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Fainting Part I of II

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Fainting (syncope), a sudden loss of consciousness, most often occurs when blood pressure is too low (hypotension) so the heart doesn’t pump enough oxygen to the brain.   Typically, a fainting spell will last only a few seconds or minutes, before the individual regains consciousness.   Fainting is quite common and usually a single spell isn’t serious.  It may be explained by many factors such as grief, stress, dehydration, overheating, illness or exhaustion.  Profound fluid loss from diarrhea or vomiting or blood loss may also cause syncope.


Some causes of syncope are life threatening.   The most dangerous causes of syncope are caused by electrical disorders or heart damage that alter the ability of the heart to effectively pump blood.   In some cases, the only warning sign of an abnormal heart rhythm (ie. an arrhythmia) that could cause sudden cardiac arrest and death is fainting.

syncope image

Types of Syncope

  • Cardiovascular syncope – This is the most dangerous type of fainting.   It is caused by structural damage to the heart or an abnormal heart rhythm (arrhythmia).


  • Non-cardiovascular syncope – There are numerous causes of syncope that are not heart related.   These are usually related to problems with the autonomic nervous system (ANS).   The ANS controls functions such as blood pressure and heart rate.  Non-cardiovascular syncope may even occur in young, otherwise healthy people with normal heart function.


Individuals with an underlying arrhythmia or heart disease are at a higher risk for cardiovascular syncope, although this may be the initial symptom that suggests such a problem.

Risk Factors for Cardiovasular Syncope

Cardiovascular syncope risk increases with age.  People at greatest risk have any of the following conditions:


  • Chest pain (angina)
  • Ventricular dysfunction
  • An abnormal ECG (an electrocardiogram)
  • Coronary artery disease (clogged heart arteries)
  • Prior heart attack
  • Cardiomyopathy (heart muscle structural problems)
  • Recurrent episodes of fainting that occur suddenly and without warning.


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