Fainting (syncope) has many different causes.
Vasovagal syncope: Also known as the "common faint," this is the most frequent cause of syncope. It results from an abnormal circulatory reflex. The heart pumps more forcefully and the blood vessels relax, but the heart rate does not compensate fast enough to maintain blood flow to the brain. People older than 45 years of age rarely experience a first "common faint." Causes of vasovagal syncope include the following:
- Environmental factors: Most commonly in a hot, crowded setting
- Emotional factors: Stress or the sight or threat of injury
- Physical factors: Standing too long
- Illness: Fatigue, dehydration, or other illnesses
Situational syncope: This is a type of vasovagal syncope that only occurs in particular situations. Causes of situational syncope include the following:
- Cough syncope occurs in some people when coughing forcefully.
- Swallow syncope occurs upon swallowing in some people with disease in the throat or esophagus.
- Micturition syncope occurs when a susceptible person empties an overfilled bladder.
- Carotid sinus hypersensitivity occurs in some people when turning the neck, shaving, or wearing a tight collar.
- Postprandial fainting can occur in elderly people when their blood pressure falls about an hour after eating.
Postural syncope: This occurs when a person lying down, who feels perfectly well and alert, suddenly faints upon standing up. The brain's blood flow decreases when the person stands due to a temporary drop in blood pressure. This sometimes occurs in people who have recently started or changed certain cardiovascular medications. This type of fainting results from either or both of the following causes:
- Low circulating blood volume, caused by blood loss (external or internal), dehydration, or heat exhaustion
- Impaired circulatory reflexes, caused by many medications, disorders of the nervous system, or congenital problems
Cardiac syncope: Heart disease causes a person to faint by a variety of mechanisms. Cardiac causes of fainting are generally life-threatening and include the following:
- Cardiac rhythm abnormality (arrhythmia): Electrical problems of the heart impair its pumping ability. This causes a decrease in blood flow. The heart rate may be either too fast or too slow to pump blood well. This condition usually causes fainting without any warning symptoms.
- Cardiac obstruction: Blood flow can be obstructed within the blood vessels in the chest. Cardiac obstruction can cause fainting during physical exertion. A variety of diseases cause obstruction, including heart attacks, diseased heart valves, pulmonary embolism, cardiomyopathy, pulmonary hypertension, cardiac tamponade, and aortic dissection.
- Heart failure: The heart's pumping ability is impaired. This lowers the force with which blood circulates through the body and may decrease blood flow in the brain.
Neurologic syncope: This syncope can be due to a neurologic condition or event listed below.
- Stroke (bleeding in the brain) can cause syncope associated with headache.
- Transient ischemic attack (TIA or mini-stroke) can cause fainting, usually preceded by double vision, loss of balance, slurred speech, or vertigo (a spinning sensation).
- Migraines can cause fainting on rare occasions.
Psychogenic syncope: Hyperventilation from an anxiety disorder can cause fainting. Rarely, people pretend to faint to minimize stress or for some recognized gain. The diagnosis of psychogenic syncope should only be considered after all other causes have been excluded.
Medically Reviewed by a Doctor on 12/15/2014
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