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Vasovagal Syncope: Symptoms, Diagnosis, Treatments

Written by Helen Quach, BS (Biochemistry) | Last updated:
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology) | Written by Helen Quach, BS (Biochemistry) | Last updated:

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There are many types of syncope (fainting) episodes, and they can even be misdiagnosed. Vasovagal syncope is usually not serious, but it can signal a potentially dangerous medical condition. Being able to recognize a fainting event can greatly improve safety, especially when operating dangerous equipment. Read on to find out about self-diagnostic and prevention techniques.

What Is Vasovagal Syncope?

Vasovagal syncope is a sudden but brief loss of consciousness. It is usually triggered by emotional distress, such as the sight of blood or a shocking event. These episodes may be isolated or recurrent events [1].

Other common terms used to refer to syncope include:

  • Blackout spells
  • Passing out
  • Swooning
  • Fainting

Vasovagal syncope is also referred to as neurocardiogenic syncope [1].

Types of Syncope

There are several reasons why someone might faint. Vasovagal is one of the most common types of fainting (about 50% of cases), together with orthostatic fainting (caused by low blood pressure) [2].

Types of fainting include:

  • Classical vasovagal – Fainting occurs after emotional distressing events, severe pain or prolonged standing [3].
  • Situational – Fainting occurs immediately after urination, defecation, coughing, or swallowing [3].
  • Orthostatic – Fainting occurs when blood pressure drops too low (hypotension) [3].
  • Carotid sinus-related – The carotid sinus (located in the throat) is responsible for maintaining blood pressure in the body functioning as a communicator between the brain and body. A sensitive carotid sinus can cause a rapid decrease in blood pressure when stimulated by body movement or pressure [4, 5].
  • Heart ischemia-related – Fainting occurs with a quick drop of blood flow possibly as a result of a heart attack [3].
  • Arrhythmia-related – Fainting occurs due to the improper beating of the heart – either too fast, too slow, or too irregular [3].

Why do we faint? In some cases, it is because of the low blood/oxygen supply to the brain. The faint brings our body into a gravitationally neutral position, thereby offering a better chance of restoring brain blood supply and preserving brain function [6, 7].

In other cases (such as after emotional distress), fainting protects the heart against too much sympathetic (fight-or-flight) activity [8].


Symptoms Before Fainting Episode [5]:

  • Dizziness
  • Feeling of vertigo
  • Chest pain
  • Difficulty breathing
  • Nausea
  • Feeling warm
  • A feeling of abnormal heartbeat (heart palpitations)
  • Weakness
  • An unusual degree of cold sweating
  • Blurred vision
  • Yawning

Symptoms During Fainting Episode [5, 9]:

  • Fainting
  • Slow, weak pulse
  • Dilated pupils
  • Narrowing field of vision “greying out”
  • Loss of vision “blacking out”
  • Abnormal movements

Symptoms After Fainting Episode [5]:

Defects in salt metabolism may be associated with more severe symptoms. Low dietary salt can lead to a lower blood volume and make the body more susceptible to fainting. However, more conclusive evidence is needed [10].


Common vasovagal syncope is diagnosed if the fainting event is associated with emotional distress, such as fear or pain. Prolonged standing can also cause fainting [3].

Usually, syncope is diagnosed based on the patient’s fainting episode, medical history, physical examination, and blood tests [11].

Fainting episodes can either be one-time events or recurrent. They can even serve as a signal for more serious clinical disorders, such as allergies and diabetes [11].

The tilt table test is used to replicate and document fainting symptoms. Patients are usually strapped to a tilt table, then suspended upright while medical data is collected [12].

An implantable loop recorder can be surgically implanted under the skin to track heartbeat patterns. The recorder detects any abnormal heart rhythms during fainting events [12].

The treadmill test is the newest method to diagnose syncope. Patients start walking at 1.7 mph at a flat incline. Speed and incline increase every 3 minutes and it ends after 30 minutes. After a 1-minute rest, the patient is administered nitroglycerin and medical data is collected [13].

Vasovagal Syncope Can Be Misdiagnosed as a Seizure

Vasovagal syncope is commonly misdiagnosed as an epileptic seizure due to occasional involuntary movements (myoclonic jerks) after fainting. However, fainting does not show the same responses as a seizure on different diagnostic tools (ECG, EEG, etc.) [14].

Syncope is caused by defects due to improper blood flow, while epileptic seizures are caused by defects in brain activity. Misdiagnosis can lead to improper treatment of the patient [14].


Many mechanisms have been linked to fainting episodes, but these factors and their relative contributions are still not fully understood [12].

Vasovagal syncope occurs by the activation of a heart reflex (hypotension/bradycardia reflex) through the stimulation of the vagus nerve. This reflex causes a rapid decrease in heartbeat and widening of blood vessels [15].

The vagus nerve is part of the parasympathetic nervous system, sometimes referred to as the rest-and-digest system [16].

Children (7-18 years) with vasovagal syncope had significant imbalances in the involuntary control of their body (autonomic nervous system) when compared to healthy children. They had decreased sympathetic (fight-or-flight) and increased vagal tone. These imbalances may be more severe for adolescents [17].

In patients with syncope induced by the tilt table test, images of their hearts revealed a sudden loss of blood flow into the heart. This caused decreased blood outflow from the heart just moments before fainting [18, 19].

Safety sensors in the heart respond with a heart reflex to restore blood circulation informing the brain to signal a fainting event [18].


