Description

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

Epidemiology

Prevalence

• Approximately 20–35% of adults report ≥1 episode during their lifetime; 15% of children <18 years of age
• The prevalence in institutionalized elderly (>75 years of age) is 23%.

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.

• Cardiac obstructions to outflow (e.g., pulmonary embolus [PE], hypertrophic cardiomyopathy, aortic stenosis)
• Cardiac arrhythmias
• Noncardiac
  • Reflex-mediated vasovagal (neurally mediated syncope [NMS]): inappropriate vasodilation leading to neurally mediated systemic hypotension and decreased cerebral blood flow; 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
  • Secondary autonomic failure: diabetes, amyloidosis
  • Carotid sinus hypersensitivity
• 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