Definitions

What is syncope?
Syncope is the transient loss of consciousness (fainting) and tone in the body that results from inadequate blood supply to the brain. This is a temporary phenomenon and patients usually recover on their own in a short period of time.

What is presyncope?
Presyncope is the feeling that one is about to faint, and it is often experienced immediately before a syncopal episode.

What are some common signs and symptoms?
Children may often complain of "dizziness", however, as a parent or physician, one must ask the child to be more specific, as presyncope may be confused with other conditions. The table below may be of some help.

  Vertigo Presyncope Disequilibrium Lightheadedness
Complaint "Head is spinning"
"Room is whirling"
"I might pass out"
"I feel faint"
"Feel unsteady"
"Balance is off"
"Feel dizzy"
"Feel disconnected, drugged"
Usual Cause Inner ear problems Decreased blood Flow to the brain Sensory or Central nervous system Dysfunction Anxiety or Depressive disorders
Possible Diagnoses Peripheral (in the ear) vs Central neurologic Disorder Neurocardiogenic vs cardiac syncope vs neuropsychiatric Disorder Sensory deficit vs central neurologic disorder Anxiety/Depression vs hyperventilation vs medication effects

From:  Ped Clinics of North America 1999;46(2): p.206.

Children may also first present with an actual loss of consciousness which may be worrisome to parents but is still due to one of the above causes.

 

Causes

Why does syncope happen?
There is a common pathway for the onset of syncope, but there are many different causes that can set off that pathway. Basically, there is a decrease in blood flow to the brain due to decreased blood leaving the heart, and with this, we may see a decrease in blood pressure, decrease or increase of  heart rate, and occasionally, a different/abnormal heart rhythm. There can be many reasons why there is a decreased amount of blood leaving the heart.  At this site, only the cardiac reasons will be reviewed.

 

Cardiac causes for syncope

This includes:

1. Cardioneurogenic Syncope (Vasovagal)
This is the most common type of syncope (fainting).  It occurs when a person stands up, or continues to stand for sometime, resulting in less blood going back to the heart as it will tend to pool in the lower extremities as a result of gravity.   Consequently causing less blood to be pumped out of the heart (cardiac output).   When the heart senses the decrease in blood returning to it, it contracts more forcefully than usual in attempt to compensate for the drop in blood volume.  In certain individuals this forceful contraction is exaggerated and may trigger special fibers in the heart called the C-fibers. 

C-fibers are designed to be triggered by high blood pressure causing the walls of the heart to stretch.  So, when these C-fibers get a false message by the forceful contraction, it will send the wrong message to the brain.  The brain will think that the blood pressure is high when in reality it is lower than normal because of the drop in blood volume returning to the heart.

The Brain, thinking that the blood pressure is too high, will force the heart to slow down to lower the perceived "high blood pressure".  The slow heart rate coupled with the already lower than normal amount of blood being pumped out of the heart will result in further drop in cardiac output resulting in poor blood supply to the brain causing the patient to faint.

 

2. Left ventricle outflow tract obstruction:
There are two pumping chambers. The right ventricle pumps blood to the lungs so the blood can become oxygenated, and the left ventricle pumps oxygen rich blood to the rest of the body. If there is any type of obstruction to the flow of blood out of the left ventricle, the brain may temporarily not have enough blood flow to function, thus resulting in syncope.

3. Pulmonary hypertension
Increased blood pressure in the vessels going to the lungs.

4. Myocarditis
Inflammation of the heart muscle.   When an episode of myocarditis occurs, the heart muscle becomes weakened from the inflammation and is not able to pump as well.

5. Tumor or mass:
Occasionally there will be a tumor, or tumor-like mass in the heart which may block flow of blood into, or out of, the heart. This is a rare condition.

6. Coronary artery disease
This cause is not seen in children that often, but nevertheless, it must be considered

7.  Arrhythmia
Abnormal heart beat.

 

Tests

What are some ways to evaluate for the different causes of syncope?
The details of how syncope happened, how frequently and other symptoms are very helpful in determining the cause of fainting.  Some of the following tests may be performed to help make diagnosis:

1. Electrocardiogram (ECG)
This will show the baseline heart rhythm.  Abnormalities in the ECG even when the patient is feeling well may provide clues to the cause of syncope.

2. Head up tilt table test
Used to diagnose cardioneurogenic syncope.
In this test the patient rests flat on a special table which would then tilt to make the person laying on it in an almost upright position.  This will tend to induce fainting.  A special medication may also be given to enhance fainting.  Once the patient feels dizzy, usually with drop in blood pressure and slowing of the heart (the patient's heart rate and rhythm and blood pressure are constantly monitored) this would confirm the diagnosis of cardioneurogenic syncope.

3. 24 Hour Holter monitor
Records the patient's ECG for a whole day to catch any abnormalities while the person is going about their routine daily activities.

4. Event monitor
This is given to the patient for a whole month.  The heart rhythm during syncope could be recorded and transmitted to the physician through the telephone line.

5. Echocardiography
May be used to visualize the heart if abnormalities of cardiac structure or function are suspected.

One must keep in mind that not everyone needs all of these tests, but that when indicated (when the patient has the right symptoms and history), these more extensive tests can easily lead to a diagnosis. Once the diagnosis is made, cardiac causes of syncope are often easily treated.