may provide valuable prognostic information in children at risk of IESS allowing early detection and optimization of cognitive outcomes. Whether early intervention to restore sympathovagal balance per se would provide clinical benefit must be addressed by future studies.

Seizure-related differences in biosignal 24-h modulation patterns

A seizure likelihood biomarker could improve seizure monitoring and facilitate adjustment of treatments based on seizure risk. Here, we tested differences in patient-specific 24-h-modulation patterns of electrodermal activity (EDA), peripheral body temperature (TEMP), and heart rate (HR) between patients with and without seizures. We enrolled patients who underwent continuous video-EEG monitoring at Boston Children's Hospital to wear a biosensor. We divided patients into two groups: those with no seizures and those with at least one seizure during the recording period. We assessed the 24-h modulation level and amplitude of EDA, TEMP, and HR. We performed machine learning including physiological and clinical variables. Subsequently, we determined classifier performance by cross-validated machine learning. Patients with seizures (n = 49) had lower EDA levels (p = 0.031), EDA amplitudes (p = 0.045), and trended toward lower HR levels (p = 0.060) compared to patients without seizures (n = 68). Averaged cross-validated classification accuracy was 69% (AUC-ROC: 0.75). Our results show the potential to monitor and forecast risk for epileptic seizures based on changes in 24-h patterns in wearable recordings in combination with clinical variables. Such biomarkers might be applicable to inform care, such as treatment or seizure injury risk during specific periods, scheduling diagnostic tests, such as admission to the epilepsy monitoring unit, and potentially other neurological and chronic conditions.

Generalized tonic-clonic seizures are accompanied by changes of interrelations within the autonomic nervous system

PURPOSE

A seizure is a strong central stimulus that affects multiple subsystems of the autonomic nervous system (ANS), and results in different interactions across ANS modalities. Here, we aimed to evaluate whether multimodal peripheral ANS measures demonstrate interactions before and after seizures as compared to controls to provide the basis for seizure detection and forecasting based on peripheral ANS signals.

METHODS

Continuous electrodermal activity (EDA), heart rate (HR), peripheral body temperature (TEMP), and respiratory rate (RR) calculated based on blood volume pulse were acquired by a wireless multi-sensor device. We selected 45 min of preictal and 60 min of postictal data and time-matched segments for controls. Data were analyzed over 15-min windows. For unimodal analysis, mean values over each time window were calculated for all modalities and analyzed by Friedman's two-way analysis of variance.

RESULTS

Twenty-one children with recorded generalized tonic-clonic seizures (GTCS), and 21 age- and gender-matched controls were included. Unimodal results revealed no significant effect for RR and TEMP, but EDA (p = 0.002) and HR (p < 0.001) were elevated 0-15 min after seizures. The averaged bimodal correlation across all pairs of modalities changed for 15-min windows in patients with seizures. The highest correlations were observed immediately before (0.85) and the lowest correlation immediately after seizures. Overall, average correlations for controls were higher.

SIGNIFICANCE

Multimodal ANS changes related to GTCS occur within and across autonomic nervous system modalities. While unimodal changes were most prominent during postictal segments, bimodal correlations increased before seizures and decreased postictally. This offers a promising avenue for further research on seizure detection, and potentially risk assessment for seizure recurrence and sudden unexplained death in epilepsy.

Twenty-four-hour patterns in electrodermal activity recordings of patients with and without epileptic seizures

OBJECTIVE

Daytime and nighttime patterns affect the dynamic modulation of brain and body functions and influence the autonomic nervous system response to seizures. Therefore, we aimed to evaluate 24-hour patterns of electrodermal activity (EDA) in patients with and without seizures.

METHODS

We included pediatric patients with (a) seizures (SZ), including focal impaired awareness seizures (FIAS) or generalized tonic-clonic seizures (GTCS), (b) no seizures and normal electroencephalography (NEEG), or (c) no seizures but epileptiform activity in the EEG (EA) during vEEG monitoring. Patients wore a device that continuously recorded EDA and temperature (TEMP). EDA levels, EDA spectral power, and TEMP levels were analyzed. To investigate 24-hour patterns, we performed a nonlinear mixed-effects model analysis. Relative mean pre-ictal (-30 min to seizure onset) and post-ictal (I: 30 min after seizure offset; II: 30 to 60 min after seizure offset) values were compared for SZ subgroups.

