Elayne Forbes. Other Causes, Don't Forget the Bubbles, 2015. Available at:
We’ve already consider reflex causes and cardiac causes of syncope. Here’s a few others that don’t fit neatly into either category…
This is often a continuity from early childhood reflex asystolic syncope (although not necessarily) which extends into adulthood.
The mean age of onset is 7 years.
The sight of blood leads to a reflex transient tachycardia, bradycardia and eventual brief asystolic period.
There is a strong family history for both reflex asystolic syncope and blood injury phobia.
There is also a crossover here with reflex asystolic syncope, and a similar presentation.
Sudden increased intrathoracic pressure impedes venous return to the heart and thus decreases the cardiac output (essentially a valsalva manoeuvre).
Typical history : child crying, silence, blue, syncope. The history is vital.
Is syncope easily confused with seizures?
This is a common misdiagnosis.
Any syncope can cause limb jerks and often present to ED as a ‘seizure’.
The wrong diagnosis has consequences:
- Unnecessary investigations and specialist referral
- Medication and restrictions to life
- Underlying risk of arrhythmic death missed
Postural orthostatic tachycardia syndrome (POTS) is a disorder of the autonomic nervous system. It is defined as sustained increase in HR > 40bpm in the 12–19 year age group, within 10 mins of standing associated with symptoms of orthostatic intolerance.
- No postural BP drop
It is poorly understood.
The pathophysiology is that the patient goes from lying to sitting, and >300mls blood is redistributed from the thoracic cavity to limbs in a few secs. There is compensatory baroreceptor reflex to maintain cerebral perfusion. This causes increased HR, contractile force and peripheral vasoconstriction.
Dysautonomia is failure of vasoconstriction -> increased compensation of the other components of the triad. Inadequate compensation -> pounding palpations syncope.
It often presents following a viral illness, immunisation, stressors such as sepsis,surgery, growth spurt. It is exacerbated by extremes of temp, exercise, meals and menstruation. There are typical symptoms but long list of nonspecific ‘others’.
Typical symptoms: palpitations with fatigue presyncopal sensation, difficulty to perform exercise,(note symptoms not during exercise necessarily but preventing from participating), tremulousness, weakness, loss of concentration often described as brain fog and syncope.
Others: chest wall pain, SoB, anorexia and GI upset, – IBS misdiagnosed , headaches – misdiagnosed migraines, occipital shoulder coathanger headaches, pain, sleep difficulty, anxiety and panic attacks.
It can be secondary to other conditions – most common being joint hypermobility syndrome/Ehlers Danlos hypermobility.
- ECG and echo – differential of tachycardia
- 24 hour holter
- Baseline bloods (including ferritin, which is often deficient)
- TFT and adrenal axis
- 24 hour urinary catecholamines – pheochromocytoma – symptoms more common when lying down
- 24 hour urinary sodium – evidence of sufficient fluid and sodium intake and thus likely normal plasma volume
- Head upright tilt test – baseline BP and HR when supine, inclined to 70 degree head up angle with continuous BP and HR measurements
- Active stand test – requires skeletal muscle pump and mimics real life
- Autonomic function test
Both HUTT and the active stand test are sensitive for a diagnosis of of POTS with a 30bpm threshold for orthostatic tachycardia AST > specific (79% : 23%)
- Withdrawal of medications (unlikely in children)
- Treat associated conditions
- 2 -3 litres water/day
- Adequate salt intake
- Compression stockings; pumping calves before rising and rising slowly; exercise to build up skeletal muscle pump
- Bed head elevation
- Counter-manoeuvres before rising
- Encourage exercise
- Pharmacological treatment – beta blockers (alpha and beta blocking effects), clonidine (alpha 2 agonist inhibits SNS – low BP), fludrocortisone (increased sodium retention to expand plasma volume), midodrine (alpha 1 agonist – vasoconstrictor), octreotide (refractory – vasoconstrictor)