Ordinary Autonomic Unbalance Can Reflect Diagnosis of Neurally Mediated Reflex Syncope

Abstract

Background: In the present study we investigated autonomic dysfunction using hemodynamics and analysis of heart rate variability (HRV) following ambulatory blood pressure monitoring (APBM) in patients with neurally mediated reflex syncope (NMRS). In addition, we evaluated the usefulness of ABPM for diagnosing NMRS. Methods: In all, 88 consecutive patients with syncope and 12 controls (Group C) were subjected to a head-up tilt (HUT) test (80°, 30 min). If no syncope or presyncope occurred, the HUT test was repeated in the patient group following drug loading (ATP, isoproterenol, and/or isosorbide dinitrate). Results: Forty patients had a positive HUT test, with or without drug loading (Group P) ; the HUT test was negative in 48 patients, even after drug loading. Average daytime systolic and diastolic blood pressure (SBP and DBP, respectively) was significantly lower in Group P than in Group C (P = 0.042 and P = 0.047, respectively). The average standard deviation of SBP at night (SD-SBP_Night) was significantly higher in Group P than in Group C (P = 0.004). HRV analysis revealed a significantly higher daytime high-frequency component in Group P than in Group C (P = 0.041). Conclusion: The results of the present study suggest that lower daytime blood pressure and a larger SD-SBP_Night, as determined by ABPM, are associated with vagal nerve hyperactivity and sympathetic hypoactivity in patients with NMRS. Thus, an inadequate circadian rhythm in blood pressure variation, as identified by ABPM, may be useful for the diagnosis of NMRS.