Vasovagal Syncope

What is vasovagal syncope?

Vasovagal syncope, also called a “common faint”, is a brief loss of consciousness due to a vasovagal reflex. The vasovagal reflex is the combination of: sympathetic withdrawal causing vasodilation (vaso), and parasympathetic (vagal) disinhibition causing bradycardia. It is thus a combination of vasodilation and bradycardia. When blood pressure falls and the supply of oxygen to the brain is not sufficient, syncope occurs. Syncope is defined as transient (short) loss of consciousness (amnesia, fall, unresponsive) due to cerebral hypoperfusion.

The prevalence is high. In several questionnaire studies in medical students a prevalence of up to 40% was found (see Epidemiolgy).

Signs and symptoms of vasovagal syncope

Symptoms and signs of syncope can be divided based on the timing of the events. Symptoms and signs of vasovagal syncope are caused by both the reflex autonomic activation and the systemic hypotension.

Prodromal signs and symptoms

First

  • Feeling of warmth
  • Vague nausea
  • Abdominal cramps
  • Desire to sit down
  • Desire to leav the room

If no preventative measures are taken

  • Light-headedness
  • Swimming sensation
  • Dizziness
  • ‘Cold sweat’
  • Fatigue
  • Blurred and fading vision
  • Palpitations (in young patients)
  • Sounds ‘coming from a distance’
  • Buzzing in the ears

Just prior to the faint

  • Facial pallor (or green)
  • Yawning
  • Sighing
  • Tachypnoea
  • Sweating
  • Restlessness
  • Salivation
  • Pupillary dilatation
  • Accentuated peristaltic sounds
  • Difficulty concentrating
  • Loss of vision
  • Staring
  • Hearing loss

Syncopal signs and symptoms

During syncope

  • Unresponsive
  • Falls (if standing)
  • Eyes open and turned upwards
  • Short duration (altough longer periods have been reported)
  • Myoclonic jerks (< 10; see epilepsy) can occur
  • Urinary incontinence (in < 25 %; faecal incontinence is very rare)
  • Abnormal breathing

Post-syncopal signs and symptoms

After syncope

  • Consciousness recovers quickly
  • Fatigue
  • Persistent pallor
  • Nausea
  • Yawning
  • Weakness
  • Sweating
  • Oliguria
  • Recurrence when standing up

Emotional vasovagal syncope example

In the video below you can see a man who has a vasovagal syncope while getting a piercing. This is caused either by pain or by fear of needles, and is thus an emotional vasovagal syncope. Note the prodromal signs prior to syncope and the open eyes during syncope.

Triggers of vasovagal syncope

Vasovagal syncope has two different triggers from a pathophysiological viewpoint. A combination of the triggers below is also possible.

Orthostatic vasovagal syncope

Vasovagal syncope can be triggered by prolonged standing. This is called an orthostatic vasovagal syncope (not to be confused with orthostatic hypotension). The most common trigger for orthostatic vasovagal syncope is prolonged standing, but combinations with triggers like a hot environment can cause vasovagal syncope to occur much earlier

  • Prolonged standing
  • Hot environment
 

Emotional vasovagal syncope

Vasovagal syncope can also be triggered by strong emotions. Specific emotional events that are often a trigger for vasovagal syncope are:

Epidemiology of vasovagal syncope

Vasovagal syncope is the most common cause of syncope making up > 60% of the cases. The prevalence in the general population is ~40%. Most people don’t attend a physician after a ‘common’ vasovagal faint.
The age at which people experience their first faint shows two peaks: one in adolescents and one peak in people > 60 years-old (figure 1)

epidemiology of vasovagal syncope
Figure 1. Epidemiology of vasovagal syncope. The top figure shows the percentage per year of the total amount of first faints. The bottom figure shows the cumulative amount of faints in the population.

Pathophysiology of vasovagal syncope

The vasovagal reflex consists of vasodilation (vaso) and bradycardia/asystole via the vagal nerve (vagal). These factors produce a fall in blood pressure, ultimately resulting in cerebral hypoperfusion and syncope. 

arterial baroreflex
Figure 2. A schematic figure of the arterial baroreflex, with on the left the afferent arm and on the right the efferent arm. IX = glossopharyngeal nerve. X = vagal nerve

Diagnosing vasovagal syncope

History taking

History taking is the most important diagnostic test in patients with suspected syncope. As vasovagal syncope and other causes of syncope are episodal in nature, tests are often normal when the patient is seen by a physician. 

A few things are very important in making a diagnosis in these patients:

  1. Not taking, but building a history. Ask open questions, take your time, and be curious. 
  2. Physiological reasoning. When building a history, knowledge of the physiology of short term blood pressure regulation can really help to recognize the historical clues that a patient tells. 
  3. Build the history around every episodes of loss of consciousness. Not only the last episodes can tell you more abou the diagnosis. Did this happen before? Did you faint when you where a child? 
  4. In every episode one should know:
    1. The circumstances around the episode
    2. What happened/did you feel prior to the episode?
    3. What happened during the episode (eyewitness report)? 
    4. How did you feel upon recovery?

For a detailed description of the initial evaluation of suspected syncope go to Initial Evaluation

Treatment of vasovagal syncope

In vasovagal syncope, recognizing the diagnosis is the first part of the treatment. As it is an episodal event, most patients don’t need more than a few lifestyle measures to learn how to prevent the vasovagal faints. 

Physical counterpressure manoeuvres

By tensing the abdominal muscles and the muscles in the extremities the venous return can be increased almost instantaneously (Figure 3). This can be done by whole body muscle tensing or by leg crossing and tensing the calves. Prodromes have to be present, otherwise the counter pressure manoeuvres can not be applied in time to prevent the faint. This makes this a very useful method under the younger population, as they have prodromes most of the time. In older patients, prodromes are often absent, and physical counterpressure manoeuvres and thus not a good intervention in these patients
When teaching a patient how to perform the manoeuvres, continuous blood pressure measurements during the training can be very insightful. For a detailed report see teaching a patient counter pressure manoeuvres using biofeedback.

increasing blood pressure using muscle tensing for vasovagal syncope
Figure 3. The effects of muscle tensing on the blood pressure in a patient with vasovagal syncope. Note the immediate increase upon tensing of the muscles.

Water and salt

The goal of drinking enough water and eating salt is to increase the central blood volume and prevent a vasovagal reaction. When building a history with the patient, be sure to ask about their water and salt intake. Patients with frequent episodes of (pre)syncope should at least drink 3 L of water every day and they should always have clear urine. 

Eating more salt increases central blood volume but also increases the overall blood pressure. When advising a patient to increase their salt intake, be sure to take notice of the blood pressure of the patient.

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