Endothelial Function and Cardiovascular Autonomic Activity in Neurally Mediated Syncope

The aim of this study was to investigate endothelial function and cardiovascular autonomic activity in patients with neurally mediated syncope (NMS).

Patients with a typical history of NMS were divided according to the result of a head-up tilt (HUT) test. There were 25 patients each in the HUT-positive (HUT+), HUT-negative (HUT-) and control groups. Flow-mediated dilation (FMD) and 24-hour ambulatory electrocardiography (AECG) were performed before the HUT tests.

The HUT+ group had a significantly higher FMD than that of the HUT- group and the control group (8.8 ± 3.3 vs. 6.4 ± 2.9%, p = 0.006, and 8.8 ± 3.3 vs. 5.7 ± 2.2%, p = 0.001, respectively). On a 24-hour AECG, the parasympathetic indexes of time domain, such as rMSSD and the pNN50, were significantly higher in the HUT+ group than in the HUT- group (39.0 ± 9.6 vs. 31.6 ± 9.6 ms, p = 0.016, and 16.5 ± 8.1 vs. 10.2 ± 7.2%, p = 0.002, respectively) and the control group (39.0 ± 9.6 vs. 28.9 ± 9.6%, p = 0.001 and 16.5 ± 8.1 vs. 8.7 ± 6.7%, p = 0.001, respectively). High-frequency spectra (parasympathetic activity) of the frequency domain showed similar results.

Not only parasympathetic activity, but also endothelial function may affect the results of HUT tests in patients with NMS.