Can the result of a tilt test be predicted in the first five minutes?

BACKGROUND Head-up tilt testing (HUT) plays a pivotal role in the management of vasovagal syncope (VVS). Heart rate variability (HRV) is a well-known method used for noninvasive evaluation of autonomic nervous system activity. However, different results have been obtained in studies that have evaluated the HRV response to HUT in patients with VVS. METHODS One hundred fourteen patients with recurrent VVS were enrolled in the study. According to the results of HUT, patients were divided into five groups: positive (n = 30) and negative (n = 23) Westminster; positive (n = 44) and negative (n = 11) Italian. Fourteen healthy volunteers with no history of syncope comprised the control group. Spectral indices of HRV variability were analyzed for three short-term intervals. RESULTS Both protocols showed similar distribution of responses to tilt-testing. In the supine position, significant differences were observed between patients from groups 1, 2 and 3 in comparison with the control and Italian negative groups. They had significantly lower initial results of LF(1) [nu] and LF(1)/HF(1) ratio, and higher HF(1) [nu] values. The onset of HUT in patients with positive Westminster protocol was characterized by an almost two-fold increase in LF [nu] and decrease in HF [nu] compared to all other patients. LF(2)/HF(2) ratio in the Westminster positive group had increased more than five times since the baseline level, while during the last period, LF(3)/HF(3) ratio had increased more than six times. CONCLUSIONS Patients with VVS have disturbed sympathovagal balance at rest. Our data suggests that the results of HUT could be predicted by analyzing the spectral parameters of HRV during the first five minutes of the test. The reaction to orthostasis in patients with syncope during the Westminster protocol was more severe compared to the Italian protocol group and the control group. Vasovagal response during the Italian protocol may be triggered by drug-induced vasodilatation.