IMPAIRED ENDOTHELIN-1 RELEASE IN TILT-INDUCED SYNCOPE

The neurohumoral events associated with neurocardiogenic syncope remai n unclear. The simultaneous assessment of changes in endothelium-depen dent and independent hormones and in autonomic balance in patients wit h tilt-induced syncope has been incompletely studied. Forty-six health y subjects aged between 21 and 83 years (mean +/- SEM 47 +/- 3) underw ent a 30-minute head-up tilt test at 60 degrees, Fourteen subjects (10 females and 4 male subjects) exhibited syncope at 16 +/- 2 minutes in to the tilt. Hemodynamics were recorded every 5 minutes and blood samp les for the measure of catecholamines, endothelin-1 (ET-1), and angiot ensin-II (AT-II), were drawn at baseline, and 5, 10, 15, and 30 minute s into the tilt and immediately before syncope. Heart rate variability was analyzed by 5-minute segments during the test. Both catecholamine s and ET-1 levels increased consistently in response to head-up tilt i n subjects able to tolerate the test, Epinephrine increased to a great er extent before syncope. In contrast, ET-1 failed to increase at any time during the tilt and lust before syncope. AT-II increased at 30 mi nutes into the tilt only in the control group. Finally, power in high- frequency bands decreased less in the group with syncope, Thus, compar ed with subjects able to tolerate a head-up tilt test, patients with s yncope exhibit a greater increase in adrenomedullary activation, no si gnificant increase in ET-1 levels, and a blunting in the decrease of v agal tone before syncope. The lack of increase in ET-1 during tilt may play a role in the inability to support orthostatic stress. (C) 1998 by Excerpta Medico, Inc.