Syncope, Reflex (Vasovagal Syncope)

BASICS

Definition: Sudden, reversible loss of consciousness/postural tone due to systemic hypotension and cerebral hypoperfusion (vasodilation and/or bradycardia), with spontaneous recovery and no neurologic sequelae.
Excludes: Seizures, coma, shock, or other states of altered consciousness.

Age: Any; common in all age groups, especially without cardiac/neurologic disease
Incidence:
Children <18 yrs: 7%
Adults >70 yrs: 15%
36–62% of all syncopal episodes
30% recurrence rate
Prevalence: 22% of the general population
Mortality: Cardiac-related syncope 20–30%; idiopathic syncope 5%

Main types of syncope:
Vasovagal (neurocardiogenic)
Situational (micturition, defecation, cough, postexercise, swallowing)
Orthostatic hypotension
Carotid sinus hypersensitivity
Glossopharyngeal/trigeminal neuralgia syncope (rare)
Pathophysiology:
Abnormal response of mechanisms maintaining BP upright
Vasovagal: upright posture (≥10 min) → venous pooling → transient ↓BP
Cardioinhibitory response (bradycardia/asystole), vasodepressor response (vasodilation), or both
Precipitated by fright, pain, panic, exercise, noxious stimuli, heat
Genetics: Serotonin/dopamine signaling genes implicated

Cardiopulmonary: CHF, MI, arrhythmias, HOCM, HTN, PE
Neurologic: Autonomic dysfunction, Parkinson, multiple system atrophy, TIA, vertebrobasilar insufficiency, peripheral neuropathy
Psychiatric: Anxiety, panic, depression, alcohol dependence

Prodrome: Blurred vision, palpitations, nausea, warmth, diaphoresis, light-headedness, fatigue
Phases: Prodrome → LOC → postsyncope (may be prolonged, nausea, pallor, diaphoresis, but no neuro deficit/confusion)
Precipitating event: Panic, pain, emotion, exercise, micturition, defecation, cough, swallowing
Position: Often prolonged standing; resolves supine
Special types:
Carotid sinus: neck turning, tight collar
Situational: micturition, defecation, cough
Glossopharyngeal: facial/throat pain
Pregnancy: Movement from supine to lateral decubitus/upright

Seizure, arrhythmia, hypoglycemia, cardiac syncope, cerebrovascular syncope, orthostatic hypotension, drop attacks, psychiatric

Initial:
Blood glucose (hypoglycemia)
ECG (arrhythmia, cardiac cause)
CBC (anemia)
Further testing as needed: Head CT/MRI/carotid US (neurologic cause); Holter if cardiac suspicion
Special tests:
Head-up tilt table (recurrent syncope or with injury/risk to others): contraindicated in cardiac/neurovascular disease or pregnancy
Carotid sinus massage (monitored setting only): contraindicated if carotid disease
Psychiatric evaluation for anxiety, depression, alcohol abuse

Identify/avoid triggers
Nonpharmacologic first:
Counseling, coping skills
Increased salt/fluid intake
Moderate exercise, isometric contractions (leg crossing, buttocks clenching, gripping hands, tensing arms)
Tilt-table training (enforced upright posture)

Pacemaker: Frequent, refractory vasovagal syncope (prevents bradycardia/asystole during episodes)

No proven therapies. Nutrition/supplements (omega-3, multivitamins, CoQ10, L-carnitine, lipoic acid, L-arginine), herbs (green tea, bilberry, ginkgo), homeopathy (carbo vegetabilis, opium, sepia). Acupuncture may precipitate fainting.

Indications:
Severe CAD or structural heart disease
Arrhythmic syncope (abnormal ECG)
Severe anemia/electrolyte abnormalities
Family history sudden death
Management: Isotonic fluids, monitoring, discharge when stable/workup complete

Diet: Increased salt and fluid (if not contraindicated)
Education: Avoid triggers (dehydration, alcohol, warm environments, tight clothing, prolonged standing); recognize presyncopal symptoms, use preventative behaviors (lie down)

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Rocha BML, Gomes RV, Cunha GJL, et al. Rev Port Cardiol (Engl Ed). 2019;38(9):661-673.
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Sheldon R, Faris P, Tang A, et al. Ann Intern Med. 2021;174(10):1349-1356.