RESULTS

We included 119 patients (40 SZ, 17 NEEG, 62 EA). EDA level and power group-specific models (SZ, NEEG, EA) (h = 1; P < .01) were superior to the all-patient cohort model. Fifty-nine seizures were analyzed. Pre-ictal EDA values were lower than respective 24-hour modulated SZ group values. Post hoc comparisons following the period-by-seizure type interaction (EDA level: χ 2  = 18.50; P < .001, and power: χ 2  = 6.73; P = .035) revealed that EDA levels were higher in the post-ictal period I for FIAS and GTCS and in post-ictal period II for GTCS only compared to the pre-ictal period.

SIGNIFICANCE

Continuously monitored EDA shows a pattern of change over 24 hours. Curve amplitudes in patients with recorded seizures were lower as compared to patients who did not exhibit seizures during the recording period. Sympathetic skin responses were greater and more prolonged in GTCS compared to FIAS. EDA recordings from wearable devices offer a noninvasive tool to continuously monitor sympathetic activity with potential applications for seizure detection, prediction, and potentially sudden unexpected death in epilepsy (SUDEP) risk estimation.

Pre-ictal heart rate variability alterations in focal onset seizures and response to vagus nerve stimulation

PURPOSE

Vagus nerve stimulation (VNS) is an effective and well-known treatment for drug resistant epilepsy (DRE) patients since 1997, yet prediction of treatment response before implantation is subject of ongoing research. Neuroimaging and neurophysiological studies investigating the vagal afferent network in resting state documented that differences in between epilepsy patients were related to treatment response. This study investigated whether an event-related parameter, pre-ictal heart rate variability (HRV) is associated with response to VNS therapy.

METHODS

DRE patients underwent video-electroencephalography (EEG) recording before VNS implantation. HRV parameters (time, non-linear and frequency domain) were assessed for every seizure during two 10 min timeframes: baseline (60 min before seizure onset) and pre-ictal (10 min before seizure onset). Pre-ictal HRV parameter alterations were correlated with VNS response after one year of VNS therapy and seizure characteristics (temporal/extratemporal, left/right or bilateral).

RESULTS

104 seizures from 22 patients were evaluated. Eleven patients were VNS responders with a seizure frequency reduction of ≥ 50 % after one year of VNS. In VNS responders no changes in HRV parameters were found while in VNS non-responders the time domain and non-linear HRV variables decreased significantly (p = 0.024, p = 0.005, p = 0.005) during the pre-ictal time frame. 10/11 VNS non-responders had a seizure lateralization to the left compared to 4/11 VNS responders.

CONCLUSION

VNS non-responders were characterized by a significant decrease of pre-ictal HRV (time domain/non-linear variables) suggesting a sudden autonomic imbalance probably due to an impaired central autonomic function that makes it at the same time unlikely to respond to VNS.

Peripheral multimodal monitoring of ANS changes related to epilepsy

The goal of this study was to evaluate and summarize the current literature on multimodal changes of the autonomic nervous system (ANS) in people with epilepsy (PWE). We included studies reporting ANS measures of at least two modalities and with a minimum of one group of people with epilepsy. We screened two hundred eighty-three abstracts and sixty-six full texts, of which twenty-two met our inclusion criteria. Eleven studies reported ictal and interictal cardiac and respiratory changes. Three studies investigated the correlation between cardiac and respiratory markers, whereby two found no correlation and one showed a relation. Six studies evaluated electrodermal and cardiac parameters and showed effects on both ANS subsystems that jointly indicate a shift toward increased sympathetic activity for people with epilepsy during rest and during activity. Two studies assessed three modalities and reveal epilepsy-related alterations within the ANS. In summary, there is a growing interest in multimodal monitoring approaches, such as combining at least two ANS modalities, to describe epilepsy-related changes in ANS activity and to test for the potential to use ANS markers for seizure detection and prediction. Most studies report multiple unimodal analyses while only few studies analyzed multimodal patterns. Patterns of changes depend on the type of epilepsy and differ on an individual level; therefore, a multimodal approach might offer an approach to more individualized monitoring and, ultimately, management.

