Abstracts

RATIONALE: We studied stimulation parameters tolerated by patients undergoing vagus nerve stimulator (VNS) pulse generator reimplant.
METHODS: Patients who had VNS generators replaced when approaching end of service, or for actual end of service, were assessed for tolerance of their pre-reimplant current. Stimulation was programmed in the operating room to the following parameters: current = 0.25 mA, frequency = 30 Hz, pulse width = 250 usec, time on = 7 sec, time off = 30 min. Within the next week the patient[ssquote]s pre-reimplant parameters, with the exception of the current, were programmed. Next the current was increased by 0.25 mA increments to patient tolerance or pre-reimplant current. With each current increase, the patient was observed for 4 times the duration of their time off. Patients that were unable to achieve pre-reimplant current initially were seen again for further programming within one week and then monthly.
Statistical analyses were Chi-square with cross tabulation, one way ANOVA and Pearson[ssquote]s bivariate correlation.
RESULTS: Twenty-eight patients were evaluated (14 males, 14 females). The mean age was 35 years (range 16-56). The mean duration of VNS therapy before reimplant was 39 months (range 23 [ndash]80). Twenty-one patients were reimplanted electively and 7 were reimplanted because of end of service. Twenty-six of 28 patients had VNS [dsquote]model 100[dsquote] replaced with [dsquote]model 101.[dsquote] Mean baseline current was 1.85 mA (range 0.25 -3.25). Mean baseline off time was 1.0 min. (range 0.2-5.0). We were able to achieve pre-reimplant current within 1 week post-operatively in only 7 of 28 patients (25%). An additional 2 patients achieved their baseline current after 4 months and 1 year, respectively. The other 19 patients did not tolerate their pre-reimplant current after a mean follow-up of 2.5 months (range 1 wk.-52mos.). Adverse events limiting current were coughing in 10 patients and throat pain in 9 patients. Patients with a higher baseline current were less likely to return to their current within 1 week. Patients with shorter off times also were less likely to return to their baseline current within 1 week.
CONCLUSIONS: Most patients undergoing VNS replacement are unable to tolerate their pre-reimplant current settings within the first week post operatively. This is most noticeable in patients with higher baseline currents and shorter off times. These results may be helpful for selecting stimulation parameters after VNS replacement.
(Disclosure: Honoraria - Cyberonics)