A number of conditions can cause fainting, including heart rhythm abnormalities, seizures, low blood sugar (hypoglycemia), and anemia. More common than these, however, is a relatively benign condition called vasovagal syncope, also known as the “common faint”. Syncope [sing-kuh-pee] is themedical term for “blacking out” and vasovagal refers to the abnormal stimulation
of blood vessels by the vagus nerve.
What causes vasovagal syncope? One of the normal functions of the vagus nerve is to lower the heart rate. If excessive activation of the vagus nerve occurs, however, pooling of blood in the legs along with a sudden drop in blood pressure and heart rate can occur. Some of the reasons for this excessive activation include:
- Emotional stress
- Pain, such as having blood drawn
- Environmental factors, such as being in a hot, crowded setting
- Illness, especially when associated with dehydration
- Straining, as when having a bowel movement
- Visual stimuli, such as the sight of blood
The drop in blood pressure and heart rate temporarily causes decreased blood flow to the brain with subsequent loss of consciousness. Fortunately, the body is able to correct this temporary abnormality of the circulatory system and return blood pressure and blood flow to the brain in a matter of seconds. While the faint itself is usually not a sign of a serious disease, the consequences of fainting can be serious. Serious injuries can occur with falling and injuries to others could occur if fainting occurs while driving.
How is vasovagal syncope diagnosed? Since not all losses of consciousness are due to overstimulation of the vagus nerve, some amount of evaluation is usually required in order to distinguish between a benign type of syncope and a more serious cause. In many cases, the doctor can make the determination by asking questions about what occurred surrounding the event. Commonly, a person experiencing vasovagal syncope will remember experiencing certain symptoms prior to losing consciousness, such as being extremely hot, sweating, having ringing in the ears, feeling weak, and experiencing visual disturbances such as tunnel vision. When the specific cause is uncertain, special tests may be required, particularly if a serious cause, such as a heart rhythm disturbances or seizures are suspected. These tests could include:
- Blood tests, including a complete blood count to check for anemia and glucose
tolerance test looking for evidence of hypoglycemia. - Electroencephalogram (EEG), to look for abnormal brain wave activity if seizures
are suspected. - Holter monitor, which monitors the heart rhythm over a number of hours to look
for disturbances. - Exercise stress test and/or echocardiogram to look for heart conditions that could
be responsible.Tilt-table testing, perhaps the most sensitive test to diagnose vasovagal syncope.
Special mention should be made of the tilt-table test in diagnosing this condition. During this test, subjects lie down on a table that can be moved from a horizontal to a vertical position. The heart rate and blood pressure are monitored while the bed is moved to a vertical position. Sometimes this is enough to produce the blood pooling and blood pressure drop that precipitates fainting. If not, a medication (isoproterenol) may be given through the vein that produces the abnormal reflex that causes vasovagal syncope.
Is there a treatment for vasovagal syncope? The best treatment is usually avoidance of the triggers that cause the episodes. For recurrent or severe spells, certain medications may be used including blood pressure drugs (e.g. metoprolol), antidepressants of the SSRI class (Paxil, Prozac, others), and blood vessel constrictors that are used to treat low blood pressure. Other “lifestyle” therapies include foot exercises, compression stockings, increasing dietary salt, and avoiding prolonged standing.
What should you do if you witness someone fainting? The appropriate steps to take for the fainting victim are:
- Check the person’s airway and breathing. If necessary, call 911 and begin rescue breathing.
- Loosen tight clothing around the neck.
- Raise the person’s feet above the level of the heart (about 12 inches).
- If the person has vomited, turn onto his or her side to prevent choking.
- Keep the person lying down for at least 10 – 15 minutes, preferably in a cool and quiet space. If this is not possible, sit the person forward with the head between the knees.
What is the prognosis for someone with vasovagal syncope? Brief periods of unconsciousness are generally harmless and do not necessarily indicate the presence of a serious medical problem. The main danger of fainting or vasovagal syncope is the risk of injury by falling while unconscious.