vasovagal reaction (fainting)

Introduction

A form of syncope.

Etiology

• precipitating factors
  • fear
  • pain
  • emotional stress
  • prolonged standing
• predisposing factors
  • fatigue
  • hunger
  • hot, humid environment
  • bed rest

Epidemiology

• occurs less frequently in the elderly

Pathology

• orthostatic stress
  • pooling of blood in the lower extremities (500-800 mL)
• compensatory increased adrenergic tone
• parasympathetic reflex
  • decreased preload results in stimulation of mechano-receptors in the left ventricular wall by vigorous cardiac contraction against a relatively empty ventricle
  • signals sent to midbrain from left ventricular mechano-receptors resulting in withdrawal of peripheral sympathetic tone & augmentation of vagal tone
  • sudden peripheral vasodilatation, especially in skeletal muscle without compensatory rise in cardiac output
    • decrease in reflex peripheral vasoconstriction
  • drop in blood pressure
  • bradycardia may occur

Physical examination

• orthostatic blood pressure examination

Clinical manifestations

• prodrome
  • restlessness
  • weakness
  • pallor
  • nausea
  • salivation
  • sweating
  • yawning
• generally occurs when standing, possibly sitting
• recovery
  • prompt return of consciousness when supine
  • pallor, nausea, weakness & slight confusion may persist for a short time
• a few clonic jerks or urinary incontinence may be noted

Diagnostic procedures

• electrocardiography (all)
• tilt table testing for multiple episodes of syncope suspected to be of vasovagal origin

Differential diagnosis

• orthostatic syncope
  • rapid onset syncope after positional changes (GRS11)
    • syncope after prolonged standing more consistent with vasovagal syncope
  • autonomic dysfunction is more prevalent with orthostatic syncope

Management

• place patient in supine position or with head in dependent position (below heart, i.e. between legs)
• prophylaxis:
  • drinking 16 oz (1 pint) of water prior to risky setting
  • compression stockings reduce pooling of blood in the lower extremities
  • first line
• muscle-tensing exercises when a prodrome is sensed
  • hand-clasping with interlocking fingers while pulling the elbows in opposite directions
  • squeezing a ball or other object
  • standing leg cross-over firmly pushing in thighs while tensing abdominal muscles
  • counterpressure maneuvers include leg crossing, limb &/or abdominal contraction & squatting
  • first line
• pharmacotherapy
  • see neurocardiogenic vasopressor dysfunction
  • fludrocortisone may benefit some patients
  • midodrine 2.5 mg BID - 10 mg TID may be effective for recurrent vasovagal syncope
    • failure of first line therapy
    • without hypertension, heart failure, or urinary retention
  • beta-blockers for recurrent vasovagal syncope in patients > 42 years
• ablation of ganglionated plexus in the left atrium & right atrium may reduce recurrence of vasovagal syncope
• prognosis:
  • reassurance for young patients
  • worse for elderly
    • 16% have major morbidity/mortality within 6 months

More general terms

• neurocardiogenic vasopressor dysfunction

Additional terms

• syncope

Patient information

vasovagal reaction (fainting) patient information