Cardiac autonomic disturbances in patients with vasovagal syndrome: comparison between iodine-123-metaiodobenzylguanidine myocardial scintigraphy and heart rate variability.

AIMS: The aim of this study was to examine autonomic disorders in patients with different types of vasovagal syndrome by performing both a cardiac sympathetic innervation evaluation and a head-up tilt-test with heart rate variability (HRV) analysis. METHODS AND
RESULTS: We enrolled 60 patients with vasovagal syncope (32 women, mean age 40 ± 16 years), and 20 age-matched controls. We assessed the integrity and function of the myocardial pre-synaptic nerve endings and in the sympathovagal activity, using (123)I-metaiodobenzylguanidine (MIBG) scintigraphy and time-domain indexes of HRV. A significantly lower heart/mediastinum ratio was found in the syncopal patients compared with the control group, both at 10 min (1.9 ± 0.25 vs. 3.6 ± 1.7, P = 0.02) and at 4 h (1.79 ± 0.12 vs. 2.07 ± 0.19, P = 0.04), whereas washout rate was significantly greater in syncopal patients (5.5 ± 3.7 vs. 2 ± 0.19, P = 0.04). There were no significant differences in any of the above parameters between patients with different types of syncope. In addition, the majority of the patients showed multiple adrenergic innervation defects in the left ventricular myocardium. No significant difference was found in any of the HRV time-domain indexes. However, a correlation was found between root-mean-square of the difference between successive RRs and washout rate in syncopal patients (r = -0.256, P = 0.48).
CONCLUSION: Patients with vasovagal syncope induced by tilt testing reveal a high degree of disturbance of myocardial adrenergic innervation and multiple adrenergic innervation defects. This suggests a possible predominance of cardiac adrenergic activity in those with abnormal cardiac MIBG scintigraphy.