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 observation, patients were tilted to 60 degrees 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 immediately after onset of HUT and before syncope or after 30-35 minutes of tilt in patients without syncope. 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 +/- 5 vs 23 +/- 19 and 40 +/- 32 ms, P < 0.05). Thus, HRV analysis in the baseline supine position was not a predictor of HUT outcome in patients with suspected NMS. Syncope during HUT seemed to be preceded by increased sympathetic activity manifested 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.

Syncope recurrence can better be predicted by history than by head-up tilt testing in untreated patients with suspected neurally mediated syncope.

BACKGROUND: Head-up tilt testing is widely used in the evaluation of patients with suspected neurally mediated syncope. Although it remains unclear which patients require medical therapy to prevent recurrent syncope, most centres initiate empiric medical therapy in all patients in whom neurally mediated syncope has been diagnosed. To determine the natural history of this condition, we followed 80 untreated patients. METHODS: All 80 study patients fulfilled the following inclusion criteria: (1) > or = 1 syncope in the upright position, (2) absence of structural heart disease, (3) unremarkable work-up for other known causes of syncope. Thirty-nine patients had a history of one episode of syncope (group A) and 41 > or = 2 episodes of syncope (group B). Head-up tilting was performed in all patients at 60 degrees for a maximum of 45 min without medical provocation ('Westminster Protocol'). RESULTS: Suspected neurally mediated syncope could be reproduced by tilt testing in four of 39 patients from group A vs 10 of 41 patients from group B (10% vs 24%, P = 0.1). Independent of the result of head-up tilt testing, all patients were prospectively followed without medical therapy. During 23 +/- 8 months follow-up, syncope recurred in four of 39 group A patients vs 22 of 41 group B patients (10% vs 54%, P < 0.05). The incidence of syncope during follow-up was not significantly different between patients with and without positive baseline tilt test (43% vs 30%, P = ns). CONCLUSIONS: (1) 90% of patients with a single episode of syncope remain free of recurrent syncope without medical therapy irrespective of the result of tilt testing. (2) About half of patients with a history of > or = 2 syncopal episodes have recurrent syncope and, thus, may be appropriate candidates for prophylactic medical therapy. (3) Although head-up tilt testing at 60 degrees for up to 45 min does not appear to be useful to predict recurrent syncope in untreated patients, it is still a useful test in its evaluation.