Effects of aging on responses to isoproterenol tilt-table testing in patients with syncope

The diagnosis of neuromediated syncope is often established with isoproterenol head-up tilt-table testing. Previous work has demonstrated changes in autonomic nervous system function with progressive age, suggesting that responses to tilt-table testing may depend on the age of the patient. The purpose of this study was to assess the effects of age on the clinical and hemodynamic responses to isoproterenol tilt testing in patients with syncope of undetermined etiology. Accordingly, 85 patients with syncope of undetermined etiology underwent tilt testing with infusions of 0, 2, and 5 micrograms/min of isoproterenol in 3 successive stages. Of 85 patients tested, 66 had a positive outcome. The proportions of patients with a positive test and with tests ending in syncope declined significantly with age, with positive outcomes seen in 100%, 86%, 69%, and 61% of patients aged 12 to 20, 21 to 35, 36 to 60, and 61 to 88 years, respectively (p = 0.033, chi-square). Presyncope developed more slowly in patients aged 61 to 88 years (half-time to presyncope 2.5 minutes) than in younger patients (half-times to presyncope 0.7 to 0.9 minute). There were no significant age-related changes in peak and trough systolic blood pressures and rate-pressure products, but trough heart rate increased significantly with age (r = 0.40, p = 0.003). In conclusion, the likelihood of a positive outcome to isoproterenol tilt-table testing declines with age. Older patients take longer to develop presyncope, are less likely to develop syncope, and are less able to develop a relative bradycardia. These results guide interpretation of isoproterenol tilt-table testing.