Progressive Impairment of Cardiac Autonomic Regulation as the Number of Metabolic Syndrome Components Increases

Background: Metabolic syndrome (MetS) is associated with an increased risk of cardiovascular diseases. Compelling evidence supports the key role of dysfunction in the autonomic nervous system in that association, as well as mutual correlation among the components of MetS. The autonomic nervous system index (ANSI) is a percentile-ranked unitary proxy of cardiac autonomic regulation (CAR) that is designed to be free of age and sex bias, with higher values indicating better autonomic control. This study investigates CAR using the ANSI in patients with MetS. Methods: A total of 133 patients referred to the Exercise Medicine Clinic of Istituto Auxologico Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) underwent CAR assessment using the ANSI and answered lifestyle questions in ad hoc questionnaires. The participants were retrospectively subdivided into two groups according to the presence or absence of MetS criteria. Results: Of the subjects, 58 were diagnosed with MetS, and 75 were not (no MetS). The ANSI was significantly impaired (32.9 vs. 44.8, P<0.01) in the MetS group, and ANSI scores showed a decreasing trend (P=0.004) as the number of MetS components increased. No significant lifestyle differences were found between the groups. Conclusion: The ANSI was significantly reduced in subjects with MetS, and, net of age and sex effects, CAR impairment became progressively more apparent as the number of MetS components increased.