Syncope, also known as fainting, or a sudden and brief loss of consciousness, occurs when the brain does not get enough blood flow and oxygen.
There are many causes of syncope. A common type of syncope — vasovagal syncope or neurocardiogenic syncope — is caused by a malfunction of the nerves that control the action of the heart and blood vessels, called the autonomic nervous system. This type of syncope may be triggered by fear, severe pain, emotional distress or standing for a long time. Dehydration and low salt intake may also contribute to the condition.
Syncope may also be caused by very fast heart rhythms or arrhythmias called tachycardias, as in supraventricular tachycardia (SVT) or ventricular tachycardia. In some cases, syncope is caused by very slow heart rhythms, called bradycardias, as in sinus node dysfunction or heart block.
Signs & symptoms
The hallmark symptom of syncope is fainting, or near fainting. The condition may also cause the following symptoms:
- Chest pressure or pain
- Lightheadedness or dizziness
- Palpitations, which can be skipping, fluttering or pounding in the chest
- Shortness of breath
Syncope or near syncope may occur spontaneously with unpredictable timing. Therefore, in many cases, specialized tests are needed to make an accurate diagnosis. Your child's doctor may order one or more of the following diagnostic tests to determine the source of your child's symptoms.
- Electrocardiogram (ECG or EKG) — An electrocardiogram records the heart's electrical activity. Small patches called electrodes are placed on your child's chest, arms and legs, and are connected by wires to the ECG machine. The electrical impulses of your child's heart are translated into a graph or chart, enabling doctors to determine the pattern of electrical current flow in the heart and to diagnose arrhythmias.
- Electrophysiology (EP) Study — In an EP study, doctors insert special electrode catheters — long, flexible wires — into veins and guide them into the heart. These catheters sense electrical impulses and also may be used to stimulate different areas of the heart. Doctors can then locate the sites that are causing arrhythmias. The EP study allows doctors to examine an arrhythmia under controlled conditions and acquire more accurate, detailed information than with any other diagnostic test.
- Exercise Stress Test — An exercise stress or treadmill test records the electrical activity of your child's heart during exercise, which differs from the heart's electrical activity at rest.
- Event Monitor — This is a small monitor about the size of a pager that your child can have for up to a month. Since the arrhythmia may occur at unpredictable times, this will help to record the abnormal rhythm when your child is experiencing symptoms. He or she can just push a button on the pager and record the heartbeat. The recording can then be transmitted by phone to the doctor.
- Holter Monitor — A Holter monitor is a small, portable machine that your child wears for 24 hours. It is about the size of a portable tape player and provides a continuous 24-hour recording of your child's heartbeat onto a tape. You will be asked to keep a diary of your child's activities and symptoms. This monitor may detect arrhythmias that might not show up on a resting electrocardiogram, which only records a heartbeat for a few seconds at rest.
- Tilt Table Test — Your child's doctor may perform a tilt table test to determine how your child's body responds to changes in position. During the test, your child will lie on a table that can be tilted upright to 70 degrees with constant monitoring of blood pressure and heart rate.
The tilt test is designed to provoke syncope under controlled conditions. It is especially helpful in the diagnosis of children with vasovagal syncope. While the child is tilted upright blood will collect or pool in the lower part of the body, which causes less blood to return to the heart and the blood pressure to drop. Normally, the body's nervous system responds by increasing the heart rate and constricting the blood vessels to maintain blood pressure. However, in children with vasovagal syncope, the nervous system does not respond as it should, and the heart rate slows and the blood pressure drops, which may cause a loss of consciousness. If this occurs, the child is placed flat immediately and normal blood flow is restored.
Because there are various reasons for syncope, the treatment for your child's syncope will depend on the cause. Syncope may be caused by very fast heart rhythms — tachycardias — such as in supraventricular tachycardia (SVT) or ventricular tachycardia. In other cases, syncope may be caused by very slow heart rhythms — bradycardias — such as in sinus node dysfunction or heart block.
If your child's syncope is due to a blood pressure problem, medications, extra fluid intake and salt may be recommended.
UCSF Benioff Children's Hospitals medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your child's doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your child's provider.
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