What Is Vasovagal Syncope: Overview and More

The Most Common Cause of Fainting

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Syncope—also known as fainting—is the medical term for a temporary loss of consciousness.

Syncope can cause injuries, so it is important to try to prevent it from recurring. And it can sometimes be a sign of a serious underlying medical problem that needs medical attention. Several medical conditions can lead to syncope, and the most common type of syncope is vasovagal syncope.

vasovagal syncope
Verywell / Brooke Pelczynski

Overview

Vasovagal syncope (also called neurocardiogenic syncope) is a temporary loss of consciousness caused by a neurological vasovagal reflex that produces either sudden dilation of the blood vessels in the legs, or a very slow heart rate (bradycardia), or both.

Vasovagal syncope accounts for more than half of all episodes of syncope. While it's sometimes referred to as a "simple fainting spell," the mechanism of vasovagal syncope actually is not all that simple.

Vasovagal Syncope Symptoms

The loss of consciousness with vasovagal syncope can be quite sudden, or it can be preceded by a few seconds or a few minutes of warning symptoms.

  • The warning symptoms are sometimes referred to as a prodrome of syncope.
  • Those that occur after you are revived are called postdrome.

Prodromal Symptoms

Prodromal symptoms of syncope can include:

  • Lightheadedness
  • Ringing or buzzing in the ears
  • Visual disturbances, such as shimmering vision or tunnel vision
  • Sudden sweating
  • Sudden nausea

Prodromal symptoms are followed by a sensation of "graying out," then finally by loss of consciousness. The time between the onset of prodromal symptoms and actually passing out can range from a few minutes to just a second or two.

If you feel like you’re going to faint, you may be able to stop the episode by lying down with your legs elevated or sitting in a chair with your head between your knees. Wait until you feel better before trying to stand up.

Syncope Characteristics

A vasovagal syncopal episode has several characteristic features:

  • They almost always occur while standing or sitting up because the blood in the body disproportionately flows down to the legs and the blood pressure drops. It virtually never happens while lying down.
  • People who have vasovagal syncope usually regain consciousness a few seconds after falling or being helped to the ground. This is because gravity no longer causes blood to pool in your legs when you're on the ground, and blood pressure improves almost immediately in the lying down position.
  • If someone tries to hold you up during a vasovagal episode, your standing position can prolong your episode of unconsciousness. This is a potentially dangerous situation because it prevents adequate blood from flowing to your head.

If you see somebody faint, lay that person on their back and elevate their legs above the level of their heart. Loosen any belt, collar, or constrictive clothing and call for professional medical help.

Postdromal Symptoms

After an episode of vasovagal syncope, many people will feel terrible for a few hours, and sometimes for days or longer. The postdrome period is characterized by extreme fatigue, nausea, dizziness, and loss of appetite. 

It is particularly important to note that, until these lingering symptoms disappear, people are particularly prone to fainting again—so they need to avoid driving, climbing ladders, or other dangerous activities and be alert for the warning signs of another syncopal episode. 

Recurrent Syncope

People who have had one or two episodes of vasovagal syncope often learn to recognize the warning signs. You can often prevent an episode by lying down and elevating your legs.

On the other hand, trying to "fight off" an impending episode of vasovagal syncope by forcing yourself to remain standing or sitting up and "willing yourself" not to faint almost never works out very well.

Older people with vasovagal syncope are more likely to have atypical syncope, without any identifiable trigger and without any warning symptoms.

In general, vasovagal syncope is not life-threatening, but injuries that result from falling may be dangerous. And if episodes are frequent, this condition can be quite disruptive to a normal life.

When to See a Healthcare Provider

You should contact your doctor if you experience your first ever episode of syncope. If you have already been diagnosed with vasovagal syncope, you should see your doctor if you are pregnant. have recurrent episodes, or experience blurred vision, chest pain, confusion, trouble talking, shortness of breath, or irregular heartbeat prior to fainting.

Causes

Vasovagal syncope occurs when something triggers the vasovagal reflex, causing the blood vessels to dilate (widen) suddenly. Dilation of the blood vessels causes a significant proportion of the blood volume to pool in the legs.

This pooling is often accompanied by a slowing heart rate. As a result, the blood pressure will suddenly drop. If the drop in blood pressure is enough to rob the brain of adequate oxygen, fainting occurs.

Common triggers of vasovagal syncope include:

  • Sudden, severe pain
  • Having your blood drawn
  • Being exposed to a traumatic sight or event
  • Extremely difficult urination or defecation
  • A severe coughing spell
  • Hyperventilation
  • Standing motionless for long periods of time
  • Overexerting yourself in hot weather
  • Excessive alcohol or substance use

If a fainting episode follows any of these events, vasovagal syncope is often the cause.

