Sympathoadrenal imbalance before neurocardiogenic syncope

Am J Cardiol. 2003 Jan 1;91(1):53-8. doi: 10.1016/s0002-9149(02)02997-1.


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.

MeSH terms

  • Adult
  • Analysis of Variance
  • Epinephrine / blood*
  • Female
  • Forearm / blood supply
  • Hemodynamics / physiology
  • Humans
  • Linear Models
  • Male
  • Norepinephrine / blood*
  • Plethysmography / methods
  • Posture*
  • Syncope, Vasovagal / blood*
  • Syncope, Vasovagal / physiopathology
  • Tilt-Table Test
  • Vascular Resistance


  • Norepinephrine
  • Epinephrine