Vasovagal Syncope, Vasovagal Attack

What is Vasovagal syncope?

Vasovagal syncope, the most common cause of fainting, is due to a transient inadequate blood flow to the brain. Healthy individuals can experience episodes of fainting when faced with unexpected emotional or physical pain, an unpleasant sight, sound, or smell, prolonged standing, even overheating. Fainting can also be caused by what is called orthostatic or postural hypotension in which the body fails to compensate adequately when an individual gets up from lying down, particularly when the individual has been bedridden.

In vasovagal syncope, the vagus nerve response is inappropriate. The vagus nerve innervates regions in the thoracic and abdominal cavities. When faced with emotional pain, for example, the higher brain centers act, via the vagus nerve, to inappropriately decrease sympathetic nervous output to the peripheral vasculature. This causes blood vessels all over the body to dilate and, as a result of gravity, blood pools in the lower extremities and is not returned to the heart for oxygenation and transport to the brain. The condition rapidly corrects itself when an individual faints or lies down because the blood is returned to the heart for oxygenation, and sufficient blood flow to the brain resumes.

How is it diagnosed?

History: If an individual is observed at the time of a fainting episode, he or she may complain of nausea, profuse sweating, and an upset stomach. If the individual is observed following the event, the history should elicit information regarding the person's activity, emotional state, physical condition prior to the episode, any accompanying symptoms, history of any underlying disease, time and frequency of previous fainting spells, and if there was any associated injury.

Physical exam: The findings upon physical examination will depend on when it is conducted in relation to the fainting episode. If immediately afterward, the physical examination may reveal decreased blood pressure, decreased heart rate, profuse sweating, and pale skin. Unfortunately, however, most physical examinations do not occur until long after the event.

Tests: Normally, no tests are required. However, should episodes occur frequently, the physician should test for orthostatic hypotension by comparing the individual's blood pressure when lying flat and when sitting and/or standing.

The physician may wish to administer an electrocardiogram (EKG) test to look for cardiovascular problems, particularly the presence of an abnormal heart rhythm (arrhythmia). An additional test that is sometimes conducted is the tilt test, which is used to artificially produce a vasovagal syncope episode. There are two types of tilt testing available: passive and with the use of intravenously administered adrenergic agent.

How is it treated?

Generally, treatment is symptomatic. Since many individuals know that they are about to experience an episode, they are generally able to get into a position that either alleviates the response or at least where a potentially dangerous fall is less likely.

Following an episode, individuals should remain lying on the ground or floor until all symptoms have subsided. His or her legs should be elevated. If the person is sitting, his or her head should be placed between the knees. Tight clothing should be loosened and head turned.

Individuals should be advised to avoid (if possible) those situations that caused the syncope. Individuals with recurrent vasovagal syncope may be treated with beta-adrenergic agents. Rarely, cardiac pacing may be used.

Additional Information


Medication usually is not necessary for fainting. Medication may be necessary for underlying disorders.

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What might complicate it?

Since most individuals have some indication that they are going to faint prior to fainting, they are able to take precautions and prevent any associated injuries. However, elderly persons suffering a vasovagal syncope episode frequently sustain fractures. In addition, should individuals rise too soon following an episode, they may experience another episode.

Predicted outcome

Typically, individuals quickly regain consciousness.


Differential diagnoses include hysterical fainting, hypoglycemia, anxiety attack, and seizure.

Appropriate specialists

Internist, family practitioner, cardiologist, and neurologist.

Notify your physician if

  • An unconscious person has no pulse and is not breathing. Get emergency help. Give CPR. This is an emergency!
  • Someone faints and does not regain consciousness quickly.