Syncope, Reflex (Vasovagal Syncope)
BASICS
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.
DESCRIPTION
- 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)
EPIDEMIOLOGY
- Mortality: cardiac-related syncope 20–30% and 5% in idiopathic syncope
- Age: any age
Incidence
- Ranges from 7% in children aged <18 years and 15% in adults aged >70 years
- 36–62% of all syncopal episodes
- 30% recurrence rate
Prevalence
22% in the general population
ETIOLOGY AND PATHOPHYSIOLOGY
Cause: an abnormal response of the normal mechanisms that maintain blood pressure (BP) in an upright posture; vasovagal syncope typically occurs when an individual is in 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, cough, or swallow.
- Glossopharyngeal syncope is related to throat or facial pain.
Genetics
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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