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 fo r the evaluation of patients with recurrent unexplained syncope. To de termine the specificity of head upright tilt table testing with and wi thout a low dose isoproterenol infusion, the following study was under taken. 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 un derwent head upright tilt table testing for 45 minutes. A positive tes t was defined as the production of syncope or presyncope associated wi th hypotension and bradycardia. If the test was negative the patient w as lowered to the supine position and a low dose isoproterenol infusio n started (sufficient to raise the heart rate 20-25% above baseline) a nd 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 bas eline tilt, and one during isoproterenol infusion. interestingly, one of these subjects later had a clinical syncopal episode. We conclude t hat head up tilt table testing at 80 degrees with or without low level isoproterenol infusion provides an adequate specificity.