Does an early increase in heart rate during tilting predict the results ofpassive tilt testing?

Head-up tilt testing is a useful but time-consuming procedure. If we could accurately predict the tilt testing results; we would be able to substantia lly shorten the duration of tilt protocol. To clarify the hypothesis that a n early increase in heart rate (HR) during tilting can predict the passive tilt results in our protocol (30-degree angle for 30 minutes), we studied 1 15 consecutive patients (72 men, 43 women, mean age 46 +/- 19 years) who we re clinically diagnosed with neurally mediated syncope. Twenty-nine (25%) p atients had a positive tilt test (P group), whereas 86 (75%) patients had a negative test (N group). The early HR increase was defined as the maximum HR during the first 5 minutes of tilting minus the resting HR before tiltin g. The early HR increase was significantly higher in the P group (23.8 +/- 9.5 beats/min) than in the N group (17.5 +/- 8.2 beats/min, P = 0.0008), bu t it was negatively correlated with the tilt duration to positive response (r = -0.52, P = 0.0032) and the patient age in the entire study population (r = 0.62, P < 0.0001). Results of multiple regression analysis indicated t hat age, tilt result, and tilt duration were independently associated with the early HR increase. As a result, an early HR increase <greater than or e qual to> 18 beats/min, the best apparent cut-off point obtained in our stud y, wets a sensitive (100%) marker for prediction of a positive response at less than or equal to 15 minutes of tilting, but it showed a low specificit y (61%). In conclusion, an early HR increase during 80-degree tilting may b e only predictive for a positive result less than or equal to 15 minutes be cause it depends on the tilt duration to a positive response and patient ag e.