A randomized study of tilt test angle in patients with undiagnosed syncope

A widely used tilt test protocol involves passive head-up tilt followed by tilt with isoproterenol infusion if necessary. Little is known about the effects of passive tilt angle and duration, duration of isoproterenol infusion or hemodynamic diagnostic criteria.

To assess whether tilt angle and duration of isoproterenol infusion affected test outcomes in patients with undiagnosed syncope.

Two hundred one syncope patients (87 men, age 45+/-20 years, median five faints) were randomly assigned to undergo 60 degrees versus 80 degrees tilt for 45 min, then, if necessary, to receive isoproterenol 30 ng/kg/min for 20 min or less. Positive tests ended in presyncope or syncope.

Overall, 49% and 71% of patients fainted at 60 degrees and 80 degrees, respectively (P=0.002). In the drug-free stage, 27% and 50% of patients fainted at 60 degrees and 80 degrees, respectively (P=0.0005). In the 119 patients who received isoproterenol, there was no significant difference in the probability of a positive isoproterenol test at 60 degrees and 80 degrees, respectively (31% compared with 43% of exposed patients, P=0.25). Symptoms developed in adults during drug-free tilt linearly with time at both 60 degrees and 80 degrees at 0.6% and 1.1%/min, respectively, while symptoms during isoproterenol tilt reached an asymptote after about 10 min. Rate-systolic pressure products of 7000 mmHg/min and 9000 mmHg/min best distinguished positive from negative passive and isoproterenol stages, respectively.

The positive yield of passive tilt tests is higher at 80 degrees and increases linearly with the duration of tilt. A subsequent 10 min isoproterenol infusion maximizes positive yield. Evidence-based outcome criteria accurately distinguish negative from positive tilt tests.