The commonest cause of syncope is the neuro-cardiogenic or vasovagal syncope .
The following is the possible neural circuit of this syncope . In fact . it is a “Neuro -vascular circuit”
The afferent* (Two components are present -Both trigger sympathetic signal )
- Sympathetic (Prodrome /Anxiety /fear )
- Cardiac mechano /stetch receptors located mainly in LV .(Can be in Aorta/Carotid )
* In some cases sensors and afferent can be same entities.
The centre – Medullary Nucleus ambiguous /Tractus solitarius
The efferent -Strong parasympathetic overshoot and sympathetic withdrawal
Parasympathetic excess lead to bradycardia primarily, while sympathetic withdrawal lead to
As patient recumbent posture ; LV gets filled and LV mechanoreceptors are passified .
The exact pathophysiologic basis of this syncope still not elucidated.But one thing is clear , the syncope is due to sympatho- parasympatho signal mismatch( and sort of a rivalry reaction) !In this neural game , heart’s behavior is all the more funny , it initiates the reflex while the brain stem “Boomerangs” it back to heart and vascular system , with a vagal onslaught .
To call this simply as vasovagal is not proper , that is why neuro -cardiogenic syncope was used.
Ideal terminology would be to call it as cardio -neuro -cardiac syncope as the cardiac component form the afferent limb as well as the efferent (target organ )