Syncope, Reflex (Vasovagal Syncope)


A reversible loss of consciousness and postural tone secondary to systemic hypotension and cerebral hypoperfusion due to vasodilation and/or bradycardia (rarely, tachycardia) with spontaneous recovery and no neurologic sequelae; the term syncope excludes seizures, coma, shock, or other states of altered consciousness.


  • Derived from the Greek syncopa, “to cut short”
  • Sudden, transient loss of consciousness characterized by unresponsiveness, falling, and spontaneous recovery
  • Common cause of syncope in all age groups, especially in patients with no evidence of neurologic or cardiac disease
  • Five main types of syncope: vasovagal or neurocardiogenic syncope, situational syncope, orthostatic hypotension, carotid sinus hypersensitivity, and glossopharyngeal/trigeminal neuralgia syncope (uncommon) (1)


  • Mortality: cardiac-related syncope 20–30% and 5% in idiopathic syncope
  • Age: any age


  • Ranges from 7% in children aged <18 years and 15% in adults aged >70 years
  • 36–62% of all syncopal episodes
  • 30% recurrence rate

22% in the general population

Etiology and Pathophysiology

Cause: an abnormal response of the normal mechanisms that maintain BP in an upright posture; vasovagal syncope typically occurs when an individual is an upright position for a comparatively long duration (up to ≥10 minutes), compared with orthostatic hypotension which generally develops in a short period (such as a quick positional change).

  • In normal individuals, upright posture results in venous pooling and transient decrease in BP.
  • Neurally induced syncope may result from a cardioinhibitory response, a vasodepressor response, or a combination of the two.
  • Increased cardiovagal tone leads to bradycardia or asystole, and decreased peripheral sympathetic activity leads to venodilation and hypotension (2).
  • Vasovagal syncope usually has a precipitating event, often related to fright, pain, panic, exercise, noxious stimuli, or heat exposure (2).
  • Carotid sinus syncope is precipitated by position change, turning head, or wearing a tight collar (possible neck tumors or surgical scarring).
  • Situational syncope is related to micturition, defecation, postexercise, coughing, or swallowing.
  • Glossopharyngeal syncope is related to throat or facial pain.

Vasovagal syncope is associated with certain genetic markers, particularly involving serotonin and dopamine signaling (3).

Risk Factors

  • Low-resting BP
  • Age: older age
  • Prolonged supine position with resulting deconditioning of autonomic control

General Prevention

Avoid precipitating events or situations. Optimize diabetes control, use of elastic stockings, and adequate hydration.

Commonly Associated Conditions

  • Cardiopulmonary disorders: CHF, MI, arrhythmias, hypertrophic obstructive cardiomyopathy, HTN, pulmonary embolism (PE)
  • Neurologic disorders: autonomic dysfunction, Shy-Drager syndrome, Parkinson disease, multiple system atrophy, transient ischemic attack, vertebrobasilar insufficiency, peripheral neuropathy
  • Psychiatric disorders:
    • Generalized anxiety disorder
    • Panic disorder
    • Major depression
    • Alcohol dependence

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