Reproducibility of time domain indexes of heart rate variability in normal subjects and patients with vasovagal syncope

The reproducibility of time domain indexes of heart rate variability (HRV) was evaluated in 19 syncopal patients and 15 controls who each underwent two tilt-table tests. Eleven of the patients (Group P-P) had 2 positive tests, while 8 (Group P-N) had a negative second test. The control group showed good reproducibility of all HRV indexes. The syncopal patients overall had significantly less reproducibility than the controls in the pNN50 parameter. This was due entirely to the patients in the P-N group, who lacked reproducibility in both the pNN50 and rMSSD measures, while the reproducibility of all HRV indexes in the P-P group was no different from the controls. Some syncopal patients lack reproducibility both in some HRV parameters and in the clinical result of tilt testing. This could explain the variability in the clinical outcome of tilt-table testing and the sporadic nature of vasovagal syncope.