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Syncope, commonly known as fainting, is a loss of
consciousness Consciousness, at its simplest, is sentience or awareness of internal and external existence. Despite millennia of analyses, definitions, explanations and debates by philosophers and scientists, consciousness remains puzzling and controversial ...

consciousness
and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tis ...

brain
, typically from
low blood pressure Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dia ...
. There are sometimes symptoms before the loss of consciousness such as
lightheadedness Lightheadedness is a common and typically unpleasant sensation of dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-speci ...
,
sweating Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), cla ...
,
pale skin Pallor is a pale color of the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as t ...
, blurred vision, nausea, vomiting, or feeling warm. Syncope may also be associated with a short episode of muscle twitching. Psychiatric causes can also be determined when a patient experiences fear, anxiety, or panic; particularly before a stressful event usually medical in nature. When consciousness and muscle strength are not completely lost, it is called
presyncope Lightheadedness is a common and typically unpleasant sensation of dizziness or a feeling that one may faint. The sensation of lightheadedness can be short-lived, prolonged, or, rarely, recurring. In addition to dizziness, the individual may feel ...
. It is recommended that presyncope be treated the same as syncope. Causes range from non-serious to potentially fatal. There are three broad categories of causes:
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
or
blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a comp ...
related;
reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
, also known as mediated; and
orthostatic hypotension Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure Blood pressure (BP) is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (fr ...
. Issues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common. Heart related causes may include an abnormal heart rhythm, problems with the
heart valve A heart valve is a one-way valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valv ...
s or heart muscle and blockages of blood vessels from a
pulmonary embolism Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain p ...

pulmonary embolism
or
aortic dissection Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of severe chest or ...
among others. Neurally mediated syncope occurs when blood vessels expand and heart rate decreases inappropriately. This may occur from either a triggering event such as exposure to blood, pain, strong feelings or a specific activity such as
urination Urination is the release of urine Urine is a liquid by-product A by-product or byproduct is a secondary product derived from a production process, process or ; it is not the primary product or service being produced. A by-product can b ...
,
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other anim ...

vomiting
, or
coughing A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and Microorganism, microbes. As a protective reflex, coughing can be repetitive with the cough reflex follow ...
. Neurally mediated syncope may also occur when an area in the neck known as the
carotid sinus In human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a ta ...
is pressed. The third type of syncope is due to a drop in blood pressure when changing position such as when standing up. This is often due to medications that a person is taking but may also be related to
dehydration In physiology, dehydration is a lack of total body water In physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studie ...

dehydration
, significant bleeding or
infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may ...

infection
. There also seems to be a genetic component to syncope. A medical history, physical examination, and
electrocardiogram Electrocardiography is the process of producing an electrocardiogram (ECG or EKG). It is a graph of voltage Voltage, electric potential difference, electromotive force emf, electric pressure or electric tension is the difference in elec ...

electrocardiogram
(ECG) are the most effective ways to determine the underlying cause. The ECG is useful to detect an abnormal heart rhythm, poor blood flow to the heart muscle and other electrical issues, such as
long QT syndrome Long QT syndrome (LQTS) is a condition in which repolarization of the heart after a Cardiac cycle, heartbeat is affected. It results in an increased risk of an cardiac arrhythmia, irregular heartbeat which can result in Syncope (medicine), faintin ...
and
Brugada syndrome Brugada syndrome (BrS) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics, a genome is all genetic information of an orga ...
. Heart related causes also often have little history of a
prodrome In medicine Medicine is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable ...
. Low blood pressure and a fast heart rate after the event may indicate blood loss or dehydration, while low blood oxygen levels may be seen following the event in those with pulmonary embolism. More specific tests such as implantable loop recorders, tilt table testing or carotid sinus massage may be useful in uncertain cases.
Computed tomography A CT scan or computed tomography scan (formerly known as computed axial tomography or CAT scan) is a medical imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of ...
(CT) is generally not required unless specific concerns are present. Other causes of similar symptoms that should be considered include
seizure An epileptic seizure, formally known as a seizure, is a period of symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower tem ...
,
stroke A stroke is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Di ...

stroke
,
concussion A concussion, also known as a mild traumatic brain injury (mTBI), is a head injury A head injury is any injury that results in trauma to the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that con ...

concussion
, low blood oxygen,
low blood sugar Hypoglycemia, also known as low blood sugar, is a fall in blood sugar The blood sugar level, blood sugar concentration, or blood glucose level is the concentration of glucose present in the blood of humans and other animals. Glucose is a simpl ...

