Association Between Heart Rate Variability and Parkinson's Disease: A Meta-analysis

Aim: A systematic review which aims to assess the evidence regarding the function of the autonomic heart rate regulation system among Parkinson's disease (PD) patients. The main objective of the study is to compare heart rate variability (HRV) between those with and without PD from published studies. The subgroup analyses aimed to investigate the impact of treatment and disease duration on heart rate variability (HRV), assessed by measuring sympathetic and parasympathetic activity via low-frequency (LF) and high-frequency (HF) power spectrum scores, in patients with Parkinson's disease (PD). Methods: PubMed, Cochrane Library, Embase and Web of Science were searched using the keywords "Parkinson's disease" and "heart rate variability". Studies that reported at least one HRV variable were included. The quality of the included studies was evaluated, and the relevant information was extracted. A meta-analysis was carried out with Stata software. We followed the PRISMA guidelines for all stages of the meta-analysis. PROSPERO registration number: CRD42021242766. Results: Thirteen references (16 studies) were included in our analysis. The LF values (g -0.27; 95% confidence interval (CI) -0.53 to -0.01) of the patients with PD were lower than the controls. No significant differences in HF values (g -0.11; 95% CI -0.28 to 0.06) were observed between groups. Subgroup analyses of HRV outcomes in patients stratified by treatment status and disease duration were performed. For LF, patients with a disease duration of less than 5 years presented lower HF (g -0.25; 95% CI -0.44 to -0.06) values than controls. Regarding HF, patients receiving treatment presented lower HF (g -0.22; 95% CI -0.40 to 0.05) values than controls, and patients with a disease duration greater than 5 years also presented lower HF (g -0.29; 95% CI -0.56 to -0.03) values than controls. Discussion: We have confirmed and elaborated on the hypothesis of sympathovagal imbalance in PD. Knowledge of the effect of sympathovagal balance on HRV may inform the design of therapeutic regimens for PD. However, between-study heterogeneity and methodological issues limit the generalizability of the evidence; thus, future studies employing strict methodologies are warranted. Conclusion: Our meta-analysis found that PD is associated with reduced HRV values, which indicates that both sympathetic and vagal activities are decreased. Patients in the early stage of PD have sympathetic autonomic nerve dysfunction, with only minor damage to sympathetic activity.