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The Child Who Passes Out

2000; American Academy of Pediatrics; Volume: 21; Issue: 11 Linguagem: Inglês

10.1542/pir.21-11-384

1529-7233

Hassib Narchi,

Epilepsy research and treatment

After completing this article, readers should be able to:A previously well 2-year-old boy who had an uneventful neonatal period; normal growth parameters and developmental milestones; and a negative family history for seizures,syncope, or sudden death was referred for evaluation of episodes of loss of consciousness that were stereotypic and occurred twice weekly over the previous 6 months. He developed unexpected episodes of sudden pallor after a minor trauma, followed by a fall, loss of consciousness, turning of the eyes,opisthotonos, and clonic movements for 30 seconds. He recovered normal consciousness and activity over the next few minutes before drifting to sleep. There was no cyanosis or sweating, and the episodes were not related to exercise or fasting. Results of a complete physical examination, including growth parameters, vital signs, and neurologic examination, were normal. Results of a tilt table test were normal,electrocardiography (ECG)showed a sinus rhythm, the corrected QTc interval was 0.40 seconds,and electroencephalographic(EEG) findings were normal. An EEG with an ocular compression test revealed bradycardia with a brief reversible asystole of 4 seconds,which recovered spontaneously,confirming the diagnosis of pallid spells or reflex anoxic seizures.Syncope or fainting, defined as a sudden and usually brief loss of consciousness and postural tone, is caused by a transient decrease in cerebral blood flow. Presyncope is the feeling that one is “about to pass out.” Both conditions are common,and although they may not have the same pathophysiology, the diagnostic approach to them is the same. Syncope causes considerable anxiety for the parents, siblings, schoolmates,and teachers of affected children. The etiologies include breath-holding spells, vasovagal syncope,postural or orthostatic hypotension,arrhythmias, seizures, hypoglycemia,and other nonepileptic phenomena.Breath-holding spells are very common(incidence of 4.6%) and can be a frightening experience for the parents,who may think that their child is dying. They occur primarily between ages 1 and 5 years and resolve by school age. Approximately 80% are the cyanotic form,and 20% are the pallid form. They can be diagnosed and distinguished by careful history because pain,anger, or frustration always provokes them. Findings on physical and neurologic examinations are normal. Reassurance is sufficient therapy; neither type represents epilepsy or epilepsy equivalents.The cyanotic type (“classic”breath-holding spell) is rare prior to 6 months of age, peaks at about age 2 years, and resolves spontaneously by 5 years of age. It is self-limited and has a uniformly favorable prognosis. The prodromal period of crying followed by forced expiration and apnea (breath-holding) is the single most important clinical feature of a breath-holding attack. The syncopal spell probably occurs through involuntary activation of the Valsalva maneuver, which increases the intrathoracic pressure, interferes with venous return to the heart, and decreases cardiac output, resulting in cerebral ischemia, unconsciousness,and loss of muscle tone. The rapid onset of generalized cyanosis and a loss of consciousness may be associated with generalized clonic jerks,opisthotonos, and bradycardia. The interictal EEG shows normal findings. A thorough examination followed by an explanation of the mechanism of breath-holding spells is reassuring for most parents.Pallid spells typically are initiated by a seemingly innocuous stimulus,such as frustration at play or scolding;a painful experience, such as falling or trapping a finger in the door; a sudden startle; or a minor trauma, such as venipuncture. There is an initial quieting, with breath-holding in the end-expiratory phase,followed by pallor, brief loss of consciousness,loss of muscle tone, and a fall to the ground. Some cases occur without pallor. By the time the parent arrives, the child is lying motionless, with a fixed stare and perioral cyanosis. Tonic rigidity involving clenched hands and jaw and clonic jerking may occur before the episode terminates. Incontinence is rare, and consciousness returns rapidly. Bradycardia with periods of asystole longer than 2 seconds may be documented. The spells are self-limited and have an excellent prognosis;affected