Fainting, also known as syncope (SIN-cuh-pee), is a brief, sudden loss of consciousness, usually followed by a rapid return to consciousness. Syncope is a symptom of an underlying cause or condition, not a disease itself. It may be due to harmless causes or it may be due to more serious underlying cardiovascular or neurologic conditions.
In patients with heart disease, the possibility that a fainting spell may have been caused by an abnormal heart rhythm (arrhythmia) needs to be carefully considered. Therefore, patients with heart disease (and, indeed, anyone) should inform their physician of any episodes of fainting or near-fainting as soon as possible after the event.
Tests that may be run include a tilt table test, which is used to assess neurocardiogenic syncope – fainting due to a reflex that leads to a sudden drop in heart rate and blood pressure. Other tests that may be run include an echocardiogram, a stress test, a Holter monitor (or event monitor), a cardiac catheterization or an electrophysiologic study. In addition, a CAT scan or an MRI may be used to evaluate possible neurologic causes.
Treatment will depend on the underlying cause.
About fainting
Fainting, also known as syncope, is a brief, sudden loss of consciousness, typically followed by a complete recovery. Fainting occurs when the brain is starved for oxygen due to temporarily inadequate blood flow.
In general, syncope is characterized as either cardiac syncope or noncardiac syncope. Cardiac syncope is caused by underlying heart disease, while non-cardiac syncope has a number of possible causes. Episodes of non-cardiac syncope may be triggered by standing up too quickly, working or playing too hard, stress, or various diseases. Cardiac syncope is associated with increased mortality, whereas most causes of noncardiac syncope are relatively benign. In fact, the patients' greatest risk may be injury from falling.
Importantly, syncope is not a disease by itself. It may be a symptom of an underlying condition. Or, in about a third of cases, episodes of syncope may prove impossible to explain. Episodes of syncope are more common with age, perhaps due to an increased prevalence of disease or an age-related inability to respond to stressors that would not have caused fainting at a younger age.
However, because of its link to serious cardiovascular problems, it is important for anyone experiencing syncope – especially patients with known heart disease – to report the episode to their physician as soon as possible. Common causes of cardiac syncope include:
Arrhythmias. Abnormal heart rhythms, either too slow (bradycardia) or too fast (tachycardia) are the leading cardiovascular cause of syncope. The most common arrhythmias associated with syncope include ventricular tachycardia and sinus bradycardia. Ventricular fibrillation, a particularly dangerous abnormal heart rhythm, does not cause syncope. Structural heart disease (e.g., cardiomyopathy or heart failure) is a risk factor for arrhythmias that may lead to syncope.
Heart block. Where the heart may suddenly stop for 10 to 30 seconds, or abruptly slow down, due to an abnormality in the flow of electricity through the heart.
Valvular heart disease. Abnormal function of the heart’s valves can obstruct the flow of blood from the heart to the brain. The most common cause of valve-related syncope is aortic stenosis, which is characterized by reduced blood flow through the aortic valve that regulates blood flow between the left ventricle and the aorta. Less frequently, it may be caused by stenosis of the pulmonic valve, which regulates blood flow between the right ventricle and the pulmonary arteries.
Cardiac ischemia. A lack of oxygen reaching the heart muscle, often caused by atherosclerosis, or "hardening of the arteries.”
Hypertrophic cardiomyopathy. Characterized by an abnormal growth of muscle fibers on the heart muscle. This abnormal growth results, in many cases, in the thickening and stiffening of the septum – a muscular structure separating the right and left sides of the heart. Because of the rigidity of the muscle, the ventricle cannot relax properly. Patients with hypertrophic cardiomyopathy may faint due to arrhythmias (see above) or due to obstruction of blood flow out of the heart caused by the enlarged muscle of the septum.
Heart medications. Some heart medications may cause syncope by dilating the blood vessels, resulting in a drop in blood pressure. Therefore, if any new medication is utilized and syncope occurs, one can be suspicious that it is caused by the medication. Patients should immediately alert their physician if this occurs.
Long QT syndrome (LQTS), a rare heart abnormality, can be a cause of syncope. When an LQTS patient has periods of high emotional stress (e.g., when suddenly feeling afraid) or physical stress (e.g., during exercise), the heart may not be able to pump effectively. When the heart is no longer pumping as it should be, the blood flow to the brain is slowed and the patient may experience syncope without warning.
No one should disregard any sudden loss of consciousness. Fainting or “blacking out” is not a normal part of the aging process. Even “falling asleep at the wheel” may not be just fatigue, but may indicate a heart rhythm disorder (e.g., supraventricular tachycardia, ventricular tachycardia, heart block).
Types and differences of fainting
Fainting (syncope) is classified by the mechanism that causes the reduction in blood flow to the brain, such a rapid drop in blood pressure. It is important to understand that these descriptions of fainting are not diseases themselves, but ways for physicians to classify the type of fainting a person is experiencing. Once a physician has identified the type of fainting, he or she will be better able to diagnose the underlying condition.