low blood sugar
,
drug intoxication Substance intoxication is a transient condition of altered consciousness , an English Paracelsian physician Consciousness, at its simplest, is "sentience or awareness of internal and external existence". Despite millennia of analyses, definitio ...
and some psychiatric disorders among others. Treatment depends on the underlying cause. Those who are considered at high risk following investigation may be admitted to hospital for further monitoring of the heart. Syncope affects about three to six out of every thousand people each year. It is more common in older people and females. It is the reason for one to three percent of visits to emergency departments and admissions to hospital. Up 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. Of those presenting with syncope to an emergency department, about 4% died in the next 30 days. The risk of a poor outcome, however, depends very much on the underlying cause.


Causes

Causes range from non-serious to potentially fatal. There are three broad categories of causes:
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
or
blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a comp ...
related;
reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
, also known as mediated; and
orthostatic hypotension Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure Blood pressure (BP) is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (fr ...
. Issues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common. There also seems to be a genetic component to syncope. A recent genetic study has identified first risk locus for syncope and collapse. The lead genetic variant, residing at chromosome 2q31.1, is an intergenic variant approximately 250 kb downstream of the ZNF804A gene. The variant effected the expression of ZNF804A, making this gene the strongest driver of the association.


Neurally mediated syncope

Reflex syncope Reflex syncope is a brief loss of consciousness Unconsciousness is a state which occurs when the ability to maintain an awareness of self and environment is lost. It involves a complete, or near-complete, lack of responsiveness to people an ...
or neurally mediated syncope occurs when blood vessels expand and heart rate decreases inappropriately leading to poor blood flow to the brain. This may occur from either a triggering event such as exposure to blood, pain, strong feelings, or a specific activity such as
urination Urination is the release of urine Urine is a liquid by-product A by-product or byproduct is a secondary product derived from a production process, process or ; it is not the primary product or service being produced. A by-product can b ...
,
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach The stomach is a muscular, Organ (anatomy), hollow organ in the gastrointestinal tract of humans and many other anim ...

vomiting
, or
coughing A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and Microorganism, microbes. As a protective reflex, coughing can be repetitive with the cough reflex follow ...
.


Vasovagal syncope

Vasovagal (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. There are many different syncope syndromes which all fall under the umbrella of vasovagal syncope related by the same central mechanism. First, the person is usually predisposed to decreased blood pressure by various environmental factors. A lower than expected blood volume, for instance, from taking a low-salt diet in the absence of any salt-retaining tendency. Or heat causing vaso-dilation and worsening the effect of the relatively insufficient blood volume. The next stage is the adrenergic response. If there is underlying fear or anxiety (e.g., social circumstances), or acute fear (e.g., acute threat,
needle phobia Fear of needles, known in medical literature as needle phobia, is the extreme fear of medical procedures involving injections or hypodermic needle Syringe on left, hypodermic needle with attached colour coded Luer Taper, Luer-Lok connector ...
), the vaso-motor centre demands an increased pumping action by the heart (flight or fight response). This 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. A feedback response to the
medulla Medulla or Medullary may refer to: Science * Medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is ...

