Syncope Fast Facts

Syncope is a brief loss of consciousness caused by an interruption of blood flow to the brain. It’s more commonly called fainting.

Most fainting episodes, especially if they occur infrequently, don’t indicate a serious problem and aren’t usually a cause for concern.

In some cases, syncope can be caused a serious heart condition that can be life-threatening.

The most common cause of syncope is a sudden drop in blood pressure caused by a dysfunctional reflex of the nervous system.

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Most fainting episodes, especially if they occur infrequently, don’t indicate a serious problem and aren’t usually a cause for concern.

What is Syncope?

Syncope is a sudden, brief loss of consciousness caused by a reduction of blood flow to the brain. The condition is commonly called fainting. Most occasional episodes of syncope are not cause for concern. However, fainting can be a sign of a serious, life-threatening condition that requires emergency medical attention.

Symptoms of Syncope

The common symptoms of syncope include loss of consciousness as well as the symptoms that often precede the actual fainting. Some common symptoms of syncope include:

  • Lightheadedness
  • Blacking out or “graying” out of vision
  • Seeing spots
  • Tunnel vision
  • Dizziness
  • Sleepiness or mental fogginess
  • Weakness or unsteadiness while standing
  • Falling
  • Nausea
  • Headache
  • Irregular heartbeat

Although syncope is not cause for concern in most cases, it can indicate a serious problem, so it is important to consult a doctor if you experience a fainting episode.

What Causes Syncope?

Syncope can have many different causes, some serious and others not.

Neurally Mediated Syncope

The most common cause of syncope is a momentary malfunction of the nervous system that causes the heartbeat to slow and blood vessels to widen, resulting in reduced blood flow to the brain. This type of syncope is called vasovagal syncope, reflex syncope, neurocardiogenic syncope, or vasodepressor syncope. Fainting episodes are often a reaction to a triggering event or situation. Common triggers include:

  • Extreme heat
  • Long periods of standing
  • Long periods of exercise
  • Fear or other intense emotion
  • Pain
  • Dehydration
  • Sight of blood
  • Straining actions, such as coughing or having a bowel movement

Orthostatic Hypotension

This condition is a drop in blood pressure when a person moves to an upright position after sitting or standing. The sudden drop in blood pressure reduces blood flow to the brain and causes syncope. Orthostatic hypotension is common in older adults. It can also be caused by dehydration, medications for high blood pressure, or some neurological diseases.

Heart-Related Causes

Some heart conditions can cause syncope. These conditions are serious and potentially life-threatening, and they require immediate medical attention.

  • Bradycardia, tachycardia, and arrhythmia are abnormal changes in heartbeat rhythm that result in inefficient blood flow throughout the body, including to the brain.
  • Aortic valve stenosis is the narrowing of the valve that connects the heart to the aorta, the main blood vessel that carries blood to the rest of the body. The condition sometimes develops with age and is sometimes present from birth (congenital).
  • Aortic dissection is a spontaneous tear in the aorta. The condition is life-threatening and requires emergency treatment.

Loss of consciousness that resembles fainting can be caused by many other conditions, including epileptic seizures, heart attacks, strokes, and diabetes. However, unconsciousness stemming from these causes is not considered syncope.

Is Syncope Hereditary?

Syncope itself is not necessarily inherited, but some of the underlying conditions that cause it may be passed through families. For example, people who have a close relative with orthostatic hypotension are at increased risk of having the condition themselves. Some studies have also suggested that there may be a genetic component to vasovagal syncope, although no gene or genes have yet been definitely linked to the condition.

How Is Syncope Detected?

In some cases, a person experiences symptoms before a fainting episode. This condition is called pre-syncope. If a person sits or lies down during pre-syncope, the event may not progress to syncope.

Some potential warning signs of impending syncope include:

  • Dizziness
  • Lightheadedness
  • Unsteadiness
  • “Graying out” of vision
  • Seeing spots or having tunnel vision
  • Weakness
  • Irregular heartbeat
  • Sudden problems with hearing
  • Sweating

How Is Syncope Diagnosed?

