Presyncopal sympathetic withdrawal is the same in patients with vasodepressor syncope and controls who faint on head-up tilting.

Head-up tilt provokes vasodepressor syncope in patients with this disorder but may also cause fainting in unaffected subjects. The aims of this study were to examine autonomic function and sequential changes in heart rate variability and plasma catecholamines during graded head-up tilt in patients with vasodepressor syncope compared with healthy subjects. Studies were performed in 10 patients and 15 control subjects. Eight negative controls completed the study; presyncope or syncope developed in seven positive controls and all 10 patients. The negative control group showed a progressive increase in mid-frequency from the supine position to end tilt. Patients and positive controls showed significant and similar falls in mid-frequency in the presyncope period. The rise in plasma norepinephrine was blunted in patients and positive controls, whereas plasma epinephrine increased more in these groups compared with the negative control group. In conclusion, the patterns of heart rate variability and catecholamine changes could not be distinguished in patients and positive control subjects.