medulla
is triggered via the afferent
vagus nerve The vagus nerve, historically cited as the pneumogastric nerve, is the tenth cranial nerve Cranial nerves are the nerve A nerve is an enclosed, cable-like bundle of nerve fibers called axon An axon (from Greek ἄξων ''áxōn'', axi ...
. The high (ineffective) sympathetic activity is thereby modulated by vagal (parasympathetic) outflow leading to excessive slowing of heart rate. The abnormality lies in this excessive vagal response causing loss of blood flow to the brain. The tilt-table test typically evokes the attack. Avoiding what brings on the syncope and possibly greater salt intake is often all that is needed. Associated symptoms may be felt in the minutes leading up to a vasovagal episode and are referred to as the prodrome. These consist of light-headedness, confusion, pallor, nausea, salivation, sweating, tachycardia, blurred vision, and sudden urge to defecate among other symptoms. Vasovagal syncope can be considered in two forms: *Isolated episodes of loss of consciousness, unheralded by any warning symptoms for more than a few moments. These tend to occur in the adolescent age group and may be associated with fasting, exercise, abdominal straining, or circumstances promoting vaso-dilation (e.g., heat, alcohol). The subject is invariably upright. The tilt-table test, if performed, is generally negative. *Recurrent syncope with complex associated symptoms. This is neurally mediated syncope (NMS). It is associated with any of the following: preceding or succeeding sleepiness, preceding visual disturbance ("spots before the eyes"), sweating, lightheadedness. The subject is usually but not always upright. The tilt-table test, if performed, is generally positive. It is relatively uncommon. Syncope has been linked with psychological triggers. This includes fainting in response to the sight or thought of blood, needles, pain, and other emotionally stressful situations. One theory in
evolutionary psychology Evolutionary psychology is a theoretical approach in the social Social organisms, including humans, live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchan ...
is that fainting at the sight of blood might have evolved as a form of playing dead which increased survival from attackers and might have slowed blood loss in a primitive environment. "Blood-injury phobia", as this is called, is experienced by about 15% of people. It is often possible to manage these symptoms with specific behavioral techniques. Another
evolutionary psychology Evolutionary psychology is a theoretical approach in the social Social organisms, including humans, live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchan ...
view is that some forms of fainting are non-verbal signals that developed in response to increased inter-group aggression during the
paleolithic The Paleolithic or Palaeolithic or Palæolithic (), also called the Old Stone Age (from Greek palaios - old, lithos - stone), is a period in prehistory Prehistory, also known as pre-literary history, is the period of human history ...
. A non-combatant who has fainted signals that she or he is not a threat. This would explain the association between fainting and stimuli such as bloodletting and injuries seen in
blood-injection-injury type phobia Blood-injection-injury (BII) type phobia is a type of specific phobia characterized by the display of excessive, irrational fear in response to the sight of blood, injury, or injection, or in anticipation of an injection, injury, or exposure to blo ...
s such as
needle phobia Fear of needles, known in medical literature as needle phobia, is the extreme fear of medical procedures involving injections or hypodermic needle Syringe on left, hypodermic needle with attached colour coded Luer Taper, Luer-Lok connector ...
as well as the gender differences. Much of this pathway was discovered in animal experiments by Bezold (Vienna) in the 1860s. In animals, it may represent a defence mechanism when confronted by danger ("playing possum").


Situational syncope

Syncope may be caused by specific behaviors including coughing, urination, defecation, vomiting, swallowing (
deglutition Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of ...
), and following exercise. Manisty 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." Fainting can occur in "cough syncope" following severe fits of
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, ...
ing, such as that associated with
pertussis Whooping cough, also known as pertussis or the 100-day cough, is a highly contagious bacterial disease. Initial symptoms are usually similar to those of the common cold The common cold, also known simply as a cold, is a viral infectious d ...

pertussis
or "whooping cough." Neurally mediated syncope may also occur when an area in the neck known as the
carotid sinus In human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a ta ...
is pressed. A normal response to carotid sinus massage is reduction in blood pressure and slowing of the heart rate. Especially in people with hypersensitive carotid sinus syndrome this response can cause syncope or presyncope.


Cardiac

Heart-related causes may include an abnormal heart rhythm, problems with the
heart valve A heart valve is a one-way valve check valve Image:Check Valve.svg, 140px, Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction. A check valve, non-return valve, reflux valve, retention valve, foot valv ...
s or heart muscle, or blockages of blood vessels from a
pulmonary embolism Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain p ...

pulmonary embolism
or
aortic dissection Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of severe chest or ...
, among others.


Cardiac arrhythmias

The most common cause of cardiac syncope is cardiac
arrhythmia Arrhythmia, also known as cardiac arrhythmia or heart arrhythmia, is a group of conditions in which the is irregular, too fast, or too slow. The that is too fast – above 100 beats per minute in adults – is called , and a heart rate that i ...
(abnormal
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
rhythm) wherein the heart beats too slowly, too rapidly, or too irregularly to pump enough blood to the brain. Some arrhythmias can be life-threatening. Two major groups of arrhythmias are
bradycardia Bradycardia is a condition typically defined wherein an individual has a resting heart rateHeart rate is the speed of the heartbeat measured by the number of contractions (beats) of the heart The heart is a muscle, muscular Organ (anatom ...
and
tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (s ...
. Bradycardia can be caused by
heart block Heart block (HB) is a disorder in the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the ...

heart block
s. Tachycardias include SVT (
supraventricular tachycardia Supraventricular tachycardia (SVT) is an umbrella term for arising from the . This is in contrast to the other group of fast heart rhythms - , which start within the . There are four main types of SVT: , , (PSVT) and . The symptoms of SVT incl ...
) and VT (
ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a type of regular, fast heart rate that arises from improper electrical activity in the ventricles of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pump ...
). SVT does not cause syncope except in Wolff-Parkinson-White syndrome.
Ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a type of regular, fast heart rate that arises from improper electrical activity in the ventricles of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pump ...
originate in the ventricles. VT causes syncope and can result in sudden death. Ventricular 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 Ventricular fibrillation (V-fib or VF) is an abnormal heart rhythm in which the Ventricle (heart), ventricles of the heart Fibrillation, quiver. It is due to disorganized electrical conduction system of the heart, electrical activity. Ventricular ...

