Neurally mediated syncope: pathogenesis, diagnosis, and treatment

Area of Science:

• Cardiology
• Neuroscience
• Autonomic Nervous System

Background:

• Neurally mediated syncope is the most common cause of fainting in individuals without structural heart disease.
• It is triggered by a reflex involving afferent signals from mechanoreceptors, leading to parasympathetic overactivity.
• This results in bradycardia and sympathoinhibition, causing hypotension and vasodilation.

Purpose of the Study:

• To investigate the underlying pathophysiology of neurally mediated syncope.
• To explore the role of nitric oxide in the vasodilation observed during these episodes.
• To highlight the diagnostic utility of the upright tilt test.

Main Methods:

• Analysis of autonomic nervous system activity and neurochemical changes during syncope.
• Measurement of plasma concentrations of various hormones and vasoactive substances.
• Utilizing the upright tilt test for diagnosis and characterization.

Main Results:

• Sympathetic nerve activity and norepinephrine levels decrease inappropriately during episodes.
• Plasma levels of epinephrine, angiotensin II, vasopressin, and endothelin-1 increase appropriately.
• Evidence suggests increased nitric oxide synthesis contributes to arterial vasodilation and hypotension.

Conclusions:

• Neurally mediated syncope involves complex autonomic dysregulation.
• Nitric oxide-mediated vasodilation may be a key factor in the hypotension experienced.
• Understanding these mechanisms can pave the way for targeted therapeutic interventions.