Responses of normal subjects during 80 degrees head upright tilt table testing with and without low dose isoproterenol infusion.

Head upright tilt table testing has emerged as a standard technique for the evaluation of patients with recurrent unexplained syncope. To determine the specificity of head upright tilt table testing with and without a low dose isoproterenol infusion, the following study was undertaken. A total of 34 normal volunteers (21 men, 13 women, mean age 32.9 +/- 1.7 years) with no history of syncope, presyncope, or vertigo underwent head upright tilt table testing for 45 minutes. A positive test was defined as the production of syncope or presyncope associated with hypotension and bradycardia. If the test was negative the patient was lowered to the supine position and a low dose isoproterenol infusion started (sufficient to raise the heart rate 20-25% above baseline) and the patient retilted for 20 minutes. Three subjects (8.8%; 95% CI: 2, 26; P = 0.23) developed syncope during the test, two during the baseline tilt, and one during isoproterenol infusion. Interestingly, one of these subjects later had a clinical syncopal episode. We conclude that head up tilt table testing at 80 degrees with or with out low level isoproterenol infusion provides an adequate specificity.