ventricular fibrillation
, which is rapidly fatal without
cardiopulmonary resuscitation Cardiopulmonary resuscitation (CPR) is an emergency procedure An emergency procedure is a plan of actions to be conducted in a certain order or manner, in response to a specific class of reasonably foreseeable emergency, a situation that poses ...
(CPR) and
defibrillation Defibrillation is a treatment for life-threatening cardiac dysrhythmia Arrhythmia, also known as cardiac arrhythmia or heart arrhythmia, is a group of conditions in which the heartbeat is irregular, too fast, or too slow. The heart rate tha ...
.
Long QT syndrome Long QT syndrome (LQTS) is a condition in which repolarization of the heart after a Cardiac cycle, heartbeat is affected. It results in an increased risk of an cardiac arrhythmia, irregular heartbeat which can result in Syncope (medicine), faintin ...
can cause syncope when it sets off
ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a type of regular, fast heart rate that arises from improper electrical activity in the ventricles of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pump ...
or
torsades de pointes ''Torsades de pointes, torsade de pointes'' or ''torsades des pointes'' (TdP) (, , translated as "twisting of peaks") is a specific type of abnormal heart rhythm that can lead to sudden cardiac death Cardiac arrest is a sudden loss of blood ...
. The degree of QT prolongation determines the risk of syncope.
Brugada syndrome Brugada syndrome (BrS) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics, a genome is all genetic information of an orga ...
also commonly presents with syncope secondary to arrhythmia. Typically, tachycardic-generated syncope is caused by a cessation of beats following a tachycardic episode. This condition, called tachycardia-bradycardia syndrome, is usually caused by sinoatrial node dysfunction or block or
atrioventricular block Atrioventricular block (AV block) is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatri ...
.


Obstructive cardiac lesion

Blockages in major vessels or within the heart can also impede blood flow to the brain.
Aortic stenosis Aortic stenosis (AS or AoS) is the narrowing of the exit of the left ventricle A ventricle is one of two large chambers toward the bottom of the heart The heart is a muscle, muscular Organ (anatomy), organ in most animals, which pumps ...

Aortic stenosis
and
mitral stenosis Mitral stenosis is a valvular heart disease Valvular heart disease is any cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a muscle, muscular Organ (anatomy), organ in mo ...

mitral stenosis
are the most common examples. Major valves of the heart become stiffened and reduce the efficiency of the hearts pumping action. This may not cause symptoms at rest but with exertion, the heart is unable to keep up with increased demands leading to syncope. Aortic stenosis presents with repeated episodes of syncope. Rarely, cardiac tumors such as atrial myxomas can also lead to syncope.


Structural cardiopulmonary disease

Diseases involving the shape and strength of the heart can be a cause of reduced blood flow to the brain, which increases risk for syncope. The most common cause in this category is fainting associated with an acute myocardial infarction or ischemic event. The faint in this case is primarily caused by an abnormal nervous system reaction similar to the reflex faints. Women are significantly more likely to experience syncope as a presenting symptom of a myocardial infarction. In 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. Among 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 Hypertrophic cardiomyopathy (HCM) is a condition in which the heart becomes hypertrophy, thickened without an obvious cause. The parts of the heart most commonly affected are the interventricular septum and the ventricles. This results in the hea ...
, acute aortic dissection, pericardial tamponade, pulmonary embolism, aortic stenosis, and
pulmonary hypertension Pulmonary hypertension (PH or PHTN) is a condition of increased blood pressure within the arteries of the lungs. Symptoms include shortness of breath, syncope, tiredness, chest pain, pedal edema, swelling of the legs, and a fast heartbeat. The ...
.


