Introduction

Syncope is the term used to describe any event of sudden and transient loss of consciousness and postural tone.

The range of incidences of syncope occurring in childhood is described as being from 0.1–50%, with peak incidences occurring amongst toddlers and adolescents. The most common events seen in the paediatric setting are episodes of vasovagal syncope. Differentiating the common, benign vasovagal event from rare differential diagnoses is essential to the appropriate management of children who present with syncope.

By contrast, in the adult population syncope is the cause of 1–3% of all ED attendances, and malignant cardiac arrhythmias are commonly the underlying cause.

Aetiology

The final common pathway that leads to all episodes of syncope is a sudden decrease in delivery of metabolic substrates, namely oxygen and glucose, to the brain.

In childhood and adolescence the major cause of syncope is transient autonomic dysfunction.

In toddlers such episodes usually manifest as either blue breath-holding spells or ‘reflex anoxic seizures’ (also called ‘pallid breath-holding spells’). The mechanism for the cyanosis in blue breath-holding spells is poorly understood. The precipitant for reflex anoxic seizures may be a noxious stimulus causing reflex asystole, which leads to an anoxic seizure.

In older children and in adolescents such episodes most commonly present as episodes of vasovagal syncope. A combination of hypotension and profound bradycardia, or either bradycardia or hypotension alone leads to cerebral hypoxia. Complete understanding of the underlying mechanisms is lacking. Other terms used to describe these episodes include neurocardiogenic syncope, vasodepressor syncope or neurally mediated syncope.

The differential diagnoses of syncope in childhood include cardiovascular causes, seizures, migraines, hypoglycaemia, drugs, and psychogenic events. These are listed in more detail in Table 5.3.1. It should be noted that situational syncope (syncope that occurs during micturition, swallowing cold liquids, defecation or coughing), and carotid sinus sensitivity are rare in the paediatric population. Mitral valve prolapse has not been conclusively proven to be a cause of syncope.

Table 5.3.1 Causes of childhood syncope

Abnormality of circulation Vasovagal syncope
Reflex anoxic seizures
Blue breath-holding attacks
Cerebral syncope
Acute volume depletion
Chronic hypovolaemia
Orthostatic hypotension
Pregnancy Cardiac causes           Central nervous system disorders Seizure
Migraine Hypoglycaemia Hypoxia Drugs and poisons (no QT prolongation) Antihypertensive drugs
Antiarrhythmics
Carbon monoxide poisoning
Volatile nitrites
Others Psychogenic Hyperventilation
Hysteria
Malingering
Munchausen’s by proxy
Panic disorder

Clinical

Examination

A structured approach to the clinical examination of all children presenting with syncope is essential to ensure that all relevant findings are elucidated.

Investigations

Any child in whom a cardiac cause of syncope is either suspected or diagnosed must be referred to a cardiologist. It may be appropriate to arrange secondary investigations such as an echocardiogram or Holter monitoring prior to discharge from the ED after discussion with a paediatric cardiologist. It should be noted that Holter monitoring is often unhelpful as symptoms rarely occur whilst the patient is monitored. Some children may go on to have electrophysiological studies, exercise stress tests or cardiac angiography.

Where a history obtained suggests that the child has had a seizure, an EEG should be arranged in consultation with the neurologist or paediatrician to whom they are referred.

Head-upright tilt-table testing may be done in children with frequent, recurrent syncope, and in those children in whom a cause for syncope is not certain. Protocols for the test vary, but the requirements are that the child has a period of supine rest before tilting and is then tilted at a defined angle for a period of time. The most common positive response seen is a combination of hypotension and bradycardia prior to syncope or near syncope. Other positive responses seen are either isolated hypotension or asystole prior to syncope.

Video surveillance with continuous ambulatory EEG and cardiac monitoring may be indicated where fictitious events are suspected.

Management of syncope within the ED

For most children the diagnosis of vasovagal syncope will be made, and the majority of these will be able to be discharged well from the ED. These patients must be given advice regarding the precipitants and management of vasovagal syncope. Avoidance of usual precipitating events is important. Children can also be taught to recognise the typical prodrome of the event, and to then attempt to prevent any loss of consciousness by sitting or lying with their feet elevated. They should be discharged into the care of a capable adult.

Carers of children with a diagnosis of either reflex anoxic seizures or blue breath-holding spells should be educated and reassured prior to discharge.

Children seen with hyperventilation syncope may require treatment by rebreathing. They should be encouraged to breathe slowly and regularly, with a paper bag held over their mouth and nose. Once their breathing is regular and their symptoms improved, they should be encouraged to be calm, and to sit or lie down for a time. Both the children and their carers should be taught the technique prior to discharge.

Management of all other children should be appropriate for their particular clinical condition.

Summary

The most common cause of childhood syncope is vasovagal syncope. Careful history and examination are essential in making the correct diagnosis. All children who present with their first episode of syncope should have a 12-lead ECG.

If there is an atypical history or if there are any abnormalities in the clinical examination the child must be investigated and referred appropriately.

For children in whom a diagnosis of vasovagal syncope is made, education and reassurance of both the child and their carers must be done prior to discharge from the ED.