Syncope

Chapter 39 Syncope



Norman B. Berman




ETIOLOGY



What Is Syncope and How Common Is It?


Syncope is the sudden loss of consciousness and posture and is common, particularly in adolescents. Syncope accounts for 3% of visits to emergency departments, but many episodes of syncope never come to medical attention. Presyncopal symptoms of dizziness and lightheadedness without loss of consciousness are even more common. Syncope is generally benign; the clinical importance of syncope relates to the risk of associated injury and of underlying heart disease as the cause.



What Causes Syncope?


Neural mediated hypotension causing a transient decrease in cerebral blood pressure is the most common cause of syncope. Neurally mediated syncope often begins with decreased systemic venous return from prolonged standing. This causes an adrenergically driven increase in heart rate and contractility. In susceptible individuals, this can lead to stimulation of a vagally mediated reflex bradycardia, a drop in blood pressure and cerebral perfusion, and then syncope. Vagal stimulation is also the cause of syncope that occurs with painful stimuli, carotid sinus sensitivity, and other variants. Direct orthostatic hypotension is a common cause of presyncopal symptoms but less commonly causes frank syncope.



What Are the Cardiac Causes of Syncope?


There are relatively few primary cardiac causes of syncope. Anything causing severe left ventricular outflow obstruction can cause syncope, such as aortic stenosis or hypertrophic obstructive cardiomyopathy. Rare cardiac causes of syncope include congenital coronary artery anomalies, cardiac tumors, and pulmonary hypertension. Cardiac arrhythmias are another important cause of syncope. Any arrhythmia causing profound bradycardia (sinus node dysfunction, complete atrioventricular block) or tachycardia (supraventricular tachycardia, Wolf-Parkinson-White syndrome, ventricular tachycardia) can cause syncope. Ventricular tachycardia is uncommon in children, but when present, associated problems such as long QT syndrome and cardiomyopathies must be considered.



What Are Neurologic Causes of Syncope?


Neurologic problems, specifically seizures, are often considered in the differential diagnosis of syncope but in fact are quite rare. Seizures (Chapter 37) can appear similar to a syncopal event, but generally can be differentiated from syncope with a detailed history of the event. Seizures causing a loss of tone are rare. Generalized tonic seizures can appear similar to syncope but are differentiated by the history of stiffening.



EVALUATION



What Happens in Syncope?


Children describe the symptoms leading to a syncopal event in remarkably similar terms: An initial feeling of dizziness or lightheadedness is followed by a sensation of warmth, then progresses to visual disturbances, such as blurring or graying of the vision, and then to completely “blacking out” while maintaining the ability to hear things. Patients often do not remember beyond this point and will next remember awakening on the ground. Observers will report that the child or adolescent looked pale and was unresponsive to verbal stimuli, then slumped limply or fell to the ground. Typical syncope is brief, lasting only seconds after the patient loses posture and falls to the ground. Occasionally the patient may be observed having tonic-clonic type movements at the time of loss of consciousness.

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Jun 19, 2016 | Posted by in PEDIATRICS | Comments Off on Syncope

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