Other cardiac causes

Sick sinus syndrome Sinus node dysfunction (SND), also known as sick sinus syndrome (SSS), is a group of abnormal heart rhythms ( arrhythmias) usually caused by a malfunction of the sinus node, the heart's primary pacemaker. Tachycardia-bradycardia syndrome is a varia ...
, a sinus node dysfunction, causing alternating bradycardia and tachycardia. Often there is a long pause (asystole) between heartbeats. Adams-Stokes syndrome is a cardiac syncope that occurs with seizures caused by complete or incomplete heart block. Symptoms include deep and fast respiration, weak and slow pulse, and respiratory pauses that may last for 60 seconds.
Subclavian steal syndrome Subclavian steal syndrome (SSS), also called subclavian steal steno-occlusive disease, is a constellation of sign (medicine), signs and symptoms that arise from retrograde (reversed) blood flow in the vertebral artery or the internal thoracic artery ...
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. Symptoms such as syncope, lightheadedness, and paresthesias occur while exercising the arm on the affected side (most commonly the left).
Aortic dissection Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of severe chest or ...
(a tear in the aorta) and
cardiomyopathy Cardiomyopathy is a group of diseases that affect the heart muscle Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate Vertebrates () comprise all species of animal Animals (also called Metaz ...
can also result in syncope. Various medications, such as
beta blocker Beta blockers (beta-blockers, β-blockers, etc.) are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack (myocardial infarction A myocardial infarction (M ...
s, may cause bradycardia induced syncope. A
pulmonary embolism Pulmonary embolism (PE) is a blockage of an pulmonary artery, artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include dyspnea, shortness of breath, chest pain p ...

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.


Blood pressure

''Orthostatic (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. When the head is elevated above the feet the pull of gravity causes blood pressure in the head to drop. This is sensed by stretch receptors in the walls of vessels in the carotid sinus and aortic arch. These receptors then trigger a sympathetic nervous response to compensate and redistribute blood back into the brain. The sympathetic response causes peripheral vasoconstriction and increased heart rate. These together act to raise blood pressure back to baseline. Apparently 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. If the blood pressure is not adequately maintained during standing, faints may develop. However, the resulting "transient orthostatic hypotension" does not necessarily signal any serious underlying disease. It is as common or perhaps even more common than vasovagal syncope. This may be due to medications,
dehydration In physiology, dehydration is a lack of total body water In physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studie ...

dehydration
, significant bleeding or
infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may ...

infection
. The most susceptible individuals are elderly frail individuals, or persons who are dehydrated from hot environments or inadequate fluid intake. For example, medical students would be at risk for orthostatic hypotensive syncope while observing long surgeries in the operating room. There is also evidence that exercise training can help reduce orthostatic intolerance. More 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 Nitroglycerin (NG), also known as trinitroglycerin (TNG), nitro, glyceryl trinitrate (GTN), or 1,2,3-trinitroxypropane, is a dense, colorless, oily, explosive An explosive (or explosive material) is a reactive substance that contains a grea ...

nitroglycerin
. In a small percentage of cases, the cause of orthostatic hypotensive faints is structural damage to the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

autonomic nervous system
due to systemic diseases (e.g.,
amyloidosis Amyloidosis is a group of diseases in which abnormal protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one ...

amyloidosis
or diabetes) or in neurological diseases (e.g., Parkinson's disease). Hyperadrenergic orthostatic hypotension refers to an orthostatic drop in blood pressure despite high levels of sympathetic adrenergic response. This occurs when a person with normal physiology is unable to compensate for >20% loss in intravascular volume. This may be due to blood loss, dehydration or third-spacing. On standing the person will experience reflex tachycardia (at least 20% increased over supine) and a drop in blood pressure. Hypoadrenergic orthostatic hypotension occurs when the person is unable to sustain a normal sympathetic response to blood pressure changes during movement despite adequate intravascular volume. There is little to no compensatory increase in heart rate or blood pressure when standing for up to 10 minutes. This is often due to an underlying disorder or medication use and is accompanied by other hypoadrenergic signs.


Central nervous system ischemia

The central ischemic response is triggered by an inadequate supply of oxygenated blood in the brain. Common examples include
stroke A stroke is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Di ...

stroke
s and
transient ischemic attack A transient ischemic attack (TIA), commonly known as a mini-stroke, is a brief episode of neurological dysfunction caused by loss of blood flow (ischemia Ischemia or ischaemia is a restriction in blood Blood is a body fluid in humans and ...
s. While these conditions often impair consciousness they rarely meet the medical definition of syncope. Vertebrobasilar transient ischemic attacks may produce true syncope as a symptom. The respiratory system may compensate for dropping oxygen levels through
hyperventilation Hyperventilation occurs when the rate or tidal volume Tidal volume (symbol VT or TV) is the volume of air moved into or out of the lungs during a normal breath. In a healthy, young human adult, tidal volume is approximately 500 ml per i ...
, though a sudden
ischemic Ischemia or ischaemia is a restriction in blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressi ...
episode may also proceed faster than the respiratory system can respond. These processes cause the typical symptoms of fainting: pale skin, rapid breathing, nausea, and weakness of the limbs, particularly of the legs. If the ischemia is intense or prolonged, limb weakness progresses to collapse. The weakness of the legs causes most people to sit or lie down if there is time to do so. This may avert a complete collapse, but whether the sufferer 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. An individual with very little skin pigmentation may appear to have all color drained from his or her face at the onset of an episode. This effect combined with the following collapse can make a strong and dramatic impression on bystanders.


