Syncope is the medical term for fainting or passing out. It is caused by a temporary drop in the amount of blood that flows to the brain. This leads to loss of consciousness and muscle control. The person then falls down or over, which allows blood flow to return to the brain. Returning blood flow allows the person to regain consciousness, although feeling confused for a bit. Syncope usually lasts only seconds or minutes.
For most people, syncope occurs once in a great while, if ever, and is not a sign of serious illness. However in others, syncope can be the first and only warning sign prior to an episode of sudden cardiac death. Syncope can also lead to serious injury.
Pre-syncope is the feeling that you are about to faint. Someone with pre-syncope may be lightheaded (dizzy) or nauseated, have a visual "gray out" or trouble hearing, have palpitations, or feel weak or suddenly sweaty.
Types of Syncope
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Vasovagal syncope: The most common type of syncope. Occurs when you faint because your body overreacts to certain triggers, such as the sight of blood, extreme emotional distress, dehydration, anxiety, pain, hunger, etc.
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Postural syncope (postural hypotension): This type of syncope occurs due to an abrupt change in body position (e.g. lying down to standing).
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Cardiac syncope: This type of syncope is caused by a heart or blood vessel condition, such as heart arrhythmias, congenital heart disease, heart valve disease, aortic stenosis, or heart failure. If fainting occurs frequently and is not because of dehydration or sudden postural change, you may need to be tested for a serious heart or vascular condition. Cardiac syncope often occurs suddenly, without dizziness or other pre-syncope symptoms.
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Neurologic syncope: This type of syncope is caused by a neurological condition such as seizure and stroke or transient ischemic attack. Migraines are a less common condition.
Becoming unconscious due to a seizure, heart attack, head injury, stroke, intoxication, blow to the head, diabetic hypoglycemia or other emergency condition is not considered syncope.
Common symptoms of syncope in addition to fainting include:
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Nausea and/or vomiting
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Sweaty palms
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Lightheadedness
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Blacking out
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Changes in vision such as seeing spots or having tunnel vision
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Headaches
It's important to identify the cause of syncope, if possible, to rule out a dangerous heart condition. Depending on your symptoms and circumstances, the following tests may be used to find the cause:
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On-site Diagnostic Tests and Procedures
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Electrocardiogram (ECG or EKG): wires taped to various parts of your body to create a graph of your heart’s electrical rhythm
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Exercise stress test: ECG recorded while strenuously exercising
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Echocardiogram or transesophageal echocardiogram: ultrasound of the heart
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Physical examination: including orthostatic vital signs and carotid sinus massage
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Tilt table test: measurement of heart rate and blood pressure in response to upright tilt, which simulates prolonged standing
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Electrophysiology study (EP): test that examines the heart’s electrical activity from the inside; used to diagnose many heart rhythm disorders
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In-home Diagnostic Monitors
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Holter monitor: a portable ECG you wear continuously for one to seven days to record your heart rhythms over time
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Event monitor: a portable ECG you wear for one or two months, which records only when triggered by an abnormal heart rhythm or when you manually activate it