Heart-type fatty acid-binding protein as a predictor of cardiac ischemia in intractable seizures in children

BACKGROUND

Children with intractable epilepsy have chronic dysfunction of the autonomic nervous system causing myocardial ischemia. Heart-type fatty acid-binding protein (H-FABP) is a sensitive biomarker for myocardial ischemia.

AIMS

We aimed to evaluate serum levels of H-FABP during seizures compared to their interictal levels and healthy controls and changes in heart rate (HR) and HR variability (HRV) in epileptic children with intractable seizures.

MATERIALS AND METHODS

We included 30 epileptic seizures in 25 children with intractable epilepsy and 30 matched controls. They were subjected to video-electroencephalography monitoring simultaneously with Holter electrocardiogram and measurement of H-FABP.

RESULTS

Mean serum levels of H-FABP were increased significantly in patients either in the ictal or interictal periods compared to that in the controls (P < 0.001 and P< 0.01, respectively). There is no significant difference in serum levels of the H-FABP in the ictal and interictal periods. The basal time domain measures of HRV were significantly lower in the patient group compared to the control group.

CONCLUSION

H-FABP might suggest a degree of myocardial ischemia in intractable epilepsy. HRV is impaired in patients with refractory seizures.

Cerebral Hemispheric Lateralization Associated with Hippocampal Sclerosis May Affect Interictal Cardiovascular Autonomic Functions in Temporal Lobe Epilepsy

It is well established that the temporal lobe epilepsy (TLE) is linked to the autonomic nervous system dysfunctions. Seizures alter the function of different systems such as the respiratory, cardiovascular, gastrointestinal, and urogenital systems. The aim of this work was to evaluate the possible factors which may be involved in interictal cardiovascular autonomic function in temporal lobe epilepsy with complex partial seizures, and with particular attention to hippocampal sclerosis. The study was conducted in 30 patients with intractable temporal lobe epilepsy (19 with left hippocampal sclerosis, 11 with right hippocampal sclerosis). All subjects underwent four tests of cardiac autonomic function: heart rate changes in response to deep breathing, heart rate, and blood pressure variations throughout resting activity and during hand grip, mental stress, and orthostatic tests. Our results show that the right cerebral hemisphere predominantly modulates sympathetic activity, while the left cerebral hemisphere mainly modulates parasympathetic activity, which mediated tachycardia and excessive bradycardia counterregulation, both of which might be involved as a mechanism of sudden unexpected death in epilepsy patients (SUDEP).

Cardiac Autonomic Dysfunction in Patients With Infantile Spasm and the Effect of Adrenocorticotropic Hormone Treatment

Infantile spasm is an age-dependent epileptic-encephalopathy syndrome. Cardiac autonomic function is frequently altered in epilepsy. In this study, we examined heart rate variability in patients with infantile spasm before and after treatment. Nineteen patients with infantile spasm and 13 healthy comparisons were enrolled in the study. Cardiac rhythm was recorded with a Holter device for 24 hours before adrenocorticotropic hormone (ACTH) (Synacthen depot) and B6 vitamin administration and 1 month after treatment. Heart rate variability analysis found lower heart rate variability parameters in patients with infantile spasm at the onset of the syndrome, prior to treatment with ACTH. The time domain parameters of heart rate variability values showed a statistically significant increase following ACTH treatment. Our data suggest that patients with infantile spasm exhibit lower heart rate variability parameters, and the treatment of spasms with ACTH and B6 together diminished the autonomic dysfunction in our cohort.

Cardiac autonomic balance in children with epilepsy: value of antiepileptic drugs

BACKGROUND

Dysfunction of the autonomous nervous system causes arrhythmias and, although previous studies have investigated the effects of epilepsy on the autonomic control of the heart, there is still uncertainty about whether imbalance of sympathetic, vagal, or both systems occurs in epilepsy as well as the effect of anticonvulsants on the autonomic system.

