Syncope

Syncope is the term used to describe the event of temporarily losing consciousness due to a disruption of blood flow to the brain, often leading to a fall. Syncopal episodes are also known as vasovagal episodes, or simply fainting.

A vasovagal episode (or attack) is caused by a problem with the autonomic nervous system regulating blood flow to the brain. When the vagus nerve receives a strong stimulus, such as an emotional event, painful sensation or change in temperature it can stimulate the parasympathetic nervous system. Parasympathetic activation counteracts the sympathetic nervous system, which keeps the smooth muscles in blood vessels constricted. As the blood vessels delivering blood to the brain relax, the blood pressure in the cerebral circulation drops, leading to hypoperfusion of brain tissue. This causes the patient to lose consciousness and “faint”.

Signs and Symptoms

Patients often remember the event and can recall how they felt prior to fainting. This is called the prodrome, and involves feeling:

• Hot or clammy
• Sweaty
• Heavy
• Dizzy or lightheaded
• Vision going blurry or dark
• Headache

A collateral history from someone that witnessed the event is essential to get an accurate impression of what happened. During a vasovagal episode they may describe the person:

• Suddenly losing consciousness and falling to the ground
• Unconscious on the ground for a few seconds to a minute as blood returns to their brain
• There may be some twitching, shaking or convulsion activity, which can be confused with a seizure

The patient may be a bit groggy following a faint, however this is different from the postictal period that follows a seizure. Postictal patients have a prolonged period of confusion, drowsiness, irritability and disorientation.

There may be incontinence with both seizures and syncopal episodes.

Causes

When assessing someone presenting with a syncopal episode the key is to establish whether this was a simple faint and the child is otherwise healthy, or whether this the syncope was due to a significant underlying health problem. Simple faints without underlying pathology are harmless and have no long term implications.

Primary syncope (simple fainting):

• Dehydration
• Missed meals
• Extended standing in a warm environment, such as a school assembly
• A vasovagal response to a stimuli, such as sudden surprise, pain or the sight of blood

Secondary causes:

• Hypoglycaemia
• Dehydration
• Anaemia
• Infection
• Anaphylaxis
• Arrhythmias
• Valvular heart disease
• Hypertrophic obstructive cardiomyopathy

History

Take a thorough history focusing on eliciting several key points, ideally with the help of a witness:

• Features that distinguish a syncopal episode from a seizure
• After exercise? Syncope after exercise is more likely to be secondary to an underlying condition.
• Triggers?
• Concurrent illness? Do they have a fever or signs of infection?
• Injury secondary to the faint? Do they have a head injury?
• Associated cardiac symptoms, such as palpitations or chest pain?
• Associated neurological symptoms?
• Seizure activity?
• Family history, particularly cardiac problems or sudden death?

Examination 

Perform a thorough examination focusing on eliciting several key points:

• Are there any physical injuries as a result of the faint, for example a head injury?
• Is there a concurrent illness, for example an infection or gastroenteritis?
• Neurological examination
• Cardiac examination, specifically assessing pulses, heart rate, rhythm and murmurs
• Lying and standing blood pressure

Investigations

• ECG, particularly assessing for arrhythmia and the QT interval for long QT syndrome
• 24 hour ECG if paroxysmal arrhythmias are suspected
• Echocardiogram if structural heart disease is suspected
• Bloods, including a full blood count (anaemia), electrolytes (arrhythmias and seizures) and blood glucose (diabetes)

Management

Fainting is common in children, particularly in teenage girls. They usually resolve by the time they reach adulthood. The most important aspect of management is making a confident diagnosis and excluding other pathology.

Seizures or underlying pathology need to be managed by an appropriate specialist.

Once a simple vasovagal episode is diagnosed, reassurance and simple advice can be given to:

• Avoid dehydration
• Avoid missing meals
• Avoid standing still for long periods
• When experiencing prodromal symptoms such as sweating and dizziness, sit or lie down, have some water or something to eat and wait until feeling better

Last updated January 2020