{"history":[],"article":{"id":"55843f84-316b-4c56-8184-a73f66396999","title":"Syncope (medicine)","slug":"syncope-medicine","content":":::summary\n![A 1744 oil painting by Pietro Longhi called Fainting](https://upload.wikimedia.org/wikipedia/commons/5/54/Pietro///Longhi///027.jpg)\n**Name:** Syncope \n**Field:** [Neurology](https://bliptext.com/articles/neurology), [cardiology](https://bliptext.com/articles/cardiology) \n**Synonyms:** Fainting, blacking out, passing out, swooning \n**Symptoms:** [Loss of consciousness](https://bliptext.com/articles/loss-of-consciousness) and muscle strength \n**Complications:** Injury \n**Onset:** Fast onset \n**Duration:** Short duration \n**Types:** Cardiac, reflex, [orthostatic hypotension](https://bliptext.com/articles/orthostatic-hypotension) \n**Causes:** Decrease in blood flow to [brain](https://bliptext.com/articles/brain) \n**Diagnosis:** Medical history, physical examination, [electrocardiogram](https://bliptext.com/articles/electrocardiogram) \n**Treatment:** Based on underlying cause \n**Prognosis:** Depends on underlying cause \n**Frequency:** ~5 per 1,000 per year \n:::\n\n# \n**Syncope**, commonly known as **fainting** or **passing out**, is a [loss of consciousness](https://bliptext.com/articles/unconsciousness) and muscle strength characterized by a fast onset, short duration, and spontaneous recovery.\nIt is caused by a decrease in blood flow to the [brain](https://bliptext.com/articles/brain), typically from [low blood pressure](https://bliptext.com/articles/hypotension).\nThere are sometimes [symptoms before the loss of consciousness](https://bliptext.com/articles/prodrome) such as [lightheadedness](https://bliptext.com/articles/lightheadedness), [sweating](https://bliptext.com/articles/diaphoresis), [pale skin](https://bliptext.com/articles/pale-skin), blurred vision, nausea, vomiting, or feeling warm.\nSyncope may also be associated with a short episode of muscle twitching.\nPsychiatric causes can also be determined when a patient experiences fear, anxiety, or panic; particularly before a stressful event, usually medical in nature.\nWhen consciousness and muscle strength are not completely lost, it is called [presyncope](https://bliptext.com/articles/presyncope).\nIt is recommended that presyncope be treated the same as syncope.\nCauses range from non-serious to potentially fatal.\nThere are three broad categories of causes: [heart](https://bliptext.com/articles/heart) or [blood vessel](https://bliptext.com/articles/blood-vessel) related; [reflex](https://bliptext.com/articles/reflex-syncope), also known as [neurally](https://bliptext.com/articles/nervous-system) mediated; and [orthostatic hypotension](https://bliptext.com/articles/orthostatic-hypotension).\nIssues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common.\nHeart related causes may include an [abnormal heart rhythm](https://bliptext.com/articles/cardiac-dysrhythmia), problems with the [heart valves](https://bliptext.com/articles/heart-valve) or heart muscle and blockages of blood vessels from a [pulmonary embolism](https://bliptext.com/articles/pulmonary-embolism) or [aortic dissection](https://bliptext.com/articles/aortic-dissection) among others.\nNeurally mediated syncope occurs when blood vessels expand and [heart rate decreases](https://bliptext.com/articles/bradycardia) inappropriately.\nThis may occur from either a triggering event such as exposure to blood, pain, strong feelings or a specific activity such as [urination](https://bliptext.com/articles/urination), [vomiting](https://bliptext.com/articles/vomiting), or [coughing](https://bliptext.com/articles/coughing).\nNeurally mediated syncope may also occur when an area in the neck known as the [carotid sinus](https://bliptext.com/articles/carotid-sinus) is pressed.\nThe third type of syncope is due to a drop in blood pressure when changing position such as when standing up.\nThis is often due to medications that a person is taking but may also be related to [dehydration](https://bliptext.com/articles/dehydration), significant bleeding or [infection](https://bliptext.com/articles/infection).\nThere also seems to be a genetic component to syncope.\nA medical history, physical examination, and [electrocardiogram](https://bliptext.com/articles/electrocardiogram) (ECG) are the most effective ways to determine the underlying cause.\nThe ECG is useful to detect an abnormal heart rhythm, [poor blood flow to the heart muscle](https://bliptext.com/articles/coronary-artery-disease) and other electrical issues, such as [long QT syndrome](https://bliptext.com/articles/long-qt-syndrome) and [Brugada syndrome](https://bliptext.com/articles/brugada-syndrome).\nHeart related causes also often have little history of a [prodrome](https://bliptext.com/articles/prodrome).\nLow blood pressure and a fast heart rate after the event may indicate blood loss or dehydration, while [low blood oxygen levels](https://bliptext.com/articles/hypoxia-medical) may be seen following the event in those with pulmonary embolism.\nMore specific tests such as [implantable loop recorders](https://bliptext.com/articles/implantable-loop-recorder), [tilt table testing](https://bliptext.com/articles/tilt-table-testing) or [carotid sinus massage](https://bliptext.com/articles/carotid-sinus-massage) may be useful in uncertain cases.\n[Computed tomography](https://bliptext.com/articles/computer-tomography) (CT) is generally not required unless specific concerns are present.\nOther causes of similar symptoms that should be considered include [seizure](https://bliptext.com/articles/seizure), [stroke](https://bliptext.com/articles/stroke), [concussion](https://bliptext.com/articles/concussion), [low blood oxygen](https://bliptext.com/articles/hypoxia-medical), [low blood sugar](https://bliptext.com/articles/hypoglycemia), [drug intoxication](https://bliptext.com/articles/drug-intoxication) and some psychiatric disorders among others.\nTreatment depends on the underlying cause.\nThose who are considered at high risk following investigation may be admitted to hospital for further [monitoring of the heart](https://bliptext.com/articles/telemetry).\nSyncope affects about three to six out of every thousand people each year.\nIt is more common in older people and females.\nIt is the reason for one to three percent of visits to emergency departments and admissions to hospital.\nUp to half of women over the age of 80 and a third of medical students describe at least one event at some point in their lives.\nOf those presenting with syncope to an emergency department, about 4% died in the next 30 days.\nThe risk of a poor outcome, however, depends very much on the underlying cause.\n\n# Causes\nCauses range from non-serious to potentially fatal.\nThere are three broad categories of causes: [heart](https://bliptext.com/articles/heart) or [blood vessel](https://bliptext.com/articles/blood-vessel) related; [reflex](https://bliptext.com/articles/reflex-syncope), also known as [neurally](https://bliptext.com/articles/nervous-system) mediated; and [orthostatic hypotension](https://bliptext.com/articles/orthostatic-hypotension).\nIssues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common.\nThere also seems to be a genetic component to syncope.\nA recent genetic study has identified first risk locus for syncope and collapse.\nThe lead genetic variant, residing at chromosome 2q31.1, is an intergenic variant approximately 250 kb downstream of the ZNF804A gene.\nThe variant affected the expression of ZNF804A, making this gene the strongest driver of the association.\n\n## Neurally mediated syncope\n[Reflex syncope](https://bliptext.com/articles/reflex-syncope) or neurally mediated syncope occurs when blood vessels expand and [heart rate decreases](https://bliptext.com/articles/bradycardia) inappropriately leading to poor blood flow to the brain.\nThis may occur from either a triggering event such as exposure to blood, pain, strong feelings, or a specific activity such as [urination](https://bliptext.com/articles/urination), [vomiting](https://bliptext.com/articles/vomiting), or [coughing](https://bliptext.com/articles/coughing).\n\n### Vasovagal syncope\nVasovagal (situational) syncope is one of the most common types which may occur in response to any of a variety of triggers, such as scary, embarrassing or uneasy situations, during blood drawing, or moments of sudden unusually high stress.\nThere are many different syncope syndromes which all fall under the umbrella of vasovagal syncope related by the same central mechanism.\nFirst, the person is usually predisposed to decreased blood pressure by various environmental factors.\nA lower than expected blood volume, for instance, from taking a low-salt diet in the absence of any salt-retaining tendency.\nOr heat causing vaso-dilation and worsening the effect of the relatively insufficient blood volume.\nThe next stage is the adrenergic response.