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

Introduction: Symmetric 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 Methods: Nine patients (16 hemispheres) were included in this study. Biphasic pulses (anodic phase first) with interphase gaps of 0, 10, 20, 50, and 100 mu s 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). Results: Increasing 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 Conclusions: Introducing 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 Clinical Trial Registration: The Clinicaltrials.gov registration number for the study is NCT05177900.