Syncope, Reflex (Vasovagal Syncope)

Descriptive text is not available for this image 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 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, 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, 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

Descriptive text is not available for this image Diagnosis

History

  • History of syncope during or immediately after exertion is concerning for cardiac syncope.
  • Neurally mediated syncope is preceded by blurred vision, palpitations, nausea, warmth, diaphoresis, or light-headedness, or there may be history of nausea, warmth, diaphoresis, or fatigue after syncope.
  • Vasovagal syncope
    • Three phases: prodrome, loss of consciousness, and postsyncope
    • Precipitating event or stimulus is usually identified, such as panic, fright, pain, or exercise.
    • May be postexertional in athletes (diagnosis of exclusion)
    • Position: can be preceded by prolonged standing but can occur from any position; generally resolves when the patient becomes supine
      • Preceding events: as discussed above
      • Prodrome: as listed above for neurally mediated syncope
    • Duration: generally brief (seconds to minutes)
    • Recovery: may be prolonged with persistent nausea, pallor, and diaphoresis but without neurologic change or confusion
  • Carotid sinus syncope is precipitated by position change, after turning head, or wearing a tight collar.
  • Situational syncope is related to micturition, defecation, or coughing.
  • Glossopharyngeal syncope (less common) is related to throat or facial pain.
    • Precipitating events or situations may include panic, pain, exercise, micturition, defecation, coughing, or swallowing.
  • Pregnant women can have reflex syncope when moving from supine to lateral decubitus or upright positions.

Physical Exam

  • Vital signs, including orthostatics and bilateral BP
  • Cardiac exam: volume status, murmurs, rhythm, carotid bruits
  • Neurologic exam: signs of focal deficit
  • Assess for occult blood loss.
  • Dix-Hallpike if benign paroxysmal vertigo is suspected

Differential Diagnosis

  • Seizure
  • Arrhythmia
  • Hypoglycemia
  • Cardiac syncope
  • Cerebrovascular syncope
  • Orthostatic hypotension
  • Drop attacks
  • Psychiatric illness

Diagnostic Tests & Interpretation

Guided by history and physical, includes basic tests to rule out three primary causes of syncope: hypoglycemia, arrhythmia, and anemia

Initial Tests (lab, imaging)

  • Blood glucose (hypoglycemia)
  • ECG should be ordered for all patients. Abnormal ECG findings are common in patients with cardiac syncope (arrhythmia).
  • CBC (rule out anemia)
  • Head CT, MRI/MRA, carotid ultrasound only if history or physical exam suggests a neurologic cause
    • Radiology studies are not indicated for insignificant trauma in the presence of a normal neurologic exam.

Follow-Up Tests & Special Considerations

  • 24-hour Holter monitoring only if a high probability of cardiac cause and/or abnormal ECG findings is present
  • A low hemoglobin without obvious cause of bleed warrants stool guaiac, head CT (rule out subarachnoid hemorrhage), abdominal CT (rule out retroperitoneal bleed)
  • Negative imaging prompts workup for alternative causes.
  • Stroke, bleed, or carotid stenosis require appropriate disease-oriented management.
  • EEG only if history or physical exam suggests seizure
  • Implantable loop recorder

Diagnostic Procedures/Other

  • Head-up tilt table testing:
    • Contraindicated in patients with known cardiac or neurovascular disease or in pregnancy
    • Indicated for recurrent syncope or single episode accompanied by injury or risk to others (e.g., pilots, surgeons)
    • Uses positional changes to reproduce symptoms
    • Positive test diagnostic for vasovagal syncope
  • Carotid sinus massage, only in a monitored setting (i.e., BP and HR monitoring, IV access):
    • Contraindicated in patients with carotid disease (careful auscultation prior to massage is essential)
    • Pressure at the angle of the jaw for 5 seconds with simultaneous ECG monitoring
    • Positive tests (causing syncope or cardiac pause >3 seconds) are diagnostic of carotid sinus syncope.
  • Psychiatric evaluation: to rule out anxiety, depression, and alcohol abuse

Descriptive text is not available for this image Treatment

Therapy is primarily for recurrent syncope. Situational syncope does not warrant specific treatment.

General Measures

Identify and avoid precipitating events or situations.

Medication

First Line

Nonpharmacologic treatment

  • Patient counseling
    • Increased salt and fluid intake
  • Moderate exercise training
    • Isometric muscle contractions
      • These maneuvers increase cardiac output and arterial blood pressure.
    • Yoga
  • Tilt-table training
    • Progressively prolonged periods of enforced upright posture