Vertebro-basilar arterial disease

Arterial disease in the upper spinal cord, or lower brain that causes syncope if there is a reduction in blood supply. This may occur with extending the neck or with use of medications to lower blood pressure.


Other causes

There are other conditions which may cause or resemble syncope. Seizures and syncope can be difficult to differentiate. Both often present as sudden loss of consciousness and convulsive movements may be present or absent in either. Movements in syncope are typically brief and more irregular than seizures. Akinetic seizures can present with sudden loss of postural tone without associated tonic-clonic movements. Absence of a long post-ictal state is indicative of syncope rather than an akinetic seizure. Subarachnoid hemorrhage may result in syncope. Often this is in combination with sudden, severe headache. It may occur as a result of a ruptured aneurysm or head trauma.
Heat syncope Heat syncope is fainting Syncope, also known as fainting, is a loss of consciousness , an English Paracelsian physician Consciousness, at its simplest, is "sentience or awareness of internal and external existence". Despite millennia of a ...
occurs when heat exposure causes decreased blood volume and peripheral vasodilatation. Position changes, especially during vigorous exercise in the heat, may lead to decreased blood flow to the brain. Closely related to other causes of syncope related to hypotension (low blood pressure) such as orthostatic syncope. Some psychological conditions (
anxiety Anxiety is an emotion Emotions are mental state, psychological states brought on by neurophysiology, neurophysiological changes, variously associated with thoughts, feelings, behavioural responses, and a degree of pleasure or suffering, disp ...
disorder,
somatic symptom disorder A somatic symptom disorder, formerly known as a somatoform disorder,(2013) conversion disorder Conversion disorder (CD), or functional neurologic symptom disorder, is a diagnostic category used in some psychiatric classification systems. It is sometimes applied to patients who present with neurological symptoms, such as numbness, blindnes ...
) may cause symptoms resembling syncope. A number of psychological interventions are available. Low blood sugar can be a rare cause of syncope.
Narcolepsy Narcolepsy is a long-term Long-Term Capital Management L.P. (LTCM) was a hedge fund''A financial History of the United States Volume II: 1970–2001'', Jerry W. Markham, Chapter 5: "Bank Consolidation", M. E. Sharpe, Inc., 2002 based in Green ...
may present with sudden loss of consciousness similar to syncope.


Diagnostic approach

A medical history, physical examination, and
electrocardiogram Electrocardiography is the process of producing an electrocardiogram (ECG or EKG). It is a graph of voltage Voltage, electric potential difference, electromotive force emf, electric pressure or electric tension is the difference in elec ...

electrocardiogram
(ECG) are the most effective ways to determine the underlying cause of syncope. Guidelines 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. The ECG is useful to detect an abnormal heart rhythm, poor blood flow to the heart muscle and other electrical issues, such as
long QT syndrome Long QT syndrome (LQTS) is a condition in which repolarization of the heart after a Cardiac cycle, heartbeat is affected. It results in an increased risk of an cardiac arrhythmia, irregular heartbeat which can result in Syncope (medicine), faintin ...
and
Brugada syndrome Brugada syndrome (BrS) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics, a genome is all genetic information of an orga ...
. Heart related causes also often have little history of a
prodrome In medicine Medicine is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable ...
. Low blood pressure and a fast heart rate after the event may indicate blood loss or dehydration, while low blood oxygen levels may be seen following the event in those with pulmonary embolism. Routine broad panel laboratory testing detects abnormalities in <2–3% of results and is therefore not recommended. Based 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. More specific tests such as implantable loop recorders, tilt table testing or carotid sinus massage may be useful in uncertain cases.
Computed tomography A CT scan or computed tomography scan (formerly known as computed axial tomography or CAT scan) is a medical imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of ...
(CT) is generally not required unless specific concerns are present. Other causes of similar symptoms that should be considered include
seizure An epileptic seizure, formally known as a seizure, is a period of symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower tem ...
,
stroke A stroke is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Di ...

