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Related Experiment Videos

Is the heart "empty' at syncope?

V Novak1, G Honos, R Schondorf

  • 1Autonomic Reflex Laboratory Department of Neurology, McGill University, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada.

Journal of the Autonomic Nervous System
|August 27, 1996
PubMed
Summary
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Neurally-mediated syncope is not triggered by reduced cardiac filling. Stroke volume remained stable before syncope, challenging the impaired cardiac filling hypothesis for neurally-mediated syncope.

Area of Science:

  • Cardiology
  • Neuroscience
  • Physiology

Background:

  • Neurally-mediated syncope (NMS) is hypothesized to be triggered by vagal afferents activated by impaired cardiac filling.
  • This suggests maneuvers increasing venous pooling should decrease cardiac volume and trigger syncope.

Purpose of the Study:

  • To investigate the role of cardiac filling and volume changes in the pathogenesis of neurally-mediated syncope.
  • To test the hypothesis that reduced cardiac filling precedes and triggers NMS.

Main Methods:

  • Beat-to-beat hemodynamic monitoring (heart rate, blood pressure, stroke volume) during head-up tilt in healthy controls and NMS patients.
  • Echocardiography and Doppler measurements assessed cardiac chamber and stroke volumes in NMS patients.
  • Comparison of hemodynamic profiles at rest, during tilt, and preceding syncope.

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Main Results:

  • No significant decrease in cardiac volume or stroke volume was observed before syncope in NMS patients.
  • Stroke volume remained stable during the presyncopal period and increased at the onset of syncope.
  • Echocardiographic measurements confirmed stable cardiac chamber volumes throughout tilt, presyncope, and syncope.

Conclusions:

  • The findings do not support the hypothesis that impaired cardiac filling triggers neurally-mediated syncope.
  • Reduced cardiac volume is not a significant trigger for NMS.
  • Alternative mechanisms for NMS must be considered.