Vasovagal syncope - autonomic mechanism (parasympathetic surge, sympathetic withdrawal)
Core concept
- Reflex (neurally-mediated) syncope - transient global cerebral hypoperfusion from a reflex, not from structural or arrhythmic disease
- Two efferent limbs, and they are not the same limb
- Cardioinhibitory - parasympathetic (vagal) surge -> bradycardia, asystole
- Vasodepressor - sympathetic withdrawal -> loss of arteriolar tone -> vasodilatation, hypotension
- Mixed = both (commonest)
- Classic orthostatic trigger
- Standing -> ~500-800 mL pools below diaphragm
- dec venous return -> dec ventricular filling
- Compensatory inc sympathetic drive -> vigorous contraction of an underfilled LV
- Activation of inferoposterior LV C-fibre mechanoreceptors -> Bezold-Jarisch reflex
- -> paradoxical vagal surge + sympathetic withdrawal -> bradycardia + vasodilatation
- Emotional and situational triggers act centrally (limbic/insular) - the ventricular mechanoreceptor limb is not obligatory
3 more sections, plus exam facts
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