children are asymptomatic between the spells and physically and intellectually normal.The episodes are believed to involve abnormal vagal responses that are activated by sudden emotional stimulation. Although the interictal EEG is normal, an abnormal slowing of heart rate in response to ocular compression can be elicited in more than 50% of affected children. The ocular compression test is performed under EEG and ECG surveillance and involves applying firm pressure to both closed eyelids for fewer than 10 seconds. The pressure stimulates the oculocardiac reflex, a response mediated by the brainstem with afferent input from the cornea, iris,and eyelids through the ophthalmic division of the trigeminal nerve and efferent vagal inhibition of the heart. The test normally results in bradycardia or brief reversible asystole. An abnormal response consists of cardiac asystole of at least 3 seconds on ECG, triggering a pallid syncope but no epileptiform discharges on EEG, which confirms the diagnosis and demonstrates the autonomic basis of the condition. The test is generally safe, although a physician should be present and appropriate resuscitation equipment readily available.Vasovagal or neurocardiogenic syncopes are due to autonomic dysfunction and usually occur in adolescents after prolonged motionless standing in a crowded and warm environment. They also are known as vasodepressor,neurally mediated, or reflex syncope or common fainting. The mechanism involves either primary bradycardia with subsequent hypotension, a primary vasodepressor response with hypotension but no bradycardia, or a mixed response with bradycardia and hypotension. Nausea, sweating, lightheadedness,and yawning characteristically precede the episodes. The fall typically is progressive and usually terminates the attack.Some medications that lead to vasodilation may produce syncope. They include angiotensin-converting enzyme inhibitors and volatile nitrites such as amyl nitrite, butyl nitrite, and related compounds found in room deodorizers, which sometimes are used by adolescents and young adults as euphoriants, enhancers of musical appreciation, and aphrodisiacs.Arrhythmogenic or structural heart conditions always must be considered in the differential diagnosis of syncope. Abnormal rhythms may be detected only by electrocardiography,Holter monitoring, exercise testing, or electrophysiologic testing. They may lead to syncope, which can be dangerous when it occurs during swimming or driving, or to sudden death. Arrhythmias may be transient or permanent, congenital(in a structurally normal or abnormal heart), or acquired (rheumatic fever, myocarditis, Lyme disease);caused by a toxin (diphtheria); or follow surgical correction of congenital heart disease (tetralogy of Fallot, double-outlet right ventricle,truncus arteriosus, right ventriculotomy in pulmonary atresia). Electrolyte imbalance (hyperkalemia,hypocalcemia) also may be responsible for arrhythmias, as might certain medications, including digitalis, tricyclic antidepressants, theophylline,antiarrhythmic medications, and illicit drugs.Children who have prolongation of the QT interval are predisposed to episodic ventricular arrhythmias,torsades de pointe, syncope, and generalized seizures. The QT interval is prolonged when the corrected QT interval or QTc (QTc =QT÷ √RR) is above the upper normal limit for age, usually more than 0.44 seconds. The condition may be due to acquired heart disease (myocarditis,mitral valve prolapse, electrolyte abnormalities, drug-induced),but more often is congenital and inherited. In the Jervell and Lange-Nielsen syndrome, the associated sensorineural deafness is inherited as an autosomal recessive trait related to the KVLQT1 gene mutation on chromosome 11; prolonged QT is inherited as an autosomal dominant trait, with the phenotype being more severe if both alleles are mutant. The Romano-Ward syndrome is an autosomal dominant form of the long-QT syndrome and is not associated with deafness. Other genes that have been identified for the prolonged QT syndrome are 7q35 to 36(LQT2), a3p21 to 24 (LQT3), and the LQT4 gene mapped to chromosome 4 (4q25 to 27). The genotype influences the clinical course. The risk of arrhythmias is significantly higher among those who have mutations at the LQT1 or LQT2 locus,but the percentage of lethal cardiac events is significantly higher with mutations at the LQT3 locus. Patients who have the long QT syndrome may develop fatal ventricular arrhythmias at any time, especially if exposed