Fainting is a sudden loss of consciousness. It most often occurs when the blood pressure is too low (hypotension) and the heart does not pump a normal supply of oxygen to the brain. Typically, a faint lasts only a few seconds or minutes, and then the person regains consciousness.
The medical term for fainting is syncope (SIN koe pee). It is a common problem that affects one million people in the U.S. every year. About one-third of us will faint at least once during our lifetime. A single fainting spell usually is not serious. It may be explained by factors such as stress, grief, overheating, dehydration, exhaustion or illness. Profound blood loss or fluid loss (severe diarrhea) may also cause syncope.
Many causes of fainting, however, are not easy to explain. Some are life-threatening. The most serious causes of syncope are related to heart damage or electrical system disorders that affect the heart's ability to pump blood efficiently. In some cases, fainting is the only warning sign of an abnormal heart rhythm (arrhythmia) that could cause sudden cardiac death (arrest).
If you faint suddenly and without explanation, however, contact your physician.
Some people with so-called "fainting disorders" do not actually faint. They may experience recurrent episodes of presyncope (signs such as nausea, dizziness or the feeling that they are about to faint) without losing consciousness.
For most people, syncope is an unusual event. Some individuals, however, have frequent episodes of fainting. Syncope is a serious health problem that may be a symptom of life-threatening disease. Even when the cause is harmless, the results of fainting can be dangerous. People who lose consciousness without warning are at risk of hurting themselves or others. They may be unable to drive a car or hold down a job. Fainting is responsible for 6 percent of all emergency room visits and 3 percent of hospitalizations. In 20 to 30 percent of cases, the cause of syncope is unknown.
Types of Fainting
Cardiovascular syncope. This is the most dangerous type of fainting. It is caused by an abnormal heart rhythm (arrhythmia) or by structural damage to the heart.
Non-cardiovascular syncope. There are a variety of non-cardiovascular causes of syncope. These types of syncope often are related to problems with the autonomous nervous system (ANS), which controls "automatic" bodily functions such as heart rate and blood pressure. They may occur even in young, otherwise healthy people with normal heart function.
About 90 percent of people who faint have cardiovascular syncope, the most serious type of fainting disorder. The risk of cardiovascular syncope increases with age, and those at greatest risk are people who have:
Coronary artery disease, or CAD (clogged blood vessels to the heart), angina (chest pain caused by reduced blood flow to the heart) or a prior heart attack (myocardial infarction).
Ventricular dysfunction, a weakness in the ventricles, the heart's major pumping chambers.
Structural heart disease, such as problems with the heart valves or muscles (cardiomyopathy).
An abnormal electrocardiogram (ECG). An ECG is a common test that prints out a graph that shows how the heart is beating and records its electrical activity.
Recurrent episodes of fainting that come on suddenly and without warning.
Signs of Cardiovascular Syncope
Cardiovascular syncope usually is sudden. There may be no warning signs that an individual is about to faint. People sometimes feel tightness in the chest, shortness of breath, apprehension or an unusual awareness of the heartbeat (palpitations). Palpitations may feel as if the heart is fluttering, racing, skipping beats or pounding with unusual force in the chest. If syncope occurs after palpitations that end abruptly, a heart rhythm disorder often is the cause.
Fainting during physical exercise or a history of unexplained fainting in childhood may be signs that syncope is related to a heart problem.
Orthostatic (Postural) Hypotension is a condition in which the blood pressure drops suddenly when a person stands up. Sometimes the underlying cause is a cardiovascular condition called "pump failure." This means that the heart pump sometimes "fails" to maintain normal blood pressure. This may be due to muscle damage from a prior heart attack, inflammation of the heart, structural defects in the heart's valves or muscle (cardiomyopathy) or medications. Disorders of the electrical system that regulates the rate and strength of the heartbeat can cause pump failure. Heart rhythm disorders (arrhythmias) include bradycardia (a too-slow heartbeat), tachycardia (a rapid heartbeat) and fibrillation (a rapid heartbeat that also is chaotic, or irregular).
Cardiovascular Syncope and Long QT Syndrome
Fainting is the primary symptom - and may be the only warning sign - of Long QT Syndrome (LQTS), an inherited electrical disorder of the heart.
LQTS is believed to be a common cause of sudden and unexplained death in children and young adults. It may occur in as many as 1 in 5,000 individuals and causes up to 4,000 deaths in children and young adults each year in the United States.
Neurocardiogenic and Non-Cardiovascular Syncope
There are many types of syncope that have non-cardiovascular causes.
Neurocardiogenic syncope - the "common faint" - also is called "vasovagal syncope." It usually (but not always) occurs when a person who is lying or sitting down moves to a standing position. From 25 percent to 40 percent of fainting disorders are due to neurocardiogenic syncope. It is the most common cause of fainting in young people. Some adolescents have frequent fainting spells, but many electrophysiologists and other physicians who treat syncope report that most of their young patients have "grown out" of the condition by the time they reach their mid-twenties.
