Modifications of short-term heart rate variability in metabolic syndrome: a systematic review and meta-analysis

Abstract Introduction Metabolic syndrome (MS) is a clinical condition in which different non-communicable chronic diseases converge, such as hypertension, diabetes, dyslipidemia and obesity. MS has been related to dysregulation of the autonomic nervous system (ANS). Heart rate variability (HRV) has been widely used as a tool to assess the activity of autonomic function, which could be very useful for diagnosis or monitoring in patients with MS; however, to date, no quantitative analysis of ANS dysfunction in MS has been performed. For this reason, the objective of this systematic review and meta-analysis (MA) is to determine the impact that MS produces in short-term HRV, characterizing the cardiac autonomic dysfunction induced by this pathological condition and the most frequently reported explanatory variables. Methods We searched PubMed, Web of Science and Scopus electronic databases for original works with short-term HRV recordings (15 minutes or shorter) that compared people with MS (MS+) versus healthy people as a control group (MS-). The search was carried out between June 25th, 2022 and September 1st, 2022. Within these databases, the terms used were "metabolic syndrome" linked to "heart rate variability" (HRV), "cardiac autonomic control", "cardiac autonomic function", or "cardiac autonomic modulation". This systematic review and MA was performed according with PRISMA guidelines and registered at the International Prospective Register of Systematic Reviews. Results are reported as standard mean difference [95% CI]. Results Twenty-eight articles were included in the qualitative synthesis and nineteen of them met required criteria to be included in the MA. MS decreased SDNN (-0.40 [-0.5, -0.3], p<0.001), rMSSD (-7.59 [-9.98, -5.19], p<0.001), HF (-0.32 [-0.46, -0.18], p<0.001) and LF (-0.22 [-0.39, -0.06], p<0.01). The ratio LF/HF did not change (0.24 [-0.22, 0.69]). In subsequent subanalyses, we found a decreased in SDNN (-0.99 (-1.45, -0.52], p<0.001), rMSSD (-10.18 [-16.85, -3.52], p<0.01) and HF (-1.04 [-1.97, -0.1] p<0.05) in women. In men, only LF showed a significant decrease (-0.26 [-0.5, -0.2], p<0.05). We could not perform MA for the non-linear variables, but the qualitative analyses showed a decrease in SD1 and increase in SD2 of the Poincare-plot for the MS group. Conclusions MS produced changes in short-term HRV in the time-domain analyses, showing a decrease of SDNN and rMSSD. Regarding the frequency-domain analyses, MS induced a decrease in HF and LF, with the exception of the LF/HF relationship, which was not modified. When gender was taken into account, the MA was only possible in one of both genders (men or women) in rMSSD and LF/HF. Lastly, when data for both men and women were available, gender subanalyses showed a different behavior than the mixed analyses for SDNN, HF and LF, which might point towards a different impact of MS in men and women.