\nIf there is underlying fear or anxiety (e.g., social circumstances), or acute fear (e.g., acute threat, [needle phobia](https://bliptext.com/articles/trypanophobia)), the vaso-motor centre demands an increased pumping action by the heart (flight or fight response).\nThis is set in motion via the adrenergic (sympathetic) outflow from the brain, but the heart is unable to meet requirements because of the low blood volume, or decreased return.\nA feedback response to the [medulla](https://bliptext.com/articles/medulla-oblongata) is triggered via the afferent [vagus nerve](https://bliptext.com/articles/vagus-nerve).\nThe high (ineffective) sympathetic activity is thereby modulated by vagal (parasympathetic) outflow leading to excessive slowing of heart rate.\nThe abnormality lies in this excessive vagal response causing loss of blood flow to the brain.\nThe tilt-table test typically evokes the attack.\nAvoiding what brings on the syncope and possibly greater salt intake is often all that is needed.\nAssociated symptoms may be felt in the minutes leading up to a vasovagal episode and are referred to as the prodrome.\nThese consist of light-headedness, confusion, pallor, nausea, salivation, sweating, tachycardia, blurred vision, and sudden urge to defecate among other symptoms.\nVasovagal syncope can be considered in two forms:\nSyncope has been linked with psychological triggers.\nThis includes fainting in response to the sight or thought of blood, needles, pain, and other emotionally stressful situations.\nOne theory in [evolutionary psychology](https://bliptext.com/articles/evolutionary-psychology) is that fainting at the sight of blood might have evolved as a form of [playing dead](https://bliptext.com/articles/apparent-death) which increased survival from attackers and might have slowed blood loss in a primitive environment.\n\"Blood-injury phobia\", as this is called, is experienced by about 15% of people.\nIt is often possible to manage these symptoms with specific behavioral techniques.\nAnother [evolutionary psychology](https://bliptext.com/articles/evolutionary-psychology) view is that some forms of fainting are non-verbal signals that developed in response to increased inter-group aggression during the [paleolithic](https://bliptext.com/articles/paleolithic).\nA non-combatant who has fainted signals that they are not a threat.\nThis would explain the association between fainting and stimuli such as bloodletting and injuries seen in [blood-injection-injury type phobias](https://bliptext.com/articles/blood-injection-injury-type-phobia) such as [needle phobia](https://bliptext.com/articles/needle-phobia) as well as the gender differences.\nMuch of this pathway was discovered in animal experiments by Bezold (Vienna) in the 1860s.\nIn animals, it may represent a defense mechanism when confronted by danger (\"playing possum\").\nA 2023 study identified [neuropeptide Y receptor Y2](https://bliptext.com/articles/neuropeptide-y-receptor-y2) vagal sensory neurons (NPY2R VSNs) and the [periventricular](https://bliptext.com/articles/periventricular-nucleus) zone (PVZ) as a coordinated neural network participating in the cardioinhibitory Bezold–Jarisch reflex (BJR) regulating fainting and recovery.\n\n### Situational syncope\nSyncope may be caused by specific behaviors including coughing, urination, defecation, vomiting, swallowing ([deglutition](https://bliptext.com/articles/deglutition)), and following exercise.\nManisty et al. note: \"Deglutition syncope is characterised by loss of consciousness on swallowing; it has been associated not only with ingestion of solid food, but also with carbonated and ice-cold beverages, and even belching.\"\nFainting can occur in \"cough syncope\" following severe fits of [coughing](https://bliptext.com/articles/cough), such as that associated with [pertussis](https://bliptext.com/articles/pertussis) or \"whooping cough\".\nNeurally mediated syncope may also occur when an area in the neck known as the [carotid sinus](https://bliptext.com/articles/carotid-sinus) is pressed.\nA normal response to carotid sinus massage is reduction in blood pressure and slowing of the heart rate.\nEspecially in people with [hypersensitive carotid sinus syndrome](https://bliptext.com/articles/hypersensitive-carotid-sinus-syndrome) this response can cause syncope or presyncope.\n\n## Cardiac\nHeart-related causes may include an [abnormal heart rhythm](https://bliptext.com/articles/cardiac-dysrhythmia), problems with the [heart valves](https://bliptext.com/articles/heart-valve) or heart muscle, or blockages of blood vessels from a [pulmonary embolism](https://bliptext.com/articles/pulmonary-embolism) or [aortic dissection](https://bliptext.com/articles/aortic-dissection), among others.\n# [Syncope from bradycardia | upload.wikimedia.org/wikipedia/commons/e/e0/Blausen///0100///Bradycardia///Fainting.png]\n\n### Cardiac arrhythmias\nThe most common cause of cardiac syncope is cardiac [arrhythmia](https://bliptext.com/articles/[heart](https://bliptext.com/articles/heart)-arrhythmia) (abnormal [heart](https://bliptext.com/articles/heart) rhythm) wherein the [heart](https://bliptext.com/articles/heart) beats too slowly, too rapidly, or too irregularly to pump enough blood to the brain.\nSome arrhythmias can be life-threatening.\nTwo major groups of arrhythmias are [bradycardia](https://bliptext.com/articles/bradycardia) and [tachycardia](https://bliptext.com/articles/tachycardia).\nBradycardia can be caused by [heart blocks](https://bliptext.com/articles/heart-block).\nTachycardias include SVT ([supraventricular tachycardia](https://bliptext.com/articles/supraventricular-tachycardia)) and VT ([ventricular tachycardia](https://bliptext.com/articles/ventricular-tachycardia)).\nSVT does not cause syncope except in [Wolff-Parkinson-White syndrome](https://bliptext.com/articles/wolff-parkinson-white-syndrome).\n[Ventricular tachycardia](https://bliptext.com/articles/ventricular-tachycardia) originate in the ventricles.\nVT causes syncope and can result in sudden death.\nVentricular tachycardia, which describes a heart rate of over 100 beats per minute with at least three irregular heartbeats as a sequence of consecutive premature beats, can degenerate into [ventricular fibrillation](https://bliptext.com/articles/ventricular-fibrillation), which is rapidly fatal without [cardiopulmonary resuscitation](https://bliptext.com/articles/cardiopulmonary-resuscitation) (CPR) and [defibrillation](https://bliptext.com/articles/defibrillation).\n[Long QT syndrome](https://bliptext.com/articles/long-qt-syndrome) can cause syncope when it sets off [ventricular tachycardia](https://bliptext.com/articles/ventricular-tachycardia) or [torsades de pointes](https://bliptext.com/articles/torsades-de-pointes).\nThe degree of QT prolongation determines the risk of syncope.\n[Brugada syndrome](https://bliptext.com/articles/brugada-syndrome) also commonly presents with syncope secondary to arrhythmia.\nTypically, tachycardic-generated syncope is caused by a cessation of beats following a tachycardic episode.\nThis condition, called tachycardia-bradycardia syndrome, is usually caused by sinoatrial node dysfunction or block or [atrioventricular block](https://bliptext.com/articles/atrioventricular-block).\n\n### Obstructive cardiac lesion\nBlockages in major vessels or within the heart can also impede blood flow to the brain.\n[Aortic stenosis](https://bliptext.com/articles/aortic-stenosis) and [mitral stenosis](https://bliptext.com/articles/mitral-stenosis) are the most common examples.\nMajor valves of the heart become stiffened and reduce the efficiency of the hearts pumping action.\nThis may not cause symptoms at rest but with exertion, the heart is unable to keep up with increased demands leading to syncope.\nAortic stenosis presents with repeated episodes of syncope.\nRarely, cardiac tumors such as atrial myxomas can also lead to syncope.\n\n### Structural cardiopulmonary disease\nDiseases involving the shape and strength of the heart can be a cause of reduced blood flow to the brain, which increases risk for syncope.\nThe most common cause in this category is fainting associated with an acute myocardial infarction or ischemic event.\nThe faint in this case is primarily caused by an abnormal nervous system reaction similar to the reflex faints.\nWomen are significantly more likely to experience syncope as a presenting symptom of a myocardial infarction.\nIn general, faints caused by structural disease of the heart or blood vessels are particularly important to recognize, as they are warning of potentially life-threatening conditions.\nAmong other conditions prone to trigger syncope (by either hemodynamic compromise or by a neural reflex mechanism, or both), some of the most important are [hypertrophic cardiomyopathy](https://bliptext.com/articles/hypertrophic-cardiomyopathy), acute aortic dissection, pericardial tamponade, pulmonary embolism, aortic stenosis, and [pulmonary hypertension](https://bliptext.com/articles/pulmonary-hypertension).\n\n### Other cardiac causes\n[Sick sinus syndrome](https://bliptext.com/articles/sick-sinus-syndrome), a sinus node dysfunction, causing alternating bradycardia and tachycardia.