Although there is some variation in the classification of fainting, most physicians generally break it down into cardiac and noncardiac causes. Noncardiac syncope is usually caused by disorders of blood volume and vascular tone. Cardiac syncope is caused by a reduction in cardiac output due to heart disease. In general, only cardiac syncope is associated with increased mortality. Specific types of syncope include:
Neurocardiogenic syncope. Neurocardiogenic syncope accounts for about half of all episodes of fainting. The term includes vasovagal syncope and vasodepressor syncope. In general, neurocardiogenic syncope is caused by abnormalities in the autonomic nervous system, which controls the heart rate and circulation. Technically speaking, vasovagal syncope is caused by both widening of the arteries and a depressed heart rate (e.g., bradycardia), whereas vasodepressor syncope is caused by widening of the arteries alone. In either case, the syncope may be preceded by a presyncopodal syndrome that might include weakness, nausea, lightheadedness, blurred vision, and a rapid heartbeat followed by cardiac slowing. Neurocardiogenic syncope may be caused by standing for a long time, alcohol, a hot and crowded environment, hunger, pain, and stressful or emotional situations. Episodes of neurocardiogenic syncope usually last only a few minutes, with varying degrees of consciousness ranging from a turgid state of awareness to complete unconsciousness.
Orthostatic syncope. This form is syncope is caused by rising rapidly from a reclined position, which results in a rapid decline in blood pressure in the head. It is thought to account for about 30 percent of all episodes of syncope among the elderly. The use of antihypertensive and antidepressant medications may contribute to orthostatic syncope.
Carotid sinus syncope. Carotid sinus syncope is caused by a sudden loss of consciousness due to compression of the carotid sinus, a blood vessel in the neck. It can be caused by turning the head to one side or wearing clothing or jewelry too tight on the neck. This is sometimes called carotid sinus syndrome. It occurs mostly in men over 50 years of age.
Situational syncope. A number of normal activities, such as urinating, coughing, swallowing and defecating, may also cause syncope. Situational syncope may have elements of both vasodepressor syncope and vasovagal syncope. The straining that accompanies these activities also contributes to the reduction of blood flow. Conditions associated with situational syncope include lung diseases, benign prostatic hyperplasia (BPH), bladder obstruction, esophageal disorders and constipation.
Cardiac syncope. This form of syncope is caused by a sudden reduction in cardiac output, usually as a result of an abnormal heart rhythm, or arrhythmia. This condition can be caused be either a slow heart rate (bradycardia) or abnormally rapid heart rate (tachycardia). People who suffer from a number of diseases may be susceptible to cardiac syncope, including cerebrovascular disease, anemia, coronary artery disease or heart valve disease.
Syncope of unknown origin, or idiopathic syncope. As the name implies, this describes syncope for which a cause cannot be found. This applies to about a third of cases of syncope. In most of these cases, the syncope is a singular episode from which the patient recovers quickly and suffers no long-term damage. When injury does occur, it is usually due to falling.
Despite its name, local syncope is not a loss of consciousness. It is when an area of the body becomes numb and/or white from lack of blood flow. “Local” refers to the fact that it is occurring only in a section of the body, usually the fingers or toes. It is associated with Raynaud syndrome.
Other symptoms associated with fainting
A person who is about to faint may become unresponsive and “floppy.” Immediately before the incident, an individual may have symptoms such as:
Palpitations (fast, pounding or “galloping” heartbeat)
Dizziness
Coldness or warmth
Feeling confused, disoriented or generally “strange”
Sweating
Nausea
Blurred vision
Clinical signs that might be noticed by a physician instead of the patient include:
Low blood pressure (hypotension)
Low blood sugar (hypoglycemia)
Low pulse rate
Paleness
Diagnosis methods for causes of fainting
Fainting (syncope) can present a challenge for the diagnosing physician. There are a wide range of conditions that can cause fainting, ranging from life-threatening heart disease to poor physical conditioning to adrenal disease and neuropathy. In addition, a number of conditions can closely resemble syncope, including anxiety attacks and hysterical fainting.
Finally, minor strokes and transient ischemic attacks can sometimes produce syncope-like symptoms, but are not actually true syncope. In this case, it is very important to see a physician and obtain a correct diagnosis because transient ischemic attacks and minor strokes are highly predictive of future, more devastating strokes.
A close medical history and physical examination are indispensable tools to help a physician diagnose the underlying cause of fainting. During the history, patients should be detailed about the syncope episode and include information about any other episodes of fainting. It is also very important to let the physician know about any existing heart disease, as heart disease and syncope are closely linked.
This information will help the physician decide what further tests should be ordered. Whatever the cause, the physician will diagnose it as soon as possible so that any potentially life-threatening conditions, such as ventricular tachycardia, can be treated or avoided.
To make a diagnosis, the physician may order a number of tests, which include:
Tilt table test. There are a number of different factors that may cause fainting spells, and the tilt table test is used to assess one in particular – a sudden drop in blood pressure caused by a widening of the blood vessels. Fainting that results from this change in blood pressure and blood vessels is called neurocardiogenic syncope. It accounts for about half of all cases of syncope and is not associated with increased mortality. The tilt table test is conducted on a pivoting table. By securing the patient on his or her back to the tilt table, and then tilting the table upright, the factors leading to neurocardiogenic syncope may be simulated.