Risk Factors

The reflex that causes vasovagal syncope can affect anyone, so almost anyone can have a vasovagal episode if a sufficiently strong triggering event occurs. Indeed, it is likely that most people will have a fainting episode sometime during their lives.

Vasovagal syncope can occur at any age, and it is much more common in adolescents and young adults than in older people.

Some people are particularly prone to vasovagal episodes and may faint even with relatively mild triggering events. These people tend to have recurrent episodes of syncope, beginning in adolescence, and will often experience syncope following several different kinds of triggering events.

Rarely, some people have frequent vasovagal syncope that is so difficult to treat that they become virtually disabled by it. This can be associated with a form of dysautonomia (imbalance of the autonomic nervous system) that makes a person very prone to the vasovagal reflex that causes syncope. It's often accompanied by other symptoms of the dysautonomias, such as abdominal bloating or cramps, diarrhea, constipation, extreme fatigue, and various aches and pains.

Diagnosis

Vasovagal syncope is more likely to occur after a viral illness, after exercise, after a warm shower, or early in the morning—any time that a person is dehydrated.

Your healthcare provider will review your symptoms, medical history, family history, and sequence of events leading up to your fainting episode.

The physical examination of people with vasovagal syncope is usually completely normal. The exam is often helpful in identifying similar conditions, including orthostatic hypotension or postural orthostatic tachycardia syndrome (POTS).

Sometimes diagnostic testing is needed.

You might need to have a tilt table study to help distinguish vasovagal syncope from orthostatic hypotension.

Treatment

People who have a single, isolated episode of vasovagal syncope generally do not require any medical therapy at all. But if you have had recurrent episodes, you are likely to have even more episodes unless you are effectively treated.

As anyone with vasovagal syncope knows, these fainting episodes often come at the most inconvenient or impractical times, and can greatly disrupt your life. Fortunately, treatment is usually helpful. There are several types of therapy for vasovagal syncope: medication, exercise, and pacemakers. Finding the right combination of medical treatments often takes time.

Medications

Medications can help regulate blood pressure and heart rate.

Medications that have been shown to be of some help in the treatment of vasovagal syncope include:

  • Midodrine, a vasoconstricting drug that dilates blood vessels
  • Norpace (disopyramide), an antiarrhythmic drug 
  • Serotonin re-uptake inhibitors 
  • Theophylline, which is typically used to treat asthma

Exercise

Exercise may likely have a similar benefit to people with vasovagal syncope.

If you have recurrent syncope, be sure to meet with your healthcare provider before embarking on any fitness plan. Depending on the underlying cause, you may need to undergo stress testing and other exams to determine how much exercise you can safely tolerate.

Interestingly, some people have been able to stop an episode of vasovagal syncope by immediately engaging in muscle-tensing exercises. These exercises can reduce blood vessel dilation and increase the amount of blood being returned to the heart.

Examples include

  • Crossing your leg while tensing the legs, abdomen, and buttocks
  • Tensing your arms with clenched fists
  • Tensing your leg muscles
  • Squeezing a rubber ball

Pacemakers

Several years ago there was a lot of enthusiasm for using pacemakers to treat vasovagal syncope since vasovagal syncope is usually accompanied by a sudden drop in heart rate.

The enthusiasm for pacemaker therapy dropped off rapidly, however, after it was noted that many patients with vasovagal syncope who received pacemakers continued to pass out—they just did it without slow heart rates.

A pacemaker should only be considered if the syncope is severe or recurrent, conservative measures aren't working, and there is significant slowing of the heart as evidenced by a tilt-table test or ambulatory ECG monitoring.

Frequently Asked Questions

Is there anything I can do to prevent vasovagal syncope?

If you know you are prone to fainting, avoid potential triggers such as excessive heat, stressful and intensely emotional situations, dehydration, extreme pain, and prolonged exercise.

Can certain foods impact vasovagal syncope symptoms?

Eating a diet that is slightly higher in salt may help prevent syncope symptoms by keeping blood pressure up for some people. Check with your doctor before adding extra salt to your diet, because it can have other adverse health effects.

A Word From Verywell

Vasovagal syncope is a very common condition. Most people who have episodes of vasovagal syncope lead entirely normal lives.

If you have had vasovagal syncope—especially more than one episode—you should learn as much as you can about this condition, including what kinds of things provoke it, how to recognize the warning symptoms, and how you might stop an episode.

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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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