Syncope (fainting)

Syncope is a sudden, temporary loss of consciousness, also known as fainting or ‘passing out’, which is caused by a reduction in the blood flow to the brain.

Causes of syncope

Syncope can be due to a number of different causes. The most common cause is vasovagal syncope (also known as neurally mediated syncope), where in response to a certain stimulus there is a simultaneous drop in heart rate and dilatation (widening) of blood vessels. This causes pooling of blood in the legs, leading to a lack of blood flow to the brain.

There are a number of common triggers for vasovagal syncope, including prolonged standing (especially in a hot environment), severe pain, emotional distress, the sight or smell of something unpleasant, severe coughing, urinating or opening the bowels.

Other less common causes of syncope include:

  • arrhythmias (abnormal heart rhythms);
  • orthostatic hypotension (a drop in blood pressure when standing), which may in turn be due to a number of causes;
  • structural heart disease; and
  • cerebrovascular diseases (conditions caused by problems with the blood vessels in the brain).

Conditions that are sometimes misdiagnosed as syncope include epilepsy, intoxication and certain psychiatric disorders.

How is syncope evaluated?

Your doctor will take a detailed history from you and perform a physical examination to try to determine the cause of the syncope.

An electrocardiogram (ECG), which records the electrical activity of your heart, will usually be performed.

If the cause of the fainting is still not apparent after the initial assessment, further tests may be performed including blood tests, an echocardiogram (ultrasound of the heart) and prolonged ECG monitoring. Sometimes additional specialised testing is required.

Treatment for syncope

Treatment for syncope depends on the underlying cause.

People with vasovagal syncope should watch for warning signs of fainting — such as light-headedness, sweating, nausea, ringing in the ears — and try to lie down (preferably with legs elevated), or if this is not possible, to sit down at the earliest warning signs.

Other measures that can help to temporarily increase blood pressure and avoid collapse include squeezing the calf muscles or buttocks together.

They should also avoid becoming dehydrated and generally try to avoid situations likely to trigger fainting. Occasionally, other treatments such as medication may be required for vasovagal syncope.

If the syncope is due to another condition — such as underlying heart disease — specific treatment for that condition will be arranged. Your doctor will advise you as to the appropriate treatment in your case.

Last Reviewed: 28 November 2012
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References

1. Syncope (revised June 2008). In: eTG complete. Melbourne: Therapeutic Guidelines Limited; 2012 Nov. http://online.tg.org.au/complete/ (accessed Nov 2012).
2. National Institute of Neurological Disorders and Stroke (NINDS). NINDS syncope information page (updated 4 October 2011). http://www.ninds.nih.gov/disorders/syncope/syncope.htm (accessed Dec 2012).
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