Heart rate variability in patients with epilepsy1
Introduction
Partial and generalised tonic-clonic seizures are frequently accompanied by symptoms from the autonomic nervous system (Van Buren, 1958, Van Buren and Ajmone-Marsan, 1960). The effects of seizure discharges are thought to be mediated through the cortical, limbic and hypothalamic systems (Wannamarker, 1958). Experimental data, however, suggest that interictal epileptogenic activity may also induce an autonomic imbalance and that such altered autonomic neural discharges may be associated with cardiac arrhythmias (Lathers and Schraeder, 1982, Lathers et al., 1987). Studies of autonomic control of cardiac function in epileptic patients in the interictal state are few (Frysinger et al., 1993, Devinsky et al., 1994, Faustmann and Ganz, 1994). In these, autonomic nervous system function have been assessed by orthostatic provocation, cold pressor tests, cold face tests with apnoea and heart rate variability. In the last decade, computerised methods have been developed for spectral analysis of heart rate variability (Akselrod et al., 1981, Guzetti et al., 1988). These methods have lately been applied in studies of patients with epilepsy, in particular seizure-related alterations of cardiac autonomic regulation (Messenheimer et al., 1990, Vaughn et al., 1996) and more recent data suggests a decreased heart rate variability in patients with temporal lobe epilepsy (TLE) (Massetani et al., 1997).
The present study set out to assess autonomic cardiac control by use of spectral analysis of heart rate variability in the interictal state of patients with two different types of epilepsy, one localisation related and one generalised idiopathic and to explore the possible contribution of the drug therapy to alterations in heart rate variability.
Section snippets
Subjects
In the study 21 patients with juvenile myoclonic epilepsy (JME) and 21 patients with complex partial seizures with a temporal lobe focus on surface EEG were included (Commission of Classification and Terminology of the International League Against Epilepsy, 1981, Commission of Classification and Terminology of the International League Against Epilepsy, 1989). The ages in the group with JME ranged from 20 to 49 years (mean±S.D. 29±7 years) and in patients with TLE from 24 to 49 years (mean±S.D.
Results
None of the patients reported any seizures during the EKG-recording. The trough plasma concentration of CBZ at the day of the investigation was 32±9 μmol/l (mean±S.D.), of VPA 587±175 μmol/l and of PHT 48±19 μmol/l. Heart rate variability in time and frequency domains for patients and controls is presented in Table 1. Patients with TLE had significantly lower S.D. of the RR-intervals (SD-NN-index) than their controls (P=0.01), lower low frequency power (P=0.002) and a lower low frequency/high
Discussion
The presumed advantage of spectral analysis of heart rate variability is that in determining frequency domain indices, it may be possible to separate the sympathetic component from the vagal components of the power spectrum (Ravenswaaij-Arts et al., 1993), although admittedly the mechanisms behind the spectral power in the very low frequency band have not yet been fully understood (Kitney, 1973). Low frequency oscillations are associated with baroreflex control of sympathetic activity (Akselrod
Conclusion
The present study has found a decreased heart rate variability and decreased sympathetic tone in patients with epilepsy which may be related to treatment with CBZ or to TLE. Further studies are needed to clarify the contribution of drug therapy and the epilepsy as such. Such studies should analyse heart rate variability in untreated patients with epilepsy and assess the effects of anti-epileptic drugs on heart rate variability in healthy subjects.
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Presented in part at the 2nd European Congress of Epileptology, The Hague, September, 1996.