Defined by the consensus group of the American Autonomic Society as a sustained decrease in blood pressure exceeding 20 mmHg systolic or 10 mmHg diastolic occurring within 3 minutes of upright tilt.
Orthostatic hypotension is a sign of autonomic dysfunction and dysautonomia in adults and in children. It may also occur with reductions of blood or plasma volume. However, the experience of transient hypotension often associated with the symptom of lightheadedness with standing is common among teenagers and is familiar to pediatricians. Transient orthostatic hypotension in children and teenagers is a normal phenomenon related to the relative rapidity of blood translocating from the thorax to the dependent parts of the body during orthostasis. This may be sufficiently rapid that there is not sufficient time for neurovascular compensation and blood pressure falls.
We hypothesized that transient hypotension is a normal phenomenon which may be mistaken for orthostatic intolerance. We measured peripheral blood flow and venous pressure in the arms and legs using venous plethysmography. Data indicate that healthy subjects with normal vasoconstrictive responses to sustained upright tilt, uniformly experience a transient fall in blood pressure during 70o upright tilt which varies from almost undetectable to large decreases in blood pressure easily exceeding the 20mmHg threshold for orthostatic hypotension. Large decreases are associated with short-lived symptoms of dizziness and are most marked in those with the largest calf blood flow. The higher the flow, the lower the blood pressure falls. There is appropriate reflex tachycardia.
What is syncope?
Syncope is a temporary loss of consciousness and muscle tone caused by inadequate blood supply to the brain. Syncope is better known as fainting.
Syncope affects people of all ages, from toddlers to the elderly. More than 100,000 adults and children visit a physician each year with complaints of fainting spells.
What causes syncope?
The common reason behind each syncopal or fainting episode is a temporary lack of oxygen-rich (red) blood getting to the brain. Many different problems can cause a decrease in blood flow to the brain. Types of syncope include:
Some children have abnormalities of the structures of the heart that can cause syncopal episodes. Heart defects causing "outflow obstruction" may produce fainting, because they restrict the blood flow to the body out of the left ventricle. Aortic stenosis and hypertrophic cardiomyopathy diminish the blood flow from the left ventricle through the aorta, and children with these problems may experience syncope.
Irregular or rapid heart rhythms also can trigger syncope. When the heart beats rapidly or irregularly, the ventricles have less time to fill with blood before it is time to pump whatever blood is within them to the lungs or to the body. Not as much blood as normal leaves the heart and flows through the aorta with these abnormal rhythms, and the body reacts to the diminished blood flow to the brain by fainting.
Yet another cause of syncope can be an inflammation of the heart muscle known as myocarditis. The heart muscle becomes weakened and is not able to pump as well as normal. The body again reacts to decreased blood flow to the brain by fainting.
Other situations or illnesses that can cause syncope include, but are not limited to, the following:
What are the symptoms of syncope?
The following are the most common symptoms of syncope. Each child may experience symptoms differently, and the symptoms of syncope may resemble other conditions or medical problems. Consult your child's physician for a diagnosis.
Some children will experience presyncope, which is the feeling that they are about to faint. Your child may be able to tell you that he/she is "about to pass out," "feels like I might faint," "feels like the room is spinning," or "feels dizzy." These sensations usually occur immediately before fainting occurs. There may be enough warning to enable your child to sit or lie down before loss of consciousness occurs; this can prevent injuries that may occur due to falling during syncope.
In other instances, the child will have no presyncopal sensations, but will simply faint.
Should my child be seen by a physician after fainting?
Some types of syncope are caused by a serious problem, so it is recommended that your child be seen by a physician to determine the cause of all fainting spells.
Your child's physician will obtain a medical history and perform a physical examination. The details about the syncopal episodes are helpful in pinpointing the cause: how often they occur, what activity your child was participating in prior to fainting, if there were any presyncopal sensations, and other symptoms. Blood pressure may be taken in sitting and standing positions to check for orthostatic hypotension.
Other diagnostic tests may include:
Treatment for syncope:
Specific treatment for syncope will be determined by your child's physician based on:
For vasovagal syncope, avoiding the situations that trigger the episodes is recommended.
For illnesses causing syncope, such as irregular heart rhythms or epilepsy, medications may be prescribed by your child's physician to help control the disease.
With outflow obstructions, surgical repair of the heart problem may be indicated. Consult your child's physician regarding specific information for your child.
How do you determine the cause of syncope?
The most important job of the cardiologist is to determine whether a patient's complaint of syncope and / or dizziness has a life threatening cause.
One's description of his / her symptoms (history) constitutes the most important part of the evaluation.
Both cardiac and neurologic causes of syncope can usually be excluded with a good history and physical examination.
An electrocardiogram (ECG) will often be done to screen for heart rhythm abnormalities.
Occasionally, other tests will be performed including a Holter monitor, ambulatory event monitor, echocardiogram, graded exercise test (GXT), and / or electroencephalogram (EEG).
In addition, some patients will undergo a tilt table study. During this test, the patient is strapped to a table and tilted to a near standing position in an effort to provoke the common, non-life threatening form of syncope.
How is syncope treated?
Most causes of syncope can be successfully treated. Syncope secondary to neurologic causes can be treated with medications.
Cardiac causes of syncope have a wide range of treatment options dependent upon the specific cause.
Neurally mediated syncope can often be treated without medications by avoiding situations that may provoke syncope, avoiding caffeine, increasing one's salt intake, and by staying well hydrated.
Fluid intake should be increased to the point that one's urine is colorless.
Various maneuvers can also be performed to prevent dizziness from progressing to syncope. These include lying down, squatting, tensing one's abdominal muscles, crossing one's legs at the ankles, and placing one foot on a stool or chair while the other foot remains on the ground.
If non-pharmacologic measures fail to adequately decrease the frequency and severity of one's symptoms, a number of different medications can be tried.
The most commonly prescribed medication for children with neurally mediated syncope is Florinef. This medication works by helping the kidneys retain fluid and sodium. Rare side effects include minimal weight gain, excessively high blood pressure (hypertension), and leg cramping. Leg cramping is caused by low potassium. Patients on Florinef should increase their potassium intake by eating bananas and drinking fruit juices.
Beta-blockers (propranalol, atenolol, nadolol, metoprolol) are also frequently prescribed. These medications work by preventing the inappropriate reflex that leads to syncope. Potential side effects include fatigue, decreased exercise performance, moodiness, and depression.
Disopyramide (Norpace), another medicine occasionally prescribed, also works by preventing the inappropriate reflex from occurring. Common side effects of Disopyramide (Norpace) include dry mouth, blurred vision, and constipation. In rare cases of neurally mediated syncope, pacemaker implantation is warranted.
Most patients with neurally mediated syncope will eventually outgrow their symptoms, though this may take several years.
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