Doctors may take several different diagnostic steps when a patient presents with syncope. The exact steps will vary depending on your symptoms and medical history. Possible diagnostic procedures include:

  • Echocardiogram or electrocardiogram tests measure heart function.
  • Exercise stress tests measure heart function during exertion.
  • Laboratory tests may be used to test for conditions such as anemia that could cause dizziness or fainting.
  • A tilt table test looks for causes of dizziness related to blood pressure.
  • Autonomic reflex testing assesses the function of your autonomic nervous system, which controls automatic body functions such as heart rate and blood pressure.

How Is Syncope Treated?

The type of treatment plan your doctor will prescribe for syncope will vary depending on the underlying cause.

Common treatments for neurally mediated syncope include:

  • Avoidance of known triggers
  • Increasing salt intake
  • Adjusting medications that lower blood pressure
  • Medications such as fludrocortisone acetate or SSRI antidepressants
  • Therapies or compression stockings to decrease the pooling of blood in the legs

Common treatments for heart problems that cause syncope include:

  • Surgical implantation of a pacemaker to regulate heartbeat
  • Catheter ablation is a procedure that cauterizes heart cells that are causing syncope-inducing changes in heartbeat rhythm
  • Implantation of an implantable cardioverter-defibrillator (ICD), a device that resets an irregular heart rhythm using electricity

How Does Syncope Progress?

Neurally mediated syncope is usually not a serious problem in itself. However, syncope could indicate a potentially dangerous heart problem, making it important to see your doctor if you experience fainting episodes. Syncope episodes that cause extreme dizziness or fainting also can cause injury from falls or accidents.

How Is Syncope Prevented?

There is no known way to prevent syncope. However, some lifestyle changes may help lower the risk of developing problems that can lead to neurally mediated syncope. These changes include:

  • Eating a healthy diet
  • Getting plenty of exercise
  • Practicing relaxation techniques such as yoga or meditation
  • Consistently managing underlying conditions such as diabetes or blood pressure problems

Sitting or lying down when you begin to feel pre-syncope symptoms (e.g., lightheadedness, tunnel vision) may help prevent fainting. Even if it doesn’t prevent loss of consciousness, getting off your feet if you feel signs of an impending faint can prevent falls and injuries.

Syncope Caregiver Tips

Many people with neurally mediated syncope also suffer from other brain and mental health-related issues, a condition called co-morbidity. Here are a few of the disorders commonly associated with the condition:

Syncope Brain Science

The most common cause of syncope is a malfunction of the vagus nerves, a part of the nervous system that carries signals from the brain to various organs. This type of syncope is called vasovagal syncope.

The vagus nerves, also called vagal nerves, are long, branching nerves that emerge from the brain and connect to several different parts of the body. The vagus nerve originates at the brain stem and branches to many of the body’s major organs, including the larynx, lungs, heart, liver, stomach, intestine, and kidneys. One of the vagus nerve’s central roles is to serve as part of the body’s parasympathetic nervous system, the network of communication that controls automatic body functions such as breathing, heartbeat, and digestion.

In the case of vasovagal syncope, the vagal nerves are more active than normal, and their activity affects heart rate and blood pressure, causing a steep reduction in blood flow to the brain.

Scientists don’t know what causes vagal nerve dysfunction, but emotional stimuli often trigger the syncope. This suggests, in some cases, the cause may lie in the connections between areas of the brain responsible for emotional processing and the parasympathetic nervous system.

Syncope Research

Title: The Effect of CPC on Aborting Tilt-Induced Syncope in Patients With a History of Vasovagal Syncope

Stage: Recruiting

Principal investigator: Mohamed H. Hamdan, MD

University of Wisconsin

Madison, WI

Syncope is defined as transient loss of consciousness associated with an inability to maintain postural tone with rapid and spontaneous recovery. This study aims to assess the effects of sublingual administration of a new medication called CPC on tilt-induced syncope in patients with a history of vasovagal syncope (VVS). One hundred thirty-two participants will be enrolled at the University of Wisconsin – Madison. Each participant will be in the study for one day.

