Understanding Vasovagal Syncope

Vasovagal syncope is fainting caused by a complex nerve and blood vessel reaction in the body. It's the result of an abnormal reflex in the body and is often called reflex syncope. It’s the most common cause of fainting. Unlike other causes of fainting, it’s not a sign of a problem with the heart or brain.

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How vasovagal syncope happens

Many nerves connect with your heart and blood vessels. These nerves help control the speed and force of your heartbeat. They also regulate blood pressure. They control whether your blood vessels should be more open or more closed.

Usually these nerves work together so you always get enough blood to your brain. In certain cases, these nerves may give a wrong signal or be slow to respond to input received from the body. This may cause your blood vessels to open wide or cause them not to get more narrow when they need to. At the same time, your heartbeat may slow down. Blood can start to pool in your legs, and not enough of it may reach the brain. If that happens, you may briefly lose consciousness. When you lie down or fall down, blood flow to the brain resumes.

What causes vasovagal syncope?

Many triggers can cause vasovagal syncope, such as:

  • Standing for long periods

  • Too much heat

  • Intense emotion, such as fear

  • Intense pain

  • The sight of blood or a needle

  • Exercising for a long time

  • Dehydration

Older adults may have additional triggers, such as:

  • Urinating

  • Swallowing

  • Coughing

  • Having a bowel movement

Symptoms of vasovagal syncope

Fainting is the main symptom of vasovagal syncope. You may have symptoms before fainting, such as:

  • Nausea

  • Warm, flushed feeling

  • Face that turns pale

  • Sweaty palms

  • Feeling dizzy

  • Blurred vision

If you lie down and elevate your legs at the first sign of these symptoms, you will often be able to prevent fainting. Not everyone notices symptoms before fainting, however.

When a person does faint, lying down restores blood flow to the brain. Consciousness should return fairly quickly. You might not feel normal for a little while after you faint. You might feel depressed or fatigued for a short time. You may even feel nauseous afterward and vomit.

Some people have only one or two episodes of vasovagal syncope in their life. For others, it happens more often and with no warning.

Diagnosing vasovagal syncope

Your healthcare provider will ask about your health history and your symptoms. They will give you a physical exam. Your blood pressure may be measured while lying down, seated, and standing. You may also have an electrocardiogram (ECG). This is a simple test that looks at the heart’s rhythm.

You may be checked for other possible causes of fainting. You may have other tests, such as:

  • Continuous portable ECG monitoring, to look at heart rhythms over time, such as with a Holter or event monitor

  • Echocardiogram, to look at the blood flow in the heart and the heart’s motion

  • Exercise stress testing, to see how your heart does during exercise

  • Blood tests to check for signs of disease

If these tests are normal, you may have a tilt table test. For this test, you lie down on a platform with straps around you to keep you from sustaining an injury. Your heart rate and blood pressure are measured while you are lying down. The platform is then tilted upright. Your heart rate and blood pressure are measured again. If you have vasovagal syncope, you may faint during the upward tilt. Sometimes medicines that increase heart rate and the force of heart contractions or decrease blood pressure are used to try and provoke a syncopal episode.

There are many causes of syncope. Some causes are not dangerous. In older persons, unexplained syncope can be a sign of a serious infection or a heart attack. Call 911 or seek medical attention right away to be evaluated, especially if there has been a fall and injury with the syncope. You should not drive yourself to the hospital or emergency department after a syncopal episode for the safety of yourself and other drivers and passengers. Have someone drive you. Your provider may restrict your driving until the cause of the syncope is better understood and to make sure the syncope does not become chronic, or if it is unpredictable.

© 2000-2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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