title: Sympathoadrenal imbalance before neurocardiogenic syncope.
abstract: Neurocardiogenic syncope is the most common cause of acute loss of consciousness in adults. The present study attempted to identify neuroendocrine and hemodynamic changes before syncope that could therefore play a pathophysiologic role. Twenty-five patients referred for chronic orthostatic intolerance had plasma catecholamines measured serially; 21 patients during tilt-table testing (evoking syncope in 13) and 4 others with spontaneous syncope while supine. Forearm blood flow was measured by impedance plethysmography. All 12 patients with blood sampled before tilt-induced syncope had progressive, marked increases in plasma epinephrine levels (mean 11 times baseline, p <0.0001) before syncope. Simultaneously obtained norepinephrine levels increased to a much smaller extent than did epinephrine levels ("sympathoadrenal imbalance"). In the same patients, forearm vascular resistance decreased by 21% before syncope. Proportionate changes in forearm vascular resistance before syncope correlated negatively with those in the epinephrine:norepinephrine ratio (r = -0.75, p = 0.005). Patients without syncope had forearm vasoconstriction and no sympathoadrenal imbalance during tilt. Patients with syncope while supine also had sympathoadrenal imbalance before loss of consciousness. Sympathoadrenal imbalance precedes tilt-evoked and spontaneous neurocardiogenic syncope and correlates with concurrent skeletal muscle vasodilation. Sympathoadrenal imbalance may contribute to hemodynamic derangements precipitating neurocardiogenic syncope.
authors.affiliation: Clinical Neurocardiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1620, USA. goldstein@ninds.nih.gov
authors.forename: David S
authors.initials: DS
authors.lastname: Goldstein
authors.forename: Courtney
authors.initials: C
authors.lastname: Holmes
authors.forename: Steven M
authors.initials: SM
authors.lastname: Frank
authors.forename: Mohammad
authors.initials: M
authors.lastname: Naqibuddin
authors.forename: Raghuveer
authors.initials: R
authors.lastname: Dendi
authors.forename: Sally
authors.initials: S
authors.lastname: Snader
authors.forename: Hugh
authors.initials: H
authors.lastname: Calkins
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004837:Epinephrine / Q000097:blood*; D005260:Female; D005542:Forearm / Q000098:blood supply; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008297:Male; D009638:Norepinephrine / Q000097:blood*; D010991:Plethysmography / Q000379:methods; D011187:Posture; D019462:Syncope, Vasovagal / Q000097:blood* / Q000503:physiopathology; D018667:Tilt-Table Test; D014655:Vascular Resistance
chemical_list: D009638:Norepinephrine; D004837:Epinephrine