Vasovagal syncope (VVS) is the most common type of syncope. The mechanism is reflex-mediated and triggered by various afferent inputs to the brain. The event is usually preceded by diaphoresis, warmth, nausea, and pallor, and is followed by fatigue. While several drugs are indicated in the treatment of VVS, there is no current treatment for an impending syncopal attack. In the present study, the investigators hypothesize that a single administration of sublingual CPC preparation during the prodromal phase aborts tilt-induced syncope or near syncope with SBP less than or equal to 70 mmHg in patients with a history of VVS. Patients with an established diagnosis of typical VVS will be randomized to receive CPC or placebo in a 1:1 ratio. Drug or placebo will be administered at the onset of prodromes during tilt table testing. In addition to the primary endpoint (syncope or near syncope with SBP less than or equal to 70 mmHg), the investigators will be assessing the effects of the drug on time to event, incidence of asystole (> 3 sec), and fatigue after tilt table testing.


Title: Presyncope (Syncope) Prevention Study (PS^2)

Stage: Recruiting

Principal investigator: Emmanual B. Walter, MD, MPH

Duke University

Durham, NC

This study is a prospective, randomized clinical trial that will be conducted in adolescents (10 through 14 years of age) receiving at least one recommended intramuscularly administered vaccine to evaluate the efficacy and acceptability of using two different, simultaneously administered interventions that might prevent post-vaccination pre-syncope, and by extension syncope. The two interventions to be evaluated together are Buzzy®, which is a medical device designed to reduce vaccination pain, and an electronic game. The investigators will evaluate both interventions when administered simultaneously (Buzzy® and electronic game). The investigators will enroll approximately 340 subjects in this study. Eligible adolescents will be randomized (1:1) to either the intervention or control group: 1) intervention (Buzzy® and electronic game); or 2) control (usual care) to assess for acceptability and efficacy. Detailed data will be collected and described from study participants, including demographics, medical history, baseline anxiety, and needle phobia. Participants will be observed for 20 minutes following receipt of vaccines and reassessed for post-vaccination anxiety, immediate and subsequent post-vaccination pain (within 1 minute and at 10 minutes), and the occurrence of witnessed syncope or pre-syncope, and pre-syncopal symptoms as rated by the modified Blood Donation Reactions Inventory (BDRI). Participants will also be asked to assess their acceptability of the intervention.


Title: Practical Approaches to Care in Emergency Syncope (PACES)

Stage: Recruiting

Principal investigator: Marc A. Probst, MD, MS

Columbia University

New York, NY

Syncope, or transient loss of consciousness, is a common reason for a visit to the Emergency Department and often leads to extensive testing and hospitalization. Using objective risk scores to determine which patients with syncope will actually benefit from these interventions and which can be safely discharged home with minimal testing, is critical to providing sensible medical care. This study will evaluate the validity of two syncope risk-stratification tools and investigate their impact on healthcare utilization and patient safety, thus improving the quality of care for the 1-2 million patients who experience syncope every year in the United States.

The goal of this project is to improve risk-stratification for patients who present to the emergency department (ED) with syncope (transient loss of consciousness), to better delineate which patients require admission and which can be safely discharged home. Syncope and pre-syncope (the sensation of impending loss of consciousness) are common reasons to present to the ED, representing over 1.3 million visits per year in the United States.

Although syncope is most often benign, it can occasionally be caused by serious cardiopulmonary diseases such as cardiac arrhythmia, acute coronary syndrome, or pulmonary embolism. Despite thorough evaluation in the ED, the cause of syncope remains unknown in over 50% of cases, which leads to a large number of syncope patients being admitted for observation and/or further testing. These admissions to the hospital or observation unit are low-yield, costly, and expose patients to the possibility of iatrogenic harm.

In response to this, two groups of researchers have developed distinct syncope risk-stratification tools: the US Syncope Risk Score (FAINT) and the Canadian Syncope Risk Score. These scores use a combination of clinical, electrocardiographic, and laboratory variables to predict the risk of serious clinical outcomes at 30 days. While promising, these two risk scores require external validation before widespread clinical implementation. The study team will prospectively collect data on ~1,270 ED patients with syncope/pre-syncope and follow them for 30 days to validate the predictive accuracy of these two risk scores. The study team will then assess the impact of implementing these scores by measuring their potential effect on healthcare utilization and costs.

If validated and shown to safely reduce healthcare utilization, these syncope risk scores could play a major role in improving emergency syncope care by reducing low-yield admissions and identifying patients who are unsafe for discharge from the ED. This study, entitled PACES: Practical Approaches to Care in Emergency Syncope, will help increase the quality and value of emergency care and advance the field of syncope research.

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