5.3 Syncope
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.
| Abnormality of circulation | Vasovagal syncopeReflex anoxic seizuresBlue breath-holding attacksCerebral syncopeAcute volume depletionChronic hypovolaemiaOrthostatic hypotensionPregnancy |
| Cardiac causes | |
| Central nervous system disorders | SeizureMigraine |
| Hypoglycaemia | |
| Hypoxia | |
| Drugs and poisons (no QT prolongation) | Antihypertensive drugsAntiarrhythmicsCarbon monoxide poisoningVolatile nitritesOthers |
| Psychogenic | HyperventilationHysteriaMalingeringMunchausen’s by proxyPanic disorder |
Clinical
History
A careful and detailed history will usually enable the correct diagnosis of the most common cause of childhood syncope, vasovagal syncope, to be established with confidence. Any unusual features of the history should raise suspicion of an alternate diagnosis.
A complete history should include the following:
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