to some medications such as cisapride, antihistamines, macrolide antibiotics, phenothiazines, and antiarrhythmics.Other arrhythmias include the Wolff-Parkinson-White syndrome,with shortened PR interval and delta wave on the proximal part of the QRS complex, which may predispose to episodes of reentrant supraventicular tachycardia via the abnormal pathway. Congenital complete atrioventricular block in children most frequently is caused by autoimmune injury of the fetal conduction system in a mother who has systemic lupus erythematosus. Complete heart block also is seen in patients who have rheumatoid arthritis,dermatomyositis, Sjögren syndrome,complex congenital heart disease, abnormal embryonic development of the conduction system,myocardial tumors, myocarditis,postsurgical repair of congenital heart disease involving the ventricular septum, and the Kearns-Sayre syndrome or who are taking tricyclic antidepressants. The sick sinus syndrome,resulting from abnormalities in the sinus node or atrial conduction pathways, may occur in the absence of congenital heart disease,but it is seen most commonly after surgical correction of congenital heart defects, especially the Mustard procedure for transposition of the great arteries. Supraventricular tachycardias may alternate with bradycardias(bradycardia-tachycardia syndrome), causing palpitations,exercise intolerance, or dizziness. Arrhythmogenic right ventricular dysplasia is a distinct entity predisposing to ventricular arrhythmias.Familial hypertrophic cardiomyopathy,particularly idiopathic hypertrophic subaortic stenosis, may cause exercise-induced syncope by a decreased cardiac output and cardiac ischemia. A careful family history;the association of symptoms with exercise; and suggestive auscultatory,electrocardiographic, and echocardiographic findings usually lead to the diagnosis. Severe pulmonary or aortic stenosis, anomalous origin of the left coronary artery, and pulmonary hypertension also may induce syncope with exercise,although the clinical, electrocardiographic,and echocardiographic findings usually are obvious. Coronary aneurysms complicating Kawasaki disease predispose to coronary heart disease and may manifest with exercise-induced chest pain prior to syncope.Myxomas attached to the inter-atrial septum may cause intermittent obstruction through the mitral valve,explaining the influence of position changes (supine versus erect) on fainting spells. The presence of a murmur, fever, malaise, arthralgias,signs of systemic embolization mimicking endocarditis, rheumatic fever,or systemic lupus erythematosus are suggestive. They may be associated with multiple skin lentiginosis, myxoid fibroadenomas of the breast, and cutaneous myxomas.Syncope may be a manifestation of the hyperventilation syndrome or panic attacks with normocalcemic tetany. The hyperpnea induces a respiratory alkalosis that leads to a drop in the ionized serum calcium. Paresthesias and carpopedal spasms may precede the syncope. A hyperventilation test provokes these episodes,which resolve quickly with rebreathing in a bag.Atonic seizures or “drop attacks”need to be ruled out. They vary considerably in presentation and severity. The “pure atonic” subtype consists of a sudden and complete loss of antigravity muscle tone reminiscent of a marionette whose lifting strings have been cut. They may result in craniofacial injury, skull fracture, facial laceration, or dental trauma. Sometimes they can be one manifestation of the Lennox-Gastaut syndrome, which is characterized by mixed seizures with atonic, atypical absence, myoclonic, or tonic components as well as mental retardation and abnormal EEG results. Findings on physical examination are abnormal in many cases, and the interictal EEG background activity often consists of poorly organized synchronous spike and wave complexes.Hypoglycemia may cause syncope,usually in those who have diabetes. Associated symptoms include weakness, hunger, sweating, agitation,and confusion. The onset is always gradual.Vertebrobasilary vascular spasm in migraine may be heralded by an aura, such as visual changes, prior to the loss of consciousness. Characteristically,the headache persists after consciousness has been regained.Benign paroxysmal vertigo is a self-limited disorder in children younger than 6 years of age who experience sudden falling attacks with dizziness. Consciousness is never lost, and pallor, sweating, nausea,and vomiting may be prominent. The prominent dizziness and vertigo distinguish these attacks from