syncope

Syncope (/ˈsɪŋkəpi/ , 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.