Syncope is defined as a loss of consciousness secondary to decreased cerebral perfusion pressure occurring in brain areas responsible for a state of alertness which include the bilateral cortex, the reticular activation system, and the brainstem.
Syncope in children is a not uncommon clinical condition estimated to occur in 126 out 100,000 children with cardiogenic and neurogenic causes representing 80% and 9% of cases, respectively. Other etiologies include metabolic, psychological, and toxicological causes, as listed below.
Syncope at rest
Syncope that occurs when the patient is in standing position or that occur when moving from a supine to sitting position can be a type of vasovagal response. This is characterized by a systemic hypotension secondary to a sudden loos of vasomotor tone known as the vasodepessor response. If it is also accompanied by significant bradycardia or aystole it is termed a cardioinhibitory response.
This type of syncope happens most frequently when the patient has been standing for prolonged periods of time such as in church or at a military parade or after a period of sleep. The loss of consciousness is brief (1-2 minutes) and often an emotional or physiological component such as dehydration, fatigue, hunger and other illness contributes to precipitating the event.
Syncope during activity
Syncope during physical activity demands a workup for an underlying cardiac abnormality that causes an inability of the body to meet the increased cardiac output requirement. The differential diagnosis should include Wolff-Parkinson-White syndrome, long QT syndrome (LQTS), hypertrophic obstructive cardiomyopathy, and more rare arrhythmogenic right ventricular dysplasia. In all cases, a careful family history for syncopal episodes, sudden unexplained death, and seizures should be obtained.
Causes of Syncope in Children
vasovagal (fainting) – most common cause in children
excessive vagal tone – adolescents, athletes
reflex – micturation, cough, hair grooming, breath holding
orthostatic – blood loss, dehydration
obstructive lesions – hypertrophic obstructive cardiomyopathy, aortic stenosis, primary pulmonary hypertension,
arrhythmia – long QT syndrome, heart block, ventricular tachycardia, supraventricular tachycardia
hypercyanosis – Tetralogy of Fallot episodes
miscellaneous – myocardial infarction, anomalous coronary artery
neurologic – seizures, migraine
metabolic – hypoglycemia
vascular – vertebrobasilar insufficient
(adapted from Avoiding Common Pediatric Errors, p. 301)