SUMMARY

The Authors examined syncope and breath holding

Introduction

Introduction

Syncope is common in children and most episodes go unreported. Syncope is a sudden, brief, and transient loss of consciousness associated with an inability to maintain normal muscle posture and tone. A reversible, short-lived impairment of cerebral perfusion occurs. Not uncommonly, seizure-like activity may follow a primary syncopal event. Other causes of altered mental status such as shock, vertigo, drug intoxication, sepsis, coma, and seizures must be excluded. The most important task is answering the clinical question Does this represent a potentially lethal condition or one with significant morbidity? Fortunately in most cases of pediatric syncope the answer to this question will be No, but this is precisely the clinical dilemma. Syncope in children must be evaluated carefully because it can be the sole manifestation of a serious underlying condition.

Incidence

The incidence of childhood syncope is undoubtedly underreported. However, at least 15 percent of children will experience an episode of syncope brought to the attention of a physician before they complete adolescence, and approximately 1 percent of pediatric admissions are for the evaluation of a syncopal episode. Vasovagal syncope is estimated to occur in 15 to 25 percent of adolescents.

Etiology

For practical purposes the causes can be divided into cardiac, noncardiac, and unknown etiology. Cardiac causes are always worrisome; noncardiac and unknown causes are less likely to be as serious. Noncardiac causes can be further divided into neurologic, respiratory, autonomic, and metabolic etiologies.

Cardiac Syncope

Cardiac syncope is usually caused by arrhythmias or ventricular outflow obstruction and is the most serious form of syncope in children. Historical factors suggestive of a cardiac etiology include a family history of sudden unexplained death (congenital, prolonged QT interval), prior history of Kawasaki disease (coronary artery insufficiency secondary to aneurysm formation), prior cardiac surgery (complete heart block or other arrhythmia), recent unexplained change in exercise tolerance associated with tachypnea or fever (myocarditis or cardiomyopathy), or known congenital pulmonary outflow obstruction ("tet" spell).

Syncope associated with exercise is worrisome and should bring to mind conditions such as idiopathic hypertrophic subaortic stenosis (IHSS) associated with ventricular outflow obstruction. A complete cardiac evaluation including an electrocardiogram (ECG), chest x-ray, and, if possible, an echocardiogram should be performed in the emergency department. Chest pain in an adolescent is generally not serious, but in a young child palpitations may be reported as chest pain. Particularly if a young child reports chest pain associated with dizziness, lightheadedness, or syncope, an evaluation for an arrhythmia is necessary. A single ECG in the emergency department is not enough; such children should be admitted for monitoring.

Physical findings suggestive of a cardiac etiology include a systolic ejection click, a harsh systolic ejection murmur over the base of the heart radiating to the carotids, and a palpable thrill in the suprasternal notch (all suggestive of aortic stenosis). A systolic murmur enhanced by standing or the Valsalva maneuver may be due to IHSS. Any new onset murmur heard after a child has had a syncopal event requires evaluation. In addition, a child who has the findings of congestive heart failure, myocarditis, or cardiomyopathy (tachypnea, enlarged liver, enlarged heart, rub, rales) needs a complete cardiac evaluation. Finally, recurrent syncope of unexplained etiology, even with a negative emergency department evaluation, should be referred to a pediatric cardiologist.

Neurologic Syncope

Seizures are the primary cause of neurologic syncope. Distinguishing between a seizure disorder and the seizure-like activity that can be seen after a breath-holding spell is sometimes difficult.

In a child with syncope, the period of unconsciousness is brief, lasting only seconds, followed by a rapid recovery to normal mental status. Seizures, in contrast, result in prolonged loss of consciousness (at least several minutes) with a delay in return to the patient's normal baseline mental state. Abnormal motor activity is more likely to be seen with seizures. When associated with nonseizure syncopal episodes such as breath-holding spells, such activity is brief, lasting less than a minute. Incontinence generally does not occur with nonneurologic syncope. When present, a seizure disorder is more likely. Also a reported aura, such as an unusual taste or smell, suggests a seizure disorder.

A family history of seizures is problematic in differentiating syncope from seizures. Breath-holding spells are commonly mistaken for seizures. In addition, seizures are a common affliction, affecting about 2 percent of the population. A family history of seizures, although important, is not generally helpful in determining the etiology of a syncopal episode.

Finally, any child with a focal physical finding after a syncopal episode should be evaluated thoroughly for a seizure disorder, neurotrauma, or unsuspected central nervous system lesion or infection.

Respiratory Syncope

Excluding breath-holding spells, which will be discussed in a separate section, the most common etiology of syncope caused by a ventilation abnormality in children is hyperventilation. This excludes syncope due to pulmonary disorders resulting in prolonged hypoxia, such as severe pneumonia or severe asthma.

