Interictal change in cardiac autonomic function associated with EEG abnormalities and clinical symptoms: a longitudinal study following acute deterioration in two patients with temporal lobe epilepsy

Dysautonomia in people with epilepsy: A scoping review

BACKGROUND

Epilepsy is one of the most common neurological diseases and has high morbidity and mortality. Multiple methods for assessing dysautonomia have been reported; however, the patient characteristics and epilepsy features that drive any method selection are unclear. People with epilepsy (PWE) can experience sudden unexpected death in epilepsy (SUDEP) and one reason can be dysautonomia. If dysautonomia can be detected in PWE before a severe event, then it could complement and redirect patient treatment and monitoring.

OBJECTIVE

To map the available literature on dysautonomia in PWE and describe patients' characteristics and methods used to evaluate dysautonomia.

METHODS

We performed a scoping literature review. We searched PubMed, Scopus, Embase, and hand searched starting from the first registry in the literature until August 2019. Studies were independently assessed by three authors and two epileptologists. We present data in tables and summarize information according to the following structure: population, concepts, and context.

RESULTS

Thirty-five studies were included in the analysis with epidemiological designs including case reports (23), cross-sectional studies (4), case‒controls (7), and cohort studies (1). A total of 618 patients were enrolled. Heart rate variability, arrhythmia, blood pressure, the tilt-table test, polysomnography, respiratory function, and magnetic resonance imaging were the methods most commonly used to assess dysautonomia in PWE. A detailed description of the heart rate variability assessment is presented.

CONCLUSIONS

This review provides a broad description of the available literature identifying clinical findings, the most frequently reported assessment measurements of dysautonomia, in temporal lobe epilepsy and extratemporal epilepsies.

Corrected QT interval and QT dispersion in temporal lobe epilepsy

Background

Cardiac arrhythmias are expected among patients with epilepsy due to the effect of anti-epileptic drugs. Temporal lobe epilepsy also causes autonomic seizures that may affect heart rhythm. Prolongation of the corrected QT interval and QT dispersion is a risk factor for cardiac arrhythmia.

Objectives

We aimed to assess corrected QT interval and QT dispersion in patients with epilepsy and if there is a difference between patients with temporal epilepsy versus non-temporal epilepsy.

Methods

This study was conducted on 100 patients (50 patients with temporal epilepsy and 50 patients with non-temporal epilepsy) and 50 age- and sex-matched healthy controls. They underwent a prolonged (6 to 24 h) 22 channel computerized electroencephalogram monitor with a 10–20 system. QT dispersion, QT interval, and corrected QT interval (using Bazett’s formula) were calculated.

Results

This study showed significantly higher QT dispersion and corrected QT interval in patients with epilepsy when compared to the age- and sex-matched control group (P < 0.001, P < 0.001). Also, the corrected QT interval and QT dispersion were significantly higher in temporal epilepsy patients when compared to the non-temporal group (P < 0.001, P < 0.001).

Conclusion

Corrected QT interval and QT dispersion are higher in epileptic patients and more among temporal epilepsy patients in comparison to non-temporal epilepsy patients.

Heart rate variability measurement in epilepsy: How can we move from research to clinical practice?

Our objective was to critically evaluate the literature surrounding heart rate variability (HRV) in people with epilepsy and to make recommendations as to how future research could be directed to facilitate and accelerate integration into clinical practice. We reviewed relevant HRV publications including those involving human subjects with seizures. HRV has been studied in patients with epilepsy for more than 30 years and, overall, patients with epilepsy display altered interictal HRV, suggesting a shift in autonomic balance toward sympathetic dominance. This derangement appears more severe in those with temporal lobe epilepsy and drug-resistant epilepsy. Normal diurnal variation in HRV is also disturbed in at least some people with epilepsy, but this aspect has received less study. Some therapeutic interventions, including vagus nerve stimulation and antiepileptic medications, may partially normalize altered HRV, but studies in this area are sometimes contradictory. During seizures, the changes in HRV may be complex, but the general trend is toward a further increase in sympathetic overactivity. Research in HRV in people with epilepsy has been limited by inconsistent experimental protocols and studies that are often underpowered. HRV measurement has the potential to aid clinical epilepsy management in several possible ways. HRV may be useful in predicting which patients are likely to benefit from surgical interventions such as vagus nerve stimulation and focal cerebral resection. As well, HRV could eventually have utility as a biomarker of risk for sudden unexpected death in epilepsy (SUDEP). However, at present, the inconsistent measurement protocols used in research are hindering translation into clinical practice. A minimum protocol for HRV evaluation, to be used in all studies involving epilepsy patients, is necessary to eventually allow HRV to become a useful tool for clinicians. We propose a straightforward protocol, involving 5-minute measurements of root mean square of successive differences in wakefulness and light sleep.

