Syncope

Syncope, or sudden loss of consciousness, is the medical term for fainting. It usually is short lived, and may often be caused by a fall in blood pressure and a decrease in the heart rate. Nearly 50% of Americans – of all age groups– will experience at least one episode of syncope during their lifetime.

What are the symptoms of syncope?
Most patients usually perceive a warning that they are about to faint, they have what is known as vasovagal or neurally mediated syncope. This typically includes [Symptoms may include] light-headedness, dizziness, sweating, or nausea [before fainting]. Often s[S]itting or lying down [may prevent fainting.] will relieve the symptoms and prevent fainting from occurring. If fainting occurs, it typically lasts a few seconds. Once the person regains consciousness, they typically feel tired, which may last several hours.

What are the causes and risk factors for syncope?
There are many causes of syncope[:] The most common cause is an abnormal reflex in a nerve called the vagus that slows the heart rate and lowers blood pressure – called a "vasovagal" reaction, or neurally mediated syncope (NMS). 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:

• An abnormal reflex in the vagus nerve that slows the hear rate down and lowers blood pressure]
• 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

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 or having a motor vehicle accident. 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 on their head 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.

Key Points:
– Syncope is a medical term for fainting or “passing out”; symptoms include lightheadedness, dizziness, sweating, or nausea
– Syncope can be caused by abnormal heart rhythms, sudden lowering of blood pressure, abnormal vagal nerve responses, panic attacks, dehydration, and low blood sugar
– Spells are usually not serious, however falls can cause injuries and arrhythmias that cause syncope can sometimes be dangerous

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 Test: 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 or EKG", 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 assess[es] cardiac anatomy or pumping function
• [24 hour] monitoring [of the heart] – [assesses heart rate and rhythm] 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 patients 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 [a] 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.

• [When increased or decreased heart rate is the cause, medications to normalize heart rate can be given. For serious arrhythmias, an implanted pacemaker may be necessary.
• When an dehydration or fluid imbalance is the cause, measures to increase hydration, avoid dehydration, and medications may be recommended.
  

• 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, such as a-ten-olol (Tenormin“), pro-pran-olol (Inderal“), and meto-prolol (Toprol“). 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.
• 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, there are other treatments that may be recommended. Pacemaker implantation may be successful in decreasing the number of fainting episodes for those who have arrhythmias or abnormal heartbeats. Please consult your doctor for treatment recommendations that are appropriate for you.

Key points:
– Examination and history can sometimes reveal the cause of syncope
– Tests to determine potential heart problems or vagal nerve response abnormalities may also be necessary
– Treatment depends on the underlying cause

FAST FACTS:
– Syncope is a medical term for fainting or “passing out”
– Abnormally rapid or slow heart rates, sudden lowering of blood pressure, abnormal vagus nerve responses, panic attacks, dehydration, and low blood sugar can cause syncope
– Symptoms include lightheadedness, dizziness, sweating and nausea before fainting
– Syncope is usually not serious, but falls can result in injuries and some heart arrhythmias can be dangerous. Always see a healthcare professional if you have symptoms of syncope
– Syncope can often be diagnosed by physical examination and history, but tests to assess the heart and nerve responses may be necessary
– Treatment depends upon the cause

Tenormin and Toprol are registered trademarks of AstraZenica; Inderal is a registered trademark of Wyeth Pharmaceuticals, Florinef is a registered trademark of Bristol-Myers Squibb

References:

1. Soteriades, ES, Evans, JC, Larson, MG, et al. Incidence and prognosis of syncope.
N Engl J Med 2002; 347:878.

2. Chen, L, Chen, MH, Larson, MG, et al. Risk factors for syncope in a community-based sample (the Framingham Heart Study). Am J Cardiol 2000; 85:1189.

3. Alboni, P, Brignole, M, Menozzi, C, et al. Diagnostic value of history in patients with syncope with or without heart disease. J Am Coll Cardiol 2001; 37:1921.

4. Mathias, CJ, Deguchi, K, Schatz, I. Observations on recurrent syncope and presyncope in 641 patients. Lancet 2001; 357:348.

5. Linzer, M. Diagnosing syncope. Part 1: Value of history, physical examination, and electrocardiography. Clinical Efficacy Assessment Project of the American College of Physicians. Ann Intern Med 1997; 126:989.

6. Brignole, M, Menozzi, C, Moya, A, et al. Mechanism of syncope in patients with bundle branch block and negative electrophysiological test. Circulation 2001; 104:2045.

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