Upright postures and isoproterenol infusion for provocation of neurocardiogenic syncope: A comparison of standing and head-up tilting

Head-up tilt testing has proved to be useful in provocation of neurocardiogenic syncope. The purpose of this study was to examine whether simply assuming an upright posture by standing can be an alternative to the head-up tilt testing for diagnosis of neurocardiogenic syncope. Eight-four patients with recurrent unexplained syncope and 22 normal volunteers were recruited into the study. Forty-seven patients with syncope and all normal volunteers received the standing test. Thirty-seven of the patients with syncope received head-up tilt testing (90 degrees). All subjects lay down for 5 minutes and then assumed an upright posture until syncope or presyncope occurred or until a maximum of 10 minutes was reached in each stage of the test. The tests included four stages: baseline and infusion of 1, 2, or 3 μg/min isoproterenol in each of the successive stages. Five subjects could not tolerate the procedure, and further testing was terminated. Overall, the standing test was positive in 83% of the patients with syncope, and its specificity was 74%. The head-up tilt testing was positive in 75% of the patients with syncope. The duration of assuming an upright posture before occurrence of syncope or presyncope was significantly longer in the syncope-tilting group in the third stage (p < 0.01) and the fourth stage (p < 0.05) compared with the syncope-standing group. However, the curves of the time course for cumulative positive rates were not significantly different (p = 0.0739) in the two groups. The standing test can serve as an alternative to head-up tilt testing and can be applied to patients with recurrent unexplained syncope for confirmation of the diagnosis.