Pediatric emergency medicine trisk 1504 1504

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