\nOften there is a long pause (asystole) between heartbeats.\n[Adams-Stokes syndrome](https://bliptext.com/articles/adams-stokes-syndrome) is a cardiac syncope that occurs with seizures caused by complete or incomplete heart block.\nSymptoms include deep and fast respiration, weak and slow pulse, and respiratory pauses that may last for 60 seconds.\n[Subclavian steal syndrome](https://bliptext.com/articles/subclavian-steal-syndrome) arises from retrograde (reversed) flow of blood in the vertebral artery or the internal thoracic artery, due to a proximal stenosis (narrowing) and/or occlusion of the subclavian artery.\nSymptoms such as syncope, lightheadedness, and paresthesias occur while exercising the arm on the affected side (most commonly the left).\n[Aortic dissection](https://bliptext.com/articles/aortic-dissection) (a tear in the aorta) and [cardiomyopathy](https://bliptext.com/articles/cardiomyopathy) can also result in syncope.\nVarious medications, such as [beta blockers](https://bliptext.com/articles/beta-blocker), may cause bradycardia induced syncope.\nA [pulmonary embolism](https://bliptext.com/articles/pulmonary-embolism) can cause obstructed blood vessels and is the cause of syncope in less than 1% of people who present to the emergency department.\n\n## Blood pressure\nOrthostatic (postural) hypotensive syncope is caused primarily by an excessive drop in blood pressure when standing up from a previous position of lying or sitting down.\nWhen the head is elevated above the feet the pull of gravity causes blood pressure in the head to drop.\nThis is sensed by [stretch receptors](https://bliptext.com/articles/carotid-sinus) in the walls of vessels in the carotid sinus and aortic arch.\nThese receptors then trigger a sympathetic nervous response to compensate and redistribute blood back into the brain.\nThe sympathetic response causes peripheral vasoconstriction and increased heart rate.\nThese together act to raise blood pressure back to baseline.\nApparently healthy individuals may experience minor symptoms (\"lightheadedness\", \"greying-out\") as they stand up if blood pressure is slow to respond to the stress of upright posture.\nIf the blood pressure is not adequately maintained during standing, faints may develop.\nHowever, the resulting \"transient orthostatic hypotension\" does not necessarily signal any serious underlying disease.\nIt is as common or perhaps even more common than vasovagal syncope.\nThis may be due to medications, [dehydration](https://bliptext.com/articles/dehydration), significant bleeding or [infection](https://bliptext.com/articles/infection).\nThe most susceptible individuals are elderly frail individuals, or persons who are dehydrated from hot environments or inadequate fluid intake.\nFor example, medical students would be at risk for orthostatic hypotensive syncope while observing long surgeries in the operating room.\nThere is also evidence that exercise training can help reduce orthostatic intolerance.\nMore serious orthostatic hypotension is often the result of certain commonly prescribed medications such as diuretics, β-adrenergic blockers, other anti-hypertensives (including vasodilators), and [nitroglycerin](https://bliptext.com/articles/nitroglycerin).\nIn a small percentage of cases, the cause of orthostatic hypotensive faints is structural damage to the [autonomic nervous system](https://bliptext.com/articles/autonomic-nervous-system) due to systemic diseases (e.g., [amyloidosis](https://bliptext.com/articles/amyloidosis) or diabetes) or in neurological diseases (e.g., Parkinson's disease).\nHyperadrenergic orthostatic hypotension refers to an orthostatic drop in blood pressure despite high levels of sympathetic adrenergic response.\nThis occurs when a person with normal physiology is unable to compensate for >20% loss in intravascular volume.\nThis may be due to blood loss, dehydration or [third-spacing](https://bliptext.com/articles/fluid-compartments).\nOn standing the person will experience reflex tachycardia (at least 20% increased over supine) and a drop in blood pressure.\nHypoadrenergic orthostatic hypotension occurs when the person is unable to sustain a normal sympathetic response to blood pressure changes during movement despite adequate intravascular volume.\nThere is little to no compensatory increase in heart rate or blood pressure when standing for up to 10 minutes.\nThis is often due to an underlying disorder or medication use and is accompanied by other [hypoadrenergic signs](https://bliptext.com/articles/adrenal-insufficiency).\n\n## Central nervous system ischemia\nThe [central ischemic response](https://bliptext.com/articles/ischemia) is triggered by an inadequate supply of oxygenated blood in the brain.\nCommon examples include [strokes](https://bliptext.com/articles/stroke) and [transient ischemic attacks](https://bliptext.com/articles/transient-ischemic-attack).\nWhile these conditions often impair consciousness they rarely meet the medical definition of syncope.\n[Vertebrobasilar](https://bliptext.com/articles/vertebrobasilar-artery-stroke) transient ischemic attacks may produce true syncope as a symptom.\nThe respiratory system may compensate for dropping oxygen levels through [hyperventilation](https://bliptext.com/articles/hyperventilation), though a sudden [ischemic](https://bliptext.com/articles/ischemia) episode may also proceed faster than the respiratory system can respond.\nThese processes cause the typical symptoms of fainting: pale skin, rapid breathing, nausea, and weakness of the limbs, particularly of the legs.\nIf the ischemia is intense or prolonged, limb weakness progresses to collapse.\nThe weakness of the legs causes most people to sit or lie down if there is time to do so.\nThis may avert a complete collapse, but whether the patient sits down or falls down, the result of an ischaemic episode is a posture in which less blood pressure is required to achieve adequate blood flow.\nAn individual with very little skin pigmentation may appear to have all color drained from his or her face at the onset of an episode.\nThis effect combined with the following collapse can make a strong and dramatic impression on bystanders.\n\n### Vertebro-basilar arterial disease\nArterial disease in the upper spinal cord, or lower brain that causes syncope if there is a reduction in blood supply.\nThis may occur with extending the neck or with use of medications to lower blood pressure.\n\n## Other causes\nThere are other conditions which may cause or resemble syncope.\nSeizures and syncope can be difficult to differentiate.\nBoth often present as sudden loss of consciousness and convulsive movements may be present or absent in either.\nMovements in syncope are typically brief and more irregular than seizures.\n[Akinetic seizures](https://bliptext.com/articles/atonic-seizure) can present with sudden loss of postural tone without associated tonic-clonic movements.\nAbsence of a long post-ictal state is indicative of syncope rather than an akinetic seizure.\nSome rare forms, such as [hair-grooming syncope](https://bliptext.com/articles/hair-grooming-syncope) are of an unknown cause.\nSubarachnoid hemorrhage may result in syncope.\nOften this is in combination with sudden, severe headache.\nIt may occur as a result of a ruptured aneurysm or head trauma.\n[Heat syncope](https://bliptext.com/articles/heat-syncope) occurs when heat exposure causes decreased blood volume and peripheral vasodilatation.\nPosition changes, especially during vigorous exercise in the heat, may lead to decreased blood flow to the brain.\nClosely related to other causes of syncope related to hypotension (low blood pressure) such as orthostatic syncope.\nSome psychological conditions ([anxiety](https://bliptext.com/articles/anxiety-disorder) disorder, [somatic symptom disorder](https://bliptext.com/articles/somatic-symptom-disorder), [conversion disorder](https://bliptext.com/articles/conversion-disorder)) may cause symptoms resembling syncope.\nA number of psychological interventions are available.\nLow blood sugar can be a rare cause of syncope.\n[Narcolepsy](https://bliptext.com/articles/narcolepsy) may present with sudden loss of consciousness similar to syncope.\n\n# Diagnostic approach\nA medical history, physical examination, and [electrocardiogram](https://bliptext.com/articles/electrocardiogram) (ECG) are the most effective ways to determine the underlying cause of syncope.\nGuidelines from the American College of Emergency Physicians and American Heart Association recommend a syncope workup include a thorough medical history, physical exam with orthostatic vitals, and a 12-lead ECG.\nThe ECG is useful to detect an abnormal heart rhythm, [poor blood flow to the heart muscle](https://bliptext.com/articles/coronary-artery-disease) and other electrical issues, such as [long QT syndrome](https://bliptext.com/articles/long-qt-syndrome) and [Brugada syndrome](https://bliptext.com/articles/brugada-syndrome).