Syncope is caused by a sudden decrease in blood pressure, which temporarily deprives the brain of a sufficient amount of oxygen. Dizziness often occurs before syncope and many patients complain of dizziness without syncope.
Syncope has a variety of causes. Occasionally, syncope is caused by a neurologic problem such as a seizure or migraine headache.
Other non-cardiac causes of syncope include breath-holding spells, rapid breathing (hyperventilation), hysteria, and exposure to certain drugs or toxins.
Cardiac causes of syncope during childhood are rare but are the most worrisome because they can be life-threatening.
Cardiac-related Causes of Syncope
- Cardiac causes can be secondary to obstruction to blood flow (aortic valvar stenosis, hypertrophic cardiomyopathy, primary pulmonary hypertension, Eisenmenger's syndrome)
- Heart rhythm abnormalities (ventricular tachycardia, Wolff-Parkinson-White syndrome, long QT syndrome, sinus node dysfunction, atrioventricular block, arrhythmogenic right ventricular dysplasia)
- Diminished heart function (ventricular dysfunction from a variety of causes including dilated cardiomyopathy; inflammatory diseases such as acute myocarditis and Kawasaki disease; and ischemic heart disease secondary to an anomalous coronary artery, Kawasaki's disease, or hypercholesterolemia)
It is the job of the cardiologist to determine whether one of these serious causes of syncope exists.
By far the most common cause of syncope during childhood, accounting for more than 90 percent of syncope in children, is
- Secondary to irregularities in a normal involuntary (autonomic) reflex resulting in an inappropriate relaxation of the blood vessels (vasodilation)
- Lowering of the heart rate (bradycardia) at a time when the body actually needs the blood vessels to constrict and the heart rate to increase
These changes result in an inappropriately low blood pressure (hypotension) resulting in dizziness and syncope.
This common, non-life threatening form of syncope has been given several names including neurally mediated syncope, neurocardiogenic syncope, vasovagal syncope, and vasodepressor syncope.
Determining 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.
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 (propranolol, 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.