Hyperventilation is something most children do at one time or another because of pain, anxiety, or, in the adolescent, as a "dare" or in an effort to hold one's breath longer. The physiology of hyperventilation causing syncope is not completely understood. Hyperventilation induces hypocapnia, which in turn results in vasoconstriction of the cerebral arteries. This seems to reduce the delivery of oxygen and glucose to the brain, thus resulting in syncope.

Prolonged, severe, frequent coughing may also result in syncope. The classic example of this phenomenon is pertussis. In an infant, the persistent coughing prevents adequate oxygenation and ventilation from occurring and is perceived as apnea; in the older child, a brief episode of syncope may be the manifestation of severe cough-induced hypoxia.

Autonomic Syncope

Vasovagal, or vasodepressor, syncope is by far the most common cause of syncope in children, accounting for at least 50 percent of cases. Episodes of vasodepressor syncope usually occur in response to sudden emotional stress in a setting of perceived threats or injuries. The classic example is an adolescent who faints at the sight of blood or who witnesses someone undergoing a painful procedure in the emergency department. Such episodes are more likely to occur if one is tired, hungry, or just recovering from a recent illness. Environmental conditions such as crowding or a warm enclosed space also predispose to vasodepressor syncope. Prodromal symptoms include pallor, diaphoresis, and nausea. Witnesses to the event will sometimes report mydriasis. As mentioned earlier when discussing the distinctions between syncope and seizures, the event is usually sudden in onset, lasts less than 1 min, and the patient recovers a normal mental status rapidly, although symptoms such as nausea, weakness, pallor, and diaphoresis may persist. Tonic-clonic activity of very brief duration and, rarely, incontinence have been reported with vasodepressor syncope but should alert one to the possibility of a seizure disorder.

The pathophysiology of vasodepressor syncope is well described by Scott. "A decrease in peripheral vascular resistance leads to a drop in arterial pressure and cerebral perfusion. Decreased venous return results in a relatively empty ventricle. Vigorous myocardial contraction against an empty ventricle initiates a prominent vagal reflex, resulting in hypotension or bradycardia. While heart rate typically does increase prior to an episode, cardiac output does not increase in response to the fall in pressure, which may be related to decreased venous return. Bradycardia typically occurs late and is not usually a causal factor because neither atropine nor cardiac pacing is sufficient to abort the episode. Hyperventilation may also occur, aggravating the cerebral hypoperfusion."

Another form of autonomic syncope is that due to orthostatic hypotension. Upon standing there is a gravity-mediated loss of blood from the brain and thorax, with a net flow of intravascular volume to the peripheral vasculature. Venous return is reduced to the right ventricle, with a decline in ventricular filling. Reduced ventricular filling in turn is sensed by mechanoreceptors, which cause an afferent neural output interpreted by the brainstem as a hypotensive state. To correct the situation, a neurally induced increase in sympathetic output occurs, resulting in an increase in heart rate and blood pressure. In the healthy pediatric patient, orthostatic hypotension is uncommon because this reflex is unravaged by aging and subsequent degenerative coronary and neurovascular changes. However, children who are anemic (i.e., reduced oxygen-carrying capacity) or those who are hypovolemic (possibly due to a gastroenteritis or excessive sweating without adequate volume replacement) may become syncopal upon standing, even though their cardiac and neural mechanisms for compensating are intact. Any pediatric patient with a history of so-called orthostatic hypotension should be investigated thoroughly for an underlying cause such as anemia or hypovolemia and for rare pediatric problems such as degenerative vascular and neurologic diseases.

Other causes of autonomic syncope have been described. "Hair grooming" syncope, carotid sinus syncope due to wrestling, and "parade ground" syncope are reported. These probably share a common pathophysiology with vasodepressor or orthostatic syncope but have unusual triggering events.

Metabolic Syncope

Metabolic causes of syncope in children are uncommon. Although, usually in frustration, some physicians will ascribe syncope to hypoglycemia (not eating for a long time before the episode), hypoglycemia is a rare cause of syncope except in the insulin-dependent diabetic. Of more concern is metabolic syncope occurring as a result of drug ingestion. Alcoholism is unfortunately a major problem in adolescents, and any adolescent with a history of unexplained "black-out" spells should be questioned carefully about drug use, especially ethanol.

Syncope caused by metabolic derangements should be relatively easy to suspect by history. Unlike cardiac or vasodepressor syncope, for example, the prodrome of metabolic syncope is gradual in onset, with symptoms such as weakness, diaphoresis, confusion, and hunger. These symptoms are unrelated to position and are not usually associated with blood pressure or pulse changes.

