Mayo Clinic Health Library

Vasovagal syncope

Updated: 02-19-2013

Definition

Vasovagal syncope (vay-zoh-VAY-gul SING-kuh-pee) is one of the most common causes of fainting. Vasovagal syncope occurs when your body overreacts to certain triggers, such as the sight of blood or extreme emotional distress.

The vasovagal syncope trigger causes a sudden drop in your heart rate and blood pressure. That leads to reduced blood flow to your brain, which results in a brief loss of consciousness.

Vasovagal syncope is usually harmless and requires no treatment. But it's possible you may injure yourself during a vasovagal syncope episode. Also, your doctor may recommend tests to rule out more-serious causes of fainting, such as heart disorders.

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Symptoms

Before you faint due to vasovagal syncope, you may experience some of the following:

  • Skin paleness
  • Lightheadedness
  • Tunnel vision — your field of vision is constricted so that you see only what's in front of you
  • Nausea
  • Feeling of warmth
  • A cold, clammy sweat
  • Yawning
  • Blurred vision

During a vasovagal syncope episode, bystanders may notice:

  • Jerky, abnormal movements
  • A slow, weak pulse
  • Dilated pupils

Recovery after a vasovagal episode begins soon after fainting, generally in less than a minute. However, if you stand up too soon after fainting — within 15 to 30 minutes or so — you're at risk of fainting again.

When to see a doctor
Because fainting can be a sign of a more serious condition, such as a heart or brain disorder, you may want to consult your doctor after a fainting spell, especially if you never had one before.

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Causes

Vasovagal syncope occurs when the part of your nervous system that regulates heart rate and blood pressure malfunctions in response to a trigger, such as the sight of blood. Your heart rate slows, and the blood vessels in your legs widen. This allows blood to pool in your legs, which lowers your blood pressure. This drop in blood pressure and slowed heart rate quickly diminish blood flow to your brain, and you faint.

Common triggers for vasovagal syncope include:

  • Standing for long periods of time
  • Heat exposure
  • The sight of blood
  • Having blood drawn
  • Fear of bodily injury
  • Straining, such as to have a bowel movement
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Preparing for your appointment

It's a good idea to prepare for your appointment to make the most of your time with your doctor.

What you can do

  • Write down a detailed description of your symptoms, including any triggers that you think may have caused you to faint.
  • Make a list of any medications, vitamins and supplements.
  • Write down questions you want to ask your doctor, including what types of tests you might need and what treatments might be helpful.

What to expect from your doctor
Questions your doctor might ask you include:

  • What were you doing just before you fainted?
  • What signs and symptoms, if any, did you experience before you fainted?
  • Have you ever fainted before? If yes, what were you doing before you fainted then?
  • Have you recently started taking a new medication?
  • Have you ever had a head injury?
  • Has anyone in your family died suddenly of heart problems?

During the physical exam, your doctor will listen to your heart and take your blood pressure. He or she may also massage the main arteries in your neck to see if that causes you to feel faint.

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Tests and diagnosis

The diagnosis of vasovagal syncope often involves ruling out other possible causes of your fainting — particularly heart-related problems. These tests may include:

  • Electrocardiogram. This test records the electrical signals your heart produces. It can detect irregular heart rhythms and other cardiac problems that can cause fainting. In some cases, you may need to wear a portable monitor for at least a day or as long as a month.
  • Echocardiogram. This test uses ultrasound imaging to view the heart and look for conditions, such as valve problems, that can cause fainting.
  • Exercise stress test. This test studies heart rhythms during exercise. It's usually conducted while you walk or jog on a treadmill.
  • Blood tests. Your doctor may look for conditions, such as anemia, that can cause or contribute to fainting spells.

Tilt table test
If there appear to be no heart problems causing your fainting, your doctor may suggest you undergo a tilt table test. For a tilt table test:

  • You lie flat on your back on a table.
  • The table changes position, tilting you upward at various angles.
  • A technician monitors your heart rhythms and blood pressure to see if the postural changes affect them.
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Treatments and drugs

In most cases of vasovagal syncope, treatment is unnecessary. Your doctor may help you identify your fainting triggers and discuss ways you might avoid them. However, if you experience vasovagal syncope often enough to interfere with your quality of life, your doctor may suggest trying one or more of the following remedies.

Medications
A drug called midodrine (Orvaten) that's normally used to treat low blood pressure may be helpful in preventing vasovagal syncope.

Therapies
Your doctor may recommend specific techniques to decrease the pooling of blood in your legs. These may include foot exercises, wearing compression stockings or tensing your leg muscles when standing, and increasing salt in your diet if you don't usually have high blood pressure. Avoid prolonged standing — especially in hot, crowded places — and drink plenty of fluids.

Surgery
Rarely, the insertion of an electrical pacemaker, which helps regulate the heartbeat, may be an option for some people with vasovagal syncope who haven't been helped by other treatments.

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Prevention

Even with treatment, not all vasovagal syncope episodes can be avoided. If you feel like you might faint, lie down and lift your legs. This allows gravity to keep blood flowing to your brain. If you can't lie down, sit down and put your head between your knees until you feel better.

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