Pediatric emergency medicine trisk 1504 1504
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these conditions, cardiac output is unable to meet increased peripheral tissue
needs. Failure to increase cardiac output sufficiently, together with a fall in
peripheral resistance during exercise, may lead to syncope on exertion. There are
three main categories of syncope: autonomic (vasovagal or neurocardiogenic),
cardiac, and others ( Table 76.1 ).
AUTONOMIC (VASOVAGAL OR NEUROCARDIOGENIC)
SYNCOPE
Autonomic syncope is the most common cause of syncope in children and
adolescents, and accounts for almost 80% of cases. It belongs to a group of
neurally mediated syncope conditions in which there is a brief inability of the
autonomic nervous system to keep BP and sometimes heart rate at a level
necessary to maintain cerebral perfusion and consciousness. Other conditions in
this group include “situational” syncope, which may occur after micturition,
defecation, hair grooming, coughing, or sneezing. The precipitating causes for
vasovagal syncope include prolonged standing, a crowded and poorly ventilated
environment, brisk exercise in a warm environment, severe anxiety, perceived or
real pain, and fear. There are three clinical types. In the first, there is marked
hypotension (vasodepressor syncope). The second type is characterized by
marked bradycardia (cardioinhibitory syncope) and in the third form, there is a
combination of hypotension and bradycardia. Some symptoms that herald a
syncopal event include feelings of weakness, lightheadedness, blurring of vision,
diaphoresis, and nausea.
Breath-holding spells, a type of vasovagal syncope, occur in older infants and
toddlers and may be triggered by anger, pain, or fear. There are two forms:
cyanotic or pallid. In the cyanotic form, the child holds his or her breath, turns
cyanotic, and then loses consciousness. In the pallid form, the loss of
consciousness occurs before breath-holding. Occasionally the child may have
associated tonic or clonic motor activity.
CARDIAC SYNCOPE
There are several cardiac conditions that can lead to syncope in children ( Table
76.1 ). They account for 1.5% to 6% of pediatric syncope. The most important
causes that may be associated with significant morbidity or death are discussed
here.
Long QT Syndrome (LQTS)
This is an important cause of syncope and sudden cardiac death in children
without structural heart disease. An abnormal electrocardiogram (ECG) obtained