\nHeart related causes also often have little history of a [prodrome](https://bliptext.com/articles/prodrome).\nLow blood pressure and a fast heart rate after the event may indicate blood loss or dehydration, while [low blood oxygen levels](https://bliptext.com/articles/hypoxia-medical) may be seen following the event in those with pulmonary embolism.\nRoutine broad panel laboratory testing detects abnormalities in <2–3% of results and is therefore not recommended.\nBased on this initial workup many physicians will tailor testing and determine whether a person qualifies as 'high-risk', 'intermediate risk' or 'low-risk' based on risk stratification tools.\nMore specific tests such as [implantable loop recorders](https://bliptext.com/articles/implantable-loop-recorder), [tilt table testing](https://bliptext.com/articles/tilt-table-testing) or [carotid sinus massage](https://bliptext.com/articles/carotid-sinus-massage) may be useful in uncertain cases.\n[Computed tomography](https://bliptext.com/articles/computer-tomography) (CT) is generally not required unless specific concerns are present.\nOther causes of similar symptoms that should be considered include [seizure](https://bliptext.com/articles/seizure), [stroke](https://bliptext.com/articles/stroke), [concussion](https://bliptext.com/articles/concussion), [low blood oxygen](https://bliptext.com/articles/hypoxia-medical), [low blood sugar](https://bliptext.com/articles/hypoglycemia), [drug intoxication](https://bliptext.com/articles/drug-intoxication) and some psychiatric disorders among others.\nTreatment depends on the underlying cause.\nThose who are considered at high risk following investigation may be admitted to hospital for further [monitoring of the heart](https://bliptext.com/articles/telemetry).\nA [hemoglobin](https://bliptext.com/articles/hemoglobin) count may indicate anemia or blood loss.\nHowever, this has been useful in only about 5% of people evaluated for fainting.\nThe [tilt table test](https://bliptext.com/articles/tilt-table-test) is performed to elicit orthostatic syncope secondary to autonomic dysfunction (neurogenic).\nA number of factors make a heart related cause more likely including age over 35, prior [atrial fibrillation](https://bliptext.com/articles/atrial-fibrillation), and turning blue during the event.\n\n## Electrocardiogram\n[Electrocardiogram](https://bliptext.com/articles/electrocardiogram) (ECG) finds that should be looked for include signs of [heart ischemia](https://bliptext.com/articles/heart-ischemia), [arrhythmias](https://bliptext.com/articles/arrhythmias), [atrioventricular blocks](https://bliptext.com/articles/atrioventricular-block), a [long QT](https://bliptext.com/articles/long-qt), a [short PR](https://bliptext.com/articles/short-pr), [Brugada syndrome](https://bliptext.com/articles/brugada-syndrome), signs of [hypertrophic obstructive cardiomyopathy](https://bliptext.com/articles/hypertrophic-obstructive-cardiomyopathy) (HOCM), and signs of [arrhythmogenic right ventricular dysplasia](https://bliptext.com/articles/arrhythmogenic-right-ventricular-dysplasia) (ARVD/C).\nSigns of HCM include large voltages in the precordial leads, repolarization abnormalities, and a wide QRS with a slurred upstroke.\nSigns of ARVD/C include [T wave inversion](https://bliptext.com/articles/t-wave-inversion) and [epsilon waves](https://bliptext.com/articles/epsilon-waves) in lead V1 to V3.\nIt is estimated that from 20 to 50% of people have an abnormal ECG.\nHowever, while an ECG may identify conditions such as [atrial fibrillation](https://bliptext.com/articles/atrial-fibrillation), heart block, or a new or old heart attack, it typically does not provide a definite diagnosis for the underlying cause for fainting.\nSometimes, a [Holter monitor](https://bliptext.com/articles/holter-monitor) may be used.\nThis is a portable ECG device that can record the wearer's heart rhythms during daily activities over an extended period of time.\nSince fainting usually does not occur upon command, a Holter monitor can provide a better understanding of the heart's activity during fainting episodes.\nFor people with more than two episodes of syncope and no diagnosis on \"routine testing\", an insertable cardiac monitor might be used.\nIt lasts 28–36 months and is inserted just beneath the skin in the upper chest area.\n\n## Imaging\n[Echocardiography](https://bliptext.com/articles/echocardiography) and ischemia testing may be recommended for cases where initial evaluation and ECG testing is nondiagnostic.\nFor people with uncomplicated syncope (without seizures and a normal neurological exam) [computed tomography](https://bliptext.com/articles/computed-tomography) or [MRI](https://bliptext.com/articles/mri) is not generally needed.\nLikewise, using [carotid ultrasonography](https://bliptext.com/articles/carotid-ultrasonography) on the premise of identifying [carotid artery disease](https://bliptext.com/articles/carotid-artery-disease) as a cause of syncope also is not indicated., which cites:\n\n## Differential diagnosis\nOther diseases which mimic syncope include [seizure](https://bliptext.com/articles/epileptic-seizure), [low blood sugar](https://bliptext.com/articles/hypoglycemia), certain types of [stroke](https://bliptext.com/articles/stroke), and paroxysmal spells.\nWhile these may appear as \"fainting\", they do not fit the strict definition of syncope being a sudden reversible loss of consciousness due to decreased blood flow to the brain.\n\n# Management\nManagement of syncope focuses on treating the underlying cause.\nThis can be challenging as the underlying cause is unclear in half of all cases.\nSeveral risk stratification tools (explained below) have been developed to combat the vague nature of this diagnosis.\nPeople with an abnormal ECG reading, history of congestive heart failure, family history of sudden cardiac death, shortness of breath, HCT<30, hypotension or evidence of bleeding should be admitted to the hospital for further evaluation and monitoring.\nLow-risk cases of vasovagal or orthostatic syncope in younger people with no significant cardiac history, no family history of sudden unexplained death, and a normal EKG and initial evaluation may be candidates for discharge to follow-up with their primary care provider.\nRecommended acute treatment of vasovagal and orthostatic (hypotension) syncope involves returning blood to the brain by positioning the person on the ground, with legs slightly elevated or sitting leaning forward and the head between the knees for at least 10–15 minutes, preferably in a cool and quiet place.\nFor individuals who have problems with chronic fainting spells, therapy should focus on recognizing the triggers and learning techniques to keep from fainting.\nAt the appearance of warning signs such as lightheadedness, nausea, or cold and clammy skin, counter-pressure maneuvers that involve gripping fingers into a fist, tensing the arms, and crossing the legs or squeezing the thighs together can be used to ward off a fainting spell.\nAfter the symptoms have passed, [sleep](https://bliptext.com/articles/sleep) is recommended.\nLifestyle modifications are important for treating people experiencing repeated syncopal episodes.\nAvoiding triggers and situations where loss of consciousness would be seriously hazardous (operating heavy machinery, commercial pilot, etc.) has been shown to be effective.\nIf fainting spells occur often without a triggering event, syncope may be a sign of an underlying heart disease.\nIn the case where syncope is caused by cardiac disease, the treatment is much more sophisticated than that of [vasovagal](https://bliptext.com/articles/vasovagal) syncope and may involve [pacemakers](https://bliptext.com/articles/artificial-cardiac-pacemaker) and [implantable cardioverter-defibrillators](https://bliptext.com/articles/implantable-cardioverter-defibrillators) depending on the precise cardiac cause.\n\n## Risk tools\nThe [San Francisco syncope rule](https://bliptext.com/articles/san-francisco-syncope-rule) was developed to isolate people who have higher risk for a serious cause of syncope.\nHigh risk is anyone who has: congestive heart failure, hematocrit <30%, electrocardiograph abnormality, shortness of breath, or systolic blood pressure <90 mmHg.\nThe San Francisco syncope rule however was not validated by subsequent studies.\nThe Canadian syncope risk score was developed to help select low-risk people that may be viable for discharge home.\nA score of <0 on the Canadian syncope risk score is associated with <2% risk of serious adverse event within 30 days.\nIt has been shown to be more effective than older syncope risk scores even combined with cardiac biomarkers at predicting adverse events.\n\n# Epidemiology\nThere are 18.1–39.7 syncope episodes per 1000 people in the general population.\nRates are highest between the ages of 10–30 years old.\nThis is likely because of the high rates of vasovagal syncope in the young adult population.