Syncope ( , SING-kə-pee), commonly known as fainting or passing out, is a loss of 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, typically from low blood pressure. There are sometimes symptoms before the loss of consciousness such as lightheadedness, sweating, pale skin, 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. 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 or blood vessel related; reflex, also known as neurally mediated; and orthostatic hypotension. 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 valves or heart muscle, and blockages of blood vessels from a pulmonary embolism or aortic dissection, 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, vomiting, or coughing. Neurally mediated syncope may also occur when an area in the neck known as the carotid sinus 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, significant bleeding, or infection. There also seems to be a genetic component to syncope. A medical history, physical examination, and 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 and Brugada syndrome. Heart related causes also often have little history of a prodrome. 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 (CT) is generally not required unless specific concerns are present. Other causes of similar symptoms that should be considered include seizure, stroke, concussion, low blood oxygen, low blood sugar, drug intoxication 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 approximately 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 hospitals. 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 on the underlying cause.
Etymology The Late Latin term syncope is derived from the Ancient Greek συγκοπή (synkopē) that literally means a "cutting up," from σύν (sýn: "together", "thoroughly") and κόπτειν (kóptein: "striking", "cutting off"), and denotes the passing out of consciousness typically caused by insufficient blood flowing to the brain.
Causes Causes range from non-serious to potentially fatal. There are three broad categories of causes: heart or blood vessel related; reflex, also known as neurally mediated; and orthostatic hypotension. 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 the 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 affected the expression of ZNF804A, making this gene the strongest driver of the association.
Neurally mediated syncope Reflex syncope 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, or strong feelings, or from a specific activity such as urination, vomiting, or coughing.
Vasovagal syncope
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