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Neurocardiogenic syncope

V K Somers1, F M Abboud

  • 1University of Iowa College of Medicine, Department of Internal Medicine, Iowa City, USA.

Advances in Internal Medicine
|January 1, 1996
PubMed
Summary
This summary is machine-generated.

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The cardiac inhibitory reflex acts as a safety valve, preventing hypotension by slowing heart rate and increasing diastolic filling. Potentiation of this reflex can lead to neurally mediated syncope.

Area of Science:

  • Cardiovascular Physiology
  • Autonomic Nervous System Regulation
  • Clinical Neurocardiology

Background:

  • Physiologic reflexes like the arterial baroreflex have clear functions, but the Bezold-Jarisch reflex's purpose is less apparent.
  • The Bezold-Jarisch reflex is triggered by forceful ventricular contraction in an empty chamber, potentially worsening hypotension.
  • The cardiac inhibitory reflex may act as a protective mechanism by reducing heart rate and afterload, beneficial in conditions like myocardial infarction and aortic stenosis.

Purpose of the Study:

  • To investigate the role of the cardiac inhibitory reflex in various clinical situations causing syncope.
  • To explore alternative mechanisms and central factors contributing to syncope.
  • To understand the influence of biochemical mediators on cardiovascular reflexes and syncope.

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Main Methods:

  • Utilized direct measurements of sympathetic activity via microneurography.
  • Employed provocative testing, including upright tilt and programmed electrical cardiac stimulation.
  • Examined syncope in heart transplant recipients and its association with partial seizures.

Main Results:

  • The cardiac inhibitory reflex can be potentiated, leading to neurally mediated syncope with minor provocation.
  • Evidence suggests left ventricular mechanoreceptors are not the sole trigger for syncope; central mechanisms may be involved.
  • Biochemical mediators like nitric oxide and serotonin show potential in understanding and treating neurogenic syncope.

Conclusions:

  • The cardiac inhibitory reflex serves as a crucial "safety valve" in cardiovascular regulation.
  • Syncope can arise from various triggers, including central mechanisms and potentiation of reflexes.
  • Further research into biochemical mediators is promising for advancing cardiovascular physiology and syncope therapy.