Syncope (Fainting)

Syncope is also called fainting or passing out.

It most often occurs when blood pressure is too low and the heart doesn't pump enough oxygen to the brain. It can be harmless or a symptom of an underlying medical condition.

What causes syncope?

Syncope is a symptom that can have several causes, ranging from harmless to life-threatening conditions. Many non-life-threatening factors, such as strong emotions, heavy sweating, exhaustion or the pooling of blood in the legs due to sudden changes in body position, can trigger syncope. It’s important to determine the cause of syncope and any underlying conditions. 

However, several serious heart conditions, such as bradycardia, tachycardia or blood flow obstruction, can also cause syncope.

What is neurally mediated syncope?

Neurally mediated syncope (NMS) is the most common form of fainting and a frequent reason for emergency department visits. It’s also called reflex, neurocardiogenic, vasovagal (VVS) or vasodepressor syncope. It’s harmless and rarely requires medical treatment. 

NMS is more common in children and young adults, though it can occur at any age. It happens when the part of the nervous system that regulates blood pressure and heart rate malfunctions in response to a trigger, such as emotional stress or pain. 

NMS usually happens after standing for a long time. It is often preceded by a sensation of warmth, nausea, lightheadedness, tunnel vision or visual “gray out.” Placing the person in a reclining position restores blood flow and consciousness. 

Situational syncope, which is a type of NMS, is related to certain physical functions, such as violent coughing (especially in men), laughing, swallowing or urination. 

Other disorders can cause syncope. It can also be caused by some medications.

Some types of syncope that suggest a serious disorder are those:

• Occurring during exercise or exertion
• Associated with palpitations or irregularities of the heart
• Associated with family history of recurrent syncope, heart disease at a young age or sudden death 

What is cardiac syncope?

Cardiac (cardiovascular) syncope is caused by various heart conditions, such as bradycardia, tachycardia or certain types of low blood pressure. It can indicate an increased risk of sudden cardiac death.

People suspected of having cardiac syncope but who don’t have serious medical conditions may be managed as outpatients. Further in-patient evaluation is needed if serious medical conditions are present. Conditions that may warrant hospital evaluation and treatment include various abnormal heart rhythms, coronary artery disease, severe aortic stenosis and pulmonary embolism. If evaluation suggests cardiac vascular abnormalities, or if you have experienced multiple instances of fainting due to heart problems, an ambulatory external or implantable cardiac monitor may be required.

Sick sinus syndrome, atrial fibrillation and other serious cardiac conditions can cause recurrent syncope in older adults, with a sharp increase after age 70. 

What are the risk factors?

Syncope is common, and older adults are at greater risk of hospitalization and death. 

Younger people without heart disease but who’ve had syncope while standing or have specific stress or situational triggers aren’t as likely to have cardiac syncope. 

Cardiac syncope is a higher risk in men and those over age 60. People with the following are also at higher risk: 

• Known ischemic heart disease, structural heart disease, previous arrhythmias or reduced ventricular function
• Brief palpitations or sudden loss of consciousness
• Fainting during exertion
• Fainting while flat on one’s back
• Low number of fainting episodes (one or two)
• Abnormal heart exam
• Family history of inheritable conditions or premature sudden cardiac death (younger than age 50)
• Presence of known congenital heart disease

Initial evaluation

Anyone with syncope should receive an initial evaluation, including a detailed physical exam, medical history and blood pressure and heart rate check by a health care professional.

A resting 12-lead ECG (electrocardiogram) also is recommended as part of an initial evaluation to provide information about the cause of syncope. ECG’s are widely available and inexpensive and can provide information about the potential and specific cause of syncope, such as abnormal heart rhythms. Other tests, such as an exercise stress test, a Holter monitor and an echocardiogram, may be needed to assess for other cardiac causes.

An ECG also is recommended for children and young adults with syncope. Other noninvasive diagnostic testing may be needed if they’re suspected of having congenital heart disease, cardiomyopathy or a heart rhythm disorder.

If the initial evaluation is unclear, it may be useful for patients to undergo a tilt test. The blood pressure and heart rate will be measured while lying on a board and with the board tilted up. People with VVS, or reflex fainting, usually will faint during the tilt, due to the rapid drop in blood pressure and heart rate. When people are placed on their back again, blood flow to the brain and consciousness are restored. 

Patients with VVS and without a serious medical condition usually can be managed in an outpatient setting. For older adults, a comprehensive approach working with a geriatric expert can be helpful. 

For people who are dehydrated, it may be beneficial to increase their salt and fluid intake to prevent syncope. That recommendation – as well as the removal or reduction of low blood pressure medications and diuretics – also may be encouraged when appropriate and safe for people who’ve experienced syncope as an adverse drug reaction. 

Consuming more salt and fluids can benefit most pediatric patients, but the results are unclear in people with VVS. Other lifestyle changes, such as exercise once cardiogenic syncope is ruled out, also can benefit pediatric patients. 

Patients of any age may need medication to help control or improve syncope. 

When it comes to driving after a syncope episode, there are no restrictions for VVS patients who had no fainting spells in the previous year. But it may be helpful for health care professionals to discuss regional driving laws, restrictions and implications with all patients. 

A cardiovascular assessment by a health care professional is recommended for athletes before resuming competitive sports. Those with syncope and a structural heart rhythm disorder should also see a specialist. Extended monitoring may help athletes with unexplained exertional syncope. 

The future of syncope

Standardized national registries and large databases are needed to gather more data to better understand the incidence and prevalence of syncope, patient risks and outcomes, set lifestyle policies and improve health care delivery.

Some studies have shown that with recurrent episodes of fainting, the quality of life is reduced in both adults and pediatric patients. However, more well-designed studies that incorporate quality of life, work loss and functional capacity are needed to understand better the relationship of syncope symptoms, causes and underlying diseases to various outcomes.