Second Line

  • α-Agonists mainly used for orthostatic hypotension
    • Midodrine is commonly used, particularly in younger, healthy patients with a high “syncope burden” (4). It increases peripheral vascular resistance and venous return. Side effects include HTN, paresthesia, urinary retention, “goose bumps,” hyperactivity, dizziness, tremor, and nervousness.
  • SSRIs: Paroxetine and fluoxetine are useful in treating neurocardiogenic/vasovagal syncope.
    • Serotonin affects BP and HR via the central nervous system. Serotonin decreases a sympathetic withdrawal response to rapid increases in serotonin levels.
    • Side effects include weight gain, nausea, anxiety, sexual dysfunction, and insomnia.
  • Mineralocorticoids: Fludrocortisone has been found helpful mainly in orthostatic hypotension.
    • Helpful in renal sodium absorption and increasing the vasoconstrictive peripheral vascular response
    • Adverse reactions include fluid retention, HTN, CHF, peripheral edema, and hypokalemia.
  • β-Blockers: metoprolol, atenolol, or pindolol mainly for postural orthostatic tachycardia syndrome (POTS)
    • Block peripheral vasodilators and ventricular mechanoreceptor stimulation
    • Stabilization of HR and BP
    • Side effects: hypotension and bradycardia (with worsening of syncope), fatigue, depression, and sexual dysfunction
    • Contraindicated in asthma

Issues for Referral

Neurology or cardiology, as needed

Additional Therapies

Use of support/pressure stockings

Surgery/Other Procedures

Pacemaker placement may be of use in patients with frequent neurocardiogenic/vasovagal syncope that is refractory to other therapies.

  • Prevents prolonged bradycardia or asystole during syncopal episodes
  • Long-term effect
  • Invasive placement procedure

Complementary & Alternative Medicine

Treatments for underlying heart disease or precipitating factors (e.g., anxiety); none are proven therapies.

  • Nutrition and supplements: omega-3 fatty acids, multivitamin, CoQ10, acetyl-L-carnitine, α-lipoic acid, and L-arginine
  • Herbs: green tea (Camellia sinensis), bilberry (Vaccinium myrtillus), ginkgo (Ginkgo biloba)
  • Homeopathy: carbo vegetabilis, opium, sepia
  • Acupuncture: It may precipitate fainting.

Admission, Inpatient, and Nursing Considerations

Hospital admission or intense evaluation for:

  • Severe coronary artery disease or structural heart disease (severe CHF, low ejection fraction or previous myocardial infarction, aortic stenosis)
  • Arrhythmic syncope:
    • ECG may show bifascicular block, sinus bradycardia <40 without SA block or β-blockers, Brugada syndrome, abnormal QT interval, etc.
  • Severe anemia or electrolyte abnormalities
  • Family history of sudden death
  • Isotonic crystalloids, as needed
  • Vital sign monitoring
  • Discharge when hemodynamically stable and workup satisfactory

Descriptive text is not available for this image Ongoing Care

Diet

  • Increased salt intake may help if not otherwise contraindicated (2)[C].
  • Maintain fluid intake.

Patient Education

  • Identify and avoid precipitating events or situations.
  • Avoid dehydration, alcohol consumption, warm environments, tight clothing, and long periods of standing motionless.
  • Recognize presyncopal symptoms.
  • Use behaviors, such as lying down, to avoid syncope.

Prognosis

May be recurrent but not life-threatening

Complications

May result in injury from falls

Authors

Melinda Kwan, DO, MPH
Norton Winer, MD

References

  1. Zou R, Wang S, Lin P, et al. The clinical characteristics of situational syncope in children and adults undergoing head-up tilt testing. Am J Emerg Med. 2020;38(7):1419–1423.  [PMID:31843331]
  2. Rocha BML, Gomes RV, Cunha GJL, et al. Diagnostic and therapeutic approach to cardioinhibitory reflex syncope: a complex and controversial issue. Rev Port Cardiol (Engl Ed). 2019;38(9):661–673.  [PMID:31813672]
  3. Behnoush AH, Yazdani K, Khalaji A, et al. Pharmacologic prevention of recurrent vasovagal syncope: a systematic review and network meta-analysis of randomized controlled trials. Heart Rhythm. 2023;20(3):448–460. doi:10.1016/j.hrthm.2022.12.010.  [PMID:36509319]
  4. Sheldon R, Faris P, Tang A, et al. Midodrine for the prevention of vasovagal syncope: a randomized clinical trial. Ann Intern Med. 2021;174(10):1349–1356. doi:10.7326/M20-5415.  [PMID:34339231]

Descriptive text is not available for this image See Also

Algorithms: Syncope; Transient Ischemic Attack and Transient Neurologic Defects

Descriptive text is not available for this image Codes

ICD-10

R55 Syncope and collapse

SNOMED

  • 398665005 Vasovagal syncope (disorder)
  • 398652001 Vasovagal attack (disorder)
  • 248229009 Vasovagal symptom (finding)
  • 234163005 Neurally-mediated syncope

Clinical Pearls

  • A careful history of the events preceding the syncopal episode helps guide evaluation and management.
  • Rule out cardiac or neurogenic syncope.
  • Prodrome is common with reflex syncope.
  • Recovery may be prolonged, with persistent symptoms but there is no residual neurologic deficit or confusion.
  • Patients should avoid precipitating situations or events.

Last Updated: 2027

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