\nOlder adults are more likely to have orthostatic or cardiac syncope.\nSyncope affects about three to six out of every thousand people each year.\nIt is more common in older people and females.\nIt is the reason for 2–5% of visits to emergency departments and admissions to hospital.\nUp to half of women over the age of 80 and a third of medical students describe at least one event at some point in their lives.\n\n# Prognosis\nOf those presenting with syncope to an emergency department, about 4% died in the next 30 days.\nThe risk of a poor outcome, however, depends very much on the underlying cause.\nSituational syncope is not at increased risk of death or adverse outcomes.\nCardiac syncope is associated with worse prognosis compared to noncardiac syncope.\nFactors associated with poor outcomes include history of heart failure, history of myocardial infarction, ECG abnormalities, palpitations, signs of hemorrhage, syncope during exertion, and advanced age.\n\n# Society and culture\nFainting in women was a commonplace trope or stereotype in [Victorian England](https://bliptext.com/articles/victorian-england) and in contemporary and modern depictions of the period.\nSyncope and presyncope are common in young athletes.\nIn 1990 the American college basketball player [Hank Gathers](https://bliptext.com/articles/hank-gathers) suddenly collapsed and died during a televised intercollegiate basketball game.\nHe had previously collapsed during a game a few months prior.\nHe was diagnosed with exercise-induced ventricular tachycardia at the time.\nThere was speculation that he had since stopped taking the prescribed medications on game days.\n[Falling-out](https://bliptext.com/articles/falling-out) is a [culture-bound syndrome](https://bliptext.com/articles/culture-bound-syndrome) primarily reported in the [southern United States](https://bliptext.com/articles/southern-united-states) and the [Caribbean](https://bliptext.com/articles/caribbean).\n\n## Etymology\nThe term is derived from the [Late Latin](https://bliptext.com/articles/latin-language) syncope, from [Ancient Greek](https://bliptext.com/articles/ancient-greek) συγκοπή (sunkopē) 'cutting up', 'sudden loss of strength', from σύν (sun, \"together, thoroughly\") and κόπτειν (koptein, \"strike, cut off\").","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-26T11:14:20.498Z","updated_at":"2025-01-26T11:14:20.498Z","search_vector":"'medicin':2 'syncop':1","search_content":" \n \n**Name:** Syncope \n**Field:** [Neurology](https://bliptext.com/articles/neurology), [cardiology](https://bliptext.com/articles/cardiology) \n**Synonyms:** Fainting, blacking out, passing out, swooning \n**Symptoms:** [Loss of consciousness](https://bliptext.com/articles/loss-of-consciousness) and muscle strength \n**Complications:** Injury \n**Onset:** Fast onset \n**Duration:** Short duration \n**Types:** Cardiac, reflex, [orthostatic hypotension](https://bliptext.com/articles/orthostatic-hypotension) \n**Causes:** Decrease in blood flow to [brain](https://bliptext.com/articles/brain) \n**Diagnosis:** Medical history, physical examination, [electrocardiogram](https://bliptext.com/articles/electrocardiogram) \n**Treatment:** Based on underlying cause \n**Prognosis:** Depends on underlying cause \n**Frequency:** ~5 per 1,000 per year \n \n\n# \n**Syncope**, commonly known as **fainting** or **passing out**, is a [loss of consciousness](https://bliptext.com/articles/unconsciousness) and muscle strength characterized by a fast onset, short duration, and spontaneous recovery.\nIt is caused by a decrease in blood flow to the [brain](https://bliptext.com/articles/brain), typically from [low blood pressure](https://bliptext.com/articles/hypotension).\nThere are sometimes [symptoms before the loss of consciousness](https://bliptext.com/articles/prodrome) such as [lightheadedness](https://bliptext.com/articles/lightheadedness), [sweating](https://bliptext.com/articles/diaphoresis), [pale skin](https://bliptext.com/articles/pale-skin), blurred vision, nausea, vomiting, or feeling warm.\nSyncope may also be associated with a short episode of muscle twitching.\nPsychiatric causes can also be determined when a patient experiences fear, anxiety, or panic; particularly before a stressful event, usually medical in nature.\nWhen consciousness and muscle strength are not completely lost, it is called [presyncope](https://bliptext.com/articles/presyncope).\nIt is recommended that presyncope be treated the same as syncope.\nCauses range from non-serious to potentially fatal.\nThere are three broad categories of causes: [heart](https://bliptext.com/articles/heart) or [blood vessel](https://bliptext.com/articles/blood-vessel) related; [reflex](https://bliptext.com/articles/reflex-syncope), also known as [neurally](https://bliptext.com/articles/nervous-system) mediated; and [orthostatic hypotension](https://bliptext.com/articles/orthostatic-hypotension).\nIssues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common.\nHeart related causes may include an [abnormal heart rhythm](https://bliptext.com/articles/cardiac-dysrhythmia), problems with the [heart valves](https://bliptext.com/articles/heart-valve) or heart muscle and blockages of blood vessels from a [pulmonary embolism](https://bliptext.com/articles/pulmonary-embolism) or [aortic dissection](https://bliptext.com/articles/aortic-dissection) among others.\nNeurally mediated syncope occurs when blood vessels expand and [heart rate decreases](https://bliptext.com/articles/bradycardia) inappropriately.\nThis may occur from either a triggering event such as exposure to blood, pain, strong feelings or a specific activity such as [urination](https://bliptext.com/articles/urination), [vomiting](https://bliptext.com/articles/vomiting), or [coughing](https://bliptext.com/articles/coughing).\nNeurally mediated syncope may also occur when an area in the neck known as the [carotid sinus](https://bliptext.com/articles/carotid-sinus) is pressed.\nThe third type of syncope is due to a drop in blood pressure when changing position such as when standing up.\nThis is often due to medications that a person is taking but may also be related to [dehydration](https://bliptext.com/articles/dehydration), significant bleeding or [infection](https://bliptext.com/articles/infection).\nThere also seems to be a genetic component to syncope.\nA medical history, physical examination, and [electrocardiogram](https://bliptext.com/articles/electrocardiogram) (ECG) are the most effective ways to determine the underlying cause.\nThe ECG is useful to detect an abnormal heart rhythm, [poor blood flow to the heart muscle](https://bliptext.com/articles/coronary-artery-disease) and other electrical issues, such as [long QT syndrome](https://bliptext.com/articles/long-qt-syndrome) and [Brugada syndrome](https://bliptext.com/articles/brugada-syndrome).\nHeart related causes also often have little history of a [prodrome](https://bliptext.com/articles/prodrome).\nLow blood pressure and a fast heart rate after the event may indicate blood loss or dehydration, while [low blood oxygen levels](https://bliptext.com/articles/hypoxia-medical) may be seen following the event in those with pulmonary embolism.\nMore specific tests such as [implantable loop recorders](https://bliptext.com/articles/implantable-loop-recorder), [tilt table testing](https://bliptext.com/articles/tilt-table-testing) or [carotid sinus massage](https://bliptext.com/articles/carotid-sinus-massage) may be useful in uncertain cases.\n[Computed tomography](https://bliptext.com/articles/computer-tomography) (CT) is generally not required unless specific concerns are present.\nOther causes of similar symptoms that should be considered include [seizure](https://bliptext.com/articles/seizure), [stroke](https://bliptext.com/articles/stroke), [concussion](https://bliptext.com/articles/concussion), [low blood oxygen](https://bliptext.com/articles/hypoxia-medical), [low blood sugar](https://bliptext.com/articles/hypoglycemia), [drug intoxication](https://bliptext.com/articles/drug-intoxication) and some psychiatric disorders among others.\nTreatment depends on the underlying cause.\nThose who are considered at high risk following investigation may be admitted to hospital for further [monitoring of the heart](https://bliptext.com/articles/telemetry).\nSyncope affects about three to six out of every thousand people each year.\nIt is more common in older people and females.\nIt is the reason for one to three percent of visits to emergency departments and admissions to hospital.\nUp to half of women over the age of 80 and a third of medical students describe at least one event at some point in their lives.\nOf those presenting with syncope to an emergency department, about 4% died in the next 30 days.\nThe risk of a poor outcome, however, depends very much on the underlying cause.\n\n# Causes\nCauses range from non-serious to potentially fatal.