the outflow of the left ventricle, creating a functional obstruction In addition, anterior motion of the mitral valve into the left ventricle during systole further compromises outflow Patients may present with dyspnea, exercise intolerance, angina, syncope, or sudden death Adult congenital heart disease survivors are at risk for syncope because of the underlying cardiac condition and/or previous palliative/corrective surgeries These patients can present with heart failure, arrhythmias, or pulmonary hypertension It is important to exclude atrial arrhythmias in patients with syncope and congenital heart conditions or surgeries associated with a risk of atrial rhythm abnormalities (e.g., tetralogy of Fallot, Ebstein anomaly, and the Mustard, Senning, and Fontan procedures) Other Arrhythmias Supraventricular tachycardia is the most common symptomatic pediatric tachyarrhythmia, and syncope can theoretically result from compromised cardiac output, though such presentations are rarely seen First-degree heart block may be an incidental finding in patients with syncope However, second- and third-degree heart block need further investigation Search for evidence of myocarditis, cardiomyopathy, or congenital heart disease when such arrhythmias are observed Conduction disturbances are common after cardiac surgery Patients who have undergone correction of tetralogy of Fallot, aortic stenosis, and transposition of the great arteries may be particularly prone to syncope Ventricular arrhythmias may occur as a consequence of surgeries involving incision to the ventricles Rarely, direct blunt trauma to the chest (commotio cordis) may cause ventricular arrhythmias leading to syncope or sudden death OTHER CONDITIONS AND THOSE THAT MIMIC SYNCOPE There are several other conditions that may cause or mimic syncope The most frequent of these are seizures and migraine The rest are less frequent but still important conditions Hypoglycemia Low blood sugar is usually associated with feelings of weakness, diaphoresis, lightheadedness, and confusion that can mimic presyncope Infants may present with lethargy or jitteriness Diagnosis is rapidly established by obtaining a blood glucose level Epilepsy It may be difficult to differentiate an epileptic seizure from the convulsions or posturing that may follow a brief but severe cerebral hypoxic event caused by vasovagal syncope An important distinguishing feature is that in the latter, the patient usually displays a normal orientation after the syncopal event compared to the more prolonged postictal confusion and lethargy that usually follows a typical generalized epileptic seizure Nausea and sweating are also more common with syncope Incontinence and fall-induced trauma may be observed in both conditions and are not discriminatory A distant stare may precede an atonic seizure but is not typical of vasovagal syncope The prodromal symptoms of vasovagal syncope differ from the aura that may precede a seizure in some patients Prolonged clonic seizure activity after the patient is recumbent is not expected in a syncopal event Narcolepsy Cataplexy, muscle weakness, and collapse in a patient with narcolepsy may mimic syncope However, in these patients there are more likely to be disorders of the sleep–wake cycle, symptoms of daytime somnolence, and sometimes hallucinations Vertebrobasilar Migraine or Transient Ischemic Attacks In such migraines, symptoms such as tinnitus, vertigo or other aura, and occipital headache may be observed However, this constellation of symptoms is not specific In vertebrobasilar migraine, as in vertebrobasilar arterial insufficiency causing transient ischemic attacks, loss of consciousness may be observed Psychogenic Causes of Syncope Hyperventilation and conversion disorder can lead to syncopal events These conditions are relatively common in adolescence Hyperventilation may occur as part of a panic disorder Patients may complain of chest tightness, breathlessness, lightheadedness, palpitations, and dizziness Syncope-like symptoms due to conversion disorder occur in the presence of an audience and are not associated with injury Episodes tend to last longer than the typical vasovagal syncope and are not posture dependent Neurologic and autonomic manifestations are usually absent Orthostatic Intolerance Syncope attributable to orthostatic hypotension occurs upon assuming an upright posture (i.e., orthostasis) due to a drop in BP It is defined as a drop in systolic BP of ≥20 mm Hg or diastolic BP of ≥10 mm Hg with assumption of an upright posture Symptoms of orthostatic hypotension consist of lightheadedness, syncope or presyncope, vision changes, headaches, palpitations, tremulousness, and diaphoresis and are ameliorated by recumbent position The causes include volume depletion (e.g., hemorrhage or dehydration), febrile illness, pregnancy, anemia, eating disorders, and use of medications such as diuretics, vasodilators, or calcium channel blockers Symptoms typically abate upon treatment of the primary cause In some patients, recurrent orthostatic symptoms may occur in the absence of true orthostatic hypotension, and may be associated with an excessive increase in heart rate during upright positioning This condition is known as postural orthostatic tachycardia syndrome (POTS) It is a clinical syndrome usually characterized by (1) frequent symptoms that occur with standing, such as lightheadedness, blurred vision, palpitations, tremor, generalized weakness, exercise intolerance, and fatigue; (2) an increase in heart rate of ≥30 beats per minute (bpm) when moving from a recumbent to a standing position (or ≥40 bpm in individuals 12 to 19 years of age); and (3) the absence of orthostatic hypotension (as defined by >20 mm Hg drop in systolic BP) There are two forms of POTS, and both forms are observed more often in females than males In the first and more common type, persistent tachycardia, associated with fatigue, exercise intolerance, and palpitations, is present while the patient assumes an upright position This condition may occur after a viral illness, trauma, or surgery The second or central form of POTS is often associated with migraines, tremor, and excessive sweating Presyncope is a more common symptom than syncope in patients with POTS; however, POTS and vasovagal syncope are not mutually exclusive The clinician should make careful use of the history and physical examination to distinguish between patients with suspected POTS and those with other disorders The anxiety and somatic hypervigilance sometimes attributed to patients with POTS may be associated with other disorders such as migraine or mood disorders Similarly, fatigue and weakness could be signs of another systemic illness Dysautonomia In rare cases, a child may exhibit an inadequate vasoconstriction in response to postural changes that would normally demand sympathetic nervous system activation In such patients, the heart rate may not increase appropriately with standing, and BP may be labile, leading to syncope Drugs and Toxins Medications that decrease cardiac output, such as barbiturates and tricyclic antidepressants, may cause syncope Recreational drugs such as cocaine, alcohol, inhalants, and opiates may cause a loss of consciousness, though not true syncope Carbon monoxide is an important environmental toxin to consider in applicable clinical scenarios CLINICAL EVALUATION In children who present with syncope, the history usually offers key information to assist the clinician in making the diagnosis However, objective findings are often absent, which can pose a challenge An orderly approach to the evaluation of pediatric syncope is essential and consists of a meticulous history and physical examination, a 12-lead ECG, and the use of additional testing only in selected patients ( Fig 76.1 ) Extensive testing is usually unnecessary Determine the sequence of events leading up to the syncopal event and the position of the patient’s body just before the syncope It may be necessary to obtain information from eyewitnesses, as the patient may not recollect all aspects of the event Search for precipitating factors, such as exercise, loud noise or a startle response, rapid postural changes, anxiety or emotional stress, trauma, dehydration, medication intake, or recreational drug use Exertion-related syncope suggests a cardiac cause Sudden loud sounds or arousal may precipitate syncope in patients with long QT interval syndromes In situational syncope, some specific activities such as stretching, arising suddenly from a recumbent position, swallowing, coughing, hair brushing, voiding, or defecation may be associated with loss of consciousness ... findings are often absent, which can pose a challenge An orderly approach to the evaluation of pediatric syncope is essential and consists of a meticulous history and physical examination, a