Lack of association of heart rate variability parameters with head-up tilt-test responses in patients with syncope.

BACKGROUND: Neurocardiogenic syncope is the most common type of syncope. Head-up tilt testing is the investigation of choice for diagnosis of patients with neurocardiogenic syncope. In this study, we aimed to findout any association between heart rate variability parameters and type of tilt-test response in patients with syncope. METHODS AND RESULTS: Forty-nine cases with unexplained syncopal attacks were enrolled into our study and were grouped according to the tilt-test responses. Tilt test was performed in all patients after excluding other causes of syncope. In case of a negative basal tilt-testing, pharmacological tilt testing was performed after 30 min of 5 mg sublingual isosorbide dinitrate. Holter monitoring was done from the beginning of tilt testing upto two hours post-procedure. The heart rate variability parameters analyzed were the mean of all coupling intervals between normal beats, the standard deviation about the mean of all coupling intervals between normal beats, the mean of all 5-min standard deviations of mean of all coupling intervals between normal beats, the proportion of adjacent normal R-R intervals differing by > 50 ms, the root mean square of the difference between successive RRs, and the standard deviation of 5-min mean of all coupling intervals between normal beats and ratio between low and high frequencies. CONCLUSIONS: In 35 patients, the tilt-test was positive, 16 were cardioinhibitor type (Group 1), four cases had a vasodepressor type response (Group 2) and 15 were mixed type (Group 3). Fourteen patients had a negative test result. The heart rate variability measures did not significantly differ among the study groups. The heart rate variability measures were compared between the tilt-test negative (Group 4) and the tilt-test positive groups (Groups 1, 2 and 3) and no statistically significant difference was found.

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.