Sympathoadrenal imbalance before neurocardiogenic syncope.
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.
Goldstein
David S
DS
Clinical Neurocardiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1620, USA. goldstein@ninds.nih.gov
Holmes
Courtney
C
Frank
Steven M
SM
Naqibuddin
Mohammad
M
Dendi
Raghuveer
R
Snader
Sally
S
Calkins
Hugh
H
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
D009638:Norepinephrine; D004837:Epinephrine