Neurally mediated syncope is a heterogenous group of autonomic disorders resulting in orthostatic intolerance. It peaks in toddlers and adolescents.
There are two main groups – reflex and postural orthostatic tachycardia syndrome (or autonomic failure). In this post, we will discuss reflex syncope.
This post is part of our Syncope Sunday series – you can read Post 1 here.
Reflex syncope is a sudden failure of the autonomic nervous system to maintain vascular tone during orthostatic stress.
There is hypotension and bradycardia; along with cerebral hypoperfusion and loss of consciousness. An individual may have an event characterised by a primary vasodepressor, cardioinhibitory, or a mixed response.
In reflex syncope there is a clear provoking factor.
This is a benign reflex event.
There is depression of sympathetic vasomotor tone (‘vaso’) and associated parasympathetic mediated bradycardia (‘vagal’).
In vasovagal syncope there is clear provocation – tiredness, hunger, heat, dehydration
Often there is a prodromal sensation with short-lasting loss of consciousness and quick complete recovery.
There are non-epileptic paroxysmal events in infants and pre-school aged children provoked by pain or surprise.
8/1000 of pre-schoolers are affected.
Sudden vagal excitation following the trigger leads to a short period of asystole.
A better term to use is reflex asystolic syncope. This describes the event exactly and removes the confusion by using the word seizure – this is not a seizure
The classic presentation of reflex asystolic syncope is:
- Sudden and distressing stimulus such as injury or shock – child is described as deathly pale and lifeless.
- A period of asystole that typically lasts 5 – 30 seconds.
- Can have a brief convulsive phase.
- The child comes around confused and distressed.
The convulsive phase may be dystonic posturing with asymmetrical or symmetrical jerking and occasionally incontinence which can increase diagnostic confusion for the physician. There may even be a short post-ictal phase.
This diagnosis falls in the hinterland between neurology and cardiology. It is generally managed by a general paediatrician.
The history is vital in diagnosing this. Clues include: provocation, deathly white, then collapse. Ask the family if this happened before – note that recurrent attacks may have no provocation but a previous episode will help give clues.