\nThere are three broad categories of causes: [heart](https://bliptext.com/articles/heart) or [blood vessel](https://bliptext.com/articles/blood-vessel) related; [reflex](https://bliptext.com/articles/reflex-syncope), also known as [neurally](https://bliptext.com/articles/nervous-system) mediated; and [orthostatic hypotension](https://bliptext.com/articles/orthostatic-hypotension).\nIssues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common.\nThere also seems to be a genetic component to syncope.\nA recent genetic study has identified first risk locus for syncope and collapse.\nThe lead genetic variant, residing at chromosome 2q31.1, is an intergenic variant approximately 250 kb downstream of the ZNF804A gene.\nThe variant affected the expression of ZNF804A, making this gene the strongest driver of the association.\n\n## Neurally mediated syncope\n[Reflex syncope](https://bliptext.com/articles/reflex-syncope) or neurally mediated syncope occurs when blood vessels expand and [heart rate decreases](https://bliptext.com/articles/bradycardia) inappropriately leading to poor blood flow to the brain.\nThis may occur from either a triggering event such as exposure to blood, pain, strong feelings, or a specific activity such as [urination](https://bliptext.com/articles/urination), [vomiting](https://bliptext.com/articles/vomiting), or [coughing](https://bliptext.com/articles/coughing).\n\n### Vasovagal syncope\nVasovagal (situational) syncope is one of the most common types which may occur in response to any of a variety of triggers, such as scary, embarrassing or uneasy situations, during blood drawing, or moments of sudden unusually high stress.\nThere are many different syncope syndromes which all fall under the umbrella of vasovagal syncope related by the same central mechanism.\nFirst, the person is usually predisposed to decreased blood pressure by various environmental factors.\nA lower than expected blood volume, for instance, from taking a low-salt diet in the absence of any salt-retaining tendency.\nOr heat causing vaso-dilation and worsening the effect of the relatively insufficient blood volume.\nThe next stage is the adrenergic response.\nIf there is underlying fear or anxiety (e.g., social circumstances), or acute fear (e.g., acute threat, [needle phobia](https://bliptext.com/articles/trypanophobia)), the vaso-motor centre demands an increased pumping action by the heart (flight or fight response).\nThis is set in motion via the adrenergic (sympathetic) outflow from the brain, but the heart is unable to meet requirements because of the low blood volume, or decreased return.\nA feedback response to the [medulla](https://bliptext.com/articles/medulla-oblongata) is triggered via the afferent [vagus nerve](https://bliptext.com/articles/vagus-nerve).\nThe high (ineffective) sympathetic activity is thereby modulated by vagal (parasympathetic) outflow leading to excessive slowing of heart rate.\nThe abnormality lies in this excessive vagal response causing loss of blood flow to the brain.\nThe tilt-table test typically evokes the attack.\nAvoiding what brings on the syncope and possibly greater salt intake is often all that is needed.\nAssociated symptoms may be felt in the minutes leading up to a vasovagal episode and are referred to as the prodrome.\nThese consist of light-headedness, confusion, pallor, nausea, salivation, sweating, tachycardia, blurred vision, and sudden urge to defecate among other symptoms.\nVasovagal syncope can be considered in two forms:\nSyncope has been linked with psychological triggers.\nThis includes fainting in response to the sight or thought of blood, needles, pain, and other emotionally stressful situations.\nOne theory in [evolutionary psychology](https://bliptext.com/articles/evolutionary-psychology) is that fainting at the sight of blood might have evolved as a form of [playing dead](https://bliptext.com/articles/apparent-death) which increased survival from attackers and might have slowed blood loss in a primitive environment.\n\"Blood-injury phobia\", as this is called, is experienced by about 15% of people.\nIt is often possible to manage these symptoms with specific behavioral techniques.\nAnother [evolutionary psychology](https://bliptext.com/articles/evolutionary-psychology) view is that some forms of fainting are non-verbal signals that developed in response to increased inter-group aggression during the [paleolithic](https://bliptext.com/articles/paleolithic).\nA non-combatant who has fainted signals that they are not a threat.\nThis would explain the association between fainting and stimuli such as bloodletting and injuries seen in [blood-injection-injury type phobias](https://bliptext.com/articles/blood-injection-injury-type-phobia) such as [needle phobia](https://bliptext.com/articles/needle-phobia) as well as the gender differences.\nMuch of this pathway was discovered in animal experiments by Bezold (Vienna) in the 1860s.\nIn animals, it may represent a defense mechanism when confronted by danger (\"playing possum\").\nA 2023 study identified [neuropeptide Y receptor Y2](https://bliptext.com/articles/neuropeptide-y-receptor-y2) vagal sensory neurons (NPY2R VSNs) and the [periventricular](https://bliptext.com/articles/periventricular-nucleus) zone (PVZ) as a coordinated neural network participating in the cardioinhibitory Bezold–Jarisch reflex (BJR) regulating fainting and recovery.\n\n### Situational syncope\nSyncope may be caused by specific behaviors including coughing, urination, defecation, vomiting, swallowing ([deglutition](https://bliptext.com/articles/deglutition)), and following exercise.\nManisty et al. note: \"Deglutition syncope is characterised by loss of consciousness on swallowing; it has been associated not only with ingestion of solid food, but also with carbonated and ice-cold beverages, and even belching.\"\nFainting can occur in \"cough syncope\" following severe fits of [coughing](https://bliptext.com/articles/cough), such as that associated with [pertussis](https://bliptext.com/articles/pertussis) or \"whooping cough\".\nNeurally mediated syncope may also occur when an area in the neck known as the [carotid sinus](https://bliptext.com/articles/carotid-sinus) is pressed.\nA normal response to carotid sinus massage is reduction in blood pressure and slowing of the heart rate.\nEspecially in people with [hypersensitive carotid sinus syndrome](https://bliptext.com/articles/hypersensitive-carotid-sinus-syndrome) this response can cause syncope or presyncope.\n\n## Cardiac\nHeart-related causes may include an [abnormal heart rhythm](https://bliptext.com/articles/cardiac-dysrhythmia), problems with the [heart valves](https://bliptext.com/articles/heart-valve) or heart muscle, or blockages of blood vessels from a [pulmonary embolism](https://bliptext.com/articles/pulmonary-embolism) or [aortic dissection](https://bliptext.com/articles/aortic-dissection), among others.\n# [Syncope from bradycardia | upload.wikimedia.org/wikipedia/commons/e/e0/Blausen///0100///Bradycardia///Fainting.png]\n\n### Cardiac arrhythmias\nThe most common cause of cardiac syncope is cardiac [arrhythmia](https://bliptext.com/articles/[heart](https://bliptext.com/articles/heart)-arrhythmia) (abnormal [heart](https://bliptext.com/articles/heart) rhythm) wherein the [heart](https://bliptext.com/articles/heart) beats too slowly, too rapidly, or too irregularly to pump enough blood to the brain.\nSome arrhythmias can be life-threatening.\nTwo major groups of arrhythmias are [bradycardia](https://bliptext.com/articles/bradycardia) and [tachycardia](https://bliptext.com/articles/tachycardia).\nBradycardia can be caused by [heart blocks](https://bliptext.com/articles/heart-block).\nTachycardias include SVT ([supra[ventricular tachycardia](https://bliptext.com/articles/ventricular-tachycardia)](https://bliptext.com/articles/supraventricular-tachycardia)) and VT ([ventricular tachycardia](https://bliptext.com/articles/ventricular-tachycardia)).\nSVT does not cause syncope except in [Wolff-Parkinson-White syndrome](https://bliptext.com/articles/wolff-parkinson-white-syndrome).\n[Ventricular tachycardia](https://bliptext.com/articles/ventricular-tachycardia) originate in the ventricles.\nVT causes syncope and can result in sudden death.\nVentricular tachycardia, which describes a heart rate of over 100 beats per minute with at least three irregular heartbeats as a sequence of consecutive premature beats, can degenerate into [ventricular fibrillation](https://bliptext.com/articles/ventricular-fibrillation), which is rapidly fatal without [cardiopulmonary resuscitation](https://bliptext.com/articles/cardiopulmonary-resuscitation) (CPR) and [defibrillation](https://bliptext.com/articles/defibrillation).\n[Long QT syndrome](https://bliptext.com/articles/long-qt-syndrome) can cause syncope when it sets off [ventricular tachycardia](https://bliptext.com/articles/ventricular-tachycardia) or [torsades de pointes](https://bliptext.com/articles/torsades-de-pointes).\nThe degree of QT prolongation determines the risk of syncope.\n[Brugada syndrome](https://bliptext.com/articles/brugada-syndrome) also commonly presents with syncope secondary to arrhythmia.