Pediatric emergency medicine trisk 1503 1503
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CHAPTER 76 ■ SYNCOPE
THOMAS B. WELCH-HORAN, ROHIT SHENOI
INTRODUCTION
Syncope is a sudden, brief loss of consciousness and postural tone caused by
transient global cerebral hypoperfusion and characterized by complete recovery.
Presyncope is a feeling of impending sensory and postural changes without loss
of consciousness. Syncope is a common condition in childhood. In the United
States, it accounts for about 3% of pediatric emergency department (ED) visits.
The incidence peaks during the second decade of life, and about 30% to 50% of
children experience syncope by the end of adolescence. Girls are more commonly
affected than boys. The most common cause of syncope in children is vasovagal
syncope, which is related to a loss of vasomotor tone and is generally benign.
Occasionally, the etiology may be a life-threatening cardiac condition. When
evaluating a child who presents to the ED with syncope, the goal is to assess
whether high-risk conditions are present, or whether the symptoms can be
attributed to a more benign etiology.
When normal individuals assume an upright position, cardiac output and
cerebral arterial blood pressure (BP) are maintained by a combination of
mechanical pumping activity of the skeletal muscles on venous return to the right
atrium, the presence of one-way valves in the veins that facilitate venous return,
arterial vasoconstriction caused by the baroreceptor reflex, and cerebral blood
flow autoregulation. If stroke volume is not maintained, then reflex sinus
tachycardia develops. Vasovagal syncope (also known as neurocardiogenic
syncope) is believed to begin with excessive peripheral venous pooling that leads
to a sudden decrease in peripheral venous return. This results in increased cardiac
contractility and baroreceptor and left ventricular mechanoreceptor firing,
followed by an efferent response consisting of peripheral α-adrenergic withdrawal
and enhanced parasympathetic tone. The hallmark is vasodilatation and
bradycardia with hypotension. Sudden activation of a large number of
mechanoreceptors in the bladder, rectum, esophagus, and lungs may also provoke
such a response. In orthostatic hypotension, often caused by fluid depletion, the
compensatory responses and ensuing sinus tachycardia are insufficient to
maintain brain perfusion, and syncope develops when the patient stands.
Syncope on exertion suggests a cardiac or cardiopulmonary cause, such as
obstruction to left or right ventricular outflow or pulmonary hypertension. In
