Heart rate variability in neurally mediated reflex syncope

Objective The aim of this study was to investigate the heart rate variability (HRV) parameters in patients with neurally mediated reflex syncope. Methods Thirty-three patients (10 men, age range 16-50 years) who were scheduled to undergo head-upright tilt test (HUTT) with a typical history of vasovagal syncope (VVS) underwent 24-hour Holter monitoring in an attempt to study HRV parameters. Sixteen individuals without syncope and similar baseline characteristics made up the control group. Results Seventeen of the 33 syncopal patients showed HUTT positivity. All the time domain HRV parameters except the mean RR interval were higher in the HUTT (+) syncopal patients than in the negative responders. Although not statistically significant, the positive responders had higher NN50, pNN50, RMSSD and SDNNi values than the control group. HUTT (-) VVS patients had lower SDNN and SDANN values when compared with the control group. The other HRV parameters did not differ significantly between the HUTT (-) patients and the control group. Conclusion Increased parasympathetic tonus as reflected by significantly higher HRV parameters is associated with a greater frequency of HUTT positivity in patients with syncope and no organic heart disease.