Syncope, commonly known as fainting, refers to a sudden loss of consciousness, followed by a rapid and complete recovery.

A person with syncope recovers quickly, almost always without treatment. However, injuries can occur during a syncopal episode and recurrent episodes can be frightening. Moreover, in patients with heart problems, syncope may be a warning sign that sudden cardiac arrest (SCD) is about to occur.

There are other reasons that a person may pass out, such as low blood sugar, hyperventilation, or seizures. It is important to determine the cause of syncope so that it can be prevented or treated in the future.

Syncope is common. About one-third of people have a syncopal episode at some point in their life. In most cases, syncope is not a sign of a life-threatening problem, although some people with syncope have a serious underlying medical condition. In non-elderly people, over 75 percent of cases of syncope are not associated with an underlying medical problem.

A person who suddenly and unexpectedly loses consciousness can be injured. Up to 35 percent of people who have syncope injure themselves; elderly people are more likely to be injured during a syncopal attack.

Because of the risk of injury and the potential for serious underlying disease, any person who has a syncopal episode should seek medical attention.

To remain conscious, a supply of oxygen-rich blood must be pumped to the brain without interruption. If the brain is deprived of this blood supply, even for a brief period, loss of consciousness (passing out) will occur.

A number of medical conditions can cause syncope. These include:

  • Vasovagal syncope
  • Heart rhythm problems

Any problem with the structure of the heart that interferes with the flow of blood can cause syncope. The two most common causes of outflow obstruction are hypertrophic cardiomyopathy and aortic stenosis.

Orthostatic hypotension

Less common causes, including a heart attack, cardiac tumor, or blood clot in the arteries supplying the lungs.

In about 20% of patients, the cause of the syncopal episodes is not clear after full investigations are performed.

There are three main ways to identify the causes of syncope: the medical history, the physical examination, and cardiac testing.

A number of medical tests are available to help determine the cause of the syncope. However, testing is not always required. These tests include ECG (electrocardiogram, rhythm monitoring — Holter monitor, implantable loop recorder (ILR), echocardiogram, upright tilt table testing, electrophysiology study, exercise testing.

Treatment of syncope is based upon the underlying cause. The goal of treatment is to prevent recurrences or more serious problems.

Passing out while driving or performing other activities can potentially harm both the patient and those around him/her. As a result, driving restrictions are sometimes recommended for certain people with syncope. This generally includes people who have a history of syncope that occurs without warning or known cause. Driving restrictions in Australia, are governed by the national assessment of fitness to drive guidelines; for more information, see: