Usefulness of metoprolol for unexplained syncope and positive response to tilt testing in young persons.

The efficacy of intravenous metoprolol in preventing symptoms during a repeat tilt test was compared with the outcome of chronic oral treatment in 21 patients (14 female, 7 male), age 8 to 20 years (mean 13 +/- 3) with unexplained syncope (> or = 1 episode) and a positive response to tilt testing. A positive response was defined as the development of either syncope or presyncope. During the initial tilt test, a positive response occurred during baseline (14 patients) or isoproterenol (0.03 to 0.1 microgram/kg/min) infusion (7 patients) with a cardioinhibitory (1 patient), vasodepressor (5 patients) or mixed (15 patients) pattern. Metoprolol (0.1 to 0.2 mg/kg) was administered intravenously. During the repeat tilt test, response was negative in 18 patients, including 11 of 14 patients with a positive response in the baseline and 7 of 7 patients with a positive response during isoproterenol infusion. Metoprolol (0.8 to 2.8 mg/kg/day) was administered orally to 15 patients for an average of 10 months. Symptoms were absent (7 patients) or improved (2 patients); metoprolol was discontinued because of adverse effects (3 patients) or recurrence of symptoms (3 patients). In 7 of 12 patients with a negative response and 2 of 3 patients with a positive response after intravenous metoprolol, oral administration of metoprolol prevented or improved symptoms without adverse effects. Many young patients (60%) with recurrent syncope obtained symptomatic improvement from chronic oral metoprolol treatment without adverse effects; repeat tilt testing after intravenous metoprolol did not appear to offer any additional information than would have been obtained from a trial of chronic oral treatment.