Interphase Gaps in Symmetric Biphasic Pulses Reduce the Therapeutic Window in Ventral Intermediate Nucleus of the Thalamus–Deep Brain Stimulation for Essential Tremor

Abstract

IntroductionSymmetric biphasic pulses enlarge the therapeutic window in thalamic deep brain stimulation in patients with essential tremor. Adding an interphase gap to these symmetric biphasic pulses may further affect the therapeutic window. Materials and MethodsNine patients (16 hemispheres) were included in this study. Biphasic pulses (anodic phase first) with interphase gaps of 0, 10, 20, 50, and 100 μs were tested, in random order. The outcome parameters were the therapeutic threshold (TT) and side-effect threshold (SET), and thus also the therapeutic window (TW). ResultsIncreasing interphase gaps lowered both SET and TT (linear mixed-effects model; p < 0.001 and p < 0.001). Because SET decreased predominantly, increasing interphase gaps resulted in smaller TWs (linear mixed-effects model; p < 0.001). Discussion and ConclusionsIntroducing an interphase gap in a symmetric biphasic pulse may lead to less selectivity in fiber or neuronal activation. Our findings show that, in the context of anode-first biphasic pulses, the use of zero-interphase gaps results in the largest TW. Clinical Trial RegistrationThe Clinicaltrials.gov registration number for the study is NCT05177900.