This is the most common cause of syncope. Vasovagal, or neurocardiogenic, syncope is a form of neurally mediated syncope that leads to a transient loss of consciousness. It most frequently occurs in otherwise young and healthy individuals but may occur in older individuals. Vasovagal syncope is thought to be due to a reflexive activation of the parasympathetic nervous system, often in response to a trigger. This can lead to bradycardia and decreased cardiac contractility, termed a cardioinhibitory response. Alternatively, there may be vasodilation with a corresponding decrease in blood pressure in the absence of a significant change in heart rate, termed a vasodepressor response. These hemodynamic changes result in systemic hypotension and cerebral hypoperfusion.
Often, it is triggered by an emotional or orthostatic stress such as painful stimuli, venipuncture, fear of bodily injury, prolonged standing, exertion, or heat exposure. Some medications can also predispose to syncopal episodes due to provoking orthostatic hypotension. Patients typically describe a prodrome of nausea, pallor, and diaphoresis followed by a brief episode of syncope from either the sitting or standing position. Consciousness is restored with the supine position, but patients may feel fatigued for some time after the event, and persistent low blood pressure and bradycardia can cause syncope to recur upon standing.
Both syncope due to cardiac arrhythmias and syncope due to orthostatic hypotension can be the result of a medication, alcohol, or illicit drug. See drug-induced syncope for more information, including drug reaction data.
Carotid Sinus Syncope
Hypersensitivity of the carotid sinus such that manipulation causes a vagal response with bradycardia and vasodilation (asystole and drop in blood pressure) causes syncope. Abnormal response to carotid sinus massage is a strong indication of the condition. Other findings may include hypotension, dizziness, presyncope, sinus bradycardia, headache, nausea, pallor, and diaphoresis. It can be triggered by fast neck movements, shaving, constrictive collars, neck tumors, lymphadenopathy, or neck surgery. This condition is more common in elderly patients. Treatment is case dependent and may include permanent pacemaker placement for more severe cases.
These are neurally mediated conditions in which specific actions can cause syncope. Examples include cough syncope, syncope during sneezing or when playing a wind instrument, defecation syncope (syncope triggered by the act of defecation), micturition syncope (syncope during urination), deglutition syncope (syncope triggered by oral intake), coital syncope (syncope during coitus or orgasm), and laughter-induced syncope. Cough syncope and micturition syncope are the most common. Laughter-induced syncope in children may be caused by tickling. Situational syncope is characterized by vasodilatation and/or bradycardia resulting in transient hypotension and cerebral hypoperfusion. Treatment is case dependent and may include permanent pacemaker placement.
R55 – Syncope and collapse
271594007 – Syncope
Differential Diagnosis & Pitfalls
- Epilepsy (see seizure)
- Psychogenic pseudosyncope
- Transient ischemic attack / stroke
- Subarachnoid hemorrhage
- Vertebrobasilar occlusion (see basilar artery occlusion, vertebral artery dissection)
- Sudden increase intracranial pressure (fourth ventricular occlusion)
- Conversion disorder
- Emotional faint (autonomic surge)
- Pain (autonomic surge)
- Autonomic peripheral neuropathy
- Cardiac arrhythmia / paroxysmal arrhythmia
- Heart block
- Rapid atrial fibrillation
- Structural heart disease
- Aortic stenosis
- Pulmonary stenosis
- Hypertrophic cardiomyopathy
- Vertebrobasilar insufficiency
- Aortic dissection
- Cardiac tamponade
- Myocardial infarction
- Pulmonary embolism
- Subclavian steal syndrome