Heart Rate Variability During Head-up Tilt Testing in Patients with Suspected Neurally Mediated Syncope WOLFRAM GRIMM, ANDREAS WIRTHS, JURGEN HOFFMANN, VOLKER MENZ, and BERNHARD MAISGH From the Department of Cardiology, Hospital of the Philipps-University of Marburg, Marburg, Germany GRIMM, W., ET AL.: Heart Rate Variability During Head-up Tilt Testing in Patients with Suspected Neu- rally Mediated Syncope. The relation between heart rate variability (HRV) and outcome of head-up tilt testing (HUT) in patients with neurally mediated syncope (NMS) was studied in 30 patients with pre- sumed NMS (33 ± 13 years) and in 11 age-matched controls. After 15 minutes of baseline supine obser- vation, patients were tilted to 60° for 45 minutes or until syncope occurred. HRV parameters included RR intervals, standard deviation of normal-to-normal RR intervals (SDNN), and root mean square successive differences (RMSSD). HRV analysis was performed during 5-minute intervals in the supine position im- mediately after onset of HUT and before syncope or after 30-35 minutes of tilt in patients vrithout syn- cope. Syncope occurred after a mean tilt duration of 32 minutes in 14 (47%) of 30 patients with presumed NMS, whereas all controls had an uneventful HUT. In the supine position, RR intervals and RMSSD were comparable among HUT-positive patients, HUT-negative patients, and controls (RR intervals: 799 ± 92, 854 ± 137, and 818 ± 128 ms, P = NS; RMSSD: 43 ± 40, 36 ± 34, and 53 ± 42 ms, P = NS). Baseline SDNN was also comparable in HUT-positive patients versus HUT-negative patients with presumed NMS (50 ± 26 vs 52 ± 20 ms, P = NS). Within 5 minutes preceding syncope or after 30-35 minutes of tilt, RR intervals and RMSSD were shorter in HUT-positive patients compared to HUT-negative patients, or to controls (RR intervals: 606 ± 86 vs 710 ± 117 and 739 ± 123 ms, P < 0.05; RMSSD: 12 ±5vs23 ± 19 and 40 ± 32 ms, P < 0.05). Thus, HRV analysis in the baseline supine position was not a predictor of HUT out- come in patients viith suspected NMS. Syncope during HUT seemed to be preceded by increased sympa- thetic activity manifested by an increase in heart rate and by a decreased parasympathetic tone mani- fested by a decrease in RMSSD measured for 5 minutes before the event, in comparison with HUT-negative patients and with controls. (PACE 1998; 21[Pt.IIl:2411-2415) head-up tilt testing, heart rate variability, neurally mediated syncope Introduction Head-up tilt testing (HUT) has been found useful to verify the diagnosis of neurally mediated syncope (NMS).^~^ Analysis of heart rate variabil- ity (HRV) has been shown to be a valuable nonin- vasive test of autonomic nervous activity in vari- ous cardiovascular conditions.^ In the present study, we hypothesized that short-term HRV anal- ysis during HUT could confirm the presence of en- hanced sympathetic stimulation preceding syn- cope in HUT-positive versus HUT-negative patients. This enhanced sympathetic stimulation. Address for reprints: Wolfram Grimm, M.D., Hospital of the Philipps-University Marburg, Department of Cardiology, Baldingerstra^e, 35033 Marburg, Germany. Fax: 6421-28-8954. in conjunction with underfilling of the left ventri- cle during orthostatie stress, is thought to stimu- late ventricular mechanoreceptors and elicit the vasodepressor-cardioinhibitory Bezold-Jarisch re- flex mediated through vagal C-fiber afferents.^"^ In addition, we sought to determine whether HRV analysis in the baseline, supine position could be used to predict the outcome of HUT in patients with presumed NMS. Methods The study included 30 patients with sus- pected NMS referred to our cardiology outpatient department. All patients had a history of > 1 episode of syncope and s 2 episodes of presjm- cope in the upright position within the last 2 PACE, Vol. 21 November 1998, Part II 2411