Association Between Cardiac Acceleration Capacity and Susceptibility to Vasovagal Syncope

BACKGROUND: Vasovagal syncope (VVS) might be associated with alterations in vagal activity. Cardiac acceleration capacity (AC) is a novel index related to autonomic modulation. It remains unknown whether AC could be used to assess vagal tone and differentiate VVS patients. OBJECTIVES: This study aimed to investigate the association between AC and VVS, and evaluate the capability of AC to identify VVS susceptibility. METHODS: In this observational study, 204 VVS patients (41.2 ± 16.9 years, 40.2% [82 of 204] men) were included, of whom 87.3% (178 of 204) VVS patients had positive responses to tilt-table testing, and 116 asymptomatic individuals were included as controls. Twenty-four-hour Holter monitoring was performed for all participants. Multivariate logistic regression analysis and receiver-operating characteristic curves were performed for heart rate variability metrics. RESULTS: VVS patients exhibited significantly higher AC than control subjects (8.81 ± 2.21 ms vs 5.89 ± 1.27 ms; P < 0.001). AC correlated with deceleration capacity (VVS: r = 0.90 [95% CI: 0.83-0.96]; controls: r = 0.92 [95% CI: 0.85-1.00]) and other vagal-dominant heart rate variability metrics. In multivariate models, increased AC was significantly associated with an elevated risk of VVS (adjusted OR: 3.54 [95% CI: 2.55-4.91]). Daytime AC showed strong discriminative power for VVS (area under curve 0.910 [95% CI: 0.879-0.942]), and outperformed nighttime measures in the identification of VVS. CONCLUSIONS: Higher AC was observed in VVS patients during the nonsyncopal period, indicative of AC's potential association with vagal modulation. Daytime AC showed superior performance in detecting VVS susceptibility, offering a noninvasive approach to assisting clinical diagnosis.