stroke
,
concussion A concussion, also known as a mild traumatic brain injury (mTBI), is a head injury A head injury is any injury that results in trauma to the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that con ...

concussion
, low blood oxygen,
low blood sugar Hypoglycemia, also known as low blood sugar, is a fall in blood sugar The blood sugar level, blood sugar concentration, or blood glucose level is the concentration of glucose present in the blood of humans and other animals. Glucose is a simpl ...

low blood sugar
,
drug intoxication Substance intoxication is a transient condition of altered consciousness , an English Paracelsian physician Consciousness, at its simplest, is "sentience or awareness of internal and external existence". Despite millennia of analyses, definitio ...
and some psychiatric disorders among others. Treatment depends on the underlying cause. Those who are considered at high risk following investigation may be admitted to hospital for further monitoring of the heart. A
hemoglobin Hemoglobin or haemoglobin (spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two distinct wa ...

hemoglobin
count may indicate anemia or blood loss. However, this has been useful in only about 5% of people evaluated for fainting. The
tilt table test A tilt table test (TTT), occasionally called upright tilt testing (UTT), is a medical procedureA medical procedure is a course of action intended to achieve a result in the delivery of healthcare. A medical procedure with the intention of determi ...
is performed to elicit orthostatic syncope secondary to autonomic dysfunction (neurogenic). A number of factors make a heart related cause more likely including age over 35, prior
atrial fibrillation Atrial fibrillation (AF or A-fib) is an abnormal heart rhythm (arrhythmia) characterized by the rapid and irregular beating of the atrial chambers of the heart. It often begins as short periods of abnormal beating, which become longer or con ...

atrial fibrillation
, and turning blue during the event.


Electrocardiogram

Electrocardiogram Electrocardiography is the process of producing an electrocardiogram (ECG or EKG). It is a graph of voltage Voltage, electric potential difference, electromotive force emf, electric pressure or electric tension is the difference in elec ...

Electrocardiogram
(ECG) finds that should be looked for include signs of heart ischemia,
arrhythmias Arrhythmia, also known as cardiac arrhythmia or heart arrhythmia, is a group of conditions in which the heartbeat is irregular, too fast, or too slow. The heart rateHeart rate is the speed of the heartbeat measured by the number of contraction ...
,
atrioventricular block Atrioventricular block (AV block) is a type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired. Normally, the sinoatri ...
s, a long QT, a short PR,
Brugada syndrome Brugada syndrome (BrS) is a genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome In the fields of molecular biology and genetics, a genome is all genetic information of an orga ...
, signs of (HOCM), and signs of
arrhythmogenic right ventricular dysplasia Arrhythmogenic cardiomyopathy (ACM), arrhythmogenic right ventricular dysplasia (ARVD), or arrhythmogenic right ventricular cardiomyopathy (ARVC), is an inherited heart disease. ACM is caused by Genetic disorder, genetic defects of the parts of ...
(ARVD/C). Signs of HCM include large voltages in the precordial leads, repolarization abnormalities, and a wide QRS with a slurred upstroke. Signs of ARVD/C include
T wave inversion Normal T wave In electrocardiography Electrocardiography is the process of producing an electrocardiogram (ECG or EKG). It is a graph of voltage versus time of the electrical activity of the heart The heart is a muscle, muscular Organ ...
and epsilon waves in lead V1 to V3. It is estimated that from 20–50% of people have an abnormal ECG. However, while an ECG may identify conditions such as
atrial fibrillation Atrial fibrillation (AF or A-fib) is an abnormal heart rhythm (arrhythmia) characterized by the rapid and irregular beating of the atrial chambers of the heart. It often begins as short periods of abnormal beating, which become longer or con ...

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. Sometimes, a Holter monitor may be used. This is a portable ECG device that can record the wearer's heart rhythms during daily activities over an extended period of time. Since fainting usually does not occur upon command, a Holter monitor can provide a better understanding of the heart's activity during fainting episodes. For people with more than two episodes of syncope and no diagnosis on “routine testing”, an insertable cardiac monitor might be used. It lasts 28–36 months and is inserted just beneath the skin in the upper chest area. File:DVA2555 (CardioNetworks ECGpedia).jpg, ECG showing HOCM File:De-Acquired longQT (CardioNetworks ECGpedia) (cropped).jpg, Long QT syndrome Image:WPW09.JPG, A short PR in Wolff–Parkinson–White syndrome File:Brugada syndrome type2 example1 (CardioNetworks ECGpedia).png, Type 2 Brugada ECG pattern


Imaging

Echocardiography and ischemia testing may be recommended for cases where initial evaluation and ECG testing is nondiagnostic. For people with uncomplicated syncope (without seizures and a normal neurological exam) computed tomography or MRI is not generally needed. Likewise, using carotid ultrasonography on the premise of identifying carotid artery disease as a cause of syncope also is not indicated., which cites: #* #* #* Although sometimes investigated as a cause of syncope, carotid artery problems are unlikely to cause that condition. Additionally an electroencephalogram (EEG) is generally not recommended. A bedside ultrasound may be performed to rule out abdominal aortic aneurysm in people with concerning history or presentation.