\nTypically, tachycardic-generated syncope is caused by a cessation of beats following a tachycardic episode.\nThis condition, called tachycardia-bradycardia syndrome, is usually caused by sinoatrial node dysfunction or block or [atrioventricular block](https://bliptext.com/articles/atrioventricular-block).\n\n### Obstructive cardiac lesion\nBlockages in major vessels or within the heart can also impede blood flow to the brain.\n[Aortic stenosis](https://bliptext.com/articles/aortic-stenosis) and [mitral stenosis](https://bliptext.com/articles/mitral-stenosis) are the most common examples.\nMajor valves of the heart become stiffened and reduce the efficiency of the hearts pumping action.\nThis may not cause symptoms at rest but with exertion, the heart is unable to keep up with increased demands leading to syncope.\nAortic stenosis presents with repeated episodes of syncope.\nRarely, cardiac tumors such as atrial myxomas can also lead to syncope.\n\n### Structural cardiopulmonary disease\nDiseases involving the shape and strength of the heart can be a cause of reduced blood flow to the brain, which increases risk for syncope.\nThe most common cause in this category is fainting associated with an acute myocardial infarction or ischemic event.\nThe faint in this case is primarily caused by an abnormal nervous system reaction similar to the reflex faints.\nWomen are significantly more likely to experience syncope as a presenting symptom of a myocardial infarction.\nIn general, faints caused by structural disease of the heart or blood vessels are particularly important to recognize, as they are warning of potentially life-threatening conditions.\nAmong other conditions prone to trigger syncope (by either hemodynamic compromise or by a neural reflex mechanism, or both), some of the most important are [hypertrophic cardiomyopathy](https://bliptext.com/articles/hypertrophic-cardiomyopathy), acute aortic dissection, pericardial tamponade, pulmonary embolism, aortic stenosis, and [pulmonary hypertension](https://bliptext.com/articles/pulmonary-hypertension).\n\n### Other cardiac causes\n[Sick sinus syndrome](https://bliptext.com/articles/sick-sinus-syndrome), a sinus node dysfunction, causing alternating bradycardia and tachycardia.\nOften there is a long pause (asystole) between heartbeats.\n[Adams-Stokes syndrome](https://bliptext.com/articles/adams-stokes-syndrome) is a cardiac syncope that occurs with seizures caused by complete or incomplete heart block.\nSymptoms include deep and fast respiration, weak and slow pulse, and respiratory pauses that may last for 60 seconds.\n[Subclavian steal syndrome](https://bliptext.com/articles/subclavian-steal-syndrome) arises from retrograde (reversed) flow of blood in the vertebral artery or the internal thoracic artery, due to a proximal stenosis (narrowing) and/or occlusion of the subclavian artery.\nSymptoms such as syncope, lightheadedness, and paresthesias occur while exercising the arm on the affected side (most commonly the left).\n[Aortic dissection](https://bliptext.com/articles/aortic-dissection) (a tear in the aorta) and [cardiomyopathy](https://bliptext.com/articles/cardiomyopathy) can also result in syncope.\nVarious medications, such as [beta blockers](https://bliptext.com/articles/beta-blocker), may cause bradycardia induced syncope.\nA [pulmonary embolism](https://bliptext.com/articles/pulmonary-embolism) can cause obstructed blood vessels and is the cause of syncope in less than 1% of people who present to the emergency department.\n\n## Blood pressure\nOrthostatic (postural) hypotensive syncope is caused primarily by an excessive drop in blood pressure when standing up from a previous position of lying or sitting down.\nWhen the head is elevated above the feet the pull of gravity causes blood pressure in the head to drop.\nThis is sensed by [stretch receptors](https://bliptext.com/articles/carotid-sinus) in the walls of vessels in the carotid sinus and aortic arch.\nThese receptors then trigger a sympathetic nervous response to compensate and redistribute blood back into the brain.\nThe sympathetic response causes peripheral vasoconstriction and increased heart rate.\nThese together act to raise blood pressure back to baseline.\nApparently healthy individuals may experience minor symptoms (\"lightheadedness\", \"greying-out\") as they stand up if blood pressure is slow to respond to the stress of upright posture.\nIf the blood pressure is not adequately maintained during standing, faints may develop.\nHowever, the resulting \"transient orthostatic hypotension\" does not necessarily signal any serious underlying disease.\nIt is as common or perhaps even more common than vasovagal syncope.\nThis may be due to medications, [dehydration](https://bliptext.com/articles/dehydration), significant bleeding or [infection](https://bliptext.com/articles/infection).\nThe most susceptible individuals are elderly frail individuals, or persons who are dehydrated from hot environments or inadequate fluid intake.\nFor example, medical students would be at risk for orthostatic hypotensive syncope while observing long surgeries in the operating room.\nThere is also evidence that exercise training can help reduce orthostatic intolerance.\nMore serious orthostatic hypotension is often the result of certain commonly prescribed medications such as diuretics, β-adrenergic blockers, other anti-hypertensives (including vasodilators), and [nitroglycerin](https://bliptext.com/articles/nitroglycerin).\nIn a small percentage of cases, the cause of orthostatic hypotensive faints is structural damage to the [autonomic nervous system](https://bliptext.com/articles/autonomic-nervous-system) due to systemic diseases (e.g., [amyloidosis](https://bliptext.com/articles/amyloidosis) or diabetes) or in neurological diseases (e.g., Parkinson's disease).\nHyperadrenergic orthostatic hypotension refers to an orthostatic drop in blood pressure despite high levels of sympathetic adrenergic response.\nThis occurs when a person with normal physiology is unable to compensate for >20% loss in intravascular volume.\nThis may be due to blood loss, dehydration or [third-spacing](https://bliptext.com/articles/fluid-compartments).\nOn standing the person will experience reflex tachycardia (at least 20% increased over supine) and a drop in blood pressure.\nHypoadrenergic orthostatic hypotension occurs when the person is unable to sustain a normal sympathetic response to blood pressure changes during movement despite adequate intravascular volume.\nThere is little to no compensatory increase in heart rate or blood pressure when standing for up to 10 minutes.\nThis is often due to an underlying disorder or medication use and is accompanied by other [hypoadrenergic signs](https://bliptext.com/articles/adrenal-insufficiency).\n\n## Central nervous system ischemia\nThe [central ischemic response](https://bliptext.com/articles/ischemia) is triggered by an inadequate supply of oxygenated blood in the brain.\nCommon examples include [strokes](https://bliptext.com/articles/stroke) and [transient ischemic attacks](https://bliptext.com/articles/transient-ischemic-attack).\nWhile these conditions often impair consciousness they rarely meet the medical definition of syncope.\n[Vertebrobasilar](https://bliptext.com/articles/vertebrobasilar-artery-stroke) transient ischemic attacks may produce true syncope as a symptom.\nThe respiratory system may compensate for dropping oxygen levels through [hyperventilation](https://bliptext.com/articles/hyperventilation), though a sudden [ischemic](https://bliptext.com/articles/ischemia) episode may also proceed faster than the respiratory system can respond.\nThese processes cause the typical symptoms of fainting: pale skin, rapid breathing, nausea, and weakness of the limbs, particularly of the legs.\nIf the ischemia is intense or prolonged, limb weakness progresses to collapse.\nThe weakness of the legs causes most people to sit or lie down if there is time to do so.\nThis may avert a complete collapse, but whether the patient sits down or falls down, the result of an ischaemic episode is a posture in which less blood pressure is required to achieve adequate blood flow.\nAn individual with very little skin pigmentation may appear to have all color drained from his or her face at the onset of an episode.\nThis effect combined with the following collapse can make a strong and dramatic impression on bystanders.\n\n### Vertebro-basilar arterial disease\nArterial disease in the upper spinal cord, or lower brain that causes syncope if there is a reduction in blood supply.\nThis may occur with extending the neck or with use of medications to lower blood pressure.\n\n## Other causes\nThere are other conditions which may cause or resemble syncope.\nSeizures and syncope can be difficult to differentiate.\nBoth often present as sudden loss of consciousness and convulsive movements may be present or absent in either.