epileptic seizures. Nystagmus is frequent, especially with a rotatory component. There is no evidence of eighth nerve dysfunction,and the EEG results always are normal. Treatment almost always is ineffective.Cataplexy is a loss of muscle tone in response to an emotional precipitant; it may be associated with narcolepsy. The fall is sudden and complete, but unlike atonic seizures,cataplectic attacks are very rare in childhood. They usually begin in the second decade of life in individuals of normal intelligence who manifest a nonparoxysmal EEG recording. Such attacks are always provoked, and consciousness is fully preserved. The sleep EEG and polygraphic sleep studies reveal characteristic“sleep-onset rapid eye movement”patterns. Anticonvulsant therapy offers no benefit.Hysterical syncope is a diagnosis of exclusion, but there usually are specific characteristics. It occurs primarily in adolescents, and the episodes invariably occur in front of an audience. The patient falls gently,without injury or hemodynamic or vasomotor changes. Affected adolescents calmly relate specific details of the episodes, which would not be possible if consciousness actually had been lost. Characteristically,there is a secondary gain by the child following these dramatized episodes.This occurrence is most common among children who have asthma. The marked increase in intrapleural pressure caused by the cough is followed by a decreased venous return to the right heart, a decrease in right ventricular output, reduction of left ventricular filling, and diminished cardiac output, resulting in cerebral hypoperfusion. The coughing paroxysm abruptly awakens the child shortly after the onset of sleep. His or her face becomes plethoric, and perspiration and agitation follow. Generalized muscle flaccidity and clonic muscle contractions that last for several seconds accompany the loss of consciousness. Urinary incontinence is frequent. Recovery begins within seconds, and consciousness usually is restored a few minutes later. The child has no recollection of the attack.The history is critical for making the etiologic diagnosis, selecting confirmatory investigations, and guiding appropriate therapy. The pediatrician must pay particular attention to the time of the day that the episodes occur, the time of the last meal, and details of activities preceding the spell. The occurrence of syncope at rest or when the patient is recumbent suggests seizures or arrhythmias,exercise-associated syncope suggests hypertrophic cardiomyopathy,and syncope in the standing child suggests vasovagal syncope. Syncope without prior warning implies a primary cardiovascular etiology. Particular attention must be paid to any prodromes and associated symptoms (palpitations, tachycardia,chest pain, headache, dyspnea,nausea, sweating, visual or hearing changes). An aura prior to the spell is suggestive of migraine. The duration of loss of consciousness and the injuries that result are also important factors. A history of Kawasaki disease or of cardiac surgery must be considered. The medication history should elicit prescribed,over-the-counter, and illicit drugs or possible intentional or nonintentional exposure to medications taken by other family members. The focus should include but not be limited to antidepressants,angiotensin-converting enzyme inhibitors, and volatile nitrites, such as amyl nitrite, butyl nitrite, and related compounds marketed as room deodorizers.The family history should seek any instances of sudden unexplained death, deafness, arrhythmias, congenital heart disease, seizures, metabolic diseases, or myocardial infarction at a young age. Although a positive family history may support a particular diagnosis, it is also likely that a specific diagnosis made for a child who has syncope will lead to screening of the family for that same inherited condition.Although not always revealing, a thorough physical examination is required and should focus on the neurologic and cardiovascular system. It should include pulse and blood pressure, taken supine and after standing for 5 to 10 minutes. Heart rate should be measured meticulously, and cardiac auscultation should look for murmurs or clicks of outflow tract obstruction. A detailed neurologic examination that includes fundoscopy is mandatory. When indicated, a hyperventilation test will reproduce the hyperventilation-induced syncope.Additional studies are guided by results of the history and physical examination. Even when the history is suggestive, measurement of serum