Objective: Tilt table testing represents a valuable diagnostic method in suspected neurally mediated syncope. As sympathovagal imbalance and impaired baroreceptor sensitivity (BRS) have been observed in these patients, both methods were used in this study to investigate whether a combination of these parameters would improve sensitivity and whether specific patterns of neurally mediated syncopes would correspond to characteristic trends in heart rate variability (HRV) and BRS.
Methods and results: Fifty-one pts. (29 female, mean age 14.5 +/- 3.9 y) with unexplained syncope and 15 control subjects (9 female, mean age 14.8 +/- 3.0 y) were tested following a standard tilt table test protocol. Power spectral analysis (PSA) of HRV and BRS calculation were used additionally to beat-to-beat blood pressure and ECG-monitoring. Twenty-three out of 51 pts. (45%) experienced a syncope after 18 +/- 10.2 min of tilting. In 2/23 patients (8.6%) a postural tachycardia syndrome (POTS), in 14/23 (60.8%) a neurally mediated syncope of mixed type, in 2/23 (8.6%) a vasodepressor syncope and in 5/23 (21.7%) a cardioinhibitory syncope with asystole were observed. PSA of HRV and BRS revealed a specificity, sensitivity, and positive and negative predictive values of the cut-off points in combination (LF/HF > or = 2.7 and BRS > or = 8) of 93.3%, 65.2%, 93% and 39%, respectively.
Conclusion: In this study population, BRS and PSA of HRV were able to improve sensitivity of tilt testing after unexplained syncope. Specific BRS or HRV patterns in different mechanisms of neurally mediated syncope could not be identified possibly due to the small sample size.