AIM

To evaluate cardiac autonomic status in children with epilepsy on antiepileptic drugs.

PATIENTS AND METHODS

Sixty patients with epilepsy were recruited from the Outpatient Neurology Clinic at Ain Shams University and were divided into the following groups: group I, drug naive; and group II, patients with epilepsy on regular antiepileptic drugs. The second group was further subdivided into the following groups: group IIa, received monotherapy; and group IIb, received polytherapy. Forty age- and sex-matched healthy children served as controls. Included patients underwent videorecorded electroencephalograph, Holter electrocardiogram (EKG) for time and frequency domains of heart rate variability, and standard EKG recording for QTc, QTd.

RESULTS

Mean values of all time domain, total power, and high-frequency power were significantly lower, whereas low-frequency and low-frequency/high-frequency power, QTc. and QTd were significantly higher in group I compared with group II and in patients compared with controls. No significant difference was found between patients on different antiepileptic drug regimens regarding heart rate variability values. A significant negative correlation was found between Chalfont severity score and 50% of difference between adjacent, normal RR intervals in patient groups.

CONCLUSIONS

Children with epilepsy have cardiac autonomic dysfunction evident in their heart rate variability assessment. Patients on antiepileptic drugs had better autonomic balance than those not on antiepileptic drugs. Holter and EKG follow-up should be considered for early detection in those at high-risk cardiac complications.

Early respiratory dysfunction as a biomarker for epileptic encephalopathy

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Heart rate variability in Parkinson's disease unaffected by deep brain stimulation

OBJECTIVES

Our aim was to investigate the impact of subthalamic nucleus deep brain stimulation (STN-DBS) on the cardiovagal control of patients with advanced Parkinson's disease.

MATERIALS AND METHODS

Twenty-four patients (mean age: 62.1 ± 9.4 years) were examined 3 days before and 6 months after DBS by a questionnaire, blood pressure monitoring and a battery of neurophysiological tests: time domain analysis of RR interval variation during normal and deep breathing (DB), Valsalva manoeuvre, and tilt test. By off-line, performed frequency domain analysis of heart rate variation, total power (TP), low frequency band (LF) band, high-frequency (HF) band, and their normalized units were estimated. The neurophysiological measurements were compared to those of 24 healthy controls.

RESULTS

The values of time domain variables were pre- and postoperatively lower in patients than in controls. A significant reduction was found in LF band after the implantation. Orthostatic hypotension was present in 45.8% of the patients preoperatively and 12.5% postoperatively. There was no correlation between DBS-related changes of motor function and corresponding neurophysiological measurements, but patients with more than 60% motor improvement had higher time domain parameters' values than the others.

CONCLUSIONS

STN-DBS offered no considerable impact on autonomic cardiovascular control.

Autonomic effects of refractory epilepsy on heart rate variability in children: influence of intermittent vagus nerve stimulation

AIM

Vagus nerve stimulation (VNS) is a therapeutic option for individuals with refractory epilepsy. Individuals with refractory epilepsy are prone to dysfunction of the autonomic nervous system. Reduced heart rate variability is a marker of dysfunction of the autonomic nervous system. Our goal was to study heart rate variability in children with refractory epilepsy and the influence of VNS on this parameter.

METHODS

In 17 children (13 male; four female; mean age 7 y 6 mo; age range 3-16 y) with refractory epilepsy, electroencephalographic and electrocardiographic data were obtained before and after implantation of VNS during stage 2 and slow-wave sleep. Time and frequency domain parameters were calculated and the results were compared with an age- and sex-matched group of individuals without refractory epilepsy.

RESULTS

Our results show that autonomic cardiac control is affected in individuals with refractory epilepsy. There is a striking reduction in vagal tone during slow-wave sleep and modulation capacity is smaller than in individuals without refractory epilepsy. Implantation of VNS induces a shift in sympathovagal balance towards sympathetic predominance and an improvement in autonomic modulation.

INTERPRETATION

Heart rate variability is affected in children with refractory epilepsy, and changes after implantation of VNS. The observed changes could be of importance in the cardiac complications of individuals with epilepsy and should be explored in more detail.