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What Is Presyncope?

Medically Reviewed by Dan Brennan, MD on April 22, 2021

Prescyncope is when you feel as if you're about to pass out, but you don’t actually faint. It's sometimes referred to as near syncope. You may also feel lightheaded, sweaty, nauseous, warm, and weak, or have a fast heartbeat or blurry vision.

Presyncope can be caused by the same factors that cause syncope. This is when you actually pass out and later regain consciousness. Some of these factors are harmless, but others can be dangerous, even life-threatening.

What Causes Presyncope?

Presyncope happens when the amount of blood flowing to your brain temporarily decreases. Numerous medical conditions can cause presyncope. Presyncope can be one of the following types.

Vasovagal. This type of presyncope is caused by a drop in blood flow to your brain due to low blood pressure. This is the most common cause of syncope and presyncope. It's usually caused by a combination of being dehydrated and standing or sitting up too quickly. Vasovagal presyncope can also have emotional triggers such as:

  • Getting a shot
  • Having blood drawn
  • Seeing blood
  • Standing up too quickly
  • Standing for too long
  • Unexpected trauma, pain, or stress

Situational presyncope is another type of vasovagal presyncope. This occurs when you have a reflex response to a specific trigger. Your heart may slow or your blood vessels may widen. This causes a drop in your blood pressure, decreasing blood flow to your brain. Some additional situational triggers can include: 

  • Dehydration
  • Fear
  • Hunger
  • Urinating, called post-micturition presyncope
  • Eating
  • Lifting something heavy

Orthostatic hypotension. This is also a type of vasovagal syncope or presyncope. When you stand, your blood vessels normally get smaller to keep blood from collecting in your legs. This doesn't happen in people with orthostatic hypotension. Instead, they experience a drop in blood pressure when they stand, which can cause presyncope.

Cardiac. If your heart beats too fast, this is called tachycardia. If it beats too slow, this is called bradycardia. Both can cause presyncope or syncope. Other types of heart arrhythmias, or abnormal rhythms, can also cause presyncope.  

Cardiac presyncope or syncope can be caused by problems with a pacemaker. They might also indicate a tear in the large artery that carries blood to the rest of your body. A narrowing of the valve between your aorta and heart might also cause you to feel faint.

Neurologic. Neurologic presyncope can be caused by conditions such as a stroke or seizure. It can also result from a transient ischemic attack (TIA), which is a brief stroke that only lasts a few minutes. Other, less common causes of neurologic presyncope include migraines and normal pressure hydrocephalus (NPH), which is a type of brain disorder. 

Postural orthostatic tachycardia syndrome (POTS). This is a rare disorder that affects your blood flow. It most commonly occurs in women from ages 13 to 50. It happens when your heart rate increases by at least 30 beats per minute when you stand. It causes other symptoms when you stand such as presyncope and tiredness. POTS can also cause palpitations, which is when your heart feels like it's beating too hard or too fast.

How Common is Presyncope?

It's hard to know how common presyncope is because information about it is not usually included in reports of syncope. Presyncope is likely more common than syncope. At some point, 19% of people in the United States will experience an episode of syncope. Additionally:

  • 58% of people who experience syncope are female.
  • 3% of emergency department visits are for syncope.
  • 6% of hospitalizations are from syncope.
  • Most episodes of syncope occur either in early adulthood or after the age of 70. 

One study that focused on presyncope showed that:

  • The average age of patients was 56.
  • 61% of patients were female.
  • 49% of patients were admitted to the hospital, compared with 69% of syncopal patients.
  • 20% of patients required medical assistance or had an adverse outcome.

How Is Presyncope Diagnosed?

It's important to talk to your doctor if you have presyncope symptoms to rule out a serious condition. Your doctor will listen to your symptoms and do a physical examination. You may need other tests as well, which could include:

  • Tilt table test, which measures your blood pressure and heart rate at various positions, from lying flat to upright on a special table
  • Electrocardiogram, which measures the electrical rhythm of your heart
  • Exercise stress test, which is an electrocardiogram done while you're exercising strenuously
  • Echocardiogram, which is an ultrasound of the heart
  • Electrophysiology study, which is a test used to diagnose problems with your heart's rhythm
  • Holter monitor, which is a vest that you wear that continuously performs an electrocardiogram over 1 to 7 days
  • Event monitor, which is an electrocardiogram that you wear for 1 to 2 months

How Is Presyncope Treated?

The treatment for presyncope will depend on the cause and may include:

  • Being careful when you stand up
  • Raising the head of your bed while you're sleeping
  • Medications
  • Discontinuing or changing existing medications
  • Avoiding the situations that cause your presyncope
  • Treating any heart conditions you may have
  • A pacemaker, if needed
  • Wearing compression stockings to help your circulation
  • Changing your diet, which may mean consuming more salt or potassium, eating smaller meals more frequently, drinking more fluids, or avoiding caffeine and alcohol
WebMD Medical Reference

Sources

SOURCES:

American Family Physician: "Syncope: Evaluation and Differential Diagnosis."

Cleveland Clinic: "Postural Orthostatic Tachycardia Syndrome (POTS)," "Syncope."

JOHNS HOPKINS: "Syncope (Fainting)."

StatPearls: "Presyncope."

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