Circ Arrhythm Electrophysiol. 2020 Nov 16. doi: 10.1161/CIRCEP.120.008659. Online ahead of print.
Background - Increased parasympathetic activity is thought to play important roles in syncope events of vasovagal syncope (VVS) patients. However, direct measurements of the vagal control are difficult. The novel deceleration capacity (DC) of heart rate measure has been used to characterize the vagal modulation. This study aimed to assess vagal control in VVS patients and evaluate the diagnostic value of the DC in VVS. Methods - Altogether 161 consecutive VVS patients (43 ± 15 years; 62 males) were enrolled. Tilt table test (TTT) was positive in 101 and negative in 60 patients. Sixty-five healthy subjects were enrolled as controls. DC and heart rate variability (HRV) in 24-hour electrocardiogram, echocardiogram, and biochemical examinations were compared between the syncope and control groups. Results - DC was significantly higher in the syncope group than in the control group (9.6 ± 3.3 ms vs. 6.5 ± 2.0 ms, P0.001). DC was similarly increased in VVS patients with a positive and negative TTT (9.7±3.5 ms and 9.4±2.9 ms, P=0.614). In multivariable logistic regression analyses, DC was independently associated with syncope (OR=1.518, 95% CI 1.301-1.770, P =0.0001). For the prediction of syncope, the area under curve (AUC) analysis showed similar values when comparing single DC and combined DC with other risk factors (P=0.1147). From the receiver operator characteristic (ROC) curves for syncope discrimination, the optimal cut-off value for the DC was 7.12 ms. Conclusion - DC > 7.5 ms may serve as a good tool to monitor cardiac vagal activity and discriminate VVS, particularly in those with negative TTT.