Usefulness of intravenous metoprolol during positive isoproterenol tilt-table test in the choice of treatment for neurocardiogenic syncope.

BACKGROUND: Isoproterenol tilt-table testing provides a diagnosis of neurocardiogenic syncope in patients with syncope or near-syncope. Although acute beta-blockade may prevent the development of syncope during isoproterenol tilt-table testing, the use of beta-blockers for chronic prophylaxis may not be effective for some patients who show a positive response to isoproterenol tilt-table testing. We evaluated whether the efficacy of intravenous metoprolol in preventing symptoms during repeated tests would be helpful in selecting patients suitable for long-term therapy. METHODS AND RESULTS: We studied 55 patients (35 females, 20 males; mean age 36+/-11 years) who had been chosen from a group referred to our institute with a history of unexplained syncope (> or = 2 syncopal episodes) and a positive response to isoproterenol tilt-table testing. After a positive response to isoproterenol tilt-table testing, 5 mg metoprolol was infused intravenously as a bolus and the test repeated. Thirty-five patients (group 1) showed a positive response again and 20 (group 2) showed a negative response. We started 50 mg metoprolol once a day for patients in group 1 while group 2 was divided into 2 subgroups: the first subgroup (group 2a, 12 patients) was started on 50 mg sertraline or 20 mg paroxetine once a day and the second subgroup (group 2b, 8 patients) was started on 5 mg midodrine orally once a day. Two months later, isoproterenol tilt-table testing was repeated. In group 1, 13 of 35 patients (37%) were positive on isoproterenol tilt-table testing while in group 2, 8 of 20 patients (40%) were positive on isoproterenol tilt-table testing (p not statistically significant). The therapies of the two groups were then interchanged. Two months later (4 months from the beginning of the study), the isoproterenol tilt-table test was repeated. Eleven patients in group 1 (31%) and 6 in group 2 (30%, p not statistically significant) showed a positive response again. CONCLUSIONS: We conclude that acute beta-blockade response to positive isoproterenol tilt-table testing is not a useful predictor for the assessment of chronic prophylaxis for neurocardiogenic syncope.

Isoproterenol infusion--an alternative to exercise testing.

Isoproterenol, as an exercise simulating agent, was evaluated in twenty subjects, ten normal volunteers and ten with Coronary Artery Disease (CAD). Both groups were evaluated using 0.5 ug increments of intravenous infusion of isoproterenol every 3 minutes with computerised ECG (Marquette Electronics--MAC PC) monitoring. The normal volunteers did not have significant ST segment depression even at heart rates of 130 BPM. The CAD groups showed diagnostic ischaemic ST segment depression at heart rates below 130 BPM. None of the subjects had any serious complications during or after the test. Isoproterenol infusion is a better alternative to exercise testing.