Differential diagnosis

Other diseases which mimic syncope include Epileptic seizure, seizure,
low blood sugar Hypoglycemia, also known as low blood sugar, is a fall in blood sugar The blood sugar level, blood sugar concentration, or blood glucose level is the concentration of glucose present in the blood of humans and other animals. Glucose is a simpl ...

low blood sugar
, and certain types of
stroke A stroke is a medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is not due to any immediate external injury. Di ...

stroke
. While 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.


Management

Management of syncope focuses on treating the underlying cause. This can be challenging as the underlying cause is unclear in half of all cases. Several risk stratification tools (explained below) have been developed to combat the vague nature of this diagnosis. People 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. Low-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. Recommended 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. For individuals who have problems with chronic fainting spells, therapy should focus on recognizing the triggers and learning techniques to keep from fainting. At 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. After the symptoms have passed, sleep is recommended. Lifestyle modifications are important for treating people experiencing repeated syncopal episodes. Avoiding triggers and situations where loss of consciousness would be seriously hazardous (operating heavy machinery, commercial pilot, etc.) has been shown to be effective. If fainting spells occur often without a triggering event, syncope may be a sign of an underlying heart disease. In the case where syncope is caused by cardiac disease, the treatment is much more sophisticated than that of vasovagal syncope and may involve artificial cardiac pacemaker, pacemakers and implantable cardioverter-defibrillators depending on the precise cardiac cause.


Risk tools

The San Francisco Syncope Rule, San Francisco syncope rule was developed to isolate people who have higher risk for a serious cause of syncope. High risk is anyone who has: congestive heart failure, hematocrit <30%, electrocardiograph abnormality, shortness of breath, or systolic blood pressure <90 mmHg. The San Francisco syncope rule however was not validated by subsequent studies. The Canadian syncope risk score was developed to help select low-risk people that may be viable for discharge home. A score of <0 on the Canadian syncope risk score is associated with <2% risk of serious adverse event within 30 days. It has been shown to be more effective than older syncope risk scores even combined with cardiac biomarkers at predicting adverse events.


Epidemiology

There are 18.1–39.7 syncope episodes per 1000 people in the general population. Rates are highest between the ages of 10–30 years old. This is likely because of the high rates of vasovagal syncope in the young adult population. Older adults are more likely to have orthostatic or cardiac syncope. Syncope affects about three to six out of every thousand people each year. It is more common in older people and females. It is the reason for 2–5% of visits to emergency departments and admissions to hospital. Up 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.


Prognosis

Of those presenting with syncope to an emergency department, about 4% died in the next 30 days. The risk of a poor outcome, however, depends very much on the underlying cause. Situational syncope is not at increased risk of death or adverse outcomes. Cardiac syncope is associated with worse prognosis compared to noncardiac syncope. Factors 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.


Society and culture

Fainting in women was a commonplace trope or stereotype in Victorian England and in contemporary and modern depictions of the period. Syncope and presyncope are common in young athletes. In 1990 the American college basketball player Hank Gathers suddenly collapsed and died during a televised intercollegiate basketball game. He had previously collapsed during a game a few months prior. He was diagnosed with exercise-induced ventricular tachycardia at the time. There was speculation that he had since stopped taking the prescribed medications on game days. Falling-out is a culture-bound syndrome primarily reported in the southern United States and the Caribbean.


Etymology

The term is derived from the Latin language, Late Latin ''syncope'', from Ancient Greek συγκοπή (''sunkopē'') 'cutting up', 'sudden loss of strength', from σύν (''sun'', "together, thoroughly") and κόπτειν (''koptein'', "strike, cut off").


See also

* Voodoo death


References


External links

*
2004 European Society of Cardiology Guidelines on Management (Diagnosis and Treatment) of Syncope2017 American College of Cardiology GuidelineTilt table test

The San Francisco syncope rule
* {{Authority control Consciousness Wikipedia medicine articles ready to translate Symptoms and signs of mental disorders