Comparison of patients with syncope of unknown cause having negative or positive tilt-table tests.

Many patients without an identified cause of syncope have negative tilt tests. We hypothesized that many of these might be falsely negative tilt tests. If so, then patients with negative and positive tilt tests should have similar pretest clinical characteristics, post-test probabilities of remaining free of syncope, and similar risk factors for syncope recurrence after the tilt-table test. Demographic characteristics and historic features were compared between 153 syncope patients with a positive tilt test, and 74 syncope patients with a negative tilt test and no obvious cause of syncope. Patients with negative and positive tests had similar numbers of syncopal spells, durations of symptoms, frequency of spells, and peak heart rate during tilt test, but patients with negative tests were older (48 +/- 19 vs 39 +/- 20 years). The actuarial probabilities of remaining free of syncope were very similar, with 2-year risks of syncope of 41% and 37% in patients with negative and positive tests, respectively. The regression coefficients of risk factors predicting syncope recurrence were similar for both populations, and the confidence intervals of all regression coefficients decreased when the populations were combined. The outcome of tilt testing did not predict the clinical outcome of patients. Patients with syncope and either negative or positive tilt tests share many pretest and post-test clinical characteristics, suggesting that they may be part of the same population.