Hysteria

Adolescents are particularly prone to hysterical syncope. Perhaps a "swoon" would be better terminology since hysterical syncope involves no change in vital signs or temporary derangement of cerebral perfusion. A swoon occurs in front of an audience, the patient remains calm, is uninjured, and falls gracefully to the floor. Secondary gain and attention-getting are usually entwined with the swooning event. It is a diagnosis of exclusion, however, as, needless to say, histrionic adolescents can have serious cardiac arrhythmias. As usual a careful history is imperative when making the diagnosis.

BREATH HOLDING

Breath-holding spells are a form of autonomic syncope most common in infancy and early childhood. Because they are frequently dramatic and are commonly misdiagnosed as seizures, resulting in unnecessary workup and parental anxiety, they are discussed separately.

Historically breath-holding spells have been viewed as volitional on the part of the child; a manifestational of the spoiled brat syndrome. Children with such spells have been described as stubborn, disobedient, aggressive, and attention-seeking. Like most medical events in pediatric patients ascribed to willful behavior, breath-holding spells are not the result of a personality disorder. They are not volitional and are not associated with temperamentally difficult children. The tendency for parents to believe otherwise, however, is quite strong since most breath-holding spells are associated with an outburst of crying, anger, or pain, followed by a brief period of unconsciousness and, at times, some tonic-clonic motor activity.

Two types of breath-holding spells have been described: cyanotic and pallid. The distinction is probably not clinically significant. Each type is the result of transient cerebral anoxia. The cyanotic type occurs after vigorous crying with its consequent oxygen desaturation and is associated with vagally mediated hypotension. The pallid type is more likely to occur after a sudden unexpected fright or injury (such as a bump on the head) and is caused by a vagally mediated severe bradycardia or brief period of asystole. Cyanotic breath-holding spells are more common.

The history is paramount in helping to distinguish a breath-holding spell with a brief period of tonic-clonic motor activity from a seizure. If there is no prodrome of injury, sudden fright, vigorous crying, or painful stimuli, a seizure is more likely. On the other hand, if such prodromal stimuli are present, parents can be reassured that their child had a breath-holding spell, is not doing it on purpose, and is not a spoiled or bad child. As with uncomplicated febrile seizures, the parents need to be reassured that no brain damage has occurred and that their child should remain developmentally normal. There is a propensity for breath-holding spells to recur in children who already have had them, and a genetic predisposition to them exists. It is wise to obtain an ECG in any uncertain situation to eliminate conduction defects, such as prolonged QT interval, as a cause of the episode.

EMERGENCY DEPARTMENT EVALUATION

Most causes of syncope can be diagnosed from the history and physical examination. When the cause is obvious, as in most cases of vasodepressor syncope and breath-holding spells, laboratory testing is not necessary. For example, when a 16-year-old is donating blood for the first time and faints, rest and reassurance are the treatment of choice.

If one suspects cardiac syncope, testing for an arrhythmia, conduction abnormality, ventricular outflow obstruction, and underlying cardiac disease is in order. An ECG and chest x-ray should be done in the emergency department. An echocardiogram and Holter monitoring may need to be arranged on an outpatient basis. A referral to a pediatric cardiologist is necessary. If an arrhythmia is strongly suspected but not seen on the ECG, the patient should be considered for admission.

In cases of suspected autonomic syncope when the history is not clear-cut, referral for tilt testing should be considered. The tilt test entails placing the patient on a tilt table and passively rotating the patient 60° to 90° from the supine position and leaving the patient upright for 5 to 10 min. Vital signs are recorded throughout the maneuver, and the patient is returned to the supine position. Since both heart rate and blood pressure have been observed to increase secondary to augmented catecholamine production just prior to vasodepressor syncope, an infusion of a catecholamine such as isoproterenol is started to mimic these conditions. The tilt is repeated with the infusion. Only a small percentage of vasodepressor-prone patients have symptoms with the passive tilt, but the yield is markedly increased with the catecholamine infusion. The sensitivity of this test in children is about 80 percent, but unfortunately it is not 100 percent specific.

Tests such as glucose, electrolytes, drug screens, and hematocrit and hemoglobin need only be done if the history and physical examination are suggestive, as in the case when pallor or orthostatic hypotension or insulin-dependent diabetes is present. Probably the most commonly performed unnecessary test is the serum glucose, perpetuating the mistaken notion that a low blood sugar is the cause of a child's problem. CT scans are seldom helpful in the emergency department. EEGs may be indicated, along with a referral to a pediatric neurologist, when tonic-clonic activity is observed or return to consciousness is prolonged after an apparent syncopal event.

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