\nMovements in syncope are typically brief and more irregular than seizures.\n[Akinetic seizures](https://bliptext.com/articles/atonic-seizure) can present with sudden loss of postural tone without associated tonic-clonic movements.\nAbsence of a long post-ictal state is indicative of syncope rather than an akinetic seizure.\nSome rare forms, such as [hair-grooming syncope](https://bliptext.com/articles/hair-grooming-syncope) are of an unknown cause.\nSubarachnoid hemorrhage may result in syncope.\nOften this is in combination with sudden, severe headache.\nIt may occur as a result of a ruptured aneurysm or head trauma.\n[Heat syncope](https://bliptext.com/articles/heat-syncope) occurs when heat exposure causes decreased blood volume and peripheral vasodilatation.\nPosition changes, especially during vigorous exercise in the heat, may lead to decreased blood flow to the brain.\nClosely related to other causes of syncope related to hypotension (low blood pressure) such as orthostatic syncope.\nSome psychological conditions ([anxiety](https://bliptext.com/articles/anxiety-disorder) disorder, [somatic symptom disorder](https://bliptext.com/articles/somatic-symptom-disorder), [conversion disorder](https://bliptext.com/articles/conversion-disorder)) may cause symptoms resembling syncope.\nA number of psychological interventions are available.\nLow blood sugar can be a rare cause of syncope.\n[Narcolepsy](https://bliptext.com/articles/narcolepsy) may present with sudden loss of consciousness similar to syncope.\n\n# Diagnostic approach\nA medical history, physical examination, and [electrocardiogram](https://bliptext.com/articles/electrocardiogram) (ECG) are the most effective ways to determine the underlying cause of syncope.\nGuidelines from the American College of Emergency Physicians and American Heart Association recommend a syncope workup include a thorough medical history, physical exam with orthostatic vitals, and a 12-lead ECG.\nThe ECG is useful to detect an abnormal heart rhythm, [poor blood flow to the heart muscle](https://bliptext.com/articles/coronary-artery-disease) and other electrical issues, such as [long QT syndrome](https://bliptext.com/articles/long-qt-syndrome) and [Brugada syndrome](https://bliptext.com/articles/brugada-syndrome).\nHeart related causes also often have little history of a [prodrome](https://bliptext.com/articles/prodrome).\nLow blood pressure and a fast heart rate after the event may indicate blood loss or dehydration, while [low blood oxygen levels](https://bliptext.com/articles/hypoxia-medical) may be seen following the event in those with pulmonary embolism.\nRoutine broad panel laboratory testing detects abnormalities in , which cites:\n\n## Differential diagnosis\nOther diseases which mimic syncope include [seizure](https://bliptext.com/articles/epileptic-seizure), [low blood sugar](https://bliptext.com/articles/hypoglycemia), certain types of [stroke](https://bliptext.com/articles/stroke), and paroxysmal spells.\nWhile these may appear as \"fainting\", they do not fit the strict definition of syncope being a sudden reversible loss of consciousness due to decreased blood flow to the brain.\n\n# Management\nManagement of syncope focuses on treating the underlying cause.\nThis can be challenging as the underlying cause is unclear in half of all cases.\nSeveral risk stratification tools (explained below) have been developed to combat the vague nature of this diagnosis.\nPeople with an abnormal ECG reading, history of congestive heart failure, family history of sudden cardiac death, shortness of breath, HCT<30, hypotension or evidence of bleeding should be admitted to the hospital for further evaluation and monitoring.\nLow-risk cases of vasovagal or orthostatic syncope in younger people with no significant cardiac history, no family history of sudden unexplained death, and a normal EKG and initial evaluation may be candidates for discharge to follow-up with their primary care provider.\nRecommended acute treatment of vasovagal and orthostatic (hypotension) syncope involves returning blood to the brain by positioning the person on the ground, with legs slightly elevated or sitting leaning forward and the head between the knees for at least 10–15 minutes, preferably in a cool and quiet place.\nFor individuals who have problems with chronic fainting spells, therapy should focus on recognizing the triggers and learning techniques to keep from fainting.\nAt the appearance of warning signs such as lightheadedness, nausea, or cold and clammy skin, counter-pressure maneuvers that involve gripping fingers into a fist, tensing the arms, and crossing the legs or squeezing the thighs together can be used to ward off a fainting spell.\nAfter the symptoms have passed, [sleep](https://bliptext.com/articles/sleep) is recommended.\nLifestyle modifications are important for treating people experiencing repeated syncopal episodes.\nAvoiding triggers and situations where loss of consciousness would be seriously hazardous (operating heavy machinery, commercial pilot, etc.) has been shown to be effective.\nIf fainting spells occur often without a triggering event, syncope may be a sign of an underlying heart disease.\nIn the case where syncope is caused by cardiac disease, the treatment is much more sophisticated than that of [vasovagal](https://bliptext.com/articles/vasovagal) syncope and may involve [pacemakers](https://bliptext.com/articles/artificial-cardiac-pacemaker) and [implantable cardioverter-defibrillators](https://bliptext.com/articles/implantable-cardioverter-defibrillators) depending on the precise cardiac cause.\n\n## Risk tools\nThe [San Francisco syncope rule](https://bliptext.com/articles/san-francisco-syncope-rule) was developed to isolate people who have higher risk for a serious cause of syncope.\nHigh risk is anyone who has: congestive heart failure, hematocrit <30%, electrocardiograph abnormality, shortness of breath, or systolic blood pressure <90 mmHg.\nThe San Francisco syncope rule however was not validated by subsequent studies.\nThe Canadian syncope risk score was developed to help select low-risk people that may be viable for discharge home.\nA score of <0 on the Canadian syncope risk score is associated with <2% risk of serious adverse event within 30 days.\nIt has been shown to be more effective than older syncope risk scores even combined with cardiac biomarkers at predicting adverse events.\n\n# Epidemiology\nThere are 18.1–39.7 syncope episodes per 1000 people in the general population.\nRates are highest between the ages of 10–30 years old.\nThis is likely because of the high rates of vasovagal syncope in the young adult population.\nOlder adults are more likely to have orthostatic or cardiac syncope.\nSyncope affects about three to six out of every thousand people each year.\nIt is more common in older people and females.\nIt is the reason for 2–5% of visits to emergency departments and admissions to hospital.\nUp to half of women over the age of 80 and a third of medical students describe at least one event at some point in their lives.\n\n# Prognosis\nOf those presenting with syncope to an emergency department, about 4% died in the next 30 days.\nThe risk of a poor outcome, however, depends very much on the underlying cause.\nSituational syncope is not at increased risk of death or adverse outcomes.\nCardiac syncope is associated with worse prognosis compared to noncardiac syncope.\nFactors associated with poor outcomes include history of heart failure, history of myocardial infarction, ECG abnormalities, palpitations, signs of hemorrhage, syncope during exertion, and advanced age.\n\n# Society and culture\nFainting in women was a commonplace trope or stereotype in [Victorian England](https://bliptext.com/articles/victorian-england) and in contemporary and modern depictions of the period.\nSyncope and presyncope are common in young athletes.\nIn 1990 the American college basketball player [Hank Gathers](https://bliptext.com/articles/hank-gathers) suddenly collapsed and died during a televised intercollegiate basketball game.\nHe had previously collapsed during a game a few months prior.\nHe was diagnosed with exercise-induced ventricular tachycardia at the time.\nThere was speculation that he had since stopped taking the prescribed medications on game days.\n[Falling-out](https://bliptext.com/articles/falling-out) is a [culture-bound syndrome](https://bliptext.com/articles/culture-bound-syndrome) primarily reported in the [southern United States](https://bliptext.com/articles/southern-united-states) and the [Caribbean](https://bliptext.com/articles/caribbean).\n\n## Etymology\nThe term is derived from the [Late Latin](https://bliptext.com/articles/latin-language) syncope, from [Ancient Greek](https://bliptext.com/articles/ancient-greek) συγκοπή (sunkopē) 'cutting up', 'sudden loss of strength', from σύν (sun, \"together, thoroughly\") and κόπτειν (koptein, \"strike, cut off\").","revisionCount":0},"hasMore":false,"nextCursor":null}

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