Early Seizure Detection Based on Cardiac Autonomic Regulation Dynamics

Epilepsy is a neurological disorder that causes changes in the autonomic nervous system. Heart rate variability (HRV) reflects the regulation of cardiac activity and autonomic nervous system tone. The early detection of epileptic seizures could foster the use of new treatment approaches. This study presents a new methodology for the prediction of epileptic seizures using HRV signals. Eigendecomposition of HRV parameter covariance matrices was used to create an input for a support vector machine (SVM)-based classifier. We analyzed clinical data from 12 patients (9 female; 3 male; age 34.5 ± 7.5 years), involving 34 seizures and a total of 55.2 h of interictal electrocardiogram (ECG) recordings. Data from 123.6 h of ECG recordings from healthy subjects were used to test false positive rate per hour (FP/h) in a completely independent data set. Our methodological approach allowed the detection of impending seizures from 5 min to just before the onset of a clinical/electrical seizure with a sensitivity of 94.1%. The FP rate was 0.49 h⁻¹ in the recordings from patients with epilepsy and 0.19 h⁻¹ in the recordings from healthy subjects. Our results suggest that it is feasible to use the dynamics of HRV parameters for the early detection and, potentially, the prediction of epileptic seizures.

A systematic review and meta-analysis of heart rate variability in epilepsy and antiepileptic drugs

PURPOSE

Epilepsy is associated with near-fatal and fatal arrhythmias, and sudden unexpected death in epilepsy (SUDEP) is partly related to cardiac events. 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, the results are still mixed regarding whether imbalance of sympathetic, vagal, or both systems is present in epilepsy, and also the importance of anticonvulsant treatment on the autonomic system. Therefore, we aimed to investigate epilepsy and its treatment impact on heart rate variability (HRV), assessed by sympathetic and parasympathetic activity expressed as low-frequency (LF) and high-frequency (HF) power spectrum, respectively.

METHOD

We performed a systematic review from the first date available to July 2011 in Medline and other databases; key search terms were "epilepsy"; "anticonvulsants"; "heart rate variability"; "vagal"; and "autonomous nervous system." Original studies that reported data and/or statistics of at least one HRV value were included, with data being extracted by two independent authors. We used a random-effects model with Hedges's g as the measurement of effect size to perform two main meta-analyses comparing LF and HF HRV values in (1) epilepsy patients versus controls; (2) patients receiving versus not receiving treatment; and (3) well-controlled versus refractory patients. Secondary analyses assessed other time- and frequency-domain measurements (nonlinear methods were not analyzed due to lack of sufficient data sets). Quality assessment of each study was verified and also meta-analytic techniques to identify and control bias. Meta-regression for age and gender was performed.

KEY FINDINGS

Initially, 366 references were identified. According to our eligibility criteria, 30 references (39 studies) were included in our analysis. Regarding HF, epilepsy patients presented lower values (g -0.69) than controls, with the 95% confidence interval (CI) ranging from -1.05 to -0.33. No significant differences were observed for LF (g -0.18; 95% CI -0.71 to 0.35). Patients receiving treatment presented HF values to those not receiving treatment (g -0.05; 95% CI -0.37 to 0.27), with a trend for having higher LF values (g 0.1; 95% CI -0.13 to 0.33), which was more pronounced in those receiving antiepileptic drugs (vs. vagus nerve stimulation). No differences were observed for well-controlled versus refractory patients, possibly due to the low number of studies. Regression for age and gender did not influence the results. Finally, secondary time-domain analyses also showed lower HRV and lower vagal activity in patients with epilepsy, as shown by the standard deviation of normal-to-normal interval (SDNN) and the root mean square of successive differences (RMSSD) indexes, respectively.

SIGNIFICANCE

We confirmed and extended the hypothesis of sympathovagal imbalance in epilepsy, as showed by lower HF, SDNN, and RMSSD values when compared to controls. In addition, there was a trend for higher LF values in patients receiving pharmacotherapy. As lower vagal (HF) and higher sympathetic (LF) tone are predictors of morbidity and mortality in cardiovascular samples, our findings highlight the importance of investigating autonomic function in patients with epilepsy in clinical practice. Assessing HRV might also be useful when planning therapeutic interventions, as some antiepileptic drugs can show hazardous effects in cardiac excitability, potentially leading to cardiac arrhythmia.

The treatment of ictal asystole with cardiac pacing

Ictal asystole may contribute to seizure-related injury and mortality. The purpose of this study was to evaluate the effect of cardiac pacing on seizure-related injury rates in ictal asystole patients. A survey was conducted to determine seizure-related fall rate and other morbidity in all seven patients with ictal asystole who underwent cardiac pacing at our institution between 1990 and 2004. The rate of seizure-related falls and other morbidities before and after pacing were compared using the Wilcoxon rank-sum test. The mean fall rate was 3.28 falls/month pre-pacemaker implantation. Following pacemaker implantation, this was reduced to 0.005 falls/month (p = 0.001). Seizure-related fractures and motor vehicle accidents were also reduced following cardiac pacing. These findings may have implications in mitigating the potential morbidity associated with ictal asystole.

