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 diso rder but may also cause fainting in unaffected subjects. The aims of t his study were to examine autonomic function and sequential changes in heart rate variability and plasma catecholamines during graded head-u p tilt in patients with vasodepressor syncope compared with healthy su bjects. Studies were performed in 10 patients and 15 control subjects. Eight negative controls completed the study; presyncope or syncope de veloped in seven positive controls and all 10 patients. The negative c ontrol group showed a progressive increase in mid-frequency from the s upine position to end tilt. Patients and positive controls showed sign ificant and similar falls in mid-frequency in the presyncope period. T he rise in plasma norepinephrine was blunted in patients and positive controls, whereas plasma epinephrine increased more in these groups co mpared with the negative control group. In conclusion, the patterns of heart rate variability and catecholamine changes could not be disting uished in patients and positive control subjects.