METHODS: We searched PubMed, EMBASE, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials (CENTRAL), and CINAHL Plus for articles published from their date of inception to June 2021. RCTs investigating the efficacy or safety of VNS on post-stroke recovery were included. The outcomes were upper limb sensorimotor function, health-related quality of life, level of independence, cardiovascular effects, and adverse events. The risk of bias was assessed using the Cochrane risk-of-bias tool, while the certainty of the evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) criteria. Review Manager 5.4 was used to conduct the meta-analysis.

RESULTS: Seven RCTs (n = 236 subjects) met the eligibility criteria. Upper limb sensorimotor function, assessed by the Fugl-Meyer Assessment for Upper Extremity (FMA-UE), improved at day 1 (n = 4 RCTs; standardized mean difference [SMD] 1.01; 95% confidence interval [CI]: 0.35-1.66) and day 90 post-intervention (n = 3 RCTs; SMD 0.64; 95% CI: 0.31-0.98; moderate certainty of evidence) but not at day 30 follow-up (n = 2 RCTs; SMD 1.54; 95% CI: -0.39 to 3.46). Clinically significant upper limb sensorimotor function recovery, as defined by ≥6 points increase in FMA-UE, was significantly higher at day 1 (n = 2 RCTs; risk ratio [RR] 2.01; 95% CI: 1.02-3.94) and day 90 post-intervention (n = 2 RCTs; RR 2.14; 95% CI: 1.32-3.45; moderate certainty of the evidence). The between-group effect sizes for upper limb sensorimotor function recovery was medium to large (Hedges' g 0.535-2.659). While the level of independence improved with VNS, its impact on health-related quality of life remains unclear as this was only studied in two trials with mixed results. Generally, adverse events reported were mild and self-limiting.