Echocardiogram. This test uses sound waves to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function. It may reveal structural heart disease, such as hypertrophic cardiomyopathy, that is causing the patient to faint.
Electrocardiogram (EKG). This test uses sensors attached to the chest wall to monitor the heart's electrical activity. Although this test is used to diagnose heart disease, it may be recommended for almost all patients who suffer a fainting episode, whether or not there is a history of heart disease or heart disease is suspected. This is because the test is common and relatively inexpensive, and considering the dangers of cardiac syncope, it is better to rule it out. It is worth noting, however, that an EKG will rarely result in a definitive diagnose of the cause of syncope. Instead, an abnormal EKG will likely result in further testing.
Holter monitor. This is an EKG that is temporarily attached to a patient for 24 hours. The Holter monitor continuously records the heart’s electrical activity as the patient goes about his or her daily routine. The idea behind Holter monitoring is to match episodes of syncope to arrhythmias, which may be relatively rare and unlikely to occur in the examination room.
Event monitor. If a patient only rarely experiences symptoms, the Holter monitor may not pick up the pattern and thus may not alert the physician to the problem. Therefore, the physician may ask the patient to carry a different type of portable device called an event recorder or event monitor. Rather than monitoring the heart’s electrical activity continuously (as the Holter monitor does), an event recorder is only used when the patient is feeling symptoms. When symptoms occur, the patient activates the event recorder by pressing a button. Because these devices are “on demand” rather than continuous, these recorders may be used for weeks or months. In certain cases, they may better reveal the exact pattern of specific symptoms.
Electrophysiologic study. A procedure in which a thin tube (catheter) is inserted into a vein or artery (e.g., in the groin) and guided to the heart, where it can perform specific, essential measurements of the heart’s electrical activity and pathways. These measurements are particularly helpful in the diagnosis of heart rhythms that are particularly fast (tachycardias) or slow (bradycardias).
In addition to cardiovascular causes, loss of consciousness can be due to neurologic diseases. For example, sometimes it may be very difficult to distinguish between syncope (fainting spells) and a seizure disorder such as epilepsy. Some tests that may be ordered to evaluate neurologic causes of fainting include:
Computed axial tomography (CAT) scan. A test that uses multiple x-ray sensors to generate a three-dimensional image of the target organ. During a CAT scan, the patient is positioned so that multiple sensors (up to 64) can detect x-ray scans. A computer is used to reassemble the individual pictures into clear, cross-sectional images. It is unique because it can provide clearer, more detailed information than single x-rays and can be used on a variety of different tissues, including soft tissue, bone and blood vessels.
Magnetic resonance imaging (MRI) scan. A procedure that uses magnetic fields and a computer to produce high-resolution cross-sectional or three-dimensional images of the brain. Images from an MRI scan are similar in many ways to those of a CAT scan, but MRI generally provides much greater contrast between normal and abnormal tissues. It is done without x-rays or other forms of radiation.
Electroencephalogram (EEG). A test that measures the brain’s electrical activity. It may be used to diagnose epilepsy, head injuries, infections, sleep disorders and other problems.
Treatment and prevention of fainting
Treatment will depend on the underlying cause of the fainting (syncope), as well as the patient’s age, specific symptoms and details surrounding the incident. If heart disease is diagnosed, the physician will treat the underlying heart disease. Treatments vary widely, depending on the nature of the heart disease. It may include antiarrhythmia medications, implantation of a pacemaker or a catheter-based intervention.
No matter the underlying cause, patients are also advised to take precautions to reduce the risk of injury caused by falls and if possible prevent the fainting episode from occurring after the first symptoms are felt. Lowering the head or lying down may help prevent the fainting episode. Patients may also be advised to avoid situations that trigger episodes of syncope. If the syncope does not response to these changes, the physician may prescribe medications such as beta blockers and selective serotonin reuptake inhibitors (SSRIs), which help prevent low blood pressure. In some cases, a pacemaker may be recommended to prevent an abnormally slow heart rate.
By definition, syncope is unpredictable and unexpected. Yet, with proper personal care and medical attention, underlying conditions and damage may be detected early or prevented altogether. Some studies suggest that vasovagal syncope can be delayed or prevented by crossing one’s legs and tightening the abdomen, legs and buttocks. By causing more blood to be squeezed to the chest, blood pressure is increased, as is oxygen flow to the brain. Medical attention should be sought after any fainting episode, particularly in patients with prior heart disease.
Questions for your doctor about fainting
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to fainting (syncope):
Am I at risk for any types of heart conditions that fainting is a symptom of?
Do I have any other symptoms that may be related to fainting?
Do you think it is possible that I have an arrhythmia? Is there another underlying illness involved?
What types of tests do you recommend for further evaluating my condition?
Am I currently taking any medications that might cause me to faint?
Are there any lifestyle changes I can make to reduce the chances of fainting?
Do I need to see a specialist to further evaluate this problem?
Do you recommend any types of treatment for my fainting?
Could my fainting be related to stress?
Should I be concerned if I am pregnant and fainting?
