Chapter 127: Syncope, Dysrhythmias, and ECG Interpretation in Children

SYNCOPE

INTRODUCTION

Syncope, or fainting, is the abrupt loss of consciousness and postural tone resulting from transient global cerebral hypoperfusion, followed by complete spontaneous recovery.¹ In children, this process is usually benign, but it can be a symptom of serious cardiac, neurologic, or metabolic pathology. Assessing syncope in children is complicated by the variability of symptoms and lack of a gold standard for diagnosis. The primary goal of the emergency physician is to differentiate children with benign syncope from those with serious disease.

EPIDEMIOLOGY

Syncope is a presenting symptom in 1% to 3% of pediatric emergency visits^2,3 and 6% of hospital admissions⁴ and is more common in adolescents than in younger children. Between 15% and 25% of adolescents experience at least one episode of syncope.⁵ Only 10% to 15% of patients evaluated in the pediatric ED for syncope are ultimately diagnosed with a serious illness.⁶ About 80% of pediatric fainting is neurocardiogenic (previously known as vasovagal) syncope. Neurologic disorders, mostly seizures, account for about 10% of episodes, and 2% to 3% are due to cardiac pathology.^6,7

PATHOPHYSIOLOGY

Neurocardiogenic syncope, or neurally mediated syncope, is a mix of vasodepressor syncope (due to vasodilation) and cardioinhibitory syncope (due to vagal stimulation). Neurocardiogenic syncope can be triggered by a variety of conditions in which a reduction in venous return enhances vagal tone causing hypotension, bradycardia, and reduced cerebral perfusion. Recovery of consciousness occurs over 1 to 5 minutes, but symptoms of nausea and fatigue can last for several hours.

Cardiac syncope occurs when there is an interruption of cardiac output due to an intrinsic cardiac abnormality. These causes are divided into tachydysrhythmia, bradydysrhythmia, outflow obstruction, and myocardial dysfunction.

Any event that causes sufficient cerebral hypoperfusion can lead to sudden death. The most common causes are seizures, cardiac diseases, and metabolic diseases. Little is known about the most common dysrhythmias that cause sudden death in children, because such cardiopulmonary arrests are unwitnessed. In children, bradycardic or asystolic arrests are thought to be most common, especially in infants <1 year, but ventricular fibrillation is also seen in older children, although at much lower rates than in adults.⁸

CLINICAL FEATURES

Syncope is characterized by the sudden onset of falling with a brief episode of loss of consciousness. Other associated symptoms or signs are usually related to the cause for the syncopal event. Two thirds of children experience a prodrome of light-headedness or dizziness before the event,⁵ and vertigo is uncommon. Involuntary motor movements, related to cerebral hypoxia, occur with all types of syncopal events but are more common with seizures. A careful history can usually differentiate tonic-clonic movements associated with seizures from the myoclonus of cerebral hypoxia, by their onset after loss of consciousness, less rhythmic nature, and shorter duration.

RISK FACTORS FOR A SERIOUS CAUSE OF ...