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Syncope (Sudden Loss of Consciousness)

Syncope is the medical term for fainting. It is a temporary, sudden loss of consciousness that is often caused by a drop in blood pressure and a fall in heart rate. Nearly half of all Americans – from young children to elderly individuals – will experience at least one fainting spell during their lifetime.

What causes syncope?

There are many causes of syncope. The most common cause is an abnormal reflex that slows the heart rate and lowers blood pressure – called neurally mediated syncope (NMS) or "vasovagal" syncope. Normally, the body increases heart rate and blood pressure in response to stress. People who are susceptible to NMS experience the initial normal increase in heart rate and blood pressure under stress, but, without warning, the heart rate and blood pressure suddenly and inappropriately drop. When blood pressure falls below a critical point, the brain does not receive sufficient oxygen. This results in fainting. Fortunately, once the person is lying flat the brain will again receive enough oxygen and the patient will regain consciousness. Syncope can also result from:

  • cardiac arrhythmias – very slow heart rhythms (bradycardia) or very fast rhythms (tachycardia).
  • mechanical abnormalities of the heart, such as obstruction of a valve.
  • other causes, such as dehydration, low blood sugar, a seizure, or even a panic attack.

What are the symptoms of syncope?

NMS patients usually perceive a warning that they are about to faint. This typically includes light-headedness, dizziness, sweating, or nausea. Often sitting or lying down successfully prevents fainting from occurring. If fainting occurs, it typically lasts a few seconds. Once the person regains consciousness, they typically feel tired. This may last several hours.

Can syncope be dangerous?

Regardless of the cause, all patients with syncope should be evaluated by a doctor. Anyone who loses consciousness is at risk for injury as a result of falling. Some patients with syncope have warning signs and are able to lie down before they lose consciousness completely. Other patients may not have warning signs and may hurt themselves by falling unexpectedly. Severe arrhythmias that might cause syncope can potentially be life threatening and must be treated by a physician. Even if a patient has a benign cause of syncope, they may need treatment to protect them from the risk of injury.

How is syncope diagnosed?

An evaluation to determine the cause of syncope, can usually be done on an outpatient basis. However, if a dangerous cause is suspected, the patient should be admitted to the hospital until the precise cause is determined and treatment is begun.

  • Medical History:
    The evaluation of a patient with syncope begins with a history and a physical examination by a physician. Sometimes, the patient's description of the faint, as well as his/her medical history can be enough to suggest the cause of syncope.
  • Diagnostic Tests
    Since most patients have a cardiovascular cause of syncope, diagnostic testing usually begins with an evaluation of the heart. The tests to be done and their sequences are carefully selected based on the patient's symptoms, starting with simple, non-invasive (and generally less expensive) tests. One or more of the following tests may be used:
    • Electrocardiogram. Commonly known as an "ECG", this test assesses the heart's electrical rhythm and may identify rhythm disturbances that may produce syncope.
    • Echocardiogram. With this test, ultrasound images of the heart are used to determine whether cardiac anatomy or pumping function
    • Holter Monitoring (Recording). The Holter Monitor is a small portable device that provides a 24-hour continuous ECG 4recording. This 24-hour recording may identify transient disturbances in the heart's rhythm that can cause syncope. Occasionally, an actual recording of the patient's rhythm during an episode of lightheadedness or fainting can be obtained.
    • Event Monitors. These monitors allow the patient to record the heart rhythm at the time of symptoms. The patient can wear this monitor for days or weeks if necessary to detect an episode that might not occur while using a 24-hour monitor.
    • Implantable loop recorders. For patients with recurrent syncope in whom other tests have been inconclusive, a small monitor can be implanted under the skin to continuously monitor the heart rhythm. This device is useful for detecting the cause of syncope in patients with infrequent episodes that nevertheless pose a risk of injury or interfere with the patient’s lifestyle.

    If these tests do not determine the cause of syncope, the approach to diagnostic testing shifts to tests that explore the cause of fainting in a controlled laboratory situation.

    • Cardiac electrophysiology testing is an invasive procedure used to assess the heart's electrical conduction system and determines the heart's vulnerability to developing either fast or slow rhythms that may cause syncope.
    • Tilt table testing is used to detect abnormal reflexes that cause syncope. The patient lies flat on a table that is able to tilt. The patient is tilted upright at an angle, with the head always above the feet; patients are not tilted upside down. As the patient is tilted toward the upright position, blood pressure is measured and an ECG records the heart's electrical activity. For some patients, a medication is given through a vein while the patient is upright to provoke the fainting reflex. In susceptible patients, these approaches will reveal abnormal cardiovascular reflexes that produce syncope.

How is syncope treated?

Treatment depends on the specific cause of the syncope; not all patients with neurally mediated syncope require treatment. Many people will experience syncope only once or very infrequently. In addition, many people can prevent fainting by sitting or lying down when they feel a warning signal that they are about to faint. Some patients, however, experience frequent fainting. Several treatments are available for patients who require it.

Lifestyle modification is important in preventing neurally mediated syncope. Patients are usually encouraged to stay well hydrated and add salt to their diet. Caffeine and alcohol sometimes provoke this reflex.

The most commonly used type of medication to prevent syncope is called a beta-blocker. There are many different beta-blockers, but they all function similarly. They block the "stress" receptors on the heart and limit the heart's response to stressful situations. This is believed to block the initial stress on the heart that triggers syncope.

An alternative medication is a selective serotonin re-uptake inhibitor (SSRI) such as paroxetine (Paxil). Serotonin is a chemical released by the brain that regulates many bodily functions. The precursor of serotonin has been shown to lower blood pressure and heart rate in experimental studies. Drugs like Paxil block the effects of serotonin and have been effective in the treatment of syncope.

The medicine fludrocortisone (Florinef) has also been used to prevent this reflex. This medicine helps retain fluid and salt in the body, and prevents dehydration.

If medications fail, or in severe cases, pacemaker implantation has been successful in decreasing the number of fainting episodes.

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