These factors increase the likeliness of fainting [20]:

  • Standing upright
  • Being motionless
  • High body temperature
  • Full or empty stomach
  • Alcohol
  • Blood pressure drugs
  • Sudden postural changes
  • Dehydration
  • Emotional stress
  • Hyperventilation
  • Being in a hot and humid environment

Vasovagal Syncope and Anxiety

Anxiety may be associated with increased fainting episodes and may be a therapeutic target for patients suffering from syncope [21].

Extreme emotional triggers such as social challenges in people with social anxiety can be a primary trigger for fainting episodes. Anxiety from experiencing a phobia such as the sight of blood can cause syncope [22].

In a study of 80 participants, the patients who had higher, recurrent fainting episodes have 30% higher anxiety levels and 20% higher panic levels compared to healthy participants [23].

Vasovagal Syncope During Urination and Bowel Movements

Fainting when going to the bathroom is rare and poorly understood. It is likely that the syncope mechanisms between urination and bowel movements are similar [5].

A sudden strain to the bladder can quickly decrease blood pressure and heart rate through inadvertent activation of the vagus nerve. It is best not to force the body when on the toilet [5].

Vasovagal Syncope During Pregnancy

It is common for pregnant mothers to experience syncope and recurrent presyncope symptoms. Small strains can raise blood pressure and decrease heart rate, causing fainting [24, 25].

Pregnant women are susceptible to fainting and may experience warning signs such as paleness, sweating, nausea, fatigue, and warmth [26].

Treatments of applied tension to muscles and provoking anxiety responses increased blood pressure in pregnant patients showing no episodes of fainting after the treatment [27].


The amount of blood in the body is an important target to prevent fainting. Larger amounts of blood in the body can beneficial [15].

Methods to prevent fainting include:

  • Increasing dietary salt intake (salt loading) – Doctors recommend 10 gram of salt and 2 liters of water daily [28, 29]
  • Upright exercise (squatting and leg crossing) – However, those with a history of recurrent fainting episodes should be careful when lifting heavy training equipment [30, 31, 32]
  • Sleeping with your head raised [33]

Education on how to avoid triggers may be sufficient for those with a single fainting experience. They may not need specific therapy [3].


Different types of non-pharmacologic and pharmacologic treatments are available, with varying efficiencies. A pilot study of 37 patients with serious recurrent vasovagal syncope showed that combining different treatments had a better effect and improved the quality of life to a higher degree than standard treatment [2].

Non-Pharmacologic Treatments

Treatment focuses on reducing fainting recurrence.

Tilt training, timed sessions of upright posture against a wall, may be an effective treatment for syncope in highly motivated patients. In a study of 38 patients, 1 year after training, 82% of the patients reported no syncope recurrence [34, 35, 36].

Physical counter-maneuvers such as squatting, leg crossing, arm-tensing, and hand squeezing can help treat fainting [37, 38].

Lower limb compression bandage places pressure on parts of the legs to increase blood flow, which can treat fainting [39, 40].

Some may require more aggressive therapy, such as pacemakers. A meta-analysis of pacemaker usage as a treatment for fainting showed a 17% reduction in fainting. However, its results may be overestimated due to a lack of blinded trials [41].

Pharmacological Treatments

A minority of patients will continue to have recurrent syncope despite conservative (non-pharmacological) therapy, and they may require medication [42].

Most drugs tested have been considered ineffective but there are a few exceptions.

In a study of 16 vasovagal syncope patients, midodrine (a hypertension drug), decreased syncope symptom frequency and severity. There were no serious side effects [43, 44].

In a study of 68 syncope patients, paroxetine (an antidepressant/SSRI better known as Paxil) significantly improved their symptoms. It helped reduce symptoms in patients unresponsive or allergic to other traditional medications [45, 43].

However, in a different study of 25 healthy subjects, Paxil did not prevent syncope [46].

In a study of 210 vasovagal syncope patients, fludrocortisone (a synthetic steroid known as Florinef), significantly reduced the likelihood of fainting events [47].

Beta-blocker drugs (used to treat high blood pressure and irregular heartbeat) showed minimal benefits on patients with recurrent fainting. The European Society of Cardiology suggested stopping the usage of beta-blocker drugs for the treatment of syncope [12, 48].

Additionally, in a study of 96 vasovagal syncope patients, there was no difference between the SSRI fluoxetine (also known as Prozac or Sarafem), propranolol (a beta-blocker), or placebo (lactose pill) in treating syncope [49].

Genes Linked to Vasovagal Syncope

Evidence regarding the genetic qualities of vasovagal syncope is limited, but it is possible that the susceptibility to fainting can be inherited. Specific triggers, however, cannot be inherited [50].

An increased chance of fainting episodes is linked to a possible genetic location of yet unknown function (Chromosome 15q26). Further studies may lead to better therapeutic treatments [51, 50].

The following genes and SNPs are linked to a higher susceptibility for vasovagal syncope [52, 53]:

Experiences with Vasovagal Syncope

Patients usually feel dizzy or lightheaded prior to the blacking out event. Some have instances of vertigo, weakness, nausea, or vision problems. Syncope patients commented that their vision problems range from blurred vision to increased sensitivity to light.

After the fainting event, the patients sometimes recovered quickly, although they still had mild nausea and confusion. Some have successfully reduced blacking out events by limiting alcohol and caffeine usage.

It is easy to misdiagnose other disorders as syncope. Patients are advised to document any features of their fainting event and to talk to a doctor about a proper diagnosis.

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About the Author

Helen Quach

BS (Biochemistry)

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