Syncope toolkit

Syncope is very common and will affect 42% of people during their lifetime

Other types of blackout and syncope

In this section: 

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Syncope of unknown origin

Reported diagnostic rates can vary considerably depending on a number of factors including the setting in which patients were reviewed, the special interests of the clinicians, whether syncope guidelines are followed, and whether patient who fainted sought medical advice.

In a 2002 study reviewing patients in the original Framingham Heart and Offspring studies, a cause for syncope was not identified in 36.6% of patients, although this study included patients who reported fainting but did not seek medical help and were therefore categorised as ‘undiagnosed’.

In another study where European Society of Cardiology Syncope Guidelines were very carefully followed, 2% of patients remained undiagnosed after investigations. In recent analysis of 10 Syncope Units, a no-diagnosis-rate of the order of 10% was reported.

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Epilepsy and syncope

In comparison with syncope, epilepsy is much rarer, affecting a little under 1% of the UK population.

  • Ictal or epileptic asystole – bradycardia and asystole are rare occurrences during partial complex seizures
  • Syncopal epileptic seizures – brain hypoxia as a consequence of syncope can trigger epileptic seizures.

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‘Psychogenic’ pseudo-syncope (PPS)

There are two main types of conversion disorder associated with blackouts:

  • Non-epileptic Seizures (NES) – where limb movements are marked. These can be diagnosed using video or EEG monitoring.
  • ‘Psychogenic’ Pseudosyncope (PPS) – episodes which resemble syncope and limb movements are minimal. PPS is collapse which is associated with maintained blood pressure and slightly increased heart rate without the impairment of cerebral circulation that occurs in vasovagal syncope (VVS).


There is controversy around the terminology used to describe these episodes. Collapses that look like other conditions but are not explained by the same physiological mechanisms have tended to fall under as many labels as there are specialties encountering them. Hence historically within neurology the term ‘non-epileptic seizures’ is favoured, within cardiology ‘psychogenic pseudosyncope’, and within psychiatry ‘conversion disorders’.

The authors favour the terms non-haemodynamic and non-epileptic collapse; we hope this will be considered and recommended in future working groups but recognise that this is not yet accepted practise. Having taken advice on this with our steering committee and especially patient representatives, it was agreed that an accepted label that enables referral to the appropriate treating specialty is the priority meantime, and hence ‘psychogenic’ pseudosyncope (PPS) is used within this document.


PPS is not just a diagnosis of exclusion, but in fact such episodes can be diagnosed by appropriate history taking, with very frequent episodes being the main feature.

Diagnosis can be made when episodes are monitored by simultaneous video, beat-to-beat blood pressure and ECG recordings on a tilt-table, without hypotension/bradycardia and confirmed by the patient as being a typical attack. Importantly, there is increasing evidence that both VVS and PPS can commonly both occur in the same patient. Thus, the presence of one does not exclude the other, but different treatment approaches may be required for each.

It is important to be clear that these collapses are outside of the patient’s conscious control and are therefore not malingering or attention seeking behaviours.


Timely delivered psychological therapies to provide reassurance and improve functionality are the primary treatment modalities.

Psychotropic medications may need to be considered in patients with comorbid psychiatric disorders. There is limited evidence for therapy efficacy in PPS, however studies in related conversion disorder populations supports use of psychotherapy. Appropriate interventions include improving detection of bodily sensations and stress markers, and especially in PPS the treatment of underlying anxiety, stress or trauma. Working with a practitioner experienced in this area, motivated patients, with sufficient cognitive capacity for self-insight, can be optimistic of becoming PPS episode free.

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Rare causes of blackouts

Vertebro-basilar TIA – rarely causes syncope and always associated with neurological signs including nystagmus, dysarthria, limb weakness, ataxia, vertigo and diplopia.

Subclavian Steal – this is a rare phenomenon which occurs if blood flow is reversed in the vertebral artery toward the ipsilateral distal subclavian artery by the demand for flow to the exercising arm of the same side. The cause is a narrowing or occlusion of the proximal subclavian artery. The phenomenon is associated with neurological signs.

G-induced loss of consciousness (G-LOC) – this is due to the centrifugal effect of rapid acceleration. Although rare, it is common in aircrew, and was experienced by 15% of RAF crew in 2015, mostly during training. G-LOC has been associated with air crash fatalities.

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Non-haemodynamic collapse / Psychogenic Pseudosyncope (PPS)


A 19 year old boy attends with his mother with a history of multiple syncopal episodes in the previous 24 months.  They report frequent and witnessed episodes of syncope with several episodes occurring in a single day. There are no associated triggers or warnings of the attacks. He has no significant past medical history but also reports symptoms of body aches, fatigue and generalised weakness. You note that he has already undergone extensive investigations under a paediatrician 2 years ago including ECG, echocardiogram, Holter monitoring and EEG which were all normal. He and his family were frustrated that no cause was previously found for his symptoms and did not attend follow up after his tests.


Physical examination is normal and postural blood pressures show no significant drop.

What would you do next?

There are no further investigations in primary care that would provide additional useful information. He requires further assessment from a dedicated syncope service.


The syncope service organise tilt table testing and after 6 minutes of tilt he develops a sudden loss of consciousness with no response to verbal stimuli. Monitoring demonstrates no significant changes in heart rate, blood pressure, and no ECG changes. He is diagnosed with psychogenic pseudo-syncope (PPS) and was referred to a psychologist after full explanation to him and his family of what had happened.

Learning Points

  • Tilt table testing can induce psychogenic syncope i.e apparent loss of consciousness without a change in recorded blood pressure and EEG. A slight tachycardia if 10-20 bpm is to be expected
  • Diagnosis is based on the history and can be confirmed when a typical event is recorded during a tilt-table test with simultaneous BP, HR, EEG and video recordings of the patient
  • Some factors can help distinguish PPS from vasovagal syncope
    • Eyes are usually closed in psychogenic syncope but open in VVS
    • Recurring multiple collapses in a single day suggest PPS.

Differentiating vasovagal syncope epilepsy and psychogenic pseudosyncope

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