Vagus Nerve Stimulation and Atrial Fibrillation: Revealing the Paradox

Background and Objective: The cardiac autonomic nervous system (CANS) plays an important role in the pathophysiology of atrial fibrillation (AF). Cardiovascular disease can cause an imbalance within the CANS, which may contribute to the initiation and maintenance of AF. Increased understanding of neuromodulation of the CANS has resulted in novel emerging therapies to treat cardiac arrhythmias by targeting different circuits of the CANS. Regarding AF, neuromodulation therapies targeting the vagus nerve have yielded promising outcomes. However, targeting the vagus nerve can be both pro-arrhythmogenic and anti-arrhythmogenic. Currently, these opposing effects of vagus nerve stimulation (VNS) have not been clearly described. The aim of this review is therefore to discuss both pro-arrhythmogenic and anti-arrhythmogenic effects of VNS and recent advances in clinical practice and to provide future perspectives for VNS to treat AF. Materials and Methods: A comprehensive review of current literature on VNS and its pro-arrhythmogenic and anti-arrhythmogenic effects on atrial tissue was performed. Both experimental and clinical studies are reviewed and discussed separately. Results: VNS exhibits both pro-arrhythmogenic and anti-arrhythmogenic effects. The anatomical site and stimulation settings during VNS play a crucial role in determining its effect on cardiac electrophysiology. Since the last decade, there is accumulating evidence from experimental studies and randomized clinical studies that low-level VNS (LLVNS), below the bradycardia threshold, is an effective treatment for AF. Conclusion: LLVNS is a promising novel therapeutic modality to treat AF and further research will further elucidate the underlying anti-arrhythmogenic mechanisms, optimal stimulation settings, and site to apply LLVNS.