Factors that affect interictal cardiovascular autonomic dysfunction in temporal lobe epilepsy: role of hippocampal sclerosis

The aim of this study was to evaluate possible factors affecting interictal cardiovascular autonomic function in temporal lobe epilepsy with complex partial seizures, paying special attention to hippocampal sclerosis. The study was carried out with 88 patients with epilepsy (22 with left hippocampal sclerosis, 22 with right hippocampal sclerosis, and 44 without hippocampal sclerosis) and 44 healthy subjects. All subjects underwent three tests of cardiac autonomic function: heart rate variation during resting activity, heart rate variation in response to deep breathing and blood pressure response to rising quickly from the supine position. Hippocampal sclerosis and disease duration were found to have significantly important effects on parasympathetic autonomic function, whereas seizure control and type of antiepileptic drug had significant effects on sympathetic autonomic function. This study shows that in addition to factors related to the chronic nature of epilepsy and antiepileptic drug use, hippocampal sclerosis may cause autonomic dysfunction during the interictal period in persons with temporal lobe epilepsy.

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.

Effects of epilepsy on autonomic nervous system and respiratory function tests

We have investigated autonomic nervous system function during the interictal period in epileptic patients and the possible effects of autonomic dysfunction on respiratory functions. A total of 32 epileptic patients (23 generalized, 9 partial epilepsy) and 32 healthy volunteers were involved. Sympathetic skin response (SSR), for evaluating the sympathetic nervous system, and RR interval variation (RRIV) were measured at the beginning and third month of antiepileptic treatment, and respiratory function tests (RFTs) were performed. In patients with partial epilepsy, SSR latency in the upper extremity (1.3+/-0.2 s) was longer than that of controls (1.2+/-0.3 s) at baseline (P=0.05), and was significantly reduced (1.1+/-0.3 s) after treatment (P<0.05). RRIV values of patients with generalized epilepsy were statistically significantly lower than those of controls (P<0.01). However, deep breathing RRIV values (32.6+/-15.3%) of patients were lower than those (43.0+/-18.2%) of controls (P<0.05). Sympathetic dysfunction was determined in patients with partial epilepsy and parasympathetic dysfunction in patients with generalized epilepsy. No abnormality was observed on RFTs for both patients with partial epilepsy and patients with generalized epilepsy.

Paradoxical autonomic response to mental tasks in autism

Autonomic responses to mental tasks requiring sustained attention were examined in individuals with autism and age- and ability-matched controls. Cardiac autonomic function (CAF) was evaluated based on heart rate variability. While the control group showed a significant decrease in the parasympathetic function during mental tasks, the autistic group showed no significant changes in CAF. When examined individually, parasympathetic function was suppressed in all subjects in the control group. On the other hand, parasympathetic function was activated in half of the autistic subjects. The paradoxical autonomic response suggests that some autistic subjects were more stressed under 'resting' conditions than while performing mechanical or repetitive mental tasks. The results seem to support autonomic hyperarousal in some people with autism.

Effects of seizure repetition on postictal and interictal neurocardiac regulation in the rat

PURPOSE

Human epilepsy is associated with abnormalities in cardiac regulation, as measured by reductions of heart rate variability (HRV) and approximate entropy (ApEn), but it is not known how these abnormalities are related to seizure experience.

METHODS

Baseline electrocardiogram (ECG) was recorded from seizure-naive rats. They were subjected daily to maximal electroshock (MES), which induced tonic seizures with hindlimb extension, for a total of 10 days. ECG was obtained for 30 min before and after the first and last seizure. R-R variability, spectral variability, and ApEn were calculated to determine changes in pre- and postictal cardiac regulation. Before the last seizure, interictal parameters were compared with baseline values to determine changes in interictal HRV as a consequence of seizure repetition. Postictal values obtained after the last seizure were compared with the initial postictal data to look for changes in postictal cardiac regulation.

RESULTS

During the postictal state, a mild, but significant, loss of ApEn was present after either the first or last seizure. Seizure repetition induced loss of R-R variability and high-frequency spectral band, which was present both interictally and postictally.

CONCLUSIONS

The results suggest that convulsive seizures are associated with an immediate reduction of the complexity of cardiac rhythm regulation, as reflected by reductions of ApEn. Seizure repetition may induce long-term neural abnormalities in neurocardiac regulatory systems, especially parasympathetic, which limit appropriate autonomic responses. These acquired abnormalities may, in turn, predispose individuals to cardiac arrhythmia and sudden unexpected death in epilepsy.

Recurrence quantification analysis as a tool for nonlinear exploration of nonstationary cardiac signals

The complexity, nonlinearity and nonstationarity of the cardiovascular system typically defy comprehensive and deterministic mathematical modeling, except from a statistical perspective. Living systems are governed by numerous, continuously changing, interacting variables in the presence of noise. Cardiovascular signals can be shown to be discontinuous alternations between deterministic trajectories and stochastic pauses (terminal dynamics). One promising approach for assessing such nondeterministic complexity is recurrence quantification analysis (RQA). As reviewed in this paper, strategies implementing quantification of recurrences have been successful in diagnosing changes in nonstationary cardiac signals not easily detected by traditional methods. It is concluded that recurrence quantification analysis is a powerful discriminatory tool which, when properly applied to cardiac signals, can provide objectivity regarding the degree of determinism characterizing the system, state changes, as well as degrees of complexity and/or randomness.