Abstracts

Rationale: Heart rate variability (HRV) measures reflect modulations in autonomic tone, which may precede seizure occurrence or generalization. Previous work has investigated HRV parameter changes mainly in the context of focal epilepsy and has demonstrated significantly higher pre-ictal heart rates (HR) with secondarily generalized tonic-clonic seizures (SGTCS) in comparison to seizures that did not generalize. We performed a pilot study to investigate if similar cardiac changes are also present in the case of primarily generalized tonic-clonic seizures (PGTCS), which has not been previously studied.Methods: A database search was performed for all PGTCS recorded during admissions to our Epilepsy Monitoring Unit (EMU) from 2007-2011. Twelve patients were identified. Six were excluded due to focal ictal features. A total of eight generalized seizures were recorded among the remaining six patients, and all eight seizures were used for analysis. Patient demographics are listed in Table 1. Two minutes of pre-ictal EKG preceding EEG seizure onset were extracted, along with a remote, random two minute interictal baseline EKG segment in the same pre-ictal state (sleep or wake). Another random two-minute interictal EKG segment remote from the seizure and preceding a generalized spike-wave complex (pre-GSWC) was also obtained in the same state. MATLAB software was used for HRV and statistical analyses. The hypothesis that an elevated sympathetic tone precedes PGTCS was tested using paired t-tests.Results: Mean HR was significantly higher for the pre-ictal and pre-GSWC portions when compared to the interictal baseline (74 vs. 64 bpm and 68 vs. 64 bpm, respectively; p=0.025 and p=0.042, respectively), as shown in Figure 1. No significant differences in any other HRV parameters including SDNN, RMSSD, LF, HF, or LF:HF ratios were found between these three groups. A suitable interictal pre-GSWC segment was unobtainable in three instances. We performed separate calculations in which progressively decreasing the analyzed pre-event window durations down to as low as 30 seconds did not alter the statistical significance of our observed HR trends.Conclusions: Our data suggest that HR changes precede PGTCS, with pre-GSWC and pre-ictal HRs being significantly higher in comparison to interictal baseline HR. Thus, increased sympathetic tone may predispose to generalized EEG discharges and seizures. In addition, the finding of increased pre-ictal HR may be a useful variable for seizure prediction modeling in both PGTCS and SGTCS.