HEART-RATE-VARIABILITY DURING HEAD-UP TILT TESTING IN PATIENTS WITH SUSPECTED NEURALLY-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 presumed NMS (33 +/- 13 years) and in 11 age-matched controls. After 15 minutes of baseline supine observat ion, patients were tilted to 60 degrees for 45 minutes or until syncop e occurred. HRV parameters included RR intervals, standard deviation o f normal-to-normal RR intervals (SDNN), and root mean square :; succes sive differences (RMSSD). HRV analysis was performed during 5-minute i ntervals in the supine position immediately after onset of HUT and bef ore syncope or after 30-35 minutes of tilt in patients without syncope . Syncope occurred after a mean tilt duration of 32 minutes in 24 (47% ) of 30 patients with presumed NMS, whereas all controls had an uneven tful HUT. In the supine position, RR intervals and RMSSD were comparab le among RUT-positive patients, RUT-negative patients, and controls (R R intervals: 799 +/- 92, 854 +/- 137, and 818 +/- 128 ms, P = NS; RMSS D: 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 minute s preceding syncope or after 30-35 minutes of tilt, RR intervals and R MSSD were shorter in HUT-positive patients compared to HUT-negative pa tients,::or to controls (RR intervals: 606 +/- 86 vs 710 +/- 117 and 7 39 +/- 123 ms, P < 0.05; RMSSD: 12 +/- 5 vs 23 +/- 19 and 40 +/- 32 ms , P < 0.05). Thus, HRV analysis in the baseline supine position was no t a predictor of HUT outcome in patients with suspected NMS. Syncope d uring HUT seemed to be preceded by increased,sympathetic activity mani fested by an increase in heart rate and by a decreased parasympathetic tone manifested by a decrease in RMSSD measured for 5 minutes before the event, in comparison with HUT-negative patients and with controls.