glucose and electrolyte levels is of little value in any but acute episodes.A 12-lead ECG should be employed for evaluation of arrhythmias. A detailed interpretation must include the rhythm, conduction, premature beats, presence of a delta pre-excitation wave, chamber enlargement, and accurate measurement of the PR, QRS, and QT intervals(corrected QTc). Further testing may include exercise tests or 24-hour Holter monitoring with patient-activated monitors whenever possible. A toxicology screen may be indicated if arrhythmias are present. All family members of an affected patient who has prolonged QT interval should undergo 12-lead ECGs. The presence of Q waves in the anterolateral leads may indicate an abnormal origin of the left coronary artery from the pulmonary artery.A cardiology consultation is indicated if a pathologic heart murmur,chest pain preceding syncope,arrhythmia, prolonged QT interval,Q waves on ECG, or a family history of cardiomyopathy or sudden death is documented. Echocardiography with Doppler studies is needed to diagnose structural heart disease. A treadmill exercise test is indicated in exercise-associated syncope. Cardiac catheterization and electrophysiologic testing with invasive monitoring may be needed for some arrhythmias.If the diagnosis of pallid spells by history needs confirmation, an ocular compression test, performed under EEG and ECG surveillance,will be required.Tilt table testing is indicated for patients who have positional syncope with autonomic symptoms. Postural bradycardia and hypotension indicate autonomic imbalance.An EEG is required for patients in whom there is prolonged loss of consciousness, suspected seizure activity, postictal lethargy, drowsiness,or confusion. Neuroimaging studies are not indicated unless an abnormality is apparent on physical examination.The initial step in treatment is reassurance of the parents when indicated. Explaining the mechanisms of syncope in their child is an integral part of management.In the hyperventilation syndrome,reassurance and rebreathing in a bag during an episode usually is all that is required to prevent syncope.When the child has cyanotic breath-holding spells, the parents must be reassured that those attacks are not epileptic or life-threatening and that they will remit spontaneously.Iron therapy has been shown to decrease the incidence of cyanotic breath-holding spells, even when no anemia is present. An explanation of the pathophysiology of pallid spells and reproducing the symptoms during the EEG with ocular compression generally reassures parents. They should be told of the benign prognosis and that anticholinergic therapy is available if the spells became more frequent or severe. Oral atropine sulfate or atropine methonitrate in divided doses, both of which increase the heart rate by blocking the vagus nerve, may be used. Anticholinergic symptoms may require dose reduction. Transdermal scopolamine patches also have been used.For children in whom the syncope is neurally mediated, 1 g/d of oral salt supplementation, with or without fludrocortisone acetate 0.1 mg/kg daily, usually increases the patient’s circulating volume over a few weeks, allowing the blood pressure to be maintained even in the presence of vasodilation.The treatment of arrhythmias must be individualized. Drug therapy,radiofrequency ablation of aberrant conduction pathways, or insertion of a pacemaker depends on the underlying arrhythmia. Children who have cardiac syncope produced by the long QT syndrome should not receive medications such as macrolide antibiotics and cisapride because they may precipitate fatal arrhythmias. Beta blockers may be life-saving. Parents should be taught cardiopulmonary resuscitation because exercise restriction and drug therapy may be ineffective for some children. The treatment of an atrial myxoma consists of surgical excision.For children who have asthma and cough syncope, the only required management is aggressive prevention of bronchoconstriction. Seizures are treated with appropriate anticonvulsants.The differential diagnosis of syncope or fainting is wide-ranging. Some causes are very benign; others have a less favorable prognosis. A careful history is of paramount importance for making the diagnosis. Investigations should be targeted at the likely etiology, and many expensive tests may be unnecessary in most patients. A specific diagnosis provides accurate information to the family, helps to avoid any precipitating factor, and suggests a specific treatment when indicated.