INTRAINDIVIDUAL REPRODUCIBILITY OF HEART-RATE-VARIABILITY BEFORE AND DURING POSTURAL TILT IN PATIENTS WITH SYNCOPE OF UNKNOWN ORIGIN

Fast Fourier analysis (FFT) of heart rate may be used to characterize overall heart rate variability (HRV) as well as low (LF: 0.06-0.10 Hz) and high (HF: 0.15-0.40 Hz) frequency components, which are attributa ble to sympathetic and vagal influences. This study examined the repro ducibility of the spectral characteristics of HRV before and during po stural tilt in patients being evaluated for unexplained syncope. Twent y patients (14 men, age 55 +/- 12 years) with a history of syncopal ep isodes underwent 2 tilt table tests (T-1 and T-2) 1 to 6 weeks apart. For purposes of analyses the patients were divided into 2 groups accor ding to the results of tilt testing. In 11 patients (Group A: 7 men, m ean age 53.5 +/- 12 years) syncope was induced in 1 (5 patients) or bo th tilt tests. In the remaining 9 patients (Group B: 7 men, age 56.7 /- 14 years) syncope did not develop during either test. Spectral inde xes (SI) of HRV were computed by FFT for 2-minute segments derived fro m Holter recordings before and during 60 degrees head-up tilt. We comp ared the SI measured in the two tilt tests during the following 2-minu te periods: P1, just before tilt at rest, in a supine position; P2, im mediately after tilt; P3, just before the end of the tilt. Results: P1 and P2: There were no significant differences in SI between T-1 and T -2 for low frequencies, high frequencies, or total power in either Gro up. In Group A, LF at time of maximum tilt exposure (P3) tended to be slower during T-2 than in T-1 (5.58 +/- 1.44 vs. 6.56 +/- 1.11, P < 0. 05). However, this difference primarily reflects the findings in the f ive patients in whom syncope did not occur during T-2. When these 5 pa tients were excluded the LF were essentially identical (6.43 +/- 0.97 vs 6.80 +/- 1.30; P = NS). Conclusions: Spectral indexes of HRV before and during the early part of tilt testing are reproducible. The SI du ring the later part of the test are related to the patient's response. However this response is not predictable on the basis of sympathetic or parasympathetic tone before or during the early part of the test.