This type of syncope often affects young, healthy people who have no history of heart disease or neurological problems. It is generally thought to result from a "miscommunication" between the brain and the heart or an exaggeration of a normal reflex.
With syncope, when we stand up, our brains send signals telling the blood vessels in our legs to dilate, or open wider. Often, a signal also is sent that slows the heartbeat. When the blood vessels suddenly dilate, blood may pool in the legs so that a normal volume of blood does not return to the heart. If the heart does not pump enough blood to supply the brain's need for oxygen, we become lightheaded or faint.
Sometimes, the heart tries to raise the blood pressure by increasing the force and rate of its muscle contractions. This makes the problem worse:
As the heart beats faster and stronger, it sends a wrong message that tells receptors in the heart's chambers that the ventricle is filled with blood.
The receptors send a message telling the nervous system that blood pressure is too high. In fact, the ventricle is not full and the blood pressure is too low.
When the brain receives the faulty message, it slows the heart rate and further dilates the blood vessels.
The blood pressure drops even lower, less blood is pumped to the brain and the risk of fainting increases.
Other Types of Non-Cardiovascular Syncope
Postural tachycardia syndrome (POTS) is considered a type of neurocardiogenic syncope. It is characterized by a very fast heartbeat (tachycardia) that occurs when a person stands up. Some cases of chronic fatigue syndrome may be related to this condition.
Neurological syncope usually is caused by seizure disorders, such as epilepsy, Parkinson's and other problems of the nervous system.
Orthostatic hypotension and orthostatic intolerance - an inability to maintain normal blood pressure while standing - often are due to disorders of the autonomous nervous system (ANS), which regulates most "automatic" bodily functions. It may occur in otherwise healthy people as a result of standing for long periods, exercise, overheating or other forms of stress. Conditions that affect the nervous system, such as diabetes, Parkinson's, multiple sclerosis or age-related nerve damage may contribute to the condition.
Psychogenic syncope refers to fainting spells related to anxiety, panic or major depression.
Metabolic syncope results from problems such as low blood sugar (hypoglycemia) or hyperventilation (shallow, rapid breathing).
Non-cardiovascular syncope may be triggered by a number of factors, such as:
Any condition that causes low blood pressure.
A severe reduction in blood volume caused by bleeding, diarrhea or vomiting.
Eating a meal or drinking alcohol (fainting after a meal is called postprandial syncope.)
Overheating, dehydration or loss of salt from the body.
Medications such as diuretics that cause fluid loss. Doctors sometimes prescribe diuretics to control blood pressure. If too much fluid is lost, however, fainting may result.
Menstruation. Some young women have fainting spells around the time of their menstrual period. These may disappear and then return during or immediately after pregnancy.
A "hypersensitive" autonomous nervous system. Some people faint frequently in response to a variety of triggers such as sneezing, coughing, urinating, having a bowel movement.
Emotional or stressful situations, depression, panic attacks or anxiety.
Illness or trauma
Some medications, including those prescribed to lower blood pressure or heart rate, can cause syncope.
It is important to remember that syncope is a symptom that can be caused by many different factors. When it comes to treatment, there is no "one size fits all" approach. This is why a diagnosis is important - therapies must be aimed at treating the underlying cause of syncope.
Depending on the diagnosis, syncope may be stopped or controlled with one or more of the following therapies:
Treatments for Cardiovascular Syncope
Insertion of a pacemaker is the most common treatment for syncope caused by a too-slow heartbeat (bradycardia). The pacemaker continuously monitors the heart's natural rhythm. It delivers an electrical impulse to stimulate (pace) the heart's muscle contractions if the heart rate drops below a certain number of beats per minute.
Treatment for a rapid heartbeat (tachycardia) depends on whether it occurs in the upper chambers (atria) or lower chambers (ventricles) of the heart. These treatments may include:
Medication to control irregular heart rhythms or underlying disease.
Catheter ablation. In this procedure, one or more flexible, thin tubes (catheters) are introduced under x-ray guidance into the blood vessels and directed to the heart muscle. A burst of radiofrequency energy heats and destroys very small areas of tissue that give rise to abnormal electrical signals.
Cardioversion is a controlled, electric shock that is delivered to restore the heart's normal rhythm.
An implantable cardioverter defibrillator (ICD) is a pacemaker-like device that continually monitors the heart, and delivers a life-saving shock if a dangerous heart rhythm is detected. The device significantly improves survival in certain groups of patients who are at high risk of a deadly heart rhythm disorder called ventricular fibrillation (VF). VF is the primary cause of sudden cardiac death.