Heart Rate Variability in Insulo-Opercular Epilepsy

Abstract

Background: We aimed to evaluate heart rate variability (HRV) changes in insulo-opercular epilepsy (IOE) and after insulo-opercular surgery.

Methods: We analyzed 5-min resting HRV of IOE patients before and after surgery. Patients' SUDEP-7 risk inventory scores were also calculated. Results were compared with age- and sex-matched patients with temporal lobe epilepsy (TLE) and healthy individuals.

Results: There were no differences in HRV measurements between IOE, TLE, and healthy control groups (and within each IOE group and TLE group) in preoperative and postoperative periods. In IOE patients, the SUDEP-7 score was positively correlated with pNN50 (percentage of successive RR intervals that differ by more than 50 ms) (p = 0.008) and RMSSD (root mean square of successive RR interval differences) (p = 0.019). We stratified IOE patients into those whose preoperative RMSSD values were below (Group 1a = 7) versus above (Group 1b = 9) a cut-off threshold of 31 ms (median value of a healthy population from a previous study). In group 1a, all HRV values significantly increased after surgery. In group 1b, time-domain parameters significantly decreased postoperatively.

Conclusions: Our results suggest that in IOE, HRV may be either decreased in parasympathetic tone or increased globally in both sympathetic and parasympathetic tones. We found no evidence that insulo-opercular surgeries lead to major autonomic dysfunction when a good seizure outcome is reached. The increase in parasympathetic tone observed preoperatively may be of clinical concern, as it was positively correlated with the SUDEP-7 score.

Keywords: cardiac autonomic dysfunction; heart rate variability; insulo-opercular epilepsy.

Figure 1

Comparison of pre-operative RMSSD values for each patient in the IOE group in the first part of the study (A), the TLE group (B), and the whole IOE group in the second part of the study (C) compared to its matched control. Each dot represents a patient. x-axis represent the pre-operative RMSSD of patients, y-axis represents the percentage of difference in RMSSD between patients (x) and their matched controls (c) [y = 100 ∗ (x − c)/c]. Insets A and B showed that the difference between IOE patients’ RMSSD from that of control seemed to be greater than in TLE patients. In inset C, blue dots represent IOE patients in the first part of the study, the green dots represent IOE patients with poor outcomes after surgery, and the red dots represent patients with temporo-insulo-opercular epilepsy. IOE = Insulo-opercular epilepsy; pNN50 = percentage of successive RR intervals that differ by more than 50 ms; RMSSD = root mean square of successive RR interval differences; SUDEP = sudden unexpected death in epilepsy.

Figure 2

Comparison of pre-operative and post-operative RMSSD of each patient in the OIE group (A), TLE group (B), and IOE group in the second part of the study (C). Patients in each group were divided into two subgroups based on whether their pre-operative values were below or above the median RMSSD value (31 ms) of a population of 1315 healthy subjects aged 25 to 49 years (Voss et al., 2012). In the IOE group, low RMSSD tended to increase post-operatively, whereas high values tended to decrease after surgery. This pattern of HRV changes was not seen in the TLE group. (x-axis represents the pre-operative RMSSD measures; y-axis represents the percentage of difference between pre-operative (x) and post-operative RMSSD (p) out of pre-operative value (y = 100 ∗ (p − x)/x). Each dot represents a patient. In inset C, blue dots represent IOE patients in the first part of the study, the green dots represent IOE patients but poor seizure outcome after surgery, and the red dots represent patients with temporo-insulo-opercular epilepsy. IOE = Insulo-opercular epilepsy; TLE = Temporal lobe epilepsy; pNN50 = percentage of successive RR intervals that differ by more than 50 ms; RMSSD = root mean square of successive RR interval differences.