Description

• Abrupt, transient loss of consciousness caused by cerebral hypoperfusion, characterized by unresponsiveness and loss of postural tone with spontaneous recovery
• System(s) affected: cardiovascular, nervous

Epidemiology

Etiology and Pathophysiology

• Systemic hypotension secondary to decreased cardiac output and/or systemic vasodilation leads to a drop in cerebral perfusion and resultant loss of consciousness. Syncope can be divided into cardiac and noncardiac etiologies:
  • Cardiac
    • Arrhythmogenic: bradyarrhythmias (e.g., sinus node dysfunction, heart block), tachyarrhythmias (e.g., ventricular tachycardia [VT], ventricular fibrillation, supraventricular tachycardia), and channelopathies (e.g., Brugada syndrome, long QT syndrome)
    • Structural: aortic stenosis, pulmonary embolism, hypertrophic cardiomyopathy, myocardial infarction, coronary anomalies, tamponade, vascular dissection
  • Noncardiac
    • Reflex (neurally mediated) syncope (NMS): vasovagal (inappropriate vasodilation leading to neurally mediated systemic hypotension and decreased cerebral blood flow); carotid sinus hypersensitivity; situational (micturition, defecation, cough, pain, emotions, hair combing)—most common cause in adult cases
    • Orthostatic hypotension (OHT): volume depletion, pregnancy, anemia, medications
    • Drug/alcohol induced
    • Primary autonomic failure: pure autonomic failure, Parkinson disease
    • Secondary autonomic failure: diabetes, amyloidosis
• The vast majority of pediatric cases represent benign alterations in vasomotor tone.

Risk Factors

• Heart disease (acquired or structural)
• Dehydration
• Medications (e.g., antihypertensives, antiarrhythmics, diuretics)
• Presence of a primary autonomic degenerative disorder

General Prevention

Preventative measures are aimed at addressing underlying etiology. Common measures include maintaining adequate hydration and salt intake, moving slowly from sitting to standing position, and lying down flat when experiencing light-headedness.