DIAGNOSTIC-ACCURACY OF A LOW-DOSE ISOPROTERENOL HEAD-UP TILT PROTOCOL

The rate of positive head-up tilt (HUT), specificity, and same-day reproducibility of an HUT at 60 degrees combined with a low-dose isoproterenol infusion was assessed in the following patients: 120 consecutive patients with recurrent unexplained syncope, 30 healthy patients in a control group, and 30 patients with documented syncope not related to a vasodepressor reaction, HUT was positive in 61% (73 of 120) of patients with unexplained syncope, The false-positive rate in both the control and documented syncope groups was 6.6%. The mean isoproterenol dose infused was 1.4 +/- 0.5 mu g/min, 1.3 +/- 0.4 mu g/min, and 1.3 +/- 0.5 mu g/min, respectively (p = NS), HUT was positive during the drug free stage in 30 (25%) of 120 patients, and isoproterenol infusion was necessary in the remaining 43 (36%) patients, Immediate reproducibility was assessed in 75 patients, and HUT response was reproduced in 37 (82%) of 45 patients with a baseline positive HUT and in 28 (93%) of 30 patients with a baseline negative response, Overall, ''sensitivity,'' specificity, and reproducibility were 61%, 93%, and 86%, respectively, Clinical variables that increased the probability of a positive outcome were age less than or equal to 50 years and two or more syncopal episodes in the preceding 6 months in the absence of structural heart disease, These data support the use of an HUT protocol with low-dose isoproterenol infusion for the assessment of patients with recurrent syncope.